Extensometer structure with spaced flexures
The extensometer structure with spaced deflection arms and strain gauge sensors addresses the challenge of measuring strain in test samples by allowing vertical movement and limiting lateral stress, achieving precise strain measurement under varying loads and high temperatures.
Patent Information
- Application Number
- JP2024104743
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-06-28
- Filing Date
- 2024-06-28
- Publication Date
- 2025-01-20
AI Technical Summary
Existing extensometers face challenges in accurately measuring strain in test samples, particularly at high temperatures and under varying loads, due to limitations in contact probe movement and sensitivity.
The extensometer structure features a flexure assembly with spaced deflection arms and elongate rods or knife-edge blades, allowing vertical movement of contact probes, coupled with strain gauge sensors to measure strain accurately, and includes overtravel stops to limit movement and prevent lateral twisting.
This design enables precise measurement of strain in test samples under tensile, compression, and high-temperature conditions, enhancing accuracy and durability while minimizing mechanical stress.
Smart Images
Figure 2025010028000001_ABST
Abstract
Description
[Background technology]
[0001] background The following discussion is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
[0002] Extensometers are commonly used to measure strain in a test sample. Many forms of extensometers have been developed in the art. One type of extensometer is a contact extensometer, which contacts a test sample under load to determine properties of the sample. Strain is sensed by contact probes that engage the sample at contact points and extend to a sensor system support by a flexure assembly. The flexure assembly allows the probes to move relative to each other to measure strain in the test sample. Summary of the Invention
[0003] overview This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0004] The extensometer structure includes a flexure assembly having a support mount, a first contact device mount rigidly secured to the support mount, and a second contact device mount coupled to the support mount by an upper flexure arm and a lower flexure arm. The upper flexure arm is spaced apart from and positioned directly above and in alignment with the lower flexure arm. The second contact device mount is configured to move vertically relative to the first contact device mount.
[0005] The extensometer structure can include a first contact probe having a contact surface and fastened to a first contact device mount, and a second contact probe having a contact surface and fastened to a second contact device mount, the second contact probe configured to move vertically in a manner substantially parallel to the first contact probe.
[0006] The first and second contact probes may include a first elongated rod and a second elongated rod, the first elongated rod mounted to the first contact device mount and extending from the contact surface along the underside of the first contact device mount and the underside of the support mount and terminating at a proximal end, and the second elongated rod mounted to the second contact device mount and extending from the contact surface between the upper and lower flexible arms, through a slot in the second contact device mount, through a slot in the support mount, to the proximal end.
[0007] The first and second contact probes may include a first knife-edge blade and a second knife-edge blade, the first knife-edge blade being attached to the front end and underside of the first contact device mount by a blade mount and the second knife-edge blade being clamped into a slot recessed into the front side of the second contact device mount.
[0008] The flexure assembly may further comprise at least one over-travel stop. The at least one over-travel stop may include a first over-travel stop having a first flange mounted to the first contact device mount and having a free end that moves within a first groove recessed in the second contact device mount, and a second over-travel stop having a second flange mounted to the first contact device mount and having a free end that moves within a second groove recessed in the second contact device mount. The first and second over-travel stops provide limited travel of the second contact device mount relative to the first contact device mount.
[0009] The upper flexure arm can include a first flexure strap, a second flexure strap, and a rigid interconnect coupling the first flexure strap to the second flexure strap, and the lower flexure arm can include a first flexure strap, a second flexure strap, and a rigid interconnect coupling the first flexure strap to the second flexure strap.
