Patent Publication Number: US-7584670-B2

Title: System, apparatus and method for testing under applied and reduced loads

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a divisional patent application of application Ser. No. 11/002,211, filed Dec. 3, 2004, now U.S. Pat. No. 7,353,715 which is hereby incorporated by reference. 

   TECHNICAL FIELD OF THE INVENTION 
   This invention broadly relates to a system, apparatus and method for tensile testing of specimens under applied and reduced loads. This invention particularly relates to a system, apparatus and method for carrying out sustained-peak low cycle fatigue testing of specimens under cyclically applied and reduced loads, especially of materials used in making gas turbine engine components. 
   BACKGROUND OF THE INVENTION 
   Evaluating the condition and determining the future performance of mechanical components, such as gas turbine engine components, that operate in the high stress regime of the materials comprising such components, present a challenge because of the complexity of gas turbine components, the materials the components comprise, the variety of in-service operating conditions experienced by the components and the inherent limitations of prevailing remaining useful life, or life expended, estimation methods. Components which operate at high temperatures, such as greater than about 900° F. (482° C.), where a combination of creep and thermal aging of the material constituting the components is of prime concern, demand special consideration in order to achieve an acceptable remaining useful life estimation. 
   Many systems and methods for testing and estimating the useful life of such components involve applied mechanical loads that vary in time. Of particular interest is low cycle fatigue (LCF) testing, and especially sustained-peak LCF (SPLCF) testing, to examine the fatigue crack growth behavior over time of materials used to make gas turbine engine components. The fatigue crack growth behavior of specimens comprising these materials is characterized by applying cyclic loads using a “creep-rupture” frame. Various cyclic tensile amplitudes are applied, and the number of cycles required to pull apart the specimen under those conditions is recorded. Stress and/or fatigue damage is evidenced by a decrease in strength and stiffness. In some cases, the tests can be terminated after some number of cyclic loadings and then breaking the specimen (i.e., a tensile test) to determine the residual strength. The data from such destructive tests are usually characterized by empirical means and generalized by implication or extrapolation to a variety of service conditions for which the materials were not specifically tested in the laboratory. 
   In order to fully understand the fatigue behavior of the materials that comprise these specimens as a function of fatigue life, it is desirable to monitor the dynamic response of the specimen continuously over the time of the test. For example, one way to carry out such testing for evaluating fatigue crack growth over time is by using servo-hydraulic testing systems. However, the use of servo-hydraulic testing systems to evaluate long hold-time tests of specimens can be very expensive, especially when multiple specimens are evaluated. 
   Another, less expensive way to evaluate specimens for long hold-time fatigue and crack growth, as well as other stress-related properties, involves the use of a creep-rupture frame or lever arm tester. See FIG. 1 of U.S. Pat. No. 5,345,826 (Strong), issued Sep. 13, 1994, which schematically illustrates a typical “creep-rupture” frame/lever arm tester. This device consists of a lever arm of from typically twelve to twenty inches in length that is pivotally mounted on a vertical frame at a point along the lever arm&#39;s length between its center and an end to which one end of a test specimen is attached. The other end of the test specimen is attached to a fixed base plate. When weights are applied or loaded on the opposite end of the lever arm, a tensile force is exerted on the test specimen according to the formula t=(wl)/d, where t is the tensile force exerted on the test specimen, w is the weight applied to the far end of the lever arm,  1  is the distance between the lever arm pivot point and the end carrying the applied weights, and d is the distance between the lever arm pivot point and the end connected to the test specimen. The applied force, t, causes tensile testing of the specimen to take place. 
   Creep-rupture frames/lever arm testers can be equipped to cyclically apply and reduce the load (e.g., created by the weights) on the test specimen. Previously, the cyclical application and reduction of the load in creep-rupture frames/lever arm testers was carried out by using either a standard pneumatic cylinder or a scissor jack lift. With a standard pneumatic cylinder, the load is repeatedly applied and reduced by the respective contraction and extension of the length of the cylinder through pressurization and depressurization with air. The disadvantage of using a standard pneumatic cylinder for cyclical application and reduction of the load is that contraction and extension of the cylinder is generally dynamic. Of particular concern is that standard pneumatic cylinders, especially over time, exhibit a “stiction” phenomena such that contraction and extension of the cylinder is not always smooth, but can occur as a series of jerky, unpredictable motions because the cylinder seals temporarily stick. This has been found to be due to the seal material in the cylinder migrating into the walls thereof over time. In addition, it is more difficult to control the dynamic contraction and expansion of a standard pneumatic cylinder, and it is thus more difficult to control the application and reduction of the load. 
