Patent Publication Number: US-2023133728-A1

Title: System and method for applying dynamic loading to a test specimen

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This specification is based upon and claims the benefit of priority from Cypriot patent application number CY 202100002 filed on Oct. 29, 2021, the entire contents of which is incorporated herein by reference. 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a system and a method for applying dynamic loading to a test specimen. 
     Description of the Related Art 
     Engineering applications may require data on dynamic mechanical response of materials under high strain rate deformation. The split Hopkinson Pressure Bar (SHPB), also referred to as the Kolsky Bar, is a commonly used setup for testing materials at high strain rates. A specimen is sandwiched between two rods, each of which is instrumented with strain gauges. A stress wave, compression, tension, or torsion, is introduced into one of the rods (an input bar), which transmits the stress wave to the specimen. This causes the specimen to deform. A change in impedance between the rods and the specimen causes some of the stress wave to be reflected, and the rest to be transmitted (into an output rod). By measuring these three stress waves (incident, reflected and transmitted), a stress-strain response of the specimen can be inferred. 
     Known arrangements of SHPB for carrying out tests may allow testing in uniaxial stress in tension or in compression, and in pure shear. Some arrangements may also allow combined loading of torsion and tension/compression on the specimen. In such arrangements, torsion loading and tension/compression loading can be applied on separate rods on either end of SHPB or a single rod. Conventional SHPBs often utilize clamps to hold the rods under torsion, tension and/or compression until the load is to be released. As the clamps are released, the stress waves travel along the rods and are applied to the specimen. Multiple clamps may be utilized with SHPB based on arrangement of loading on the specimen. 
     Conventional clamps may typically include a mechanical fuse (e.g., a notched pin) which fractures to release the clamps. A release time of such mechanical clamp may not be controlled precisely and accurately by virtue of fracturing of the mechanical fuse. This may be problematic to the operation of SHPB since precise control of clamps is required to ensure that the arrival of the stress waves at the specimen is correctly synchronised in a combined loading arrangement. Further, the release time of mechanical clamps may not be accurately synchronized with the release time of other clamps if multiple clamps are utilized with SHPB. 
     SUMMARY 
     According to a first aspect there is provided a system for measuring loading on a test specimen. The system includes a first loading bar and a second loading bar arranged along a longitudinal axis. The test specimen is arranged between the first and second loading bars along the longitudinal axis. The system further includes a first loading unit coupled to the first loading bar and configured to apply a first load to the first loading bar. The system further includes a second loading unit coupled to the second loading bar and configured to apply a second load to the second loading bar. The system further includes a first clamp disposed between the first loading unit and the test specimen along the longitudinal axis. The first clamp is configured to hold the first loading bar against the first load. Upon release of the first clamp, the first loading bar is configured to apply a first loading wave to the test specimen in response to the first load. The system further includes a second clamp disposed between the second loading unit and the test specimen along the longitudinal axis. The second clamp is configured to hold the second loading bar against the second load. Upon release of the second clamp, the second loading bar is configured to apply a second loading wave to the test specimen in response to the second load. The system further includes a clamp actuating unit configured to selectively release at least the first clamp. The clamp actuating unit includes at least one first electromechanical transducer switchable between a retained state and a released state. In the retained state, the at least one first electromechanical transducer is configured to load the first clamp, such that the first clamp holds the first loading bar against the first load. In the released state, the at least one first electromechanical transducer is configured to release the first clamp. The clamp actuating unit further includes a controller configured to electrically actuate the at least one first electromechanical transducer from the retained state to the released state to release the first clamp, such that the first loading bar applies the first loading wave to the test specimen. 
     The clamp actuating unit may electrically actuate the at least one first electromechanical transducer between the retained state and the release state. Use of the at least one first electromechanical transducer may allow precise control of a release time of the first clamp, and thus, precise control of application of the first loading wave to the test specimen. Further, a response time of the first clamp may also be reduced since the system utilizes the at least one first electromechanical transducer as opposed to the conventional mechanical fuse which has relatively longer response time. 
     In some embodiments, the first clamp includes a pair of first clamping members configured to hold the first loading bar therebetween. The at least one first electromechanical transducer comprises a pair of first electromechanical transducers. Each first electromechanical transducer is configured to load a corresponding first clamping member from the pair of first clamping members. The pair of first electromechanical transducers may allow symmetric loading of the pair of first clamping members, thus eliminating any transverse bending forces on the first loading bar. 
     In some embodiments, the at least one first electromechanical transducer includes at least one first piezoelectric element configured to expand along a first transverse axis inclined to the longitudinal axis upon application of a first electrical signal. The at least one first piezoelectric element is further configured to contract along the first transverse axis upon removal of the first electrical signal. In the retained state, the at least one first piezoelectric element expands to load the first clamp, and in the released state, the at least one first piezoelectric element contracts to release the first clamp. Use of the at least one first piezoelectric element may reduce the response time of the first clamp as compared to conventional clamps utilizing mechanical fuse. 
     In some embodiments, the controller is further configured to apply the first electrical signal to the at least one first piezoelectric element to switch the at least one first piezoelectric element to the retained state. The controller is further configured to remove the first electrical signal from the at least one first piezoelectric element to switch the at least one first piezoelectric element to the released state. 
     In some embodiments, the clamp actuating unit further includes a first actuator configured to apply a first clamping force on the at least one first electromechanical transducer. In the retained state, the at least one first electromechanical transducer is configured to at least partially transmit the first clamping force received from the first actuator to the first clamp. The first actuator may apply the first clamping force on the at least one first electromechanical transducer to load the first clamp and hold the first clamp against the first loading bar. 
     In some embodiments, the clamp actuating unit further includes at least one first support member to support the at least one first electromechanical transducer between the first clamp and the first actuator. The at least one first support member is configured to receive the at least one first electromechanical transducer through the at least one first support member. 
     In some embodiments, the clamp actuating unit is further configured to selectively release the second clamp. The clamp actuating unit further includes at least one second electromechanical transducer switchable between a retained state and a released state. In the retained state, the at least one second electromechanical transducer is configured to load the second clamp, such that the second clamp holds the second loading bar against the second load. In the released state, the at least one second electromechanical transducer is configured to release the second clamp. The controller is further configured to electrically actuate the at least one second electromechanical transducer from the retained state to the released state to release the second clamp, such that the second loading bar applies the second loading wave to the test specimen. 
     Use of second clamp with the at least one second electromechanical transducer may allow precise control of the application of the second loading wave on the test specimen. Further, the release time of the at least one first electromechanical transducer may be synchronized with a release time of the at least one second electromechanical transducer. 
     In some embodiments, the second clamp includes a pair of second clamping members configured to hold the second loading bar therebetween. The at least one second electromechanical transducer includes a pair of second electromechanical transducers. Each second electromechanical transducer is configured to load a corresponding second clamping member from the pair of second clamping members. The pair of second electromechanical transducers may allow symmetric loading of the pair of second clamping members, thus eliminating any transverse bending forces on the second loading bar. 