[0010] The extensometer structure may include one or more sensors (one or more) configured to sense movement of the second contact device mount relative to the first contact device mount. For example, the one or more sensors may include four strain gauge sensors, with a first strain gauge sensor and a second strain gauge sensor positioned on the upper flexure arm and a third strain gauge sensor and a fourth strain gauge sensor positioned on the lower flexure arm. In another embodiment, the one or more sensors may include eight strain gauge sensors, with a first strain gauge sensor, a second strain gauge sensor, a third strain gauge sensor and a fourth strain gauge sensor positioned on the upper and lower surfaces of the upper flexure arm and a fifth strain gauge sensor, a sixth strain gauge sensor, a seventh strain gauge sensor and an eighth strain gauge sensor positioned on the upper and lower surfaces of the lower flexure arm.
[0011] The extensometer structure includes a first contact probe having a contact surface, a second contact probe having a contact surface and movably connected to the first contact probe, and a flexure assembly. The flexure assembly includes a support mount and a first contact device mount rigidly secured to the support mount and configured to support the first contact probe. The first contact probe is mounted to the first contact device mount. A second contact device mount is coupled to the support mount by an upper flexure arm and a lower flexure arm. The second contact probe is mounted to the second contact device mount. The second contact device mount is configured to move vertically relative to the first contact device mount, and the second contact probe is configured to move vertically relative to the first contact probe.
[0012] The first and second contact probes may include a first and second elongated rod, the first elongated rod mounted to the first contact device mount and extending from a contact surface of the first elongated rod along an underside of the first contact device mount and an underside of the support mount and terminating at a proximal end, and the second elongated rod mounted to the second contact device mount and extending from a contact surface of the second elongated rod between the upper and lower flexure arms through a slot in the second contact device mount, through a slot in the support mount, and to the proximal end. The flexure assembly may further include at least one over-travel stop. Additionally, the upper flexure arm may be spaced apart from and aligned with the lower flexure arm.
[0013] The upper flexure arm can include a first flexure strap, a second flexure strap, and an interconnect connecting the first flexure strap to the second flexure strap, and the lower flexure arm can include a first flexure strap, a second flexure strap, and an interconnect connecting the first flexure strap to the second flexure strap.
[0014] The one or more sensors can be configured to sense movement of the second contact device mount relative to the first contact device mount, the one or more sensors being positioned on the upper and lower flexure arms. The one or more sensors can be positioned on the upper and lower flexure arms.
[0015] The extensometer assembly comprises an extensometer structure having a first elongated rod extending from the contact surface to a proximal end, a second elongated rod extending from the contact surface to a proximal end, and a flexure assembly having at least one flexure arm. The flexure assembly comprises a support mount, a first contact device mount rigidly secured to the support mount, and a second contact device mount coupled to the support mount by at least one flexure arm. The first elongated rod is mounted to the first contact device mount and the second elongated rod is mounted to the second contact device mount. The extensometer assembly further comprises a hold-down system coupled to the proximal ends of the first elongated rod and the second elongated rod to provide a lifting force and a contact force.
[0016] The at least one flexure arm may include an upper flexure arm and a lower flexure arm, the upper flexure arm being spaced apart from and aligned with the lower flexure arm.
[0017] The first elongated rod can extend from a contact surface of the first elongated rod, along the underside of the first contact device mount and the underside of the support mount, terminating at a proximal end of the first elongated rod, and the second elongated rod can extend from a contact surface of the second elongated rod, between the upper and lower flexible arms, through a slot in the second contact device mount, through a slot in the support mount, to the proximal end of the second elongated rod.
[0018] The one or more sensors may be configured to sense movement of the second contact device mount relative to the first contact device mount, the one or more sensors being positioned on the upper and lower flexure arms. The one or more sensors may be positioned on the upper and lower flexure arms. [Brief description of the drawings]
[0019] [Figure 1] FIG. 1 is a front perspective view of an extensometer according to an embodiment.
[0020] [Diagram 2] FIG. 2 is a rear perspective view of the extensometer shown in FIG. 1.
[0021] [Diagram 3] FIG. 3 is a top front perspective view of the extensometer structure of the extensometer shown in FIGS. 1 and 2.
[0022] [Figure 4] FIG. 4 is a top rear perspective view of FIG. 3.