   With a scissor jack lift, the load is repeatedly applied and reduced by having the jack expand or collapse vertically in an accordion-like fashion. The disadvantage of using a scissor jack lift is that expansion/collapse is relatively slow. The scissor jack lift is also mechanically limited in that it is not designed for such cyclical use. In addition, the scissor jack lift requires a high degree of maintenance for use in cyclical application and reduction of load, and can therefore be expensive and time consuming to operate. 
   Accordingly, there exists a need for a system, apparatus and method for cyclical application and reduction of loads in tensile testing of specimens that allows for a relatively smooth application and reduction of the applied loads. There also exists a need for a system, apparatus and method for cyclical application and reduction of loads in tensile testing of specimens that allows for a more easily controlled application and reduction of the load. There further exists a need for a system, apparatus and method for cyclical application and reduction of loads in tensile testing of specimens that is responsive to the need to apply and reduce the load fairly quickly, and that does not require a high degree maintenance thereof over time. 
   BRIEF DESCRIPTION OF THE INVENTION 
   An embodiment of this invention is broadly directed at a system which cyclically applies and reduces a load on a test specimen to thereby subject the test specimen to tensile testing, wherein the system comprises a fluidic mechanical muscle that contracts and extends in length to cyclically apply and reduce the load. 
   Another embodiment of this invention is broadly directed at an apparatus, which comprises:
         a. a frame;   b. a load adjusting section associated with the frame and having a fluidic mechanical muscle that contracts and extends in length to cyclically apply and reduce a load;   c. a load train section associated with the frame for subjecting a test specimen to the load; and   d. a lever arm associated with the frame and having a load train end adjacent and connected to the load train section and a load adjusting end adjacent and connected to the load adjusting section, the arm being configured to apply and reduce the load from the load adjusting section to the load train section.       

   Another embodiment of this invention is broadly directed at a method comprising the following steps:
         (a) providing a test specimen; and   (b) cyclically applying and reducing a load on the test specimen to thereby subject the test specimen to tensile testing, wherein the cyclical application and reduction of the load is caused by the contraction and extension of a fluidic mechanical muscle associated with the load.       

   Another embodiment of this invention is broadly directed at a system or apparatus which cyclically applies and reduces a load on a test specimen to thereby subject the test specimen to tensile testing, wherein the system or apparatus comprises a mechanism for decoupling at least a portion of the load from the test specimen when the load is reduced. 
   The system, apparatus and method of this invention provides several benefits and advantages. The fluid mechanical muscle used in the system, apparatus and method of this invention allows for an automatic and relatively smooth application and reduction of the load (e.g., without the occurrence of a “stiction” phenomena) in the cyclical tensile testing of specimens. The fluid mechanical muscle used in the system, apparatus and method of this invention also allows for a more easily controlled application and reduction of the load. The fluid mechanical muscle used in the system, apparatus and method of this invention is relatively easy to maintain over time and can be integrated into existing creep-rupture systems when needed without significantly altering the original configuration or function of the creep-rupture system. The system, apparatus and method of this invention is also relatively inexpensive in comparison to servo-hydraulic systems in carrying out various types of cyclic fatigue tensile testing, especially on multiple specimens. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of an “open loop” system embodiment of this invention. 
       FIG. 2  is a more detailed perspective view with portions broken away of the apparatus that can be used in the “open loop” system of  FIG. 1 . 
       FIG. 3  is an illustrative graphical plot of a low cycle fatigue test that can be carried out using the system and apparatus of  FIGS. 1 and 2 . 
       FIG. 4  is an illustrative graphical plot of a sustained-peak low cycle fatigue test that can be carried out using the system and apparatus of  FIGS. 1 and 2 . 
       FIG. 5  is a schematic view of a “closed loop” system embodiment of this invention. 
       FIG. 6  is a more detailed perspective view with portions broken away of an apparatus that can be used in the “closed loop” system of  FIG. 5 . 
       FIG. 7  is an illustrative graphical plot of a mission cycle test that can be carried out using the system and apparatus of  FIGS. 5 and 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As used herein, the term “load” refers to any mass, weight, force, etc., to which a test specimen is subjected to by a system, apparatus and/or method of this invention. 
