Abstract:
A shock testing machine including: a movable impact mass upon which one or more components to test are mounted; one or more rails upon which the impact mass is movable; and a brake operatively engageable with the movable impact mass after the movable impact mass has moved a predetermined distance to retard the movement of the movable impact mass such that the components to be tested experience a deceleration profile.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority to U.S. Provisional Application Ser. No. 61/884,915, filed on Sep. 30, 2013, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a shock and impact testing machine for subjecting the components to be tested to an acceleration pulse of a prescribed amplitude and duration, and more particularly for testing various devices and components of gun-fired or mortar or electrically powered rail gun or the like munitions as well said munitions by subjecting them to similar launch acceleration pulses. 
         [0004]    2. Prior Art 
         [0005]    Gun-fired munitions, mortars and rail-gun munitions are subjected to high-G (setback and set-forward) acceleration during the launch. Almost all munitions are also subjected to shock loading upon target impact. High-G shock loading is also experienced by rockets during launch and by spacecrafts during launch as well as pyrotechnic shock events during powered flight and deployment. As a result, all components of the system and the system itself must survive the shock loading events and be qualified to such severe environments. 
         [0006]    Component qualification testing cannot obviously be done in an actual environment on complete assemblies. In addition to prohibitive cost involved, testing of components in actual environments would not provide the required information for determining the required component and system design margins. For these reasons, laboratory simulations of the shock loading environments are highly desirable for testing individual components, subassemblies and sometimes the complete system assembly. 
         [0007]    In the current state of the art, shock loading environments are simulated in the industry by one of the following methods: 
         [0008]    1. Electro-Dynamic Shaker.
       This method can accurately produce a desired shock response spectrum (SRS) within closely specified tolerances, but amplitude and frequency limitations of the equipment greatly restrict its applicability.       
 
         [0010]    2. Live Ordnance with System Structure.
       Since the actual system structure and live ordnance are used, this method has the potential to produce a shock virtually identical to the expected field environment. The cost of the test structure, however, is usually prohibitive, unless large numbers of identical tests are to be conducted. The use of live ordnance may have a wide repeatability tolerance, and does not easily allow the test levels to be increased so that an adequate design margin can be assured. For the case of gun-fired munitions, mortars and the like, the added problem is the “soft” recovery of the launched round to examine the state of the components being tested. In certain case, telemetry of data may be used to transmit back data related to the operation of certain components. However, in most cases it is highly desirable to examine the state of the components post firing. In addition, in many cases it is extremely difficult if not impossible to measure/determine the effect of shock loading on many components for transmission to a ground station via telemetry.       
 
         [0012]    3. Live Ordnance with Mock Structure.
       This method has most of the same features as the method “2” above, except that some cost savings are attributed to the use of a mass mock-up structure. These savings may be negated by the need for some trial-and-error testing to attain the desired component input, where geometric similarity was used in method “2” above to attain the same result. This method also suffers from the same shortcomings for testing components of gun-fired munitions and mortars and the like as indicated for the above method “2”.       
 
         [0014]    4. Live Ordnance with Resonant Fixture.
       This method further reduces test cost, and is a candidate for general purpose testing, due to the use of a generic resonant plate fixture. Since live ordnance is used, all the very high frequencies associated with near-field pyrotechnic shock events are produced with this method. However, a great amount of trial-and-error testing may be required to obtain the desired component input.       
 
         [0016]    5. Mechanical Impact with Mock Structure.
       Mechanical impacts do not produce the very high frequencies associated with the stress pulse in the immediate vicinity of a pyrotechnic device. However, most components in a typical system are isolated by enough intermediary structure such that the shock at the component location is not dominated by these very high frequencies. Instead, the shock at the component is dominated by the structural response to the pyrotechnic device, and has dominant frequencies which are typically less than 10 KHz. For these components, a mechanical impact (e.g. using a projectile or pendulum hammer) can produce a good simulation of the pyrotechnic shock environment. Test amplitudes can easily be increased or decreased by simply increasing or decreasing the impact speed. The shock level and duration can be controlled to some extent by the use of various pads affixed at the point of impact. According to this method, attempt is made to subject the structure containing the test components the impact induced acceleration (shock) profile, which close to that experienced when assembled in the actual system. The test conditions are experimentally adjusted to achieve an approximation of the actual acceleration (shock) profile. In general, a large amount of trial-and-error runs have to be made to achieve an acceptable acceleration (shock) profile. The characteristics and response of the various pads used at the impact point to increase the duration of the shock (acceleration) event is generally highly variable and dependent on temperature and moisture. In addition, due to inherent design of such mechanical impact machines and the limitations on the thickness of the pads that can be used at the impact point, high G acceleration peaks with long enough duration similar to those, e.g., experienced by munitions fired large caliber guns or mortars, cannot be achieved. For example, to achieve a peak shock acceleration level of 5000 G with a duration of 4 milliseconds, the pad deformation has to be well over 0.6 meters (considering a reasonable ramp-up and ramp-down of 0.1 meters each), which is highly impractical. It is also appreciated by those skilled in the art that for simulating firing (setback) acceleration for most gun-fired munitions and mortars, the peak acceleration levels can generally be well over the considered 5000 Gs with significantly longer durations. It can therefore be concluded that the described mechanical impact machines do not accurately duplicate the shock profile experienced by munitions during firing or target impact and are not suitable for accurate shock testing of components to be used in such munitions.       
 
         [0018]    6. Mechanical Impact with Resonant Fixture.
       In this method, a resonant fixture (typically a flat plate) is used instead of a mock structure. This significantly reduces cost, and allows for general purpose testing since the fixturing is not associated with a particular structural system. The mechanical impact excites the fixture into resonance which provides the desired input to a test component mounted on the fixture. Historically, test parameters such as plate geometry, component location, impact location and impact speed have been determined in a trial-and-error fashion. In general, this method produces a simulated environment which has its energy concentrated in a relatively narrow frequency bandwidth. It should be noted here that a suitable resonant fixture for use in this method may also be a bar impacted either at the end or at some point along the length of the bar. This method is suitable for many applications in which the components are subjected to relatively long term vibration such as those induced by the system structure. The method is, however, not suitable for testing components of gun-fired munitions and the like since in such cases the munitions is subjected primarily to a single very high G setback or impact shock with relatively long duration.       
 
         [0020]    7. Air-Gun Testing Platforms.
       In this method, the components to be tested are usually mounted in a “piston” like housing with appropriate geometry. In one method, the “piston” is then accelerated by the sudden release of pressurized air or accelerated by the rupture of a diaphragm behind which air pressure is continuously increased until the diaphragm is failed in sheared. In another type of air gun a similar air tight “piston” within which the components to be tested are securely mounted is accelerated over a certain length of a tube by pressurized gasses. The “piston” is thereby accelerated at relatively slower rates and once it has gained a prescribed velocity, the “piston” existing the tube and impacts decelerating pads of proper characteristics such as aluminum honeycomb structures to achieve the desired deceleration amplitude and duration. The components are assembled inside the “piston” such that the deceleration profile to correspond to the desired actual shock (acceleration) profile. In general, similar to the above method 5, air guns can be used to subject the test components to high G shock (acceleration) levels of over 30,000 Gs but for durations that are significantly lower than those experienced by gun-fired munitions, mortars and the like. It can therefore be concluded that the described mechanical impact machines do not accurately duplicate the shock profile experienced by munitions during firing or target impact and are not suitable for accurate shock testing of components to be used in such munitions.       
 
         [0022]    8. Rocket Sleds.
       Rocket sled is a test platform that slides along a set of rails, propelled by rockets. As its name implies, a rocket sled does not use wheels. Instead, it has sliding pads, called “slippers”, which are curved around the head of the rails to prevent the sled from flying off the track. The rail cross-section profile is usually that of a Vignoles rail, commonly used for railroads. Rocket sleds are used extensively aerospace applications to accelerate equipment considered too experimental (hazardous) for testing directly in piloted aircraft. The equipment to be tested under high acceleration or high airspeed conditions are installed along with appropriate instrumentation, data recording and telemetry equipment on the sled. The sled is then accelerated according to the experiment&#39;s design requirements for data collection along a length of isolated, precisely level and straight test track. This system is not suitable for testing components for gun-fired munitions and mortars and the like since it can produce only around 100-200 Gs.       
 
         [0024]    9. Soft Recovery System Facility (SCat Gun)
       In this system, the components to be tested are packaged inside a round, which is fired by an actual gun (in the current system located at the U.S. Army Armament Research, Development and Engineering Center (ARDEC) in New Jersey, with a 155 mm round being fired by a 155 mm Howitzer weapon with a M199 gun tube and 540 feet of catch tubes). The projectile is then recovered using a “Soft Recovery” system. The soft catch component of the system uses both pressurized air and water to help slow down the projectile. The first part of the chain of catch tubes only contains atmospheric air. The next section, 320 feet of the tubes, contains pressurized air, followed by an 80 feet section that is filled with water. A small burst diaphragm seals one end of the pressurized air and a piston seals the other end. The piston also separates the water and pressurized air sections. The burst diaphragm and piston are replaced after each test fire. Once fired, the projectile achieves free flight for approximately 6 feet and travels down the catch tubes, generating shockwaves that interact with the atmospheric air section, the burst diaphragm, the pressurized air section, the piston and the water section. The air section is compressed and pushed forward and shock and pressure cause the piston move against the water, all while slowing the projectile to a stop. Then the piston is ejected out of the end of the system, followed by the air and water, and finally the projectile comes to rest in a mechanized brake system. On-board-recorders inside the projectile measure the accelerations of the projectile from the gun-launch and the catch events. This system is currently provides the means to subject the test components to as realistic firing shock loading conditions as possible and provide the means to retrieve the round to examine the tested components. The cost of each testing is, however, very high, thereby making it impractical for use for engineering development. The system is also impractical for use for most reliability testing in which hundreds and sometimes thousands of samples have to be tested and individually instrumented. It also takes hours to perform each test.       
 