[0023] [Diagram 5] FIG. 4 is a bottom rear perspective view of FIG.
[0024] [Figure 6] FIG. 4 is a front view of FIG.
[0025] [Figure 7] FIG. 7 is a top front perspective cross-sectional view taken through the section line indicated in FIG. 6.
[0026] [Figure 8] 4 is a top front perspective view of a sensing assembly configured for use in the extensometer shown in FIGS. 1 and 2 and including the extensometer structure shown in FIG. 3, according to an embodiment.
[0027] [Figure 9]FIG. 9 is a bottom perspective view of a portion of the sensing assembly shown in FIG. 8.
[0028] [Figure 10] FIG. 10 is a schematic diagram of a portion of the sensing assembly shown in FIG.
[0029] [Figure 11] FIG. 11 is a schematic diagram of a sensing circuit corresponding to the sensing assembly shown in FIG.
[0030] [Figure 12] 4 is a top front perspective view of a sensing assembly configured for use in the extensometer shown in FIGS. 1 and 2 and including the extensometer structure shown in FIG. 3, according to another embodiment. FIG.
[0031] [Figure 13] FIG. 13 is a bottom perspective view of a portion of the sensing assembly shown in FIG.
[0032] [Figure 14] FIG. 13 is a schematic diagram of the sensing assembly of FIG. 12.
[0033] [Figure 15] FIG. 15 is a schematic diagram of a sensing circuit corresponding to the sensing assembly shown in FIG. 14.
[0034] [Figure 16] FIG. 4 is a top rear perspective view of the extensometer structure of FIG. 3 and the rear assembly of the extensometer shown in FIGS. 1 and 2, according to an embodiment.
[0035] [Figure 17] FIG. 17 is a top side perspective view of FIG. 16.
[0036] [Figure 18] FIG. 18 is a top front perspective view of the extensometer structure and hold-down system of the extensometer shown in FIGS. 16 and 17.
[0037] [Figure 19] FIG. 19 is a rear view of FIG. 18.
[0038] [Figure 20] FIG. 19 is a cross-sectional view taken through the section line indicated in FIG. 18.
[0039] [Figure 21] FIG. 13 is a top perspective view of an extensometer structure of an extensometer according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS A contact extensometer measures deformation of a sample specimen by placing contact probes, such as, but not limited to, the ends of elongated ceramic rods or knife-edge blades, directly on the specimen and coupling the contact probes to a flexure assembly to allow at least one of the contact probes to move in response to compression or elongation of the test specimen. FIG. 1 is a front perspective view of a contact extensometer assembly 100 according to an embodiment. FIG. 2 is a rear perspective view of the contact extensometer assembly 100. The extensometer assembly 100 is an embodiment of an exemplary high temperature extensometer assembly configured to measure axial strain in tension, compression, and zero fatigue testing applications at high temperatures, such as, but not limited to, 2200 degrees Fahrenheit. The contact extensometer assembly 100 has an exemplary first contact probe or elongated rod 102 and a second contact probe or elongated rod 104, made, for example, of ceramic, that sense strain by engaging the specimen at contact points or surfaces located at the distal ends 106 and 108 of the rods 102 and 104, respectively. The rods 102 and 104 extend to a rear assembly 110 that is remotely located and shielded from high temperatures by a shield 112. The rear assembly 110 provides contact force for the sample as well as lifting support for the rods 102 and 104.
[0041] The extensometer assembly 100 includes an extensometer structure 114, which in one embodiment has a first lower elongated rod 102, a second upper elongated rod 104, and a flexure assembly 116. As used herein, "extensometer structure" is defined as at least some of the interconnected mechanical components and does not include sensing devices for measuring movement of the components of the extensometer structure. Rather, various types of sensing devices, as are known, may be used with the extensometer structures disclosed herein to form an operable extensometer that provides an output signal indicative of a displacement, such as an elongation, of a test sample.