   As used herein, the term “applying the load” refers to subjecting the test specimen to a load, including increasing the amount or degree of load that the specimen is subjected to. 
   As used herein, the term “reducing the load” refers to partially or completely decreasing, diminishing, eliminating, etc., the load the test specimen is subjected to. 
   As used herein, the term “cyclically applying and reducing a load” refers to at least one cycle where the load is applied and reduced, in any order thereof, i.e., apply and reduce load, reduce and apply load, etc. Typically, the cycle involves first applying the load progressively or sequentially, and subsequently reducing the load progressively or sequentially. The cyclic application and reduction of the load can be a single cycle, or more typically is a plurality of such cycles (i.e., for at least two cycles). The load can be applied and reduced in the same manner or pattern each cycle, or can be applied and reduced in a different manner or pattern each cycle. The load can also be applied and held (i.e., sustained) at a specified level (i.e., the load is neither increasing nor decreasing) for the same or different discrete period of time one or more times during the cycle, can be increased and/or can be decreased progressively or sequentially at the same or different rates, or any combination thereof, during each cycle. 
   As used herein, the term “closed loop system” refers to a control system having a feedback mechanism (e.g., a mechanical and/or electronic signal or plurality of signals) for adjusting, altering, controlling, etc., the application and/or reduction of the load on the test specimen. The feedback mechanism used in a closed loop system typically provides a substantially linear and proportional application and/or reduction of the load on the test specimen. 
   As used herein, the term “open loop system” refers to a control system that does not utilize a feedback mechanism. 
   As used herein, the terms “creep-rupture frame” and “lever arm tester” refer interchangeably to a device that typically comprises a lever arm of mechanical advantage typically from about twelve to about twenty inches (from about 30.5 to about 51 cm.) in length that is pivotally supported on a fixed vertical member of a frame at a point along the lever arm&#39;s length between its center and an end to which one end of a test specimen is attached, with the other end of the test specimen typically being attached to a base plate or platform (e.g., of a cross-frame), and where one or more weights are applied or loaded on the opposite end of the lever arm. See  FIG. 1  and the corresponding description in U.S. Pat. No. 5,345,826 (Strong), issued Sep. 13, 1994 (herein incorporated by reference), which schematically illustrates a typical “creep-rupture” frame/lever arm tester. Suitable creep-rupture frame/lever arm testers for use herein include those made by SATEC, ATS, etc. 
   As used herein, the term “fluidic mechanical muscle” refers to a device which typically contracts in length in a relatively controlled manner upon being pressurized with a fluid (i.e., a gas such as air or a liquid such as ethylene glycol) and extends in length in a relatively controlled manner upon the release of the pressurized fluid. In the system, apparatus and method of this invention, contraction of the fluidic mechanical muscle typically causes the application of the load to the test specimen, while the extension of the fluidic mechanical muscle typically causes the reduction of the load. The fluidic mechanical muscle has characteristics such that when it is pressurized, the relative length of the muscle typically contracts substantially linearly with the applied pressure while at the same time creating substantial forces suitable for actuating, lifting, moving, positioning, etc, the load, and conversely extends substantially linearly with the reduction (release) of pressure. 
