Abstract:
A testing apparatus is disclosed that includes a turntable, an upper scissor jack assembly and a lower scissor jack assembly positioned in parallel planes, about a longitudinal axis and affixed to a base. The apparatus is powered by at least three motors with supporting controllers. The lower assembly is affixed to the base mechanically via the turntable which allows the lower assembly to rotate with respect to the upper assembly. There are two loading plates attached to the hinges of each scissor jack. The test specimen is secured by the loading plate. Each scissor jack operates by a screw-gear powered by one of the motors. Upon energizing a stepper motor; the screw-gear positions a scissor jack to apply a tension or compression on the specimen. While subjected to tension or compression, the lower jack assembly can be rotated with respect to the upper assembly for in-plane shear loading.

Description:
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/215,967 filed on Apr. 28, 2009 and entitled “Compact and Stand-Alone Combined Multi-Axial and Shear Test Apparatus” by the inventors, Paul V. Cavallaro, Ali Sadegh and Claudia Quigley. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     CROSS REFERENCE TO OTHER PATENT APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to a compact, stand-alone in-plane shear loading and biaxial tension or compression testing apparatus employable for studies of the mechanical properties of materials such as metals, plastics and composites. 
     (2) Description of the Prior Art 
     Fabrics typically used in air-inflated structures (air beams, temporary shelters, tents, temporary bridges, and space structures) are often manufactured in woven or braided forms. These structures rely on inflation pressure to pre-tension the fabric (or membrane) so that the necessary planar stiffness can be developed to achieve rigidity and resistance to in-plane and lateral loads. 
     Unlike metallic structures, air-inflated structures are designed to be lightweight; to have deployed-to-stowed volume ratios that can be in the range of 1000-to-1; and possibly be self-erecting. Although these technologies have been known in the art for many years, the technologies have not been refined to a level that reliable structures can be designed by structural analysis. 
     The advent of fiber-based structural material and weaving/braiding technologies has improved the load carrying capacity of pressurized structures. Accordingly, there has been increasing interest in modeling the mechanical behavior of woven fabrics. However, this class of composite material has complex microstructures that can produce complex mechanical responses. In particular, the mechanical characteristics of plain-woven fabrics used in inflated structures (unlike traditional composite materials) exhibit high non-linearity with a dependence on the internal pressure and contact interactions within the woven fabric. 
     Therefore, there is a need for a testing apparatus which allows the measurement of the elastic and shear moduli for air beams. Specifically, the need is for a compact and independent testing apparatus that is capable of applying a combined in-plane shear load and biaxial load. This need includes the capability of loading non-orthogonal composite or fabric materials with equi biaxial or non-equi biaxial loading. 
     While biaxial testing apparatuses with compression and tension loading or in-plane shear testing apparatuses exist in the prior art, only those disclosed in U.S. Pat. Nos. 6,860,156, 7,051,600 and 7,204,160 to Cavallaro et. al have a combined feature of in-plane shear and compression/tension testing capabilities and the capability to apply a non-orthogonal biaxial loading. 
     Cavallaro et al., (U.S. Pat. No. 6,860,156), describes a multi-axial tension or compression and an in-plane shear loading testing apparatus in which the apparatus is capable of determining the mechanical properties of metal, plastic, woods, fabrics, elastomers and other materials. The testing apparatus uses a mechanical testing machine for applying the tension, compression and rotation loading on the apparatus. The loading is applied to the test specimen in a displacement-controlled mode by which an equal biaxial extension (or contraction) results. 
     Sadegh et al, (U.S. Pat. No. 7,204,160), describes a combined multi-axial tension or compression and in-plane shear loading apparatus with a choice of displacement-controlled or force-controlled modes of loading. This apparatus improves upon the apparatus of (U.S. Pat. No. 6,860,156) and can be used to subject a test specimen to proportionately controlled loads among the axial directions. The force control feature is crucial in creep testing of composite, anisotropic and fabric materials, wherein constant tension or compression forces on the test specimen is desired. 