[0042] As previously mentioned, the extensometer structure 114 is supported by the rear assembly 110, which includes a hold-down system 120 configured to exert a contact force on the sample through the extensometer structure 114 and provide a lifting force to the extensometer structure 114. As shown in FIG. 2, the hold-down system 120 includes a support bridge 122 coupled to a lower flexible bridge 124 and an upper flexible bridge 126. The lower flexible bridge 124 is coupled to a proximal end of the first elongated rod 102 (not shown in FIGS. 1 and 2), and the upper flexible bridge 126 is coupled to a proximal end of the second elongated rod 104 (not shown in FIGS. 1 and 2). In this embodiment, the extensometer structure 114 provides a contact force to the test sample through the rods 102 and 104. The rear assembly 110 is discussed in more detail below.
[0043] Figure 3 is a top front perspective view of the extensometer structure 114 shown in Figures 1 and 2. Figure 4 is a top rear perspective view of Figure 3, Figure 5 is a bottom rear perspective view of Figure 3, and Figure 6 is a front view of Figure 3. Figure 7 is a top front perspective cross-sectional view taken through the section line shown in Figure 6. The flexure assembly 116 feature of the extensometer structure 114 acts as a compliant spring and allows the second elongated rod 104 to move vertically in a substantially parallel manner relative to the first elongated rod 102 while in contact with the sample.
[0044] The flexure assembly 116 includes a first contact device mount 128 that extends from the front to the rear of the flexure assembly 116 at a support mount 136, and a second contact device mount 130 that is coupled to the support mount 136 with an upper flexure arm 160 and a lower flexure arm 162. The second contact device mount 130 moves vertically relative to the first contact device mount 128 due to flexure of the flexure arms 160, 162. As shown in FIG. 5, the rear of the first contact device mount 128 may be rigidly secured to the support mount 136, for example by matching fasteners such as mechanical fasteners 138 and 139, adhesives, welding, etc., or may be formed with the flexure assembly 116 from a single, integral piece.
[0045] If desired, over-travel stops may be provided to limit the range of movement of the second contact device mount 130 relative to the first contact device mount 128. Typically, the over-travel stops allow the second contact device mount 130 to move freely, with movement limited by contacting surfaces that prevent further movement. In the illustrated embodiment, the over-travel stops include a pair of first and second over-travel stops 132, 134. The over-travel stops 132 and 134 are secured to the front of the first contact device mount 128 and to opposing sides of the first contact device mount 128, respectively, and include first and second flanges 140, 142. As illustrated, the over-travel stops 132 and 134 may be rigidly secured to the sides of the first contact device mount by mechanical fasteners 133 and 135.
[0046] The second contact device mount 130 is configured to move vertically relative to the first contact device mount 128 and the rear support mount 136 and includes a pair of first and second grooves 144 and 146 recessed into the second contact device mount 130. The grooves 144 and 146 are configured to receive the free ends of the first and second flanges 140 and 142. The first groove 144 is located on a first side of the mount 130, and the free end of the first flange 140 moves within the first groove 144. The second groove 146 is located on a second, opposing side of the mount 130, and the free end of the second flange 142 moves within the second groove 146. In this manner, the grooves 144 and 146 define the distance the second contact device mount 130 can move relative to the first contact device mount 128, thereby accommodating tensile and compressive movement margins on either side of the second contact device mount 130. Figure 6 best illustrates this relative distance by showing the separation distance between the tops of the flanges 140 and 142 and the tops of the grooves 144 and 146, as well as the separation distance between the bottoms of the flanges 140 and 142 and the bottoms of the grooves 144 and 146. In other words, the over-travel stops 132 and 134, in combination with the grooves 144 and 146, respectively, provide limited movement of the second contact device mount 130 relative to the first contact device mount 128. In addition, the over-travel stops 132 and 134 limit lateral movement of the second contact device mount 130 relative to the first contact device mount 128, and thus limit lateral movement of the flexible arms 160 and 162, for example, due to lateral movement and / or twisting of the first elongated rod 102 and the second elongated rod 104.