   Because of their different construction, and especially their inherent non-dynamic, relatively controlled contraction and extension in length, the fluidic mechanical muscles useful herein differ from standard dynamic pneumatic cylinders. Fluidic mechanical muscles suitable for use herein can be of the “McKibben” type of fluid contractile actuator or “muscle” that typically includes a cylindrical sheath formed from a flexible mesh (sometimes referred to as a “braiding” structure) comprising a plurality of interconnected rhomboidal or rhombus shaped segments that are secured to connectors at each end of the sheath with a bladder comprising a strong expandable material disposed within the sheath, and with an inflation line connected to the bladder through which a pressurizing fluid may be introduced for the purpose of inflating or expanding the bladder within the cylindrical sheath, along with appropriate valves on the inflation line to direct fluid from a pressurizing source into the bladder for inflation (contraction), as well as to allow fluid to escape from the bladder for release/deflation (extension) See, for example, U.S. Pat. No. 4,739,692 (Wassam et al), issued Apr. 26, 1988 (herein incorporated by reference), which describes the operation of a “McKibben” type of fluid contractile actuator or “muscle.” In operation, the “McKibben” type fluidic contractility actuator or “muscle” is connected between two fixed points using a connector with the bladder deflated. The cylindrical sheath formed from the flexible mesh is connected between two flexible points and ideally experiences a very slight tensile stress in order to ensure that the sheath when connected in its extended or “relaxed” position between the two points is at a minimum diameter. The inflation line is connected to the source of pressurizing fluid that may be compressible, i.e., a gas, or incompressible, i.e., a liquid. The fluid when introduced into the bladder expands it against the enclosing mesh sheath, causing it to expand diametrically and contract longitudinally generating an extremely large contractile force between the connectors. See also U.S. Pat. No. 4,615,260 (Takagi et al), issued Oct. 7, 1986; U.S. Pat. No. 5,158,005 (Negishi et al), issued Oct. 27, 1992; U.S. Pat. No. 5,165,323 (Sato), issued Nov. 24, 1992; and U.S. Pat. No. 5,201,262 (Negishi et al), issued Apr. 13, 1993 (herein incorporated by reference), as well as U.S. Pat. No. 4,841,845 (Beullens), issued Jun. 27, 1989; U.S. Pat. No. 6,067,892 (Erickson), issued May 30, 2000; and U.S. Pat. No. 6,223,648 (Erickson), issued May 21, 2001 (herein incorporated by reference), for other fluidic mechanical muscles of the “McKibben” type of fluid contractile actuator or “muscle” that are potentially suitable for use herein. Examples of commercially available fluidic mechanical muscles suitable for use herein include those made by Festo Corporation of the “Fluidic Muscle MAS” series, including Model No. MAS-10-N-AA-MCFK, Part 187594; Model No. MAS-10-N-AA-MOFK, Part 187595; Model No. MAS-40-N-459-AA-MCIK, Part 187605; Model No. MAS-40-N-AA-MCIK, Part 187606); Model No. MAS-40-N-AA-MOKK, Part 187607; Model No. MAS-20-N-AA-MCHK, Part 187617; Model No. MAS-20-N-AA-MCGK, Part 187618; Model No. MAS-20-N-AA-MOHK, Part 187619; Model No. MAS-10-, Part 534201; Model No. MAS-20-, Part 534202; and Model No. MAS-40-, Part 534203, etc. 
   As used herein, the term “test specimen” refers to any specimen, including a component, part, etc., comprising a material of interest, or a specimen fabricated, manufactured, etc., from a material of interest that is subjected to a load by the system, apparatus and/or method of this invention. The test specimen can be of any suitable shape or configuration, including rectangular, cylindrical, etc. Typically, the test specimen has a reduced gauge or width at the middle section thereof (e.g., is “dog-bone shaped”) to force elongation of the material at the middle of the specimen when subjected to the load. 
   As used herein, the terms “tension testing” and “tensile testing” refer interchangeably to a test format where the test specimen is subjected to a substantially longitudinal stretching, pulling, etc, force when the load is applied thereto. Representative, but non-limiting examples of tension or tensile testing include low cycle fatigue testing, sustained-peak low cycle fatigue testing, creep-rupture testing, high strain rate peak testing, bend testing, crack growth testing, etc. 
   As used herein, the terms “low cycle fatigue testing” or “LCF testing” refer interchangeably to a slower or lower loading cycle speed fatigue type test where the cycle is usually about 30 Hertz or less, and is typically in the range of from about 0.3 to about 1 Hertz. 
   As used herein, the terms “sustained-peak low cycle fatigue testing” or “SPLCF testing” refer interchangeably to a type of LCF test where the peak load applied to the test specimen is held or sustained at a specified level for a discrete period of time. 
   As used herein, the term “bend testing” refers to a test format where the test specimen is supported at its respective ends and the load is applied proximate to the midpoint thereof between the respective ends. 
   As used herein, the terms “mission cycle testing” or “simulation testing” refer interchangeably to testing that is intended to represent an actual operation (i.e., real life phenomena) and is typically carried out using a closed loop test system. Mission cycle/simulation testing typically refers to a type of field testing (e.g., of an engine) where the engine is operated, data is taken and brought back to a mission or simulator operation lab (either manually or more typically electronically), and the data is then used to program (typically using a computer), for example, a simulated, but real life stress cycle on the test specimen of interest. 
