Abstract:
An apparatus for testing panel products in edgewise shear in which the shear stress is applied in a diagonal direction with a first rotational degree of freedom in a first grip means and a second rotational degree of freedom in a second grip means as a first loading configuration. A second loading configuration is provided in which the second rotational degree of freedom of the second grip means is locked in place and motion is prevented. A third preferred method of loading is available in which shear forces in a horizontal direction through a centerline of a specimen, with the centerline in the plane of the specimen and extending across a widest dimension of said specimen. Control and data collection are under computer control and operator safety is enhanced by a locking guard door which is electrically locked while the various parts of the machine are in motion.

Description:
RELATED APPLICATION 
     Benefit is claimed of provisional application titled: “Rail Shear Tester Apparatus with multiple loading configurations” Application No. 61/987,311 filed 2014 May 1. 
    
    
     REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was funded entirely by private funds in privately owned facilities. This invention did not arise from any funding or sponsorship of the federal government or any other government entity. There was no joint research agreement of any kind that contributed in any way to this invention. 
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to testing and qualification of panel products and more specifically to the panel products destined to be used under shear stress such as wood I-joist web members or similar applications in which the shear strength of the panel materials is an important design parameter. 
     2. Importance of the Invention and Prior Art 
     Particleboard panel products are manufactured by producing a flow of wood pieces of varying dimension ranging in size from wood dust to large flakes or strands, mixing with a resin-wax binding agent and followed by forming a mat of the wood particle—resin—wax mix and placing the mat in a press where the resin is cured under heat and pressure thereby binding the particles together and forming a useful panel product. A wide variation in wood particle type and resin content is used and therefore a wide variation in physical properties of the panel products is available for various applications. When such a panel is to be used for a structural application it is essential that the characteristics of the wood particles, resin, wax and pressing time and temperature be controlled so that the desired properties emerge in the finished goods. For enhanced properties the wood is prepared in strands cut along the grain direction of the wood, and the strands are oriented in a preferred direction in the process of forming the mat before it goes into the press. 
     Plywood may be manufactured using a wide variety of wood veneer species and grades, and varying in the number of plies, thickness of the wood veneer, as well as resin and pressing time and temperature. If plywood is to be used in a shear loading configuration it is important to know the shear strength in plywood. 
     For the manufacturer of the wood I joist product, web material may be purchased from a variety of sources and it is essential to the integrity of the I-joist product that the panel products meet requirements for durability, thickness and shear strength. Because the wood I-joist is replacing the wide solid-sawn wood joist in much residential and light commercial construction, it is important to public safety that these materials be properly tested in an on-going quality control program. 
     ASTM D5055 “Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists” refers to ASTM D1037 in respect of shear strength in the web members of the composite wood I-joist. Therefore the need is established for an accurate testing machine that will perform the required testing. With increasing volume of these products going into construction, a test that requires a minimum of labor input is also very desirable. 
     With panel products manufactured as plywood or particleboard being used more extensively as web members in a wood “I” joist configuration it is imperative that the horizontal shear strength of these panel products be verified and properly characterized so that the design of these wood I-joist products will perform as bending members in structural service. 
     DEFINITIONS 
     “Guard door”—An operator safety door that prevents access to moving parts while the equipment is in motion. 
     “Testing rails”—Part of a prior art “rail testing” apparatus which capture a rectangular panel specimen for performing a shear test in a universal testing machine. 
     “Roller rails”—In the present invention the roller rails provide a working surface upon which cam rollers ride to carry the weight of a clamp assembly. 
     “Unclamped area”—That portion of a panel specimen which is outside the grip area of an upper clamp means and a lower clamp means. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a tester for performing edgewise shear tests on samples of panel product in which three loading configurations are provided to simulate prior art diagonal loading with or without rotational constraint, and a third configuration to simulate the shear stresses that exist in a structural assemblage including panel or sheet goods in which such goods are used as a web member in a beam configuration as a box beam or an “I” beam and knowledge of the shear strength is essential for producing a safe structure. The present apparatus operates under computer-control to automatically perform the shear test and record the test results 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is presented in a preferred embodiment in the following drawings. 