[0047] The first elongated rod 102 and the second elongated rod 104 are coupled to a flexure assembly 116. As shown, the first elongated rod 102 is stationary and extends from the contact device end 106 to a proximal end 148. The second elongated rod 104 is configured to move or be displaced upwardly and downwardly in a substantially parallel manner relative to the stationary first elongated rod 102 and extends from the contact device end 108 to a proximal end 150. The first elongated rod 102 is made stationary by being rigidly secured to the underside of the first contact device mount 128 along a channel 129 recessed into a portion of the bottom surface of the first contact device mount 128. At the front of the first contact device mount 128, a rod support block 152, which includes its own channel for holding the rod 102, is used to hold the first elongated rod 102 in the channel 129 of the first contact device mount 128. For example, as shown, the rod support block 152 may rigidly secure the first elongated rod 102 to the first contact device mount 128 using mechanical fasteners 153 and 154.
[0048] The second elongated rod 104 extends through a slot 131 in the second contact device mount 130 and through a slot 137 in the support mount 136. The second elongated rod 104 is movable within the slot 137 of the support mount 136, while the second elongated rod 104 is fixed in the slot 131 of the movable second contact device mount 130. In the illustrated embodiment, a V-block 156 and a set screw 158 (shown in FIGS. 5, 6 and 7) provide a holding or clamping force against the second elongated rod 104. In this manner, the second elongated rod 104 is configured to move vertically with the second contact device mount 130 in a manner substantially parallel to the first elongated rod 102, which is rigidly attached to the first contact device mount 128.
[0049] The flexure assembly 116 further includes an upper flexure arm 160 and a lower flexure arm 162, although it is possible for the flexure assembly 116 to include a single flexure arm. As shown, the second contact device mount 130 is coupled to the support mount 136 by an upper flexure arm 160 and a lower flexure arm 162. The flexure arms 160 and 162 are spaced apart from each other and aligned with each other, with the upper flexure arm 160 located directly above the lower flexure arm 162. In the illustrated embodiment, a longitudinal axis 160A along the centerline of the upper flexure arm 160 is substantially aligned with a longitudinal axis 162A along the centerline of the lower flexure arm 162. Preferably, the longitudinal axes 160A and 162A are also substantially aligned with the longitudinal axes of the rods 102 and 104. Both the upper flexure arm 160 and the lower flexure arm 162 are coupled at a front end to the second contact device mount 130 and at a rear end to the support mount 136. Additionally, the upper flexure arm 160 is located above the second elongated rod 104 and the lower flexure arm 162 is located below the second elongated rod 104. In one embodiment, the second contact device mount 130, the rear support mount 136, the upper flexure arm 160 and the lower flexure arm 162 may all be integral, i.e., formed as a single, unitary piece.
[0050] The upper flexure arm 160 and the lower flexure arm 162 allow the second elongated rod 104 to move in response to compression or extension of the test sample, as well as to handle moments caused by contact or shear forces at the contact surfaces 106 and 108 of the rods 102 and 104. The upper flexure arm 160 includes a first flexure strap 164, a second flexure strap 166, and a rigid interconnect 168 connecting the first flexure strap 164 to the second flexure strap 166. The lower flexure arm 162 includes a first flexure strap 170, a second flexure strap 172, and a rigid interconnect 174 connecting the first flexure strap 170 to the second flexure strap 172. 1-7 show the upper flexure arm 160 and the lower flexure arm 162 as having two flexure straps connected by a rigid interconnect, other variations are possible including a single flexure strap or three or more flexure straps with interconnects. One purpose of the length of each of the upper flexure arm 160 and the lower flexure arm 162 is to position the rear assembly 110 as far away from the shield 112 as possible by extending the length of the flexure assembly 116 and the length of the rods 102 and 104. In this way, ease of assembly for the operator is achieved. Additionally, the flexure assembly 116 includes thin flexure straps 164, 166, 170 and 172, which makes the assembly as light as possible by eliminating excess joints that are held together using heavy mechanical fasteners.