         [0026]    The methods 1-6 described above are more fully explained in the following references: Daniel R. Raichel, “Current Methods of Simulating Pyrotechnic Shock”, Pasadena, Calif.: Jet Propulsion Laboratory, California Institute of Technology, Jul. 29, 1991; Monty Bai, and Wesley Thatcher, “High G Pyrotechnic Shock Simulation Using Metal-to-Metal Impact”, The Shock and Vibration Bulletin, Bulletin 49, Part 1, Washington D.C.: The Shock and Vibration Information Center, September, 1979; Neil T. Davie, “The Controlled Response of Resonating Fixtures Used to Simulate Pyroshock Environments”, The Shock and Vibration Bulletin, Bulletin 56, Part 3, Washington D.C.: The Shock and Vibration Information Center, Naval Research Laboratory, August 1986; Neil T. Davie, “Pyrotechnic Shock Simulation Using the Controlled Response of a Resonating Bar Fixture”, Proceedings of the Institute of Environmental Sciences 31st Annual Technical Meeting, 1985; “The Shock and Vibration Handbook”, Second Edition, page 1-14, Edited by C. M. Harris and C. E. Crede, New York: McGraw-Hill Book Co., 1976; Henry N. Luhrs, “Pyroshock Testing—Past and Future”, Proceedings of the Institute of Environmental Sciences 27th Annual Technical Meeting, 1981. 
         [0027]    The aforementioned currently available methods and systems for testing components to be used in systems that subject them to acceleration (shock) events have a number of shortcomings for use to simulate high G acceleration (shock) events with relatively long duration, such as those encountered in large caliber guns and mortars, for example, to simulate gun-firing events with setback accelerations of over 5,000 Gs and durations of around 5 milliseconds. Firstly, most of the available methods and devices, except those that are based on actual firing of the projectile from the actual gun or mortar or the like, cannot provide long enough acceleration pulse duration. Secondly, those methods that are based on actual firing of the projectile from the actual gun or mortar or the like have prohibitive cost, thereby making them impractical for engineering development tasks which requires countless iterations to achieve the desired results for individual components as well as for their assemblies. In addition, reliability tests for munitions components required testing of a very large number of components, which would make the total cost of munitions development prohibitive. Thirdly, in many component tests, it is highly desirable to instrument each component so that its behavior during the total shock environment can be monitored. Such instrumentation and monitoring is very difficult to achieve when the components to be tested have to be assembled in a rather small volume of fired projectiles. 
         [0028]    A basic design of a mechanical shock testing machine  10  of the prior art that uses the aforementioned method “6” (Mechanical Impact with Resonant Fixture) is illustrated in the schematic of  FIG. 1 . The schematic of  FIG. 1  is intended to show only the main components of such a mechanical shock testing machine. The mechanical shock machine  10  is constructed with some type of rails  12  along which the impact mass element  11  travels. The rails (one or more) may have any cross-sectional shape and the sliding surfaces between the mass element  11  and the rails  12  may be covered with low friction material or may utilize rolling elements to minimize sliding friction. The rails  12  are generally mounted on a relatively solid and massive base  13 , which in turns rests on a firm foundation  14 . Certain relatively stiff shock absorbing elements (not shown) may be provided between the base  13  and the ground  14  to prevent damage to the foundation structure. In heavier machinery, a relatively large (usually reinforced concrete) foundation block (not shown) is used with shock isolation elements having been positioned between the foundation block and the surrounding structure. 
         [0029]    The components to be tested  15  are attached fixedly to the mass element  11 , usually via a fixture  16 . In the mechanical shock machine  10 , the mass element  11  acts as a “hammer” that is designed to impact an anvil  17  to impart the desired shock loading (deceleration profile in the present mechanical shock testing machine) onto the components  15  that are to be tested. The anvil  17  is generally desired to be very rigid as well as massive and be securely attached to the base  13  of the mechanical shock testing machine. In many cases, the mass element  11  is provided with an impact element  18 , which is designed to have a relatively sharp and hard tip  19 . 
         [0030]    To perform shock testing of the components  15 , the mass element  11  (“hammer” element) is accelerated downwards in the direction of the arrow  20  towards the anvil  17 . The shock testing machines are usually installed vertically. In which case and when relatively low impact shock (deceleration) levels or very short shock durations are desired, the mass element  11  is accelerated in the direction of the arrow  20  under the gravitational acceleration, with the height of travel determining the level of velocity attained by the mass element (“hammer”) at the time of impacting the anvil  17 . In other mechanical shock testing machines, particularly when higher mass element  11  velocity at impact velocity is desired, other means such as pre-tensioned bungee cords or pneumatic cylinders (not shown) are also used to significantly increase downward acceleration of the mass element  11  (in the direction of the arrow  2 ), thereby significantly increasing the impact speed between the mass element  11  (the “hammer” element) and the anvil  17 . In those cases in which the mechanical shock testing machine  10  is installed horizontally (not shown), the mass element  11  is accelerated in the direction of the arrow  20  by the aforementioned pre-tensioned bungee cords, pneumatic cylinders or even linear motors. 
         [0031]    The shock (deceleration) level experienced by the mass element  11  and thereby the test components  15  and its duration can be controlled to some extent by the use of various pads  21  affixed at the point of impact, i.e., between the anvil  17  surface and the impacting tip  19  of the impact element  18  of the mass element  11  (“hammer”). The shock (deceleration pulse) amplitude can also be increased or decreased by simply increasing or decreasing the impact speed. The test conditions are experimentally adjusted to achieve as close an approximation of the actual acceleration (shock) profile as possible. 
       SUMMARY OF THE INVENTION 
       [0032]    A need therefore exists for the development of novel methods and resulting testing apparatus (shock testing machines) for testing components of gun-fired munitions, mortars and other devices and systems that are subjected high G acceleration (shock loading) with a relatively long duration such as projectiles fired by large caliber guns, mortars and the like. The developed methods should not be based on the use of the actual or similar platforms, for example, firing projectiles carrying the test components with similar guns such as the described in the method “9” above, due to the cost and difficulty in providing full instrumentation which would allow testing of a few components at a time, thereby making the cost of engineering development of such components and their reliability testing which requires testing of a large number of samples prohibitively high. 
         [0033]    A need also exists for novel mechanical shock testing machines that can provide the means of testing a large number of fully instrumented components in a relatively short time. This requires that the mechanical shock testing machine allows rapid mounting of test components onto the test platform while allowing relatively free access to the components, unlike the “piston” platforms used in air guns (aforementioned method “7”) or inside projectiles that are gun-launched (aforementioned method “9”). 
         [0034]    The novel mechanical sock testing must also provide highly predictable and repeatable shock loading (acceleration) provide for testing the intended components so that the results can be used for detailed analytical model validation and tuning; for predicting the performance of the components in actual applications; and for providing the required information for the design of the components and optimization of the developed designs. 
         [0035]    Herein is described a novel method for the design of shock testing machines and the resulting shock testing machines that can subject test components and systems to high G acceleration pulse (shock) of relatively long duration. The resulting shock testing machines are shown to address the aforementioned needs and are particularly suitable for engineering development and testing of components to be used in gun-fired munitions, mortars and the like. 
         [0036]    Accordingly, a shock testing machine is provided. The shock testing machine comprising: a movable impact mass upon which one or more components to test are mounted; one or more rails upon which the impact mass is movable; and a brake operatively engageable with the movable impact mass after the movable impact mass has moved a predetermined distance to retard the movement of the movable impact mass such that the components to be tested experience a deceleration profile. 
         [0037]    The one or more rails can comprise two or more rails. The brake can comprises a brake element corresponding to each of the two or more rails. 
         [0038]    The brake can be fixed to the movable impact mass. The brake can be movable on the one or more rails. 
         [0039]    The one or more rails can comprise two or more rails and the brake can comprise a brake element corresponding to each of the two or more rails, in which case the shock testing machine can further comprise a rigid member connecting the brake elements such that the movable impact mass engages the brake elements at the same time after moving the predetermined distance. 
         [0040]    The brake can be disposed on the one or more rails at the predetermined distance from the movable impact mass and the brake can be preset to be engaged with the one or more rails. 
         [0041]    The brake can be mounted on the movable impact mass and the brake can be engaged with the one or more rails only after moving the predetermined distance. 
         [0042]    The brake can at least partially surround an outer periphery of the one or more rails. The brake can include at least a circular portion for surrounding the outer periphery of the one or more rails. 
         [0043]    The brake can include one or more first portions fixed to the movable impact mass that are engageable with one or more second portions fixed to a base structure. 
         [0044]    The brake can include a cable having one end fixed to a base structure and another end removably connected to the brake, wherein the brake is engaged by movement of the movable impact mass through the predetermined distance tending to pull the another end from the brake. 
         [0045]    The rails can be positioned vertically such that gravity assists the movement of the movable impact mass. 
         [0046]    The rails can be positioned horizontally such that gravity does not assist the movement of the movable impact mass. 
         [0047]    The movable impact mass can include a pocket for housing the one or more components to be tested. 
         [0048]    The one or more rails can comprise two or more rails and the brake can comprise a brake element corresponding to each of the two or more rails, in which case the shock testing machine can further comprise a mechanism for applying equal pressure to each of the brake elements. 
         [0049]    Also provided is a method for shock testing one or more components. The method comprising: mounting the one or more components to a movable impact mass; movably disposing the movable impact mass on one or more rails; moving the movable impact mass a predetermined distance; and engaging a brake after the movable impact mass has moved a predetermined distance to retard the movement of the movable impact mass such that the components to be tested experience a deceleration profile. 
         [0050]    The brake can be disposed on the one or more rails at the predetermined distance from the movable impact mass and the brake can be preset to be engaged with the one or more rails. 
         [0051]    The brake can be mounted on the movable impact mass and the brake can be engaged with the one or more rails only after moving the predetermined distance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0053]      FIG. 1  illustrates the basic design of a mechanical shock testing machine of prior art. 
           [0054]      FIG. 2  illustrates the schematic of the first embodiment of the mechanical shock testing machine. 
           [0055]      FIG. 3A  illustrates a cross-sectional view of one possible design of the braking element of the mechanical shock testing machine of  FIG. 2 . 
           [0056]      FIG. 3B  illustrates a cross-sectional view of another possible design of the braking element of the mechanical shock testing machine of  FIG. 2 . 
           [0057]      FIG. 4  illustrates the method and means of setting the braking force levels of the braking elements of the mechanical shock testing machine embodiment of  FIG. 2 . 
           [0058]      FIG. 5  illustrates the schematic of the second embodiment of the mechanical shock testing machine. 
           [0059]      FIG. 6  illustrates the schematic of the basic design and operation of the braking elements for the mechanical shock testing machine embodiment of  FIG. 5 . 
           [0060]      FIG. 7  illustrates the schematic of a brake engagement mechanism for the mechanical shock testing machine embodiment of  FIG. 5 . 
           [0061]      FIG. 8  illustrates the schematic of another brake engagement mechanism for the mechanical shock testing machine embodiment of  FIG. 5 . 
           [0062]      FIG. 9  illustrates the schematic of another brake engagement mechanism with piezoelectric actuation device for the mechanical shock testing machine embodiment of  FIG. 5 . 
           [0063]      FIG. 10  illustrates the schematic of a cross-sectional view of the piezoelectric actuated clamping device of the brake engagement mechanism of  FIG. 9 . 
           [0064]      FIG. 11  illustrates the schematic of another brake linkage type engagement mechanism for the mechanical shock testing machine embodiment of  FIG. 5 . 
           [0065]      FIG. 12  illustrates the schematic of the third embodiment of the mechanical shock testing machine. 
           [0066]      FIG. 13  illustrates the schematic of the top view of the third embodiment of the mechanical shock testing machine showing the mass element, rails and their support structure in which the rails are horizontally installed. 
           [0067]      FIG. 14  illustrates the schematic of a cross-sectional view A-A of the horizontally installed mechanical shock testing machine of the embodiment shown in the top view of  FIG. 13 . 
           [0068]      FIG. 15  illustrates a cross-sectional view of one possible design of the braking element of the third embodiment of the mechanical shock testing machine of  FIG. 12 . 
           [0069]      FIG. 16  illustrates a cross-sectional view of another possible design of the braking element of the third embodiment of the mechanical shock testing machine of  FIG. 12 . 
           [0070]      FIG. 17  illustrates a cross-sectional view of another possible design of the braking element of the third embodiment of the mechanical shock testing machine of  FIG. 12 . 
           [0071]      FIG. 18  illustrates a cross-sectional view of the rail, mass element and the anti-rotation guide for mechanical shock testing machines constructed with a single rail. 
           [0072]      FIGS. 19A and 19B  illustrate arrangements of the rails for mechanical shock testing machines constructed with three and four rails. 
           [0073]      FIG. 20  illustrates a cross-sectional view of another possible design of the braking element of the third embodiment of the mechanical shock testing machine of  FIG. 12  with the braking elements attached to the mass element of the machine. 
           [0074]      FIG. 21  illustrates the schematic of the brake release element for the brake embodiment of  FIG. 20  of the mechanical shock testing machine of  FIG. 12 . 
           [0075]      FIG. 22  illustrates another embodiment of the brake engagement mechanism of the mechanical shock testing machine of  FIG. 12  with the braking elements attached to the mass element of the machine. 
           [0076]      FIG. 23  illustrates a cross-sectional view of the brake assembly section of one of the rails of the brake engagement mechanism of the embodiment of  FIG. 22 . 
           [0077]      FIG. 24  illustrates a cross-sectional view of the provided sleeves over the mechanical shock testing machine rails to engage the braking pads under pressure to generate the desired mass element decelerating braking force. 
           [0078]      FIG. 25  illustrates the schematic of the fourth embodiment of the mechanical shock testing machine. 
           [0079]      FIG. 26  illustrates a cross-sectional view F-F of the mechanical shock testing machine embodiment of  FIG. 25 . 
           [0080]      FIG. 27  illustrates the cross-sectional view F-F of the alternative design of the mechanical shock testing machine embodiment of  FIG. 25 . 
           [0081]      FIG. 28  illustrates the cross-sectional view of the fifth embodiment of the mechanical shock testing machine of the present invention designed based on the third embodiment of the mechanical shock testing machine of  FIG. 12 . 
           [0082]      FIG. 29  illustrates the cross-sectional view G-G across the mass element of the mechanical shock testing machine embodiment of  FIG. 28 . 
           [0083]      FIG. 30  illustrates a cross-sectional view of the mass element of the third embodiment  100  of  FIG. 21  with braking mechanism of  FIG. 22  with brake pad pressure equalizing mechanism. 
       