         FIG. 1  is an isometric view of the Apparatus with covers removed to show internal components. 
         FIG. 2  is an isometric view of the Apparatus with covers installed showing location of major components. 
         FIG. 3  is an isometric view of the Apparatus with covers installed showing location of hydraulic pump, tank fill gauge and thermometer. 
         FIG. 4  is a top view of the Apparatus showing the arrangement of clamps and loading cylinder. 
         FIG. 5  is a mechanical schematic describing the loading arrangement for shear testing in the present invention in a first and second loading configuration. 
         FIG. 6  is a mechanical schematic describing the loading arrangement for shear testing in the present invention in a third loading configuration. 
         FIG. 7  is a hydraulic schematic showing pump, controls, and cylinders. 
         FIG. 8  is an electrical connection diagram showing components inside the electrical control cabinet. 
         FIG. 9  is an electrical connection diagram showing components outside control cabinet. 
         FIG. 10  is a vertical side view of a lower clamp including a pneumatic gate. 
         FIG. 11  is a bottom view of a lower clamp showing arrangement of hydraulic cylinder, coupler, slider, jaws and pneumatic gate. 
         FIG. 12  is a vertical cross section of a lower clamp showing pneumatic gate, pneumatic lift cylinder and travel stops for lower clamp assembly. 
         FIG. 13  is an isometric view of clamp slider showing slide bearings, jaw insert and jaw retaining means. 
         FIG. 14  is a pneumatic schematic diagram showing input connection, valve, filter, lubricator and valves. 
         FIG. 15  is a prior art specimen showing preparation for connection to testing rails for testing in a conventional universal test machine. 
         FIG. 16  is a prior art fixture connection to a test specimen using bolts. 
         FIG. 17  is a prior art apparatus with specimen under load in a conventional test machine. 
         FIG. 18  is an edge-view of a prior art specimen under load in a conventional test machine. 
         FIG. 19  is a state diagram for the control functions of the present invention. 
         FIG. 20  is a diagram of a computer control screen showing specimen data entry, testing methodology settings, control panel for controlling individual functions, and a state screen where operator inputs are entered to start the test sequence and save test results. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the present apparatus in an isometric view. A framework  2  encloses a hydraulic pump  6  with tank sight gauge and thermometer  8 , a load cylinder  14 , a displacement sensor  28 , a load cell  4  a clevis eye connection  10  a guard door lock  26  a guard door  24 , a photo sensor transmitter  16 , a photo sensor receiver  18 , an upper clamp assembly  22 , and a lower clamp not shown with a pivot means  12 , an electrical control cabinet  20 , a panel-type touch-screen PC computer  31  and mounting means  30  and resting on adjustable feet  34 . The present apparatus is shown in  FIG. 1  arranged to perform a rail shear test according to ASTM D 1037 Sec 130 with full conformance with the loading arrangement in which the edgewise specimen is loaded along a diagonal direction. 
     The load cylinder  14  mounting arrangement includes an angled bracket  32  that establishes the loading angle in the specimen. An alternative loading arrangement of horizontal shear through the horizontal centerline of the specimen is achieved by removing angled bracket  32 , changing clevis eye connection  10  for a new part not shown, and replacing angled roller rails  11 ,  13  and  15  shown in  FIG. 4  for the upper clamp assembly with non-angled roller rails. The lower clamp assembly is then locked in place for operation in horizontal shear mode. 
       FIG. 2  shows the apparatus of the present invention with safety covers in place. The guard door  24  is unlocked only when the hydraulic system is disabled and the clamp cylinders and the load cylinder cannot move. Computer mounting arm  30  can pivot about its mount in the frame for convenient location of the computer screen not shown. Electrical power is connected to the electrical control enclosure  20  and the machine rests on adjustable mounts  34  for leveling the machine and allowing for uneven floor surface. 