[0051] In some embodiments, one or more strain sensor gauges, not shown in FIGS. 1-7, are provided on the flexible arms 160 and 162 to sense movement of the second elongated rod 104 relative to the first elongated rod 102 or the second contact device mount 130 relative to the first contact device mount 128. In other embodiments, other forms of sensors sense movement of the rod 104 relative to the rod 102. For example, sensors based on changes in capacitance, inductance or resistance may be used. Similarly, optically based sensors may be used if desired. Such sensing devices are well known. The aspects disclosed herein are not dependent on the type of sensor or sensing device used, although strain sensor gauges are described.
[0052] Figure 8 is a top front perspective view of a sensing assembly 180 configured for use in the extensometer assembly 100, and therefore in the extensometer structure 114, according to an embodiment. Figure 9 is a bottom perspective view of a portion of the sensing assembly 180, and Figure 10 is a schematic diagram of the portion of the sensing assembly 180 shown in Figure 9. In the embodiment shown in Figures 8-10, four strain sensor gauges are used to sense the displacement of the second contact device mount 130, and therefore the displacement of the second elongated rod 104. In particular, a first strain sensor gauge 181 (FIG. 10) is applied to the bottom or outward facing surface of the second flexure strap 172 of the lower flexure arm 162 to measure the strain thereof, a second strain sensor gauge 182 is applied to the bottom or inward facing surface of the second flexure strap 166 of the upper flexure arm 160 to measure the strain thereof, a third strain sensor gauge 183 is applied to the top or inward facing surface of the second flexure strap 172 of the lower flexure arm 162 to measure the strain thereof, and a fourth strain sensor gauge 184 is applied to the top or outward facing surface of the second flexure strap 166 of the upper flexure arm 160 to measure the strain thereof.
[0053] 11 is a schematic diagram of a sensing circuit 185 corresponding to the sensing assembly 180. The sensing circuit 185 is a Wheatstone bridge circuit. As shown, the Wheatstone bridge circuit has two excitation voltage terminals and two output or signal terminals. As shown, strain sensor gauges 181 and 182, which typically sense tensile strain, face each other, and strain sensor gauges 183 and 184, which typically sense compressive strain, face each other.
[0054] Figure 12 is a top front perspective view of a sensing assembly 186 configured for use in the extensometer assembly 100, and therefore for use in the extensometer structure 114, according to an embodiment. Figure 13 is a bottom perspective view of a portion of the sensing assembly 186, and Figure 14 is a schematic diagram of the portion of the sensing assembly 186 shown in Figure 14. In the embodiment shown in Figures 12-14, eight strain sensor gauges are used to sense the displacement of the second contact device mount 130, and therefore the displacement of the second elongated rod 104. In particular, a first strain sensor gauge 181 (FIG. 14) is applied to the bottom or outward facing surface of the second flexure strap 172 of the lower flexure arm 162 to measure the strain thereof, a second strain sensor gauge 182 is applied to the bottom or inward facing surface of the second flexure strap 166 of the upper flexure arm 160 to measure the strain thereof, a third strain sensor gauge 183 is applied to the top or inward facing surface of the second flexure strap 172 of the lower flexure arm 162 to measure the strain thereof, and a fourth strain sensor gauge 184 is applied to the top or outward facing surface of the second flexure strap 166 of the upper flexure arm 160 to measure the strain thereof. In addition, a fifth strain sensor gauge 187 is applied to the top or outward facing surface of the first flexure strap 164 of the upper flexure arm 160 to measure the strain thereon, a sixth strain sensor gauge 188 is applied to the top or inward facing surface of the first flexure strap 170 of the lower flexure arm 162 to measure the strain thereon, a seventh strain sensor gauge 189 is applied to the bottom or inward facing surface of the first flexure strap 164 of the upper flexure arm 160 to measure the strain thereon, and an eighth strain sensor gauge 190 (FIG. 14) is applied to the bottom or outward facing surface of the first flexure strap 170 of the lower flexure arm 162 to measure the strain thereon.