     In some embodiments, the at least one second electromechanical transducer includes at least one second piezoelectric element configured to expand along a second transverse axis inclined to the longitudinal axis upon application of a second electrical signal. The at least one second piezoelectric element is further configured to contract along the second transverse axis upon removal of the electrical signal. In the retained state, the at least one second piezoelectric element expands to load the second clamp, and in the released state, the at least one second piezoelectric element contracts to release the second clamp. Use of the at least one second piezoelectric element may reduce the response time of the second clamp as compared to conventional clamps utilizing mechanical fuse. 
     In some embodiments, the controller is further configured to apply the second electrical signal to the at least one second piezoelectric element to switch the at least one second piezoelectric element to the retained state. The controller is further configured to remove the second electrical signal from the at least one second piezoelectric element to switch the at least one second piezoelectric element to the released state. The controller may independently control release of the first clamp and the second clamp using the first electrical signal and the second electrical signal, respectively. 
     In some embodiments, the clamp actuating unit further includes a second actuator configured to apply a second clamping force on the at least one second electromechanical transducer. In the retained state, the at least one second electromechanical transducer is configured to at least partially transmit the second clamping force received from the second actuator to the second clamp. The second actuator may apply the second clamping force on the at least one second electromechanical transducer to load the second clamp and hold the second clamp against the second loading bar. 
     In some embodiments, the clamp actuating unit further includes at least one second support member to support the at least one second electromechanical transducer between the second clamp and the second actuator. The at least one second support member is configured to receive the at least one second electromechanical transducer through the at least one second support member. 
     In some embodiments, the first loading unit is further configured to apply a static torque on the first loading bar, such that the first load is the static torque. In some embodiments, the second loading unit is further configured to apply a static axial force on the second loading bar, such that the second load is the static axial force. In some embodiments, the first loading wave is a torsion wave and the second loading wave is an axial wave. In some embodiments, the first clamp is configured to hold the first loading bar in torsion. In some embodiments, the second clamp is configured to hold the second loading bar in tension or compression. 
     According to a second aspect, there is provided a method for measuring loading on a test specimen. The method includes arranging a test specimen between a first loading bar and a second loading bar. The first and second loading bars are arranged along a longitudinal axis. The method further includes holding, via a first clamp, the first loading bar against a first load. Upon release of the first clamp, the first loading bar is configured to apply a first loading wave to the test specimen in response to the first load. The method further includes electrically actuating, via a controller, at least one first electromechanical transducer to a retained state. In the retained state, the at least one first electromechanical transducer loads the first clamp, such that the first clamp holds the first loading bar. The method further includes holding, via a second clamp, the second loading bar against a second load. Upon release of the second clamp, the second loading bar is configured to apply a second loading wave to the test specimen in response to the second load. The method further includes applying, via a first loading unit, the first load to the first loading bar. The method further includes applying, via a second loading unit, the second load to the second loading bar. The method further includes electrically actuating, via the controller, the at least one first electromechanical transducer from the retained state to a released state. In the released state, the at least one first electromechanical transducer releases the first clamp, such that the first loading bar applies the first loading wave to the test specimen. 
     In some embodiments, electrically actuating the at least one first electromechanical transducer to the retained state further includes applying a first electrical signal to the at least one first electromechanical transducer, such that the at least one first electromechanical transducer expands along a first transverse axis inclined to the longitudinal axis to load the first clamp. In some embodiments, electrically actuating the at least one first electromechanical transducer from the retained state to the released state further includes removing the first electrical signal from the at least one first electromechanical transducer, such that the at least one first electromechanical transducer contracts along the first transverse axis to release the first clamp. 
     In some embodiments, the method further includes applying, via a first actuator, a first clamping force on the at least one first electromechanical transducer. In the retained state, the at least one first electromechanical transducer is configured to at least partially transmit the first clamping force received from the first actuator to the first clamp. 
     In some embodiments, the method further includes electrically actuating, via the controller, at least one second electromechanical transducer to a retained state. In the retained state, the at least one second electromechanical transducer loads the second clamp, such that the second clamp holds the second loading bar. In some embodiments, the method further includes electrically actuating, via the controller, the at least one second electromechanical transducer from the retained state to a released state. In the released state, the at least one second electromechanical transducer releases the second clamp, such that the second loading bar applies the second loading wave to the test specimen. 
     In some embodiments, electrically actuating the at least one second electromechanical transducer to the retained state further includes applying a second electrical signal to the at least one second electromechanical transducer, such that the at least one second electromechanical transducer expands along a second transverse axis inclined to the longitudinal axis to load the second clamp. In some embodiments, electrically actuating the at least one second electromechanical transducer from the retained state to the released state further includes removing the second electrical signal from the at least one second electromechanical transducer, such that the at least one second electromechanical transducer contracts along the second transverse axis to release the second clamp. 
     In some embodiments, the method further includes applying, via a second actuator, a second clamping force on the at least one second electromechanical transducer. In the retained state, the at least one second electromechanical transducer is configured to at least partially transmit the second clamping force received from the second actuator to the second clamp. 
     In some embodiments, the method further includes simultaneously or timely sequentially releasing the first clamp and the second clamp. 
     The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described by way of example only, with reference to the Figures, in which: 
         FIG.  1    is a schematic perspective view of a system for measuring loading on a test specimen, according to an embodiment of the present disclosure; 
         FIG.  2    is an enlarged schematic perspective view of the system of  FIG.  1   , according to an embodiment of the present disclosure; 
         FIG.  3    is an enlarged schematic side view of the system of  FIG.  1   , according to an embodiment of the present disclosure; 
         FIG.  4    is a schematic perspective view of a clamp actuating unit and a first clamp, according to an embodiment of the present disclosure; 
         FIGS.  5 A and  5 B  illustrate schematic side views of the clamp actuating unit and the first clamp of  FIG.  4    in a retained state and a released state, respectively, of at least one first electromechanical transducer, according to an embodiment of the present disclosure; 
         FIG.  6    is a schematic perspective view of the clamp actuating unit and a second clamp, according to an embodiment of the present disclosure; 
         FIGS.  7 A and  7 B  illustrate schematic side views of the clamp actuating unit and the second clamp of  FIG.  6    in a retained state and a released state, respectively, of at least one second electromechanical transducer, according to an embodiment of the present disclosure; and 
         FIG.  8    illustrates a flow chart of a method for measuring loading on a test specimen, according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. 
       FIG.  1    illustrates a schematic perspective view of a system  100  for measuring loading on a test specimen  102 . In some embodiments, the system  100  is a split-Hopkinson bar (SHPB) apparatus that enables a high strain rate application of combined torsional loading and axial loading on the test specimen  102 . In other words, the system  100  may be used for measuring torsional loading combined with axial loading on the test specimen  102 . In some embodiments, the system  100  may be used to obtain a mechanical response of a material under high strain rate deformation. In some embodiments, the strain rates may be between approx. 100 s −1  and 10,000 s −1 . A material model may then be built based on the mechanical response of the material. 