       FIG. 3  shows a view of the present apparatus in which an opening  7  is provided for inserting a bin for catching tested specimens when they drop out of the machine after test. The hydraulic pump  6  and sight gauge for oil tank  8  are located in view of an operator for convenient checking. 
     The top view of the present apparatus in  FIG. 4  shows the location of hydraulic pump assembly  6 , loading cylinder  14 , load cell  4 , clevis connection  10 , and replaceable angled roller rails  11 ,  13  and  15  which carry the weight of the upper clamp assembly  21  including clamp cylinder  22  coupling device  40 , clamp slide  41  and lubrication connections  42 . A lower clamp assembly  188  is suspended on a distal side by pivot pins,  12  and on a proximal side by pneumatic cylinder means  190  shown in  FIG. 12 . Lower clamp assembly  188  includes a clamp cylinder  38 . In operation a specimen is placed in opening  36  shown in  FIG. 4  where it is held in place by pneumatic gate means  166  shown in  FIG. 12 . Hydraulic closure of clamp assemblies  21  and  188  shown in  FIG. 4  is followed by load applied by load cylinder  14  while testing force is measured by load cell  4  and displacement is monitored by displacement sensor  28  (shown in  FIG. 1 .) 
       FIG. 5  is a mechanical schematic showing the specimen  400  captured by grips  402  and  403  with shear force  406  and  408  being delivered through pivot connections  404  and  410 . Pivot  410  is attached to beam  422  by means (not shown), and shear force  406  is delivered such that the line of force through the specimen  322  is in a diagonal direction through the specimen from corner-to-corner of the unclamped area. The weight of the lower grip assembly  403  is supported by pneumatic lift cylinder  416  coupled by pivot means  418  to the lower clamp assembly. Pneumatic lift cylinder  416  is attached to support beam  422  by pivot mount  420 . Stop bolt  412  is attached to support beam  422  and jam nuts  414  are placed allowing the lower clamp mechanism to rotate between limits established by the head of stop bolt  412  and the location of jam nuts  414  so that displacement of the specimen arising from shear deflection will allow the lower clamp  403  to pivot about its mounting pivot  410  thereby displacing pneumatic lift cylinder  416 . 
     A second loading method places lower clamping means  403  in a fixed position by adjusting jam nuts  414  to prevent the lower clamping means from pivoting, thereby holding it in a fixed position. 
     In an alternative loading arrangement shown in  FIG. 6  the line of force  430  is directed along the centerline of the specimen by the present invention apparatus by making some simple adjustments to the apparatus whereby the shear force  428 ,  434  is directed through a pivot point  426  and  432  the centerline of which coincides with the centerline of the specimen  400 . This mode of operation is enabled by removing the load cylinder angled bracket  32  shown in  FIG. 1 , and mounting the load cylinder directly to the support frame  33 , also shown in  FIG. 1  replacing angled roller rails  11 ,  13  and  15  shown in  FIG. 4  are removed and replaced with non-angled roller rails. Thus an important feature of the present invention is its adjustability to 3 different loading arrangements. 
       FIG. 7  shows the hydraulic schematic diagram, including reservoir  78  from which oil is drawn through input screen  50  by pump  52  and delivered to clamp valve  74  and hydraulic shear valve  58 . With the clamp cylinders  68  and  70  (schematic representation of clamp cylinders  22  and  38  respectively in  FIG. 4 ) activated and closed as indicated by pressure switch  56 ; the load cylinder  66  (a schematic representation of load cylinder  14  on  FIG. 1  and  FIG. 4 ) is then activated by valve  58 . A proportional control valve  60  with check valve  72  and pilot bypass valve  62  operate to deliver a controlled flow of hydraulic oil to load cylinder  66  until failure of the specimen which is indicated by a reduction of force in load cell  4  ( FIG. 1 ). Proportional control valve  60  is electrically driven by means of a pulse-width modulated control voltage whereby the flow rate of hydraulic fluid is adjustable under computer control. The maximum pressure delivered to load cylinder  66  is limited by adjustable bypass pressure relief valve  64 . Upon failure of the specimen, gate  166  shown in  FIG. 12  is opened, the clamp cylinders  68  and  70  are retracted, and finally the load cylinder  66  is retracted. Upon full retraction of all the cylinders, the pump is turned off and the guard door lock  26  in  FIG. 1  is deactivated. 