[0055] 15 is a schematic diagram of a sensing circuit 191 corresponding to the sensing assembly 185. The sensing circuit 191 is a Wheatstone bridge circuit. As shown, the Wheatstone bridge circuit has two excitation voltage terminals and two output or signal terminals. As shown, the strain sensor gauges 181 and 182, which typically sense strain tension on the second flexure straps 172 and 166, face each other, the strain sensor gauges 183 and 184, which typically sense strain compression on the second flexure straps 172 and 166, face each other, while the strain sensor gauges 187 and 188, which typically sense strain tension on the first flexure straps 170 and 164, face each other, and the strain sensor gauges 189 and 190, which typically sense strain compression on the first flexure straps 170 and 164, face each other. It should be appreciated that other embodiments of the strain sensor gauges are possible. For example, two strain sensor gauges 181 and 187, which typically measure tension strain on the outward facing surfaces of flexure straps 172 and 164, may be used in opposing circuits, and two strain sensor gauges 184 and 190, which typically measure compression strain on the outward facing surfaces of flexure straps 166 and 170, may be used in opposing circuits. In another example, two strain sensor gauges 182 and 188, which typically measure tension strain on the inward facing surfaces of flexure straps 166 and 170, may be used in opposing circuits, and two strain sensor gauges 183 and 189, which typically measure compression strain on the inward surfaces of flexure straps 172 and 164, may be used in opposing circuits.
[0056] FIG 16 is a top rear perspective view of the extensometer structure 114 and rear assembly 110 of the extensometer assembly 100, and FIG 17 is a top side perspective view of FIG 16. As discussed above, the extensometer structure 114 is supported by the rear assembly 110, and the hold-down system 120 is configured to exert a contact force on the sample through the extensometer structure 114 and provide a lifting force to the extensometer structure 114. As shown in FIG 16 and FIG 17, the hold-down system 120 includes a support bridge 122 that provides support to a lower flexible bridge 124 and an upper flexible bridge 126. The lower flexible bridge 124 is coupled to the support bridge 122 by a lower bridge mount 121, and the upper flexible bridge 126 is coupled to the support bridge 122 by an upper bridge mount 123. Opposite ends of lower flexible bridge 124 and upper flexible bridge 126 are coupled to one of the proximal ends of first elongated rod 102 and second elongated rod 104. In particular, lower flexible bridge 124 is coupled to first elongated rod 102 through a first proximal end mount 125, and upper flexible bridge 126 is coupled to second elongated rod 104 through a second proximal end mount 127.
[0057] FIG 18 is a top front perspective view of a portion of the extensometer structure 114 and hold-down system 120 of the extensometer assembly 100 shown in FIG 16 and FIG 17. FIG 19 is a rear view of FIG 18, and FIG 20 is a cross-sectional view taken through the section line shown in FIG 19. Each of the first proximal end mount 125 and the second proximal end mount 127 includes a dimple or socket 141 and 143, respectively, configured to receive a proximal end of one of the elongated rods 102 and 104. As shown in FIG 20, the dimple 141 of the first proximal end mount 125 is configured to receive the proximal end 148 of the first elongated rod 102, and the dimple 143 of the second proximal end mount 127 is configured to receive the proximal end 150 of the second elongated rod 104. The first and second proximal mounts 125, 127 are assembled such that each dimple 141 and 143 provides lifting and contact forces to the extensometer structure 114 via the first and second elongated rods 102, 104, but allows the first and second elongated rods 103, 104 to move within the dimples or sockets 141 and 143. For example, the dimples or sockets 141 and 143 may include 120 degree angle openings and the proximal ends 148 and 150 may provide 90 degree ends. In this manner, contact of the 90 degree ends with the surfaces of the respective sockets 141 and 143 is minimal, but still provides the necessary lifting support and contact forces while allowing for any slight misalignment.