     The system  100  includes a first loading bar  104  and a second loading bar  106  arranged along a longitudinal axis A-A′. The longitudinal axis A-A′ may extend along a longitudinal direction of the system  100 . In some embodiments, the first loading bar  104  and the second loading bar  106  are arranged in a straight line along the longitudinal axis A-A′. The test specimen  102  is arranged between the first and second loading bars  104 ,  106  along the longitudinal axis A-A′. 
     A stress wave (compression, tension, or torsion) may be introduced into one of the first loading bar  104  and the second loading bar  106 , which transmits the stress wave to the test specimen  102 . This causes the test specimen  102  to deform. A change in impedance between the first and second loading bars  104 ,  106  and the test specimen  102  causes a portion of the stress wave to be reflected, and the rest to be transmitted into a subsequent rod. By measuring the three stress waves (incident, transmitted, and reflected), a stress-strain response of the test specimen  102  can be inferred. 
     In some embodiments, the first and second loading bars  104 ,  106  may be solid cylindrical bars. In alternative embodiments, the first and second loading bars  104 ,  106  may have a non-circular cross-section, for example, polygonal, elliptical, or oval. A size of each of the first and second loading bars  104 ,  106  may be selected based on various factors, such as a duration of an event during testing and a size of the test specimen  102 . In some embodiments, a length of the first loading bar  104  may be different from a length of the second loading bar  106 . In some embodiments, the first and second loading bars  104 ,  106  may be constructed from any suitable material, such as, for example, metal or metal alloys (e.g., titanium alloy, high strength steel, phosphor bronze, etc.), plastic, elastomer, or composite material. In some embodiments, the first and second loading bars  104 ,  106  are made of same material and include same cross-sectional area. In some embodiments, the first and second loading bars  104 ,  106  may be elastic. 
     The system  100  further includes a first loading unit  112  coupled to the first loading bar  104  and configured to apply a first load  114  to the first loading bar  104 . In some embodiments, the first loading unit  112  may be coupled to the first loading bar  104  though any suitable coupling mechanisms. In some embodiments, the first loading unit  112  is arranged to apply the first load  114  at an end of the first loading bar  104  opposite to the end where the test specimen  102  is secured. In some embodiments, the first loading unit  112  is further configured to apply a static torque  114   a  on the first loading bar  104 , such that the first load  114  is the static torque  114   a.  In some embodiments, the first loading unit  112  may include a torque pump configured to apply the first load  114  on the first loading bar  104 . In some embodiments, impact devices may also be used to apply the first load  114 . 
     The system  100  further includes a second loading unit  116  coupled to the second loading bar  106  and configured to apply a second load  118  to the second loading bar  106 . In some embodiments, the second loading unit  116  may be arranged to apply the second load  118  at an end of the second loading bar  106  opposite to the end where the test specimen  102  is secured. In some embodiments, the second loading unit  116  is further configured to apply a static axial force  118   a  on the second loading bar  106 , such that the second load  118  is the static axial force  118   a.  In some embodiments, the first loading unit  112  and the second loading unit  116  may be controlled independently to apply the first load  114  and the second load  118 , respectively. In some embodiments, the second loading unit  116  may include either energy storage (e.g., by holding a bar in tension) or impact devices configured to apply the second load  118  or the static axial force  118   a  on the second loading bar  106 . 
     In some embodiments, the first loading unit  112  and the second loading unit  116  may be configured to apply the first load  114  and the second load  118  on either the first loading bar  104  or the second loading bar  106 . Thus, the first and second loading units  112 ,  116  may be mounted on one side of the SHPB only. 
     In some embodiments, the first and second loading units  112 ,  116  are mounted on a frame  108 . The frame  108  may provide structural support to the system  100 . Further, the first and second loading bars  104 ,  106  may be coupled to the frame  108  through one or more supporting members  110 . In some embodiments, the first and second loading bars  104 ,  106  may pass through the one or more supporting members  110  for support. 
     In some embodiments, each supporting member  110  may allow movement of the first and second loading bars  104 ,  106  therethrough. In some embodiments, the one or more supporting members  110  may be low friction supports that allow near frictionless movement of the first and second loading bars  104 ,  106  through the one or more supporting members  110 . It should be understood that the system  100  may include any number of supporting members  110 . Further, the shape and configuration of the one or more supporting members  110  may vary based on a geometric shape and design of the first and second loading bars  104 ,  106 . Additionally, some of the supporting members  110  may be different from the other supporting members  110 . The relative positioning of the one or more supporting members  110  may be selected based on the length of the first and second loading bars  104 ,  106 . Further, the one or more supporting members  110  may be movable along the longitudinal axis A-A′ with respect to the frame  108 . 
     The system  100  further includes a first clamp  120  disposed between the first loading unit  112  and the test specimen  102  along the longitudinal axis A-A′. The first clamp  120  is configured to hold the first loading bar  104  against the first load  114 . In some embodiments, the first clamp  120  may be arranged and secured to the frame  108  at a location between the first loading unit  112  and the test specimen  102 . The first clamp  120  may hold the first loading bar  104  such that when the first loading unit  112  applies the first load  114  to the first loading bar  104 , the first load  114  is not transferred to the test specimen  102 . A clamping force applied by the first clamp  120  may be sufficient to hold the first loading bar  104  against the first load  114 . In some embodiments, the first clamp  120  is configured to hold the first loading bar  104  in torsion. 
     The system  100  further includes a second clamp  130  (shown partially) disposed between the second loading unit  116  and the test specimen  102  along the longitudinal axis A-A′. The second clamp  130  is configured to hold the second loading bar  106  against the second load  118 . The second clamp  130  may be arranged and secured to the frame  108  at a location between the second loading unit  116  and the test specimen  102 . The second clamp  130  may hold the second loading bar  106  such that when the second load unit  116  applies the second load  118  to the second loading bar  106 , the second load  118  is not transferred to the test specimen  102 . In other words, a clamping force applied by the second clamp  130  may be sufficient to hold the second loading bar  106  against the second load  118 . In some embodiments, the second clamp  130  is configured to hold the second loading bar  106  in tension. In some embodiments, the second clamp  130  may be similar to the first clamp  120 . 
       FIG.  2    illustrates an enlarged schematic perspective view of the system  100 . In some embodiments, the first load  114  or the static torque  114   a  may be stored by means of the first clamp  120  holding the first loading bar  104  until the first load  114  or the static torque  114   a  needs to be released. Thus, a stress-wave can be introduced into the first loading bar  104  by rapid release of the first load  114  or the static torque  114   a  stored with the first clamp  120  remote from the test specimen  102 . The system  100  further includes a clamp actuating unit  140  configured to selectively release at least the first clamp  120 . 