     Cavallaro et al. (U.S. Pat. No. 7,051,600) describes a testing apparatus capable of simultaneously applying a three-dimensional tension or compression state of stress combined with in-plane shear loading in a displacement-controlled mode. This apparatus improves over the previous apparatus in which of U.S. Pat. No. 6,860,156 in which the compression and tension was in only in two dimensions (planar). That is, the test specimen could be subjected to tension, compression, independently or simultaneously, in the three orthogonal directions, X, Y and Z, with the specimen optionally subjected to a shear load in one plane. A restriction of the apparatus is the required use of a mechanical testing machine for applying the tension, compression and rotation loading to the apparatus. 
     Instead prior art methods have employed two or more separate actuators in complex test fixtures and/or pressurization techniques for applying a biaxial load to a test specimen. A disadvantage of these methods is the need for two or more loading devices and the relatively high cost of the equipment. 
     U.S. Pat. No. 5,905,205 describes an in-plane biaxial test apparatus comprising a rhombus and linkages to transfer the load to the orthogonal direction of the loading. The disadvantage of this apparatus is that the apparatus is not capable of applying in-plane shear to the test specimen. Another disadvantage of this apparatus is that the biaxial loading is limited to an orthogonal configuration. 
     Lynch et al. (U.S. Pat. No. 3,776,028) describes an apparatus requiring three independent loading mechanisms. The test fixture of Lynch is a load point application device that is used to position the application of a single point force acting normal to a flat rectangular panel (specimen) such as those found in aircraft structures. The device does not enable the application of multi-axial tension/compression forces in optional combination with in-plane shear forces. 
     U.S. Pat. No. 4,192,194, describes an apparatus for bi-axially loading a specimen through pressurizing the inside surface of a cylinder. The disadvantage of this apparatus includes the requirement of cylindrical shape of the specimen and the high cost and added equipment of pressurization. 
     Simonelli et al (U.S. Pat. No. 5,913,246) does not enable multi-axial loads (tension-tension, tension-compression, compression-compression) applied simultaneously along orthogonal or oblique orientations with or without in-plane shear regardless of the shape of the test specimen. 
     Other prior art reference include U.S. Pat. No. 5,448,918 which describes an apparatus with X-shape that is only used for compression load and U.S. Pat. No. 5,279,166 which describes an apparatus for self-alignment of a biaxial loading device. U.S. Pat. No. 5,144,844 describes a cruciform planar specimen for biaxial material testing. 
     Although the advantages over the prior art by the cited Cavallaro and Sadegh references are numerous, a significant disadvantage is that the apparatuses of the cited references require a mechanical testing machine with the capabilities of applying tension, compression and rotation loading. That is, to use any apparatus of the cited patent references, one needs to acquire the mechanical testing machine. The machine can be costly and requires a large space for operation. 
     Thus, there is a need for a compact, comparatively low cost and stand-alone material testing apparatus that is capable of applying combined multi-axial tension/compression and in-plane shear loads to a specimen in displacement-controlled or force-controlled modes without requiring a materials testing machine for the operation of the apparatus. 
     SUMMARY OF THE INVENTION 
     It is therefore a general purpose and primary object of the present invention to provide a compact, low cost and stand-alone material testing apparatus that is capable of applying combined multi-axial tension/compression and in-plane shear loads to a test specimen in optional displacement-controlled or force-controlled modes without requiring a materials testing machine for operation of the apparatus. 
     It is a further object of the present invention to provide, independently and without the need for a testing machine, the ability to test a specimen by subjecting the specimen to a combined in-plane, compression or tension as well as in-plane shear. 
     In order to attain the objects described, the present invention relates generally to a combined (simultaneously or independently) in-plane shear and compression or tension loading of a test specimen such as but not limited to metals, plastics, composites, woods, fabrics or anisotropic materials. The apparatus is self-contained to operate independent of an external testing device. The apparatus can apply unequal, orthogonal or oblique stress states on a specimen by the use of load transfer systems comprising two rhombus-shaped scissor jack assemblies and a turntable. 