     The control cabinet  20  in  FIG. 1  and  FIG. 2  contains the electrical apparatus shown in  FIG. 8 . This includes an Ethernet connection  90 ; a processor  92 , relays  94  and  96 , input power connections  122  and  124 , power switch  118 , terminal blocks  117 , fuse  116 , Rino PSB24-240 power supply  115 , a Leuze RL-11 safety switch  114 , load cell amplifier  112 , and safety lockout switch  110  and connection  106  to guard door lock. In one preferred embodiment of the present invention the processor  92  is a Galil RIO-47112 processor card. Hydraulic valve control connector  98 , gate control connector  100 , load cell connector  102 , external safety lockout switch connector  104  and hydraulic pump motor connections  108  are included in the control cabinet. 
     Electrical connections external to the electronics enclosure  20  in the apparatus of the present invention shown in  FIG. 9  include electrical power connections  146  and  156 , an external moveable lockout safety switch  154 , guard door lock  148  with its connector  150 , and a dummy plug  152  that can be used to deactivate the guard door lock when the top cover is removed for calibration activities. Connection  132  provides switched electrical power for pump  52 . The guard door is locked by means of an electrically activated lock  148 , a Leuze MLM24, which prevents the apparatus from operating with guard door open, and prevents the guard door from being opened while the apparatus is in motion. A connection  128  to a displacement sensor  28  shown in  FIG. 1  for measuring the motion of the top clamp assembly is shown on  FIG. 9 . Also included are connection  131  to hydraulic shear valve  58  in  FIG. 7 , connection  134  to hydraulic clamp valve  74  in  FIG. 7  and connection  138  to hydraulic proportional control valve  60  in  FIG. 7 , connection  135  to pressure switch  56  in  FIG. 7 , connections to photo sensor transmitter  16  and receiver  18 , connection  140  to pneumatic gate air valve  216  in  FIG. 14 , connection  142  to pneumatic lift cylinder valve  212  in  FIG. 14 , and connection  144  to load cell in  FIG. 1  and  FIG. 4 . 
       FIG. 10  shows an elevation view of the lower clamp assembly including a pneumatic gate  166  which is activated by a pneumatic cylinder  164 . The pneumatic cylinder  164  is mounted to bracket  167  by means of pivot brackets  162 . Hydraulic cylinder  38  activates the clamp mechanism through coupler device  40  which allows for radial misalignment and prevents binding in the assembly. 
       FIG. 11  shows lower clamp assembly  188  with cylinder  38 , coupling device  40  provide clamping force to the specimen under test. Bearings  172  are captured by bearing retainer  170  which bearing retainers are secured by cap screws  180 . Pneumatic gate  166  pivots about bearings mounted in brackets  168 . Removable jaw grips  186  are held in place by plates  176  and secured by screws  178 . When the pneumatic gate  166  is in its closed position (cylinder  164  extended), the gate is flush against the bottom of the grip surfaces  186 , and the notches in gate  166  clear the mounting screws  184  allowing the clamp to open or close with the gate in its cylinder-extended position. After the testing is complete on a specimen the clamp jaws are opened, the gate is opened and the loading cylinder  14  (in  FIG. 1 ) is retracted. These actions will normally dislodge a specimen that may be stuck to the clamp jaws. The arrangement of gate and clamp grip pieces of the present invention provides for very accurate positioning of a specimen when it is simply dropped into the clamp jaws. 