    
    
     DETAILED DESCRIPTION 
       [0084]    A schematic of a first mechanical shock testing machine embodiment  30  is shown in  FIG. 2 . The basic structure of the mechanical shock testing machine  30  is the same as the shock testing machine  10  of the prior art shown in the schematic of  FIG. 1 . The schematic of  FIG. 2  is intended to show only the main components of the present mechanical shock testing machine  30 . The mechanical shock machine  30  is similarly constructed with some type of rails  22  along which the impact mass element  23  travels. The rails (one or more) may have any cross-sectional shape and the sliding surfaces between the mass element  23  and the rails  22  may be covered with low friction material or may utilize rolling elements to minimize sliding friction. The rails  22  are generally mounted on a relatively solid and massive base  24 , which in turns rests on a firm foundation  25 . Certain relatively stiff shock absorbing elements (not shown) may be provided between the base  24  and the ground  25  to prevent damage to the foundation structure. In heavier machinery, a relatively large (usually reinforced concrete) foundation block (not shown) is used with shock isolation elements positioned between the foundation block and the surrounding structure. 
         [0085]    The component(s) to be tested  26  is/are attached fixedly to the mass element  23 , usually via a fixture  27 . To perform shock testing of the components  26 , the mass element  23  is similarly accelerated downwards in the direction of the arrow  28 . The shock testing machines may be installed vertically, in which case and when relatively low impact shock (deceleration) levels are desired, the mass element  23  is accelerated in the direction of arrow  28  under gravitational acceleration. When using gravity to accelerate the mass element downwards, the height of vertical travel of the mass element  23  determines the level of velocity that is attained by the mass element  23 . Alternatively, particularly when higher mass element  23  velocities is desired to be attained, other aforementioned means such as pre-tensioned bungee cords or pneumatic cylinders (not shown) are also used to significantly increase downward acceleration of the mass element  23 , thereby significantly increasing its attainable velocity for a length of travel. In the case of the present mechanical shock testing machine  30 , for the reasons that are described later in this disclosure, the machine can be configured horizontally (i.e., the rails are horizontally installed so that the mass element  23  travels horizontally). In which case, the mass element  23  has to be accelerated by externally applied forces such as by the aforementioned pre-tensioned bungee cords or pneumatic cylinders or even linear motors. In general, the means of accelerating the mass element  23  in the present mechanical shock testing machines can be the use of pre-tensioned bungee cords, which are simple to use, have a compact design, light weight, low cost, and ease of varying the force, among other reasons. 
         [0086]    In the prior art mechanical shock machine  10 ,  FIG. 1 , the mass element  11  acts as a “hammer” that impact an anvil  17  at certain appropriate velocity to impart the desired shock loading (deceleration profile) onto the components  15  that are being tested. The shock (deceleration) level experienced by the mass element  11  and thereby the test components  15  and its duration can be controlled to some extent by the use of various pads  21  affixed at the point of impact between the anvil  17  surface and the impacting tip  19  of the impact element  18  of the mass element  11 . As was previously described, the use of such pads  21  between the impacting components can only provide very short duration shock loading (deceleration pulse) due to the limitations on the thickness of such pad  21  systems. In the embodiment  30 , this shortcoming is eliminated. 
         [0087]    In the embodiment  30  of the present mechanical shock testing machine, the shock testing machine is provided with brake elements  29 , which are mounted on the rails  22  at certain height as shown in the schematic of  FIG. 2 . The brakes elements  29  are positioned such that as the mass element  23  travels down, the bottom surface  31  of the mass element  23  engages the brake elements  29  essentially simultaneously. The brake elements  29  can be designed to have minimal mass, provide appropriate mechanisms to rapidly and accurately adjust the provided friction forces, and provide a relatively constant braking force with close static and dynamic coefficients of friction (examples of such braking elements and their various braking force adjustment mechanisms are provided below). 
         [0088]    To perform shock testing of the components  26 , the mass element  23  is accelerated downwards in the direction of the arrow  28  as was previously described. The mass element  23  while traveling at the predetermined velocity would engage the brake elements  29 . If the mass of the brake elements  29  compared to the mass of the mass element  23  is negligible, then the braking force will begin to decelerate the mass element  23 . If the braking force provided by the braking elements  29  and the mass of the mass element  23  are indicated as F and m, respectively, then the deceleration a of the mass element  23  and thereby the testing components is given as 
         [0000]    
       
      
       a=F/m  
      
     
         [0000]    The mass element  23  together with the brake elements  29  will then travel down in the direction of the arrows  32  until they come to a stop. If the mass element  23  comes into contact with the brake elements  29  at the time t=0, and if the downward velocity of the mass element at this time is V 1 , then the velocity V 2  of the mass element  23  until it comes to a stop is given by 
         [0000]    
       