     In some embodiments, the second load  118  or the static axial force  118   a  can be stored by means of the second clamp  130  holding the second loading bar  106  until the second load  118  or the static axial force  118   a  needs to be released. Thus, a stress-wave can be introduced into the second loading bar  106  by rapid release of the second load  118  or the static axial force  118   a  stored with the second clamp  130  remote from the test specimen  102 . In some embodiments, the clamp actuating unit  140  is further configured to selectively release the second clamp  130 . Specifically, the clamp actuating unit  140  is configured to release the first clamp  120  and the second clamp  130 . 
     In some embodiments, one or more strain gauges  128  are suitably positioned on the first loading bar  104  and the second loading bar  106 . In some embodiments, the one or more strain gauges  128  may measure shear and axial strains in the first and second loading bars  104 ,  106 . In some embodiments, the one or more strain gauges  128  may be fixed to a surface of the first and second loading bars  104 ,  106 . In some embodiments, the strains in the first and second loading bars  104 ,  106  may be determined from a surface velocity of the first and second loading bars  104 ,  106  measured using Photon Doppler Velocimetry (PDV) or Laser Doppler Velocimetry (LDV). In some embodiments, measurement of a deformation of the test specimen  102  may also be made using lasers, high speed photography or strain gauges. Measurements of force at a bar-specimen interface may be made using stress gauges. 
       FIG.  3    illustrates an enlarged schematic side view of the system  100  of  FIG.  2   . Upon release of the first clamp  120 , the first loading bar  104  is configured to apply a first loading wave  122  to the test specimen  102  in response to the first load  114 . Thus, upon release of the first clamp  120 , the first loading wave  122  may reach the test specimen  102 . In some embodiments, the first loading wave  122  is a torsion wave  124 . 
     Upon release of the second clamp  130 , the second loading bar  106  is configured to apply a second loading wave  132  to the test specimen  102  in response to the second load  118 . Therefore, upon release of the second clamp  130 , the second loading wave  132  may reach the test specimen  102 . In some embodiments, the second loading wave  132  is an axial wave  134 . 
     When the first clamp  120  is released, the first loading wave  122  travels along the first loading bar  104  and is applied to the test specimen  102 . Likewise, when the second clamp  130  is released, the second loading wave  132  travels along the second loading bar  106  and is applied to the test specimen  102 . Such an arrangement may allow a combination of torsional loading and axial loading (i.e., compression or tension) to be applied to the test specimen  102  at very high strain rates. Thus, a response to such combined loading of the test specimen  102  can be investigated. In some embodiments, the clamp actuating unit  140  may independently control the first clamp  120  and the second clamp  130  for applying the first loading wave  122  and the second loading wave  132  to the test specimen  102 , respectively. 
     in some embodiments, the clamp actuating unit  140  may be configured to release the first and second clamps  120 ,  130  simultaneously. In such an arrangement (shown in  FIGS.  1 - 3   ), the first and second clamps  120 ,  130  may be suitably positioned along the longitudinal axis A-A′ such that the first and second loading waves  122 ,  132  may arrive at the test specimen  102  simultaneously. Since first loading wave  122  (e.g., torsion wave  124 ) may travel slower than the second loading wave  132  (e.g., axial wave  134 ), the second clamp  130  may be positioned further from the test specimen  102  that the first clamp  120 . A distance between each of the first and second clamps  120 ,  130  and the test specimen  102  may be chosen so as to control a timing of arrival of the first and second loading waves  122 ,  132  at the test specimen  102 . A position of the first and second clamps  120 ,  130  along the longitudinal axis A-A′ may be determined previously based on calculations and experimental data. 
     In some embodiments, the clamp actuating unit  140  may be configured to release the first and second clamps  120 ,  130  in a timely sequential manner. For example, the clamp actuating unit  140  may release the second clamp  130  after releasing the first clamp  120  with a predetermined time delay. In such an arrangement, the first and second clamps  120 ,  130  may be positioned at equal distance from the test specimen  102 . A time of releasing of the first clamp  120  and a time of releasing of the second clamp  116  may be determined previously based on calculations and experimental data to allow the first and second loading waves  122 ,  132  to reach the test specimen  102  simultaneously. 
     In some embodiments, the positions of the first and second clamps  120 ,  130  and the times of releasing of the first and second clamps  120 ,  130  may both be controlled to allow the first and second loading waves  122 ,  132  to reach the test specimen  102  simultaneously. In some other embodiments, the positions and/or the times of releasing of the first and second clamps  120 ,  130  may be chosen such that the first and second loading waves  122 ,  132  arrive at the test specimen  102  at different points in time. Based on the desired time of arrival of each of the first and second loading waves  122 ,  132  at the test specimen  102  and a speed of travel of each of the first and second loading waves  122 ,  132  through the first and second loading bars  104 ,  106 , the respective distances of the first and second clamps  120 ,  130  from the test specimen  102  may be chosen. 
     In the illustrated embodiments of  FIGS.  1 - 3   , the system  100  is used for measuring combined torsional and tensile loading on the test specimen  102 . However, in some embodiments, the system  100  may also be adapted for measuring combined torsional and compression loading on the test specimen  102 . In such embodiments, the second loading unit  116  may be configured to apply a compression load on the test specimen  102 . Thus, a compression stress-wave may be introduced into the second loading bar  106  by the second loading unit  116 . For compression loading, the second loading unit  116  may include a striker bar, impacted into the second loading bar  106  by, for example, a gas gun. Further, the second clamp  130  may be configured to hold the second loading bar  106  in compression. 
     It will be appreciated that other arrangements are possible where the first and second loading units  112 ,  116  are both axial force systems (i.e., arranged to apply a static axial force to the first and second respective loading bars  104 ,  106 ), or are both torsional force systems (i.e., arranged to apply a static torque to the first and second respective loading bars  104 ,  106 ). Further, in arrangements where the first and second loading units  112 ,  116  are both axial force systems, one loading unit may provide a tension force and the other may provide a compression force, or both loading units may provide the same type of force (i.e., tension or compression). Additionally, in arrangements where the first and second loading units  112 ,  116  are both torsional force systems, the directions of the torsional forces may be same or opposite to each other. 
       FIG.  4    illustrates a schematic perspective view of the clamp actuating unit  140  and the first clamp  120 . An outer housing of the clamp actuating unit  140  may be omitted in  FIG.  4    for the purpose of illustration. The clamp actuating unit  140  includes at least one first electromechanical transducer  142  switchable between a retained state P 1  (shown in  FIG.  5 A ) and a released state P 2  (shown in  FIG.  5 B ). The at least one first electromechanical transducer  142  may be any type of electromechanical transducer operable to convert electrical energy to mechanical energy (e.g., a piezoelectric device). In some embodiments, the at least one first electromechanical transducer  142  includes a pair of first electromechanical transducers  142   a,    142   b  such that both the first electromechanical transducers  142   a,    142   b  are switchable between the retained state P 1  and the released state P 2 . 