     The cross sectional drawing of  FIG. 12  shows the lower clamp assembly  188  in vertical cross section with suspension system rotated 90 degrees about a vertical axis. Features of the lower clamp including clamp cylinder  38 , coupling means  40 , grip surface  186  and gate  166  with its actuating air cylinder  164 , cylinder pivot mount  162  and mounting bracket  167  are visible along with the lift means actuator and motion limit means. In this embodiment the travel stop bolt  192  is separate from the travel limit stop bolt  194 . It is noted that the function of cylinder  190  may be replaced by a compression spring means or air bag means to perform the same function in operation of the apparatus. 
       FIG. 13  is an exploded view of the sliding part of clamp assembly  188  with bronze bearing members  172  fitting in machined pockets on opposite sides of clamp slide  41 , and end  189  of removable grip  186  fitting into matching receptacle  191  with projection  189  providing a capture of removable grip  186 . Access holes  193  at the two corners of clamp slide  41  are provided in case of difficulty in removing grip  186  so that a drift punch may be used as a persuading influence. Grip  186  is captured by its ends and with a retainer plate  182  held in place by screws  184 . The grip surface of  186  is roughened by means of a metal spraying process that leaves a rough sandpaper-like finish of hard metal welded to the treated part. Identical grip parts  186  are used for both faces of upper and lower clamp assemblies. 
     The pneumatic controls shown in  FIG. 14  include an attachment  200  for an air hose, a stop/waste shutoff valve  202  which in the preferred embodiment also has a lock-out capability. In line are filter  204 , regulator  205 , lubricator  206 , and pneumatic 4-way valves  212  and  216  for the lift and gate cylinders respectively. Connections  208  and  210  attach to pneumatic lift cylinder  416  in  FIG. 5 or 190  in  FIG. 12 . The gate cylinder can be operated at a lower pressure, so pressure regulator  214  reduces the air pressure to valve  216  which is attached to the gate cylinder by connections  220  and  222 . Mufflers  218  and  224  provide a more pleasant environment for the work force which may be operating in the vicinity. 
     The pneumatic lift cylinder  190  of  FIG. 12  may be alternatively connected to the output of the lubricator  206  because operation of the apparatus does not require that pneumatic lift cylinder  416  be deactivated thereby eliminating the need for valve  212 . 
       FIG. 15  shows a prior art specimen prepared according to ASTM D1037 for testing by means of prior-art rail shear fixtures in a conventional universal test machine. In addition to cutting the specimen  300  to size with length  304 , thickness  305  and width  306 , holes  302  must be drilled in the specimen with care taken to make clean, accurate holes, which can be a challenge with some particleboard materials. 
       FIG. 16  shows the arrangement of rail shear fixture pieces  312 ,  314 ,  316  and  318  attached with bolts  308  and nuts  310  through all the matching holes. The fixtures have a machined grip surface on the contact side, and all the bolts must be tightened to prevent slipping under test load. Test results may vary with bolt tension, a factor that is eliminated with the controlled clamping pressure of the present invention. 
       FIG. 17  shows a side view of the specimen when placed in a universal test machine and placed under load. Once the specimen is prepared and fastened in the test fixtures, a load  320  is applied so the line of shear force  322  is diagonal from corner-to-corner of the unclamped area of specimen  300 . Bolts  308  hold the testing rails  314  in place. 
       FIG. 18  shows an edge view of the specimen  300  when rail shear fixtures are attached and the specimen is placed under load. This view illustrates the position of bolts  308 , nuts  310 , and testing rails  314  and  318  with the specimen under load force  320 . 
       FIG. 19  illustrates the operating sequence for the present invention. The control function can be illustrated as a state machine that goes through a series of states or stages in the testing sequence. In the first operating state  450 , the control outputs unlock the guard door  24 , open the gate  166 , the hydraulic pump  6  is OFF and clamp cylinders  22  and  38  and load cylinder  14  are retracted. 