      
       V 
       2 
       =V 
       1 
       −at  
      
     
         [0000]    It will be appreciated by those skilled in the art that the present method of decelerating the mass element  23  to which the components  26  that are being tested are attached and the fact that the brake elements  29  can freely travel the required length of the rails  22  while decelerating the mass element with a nearly constant acceleration level allows the present mechanical shock testing  30  to achieve relatively very long and nearly constant deceleration levels that would otherwise be impossible with any currently available impact based mechanical shock testing machines. 
         [0089]    It will be appreciated by those skilled in the art that in the above formula, it is assumed that the mass of the braking elements is negligible as compared to the mass m of the mass element  23 . However, if the mass of the brake elements relative to the mass of the mass element  23  is not negligible, as the mass element  23  comes into contact with the brake elements  29 , the impact between the two elements will impart a shock (deceleration) pulse on the mass element  23 . The amplitude and duration of the initial shock pulse is dependent on the mass of the brake elements  29  relative to the mass of the mass element  23 . In cases where such initial shock loading is not desirable, its amplitude can be significantly reduced or if desired totally eliminated by providing resilient and high damping pads  33  (e.g., similar to the pads  21  described for the prior art mechanical shock testing machine of  FIG. 1 ) above the brake elements  29 . The pads  33  can be designed to smoothly increase their resistance to the downward travel of the mass element  23  until the resistance force equals to the braking force of the braking elements  29 , at which time the braking elements  29  would begin to slide down the tracks  22 , decelerating the mass element  23  (thereby the components  26  that are being tested) at an essentially constant rate. 
         [0090]    Alternatively, a relatively rigid member  34  may be used to bridge over the brake elements  29 . A resilient and high damping pad  35  or an appropriately pressurized air spring or the like can be provided on the surface of the rigid member  34  so that as the downward traveling mass element  23  engages the rigid member  34 , its rate of increase in deceleration, i.e., jerk, is relatively small and smooth. The pad  35  will then smoothly increase its resistance to the downward travel of the mass element  23  until the resistance force equals to the braking force of the braking elements  29 , at which time the braking elements  29  would begin to slide down the tracks  22 , decelerating the mass element  23  (thereby the components  26  that are being tested) at an essentially constant rate. The pads  29  may also be used to assist the process. It will be appreciated by those skilled in the art that the total mass of the rigid member  34 , braking elements  29  and the pad  35  is desired to be as small as possible relative to the mass of the mass element  23  to minimize the amount of kinetic energy of the mass element  29  that has to be absorbed by the resilient and high damping pad  35  (and pads  29 , if present), thereby reducing the duration of the (nearly constant) deceleration that is applied to the mass element and thereby the test components  26  as the braking elements  29  are pushed downward along the rails  22 . In addition, a relatively rigid protrusion  36  may be provided on the mass element  23  to concentrate pressure applied to the resilient and high damping pad  35  as it is engaged by the downward traveling mass element  23  during the above described shock testing of the components  26 . 
         [0091]    It will be appreciated by those skilled in the art that by providing the brake elements  29  for decelerating the mass element  23  as was described above, an essentially constant deceleration pulse (shock) can be achieved with the mechanical shock testing machine embodiment  30  shown schematically in  FIG. 2 . In addition, the duration of the deceleration pulse can be increased by simply increasing the initial velocity of the mass element  23  as it engages the braking elements  29 . With the disclosed mechanical shock testing machine embodiment  30 , relatively long deceleration pulse durations can be achieved since the length of the rails  22  under the braking elements  29  can be made arbitrarily long. This is in contrast with the amount of deformation that impact pads element  21  of the prior art mechanical testing machines shown in  FIG. 1  can practically provide as was previously described, thereby significantly limiting the duration of deceleration pulses that the prior art mechanical shock testing machines can provide. 
         [0092]    It will also be appreciated by those skilled in the art that since the braking force provided by the braking elements  29  is essentially constant as the braking elements are pushed down along the rails  22  by the mass element  23 , therefore the deceleration of the mass element  23  stays essentially constant during this time (i.e., during the deceleration pulse duration). This is also in contrast with the prior art mechanical shock testing machines shown schematically in  FIG. 1  in which it is almost impossible to design impact pads  21  such that their generated resisting force is constant at every speed of the impacting mass element  11  and at every depth of deformation of the impact pads. 
         [0093]    In the embodiment  30  of  FIG. 2 , the braking elements  29  are desired to have minimal mass as was previously described to minimize the impact pulse generated as the mass element  23  comes into contact with the braking elements via the resilient and high damping pads  33  and until the braking elements begin to travel downward together with the mass element  23 . The impact pulse becomes more severe when the resilient and high damping pads  33  are not provided. 
         [0094]      FIG. 3A  illustrates the cross-sectional view A-A of an embodiment of the braking elements  29  designed for minimal mass and to provide a simple mechanism for adjusting the provided braking force. As can be seen in  FIG. 3A , the braking element  29  consists of several braking pad segments  37  (in the schematic of  FIG. 3A , four braking pad segments) that are in close contact with the surface of the rail  22 . Gaps  38  can be provided between the braking pad segments  37  in the circumferential direction to minimize their interference during testing (as they slide down the rail  22 ) as well as while adjusting the braking pads  37  pressure on the surface of the rail  22  as described below. 
         [0095]    It will be appreciated by those skilled in the art that numerous methods may be used to apply pressure to the braking pad segments  37  against the surface of the rail  22  to generate the desired braking forces. However, as previously discussed, it is highly desirable for the braking elements  29  to be as lightweight as possible to minimize the aforementioned impulsive impact forces generated as the mass element  23  comes into contact with the braking elements. A simple and lightweight and readily adjustable means of applying relatively uniform pressure to the braking pads  37  is a relatively thin (flexible) strap  39  of high strength material that is wrapped around the braking pads as shown in the schematic of  FIG. 3A , leaving a small gap  40  open between extended ends  41  of the strap  39  to allow a bolt and nut fastener  42  (passing through holes provided in the extended ends  41 —and collectively shown as the center line  42  for the sake of simplicity) to be tightened to generate the desired pressure on the braking pads  37 . In general, since most braking pad materials are relatively soft and fragile, they are provided with relatively strong and stiff backing plates (collectively indicated as the braking pads  37 ) to ensure relatively uniform distribution of pressure generated by the straps  39 . In addition, when the length of the braking pads  37  is relatively long, multiple and relatively narrow straps  39  can be used to ensure relatively uniform distribution of pressure between the pads  37  and surfaces of the rail  22 . 
         [0096]    It will be appreciated by those skilled in the art that the straps  39  and its bolt and nut fastener may be replaced by the commonly used and widely available “hose clamps”. The use of such “hose clamps” can be generally designed to be lightweight, capable of generating relatively large forces, adjustable, have a relatively large range of diameter adjustment, low cost and readily available. 
         [0097]      FIG. 3B  illustrates the cross-sectional view A-A of another embodiment of the braking elements  29  designed for minimal mass and to provide a simple mechanism for adjusting the provided braking force. In the embodiment of  FIG. 3B , similar to the embodiment of  FIG. 3A , several braking pad segments  37  (in the schematic of  FIG. 3B , four braking pad segments) that are in close contact with the surface of the rail  22  are used. Gaps  38  are similarly provided between the braking pad segments  37  to minimize their interference during testing (as they slide down the rail  22 ) as well as while adjusting the braking pads  37  pressure on the surface of the rail  22  as described below. To facilitate the braking element  29  assembly around the rails  22 , a fabric or a thin elastomeric sheet (not shown), which may or may not be attached to the aforementioned relatively rigid backing supports of the braking elements  37 , may be securely wrapped around the braking pad segments  37 . 
         [0098]    In this embodiment, a so-called pneumatic bag  129  (similar to pneumatic lifting bags or blood pressure measurement cuffs), commonly constructed with thin and flexible material with relatively inextensible layers is wrapped around the braking pad segments  37  (around the aforementioned holding fabric or a thin elastomeric sheet—if employed). A strong and relatively inextensible fabric or straps  128  are used to secure the pneumatic bag  129  as well as resist radial expansion of the pneumatic bag to allow it to be pressurized to the desired level. Then by pressurizing the pneumatic bags  129  through a one way valve similar to those for balls or those used for tires (not shown) to an appropriate level, the desired level of pressure is applied to the braking pad segments  37 , thereby generating the desired level of braking forces between the braking elements  29  and the rails  22 . The advantages of using such pneumatic bags  129  are their very lightweight; ease of pressure and thereby braking force adjustment; ease of assembly with the braking elements  37 ; and their availability and low cost. In addition, the use of the pneumatic bags  129  ensures highly uniform distribution of pressure between the pads  37  and surfaces of the rail  22 . 
         [0099]    In the mechanical shock testing machine embodiment  30  of  FIG. 2 , only one braking element  29  is shown to be used on each rail  22 . To cover a large range of braking forces, particularly since the amount of pressure that can be applied to commonly used brake pad materials due to their relatively low maximum allowable contact pressure (usually around 300-500 psi), in one embodiment, the braking elements  29  can be fabricated with relatively short lengths (defined as the longitudinal length along the length of the rail  22 ). Then when larger braking forces are required, two or more such braking element assemblies are stacked along the longitudinal length of the rails and their pressures adjusted to provide the desired braking force. One advantage of using multiple such braking element assemblies is that their braking pad pressures over the rail surface can more readily be distributed uniformly; the individual brakes can be operated at lower contact pressure levels; thereby minimizing the rate of brake pad wears as well as local wear of the rail surfaces. 
         [0100]    The design of the mechanical shock testing machine embodiment  30  of  FIG. 2  also allows for rapid and accurate setting of the braking force that is provided by the element  29 . A method and means of rapidly and accurately performing the brake force setting are described with reference to the schematic of  FIG. 4 . In  FIG. 4 , the mechanical shock testing machine embodiment  30  of  FIG. 2  is shown together with a commonly used mechanical or hydraulic jack  44 . The jack  44  is positioned over the base  24  and under the braking elements  29 . A force gage  46  is positioned over a top platform  45  of the jack  44 . A relatively rigid element  43  which is free to ride along the rails  22  is positioned under the braking elements  29 . The element  43  can be fabricated in two halves (not shown) that are assembled by attaching them together by the bolts  48  to accommodate the rails  22  and to remove after brake force setting. A relatively stiff spring element  47  is provided between the relatively rigid element  43  bridging the braking elements  29  and the force gage  46 . The spring element  47  can be fabricated using several helical compressive elements that are assembled between top and bottom plates (not shown). The entire jack  44 , force gage  46  and spring element  47  assembly is centered between the rails  22 . Then by raising the jack  44  (i.e., its top platform  45 ), the spring element  47  is compressed, thereby causing the relatively rigid element  43  to apply an essentially equal force to each of the braking elements  29 , while the applied force is being measured by the force gage  46 . As the force being transmitted to the braking elements  29  is increased by raising the jack  44 , at a certain point the braking elements will begin to slide over the rails  29 . The force reading of the force gage  46  at this point indicates the braking force that is provided by the braking elements  29 . Further raisings of the jack  44  should indicate the same braking force reading. The braking force that is provided by the braking elements may now be adjusted by tightening or loosening the bolt and nut  42  for the embodiment of  FIG. 3A  and by adjusting the air (gas) pressure in the pneumatic bags  129  for the embodiment of  FIG. 3B . 
         [0101]    A second embodiment  50  of the mechanical shock testing machine is shown schematically in  FIG. 5 . All components of the mechanical shock testing machine  50  are the same as those of the embodiment  30  of  FIG. 2 , except for the braking elements  51  ( 29  in the embodiment of  FIG. 2 ) which are different in design and are fixedly attached to the mass element  52  ( 23  in the embodiment of  FIG. 2 ). 
         [0102]    In the mechanical shock testing embodiment  50 , the braking elements  51  are initially applying no braking force to the rails  22 , i.e., the brake pads (similar to the pads  37  shown in  FIG. 4 ) are not pressed against the surface of the rails  22 . This would therefore allow the assembly of the mass element  52  and braking elements  51  to be accelerated downwards (under gravity for vertically installed shock testing machines and/or pre-tensioned bungee cords or pneumatic cylinders or other similar means as was previously described) to gain a predetermined velocity. Then once the mass element and braking element assembly has gained the predetermined velocity, the braking elements  51  are engaged and begin to apply a prescribed level of braking force to the rails  22 , thereby causing the mass element  52  to be decelerated at the desired rate, thereby subjecting the testing components  53  to a predetermined and essentially constant deceleration (shock) pulse that lasts until the assembly of the mass element  52  and braking elements  51  come to rest as was previously described for the embodiment of  FIG. 2 . The methods of designing and constructing the braking elements  51  and mechanisms for their activation once the mass element  52  has gained the prescribed velocity is described below. 
         [0103]    An advantage of attaching the braking elements  51  to the mass element  52  is the elimination of the aforementioned impact shock (deceleration) pulse on the mass element  52  when it would have otherwise come into contact with stationary braking elements (as was previously described for the mass element  23  of the embodiment of  FIG. 2  as it engages the stationary braking elements  29 ). In addition, it is generally difficult to totally eliminate the impact shock pulses and the generated ringing noise that it would generate. In addition, the use of resilient and high damping pads  33  in the embodiment of  FIG. 2  between the mass element  23  and the braking elements  29  results in a significant dissipation of the kinetic energy of the mass element  23 , thereby significantly reducing the level of shock (deceleration) and duration that can be achieved, and thereby requiring a higher initial velocity for the same shock loading level and duration. 
         [0104]    As it was indicated above, in the mechanical shock testing embodiment  50 , the braking elements  51  are initially applying no braking force to the rails  22 . This would allow the assembly of mass element  52  and braking elements  51  to be freely accelerated downward in the direction of the arrow  54  using one of the aforementioned methods and means. It will be appreciated by those skilled in the art that numerous methods and means are known in the art that can be used to provide the braking elements  51  with the capability of being engaged while the mass element and braking elements assembly is traveling down in the direction of the arrow  54 . 
         [0105]    It will appreciated by those skilled in the art that since the mass element  52  would be traveling down at high velocities while the braking elements  51  are engaged (i.e., to begin to apply braking force by pressing the braking pads  37  against the surface of the rails  22 ), therefore the engagement mechanisms of the braking elements must be capable of engaging the braking elements  52  very rapidly to firstly minimize the downward travel distance of the mass element  52  before the brakes are fully engaged, i.e., until the desired mass element  52  deceleration level has been reached. The travel distance during braking engagement must be minimized to minimize the required total length of the rails  22 . Secondly, while the braking forces applied by the braking elements  51  are building up as the braking elements  51  are being engaged, the assembly of mass element  52  and braking elements  51  is being decelerated, even though at slower rates than the prescribed shock testing (deceleration pulse) levels, thereby reducing (wasting) the kinetic energy of the mass element and braking elements assembly and thereby reducing the duration of the testing deceleration pulse. 