     The first clamp  120  includes a pair of first clamping members  126   a,    126   b  configured to hold the first loading bar  104  therebetween. In some embodiments, each first electromechanical transducer  142   a,    142   b  is configured to load a corresponding first clamping member  126   a,    126   b  from the pair of first clamping members  126   a,    126   b  to hold the first loading bar  104  therebetween. In other words, the first electromechanical transducer  142   a  is configured to load the first clamping member  126   a  and the first electromechanical transducer  142   b  is configured to load the first clamping member  126   b  to hold the first loading bar  104  between the pair of first clamping members  126   a,    126   b.    
     In some embodiments, the at least one first electromechanical transducer  142  includes at least one first piezoelectric element  144  configured to expand along a first transverse axis B-B′ inclined to the longitudinal axis A-A′ upon application of a first electrical signal S 1 . In some embodiments, the at least one first piezoelectric element  144  includes a pair of first piezoelectric elements  144   a,    144   b.  The pair of first piezoelectric elements  144   a,    144   b  are enclosed within a corresponding first housing  143   a,    143   b.    
     The clamp actuating unit  140  further includes a controller  150  configured to electrically actuate the at least one first electromechanical transducer  142 . In some embodiments, the controller  150  may be embodied in a number of different ways. For example, the controller  150  may be embodied as various processing means, such as one or more of a microprocessor or other processing elements, a coprocessor, or various other computing or processing devices including integrated circuits, such as, for example, an ASIC (application specific integrated circuit), or the like. In some embodiments, the controller  150  may be configured to execute instructions stored in a memory provided with the controller  150  or otherwise accessible to the controller  150 . 
     As such, whether configured by hardware or by a combination of hardware and software, the controller  150  may represent an entity (e.g., physically embodied in circuitry—in the form of processing circuitry) capable of performing operations according to some embodiments while configured accordingly. Thus, for example, when the controller  150  is embodied as an ASIC, FPGA or the like, the controller  150  may have specifically configured hardware for conducting the operations described herein. Alternatively, as another example, when the controller  150  is embodied as an executor of software instructions, the instructions may specifically configure the controller  150  to perform the operations described herein. 
     In some embodiments, the controller  150  is electrically coupled to the at least one first electromechanical transducer  142  (or the at least one first piezoelectric element  144 ). In some embodiments, the controller  150  is configured to provide one or more electrical signals to the at least one first electromechanical transducer  142  (or the at least one first piezoelectric element  144 ). In some examples, the one or more electrical signals may be in the form of a positive voltage applied across the at least one first piezoelectric element  144 . 
     In some embodiments, the controller  150  provides the first electrical signal S 1  to each of the first piezoelectric elements  144   a,    144   b.  Correspondingly, the first piezoelectric elements  144   a,    144   b  may expand along the first transverse axis B-B′. Further, the first electromechanical transducers  142   a,    142   b  (or the first piezoelectric elements  144   a,    144   b ) are configured to expand along the first transverse axis B-B′ to load the corresponding first clamping members  126   a,    126   b  upon application of the first electrical signal S 1  by the controller  150 . In some embodiments, the at least one first piezoelectric element  144  may further be configured to contract along the first transverse axis B-B′ upon removal of the first electrical signal S 1 . 
     In some embodiments, the first transverse axis B-B′ is orthogonal to the longitudinal axis A-A′. In some other embodiments, the first transverse axis B-B′ is inclined at an oblique angle with respect to the longitudinal axis A-A′. 
     In some embodiments, the clamp actuating unit  140  further includes a first actuator  146  configured to apply a first clamping force F 1  on the at least one first electromechanical transducer  142 . In some embodiments, the clamp actuating unit  140  includes a pair of first actuators  146   a,    146   b  configured to apply the first clamping force F 1  on the corresponding first electromechanical transducer  142   a,    142   b.  In other words, the first actuator  146   a  is configured to apply the first clamping force F 1  on the first electromechanical transducer  142   a  and the first actuator  146   b  is configured to apply the first clamping force F 1  on the first electromechanical transducer  142   b.    
     In some embodiments, the first actuators  146   a,    146   b  may include a hydraulic ram configured to receive a hydraulic pressure from a suitable pressure source (not shown) though corresponding inlets  147   a,    147   b.  In some embodiments, the first actuators  146   a,    146   b  may be supported along the first transverse axis B-B′ by a frame  149  of the clamp actuating unit  140  such that the first clamping force F 1  applied by the first actuators  146   a,    146   b  is along the first transverse axis B-B′. 
     In some embodiments, the clamp actuating unit  140  further includes at least one first support member  148  to support the at least one first electromechanical transducer  142  between the first clamp  120  and the first actuator  146 . In some embodiments, the at least one first support member  148  is configured to receive the at least one first electromechanical transducer  142  through the at least one first support member  148 . In some embodiments, the at least one first support member  148  supports the at least one first electromechanical transducer  142  such that the first support member  148  allows the first electromechanical transducer  142  (or the first piezoelectric element  144 ) to expand or contract along the first transverse axis B-B′. 
     In some embodiments, the clamp actuating unit  140  includes a pair of first support members  148   a,    148   b  corresponding to the pair of first electromechanical transducers  142   a,    142   b.  In other words, the first support member  148   a  is configured to receive the first electromechanical transducers  142   a  through the at least one first support member  148   a  and the first support member  148   b  is configured to receive the first electromechanical transducers  142   b  through the at least one first support member  148   b.    
       FIGS.  5 A and  5 B  illustrate schematic side views of the clamp actuating unit  140  and the first clamp  120  in the retained state P 1  and the released state P 2  of the first electromechanical transducer  142 , respectively. Referring now to  FIG.  5 A , in the retained state P 1 , the at least one first electromechanical transducer  142  is configured to load the first clamp  120 , such that the first clamp  120  holds the first loading bar  104  against the first load  114 . Specifically, the first electromechanical transducer  142   a  is configured to load the first clamping member  126   a  and the first electromechanical transducer  142   b  is configured to load the first clamping member  126   b  such that the first clamping members  126   a,    126   b  hold the first loading bar  104  therebetween. 
     In some embodiments, in the retained state P 1 , the at least one first piezoelectric element  144  expands to load the first clamp  120 .  FIG.  5 A  illustrates the at least one first piezoelectric element  144  in an expanded state of the at least one first piezoelectric element  144 . For example, the at least one first piezoelectric element  144  has a length L 1  in the expanded state. Specifically, the first piezoelectric element  144   a  expands along the first transverse axis B-B′ to load the first clamping member  126   a  and the first piezoelectric element  144   b  expands along the first transverse axis B-B′ to load the first clamping member  126   b.  In some embodiments, the controller  150  is further configured to apply the first electrical signal S 1  to the at least one first piezoelectric element  144  to switch the at least one first piezoelectric element  144  to the retained state P 1 . Specifically, each of the first piezoelectric elements  144   a,    144   b  may expand along the first transverse axis B-B′ when the first electrical signal S 1  is applied to the first piezoelectric elements  144   a,    144   b.    