     The apparatus provides flexibility in applying an unequal biaxial load to the specimen by applying different torque to each scissor jack assembly. In addition, the apparatus provides further flexibility in applying an orthogonal biaxial loading by choosing a different angle, other than orthogonal between the scissor jack assemblies. The in-plane shear load can be applied either simultaneously or independently of the biaxial tension/compression load. 
     The apparatus comprises a lower scissor jack assembly, an upper scissor jack assembly, at least four loading plates, stepper electric motors and controls, a turntable and a fixed support base. Each scissor jack assembly includes a rhombus-shape linkage system, at least one power screw-gear, loading plate assemblies and loading supports. 
     The upper scissor jack assembly is supported above the fixed base and the lower scissor jack assembly is positioned on the turntable. The turntable engages with a stepper motor to rotate in alternating directions with respect to the base. By rotating the turntable, the lower scissor jack assembly rotates relative to the upper scissor jack assembly. The angle of rotation of the lower scissor jack assembly can be measured directly. 
     The linkage system of the upper scissor jack assembly has four hinges, two hinges at either side of the screw-gear and the other two hinges that are connected to two linkages of the upper scissor jack assembly. One of the stepper motors is axially connected to the power screw-gear. Two hinges at either side of the screw-gear are restrained to move in an expansion and/or a contraction mode in collinear slots located on the support brackets. The other two hinges are restrained by co-linear sliding shafts that are supported by fixed brackets. The co-linear slots (for the screw-gear hinges) are perpendicular to the axis of the co-linear sliding shafts. Upon energizing the stepper motor, the screw-gear hinges along the screw-gears move within the slots, and the adjacent loading hinges move perpendicularly along the sliding shaft while the center of the upper scissor jack assembly remains fixed. 
     Likewise, the linkage system of the lower scissor jack assembly has four hinges, two at either side of the screw-gear and the other two hinges connecting the two linkages. The second stepper motor is axially connected to the power screw-gear of the lower scissor jack assembly. All hinges of the lower scissor jack assembly are restrained to move in four slots (two co-linear pairs) on the turntable. The co-linear slots are perpendicular allowing the adjacent hinges, screw-gear hinges and loading hinges, to move in perpendicular directions in an expansion and/or contraction mode. Upon energizing the stepper motor of the lower scissor jack assembly, all hinges move along their corresponding slots in a perpendicular manner while the center of the lower scissor jack assembly remains fixed at a center point that is vertically below the center point of the upper scissor jack assembly. 
     Each of the loading plates comprises a L-shaped bracket and a gripping/clamping means that is attached to the distal end of the bracket. The loading plates are attached to the two loading hinges of the upper scissor jack assembly and extend below the plane of the upper scissor jack assembly. Likewise, another set of loading plates are connected to the loading hinges of the lower scissor jack assembly and extend above the plane of the lower scissor jack assembly. 
     The plane of the clamp mechanism of the sets of the loading plates is co-planar. That is, when the four sides of the test specimen are clamped by the loading plates; the test specimen remains horizontal. Because the center point of the two scissor jacks are fixed in space and are located parallel to each other; the center point of the specimen remains fixed while the specimen is subjected to tension or compression. 