   As used herein, the term “creep-rupture test” refers to a test format where a static and consistent load is applied to the test specimen and where the elongation of the test specimen during the application of the load is measured. 
   As used herein, the term “fracture toughness” refers to the measurement of the resistance of a specimen being tested to extension of a crack. See Davis, ASM Materials Engineering Dictionary (1992), p. 72. 
   As used herein, the term “fatigue crack growth test” refers to a test format that measures of the rate of growth of a crack in a test specimen over time or over an applied load cycle(s). 
   Referring now to the drawings,  FIG. 1  is a schematic view of an “open loop” tensile testing system indicated generally as  10  that uses a tensile testing apparatus in the form of a lever arm tester  12 . Tester  12  includes a generally L-shaped frame indicated as  14 , a generally vertically extending load train section indicated as  18  and associated with frame  14 , a generally vertically extending load adjusting section indicated as  22  and associated with frame  14 , and a mechanism for applying and reducing a load from the load adjusting section  22  to the load train section  18 , and to thus cause the load to be applied (typically in the form of tensile stress) or reduced on the test specimen of interest, in the form of a pivoting generally horizontally extending boom or lever arm  26 . Lever arm  26  includes a fulcrum or pivot point  30  for balancing arm  26  on the top end  34  of the longer length vertical segment of frame  14  about which arm  26  swings or pivots. Lever arm  26  also has a load train end indicated as  38  and a load adjusting end indicated as  42 . As shown in  FIG. 1  and as illustrated by upward pointing arrow  46  and downward pointing arrow  50 , respectively, as load adjusting end  42  of arm  26  moves, for example, generally downwardly about a generally horizontally axis defined by pivot point  30 , the load train end  38  moves generally upwardly, and vice versa when load adjusting end  42  moves generally upwardly about the horizontal axis defined by pivot point  30 . The particular position of pivot point  30  along the length of arm  26  between ends  38  and  42  can be moved horizontally and determines the multiple of load effectively transferred by arm  26  from the load adjusting section  22  to the load train section  18 , as represented by the formula t=(wl)/d, where t is the tensile force exerted on the test specimen, w is the weight or load applied to the load adjusting end  42  of the lever arm  26 , l is the distance between pivot point  30  and load adjusting end  42 , d is the distance between pivot point  30  and load train end  38  connected or attached to or otherwise associated with the test specimen, and where the applied force, t, imparts a stress to the test specimen. The closer pivot point  30  is to load train end  38 , and conversely away from load adjusting end  42  (i.e., d is smaller and l is larger), the greater the multiple of load that is effectively transferred or applied from load adjusting section  22  to load train section  18 , i.e., the greater the value for t. For example, a load (w) of 10 units in load adjusting section  22  can be translated by arm  26  into a force (t) of 200 units applied to load train section  18  (and test specimen) if the ratio of l:d is 20:1. 
   As shown in  FIG. 1 , load train section  18  includes an upper pull rod  54  that is adjacent to and is connected or attached to or otherwise associated at its upper end as indicated generally by  56  with load train end  38  of arm  26 , and that is also adjacent to and is connected or attached to or otherwise associated at its lower end thereof with a test specimen indicated generally as  58 . Load train section  18  can also include an environmental chamber such as a furnace indicated generally as  62  which encloses specimen  58 . Load train section  18  further includes a lower pull rod indicated generally as  66  that is adjacent to and is connected or attached to or otherwise associated at its upper end with specimen  58 , and that is also adjacent to and is connected or attached to or otherwise associated at its lower end with frame  14 . Because upper pull rod  54  is vertically movable and especially moves upwardly when load train end  38  of arm  26  pivots upwardly in the direction indicated by arrow  42 , and because the lower pull rod  66  remains essentially stationery by being attached to frame  14 , test specimen  58  is subjected to a tensile force, typically in the form of a strain or stress. 