     In some embodiments, in the retained state P 1 , the at least one first electromechanical transducer  142  is configured to at least partially transmit the first clamping force F 1  received from the first actuator  146  to the first clamp  120 . Specifically, the first electromechanical transducer  142   a  is configured to at least partially transmit the first clamping force F 1  received from the first actuator  146   a  to the first clamping member  126   a.  Likewise, the first electromechanical transducer  142   b  is configured to at least partially transmit the first clamping force F 1  received from the first actuator  146   b  to the first clamping member  126   b.  Therefore, the loads applied by the first electromechanical transducers  142   a,    142   b  based on the expansion of the first piezoelectric elements  144   a,    144   b,  and the first clamping force F 1  are configured to hold the first loading bar  104  against the first load  114 . 
     Referring now to  FIG.  5 B , in the released state P 2 , the at least one first electromechanical transducer  142  is configured to release the first clamp  120 . In some embodiments, the controller  150  is configured to electrically actuate the at least one first electromechanical transducer  142  from the retained state P 1  to the released state P 2  to release the first clamp  120 . 
     In some embodiments, in the released state P 2 , the at least one first piezoelectric element  144  contracts to release the first clamp  120 .  FIG.  5 B  illustrates the at least one first piezoelectric element  144  in a contracted state of the at least one first piezoelectric element  144 . For example, the at least one first piezoelectric element  144  has a length L 2  in the contracted state such that the length L 2  is smaller than the length L 1  (i.e., L 2 &lt;L 1 ). Further, the first piezoelectric elements  144   a,    144   b  contract along the first transverse axis B-B′ to release the first clamp  120 . In some embodiments, the controller  150  is further configured to remove the first electrical signal S 1  from the at least one first piezoelectric element  144  to switch the at least one first piezoelectric element  144  to the released state P 2 . In other words, the controller  150  is further configured to remove the first electrical signal S 1  from the first piezoelectric elements  144   a,    144   b  to switch the first piezoelectric elements  144   a,    144   b  to the released state P 2 . Specifically, each of the first piezoelectric elements  144   a,    144   b  may resume initial shape when the first electrical signal S 1  is removed from the first piezoelectric elements  144   a,    144   b.    
     In the illustrated embodiment of  FIG.  5 B , a movement of the first clamping members  126   a,    126   b  and the contraction of the first piezoelectric elements  144   a,    144   b  are shown magnified for the purpose of illustration, and the actual movement of the first clamping members  126   a,    126   b  and the contraction of the first piezoelectric elements  144   a,    144   b  may vary based on actual usage requirements. 
     Additionally, in some embodiments, in the released state P 2 , the at least one first electromechanical transducer  142  is configured to remove the first clamping force F 1  from the first clamp  120 . Specifically, the first electromechanical transducers  142   a,    142   b  are configured to remove the first clamping force F 1  from the first clamping members  126   a,    126   b.  The controller  150  is configured to electrically actuate the at least one first electromechanical transducer  142  from the retained state P 1  to the released state P 2  to release the first clamp  120 , such that the first loading bar  104  applies the first loading wave  122  (shown in  FIG.  3   ) to the test specimen  102 . 
       FIG.  6    illustrates a schematic perspective view of the clamp actuating unit  140  and the second clamp  130 . An outer housing of the clamp actuating unit  140  is omitted in  FIG.  6    for the purpose of illustration. The clamp actuating unit  140  further includes at least one second electromechanical transducer  152  switchable between a retained state Q 1  (shown in  FIG.  7 A ) and a released state Q 2  (shown in  FIG.  7 B ). The at least one second electromechanical transducer  152  may be any type of electromechanical transducer operable to convert electrical energy to mechanical energy (e.g., a piezoelectric device). In some embodiments, the at least one second electromechanical transducer  152  includes a pair of second electromechanical transducers  152   a,    152   b  such that both the second electromechanical transducers  152   a,    152   b  are switchable between the retained state Q 1  and the released state Q 2 . In some embodiments, the at least one second electromechanical transducers  152  may be similar to the at least one first electromechanical transducer  142 . 
     The second clamp  130  includes a pair of second clamping members  162   a,    162   b  configured to hold the second loading bar  106  therebetween. In some embodiments, each second electromechanical transducer  152   a,    152   b  is configured to load a corresponding second clamping member  162   a,    162   b  from the pair of second clamping members  162   a,    162   b  to hold the second loading bar  106  therebetween. In other words, the second electromechanical transducer  152   a  is configured to load the second clamping member  162   a  and the second electromechanical transducer  152   b  is configured to load the second clamping member  162   b  to hold the second loading bar  106  between the pair of second clamping members  162   a,    162   b.    
     In some embodiments, the at least one second electromechanical transducer  152  includes at least one second piezoelectric element  154  configured to expand along a second transverse axis C-C′ inclined to the longitudinal axis A-A′ upon application of a second electrical signal S 2 . In some embodiments, the at least one second piezoelectric element  154  includes a pair of second piezoelectric elements  154   a,    154   b.  The pair of second piezoelectric elements  154   a,    154   b  are enclosed within a corresponding second housing  153   a,    153   b.    
     The clamp actuating unit  140  further includes the controller  150  configured to electrically actuate the at least one second electromechanical transducer  152 . In some embodiments, the controller  150  may provide the second electrical signal S 2  to each of the second piezoelectric elements  154   a,    154   b.  Correspondingly, the second piezoelectric elements  154   a,    154   b  may expand along the second transverse axis C-C′. Further, the second electromechanical transducers  152   a,    152   b  (or the second piezoelectric elements  154   a,    154   b ) are configured to expand along the second transverse axis C-C′ to load the corresponding second clamping members  162   a,    162   b  upon application of the second electrical signal S 2  by the controller  150 . In some embodiments, the at least one second piezoelectric element  154  may further be configured to contract along the second transverse axis C-C′ upon removal of the second electrical signal S 2 . 
     In some embodiments, the second transverse axis C-C′ is orthogonal to the longitudinal axis A-A′. In some other embodiments, the second transverse axis C-C′ is inclined at an oblique angle with respect to the longitudinal axis A-A′. In some embodiments, the second transverse axis C-C′ may be parallel to the first transverse axis B-B′ (shown in  FIG.  4   ). 
     In some embodiments, the clamp actuating unit  140  further includes a second actuator  156  configured to apply a second clamping force F 2  on the at least one second electromechanical transducer  152 . In some embodiments, the clamp actuating unit  140  includes a pair of second actuators  156   a,    156   b  configured to apply the second clamping force F 2  on the corresponding second electromechanical transducers  152   a,    152   b.  In other words, the second actuator  156   a  is configured to apply the second clamping force F 2  on the second electromechanical transducer  152   a  and the second actuator  156   b  is configured to apply the second clamping force F 2  on the second electromechanical transducer  152   b.    