         [0106]    One mechanism for engaging the braking elements  51  once the mass element  52  and braking element  51  assembly has gained a predetermined velocity is shown schematically in  FIG. 6 . All components of the braking element assembly  51  is identical to that of the braking element  29  of  FIG. 2 , except that the bolt and nut fastener  42  used to generate the desired pressure on the braking pads  37  are replaced as described below. 
         [0107]    As can be seen in the schematic of  FIG. 6 , the relatively thin (flexible) strap  55  (element  39  in the embodiment  29  of  FIG. 4 ) which is made out of high strength material (such as spring steel) is provided with extended ends  56 . A spacing element  57  is positioned between the extended ends  56 . A pair of bolt  58  and nut  59  is passed through provided holes (not shown) in the extended ends  56 , and is used to preload the compressive spring  60 . The spacing element  57  can be provided with a slight wedging angle to make it easier to be pulled out from between the extended ends  56  in the direction of the arrow  62  by the cable  61 . Once the spacing element  57  has been pulled out, the preloaded compressive spring  60  would apply a force to the extended ends  56  that tends to bring them together, thereby applying a compressive force to the brake pads  37 , thereby generating the desired braking force between the braking elements  51  and the rails  22  to begin to decelerate the mass element  52  and braking element  51  assembly, thereby the testing components  53  at the prescribed rate. 
         [0108]    It will be appreciated by those skilled in the art that the compressive spring  60  used in the braking element  51  is desired to be small and lightweight, and also capable of applying relatively large compressive forces to the extended ends  56  of the straps  55  of the braking elements  51 . In addition, by minimizing the mass of the compressive spring  60  and its required deflection once the spacing element  57  is pulled out, the total time for the braking element engagement is also minimized. 
         [0109]    In addition, the force in the direction of the arrow  62  with which the cable  61  would need to pull the spacing element  57  out from between the extended ends  56  of the straps  55  to engage the braking elements  51  is desired to be low to simplify the pulling mechanism for the cable  61  and minimize the total time for the braking element engagement. For these reasons, one may also provide sliding balls or rollers  63  between the surfaces of the extended ends  56  and the spacing element  57  as shown in the schematic of  FIG. 7 . As a result, the pulling cable  61  requires exerting minimal pulling force in the direction of the arrow  62  to release the spacing element  57 . 
         [0110]    In the mechanical shock testing machine embodiment  50 , the free ends of the cables  61  of the braking element assembly  51  ( FIGS. 6 and 7 ) are attached to the machine structure (indicated with numeral  64  in  FIG. 5 ). Then as the assembly of the mass element  52  and braking elements  51  is accelerated downwards in the direction of the arrow  54  as was previously described, when the assembly has gained a predetermined velocity, the free length of the cables  61  is adjusted to almost simultaneously engage the braking elements  51  by pulling the spacing elements  57  from between the extended ends  56  of the straps  55  of the braking elements  51 ,  FIGS. 6-7 . 
         [0111]    In the schematics of  FIGS. 6 and 7 , a spacing element  57  is shown to be positioned between the extended ends  56  of the strap  55  of the braking elements  51  that once removed, would allow the compressively preloaded springs  60  to apply pressure to the brake pads  37  via the straps  55  as was previously described. 
         [0112]    In an alternative embodiment, the braking element is provided with at least one “C” shaped spring element  65 ,  FIG. 6 , which is preloaded to provide the desired level of compressive pressure of the braking pads  37  over the surface of the rails  22  once the spacing element  57  re pulled out from between the extended ends  56  of the strap  55  of the braking elements  51 . The advantages of using the aforementioned at least one “C” shaped spring element  65  include the design simplicity and the elimination of the bolt  58 , nut  59  and the compressive spring  60 . The shortcoming of the use of the at least one “C” shaped spring element  65  is the lack of means to readily adjust the spring preloading levels. One method of addressing this shortcoming is the use of several such “C” shaped spring elements  65 , with different preloading levels to achieve the desired total preloading forces. 
         [0113]    In another alternative embodiment, the extended ends  56  of the strap  55  of the braking elements  51  are provided with a linear actuation device  67  as shown in  FIG. 8 . The linear actuation device  67  may be of any type known in the art, for example, it may be a pneumatic piston (such as a diaphragm type to generate large levels of force with small stroke); or may be a hydraulic cylinder type; a piezoelectric (electrostrictive) or magnetostrictive type linear actuator; solenoid or any other type of similar linear or rotary electrical motor based type; or the like. The main desired characteristics of the linear actuation devices to be used are being lightweight; very fast acting; easy to adjust the force; and ease of activation or deactivation depending how it is used in the present brake element engagement mechanisms. In the present description, the linear actuator  67  is considered to be of a pneumatic type, however, the linear actuator may be of any other of the aforementioned types. 
         [0114]    In the embodiment shown in  FIG. 8 , at least one pre-tensioned tension spring  66  is used to provide the desired brake pad  37  pressure over the surfaces of the rails  22  to generate the required braking forces for the desired mass element  52  deceleration levels. In this arrangement, the linear actuator  67  is used to counter the tension force of the springs  66  and eliminate the braking force of the braking elements  52 . This is accomplished by pressurizing the pneumatic cylinder  67  via its inlet port  68 , which is considered to be equipped with a one-way valve that only allows air flow into the cylinder (piston). The piston rod  69  of the pressurized pneumatic actuator will then tend to force the extended ends  56  of the strap  55  of the braking elements  51  apart, thereby overcoming the tension force of the springs  66 . The assembly of the mass element  52  and braking elements  51  can then be accelerated downwards using one of the aforementioned methods with the disengaged braking elements  52 . Then once the mass element  52  has gained its desired downward velocity in the direction of the arrow  54 , the cable  61  is pulled as was described previously for the embodiments of  FIGS. 6 and 7 , thereby opening the relieve valve  70 , depressurizing the pneumatic cylinder  67 , thereby allowing the springs  66  to engage the braking elements  51  and the resulting braking forces to begin to decelerate the assembly of the mass element  52  and braking elements  51  and thereby the components  53  that are to be tested. 
         [0115]    It will be appreciated by those skilled in the art that at least one “C” shaped spring element  65  shown in the schematic of  FIG. 5  may be used instead or in addition to the pre-tensioned tension spring  66  in the above embodiment shown in  FIG. 8 . 
         [0116]    Alternatively, the pneumatic cylinder  67  may be used without the aforementioned pre-tensioned tension spring  66 . In this configuration, the extended ends  56  of the strap  55  of the braking elements  51  are normally positioned such that the braking pads  37  are not pressing against the surfaces of the rails  22 , i.e., the braking elements  51  are disengaged. The mass element  52  is thereby free to be accelerated downwards as previously described. Then once the mass element  52  has gained its desired downward velocity in the direction of the arrow  54 , the cable  61  is pulled as was described previously for the embodiments of  FIGS. 6 and 7 . In this configuration, the cable  61  is connected to a pneumatic valve (not shown) that is opened by the pulling of the cable  61 , thereby allowing pressurized air (gas) to enter the pneumatic cylinder  67  through the line  71  and inlet  68 . In this case, the pneumatic cylinder  67  is pressurized to retract the piston rod, thereby tending to close the gap between the extended ends  56  of the strap  55  of the braking elements  51 , thereby engaging the braking elements  51 . The applied braking forces will then begin to decelerate the assembly of the mass element  52  and braking elements  51  and thereby the components  53  that are to be tested. 
         [0117]    It will be appreciated by those skilled in the art that among the above two configurations described for the braking element engagement mechanism of  FIG. 8 , the former option which uses the pre-tensioned tension spring elements  66  for generating the required braking pressure on the braking pads  37  can be superior in terms of speed of brake engagement and since it does not require a traveling pressurized hose  71 . An advantage of the latter configuration is the ease with which the braking pressure can be adjusted by properly setting the inlet air pressure into the pneumatic cylinder  67 . 
         [0118]    It will also be appreciated by those skilled in the art that as was previously indicated, almost any other type of linear actuator may also be used in any one of the above configurations described in the braking element  51  engagement mechanism of  FIG. 8 . Of the previously indicated linear actuator types, the piezoelectric (electrostrictive) based linear actuation devices are of particular interest due to their very fast response time, for example a fraction of a millisecond for travel distances of a few millimeters. The main disadvantage of using such linear actuation devices directly in the braking element engagement mechanism of  FIG. 8  is the limited displacement of such actuators and therefore the need to mechanically amplify their displacement. 
         [0119]    Piezoelectric type actuation devices can, however, provide very large forces. This characteristic of piezoelectric actuation devices can be used in the braking element engagement mechanism that is shown in the schematic of  FIG. 9 . In this embodiment, the braking engagement mechanism of the braking elements  51  uses piezoelectric elements to actuate as shown in  FIG. 9  and its cross-sectional view A-A, as shown in  FIG. 10 . As can be seen in  FIG. 9 , at least one pre-tensioned tension spring  72  is between the extended ends  56  of the strap  55  of the braking elements  51  to provide the desired brake pad  37  pressure over the surfaces of the rails  22  to generate the required braking forces for the desired mass element  52  deceleration levels. Relatively rigid block elements  73  and  74  are attached to each of the extended ends  56  of the strap  55  of the braking elements  51  as shown in  FIG. 9 . A locking clamp  75  is also provided that can be used to firmly clamp the block elements  73  and  74  together to prevent their relative motion as will be described below. Then to keep the braking element  51  disengaged and allow for free downward movement of the mass element  52 , the extended ends  56  are separated, subjecting the tensile springs  72  to further tension, and when the brake pads  37  no longer are pressing on the surfaces of the rail  22 , the two block elements  73  and  74  are clamped together firmly to keep the braking element  51  in the disengaged state. 
         [0120]    The design of the aforementioned piezoelectric actuated locking clamp  75  can be seen in the cross-sectional view A-A of  FIG. 9  that is shown in  FIG. 10 . As can be seen in  FIG. 10 , the clamp  75  consists of two relatively rigid side elements  76  and  77 , which are rigidly attached to the block  73 , such as by welds, to prevent any relative motion and to minimize the total size, or by fasteners  78  and pins (not shown) to minimize relative motion. The relatively rigid plate  79  is then attached to the ends of the side elements  76  and  77  as shown in  FIG. 10 , such as by welds to prevent any relative motion and to minimize the total size, or by fasteners  80  and pins (not shown) to minimize relative motion. In practice, the sides  76  and  77  and the plate  79  and even the block  73  can be integrated as one piece to minimize the total size and mass of the braking elements  51 . A piezoelectric actuator element  81  is then positioned between the plate  79  and the block  74  such that when the piezoelectric actuator  81  is energized by an appropriate voltage signal and increases its length axially, it would press the blocks  73  and  74  together firmly to prevent them from undergoing relative motion by the forces applied by the pre-tensioned tensile springs  72  ( FIG. 9 ). In  FIGS. 9 and 10 , the wire  82  indicates the electrical wires through which voltage is applied to the piezoelectric actuator  81  to apply the force to “lock” the blocks  73  and  74  together. In this embodiment of the braking elements  51 , the cable  61  ( FIG. 5 ) is considered to be attached to the wire  82  (not shown in  FIGS. 9 and 10 ) and when pulled can disconnect power to the piezoelectric actuator  81  by, for example by actuating an electric switch or by disengaging a connector or the like well known in the art (not shown). In an embodiment, a friction increasing coating such as those made out of hard rubber or the like is used on the contacting surfaces of the blocks  73  and  74  to increase the level of friction between the surfaces. 
         [0121]    The piezoelectric actuator based brake engagement mechanism shown in  FIGS. 9 and 10  for the braking elements  51  of the mechanical shock testing machine of  FIG. 5  will perform shock testing of the intended components as follows. The at least one pre-tensioned tension springs  72  are adjusted to proper tension levels to provide the desired braking forces once engaged as previously described. The extended ends  56  of the strap  55  of the braking elements  51 ,  FIG. 9 , are forced to separate until the braking pads  37  no longer apply any pressure to the surfaces of the rails  22 . The piezoelectric actuator  81  is then energized, locking the blocks  73  and  74 , thereby allowing the assembly of the mass element  52  and braking elements  51  to be free to travel over the rails  22 ,  FIG. 5 . The mass element  52  is then accelerated downwards as was previously described. Then once the mass element  52  has gained its desired downward velocity in the direction of the arrow  54 ,  FIG. 5 , the cable  61  is pulled as was described previously for the embodiments of  FIGS. 6 and 7 , thereby de-energizing the piezoelectric actuator  81  and allowing free displacement between the blocks  73  and  74 . The at least one pre-tensioned tension springs  72  are then free to apply their pre-calibrated force to the extended ends  56  of the strap  55  of the braking elements  51 , thereby engaging the braking elements  51 . The applied braking forces will then begin to decelerate the assembly of the mass element  52  and braking elements  51  and thereby the components  53  that are to be tested as was described for the previous embodiments. 
         [0122]    To disengage the braking elements  51  following pre-tensioning the at least one tension spring  72 ,  FIG. 9 , the extended ends  56  of the strap  55  of the braking elements  51  are forced to separate until the braking pads  37  no longer apply any pressure to the surfaces of the rails  22  as was indicated above. When the level of the force that has to be overcome is relatively high, the task is performed with the aid of assisting devices. Using such assistive devices would also help keep the extended ends  56  in position while the piezoelectric actuator based clamping mechanism is activated. It will be appreciated by those skilled in the art that numerous pneumatic, hydraulic, electrical and pure mechanical mechanisms that are well known in the art are available for this purpose. For example, a pneumatic or mechanical jack type or extractor type mechanism may be used for this purpose. Alternatively, a simple bolt  83  that is threaded on one of the extended ends  56  may be used to provide the above separation force. 
         [0123]    It will be appreciated by those skilled in the art that the piezoelectric actuator based brake engagement mechanism of  FIGS. 9 and 10  has the advantage of being lightweight and very fast acting for very high shock level and/or very long duration deceleration pulse testing. 
         [0124]    In the embodiment of  FIGS. 9 and 10 , the piezoelectric actuator  81  is shown to be used to provide the described “locking” force to prevent relative motion between the blocks  73  and  74  to prevent the at least one pre-tensioned tension spring  72  to apply braking force via the brake pads  37 , i.e., to keep the braking elements  51  disengaged. It will be, however, appreciated by those skilled in the art that other types of actuation mechanisms such as those based on magnetostrictive materials, pneumatic or hydraulic pistons, or the like may also be used for the same purposes. 
         [0125]    In another embodiment of the brake engagement mechanism shown in the schematic of  FIG. 11 , the piezoelectric actuator based mechanism of  FIGS. 9 and 10  is replaced with the linkage mechanism. The at least one pre-tensioned tension spring  72  is still mounted between the extended ends  56  of the strap  55  of the braking elements  51  to provide the desired brake pad  37  pressure over the surfaces of the rails  22  to generate the required braking forces for the desired mass element  52  deceleration levels. The linkage mechanism of this brake engagement mechanism consists of two links  84  and  85 , which can be of equal lengths, and which are attached to each of the extended ends  56  of the strap  55  of the braking elements  51  by pin joints  86  and  87 , respectively, as shown in the schematic of  FIG. 11 . The two links  84  and  85  are in turn attached together by the pin joint  88 . 