     When the “start test” button  608  in  FIG. 20  is activated and the guard door  24  is closed there is a brief activation of the hydraulics to assure cylinders  22 ,  38  and  14  are retracted and gate  166  is closed in the Check state  452 . Upon completion of this stage the LOAD state  454  is entered the guard door  24  is unlocked and a specimen may be placed in the apparatus. 
     When the specimen is in place and the guard door  24  is closed the clamp state  456  is entered. The guard door  24  is locked, the pump  6  is started and the clamp cylinders  22  and  38  are activated. When the hydraulic pressure reaches its preset point on pressures switch  56 , the SHEAR state  458  is entered. During this state the guard door  24  remains locked and the load cylinder  14  is activated while the load cell  4  measures force and the displacement of the specimen is recorded therewith. Upon failure of the specimen as indicated by the measured force reaching a preferred fraction of the measured peak force, and deflection in the specimen reaching a preferred distance the test is terminated and guard door  24  remains locked, the gate  166  is opened, the clamp cylinders  22  and  38  are retracted and the load cylinder  14  is retracted. Upon completion of these actions, the state is switched to FINISH  459  at which point the operator may enter notes for the record associated with the individual specimen and save the test results. The specimen count is advanced and the test results may be saved or discarded by selection of the operator. 
     These operating states are illustrated on the control screen display shown in  FIG. 20 . On this panel material information  600  is entered along with specimen information  601  and testing methodology  604 . Direct control of the various machine functions is available on the control panel  606 . For a normal test the material information, specimen information and testing methodology are entered. Then the “Start Test” button  608  is activated in the state sequence panel  610 . With the guard door  24  closed, the apparatus goes through the testing stages enumerated above to complete the shear testing of a specimen. Graphical display  613  shows a plot of load force as a function of shear strain or displacement. 
     In addition to the Shear Test screen, the operator may select to view Testing Results  612 , open a Calibration  614  screen or a Settings  616  screen to adjust machine settings. 
     In the Calibration  614  screen the top cover  25  (in  FIG. 2  and  FIG. 3 ) of the machine is removed, a dummy plug is inserted in place of the cable leading to the guard door lock  26 ; the load cylinder clevis attachment  10  in  FIG. 4  is removed and replaced with an independent load cell with a load button attachment to the upper clamp assembly  21 . An aluminum block (not shown) is placed in the specimen location, and with the load pressure relief valve  64  of  FIG. 7  adjusted to a minimum setting the pump is activated to clamp the dummy specimen and apply load to the load cell  4 . Simultaneous readings are captured in the machine electronics and on the independent load cell readout at a preferred number of load settings established by adjusting the load pressure relief valve  64  on  FIG. 7 . These reading pairs are used to adjust internal processing to establish a  1 : 1  correspondence between machine load readings and independent load cell readings. 
     The independent load cell and its associated readout act as a secondary standard, and must have their calibration checked on a periodic basis according to rules established by an independent calibration agency. 
     Control Software 
     The control software for the apparatus of the present invention consists of a graphical interface designed to run on Microsoft Windows 7 or 8. The program is implemented using C# and the Microsoft WPF/.NET platform. The hardware is controlled by sending messages via Ethernet to a Galil controller ( 92  of  FIG. 8 ). 
     Data storage for test results is managed using a MySQL database and consists of two tables: a specimens table to store the results of each specimen, and a “LoadCellData” table to store the raw load cell readings for each specimen. 
     The control architecture of the program includes a scripting language for implementing complex control sequences. The scripting language interpreter manages background processing and a halting mechanism to ensure that complex operations can be safely discontinued and the machine brought to a safe state at any time. 