     In some embodiments, the at least one second actuator  156  may include a hydraulic ram configured to receive a hydraulic pressure from a suitable pressure source (not shown) though a corresponding inlet  157   a,    157   b.  In some embodiments, the second actuators  156   a,    156   b  may be supported along the second transverse axis C-C′ by a frame  159  of the clamp actuating unit  140  such that the second clamping force F 2  applied by the second actuators  156   a,    156   b  is along the second transverse axis C-C′. 
     In some embodiments, the clamp actuating unit  140  further includes at least one second support member  158  to support the at least one second electromechanical transducer  152  between the second clamp  130  and the second actuator  156 . In some embodiments, the at least one second support member  158  is configured to receive the at least one second electromechanical transducer  152  through the at least one second support member  158 . In some embodiments, the at least one second support member  158  supports the at least one second electromechanical transducer  152  such that the second support member  158  allows the second electromechanical transducer  152  (or the second piezoelectric element  154 ) to expand or contract along the second transverse axis C-C′. 
     In some embodiments, the clamp actuating unit  140  includes a pair of second support members  158   a,    158   b  corresponding to the pair of second electromechanical transducers  152   a,    152   b.  In other words, the second support members  158   a  is configured to receive the second electromechanical transducer  152   a  through the at least one second support member  158   a  and the second support member  158   b  is configured to receive the second electromechanical transducers  152   b  through the at least one second support member  158   b.    
       FIGS.  7 A and  7 B  illustrate schematic side views of the clamp actuating unit  140  and the second clamp  130  in the retained state Q 1  and the released state Q 2  of the second electromechanical transducer  152 , respectively. Referring now to  FIG.  7 A , in the retained state Q 1 , the at least one second electromechanical transducer  152  is configured to load the second clamp  130 , such that the second clamp  130  holds the second loading bar  106  against the second load  118 . Specifically, the second electromechanical transducer  152   a  is configured to load the second clamping member  162   a  and the second electromechanical transducer  152   b  is configured to load the second clamping member  162   b  such that the second clamping members  162   a,    162   b  hold the second loading bar  106  therebetween. 
     In some embodiments, in the retained state Q 1 , the at least one second piezoelectric element  154  expands to load the second clamp  130 .  FIG.  7 A  illustrates the at least one second piezoelectric element  154  in an expanded state of the at least one second piezoelectric element  154 . For example, the at least one second piezoelectric element  154  has a length M 1  in the expanded state. Specifically, the second piezoelectric element  154   a  expands along the second transverse axis C-C′ to load the second clamping member  162   a  and the second piezoelectric element  154   b  expands along the second transverse axis C-C′ to load the second clamping member  162   b.  In some embodiments, the controller  150  is further configured to apply the second electrical signal S 2  to the at least one second piezoelectric element  154  to switch the at least one second piezoelectric element  154  to the retained state Q 1 . Specifically, each of the second piezoelectric elements  154   a,    154   b  may expand along the second transverse axis C-C′ when the second electrical signal S 2  is applied to the second piezoelectric elements  154   a,    154   b.    
     In some embodiments, in the retained state Q 1 , the at least one second electromechanical transducer  152  is configured to at least partially transmit the second clamping force F 2  received from the second actuator  156  to the second clamp  130 . Specifically, the second electromechanical transducer  152   a  is configured to at least partially transmit the second clamping force F 2  received from the second actuator  156   a  to the second clamping member  162   a.  Likewise, the second electromechanical transducer  152   b  is configured to at least partially transmit the second clamping force F 2  received from the second actuator  156   b  to the second clamping member  162   b.  Therefore, the loads applied by the second electromechanical transducers  152   a,    152   b  based on the expansion of the second piezoelectric elements  154   a,    154   b,  and the second clamping force F 2  are configured to hold the second loading bar  106  against the second load  118 . 
     Referring now to  FIG.  7 B , in the released state Q 2 , the at least one second electromechanical transducer  152  is configured to release the second clamp  130 . In some embodiments, the controller  150  is configured to electrically actuate the at least one second electromechanical transducer  152  from the retained state Q 1  to the released state Q 2  to release the second clamp  130 . 
     In some embodiments, in the released state Q 2 , the at least one second piezoelectric element  154  contracts to release the second clamp  130 .  FIG.  7 B  illustrates the at least one second piezoelectric element  154  in a contracted state of the at least one second piezoelectric element  154 . For example, the at least one second piezoelectric element  154  has a length M 2  in the contracted state such that the length M 2  is smaller than the length M 1  (i.e., M 2 &lt;M 1 ). Further, the second piezoelectric elements  154   a,    154   b  contract along the second transverse axis C-C′ to release the second clamp  130 . In some embodiments, the controller  150  is further configured to remove the second electrical signal S 2  from the at least one second piezoelectric element  154  to switch the at least one second piezoelectric element  154  to the released state Q 2 . In some embodiments, the controller  150  is further configured to remove the second electrical signal S 2  from the second piezoelectric elements  154   a,    154   b  to switch the second piezoelectric elements  154   a,    154   b  to the released state Q 2 . Specifically, each of the second piezoelectric elements  154   a,    154   b  may resume initial shape when the second electrical signal S 2  is removed from the second piezoelectric elements  154   a,    154   b.    
     In the illustrated embodiment of  FIG.  7 B , a movement of the second clamping members  162   a,    162   b  and the contraction of the second piezoelectric elements  152   a,    152   b  are shown magnified for the purpose of illustration, and the actual movement of the second clamping members  162   a,    162   b  and the contraction of the second piezoelectric elements  152   a,    152   b  may vary based on actual usage requirements. 
     Additionally, in some embodiments, in the released state Q 2 , the at least one second electromechanical transducer  152  is configured to remove the second clamping force F 2  from the second clamp  130 . Specifically, the second electromechanical transducers  152   a,    152   b  are configured to remove the second clamping force F 2  from the second clamping members  162   a,    162   b.  The controller  150  is configured to electrically actuate the at least one second electromechanical transducer  152  from the retained state Q 1  to the released state Q 2  to release the second clamp  130 , such that the second loading bar  106  applies the second loading wave  132  (shown in  FIG.  3   ) to the test specimen  102 . 
     Referring now to  FIGS.  1 - 7 B , when measuring loading on the test specimen  102 , the first loading unit  112  is configured to apply the first load  114  (e.g., the static torque  114   a ) on the first loading bar  104 . The first clamp  120  is configured to hold the first loading bar  104  against the first load  114  as the at least one first electromechanical transducer  142  is in the retained state P 1 . In the retained state P 1 , the controller  150  is configured to apply the first electrical signal S 1  to the at least one first piezoelectric element  144  (or the at least one first electromechanical transducer  142 ) such that the at least one first piezoelectric element  144  expands along the first transverse axis B-B′ to load the first clamp  120 , and thus, hold the first loading bar  104 . Further, the at least one first electromechanical transducer  142  is configured to at least partially transmit the first clamping force F 1  received from the first actuator  146  to the first clamp  120 . 