         [0126]    Then to keep the braking element  51  disengaged and allow for free downward movement of the mass element  52 , the extended ends  56  are separated, subjecting the tensile springs  72  to further tension, until the brake pads  37  no longer apply pressure to the surfaces of the rail  22 . The stiffness of the at least one tensile spring  72  and the lengths of the two links  84  and  85  are selected such that at this state of the extended ends  56 , the links  84  and  85  can be positioned in the configuration shown in  FIG. 11  with the one or both links or their connecting joint  88  resting against a relatively rigid block  89  as can be seen in  FIG. 11 . It will be appreciated by those skilled in the art that in the configuration shown in  FIG. 11 , the forces exerted by the tensile springs  72  is supported by the links  84  and  85  since the forces would tend to press the connecting joint  88  (or one or both links  84  and  85 ) against the stop block  89 . It will also be appreciated by those skilled in the art that by ensuring that in the configuration of the links  84  and  85  the angle  90  that the links make with the line  93  passing through their joints  86  and  87  is relatively small, such as around 5-10 degrees, therefore the lateral force required to be applied to the joint  88  (in this case by the cable  91 ) in the direction of the arrow  92  in order to displace the joint  88  from its indicated position in  FIG. 11  (to the left of the line  93 ) passed through the singular position (i.e., lined up with the line  93 ) of the links  84  and  85  and moved towards the right side of the line  93  as shown by the dotted line. Once the links  84  and  85  are brought past their singular position, they can no longer oppose the forces applied by the at least one tensile springs  72 , and braking elements  52  are rapidly engaged. 
         [0127]    To perform shock testing, the braking elements  52  are placed in their disengaged state as was described above, i.e., with the links  84  and  85  in their configuration shown with solid lines in  FIG. 11 . The assembly of the mass element  52  and braking elements  51  can then be accelerated downwards using one of the aforementioned methods with the disengaged braking elements  52 . Then once the mass element  52  has gained its desired downward velocity in the direction of the arrow  54  (see  FIG. 5 ), the cable  91  is pulled in the direction of the arrow  92  as was described previously for the embodiments of  FIGS. 6 and 7 , thereby moving the links  84  and  85  past their said singular position and towards the configuration shown with dotted lines in  FIG. 11 . The at least one pre-tensioned tension springs  72  will then rapidly engage the braking elements  51  and the resulting braking forces will begin to decelerate the assembly of the mass element  52  and braking elements  51  and thereby the components  53  that are to be tested. 
         [0128]    The brake engagement and disengagement mechanism of  FIG. 11  has a number of advantages. Firstly, it adds minimal weight to the braking elements  51 . Secondly, it requires relatively small amount of force (to be exerted by the cable  91 ) to engage the brake. Thirdly, since the linkage (links  84  and  85 ) has to be displaced a relatively small distance to engage the brake, the time taken to engage the brake is also very short. 
         [0129]    In the embodiments of  FIGS. 2, 4 and 5 , the mechanical shock testing machines, to increase structural rigidity of the machines, it is generally desirable to provide a relatively rigid structure  94  similar to the base structure  24  to bridge the top ends of the rails  22  to keep them from relative deflection. 
         [0130]    In the embodiments of  FIGS. 2, 4 and 5  the mechanical shock testing machines are shown to be vertically installed. The advantage of installing the machines vertically is that gravity is also used for downward acceleration of the mass elements. However, if relatively high deceleration levels with significantly longer durations are desired to be achieved, then the total length of travel of the machine mass element becomes too long to make a vertical machine practical. For example, for a deceleration level of 4,000 G and duration of 10 milliseconds, the mass element and braking element assembly of the embodiment of  FIG. 5  have to travel about 2 meters only during the pulse duration. Thus, considering the considerable travel that is required to accelerate the mass element assembly to the required velocities and the safety margins that have to be provided, it becomes clear that the total length of the required rails will be too long to make vertical installation practical. For these reasons, when relatively high deceleration pulses and long pulse durations are required, then horizontal installment becomes the only practical option. 
         [0131]    It will be, however, appreciated by those skilled in the art that when using relatively long rails over which a carriage (in this case a mass element such as the mass element  52  with the attached braking elements  51 ) is to travel, then the rail has to be supported along its length, at least at several points. This means that the carriage bearing has to have at least a section of it open to allow travel over the rail supports. Thus, round rails such as the rails  22  of the embodiments 2, 4 and 5 and their corresponding braking elements ( 29  in  FIGS. 3A and 3B and 51  in  FIG. 6 ), cannot be used. In such mechanical shock testing machines, rails of different cross-sectional areas may be used. The rail supports may be continuous or be provided at certain intervals along the length of the rail. In general, the designs can be provided with continuous rail supports to eliminate vertical deflection of the rail between supports which would cause the mass element (carriage) assembly to be subjected to an undesirable up and down and possibly lateral oscillatory motion disturbances with high frequency content. Such motion disturbances may significantly affect the shock testing results, particularly since in addition to the resulting unwanted up and down and lateral acceleration/deceleration loading of the components that are being tested; they would also cause the applied braking forces to vary during the applied deceleration pulses. 
         [0132]    The schematic of the third embodiment  100  of the mechanical shock testing machine is shown in  FIG. 12 . The shock testing machine  100  is horizontally installed e.g., so that it could accommodate relatively long rails as was described above. The rails  96  and  97  are attached to the machine structure  102  (only shown as ground) by rigid support structures  98  and  99 , which are more clearly shown in the cross-sectional view of  FIG. 14 . The rails  96  and  97  can be provided with relatively rigid end structures  108  and  109 . A mass element  95  is provided with sleeve bearings  103  and  104  as shown in the cross-sectional view of  FIG. 14  to travel along the rails  96  and  97  freely with minimal friction. Considering that the mass element  95  is accelerated from close to its left-most position as shown in  FIG. 12  using one of the aforementioned methods described for the embodiments of  FIGS. 2, 4 and 5 , a proper shock absorber  110  is provided on the rigid support structure  109  in case that the braking elements to be described below fail to bring the mass element  95  as it travels in the direction of the arrow  111  during a shock testing event. 
         [0133]    The braking elements  113  of the embodiment  100  of the mechanical shock testing machine may be configured as the embodiment  30  of  FIG. 2  in which the braking elements ( 29  in  FIG. 2 ) are normally engaged and positioned downstream for the mass element ( 23  in  FIG. 2 ) to engage at a prescribed velocity. In the schematic of the embodiment  100  of  FIG. 12 , similar and already engaged braking elements  113  are shown as similarly positioned at a certain distance from the indicated initial position of the mass element  95 . Embodiments of the braking element  113  design are described below. 
         [0134]    Alternatively, the braking elements  112  (shown in dotted lines) of the embodiment  100  of the mechanical shock testing machine may be configured as the embodiment  50  of  FIG. 5  in which the braking elements ( 51  in  FIG. 5 ) are initially disengaged and attached to the mass element ( 52  in  FIG. 5 ) and is engaged once the mass element has gained a prescribed velocity. In the schematic of the embodiment  100  of  FIG. 12 , similar (disengaged) braking elements  112  (in dotted lines) are shown as similarly attached to the mass element  95 . Embodiments of the braking element  112  design are described below. 
         [0135]    The top view of a section of the third embodiment  100  of the mechanical shock testing machine is shown in  FIG. 13 .  FIG. 13  shows the top view of a section showing the mass element  95  of the mechanical shock testing machine  100  and its rails  96  and  97  over which it travels. As can be seen in the cross-section C-C of  FIG. 13  which is shown in  FIG. 14 , the mass element  95  rides over the rails  96  and  97  with the provided bearing sleeves  103  and  104 , respectively. The rails  96  and  97  are attached to the machine structure  102  (not shown) by support structures  98  and  99 , respectively. The support structures  98  and  99  can be made out of solid steel or stainless steel to be very rigid. The machine structure  102  is can also be made out of heavy structural steel and can be firmly attached to a concrete slab to withstand the testing shock loading with negligible vibration. 
         [0136]    As can be seen in the cross-sectional view of  FIG. 14 , the rail bearings are positioned in the mass element  95  such that the center of mass of the mass element  95  is positioned essentially in the plane of long axes of the rails  96  and  97  so that as the mass element is being subjected to the shock testing deceleration pulse, the mass element would not tend to tip over. In addition, the mass element  95  is provided with a pocket  101  for positioning the components  105  ( FIGS. 13 and 14 ) which are being tested as close as possible to the center of mass of the mass element  95 . However, if a testing component  106  is too large to fit the pocket  101 , then it may be mounted over the surface  107  of the mass element  95  as shown in  FIGS. 12 and 13 . 
         [0137]    A cross-sectional view taken along line B-B in  FIG. 12  of the braking elements  113  is shown in the schematic of  FIG. 15 . The braking elements  113  are very similar to the braking elements  29  of the mechanical shock testing machine embodiment  30  of  FIG. 2 , except that the braking elements  113  have to accommodate the rail  96  support structure  98  ( 99  for the rail  97 ). As can be seen in  FIG. 15 , the braking elements  113  are similarly provided with several braking pad segments  114  (in the schematic of  FIG. 15 , four braking pad segments) that are in close contact with the surface of the rail  96 . Gaps  115  can be provided between the braking pad segments  114  to minimize their interference during testing (as they slide down the rail  96 ) as well as while adjusting the braking pads  114  pressure on the surface of the rail  96  as will be described later in this disclosure. In general, since most braking pad materials are relatively soft and fragile, they are provided with relatively strong and stiff backing plates (collectively indicated as the braking pads  114 ) to ensure relatively uniform distribution of the applied braking pressure as will be described below. Alternatively, the braking pad materials may be attached to a single “C” shaped sleeve  117  (such as being made out of thin spring material) as shown in  FIG. 15 . 
         [0138]    It will be appreciated by those skilled in the art that numerous methods may be used to apply pressure to the braking pad segments  114  against the surface of the rails  96  and  97  to generate the desired braking forces. However, as was previously discussed, it is highly desirable for the braking elements  113  to be as lightweight as possible to minimize the aforementioned impulsive impact forces generated as the mass element  95  comes into contact with the braking elements  113  as was described for the embodiment  30  of  FIG. 2 . For these reasons, the means of applying pressure to the braking pad segments  114  must also be lightweight and allow for easy adjustment of the braking forces, i.e., the pressure between the braking pads  114  and the surfaces of the rails  96  and  97 . A very simple such lightweight means for applying pressure to the braking pads  114  is the use of at least one “C” shaped spring element  116  (similar to the elements  65  in  FIG. 6 ), which is/are preloaded to apply the desired level of compressive force to the braking pad segments  114  to achieve the desired level of pressure between the braking pads and the surfaces of the rails  96  and  97 , thereby to achieve the desired braking element  113  forces. The advantages of using the at least one “C” shaped spring element  116  include design simplicity and capability of using several of them along the length of the braking pads  114  to achieve a relatively uniform distribution of braking forces. In addition, by using several such “C” shaped spring elements  116  with different levels of preloading levels, almost any braking force level can be obtained with the accuracy levels that are expected for shock testing. 
         [0139]    In another embodiment of the braking elements  113 , the forces to be applied to the braking pad segments  114  of the braking elements  113  ( FIG. 12 ) to generate the desired braking forces are provided using certain means such as those that will be described using the schematics of  FIGS. 16 and 17 . 
         [0140]    In these embodiments of the braking elements  113 , as can for example be seen in the schematic of  FIG. 16 , all components of the braking elements are the same as those of the embodiment of  FIG. 15 , except the following. Firstly, the at least one “C” shaped spring elements  116  can be eliminated. And secondly, the braking pad segments  114  materials are provided with the backing “C” shaped sleeve  117  as was previously discussed. The “C” shaped sleeve  117  can be made out of relatively thin and easily bending spring plate that would provide minimal resistance to externally applied pressure in the direction of pressing the braking pad segments  114  against the surfaces of the rails  96  and  97 ,  FIGS. 12 and 15 . In this embodiment, the braking elements  113  are provided with a relatively “rigid” and “C” shaped structure  118 , which can cover most of the surface of the backing “C” shaped sleeve  117  as shown in  FIG. 16 . The “C” shaped structure  118  can be lightweight but strong and can also be stiff and is used as a structure for applying force to the braking pad segments  114  via the “C” shaped sleeve  117 . It will be appreciated by those skilled in the art that numerous methods and means can be used for this purpose. Several such methods and means are described below, noting that it is highly desirable for such method to provide lightweight means with readily adjustable force level capability. It will, however, be appreciated by those skilled in the art that other methods and means known in the art may also be used for this purpose. 
         [0141]    In one embodiment, so-called pneumatic bags  119  (similar to pneumatic lifting bags or blood pressure measurement cuffs), commonly constructed with thin and flexible material with relatively inextensible layers are positioned between the “C” shaped sleeves  117  and the relatively rigid “C” shaped structure  118  as shown in  FIG. 16 . Then by pressurizing the pneumatic bags  119  through a one way valve, for example similar to those used in basketballs or those used for tires (not shown) to an appropriate level, the desired level of pressure is applied to the braking pad segments  114  via the “C” shaped sleeve  117 . Advantages of using such pneumatic pressure bags  119  are their wide availability; being very lightweight; ease of pressure and thereby braking force adjustment; ease of assembly with the braking elements  113 ; and low cost. 
         [0142]    In another embodiment shown in the schematic of  FIG. 17 , the braking forces are generated by the braking elements  113  by compressive forces generated using a “C” clamp  125 . The “C” clamp  125  uses the “C” shaped structure  120  to apply compressive force to the braking pad segments  114  via the “C” shaped sleeve  117 . The “C” clamp  125  is provided with the end element  121  on one end, which has curved surfaces to closely engage the “C” shaped sleeve  117  of the braking pad segments  114  as shown in  FIG. 17 . A relatively thin layer of rubber or the like lining material (not shown) can be placed on the contacting surfaces of the end element  121  to ensure that the applied compressive forces are properly distributed over the contacting surface of the “C” shaped sleeve  117 . The end element  121  can be attached to the “C” shaped structure  120  of the “C” clamp  125  by a ball joint  124  to minimize the required efforts for proper positioning of the “C” clamp over the braking elements  113 . On the opposite end  126  of the “C” shaped structure  120  of the “C” clamp  125 , a tightening bolt  123  is provided that is threaded to the end  126  of the “C” shaped structure  120  which is used to apply compressive force to the “C” shaped sleeve  117  via the element  122 . Similar to the end element  121 , the element  122  can also be made with curved surfaces to closely engage the “C” shaped sleeve  117  of the braking pad segments  114  as shown in  FIG. 17 . A relatively stiff spring  127 , such as those made with a set of Belleville washers, can be positioned between the bolt  123  and the element  122  to facilitate compressive force level adjustment. A relatively thin layer of rubber or the like lining material (not shown) can also be placed on the contacting surfaces of the end element  122  to ensure that the applied compressive forces are properly distributed over the contacting surface of the “C” shaped sleeve  117 . 
         [0143]    In the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 , respectively, rails with circular cross-sections were shown to be used. In the construction of these embodiments, particularly since these mechanical shock testing machines are intended to be used in tests in which the mass elements ( 23 ,  52  and  95  in the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 ) are required to gain very high velocities prior to impact, then the bearings to be used in the mass elements are sleeve type bearings designed for high speed operation such as “Black Racer Ceramic Coated Linear Bearings” available from Daemar USA, Inc of Atlanta, Ga. Such bearings are available as full cylindrical sleeves for embodiments  30  and  50  of  FIGS. 2 and 5  as well as sectional sleeves for the embodiment  100  of  FIG. 12 . 