     The output shaft of a third stepper motor is connected to a gear that engages with a larger gear with the axle of the larger gear connected to the turntable. Upon energizing the stepper motor, the turntable rotates with respect to the base. The stepper motors are electrically connected to corresponding motor drivers. Each driver is electrically connected to a data acquisition device which is connected to a computer. Through simple programming, one can control the use of the stepper motors; thereby, applying a tension, compression and rotation to the specimen at varying testing levels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein like reference numerals and symbols designate identical or corresponding parts throughout the several views and wherein: 
         FIG. 1  depicts a perspective view of one embodiment of the testing apparatus of the present invention with a test specimen positioned within the apparatus; 
         FIG. 2  depicts a top view of the testing apparatus of  FIG. 1 ; 
         FIG. 3  depicts a side view of the testing apparatus of  FIG. 1 ; 
         FIG. 4  depicts a perspective view of the upper scissor jack assembly and loading plates of the testing apparatus of  FIG. 1 ; 
         FIG. 5  depicts a perspective view of the lower scissor jack assembly and loading plates on a turntable with the gear system of the testing apparatus of  FIG. 1 ; 
         FIG. 6  depicts a top view of the lower scissor jack assembly and the turntable of the testing apparatus of  FIG. 1 ; 
         FIG. 7  depicts a perspective view of the lower scissor jack assembly, the test specimen and loading plates on the turntable with the gear system of the testing apparatus of  FIG. 1 ; 
         FIG. 8  depicts a perspective, view of the loading plate and the strain gauges of the testing apparatus of  FIG. 1 ; 
         FIG. 9  depicts a first variant of the tension grip assembly of the testing apparatus of  FIG. 1 ; 
         FIG. 10  depicts a first variant of the compression grip assembly of the testing apparatus of  FIG. 1 ; 
         FIG. 11  depicts a sliding coupling connection joining a stepper motor to a power screw-gear; and 
         FIG. 12  depicts a variant of the power screw-gear arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIGS. 1-3 , a compact testing apparatus  10  is shown in which the apparatus comprises an upper scissor jack assembly  11 , a lower scissor jack assembly  12 , a turntable  13  and a support base  14  (preferably sized for tabletop use). For testing, a test specimen  100  is positioned within the apparatus  10 . 
     The upper scissor jack assembly  11  comprises a four-bar linkage  21 , hinged in a rhombus shape (similar to an automotive scissor jack) and a power (lead) screw-gear  22 . The four hinges of the upper jack assembly  11  are supported by upper assembly support brackets  23 ,  27 ,  28  and  34  in which the support brackets are rigidly connected to the fixed base  14 . 
     The screw-gear  22  is activated by a first stepper motor  38  that is controllable by a computer (not shown) thru an electronic driver  91 , a data acquisition board  92  and a serial port  94 . 
     The lower scissor jack assembly  12 , similar to the upper scissor jack assembly  11 , comprises a four bar linkage  51  hinged in a rhombus shape and a power (lead) screw-gear  52 . The hinges of the lower scissor jack assembly  12  are supported by the turntable  13 . The screw-gear  52  of the lower scissor jack assembly  12  is activated by a second stepper motor  64  that is computer-controlled through the serial port  94 , the data acquisition board  92  and an electronic driver  95 . The turntable  13  is activated by a third stepper motor  84  that is computer-controlled through the serial port  94 , the data acquisition board  92  and an electronic driver  96 . 
     The testing apparatus  10  also includes a strain indicator  90  that is electrically connected to at least four strain gauges  75  (See  FIG. 8 ) in which the gauges measure the strain subjected by the test specimen  100 . In addition, the testing apparatus  10  has a standard power supply  93  for the data acquisition board  92 , the electronic drivers  91 ,  95  and  96  and the strain indicator  90 . 
     Referring now to  FIG. 4 , the four linkages  21  of the upper scissor jack assembly  11  are hinged at screw-gear hinges  33  and  65  and at loading hinges  31 . The loading hinges  31  are connected to loading supports  24  and  39  on either side of the loading hinges. 
     The loading support  24  is axially engaged with a sliding shaft  25  that is rigidly connected to the support bracket  27  such that the loading support can slide axially over the shaft. The loading support  39  is axially engaged with a sliding shaft  26  that is rigidly connected to a horizontal connector  19  and the vertical support brackets  28 . The loading support  39  can slide axially over the sliding shaft  26 . Both the sliding shafts  25  and  26  restrain the displacement of the loading hinges  31  to a co-linear motion that is perpendicular to the axis of the screw-gear  22 . 
     The screw-gear hinge  33  that is located at the proximal end of the screw-gear  22  has a nut  60  that is engaged with the screw-gear and a displacement pin  57  that slides linearly in a slot (indent)  29  that is located on the horizontal plane of the support  23 . 