     Likewise, the second loading unit  116  is configured to apply the second load  118  (e.g., the static axial force  118   a ) on the second loading bar  106 . The second clamp  130  is configured to hold the second loading bar  106  against the second load  118  as the at least one second electromechanical transducer  152  is in the retained state Q 1 . In the retained state Q 1 , the controller  150  is configured to apply the second electrical signal S 2  to the at least one second piezoelectric element  154  (or the at least one second electromechanical transducer  152 ) such that the at least one second piezoelectric element  154  expands along the second transverse axis C-C′ to load the second clamp  130 , and thus, hold the second loading bar  106 . In the retained state Q 1 , the at least one second electromechanical transducer  152  is configured to at least partially transmit the second clamping force F 2  received from the second actuator  156  to the second clamp  130 . 
     When the first clamp  120  is to be released, the controller  150  is configured to remove the first electrical signal S 1  from the at least one first piezoelectric element  144  (or the at least one first electromechanical transducer  142 ) to switch the at least one first piezoelectric element  144  to the released state P 2 . Thus, the at least one first piezoelectric element  144  contracts along the first transverse axis B-B′ to release the first clamp  120  such that the first loading bar  104  applies the first loading wave  122  to the test specimen  102 . 
     Likewise, when the second clamp  130  is to be released, the controller  150  is configured to remove the second electrical signal S 2  from the at least one second piezoelectric element  154  (or the at least one second electromechanical transducer  152 ) to switch the at least one second piezoelectric element  154  to the released state Q 2 . Thus, the at least one second piezoelectric element  154  contracts along the second transverse axis C-C′ to release the second clamp  130  such that the second loading bar  106  applies the second loading wave  132  to the test specimen  102 . Loading on the test specimen  102  is initiated by releasing the first and second clamps  120 ,  130  at predetermined times. 
     Use of the at least one first electromechanical transducer  142  and the at least one second electromechanical transducer  152  may allow the clamp actuating unit  140  to precisely and accurately control release times of the first clamp  120  and the second clamp  130 , respectively. This may help in controlling application of the first loading wave  122  and the second loading wave  132  on the test specimen  102  accurately. Further, first clamp  120  and second clamp  130  may be released quickly and reliably as compared to conventional clamps with mechanical fuse. 
     In some alternative embodiments, one of the first clamp  120  and the second clamp  130  may be loaded using a mechanical fuse (instead of electromechanical transducer) while the other may be loaded using the electromechanical transducer. In such embodiments, a release of the clamp loaded with the mechanical fuse may be configured to trigger a release of the clamp loaded with the electromechanical transducer to control the application of corresponding stress waves. 
       FIG.  8    illustrates a flow chart describing a method  170  for measuring loading on the test specimen  102 . The method  170  may be implemented using the system  100  of  FIGS.  1 - 7 B  incorporating the teachings of the present disclosure. 
     At step  172 , the method  170  includes arranging the test specimen  102  between the first loading bar  104  and the second loading bar  106 . The first and second loading bars  104 ,  106  are arranged along the longitudinal axis A-A′. At step  174 , the method  170  further includes holding, via the first clamp  120 , the first loading bar  104  against the first load  114 . Upon release of the first clamp  120 , the first loading bar  104  is configured to apply the first loading wave  122  to the test specimen  102  in response to the first load  114 . At step  176 , the method  170  further includes electrically actuating, via the controller  150 , the at least one first electromechanical transducer  142  to the retained state P 1 . In the retained state P 1 , the at least one first electromechanical transducer  142  loads the first clamp  120 , such that the first clamp  120  holds the first loading bar  104 . 
     In some embodiments, electrically actuating the at least one first electromechanical transducer  142  to the retained state P 1  further includes applying the first electrical signal S 1  to the at least one first electromechanical transducer  142 , such that the at least one first electromechanical transducer  142  expands along the first transverse axis B-B′ inclined to the longitudinal axis A-A′ to load the first clamp  120 . 
     In some embodiments, the method  170  further includes applying, via the first actuator  146 , the first clamping force F 1  on the at least one first electromechanical transducer  142 . In the retained state P 1 , the at least one first electromechanical transducer  142  is configured to at least partially transmit the first clamping force F 1  received from the first actuator  146  to the first clamp  120 . 
     At step  178 , the method  170  further includes applying, via the first loading unit  112 , the first load  114  to the first loading bar  104 . 
     At step  180 , the method  170  further includes holding, via the second clamp  130 , the second loading bar  106  against the second load  118 . Upon release of the second clamp  130 , the second loading bar  106  is configured to apply the second loading wave  132  to the test specimen  102  in response to the second load  118 . 
     In some embodiments, the method  170  further includes electrically actuating, via the controller  150 , the at least one second electromechanical transducer  152  to the retained state Q 1 . In the retained state Q 1 , the at least one second electromechanical transducer  152  loads the second clamp  130 , such that the second clamp  130  holds the second loading bar  106 . In some embodiments, electrically actuating the at least one second electromechanical transducer  152  to the retained state Q 1  further includes applying the second electrical signal S 2  to the at least one second electromechanical transducer  152 , such that the at least one second electromechanical transducer  152  expands along the second transverse axis C-C′ inclined to the longitudinal axis A-A′ to load the second clamp  130 . 
     In some embodiments, the method  170  further includes applying, via the second actuator  156 , the second clamping force F 2  on the at least one second electromechanical transducer  152 . In the retained state Q 1 , the at least one second electromechanical transducer  152  is configured to at least partially transmit the second clamping force F 2  received from the second actuator  156  to the second clamp  130 . 
     At step  182 , the method  170  further includes applying, via the second loading unit  116 , the second load  118  to the second loading bar  106 . 
     At step  184 , the method  170  further includes electrically actuating, via the controller  150 , the at least one first electromechanical transducer  142  from the retained state P 1  to the released state P 2 . In the released state P 2 , the at least one first electromechanical transducer  142  releases the first clamp  120 , such that the first loading bar  104  applies the first loading wave  122  to the test specimen  102 . In some embodiments, electrically actuating the at least one first electromechanical transducer  142  from the retained state P 1  to the released state P 2  further includes removing the first electrical signal S 1  from the at least one first electromechanical transducer  142 , such that the at least one first electromechanical transducer  142  contracts along the first transverse axis B-B′ to release the first clamp  120 . 
     In some embodiments, the method  170  further includes electrically actuating, via the controller  150 , the at least one second electromechanical transducer  152  from the retained state Q 1  to the released state Q 2 . In the released state Q 2 , the at least one second electromechanical transducer  152  releases the second clamp  130 , such that the second loading bar  106  applies the second loading wave  132  to the test specimen  102 . In some embodiments, electrically actuating the at least one second electromechanical transducer  152  from the retained state Q 1  to the released state Q 2  further includes removing the second electrical signal S 2  from the at least one second electromechanical transducer  152 , such that the at least one second electromechanical transducer  152  contracts along the second transverse axis C-C′ to release the second clamp  130 . 
     In some embodiments, the method  170  further includes simultaneously or timely sequentially releasing the first clamp  120  and the second clamp  130 . 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.