   As shown in  FIG. 1 , the load adjusting section  22  includes an upper connector  70  that is adjacent to and is connected or attached to or otherwise associated at its upper end with load adjusting end  42  of arm  26  as indicated generally by  74 . Load adjusting section  26  also includes a fluidic mechanical muscle indicated generally as  78  that is adjacent to and is connected or attached or otherwise associated at its upper end with the lower end of connector  70 . As muscle  78  contracts in length, the load in load adjusting section  22  is applied (via arm  26 ) to load train section  18 , and conversely, as muscle  78  extends in length, the load in load adjusting section  22  is reduced (via arm  26 ) on load train section  18 . Load adjusting section  22  further includes a lower connector  82  that is adjacent to and is connected or attached to or otherwise associated at its upper end with the lower end of muscle  78 , and is also adjacent to and is connected or attached to or otherwise associated at its lower end with a load indicated generally as  86 . As also shown  FIG. 1 , load  86  is above the ground or main surface  90 , thus indicating that system  10  is at a point in the testing cycle where muscle  78  is in a contracted state and where load  86  is thus being applied (via arm  26  and load train  18 ) to specimen  58 . 
   Referring to  FIG. 2  where the further details of lever arm tester  12  are shown, a generally U-shaped containment bracket  100  is provided and attached to the top end  34  of frame  14  to keep arm  26  from pivoting or swinging too much up or down about pivot point  30  and especially to prevent arm  26  from potentially falling off of frame  14 . An upper universal joint  104  is used at point  56  to connect or attach the upper end of upper pull rod  54  to the load train end  38  of arm  26 . A generally cylindrical mounting column  108  is attached to or mounted on furnace  58  by a spaced apart pair of hinges indicated as upper hinge  112  and lower hinge  116 . Column  108  is pivotally mounted to frame  14  by an upper bracket  120  having a circular recess (not shown) for receiving the upper end of column  108  and a lower bracket  124  also having a circular recess  128  for receiving the lower end of column  108 . An inline load cell  132  is mounted on lower pull rod  66  between the respective upper and lower ends thereof to directly measure the load being applied to test specimen  58 . A lower universal joint  136  connects or attaches the lower end of lower pull rod  66  to a vertically movable cross-head assembly indicated generally as  140 . Cross-head assembly  140  includes a generally horizontally extending cross-head  144  connected or attached to or otherwise associated with a generally vertically extending and spaced apart pair of rods  148  that are connected or attached to or otherwise associated with a generally horizontally extending base or platform  152 . A manual turn crank  156  is mounted on platform  152  for vertically moving or adjusting the position of load train section  18  either upwardly or downwardly relative to frame  14 . A furnace control box indicated generally as  160  that is mounted on frame  14  and that is connected to furnace  62  by control cables or lines (not shown) is used to control the environmental conditions (e.g., temperature, pressure, gas surrounding specimen  58 , etc.) within furnace  62 . 
   As also shown in  FIG. 2 , a pivoting connector  170  is used at point  74  to connect or attach load adjusting end  42  of arm  26  to upper connector  70  in the form a flexible link or chain. Chain  70  is connected or attached to or otherwise associated with an R-ratio or minimum load pan  174 . Load pan  174  is connected or attached to or otherwise associated with the upper end of fluidic mechanical muscle  78  that is shown as having a fluid inlet and outlet line  178  for pressurizing and depressurizing muscle  78 . The lower end of muscle  78  is connected or attached to or otherwise associated with lower connector  82  in the form of a flexible link or chain. Because chain  82  is flexible, it provides sufficient slack when muscle  78  is in an extended state so that load  86  is completely or substantially completely reduced, i.e., there is no force or stress exerted by load  86  on test specimen  58 . In other words, chain  82  provides a mechanism for decoupling (e.g., mechanical decoupling) at least the principal portion of the load (i.e., load  86 ) from test specimen  58  when the load is reduced during that portion of the testing cycle. Chain  82  is connected or attached to or otherwise associated with load  86  that includes a generally horizontally extending weight platform  182  and an elongated weight receiving rod  186  connected or attached to or otherwise associated with platform  182  and extends generally vertically upwardly therefrom and is then connected or attached to or otherwise associated with chain  82 . As shown in  FIG. 2  one or more weights  190  of similar or different mass can be loaded onto platform  182  and are configured with a slot  194  so that weights  190  can be securely receive by elongated rod  186 . 