     The screw-gear hinge  65  that is located at the distal end of the screw-gear  22  has a nut  66  that is engaged with the screw-gear and the pin  57  that slides linearly in a slot (indent)  35  (See  FIG. 1 ) in which the slot is located on the horizontal plane of the upper assembly support bracket  34 . The slots  29  and  35  restrain the displacement of the screw-gear hinges  33  and  65  to a co-linear motion that is perpendicular to a reference line indicating a position of the loading hinges  31 . The support brackets  23  and  34  are rigidly connected to the base  14 . 
     The upper scissor jack assembly  11  also has two loading plate assemblies  32  that are rigidly attached to the loading supports  24  and  39 . The loading plate assemblies  32  extend below the plane of the upper scissor jack assembly  11  such that when two ends of the test specimen  100  are clamped to the distal ends of the loading plates; the specimen does not contact the screw-gear  22 . 
     In the figure, the first stepper motor  38  is shown mounted on a motor support bracket  37  and to the upper assembly support bracket  34 ; however the first stepper motor may be directly affixed to the base  14 . The shaft of the stepper motor  38  is axially and operationally connected to the power screw-gear  22  through a coupling shaft  36 . The coupling shaft  36  has a pin  85  and a slot  86  (See  FIG. 11 ) that transfers the torque of the shaft of the stepper motor  38  to the power screw-gear  22  while allowing limited axial displacement between the shaft and the screw-gear. There is a limiting switch  62  on the proximal end of the slot  29  that stops the stepper motor  38  when the hinge reaches the proximal end of the slot; thereby, preventing the upper scissor jack assembly  11  from overextending. 
     Referring to  FIGS. 5 ,  6  and  7 , the linkages  51  of the lower scissor jack assembly  12  are hinged at screw-gear hinges  53  and  67  and two pairs of loading hinges  68 . The lower scissor jack assembly  12  also includes a power screw-gear  52  and the second stepper motor  64 . The loading hinges  68  are connected to two loading supports  54  on either side of the loading hinges. The axis of the screw-gear  52  is generally perpendicular and on a parallel plane to the axis of the screw-gear  22  of the upper scissor jack assembly  11 . That is, in operation, the lower scissor jack assembly  12  is rotated ninety degrees with respect to the upper scissor jack assembly  11 . 
     The screw-gear hinge  53  of the lower scissor jack assembly  12  has a nut  60  that is engaged with the screw-gear  52  and a displacement pin (not shown) that slides linearly in a slot  55  which is located on the horizontal plane of the turntable  13 . The screw-gear hinge  67  has a nut  60  that is engaged with the screw-gear  52 . The slots  55 , on either sides of the screw-gear  52 , both restrain the displacement of the screw-gear hinges  53  and  67  to a co-linear motion that is perpendicular to a reference line indicating the position of the loading hinges  68 . 
     The loading hinges  68  have displacement pins at their inferior surface (not shown) that slide linearly in a slot (not shown) that is located on the horizontal plane of the turntable  13 . The slots restrain the displacement of the loading hinges  68  to a co-linear motion that is perpendicular to a reference line indicating the position of the screw-gear hinges  53  and  67 . The lower scissor jack assembly  12  is supported by the turntable  13  through the pin and slot configuration. 
     The lower scissor jack assembly  12  has two loading plates  61  that are rigidly attached to the loading supports  54 . The loading plates  61  extend above the plane of the lower scissor jack assembly  12  such that when two ends of the test specimen  100  are clamped to the distal ends of the loading plates; the specimen does not contact the screw-gear  52 . The height of the distal ends of the loading plates  61  of the lower scissor jack assembly  12  is at the same level of the height of the distal ends of the loading plate assemblies  32  of the upper scissor jack assembly  11  such that the plane of the test specimen  100  is horizontal when four sides of the specimen are clamped to the four loading plates. 