     Features and Advantages of the Present Invention and Comparison with the Prior Art 
     The prior art test fixture shown in  FIG. 17  and  FIG. 18  was devised many years ago which consisted of a 4-piece rail arrangement including a roughened grip surface facing the specimen, and bolted to the panel specimen, then the panel specimen with rail grips was placed in a universal testing machine, load applied to the opposite ends of the rail fixture to induce a shear stress in the specimen along a diagonal direction. The shear strength was then reckoned as the force divided by the (product of thickness and length), i.e., the cross sectional area in the shear plane of the specimen is slightly larger than the shear plane area used in the calculation. The strength is reported as the force per unit area reckoned as the thickness times the specimen length. Whether the discrepancy in the calculation is significant remains to be determined. 
     Specimen preparation for the prior art apparatus involves first cutting a panel into specimens for test, drilling holes in the specimen through which clamping bolts may pass, bolting the testing rails to the specimen and then carrying out the test in a calibrated loading device in which the load is measured and the rate of movement is controlled. This is a tedious process of cutting, drilling, bolting and testing that is required to achieve a measurement of shear strength in a specimen. 
     One shortcoming of this test method is that the shear stress is applied in a diagonal direction in the specimen, whereas in the wood I joist the stress is purely in the long direction of the web member, so there may be a mischaracterization of the strength in this regard. 
     This shortcoming is removed in the present apparatus by using the horizontal shear option in testing. In this case the failure stress is calculated correctly on the basis of the cross section area of thickness times specimen length, whereas in the diagonal stress case the actual stressed area is larger than the area used in the calculation, leading to a possibly larger calculated failure stress than actually experienced by the specimen. It remains to be seen whether this is a significant factor in the error budget of this important test. 
     Another shortcoming in the prior art method is the requirement for extra specimen preparation in drilling holes and bolting the testing rails to the specimen. This shortcoming is removed by hydraulic actuated clamping which eliminates the need for drilling and bolting the test specimen. 
     A prior art apparatus provided hydraulic clamping but provides only fixed second clamping means, so the stresses in the specimen are not properly simulating those found in the conventional rail shear apparatus and said prior art apparatus was not capable of placing the shear stress along the horizontal centerline of the specimen. The present apparatus avoids this issue by providing a second pivot point for a second lower clamp assembly that is in line with the diagonal shear stress such that the apparatus can properly simulate the stresses applied in the conventional bolted rail shear means. 
     These fundamental features together with a computer numerical control system for operating the hydraulic controls and data collection provide a complete testing process that is operated by simply opening a guard door, dropping the specimen in place, closing the door and activating the system. From that point forward, the apparatus clamps the specimen, applies the shear test load and records the force and deflection until the specimen fails, stores the test data, opens the clamps, opens a pneumatic gate and retracts the loading cylinder, and allow the specimen to fall into a discard bin. The loading rate is under computer control, and the guard door is locked during the test to prevent injury to the operator while the test is in progress. 
     The present invention apparatus operates under computer control whereby the control functions are driven by computer software and data collection is performed on a continuous basis while load is applied so that both stress and strain are recorded, and failure stress (force per unit area) is calculated and recorded for each specimen. The present apparatus automatically records the data for each specimen in a computer database file which eliminates human recording errors and reduces consumption of paper and pencils thereby having a positive influence on the environment. 
     Operator safety is an important feature of this invention. Hand operation of bolt tightening means is eliminated. This means that grip pressure is controlled and adjustable. The apparatus is fully enclosed and a guard door is locked while moving parts are in motion to prevent stray fingers or other appendages from interfering with the proper operation of the apparatus as well as incidentally preventing traffic accidents while pinch victims are raced to the nearest medical facility for reattachment treatments. 
     One other prior art apparatus has been developed which embodies only one of the three loading configurations of the present invention and none of the safety features. The inventors are not aware at the time of filing of any publications in respect of this prior art apparatus. 
     The exemplary embodiments shown in the figures and described above illustrate but do not limit the invention. In compliance with the statute, the invention has been described in language more or less specific as to structural features. It is to be understood, however, that the invention is not limited to the specified features shown, because the means and construction herein disclosed comprise a preferred form of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.