     FIG. 3  is an illustrative graphical plot indicated generally as  300  of a low cycle fatigue (LCF) test that can be carried out using the system and apparatus of  FIGS. 1 and 2 . As shown in  FIG. 3 , graphical plot  300  of the LCF test has a series of peaks indicated as  310  which represent the peak application of the load on the test specimen along the portions of plot  300  indicated by upward slope  314  during the loading (i.e., load increasing) phase of a test cycle, as well as valleys indicated as  320  which represent the reducing of the load on the test specimen along the portions of plot  300  indicated by downward slope  324  during the reducing (load decreasing) phase of a test cycle. As shown in  FIG. 3 , the application and reduction of the load in an LCF test is typically relatively rapid. As also shown in  FIG. 3 , valleys  320  do not reach the base line because of the minimum load applied or sustained by load pan  174 . Because of the repeated application and reduction of the load in the LCF test, graphical plot  300  represents a plurality of cycles where the load is applied and then reduced. One such cycle is indicated as  330  in  FIG. 3  and has a start point indicated by  340  and an end point indicated by  350 . 
     FIG. 4  is an illustrative graphical plot indicated generally as  400  of a sustained-peak low cycle fatigue (SPLCF) test that can be carried out using the system and apparatus of  FIGS. 1 and 2 . As shown in  FIG. 4  and like  FIG. 3 , graphical plot  400  of the SPLCF test has a series of valleys indicated as  410  which represent the reduction of the load on the test specimen along the portions of plot  400  indicated by downward slope  414  during the reducing (load decreasing) phase of a test cycle. As also shown in  FIG. 4  and unlike  FIG. 3 , graphical plot  400  has a series of plateaus indicated as  420  which represent the sustained application (holding) of the peak load on the test specimen after that portion of plot  400  indicated by upward slope  424  representing the loading (load increasing) phase of a test cycle. As shown in  FIG. 4 , the application and reduction of the load in an SPLCF test is relatively rapid, but unlike the LCF test in  FIG. 3 , the application of the peak load (see plateaus  420 ) in the SPLCF test is held or sustained at specified level for a given or discrete period of time. Because of the repeated application and reduction of the load in the SPLCF test, graphical plot  400  represents a plurality of cycles where the load is applied, held/sustained and then reduced. One such cycle is indicated as  430  in  FIG. 3  and has a start point indicated by  440  and an end point indicated by  450 . 
     FIG. 5  shows a “closed loop” system embodiment of this invention indicated generally as  210  which differs primarily from “open loop” system  10  of  FIG. 1  in that there is no adjustable load  86 . Instead, fluidic mechanical muscle  78  of tester  212  is directly connected or attached to or otherwise associated with frame  14  by use of a connector such as link or chain  282 . See also  FIG. 6  which provides a more detailed view of lever arm tester  212  that can be used in such as “closed loop” system  210  where chain  282  is directly connected or attached to or otherwise associated with frame  14 . 
   The “closed loop” system  210  is typically used for mission cycle or simulation testing that is based on control of the test by a computer program that is derived from data from field tests of actual components, parts, materials, or operating equipment, e.g., a gas turbine engine. For example, the controller (not shown) for the fluidic mechanical muscle  78  can get a signal from the computer program to apply a specific load to the test specimen, as a result of which the muscle  78  contracts in response thereto to apply the load. The controller also receives a feedback signal from load cell  132  indicating how much load is currently being applied to the test specimen  58 . Until load cell  132  senses an applied load to the test specimen equal to that specified by the controller to muscle  78 , muscle  78  will continue to contract and apply load. When load cell  132  senses an applied load to the test specimen that is equal to that specified by the controller to muscle  78 , the controller will send a signal to muscle  78  that the applied load specified has been achieved and to discontinue further contraction. A similar process can take place when muscle  78  is instructed by the controller to reduce the applied load. 
     FIG. 7  is an illustrative graphical plot indicated generally as  700  of a possible mission cycle test that can be carried out using the system and apparatus of  FIGS. 5 and 6 . One possible test cycle of graphical plot  700  is shown in  FIG. 7  that is intended to simulate the “real life” conditions experienced by components, parts, materials or operating equipment (e.g., a gas turbine engine) during use in the field. As shown in  FIG. 7 , graphical plot  700  can have a plurality of sequential loading (load increasing) phases indicated by upward slopes  710  and  714 , a plurality of holding (sustained load at a specified level for a discrete period of time) phases indicated by plateaus  720  and  724 , a plurality of sequential reducing (load decreasing) phases indicated by downward slopes  730  and  734 , and a peak applied load phase point indicated as  740 . As suggested by upward slopes  710  and  714 , as well as downward slopes  730  and  734  of  FIG. 7 , the load can be applied and/or reduced at different rates to more closely simulate “real life” conditions. 
   While specific embodiments of the this invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of this invention as defined in the appended claims.