     The second stepper motor  64  is rigidly connected to a bracket  58  and to the turntable  13  (See  FIG. 6 ). The shaft of the second stepper motor  64  is axially and operationally connected to the screw-gear  52  through a coupling shaft  59 . The coupling shaft  59  has a pin  85  and a slot  86  (See  FIG. 11 ) that transfers the torque of the shaft to the power screw-gear  52  while allowing limited axial displacement between the shaft and the screw-gear. There is a limiting switch  63  on the distal end of the slot  55 , proximate to the screw-gear hinge  53 . This limiting switch  63  is used to stop the stepper motor  64  when the hinge  53  reaches the proximal end of the slot; thereby, preventing the lower scissor jack assembly  12  from overextending. 
     Referring to  FIG. 7 , the turntable  13  comprises a planar circular disc, a gear  82 , a pinion gear  83  and the third stepper motor  84 . The gear  82  is coaxial to the turntable  13  and is engaged with the pinion gear  83 . The third stepper motor  84  is rigidly connected to the supporting base  14  and electrically connected to the electronic driver  96  (shown in  FIG. 1 ). 
     Upon energizing the third stepper motor  84 , the turntable  13  can rotate clockwise or counter-clockwise, thereby rotating the lower scissor jack assembly  12  with respect to the upper scissor jack assembly  11 . To restrict the angle of rotation, two contact limiting switches  30  (shown in  FIG. 1  and  FIG. 4 ) are attached to the sides of the support brackets  28 . The distance between the sides and the contact limiting switches  30  of the support brackets  28  confines the maximum relative rotation of the lower scissor jack assembly  12  with respect to the upper scissor jack assembly  11 . That is, the maximum shear angle of the test specimen  100  is defined by the distance between the support brackets  28  because the contact limiting switches  30  electrically stop the rotation of the turntable  13  when contacted and therefore stops shearing of the specimen. 
     Referring to  FIG. 8 , the loading plate assembly  32  comprises an L-shape bracket  78  having an extension  79 , a distal end  80  and a locking plate  72 . The extension  79  has two strain gauges  75  attached to adjacent surfaces. In one embodiment, the distal end  80  has a slot  71 , the locking plate  72  and a plurality of screws  73 . The fabric test specimen  100  is clamped between the locking plate  72  and the slot  71  (in a tongue and groove manner) by tightening the screws  73 . 
     When the test specimen  100  is not a fabric, but instead is a solid object, and is to be subjected to a tension, another embodiment, may be used. The embodiment includes a standard tension grip  76  (shown in  FIG. 9 ) will replace the distal end of the loading plate assembly  32 . Likewise, when the test specimen  100  is not a fabric, but rather is a solid object, and is to be subjected to a compression, another embodiment, may be used. The embodiment which includes a compression grip  77  (shown in  FIG. 10 ) will replace the distal end of the loading plate assembly  32 . The strain gauges  75  are electrically connected to the strain gauge indicator  90  where the strain (and the stress) of the test specimen  100  in is measured. 
     An upper surface  69  of the bracket  78  is rigidly connected to the corresponding loading support of the upper and lower scissor jack assemblies. Specifically, the upper surface  69  of one loading plate assembly  32  is rigidly connected to the lower surface of the loading support  24 . Likewise another loading plate is rigidly connected to the lower surface of the loading support  39  (See  FIG. 4 ). Also, the upper surface  69  of the loading plate assembly  32  is rigidly connected to the upper surface of the loading support  54 , on the side of lower scissor jack assembly  12 , likewise an other loading plate is rigidly connected to the upper surface of the loading support  54 , on the another side of the lower jack assembly  12 . (See  FIG. 5 ). 
     Operation of the testing assembly  10  involves clamping sides of the test specimen  100  to the distal clamping ends of the four loading plates assemblies (Note that two of the loading plate assemblies  32  are rigidly connected to the loading supports of the upper scissor jack assembly  11  and the other two of the loading plate assemblies  61  are rigidly connected to the loading supports of lower scissor jack assembly  12 ). 