         [0144]    It will, however, be appreciated by those skilled in the art that if either of the mechanical shock testing machine embodiments  30 ,  50  or  100  of  FIGS. 2, 5 and 12 , respectively, is designed for tests in which their corresponding mass elements are not required to gain very high speeds, then one may use ball bushing type of bearings in the construction of their mass elements ( 23 ,  52  and  95  in the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 ). Such ball bushings are well known in the art and are widely available in the commercial market. 
         [0145]    In the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 , respectively, rails with circular cross-sections were shown to be used. It will, however, be appreciated by those skilled in the art that rails with other cross-section types may also be used. In general, however, when the mass elements ( 23 ,  52  and  95  in the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 ) are required to gain very high speeds, the rails are desired to be designed to constrain all possible motions of the mass elements except their translational motion along the long axis of the rail as the rails with circular cross-sections used in the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 , respectively, are designed to do. Such motion constraining mechanisms are generally required since the mass elements are desired to be lightweight and thereby prone to lateral motions during the target braking element impact (e.g., embodiment  30  of  FIG. 2 ) or braking engagement (e.g., embodiment  50  of  FIG. 5 ). 
         [0146]    The operation of the mechanical shock testing embodiment  100  of  FIG. 12  that is equipped with the braking elements  113  with either one of the “normally engaged” embodiments of  FIGS. 15-17  or the like as described above. In such mechanical shock testing machines, the mass element  95  engages the braking elements  113  at certain prescribed velocity to provide the desired deceleration pulse (shock loading) to the components being tested as was previously described for the embodiment  30  of  FIG. 2 . 
         [0147]    An alternative embodiment of the mechanical shock testing machine  100  uses the braking elements  112 ,  FIG. 12 , which are fixedly attached to the mass element  95 —similar to the braking elements  51  of the embodiment  50  of  FIG. 5  which are fixedly attached to the mass element  52 . In this embodiment of the mechanical shock testing machine, the braking elements  112  are initially not engaged, i.e., they do not resist motion of the mass element  95  along the rails  96  and  97  by exerting braking forces. As a result, the assembly of the mass element  95  and braking elements  112  can be accelerated along the rails  96  and  97  without braking force resistance using one or more of the aforementioned means such as pre-tensioned bungee cords or pneumatic cylinders or other similar means as was previously described to gain a predetermined velocity, noting that the means of accelerating the mass element  95  can be an appropriate number of appropriately sized and pre-tensioned bungee cords. Then once the mass element and braking element assembly has gained the predetermined velocity, the braking elements  112  are engaged and begin to apply a prescribed level of braking force to the rails  96  and  97 , thereby causing the mass element  95  to be decelerated at the desired rate, thereby subjecting the testing components  105 ,  FIGS. 13 and 14 , to a predetermined and essentially constant deceleration (shock) pulse that lasts until the assembly of the mass element  95  and braking elements  112  come to rest as was previously described for the embodiment  50  of  FIG. 5 . The methods of designing and constructing the braking elements  112  and mechanisms for their activation once the mass element  95  has gained the prescribed velocity are described below. 
         [0148]    In one embodiment of the mechanical shock testing machine  100  which uses the braking elements  112 ,  FIG. 12 , which are fixedly attached to the mass element  95  is shown in the schematic of  FIG. 20 .  FIG. 20  illustrates half the cross-sectional view through the braking element  112 , noting that the full view is symmetrical about the indicated centerline  142 . All the components of the brake elements are as shown in  FIG. 15  (without the at least one “C” shaped spring element  116 ). The relatively rigid elements  143  and  144  are attached to the braking pad backing “C” shaped sleeve  117  as shown in  FIG. 20 . A double scissor shaped linkage mechanism  149  is then used to keep the braking elements  112  disengaged for free travel over the rails  96  and engage it when the mass element  95  has gained its desired speed as described below. 
         [0149]    The aforementioned double scissor shaped linkage mechanism  149  is constructed with two pairs of links  145  and  146  on the illustrated half of the cross-sectional view of  FIG. 20  and symmetrically positioned pair of links  150  and  151  for the opposite half of the cross-sectional view of  FIG. 20 . The pair of links  145  and  146  and the opposing pair of links  150  and  151  are hinged together with the pin joints  152  and  155 , respectively. The pair of links  145  and  146  are attached to the relatively rigid elements  143  and  144  with the pin joints  153  and  154 , respectively, on one end, and to the opposing pair of links  150  and  151  with the pin joints  147  and  148  on the other end (pin joint  147  connecting the links  146  and  151  and the pin joint  148  connecting the links  145  and  150 ), as shown in  FIG. 20 . The links  150  and  151  are similarly attached to the elements of the braking element  112  on the rail  97 ,  FIG. 12 . 
         [0150]    In its engaged configuration, the brake pads  114  of the braking elements  112  are pressing against the surfaces of the rails  96  and  97 ,  FIGS. 12, 15 and 20 . The brake pad pressure can be provided by preloading at least one “C” shaped spring element  116  (not shown) as was described for the embodiment of  FIG. 15 ; and/or the pneumatic bags  119  (not shown) with the backing relatively stiff “C” shaped structure  118  as shown for the embodiment of  FIG. 16 ; and/or with at least one pre-tensioned tensile springs  163  which is attached to the links  145  and  146  with the pins  164  and  165 , respectively, as shown in  FIG. 20 ; or other similar means. The pressure of the brake pads  114  over the surfaces of the rails  96  and  97  is adjusted as described for the embodiments of  FIGS. 15 and 16  and for the case of the at least one pre-tensioned tensile springs  163  by selecting the proper number, spring rate and length of the springs. 
         [0151]    In the disengaged configuration, the tips  156  and  157  of a relatively rigid U-shaped element  160  shown in  FIG. 21  are used to keep the joint  147  joining the links  146  and  151  and the joint  148  joining the links  145  and  150  at a required distance to relieve pressure of the brake pads  114  over the surfaces of the rails  96  and  97 , thereby disengaging the braking element  112  and allowing free travel of the mass element  95  along the rails. It will be appreciated by those skilled in the art that the process of disengaging the braking elements  112  requires the application of compressive pressure in the direction of the arrows  158  and  159  to overcome the aforementioned forces generated by one or more of the aforementioned means to generate braking pressures, followed by the insertion of the tips  156  and  157  of the U-shaped “holder element  160  over the joints  147  and  148  to keep the braking elements  112  in their disengaged state. 
         [0152]    A cable  161  is also attached to the relatively rigid U-shaped element  160  as can be seen in  FIG. 21 . The free end of the cable  161  is then attached to the structure  102  of the mechanical shock testing machine embodiment  100  of  FIG. 12 . Then similar to the previously described embodiment  50  of  FIG. 5 , the length of the cable  161  is adjusted so that as the mass element  95  is accelerated along the rails  96  and  97  using one of the aforementioned means and once it has attained a desired velocity, then the cable  161  is similarly pulled to dislodge the U-shaped “holder element  160 , thereby causing the braking elements  112  to be engaged. 
         [0153]    It will be appreciated by those skilled in the art that other means such as pneumatic cylinders that are pressurized to an appropriate level (not shown) may also be used to generate the desired brake pad pressures. Such pneumatic means may be used in many applications since their pressure can be readily adjusted to the desired level and also since they provide near constant compressive force (against the links  145  and  146  to tend to bring them closer to each other, thereby generating the desired braking forces) due to their required small range of displacements. For the latter reasons, such pneumatic cylinders do not require permanent connection to a source of pressurized gas. Such a pneumatic cylinder may be configured and pressurized as was previously described for the pneumatic cylinder  67  of the embodiment of  FIG. 8  to keep the joints  147  and  148  at the required distance to disengage the braking elements  112 . A cable similar to the cable  61  of  FIG. 8  is then attached to the structure  102  of the mechanical shock testing machine embodiment  100  of  FIG. 12  to similarly open the valve  70  and release the cylinder pressure once the mass element  95  as attained a desired velocity, thereby causing the braking elements  112  to be engaged. 
         [0154]    Another embodiment of the engagement mechanism for the braking elements  112  is shown in the schematic of  FIG. 22 . In  FIG. 22 , a longitudinal cross-sectional view of one of the braking elements  112  is shown together with a portion of the rail around which brake engagement occurs. The braking elements  112  are shown to be constructed with relatively rigid brake housings  166 , which are attached to the mass element  95 . The at least one braking pads  167  are then fixedly attached to the inside of the brake housing  166  as shown the schematic of the cross-sectional view D-D of  FIG. 23  of the braking element  112  ( FIG. 22 ). Gaps  172  may be provided between the braking pads  167  to prevent their interference during braking operation as well as for ease of replacement. As can be seen in  FIGS. 22 and 23 , a gap  173  is provided between the braking pads  167  and the surface of the rails (rail  96  in  FIG. 22 ) while the mass element  95  and its attached braking elements  112  are beyond the sleeves  169 , which are fixedly attached symmetrically to the rails  96  and  97 , as shown in  FIG. 22 . In the indicated positioning of the mass element  95  and braking elements  112 , the assembly can travel freely along the rails  96  and  97 . 
         [0155]    The cross-sectional view E-E,  FIG. 22 , shown in the schematic of  FIG. 24  shows the positioning of the sleeve  169  over the rail  96  and similarly over the rail  97 . The sleeves  169  are provided with tapered ends  170  on the approaching side of the mass element  95  and braking elements  112  assembly as shown in  FIG. 22 . The braking pads  167  are provided with appropriate thickness to fill the gap  168 , while the backing structure  166  provides enough elasticity to achieve a prescribed braking force once the braking pads have engaged the sleeves  169 . Then as the mass element and braking element assembly is accelerated to a prescribed velocity in the direction of the arrow  111  in  FIG. 12  and arrow  171  in  FIG. 22 , noting that the sleeves  169  are positioned downstream, such as resting against the end structure  109 , then as the braking pads  167  engage the sleeves  169 , a prescribed level of pressure is generated between the braking pads  167  and the outer surface of the sleeves  169 . The resulting braking forces will then decelerate the mass element  95  and braking elements  112  assembly at a predetermined rate, thereby subjecting the testing components attached to the mass element  95  to the same deceleration event. 
         [0156]    As can be seen in  FIG. 22 , the sleeves  169  are provided with tapered ends  170  on the approaching side of the mass element  95  and braking elements  112  assembly to provide the means for smooth and gradual engagement of the braking pads  167  with the outer surfaces of the sleeves  169 . The sleeves  169  can be provided with smooth and very hard surfaces to minimize wear and achieve relatively constant braking pressure (force) as the mass element  95  and braking elements  112  assembly is decelerated. 
         [0157]    As it will be appreciated by those skilled in the art that the brake engagement mechanism illustrated in the schematics of  FIGS. 22-24  also require a means of adjusting the braking forces once the brakes are engaged. In this embodiment, the method of adjusting the braking forces, i.e., adjusting the induced braking pressure once the braking elements  112  are engaged as described above can be by adjusting the gap  168  between the braking pads  167  and the rails  96  and  97 . 
         [0158]    One method of adjusting the gap  168  is by placing shims with appropriate thickness between the brake pads  167  and the backing structure  166 . Such a design requires that the brake pads  167  be attached to the backing structure by a fastener via separate backing plates (not shown) such as those commonly used in disc brakes in cars. Shearing pins may also be required between the separate backing plates and the backing structure  166  (not shown) for high braking forces. 
         [0159]    An alternative method of adjusting the braking forces once the brake elements  112  have engaged is by varying the stiffness of the backing structure  166  in resisting the reaction forces to the pressure applied by the brake pads  167  onto the surfaces of the raids  96  and  97 . It will be appreciated by those skilled in the art that such reaction forces would tend to “open up” the end of the “C” shaped backing structure  166 . The stiffness of the “C” shaped backing structure can then be varied by any one of the previously described methods such as by the addition of “C” shaped spring elements  116  of the embodiment of  FIG. 15  (such as with no or minimal preload) with appropriate stiffness; or external clamps similar to the “C” clamp  125  shown in  FIG. 17  but without the preloaded springs  127 , with appropriate stiffness, which may also be directly connected snugly with positioning pins to provided protrusions on the backing structure  166  (not shown); or by placing pressure preloaded compressive gas springs between the positioning pins to provided protrusions on the backing structure  166 ; or other well known means in the art. 
         [0160]    It will be appreciated by those skilled in the art that when using the sleeves  169  to engage the brake pads  167  as shown in  FIG. 22 , the bearings  103  and  104  that ride on the surface of the rails  96  and  97  must accommodate the increased diameter of the outer surface of the sleeves  169 ,  FIG. 14 . This can be accomplished simply by constructing each of the bearings  103  and  104  in longitudinal sections (similar to the brake pads  114  in  FIG. 15 ), each with proper backing springs to form two or more spring loaded bearing shoes. The springs can be nearly constant force springs and can deflect an appropriate amount to accommodate the diameter of the sleeves  169 . 
         [0161]    In the schematic of  FIG. 22 , the rails  96  (and  97 ) are shown to be provided with separate sleeves  169  to engage the brake pads  167 . It will, however, be appreciated by those skilled in the art that the sleeves  169  and its tapered portions  170  may be integral to the rails  96  and  97 . However, since the sleeve sections are more prone to wear, the section of the rail comprising of the sleeves  169  and its tapered portions  170  can be constructed as separate units and are each attached to the support structures  98  and  99  and can be aligned through centering holes and steps on either sides. 
         [0162]    In an alternative embodiment of the mechanical shock testing machine  100  of  FIG. 12 , the braking pads can be attached directly to the mass element  95  and would engage a provided contact surfaces which are mounted onto the structure of the machine  102  to generate the desired braking force. In general, the braking pads may be of any shape, but flat pads are can be used since they are easy to fabricate and shape. The corresponding brake contact surfaces, which must run parallel to the rails  96  and  97 , can also consist of flat surfaces which are significantly easier to fabricate, align and maintain. 
         [0163]    It will be appreciated by those skilled in the art that numerous such design geometries are possible for such mass element attached brake pad machine designs. In the following, two such basic design geometries that utilize planar (flat) brake pads and mating contact surfaces are described. It will however be appreciated by those skilled in the art that many other planar and/or non-planar brake pad geometries with their corresponding mating contact surfaces may also be readily designed and that the presentation of the following two examples is not intended to exclude other designs with planar and/or non-planar geometries. Planar pads are, in general, highly advantageous since they do not change shape as they wear; they are very easy to fabricate; their pressure can be easily adjusted by simple means; and they can be readily replaced. Such mass element attached brake pad machine designs can be implemented on both basic embodiments  30  ( 50 ) and  100  of  FIGS. 2  ( 5 ) and  12 , respectively. 
         [0164]    The schematic of a fourth embodiment  180  of the mechanical shock testing machine is shown in  FIG. 25 . The mechanical shock testing machine  180  may be installed either vertically or horizontally or be oriented in any arbitrary orientation. The rails  175  are attached to rigid support structures  177  and  178 . When the machine  180  is installed vertically as shown in  FIG. 25 , the support structure  177  can be fixed to a relatively massive foundation  176 . When horizontally (non-vertically) installed, both supports structures  177  and  178  can be grounded but the support structure  177  may still be used to be fixed to a relatively massive foundation  176 . As was indicated for the embodiments  30  and  50  of  FIGS. 2 and 5 , unlike the embodiment  100  of  FIG. 12 , this design has a practical limitation on the length of the rails. A mass element  179  is provided with sleeve bearings  181  as shown in the cross-sectional view F-F of  FIG. 26 . The bearing sleeves  181  are selected to allow free travel of the mass element  179  along the rails  175  with minimal friction. In the schematic of  FIG. 25 , the mass element  179  is considered to be accelerated from close to its top-most position in the direction of the arrow using one of the aforementioned methods described for the embodiments of  FIGS. 2, 4 and 5  to the desired velocity prior to deceleration via the engagement of the system brakes as described below. 