     For tensile loading of planar solids, a tension grip  76  is used (See  FIG. 9 ) and for compressive loading, a compression grip  77  is used (See  FIG. 10 ), and for fabric, the tongue and groove clamping is used (See  FIG. 8 ). Second, through a laptop or desktop computer and by using standard testing software or standard C++ programming; the digital computer commands are transferred to the stepper motor drivers through the data acquisition (DAQ) device. That is, through a computer command each of the stepper motors are energized and the test specimen  100  will be subjected to a combination of biaxial tension, compression or in-plane shear. The strains of the test specimen  100  will be measured by the strain gauge indicator and fed back through the DAQ device to the computer. The rotation of the turntable  13 , or the angle of in-plane shear, is measured and controlled through the corresponding electronic driver. 
     Upon energizing the stepper motor  38  and rotating a output shaft of the stepper motor in a clockwise or counter-clockwise direction; the screw-gear hinges  33  and  65  move toward or away from each other, while the loading hinges  31  move conversely away or toward each other. Note that the movements of the hinges are restrained by the slots ( 29 ,  35 ) and the sliding shafts ( 25 ,  26 ). Therefore, by activating the gear of the motor  38  in a clockwise and a counter-clockwise rotation, the test specimen  100  will be subjected to a tension or a compression load through the direct connection of the specimen with the loading plate assemblies  32  connected to the loading supports  24  and  39 . 
     The limiting switch  62  limits the maximum expansion of the upper scissor jack assembly  11 . Likewise, upon energizing the stepper motor  64  and rotating an output shaft of the motor in a clockwise or counter-clockwise direction, the screw-gear hinges  53  and  67  move toward or away from each other, while the loading hinges  68  move conversely away or toward each other (See  FIG. 5  and  FIG. 6 ). Note that the movements of the hinges are restrained by the four slots  55  on the turntable  13 . Therefore, by rotating the gear shaft of the stepper motor  64  in the clockwise or counter-clockwise direction, the test specimen  100  will be subjected to a tension or a compression load through the direct connection of the specimen with the two loading plates  61 . The limiting switch  63  limits the expansion of the lower scissor jack assembly  12 . 
     Finally, upon energizing the third stepper motor  84  in a clockwise or counter-clockwise direction; the turntable  13  including the lower scissor jack assembly  12  will turn in either the clockwise or counter-clockwise direction. Therefore, both loading plates  61  rotate in a clockwise or counter-clockwise direction and apply the in-plane shear in a clockwise or counter-clockwise to the test specimen  100 . 
     In addition to the usage of the previously mentioned strain gauges, conventional measurement equipment systems such as force transducers can be utilized to measure forces/loads applied to the test specimen. Also, a conventional displacement wire transducer, or a conventional Linear Variable Displacement Transducer (LVDT) can be placed on the loading plates to measure the total biaxial displacements, rotation and strains of the test specimen  100 . 
     It is important to note that the testing apparatus  10  can apply a non-equi biaxial loading ratio in that the tension/compression and the displacements in each direction can be different and independent. 
     A first variant of operation is to use the testing apparatus  10  for a non-orthogonal (oblique) biaxial loading of the test specimen  100 . This use is particularly important for testing of braided fabrics and non-orthogonal composite materials. To accomplish this task the stepper motor  84  of the turntable  13  is energized and the angle between the two axes of the applied load, i.e., the angle between the upper and the lower jack, can be adjusted to a desired oblique test specimen. 
     A second variant of operation is to use the testing apparatus  10  for the alternative modes of loading the test specimen  100 : uniaxial tension, uniaxial compression, biaxial tension, biaxial compression, uniaxial tension with in-plane shear, uniaxial compression with in-plane shear, biaxial tension with in-plane shear, biaxial compression with in-plane shear, unequal biaxial tension with in-plane shear and unequal biaxial compression with in-plane shear. 
     An alternative power screw-gear arrangement is shown in  FIG. 12  that enables visual access for viewing and video recording of the specimen  100  during testing. This alternative, which also makes installation of the test specimen  100  simpler, replaces the power screw-gear  22  with two truncated power screw-gears  40 ,  42  aligned along the upper axis. The truncated power screw-gears  40 ,  42  are operated in a synchronized manner using one stepper motor  38 ,  98  for each power screw-gear. The limiting switch  62  can be used to inactivate the stepper motor for each screw-gear. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.