         [0165]    In the embodiment  180  of  FIG. 25 , the brake pads  183  are firmly attached to the mass element  179 . The brake pads  183  can be positioned symmetrically with respect to the rails  175  and the mass element  179  can be similarly symmetrical shaped relative to the rails  175  to minimize the level of rocking forces and moments that can be generated during the mass element acceleration as well as deceleration. The embodiment  180  is also provided with brake engaging elements  184  which are firmly attached to the structure  185  (not fully shown) of the mechanical shock testing machine  180 . The flat surface portions  186  of the brake engaging elements  184  are positioned parallel to the outside surfaces  187  of the brake pads  183 ,  FIG. 25 . Then as the mass element  179  is accelerated in the direction of the arrow  182 , at a prescribed velocity, it would enter the space between the brake engagement elements  184 , at which time the surfaces  187  of the brake pads  183  engage the surfaces  186  of the brake engaging elements  184 , thereby applying braking forces to the mass element  179  to cause the lmass element to decelerate as was previously described, thereby applying the generated deceleration to the testing components  188 , which are firmly attached to the mass element  179 ,  FIG. 25 . 
         [0166]    In an embodiment of the mechanical shock testing machine  180 , the brake pads  183  can be attached to the mass element  179  with relatively stiff springs (such as Belleville washers) placed between their backing plates and the surface of the mass element (not shown). Then by adjusting the spring preloads and the positioning of the surfaces  186  of the brake engaging elements  184  relative to the surfaces  187  of the brake pads  183 , the pressure exerted by the braking pads  183  to the surfaces of the brake engaging elements  184  and thereby the level of braking force and thereby the deceleration rate of the mass element can be varied as was previously described, for example for the embodiment  50  of  FIG. 5 . In addition, the brake engaging elements  184  can be provided with initial tapered regions  189  to allow for a smooth application of the braking forces to the mass element  179 . 
         [0167]    In general, a proper shock absorber  190 ,  FIG. 25 , is provided on the rigid support structure  177  in case that the braking elements fail to decelerate the mass element  179  to a stop. 
         [0168]    In an alternative embodiment  180  of the mechanical shock testing machine of  FIG. 25 , pairs of braking pads are used on each side of the mass element  179  (not shown in  FIG. 25 ). With this design, the cross-sectional view F-F is as shown in the schematic of  FIG. 27 . In the cross-sectional view of  FIG. 27 , the mass element  179 , rails  175 , sleeve bearing  181  and the machine structure  185  are identical to those shown in the cross-sectional view of  FIG. 26  and the embodiment  180  of  FIG. 25 . In this alternative design of the embodiment  180  of the mechanical shock testing machine, the mass element  179  is provided with the symmetrical “flanges”  191  on its both sides to the sides of which the brake pads  192  are attached. The brake pads  192  can be almost as long as the height of the mass element  179  while slightly clearing the top and bottom edges of the mass element. The mechanical shock testing machine can also be provided with the brake pad engaging plates  193 ,  FIG. 27 , which are fixedly attached to the rigid structure  185  of the machine. In this alternative design of the mechanical shock testing machine embodiment  180  shown in  FIG. 25 , the brake engaging elements  184  are replaced by the brake engaging plates  193  at similar locations close to the machine end structure  177 . As can be observed, the brake engaging plates  193  form “U-shape” channels with proper opening so that their inner surfaces  194  would engage both brake pads  192  on both sides of the mass element  179 . 
         [0169]    Then as the mass element  179  is accelerated in the direction of the arrow  182 ,  FIG. 25 , at a prescribed velocity the two pairs of brake pads  192  on each side of the mass element  179  will enter the “U-shape” channels formed by the brake engaging plates  193 , thereby causing the braking mechanism of the machine to be engaged, thereby applying braking forces to the mass element  179  and cause the mass element to decelerate as was previously described, thereby applying the generated deceleration to the testing components  188 , which are firmly attached to the mass element  179 ,  FIG. 25 . 
         [0170]    In an embodiment of the above alternative design of the mechanical shock testing machine embodiment  180 , the brake pads  192  can be attached to the “flanges”  191  of the mass element  179  with relatively stiff springs (such as Belleville washers) placed between their backing plates and the surface of the “flanges”  191  (not shown). Then by adjusting the spring preloads and the positioning of the surfaces  194  of the brake engaging plates  193 , the pressure exerted by the braking pads  192  to the surfaces of the “U-shape” channels of the brake engaging plates  193  and thereby the level of braking force and thereby the deceleration rate of the mass element can be varied as was previously described, for example for the embodiment  50  of  FIG. 5 . In addition, the brake engaging elements  193  can be provided with similar initial tapered regions (not shown) to allow for a smooth application of the braking forces to the mass element  179 . 
         [0171]    The above embodiment  180  of  FIG. 25  was a modification of the embodiment  50  of  FIG. 5 . In a similar manner, the embodiment  100  of  FIG. 12  with the braking elements  112  can be modified by providing the brake pads on its mass element and the mating braking surfaces attached to the machine structure. The schematic of the resulting fifth embodiment  200  of the mechanical shock testing machine is shown in  FIG. 28 . In the schematic of  FIGS. 28  and  29 , all members that are not enumerated are identical to those of the embodiment  100  of  FIG. 12 . A cross-sectional view G-G,  FIG. 29 , across the mass element  95  is shown in  FIG. 29 . 
         [0172]    The mechanical shock testing machine  200  can be installed horizontally so that there is minimal limitation on the length of its rails  96  and  97  and thereby the range of travel of the mass element  95 . 
         [0173]    In the embodiment  200  of  FIG. 28 , the brake pads  195  are firmly attached to the mass element  95 . The brake pads  195  can be positioned symmetrically with respect to the rails  96  and  97  as shown in the cross-sectional view of  FIG. 29 . The embodiment  200  is also provided with brake engaging elements  196 ,  FIGS. 28 and 29 , which are firmly attached the structure  102  (not fully shown) of the mechanical shock testing machine  200 . The flat surfaces  201  of the brake engaging elements  196 ,  FIG. 29 , are positioned parallel to the outside surfaces  197  of the brake pads  195 ,  FIG. 28 . Then as the mass element  95  is accelerated in the direction of the arrow  198 , at a prescribed velocity, it would enter the space between the brake engaging elements  196 , at which time the surfaces  197  of the brake pads  195  engages the surfaces  201  of the brake engaging elements  196 , thereby applying braking forces to the mass element  95  and cause the mass element to decelerate as was previously described, thereby applying the generated deceleration to the testing components  105 , which are firmly attached to the mass element  95 , as was described for the embodiment  100  of  FIG. 12 . 
         [0174]    In an embodiment of the mechanical shock testing machine  200 , the brake pads  195  are attached to the mass element  95  with relatively stiff springs (such as Belleville washers) placed between their backing plates and the surface of the mass element (not shown). Then by adjusting the spring preloads and the positioning of the surfaces  200  of the brake engaging elements  196  relative to the surfaces  197  of the brake pads  195 , the pressure exerted by the braking pads  195  to the surfaces of the brake engaging elements  196  and thereby the level of braking force and thereby the deceleration rate of the mass element can be varied as was previously described, for example for the embodiment  50  of  FIG. 5 . In addition, the brake engaging elements  196  can be provided with initial tapered regions  199 ,  FIG. 28 , to allow for a smooth application of the braking forces to the mass element  95 . 
         [0175]    It will be appreciated by those skilled in the art that for the braking mechanism embodiments of  FIG. 22 ;  FIGS. 25 and 26 ;  FIGS. 25 and 27 ; and  FIGS. 28 and 29 , the braking pad must be adjusted such that they come into contact with their corresponding brake engaging elements essentially at the same time. The braking forces provided by the braking pads on each side of the machine mass element are also highly desirable to be essentially at the same levels so that the machine mass element is subjected to minimal tipping and twisting forces and moments. The latter requirement, however, necessitates setting of the braking force levels on each side of the mass elements separately. However, it will be appreciated by those skilled in the art that since friction forces are very difficult to accurately control and they usually vary significantly by environmental effects and wear and it is difficult to very accurately measure, therefore one should expect certain level of difference between the braking forces that in practice will be applied to each side of the mass element. The sleeve bearings of the mass elements must therefore be designed to handle such differences in the braking forces on each side of the mass element. 
         [0176]    Therefore, the braking mechanism of the mechanical shock testing machines embodiments of  FIG. 22 ;  FIGS. 25 and 26 ;  FIGS. 25 and 27 ; and  FIGS. 28 and 29  may be provided with means to equalize the braking pad pressure on either side of the related mass elements to minimize the difference between the resulting braking forces on either side of the mass elements. In the above embodiments of the present mechanical shock testing machines, this can be achieved by linking the brake pads on both sides of the mass elements and via preloaded compressive springs as described below for the braking mechanism of the embodiment  200  of  FIGS. 28 and 29 . 
         [0177]    The above brake pad pressure equalizing mechanism for the brake engagement mechanism of the mechanical shock testing machine embodiment  200   FIGS. 28 and 29  is shown in the schematic of  FIG. 30 . In this embodiment, all components that are shown are the same as those shown in  FIGS. 28 and 29  except for the braking mechanism herein being described. In this braking mechanism, the braking pads  202  are fixedly attached to the relatively rigid backing supports  203 , which are in turn fixed to the pins  204 , which are free to slide through the corresponding guide holes provided in the mass element  95 . The pins  204  are provided with heads  205  which would limit outward motion of the braking pads  202  to position the surfaces  201  ( FIG. 29 ) of the braking pads  202  at proper distance from the surfaces  206  ( FIG. 29 ) of the brake engaging elements  196  for proper engagement and brake pressure generation. Compressive springs  207  are then provided between the heads  205  of the pins  204  and are preloaded to appropriate levels so that as the brake pads  202  engage the brake engaging elements  196  as was previously described for the embodiment  200  ( FIG. 29 ), the desired level of brake pressure is generated. 
         [0178]    It will be appreciated by those skilled in the art that as the brake pads  202  engage the brake engaging elements  196 ,  FIG. 30 , the heads  205  of the pins  204  are pushed inward, thereby separating them from the mass element  95  surfaces with which they were in contact. As a result, the springs  207  are enabled to apply equal pressure to the corresponding brake pads  202 . 
         [0179]    In the schematic of  FIG. 30 , the basic method of equalizing brake pad pressure on either side of the mass element of the mechanical shock testing machine embodiment  200  of  FIG. 28  is illustrated. It will, however, be appreciated by those skilled in the art that the same method can be applied to other similar embodiments, such as those of  FIG. 22 ,  FIGS. 25 and 26 , and  FIGS. 25 and 27  to achieve the same goal of equalizing brake pad pressure on both sides of the corresponding mass elements of the indicated mechanical shock testing machines. 
         [0180]    It will also be appreciated by those skilled in the art that many other linkage mechanisms or hydraulic or pneumatic means commonly used in the art may also be used in place of springs  207  to achieve similar braking pad pressure equalization of the mechanism of  FIG. 30 . 
         [0181]    It will be appreciated by those skilled in the art that similar to the mechanical shock testing machine embodiments  30  and  50  of  FIGS. 2 and 5 , respectively, the horizontally installed mechanical shock testing machine embodiments such as embodiments  100 ,  180  and  200  of  FIGS. 12, 25 and 28 , respectively, also allow for similar rapid and accurate setting of the braking force that is provided by their braking elements. The method and means of rapidly and accurately performing the brake force setting is as is described with reference to the schematic of  FIG. 4  for the mechanical shock testing machine embodiment  30  of  FIG. 2 . Similar set up with means of applying force such as the indicated commonly used mechanical or hydraulic jack  44  which is similarly positioned between the machine structure and the braking elements may be used together with an intermediate force gage as was described for schematic of  FIG. 4 . 
         [0182]    In all the above disclosed mechanical shock testing machine embodiments, the machines are provided with two rails over which the mass elements (for example, elements  23 ,  52  and  95  in the embodiments  30 ,  50  and  100  of  FIGS. 2, 5 and 12 ) travel. It will, however, be appreciated by those skilled in the art that one or more than two rails may also be similarly used. 
         [0183]    An advantage of using a single rail is that lighter mass elements may be used. The mass element however should be provided with a guide to prevent it from rotating about the rail when rails with circular cross-sections are used. This can, for example be accomplished as shown in the schematic of  FIG. 18 . In  FIG. 18 , the cross-sectional view of the mass element  130  is shown as assembled with a sleeve bearing  132  over the rail  131 . The mass element  130  is also provided with an appendage  133  which rides inside the U-shaped guide  134 , which is attached to the machine structure  135 . As a result, as the mass element  130  travels along the length of the rail  131 , the U-shaped guide  134  prevents the mass element  130  from rotating about the rail  131 . A disadvantage of single rail mechanical shock testing machines is their limited surface for mounting components for shock testing. In particular, such machines cannot handle large and/or relatively heavy components since they have to be mounted on one side of the rail, subjecting the mass element and the test component to tipping accelerations and forces. 
         [0184]    The use of more than two rails which are not co-planar to guide the mass element has several advantages. In general, all these advantages are achieved using three or at most four rails. The main advantage of using three or four rails that are not co-planar is that they would minimize the tendency for the mass element to tip over during the testing shock loading (deceleration pulse) due to usually unavoidable nonsymmetrical shock loading and/or mass distribution of the mass element and testing component assembly. The second advantage of using three or four rails that are not co-planar is that they could provide a significantly larger mass element surface area for testing component mounting, thereby can handle significantly larger components for shock testing. 
         [0185]    In general, since there is no advantage in using non-symmetrical positioning of the rails, the rails of a three-rail and four-rail mechanical shock testing machine can be positioned at equal distances, i.e., at the corners of an equilateral triangle and corners of a square, respectively, as shown in the schematics of  FIGS. 19A and 19B , respectively.  FIG. 19A  shows an equilateral triangle arrangement of the rails  138  of a mechanical shock testing machine to accommodate a mass element  136  (which can be symmetrically shaped) with its sleeve bearing  137 .  FIG. 19B  shows a rectangular arrangement of the rails  141  of a mechanical shock testing machine to accommodate a mass element  139  (which can be symmetrically shaped) with its sleeve bearing  140 . 
         [0186]    In the embodiments  50  and  100  of  FIGS. 5 and 12 , the braking elements  51  and  112 , respectively, are shown to be separate units that are attached to the corresponding mass elements of the mechanical shock testing machines. It will be, however, appreciated by those skilled in the art that most of the disclosed braking element designs may be integrated into the mass elements of these machines. Such integrated mass element and braking element designs could significantly reduce the total decelerated mass (i.e., the total mass of the mass element and the braking elements). Such integrated mass element and braking element designs may be more cumbersome to assemble and maintain, particularly since the braking pads have to be regularly replaced in mechanical shock testing machines, particularly if they are used to perform relatively high G shock testing. As a result, the advantages and disadvantages of the integrated designs must be considered and matched against the frequency of use of the mechanical shock testing machine. 
         [0187]    While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.