[0058] 21 is a top front perspective view of an extensometer structure 214 including a flexure assembly 216 of a contact extensometer assembly 200 according to another embodiment. Instead of the extensometer structure 214 having a first elongated rod and a second elongated rod, the contact extensometer 200 has an exemplary first knife edge blade 202 and a second knife edge blade 204 that senses strain on the sample by engaging the sample at contact points or surfaces located at the distal ends 206 and 208 of the knife edge blades 202 and 204. The flexure assembly 216 feature of the extensometer structure 214 acts as a compliant spring and allows the second knife edge blade 204 to move vertically in a parallel manner relative to the first knife edge blade 202 while contacting the sample. The extensometer structure 214 is typically supported by the test sample using clips and bands such as those shown in US Pat. No. 5,600,895, so that the hold-down system 120 is not required.
[0059] The flexure assembly 216 includes a first contact device mount 228 that extends from the front to the rear of the flexure assembly 216 at a support mount 236, and a second contact device mount 230 is coupled to the support mount 236 using an upper flexure arm 260 and a lower flexure arm 262. The second contact device mount 230 moves vertically relative to the first contact device mount 228 as the flexure arms 260, 262 flex. The rear of the first contact device mount 128 may be rigidly secured to the support mount 136, for example, by fasteners (not shown in FIG. 21 but similar to fasteners 138 and 139 in FIG. 5), adhesive, welding, etc., or may be formed with the flexure assembly 216 from a single, integral piece.
[0060] If desired, over-travel stops may be provided to limit the range of movement of the second contact device mount 230 relative to the first contact device mount 228. Typically, the over-travel stops allow the second contact device mount 230 to move freely, with movement limited by contacting surfaces that prevent further movement. In the illustrated embodiment, the over-travel stops include a pair of first and second over-travel stops 232 and 234. The over-travel stops 232 and 234 are secured to the front of the first contact device mount 128 and to opposing sides of the first contact device mount 228, respectively, and include a first flange 240 and a second flange 142. As illustrated, the over-travel stops 232 and 234 may be rigidly secured to the sides of the first contact device mount by mechanical fasteners (one fastener 233 is shown in FIG. 21 ).
[0061] Additionally, the over-travel stops 232 and 234 limit lateral movement of the second contact device mount 230 relative to the first contact device mount 128, and thus limit lateral movement of the flexible arms 260 and 262, for example, due to lateral movement and / or twisting of the first knife edge blade 202 and the second knife edge blade 204.
[0062] The first knife edge blade 202 and the second knife edge blade 204 are coupled to the flexure assembly 216. As shown, the first knife edge blade 202 is stationary and extends from the contact device end 206 to a proximal end (not shown). The second knife edge blade 204 is configured to move or be displaced upward and downward in a substantially parallel manner relative to the stationary first knife edge blade 202 and extends from the contact device end 208 to a proximal end (not shown). The first knife edge blade 202 is held stationary by being secured to the underside of the first contact device mount 228 by a blade support block 252. For example, the blade support block 252 may secure the first knife edge blade 202 to the first contact device mount 228 using a mechanical fastener.
[0063] The second knife edge blade 204 extends into a slot 231 in the second contact device mount 230 and is held down by a mechanical fastener that functions as a clamp. The second knife edge blade 204 is therefore fixed in the slot 231 of the movable second contact device mount 230. In this manner, the second knife edge blade 204 is configured to move vertically with the second contact device mount 230 in a manner substantially parallel to the first knife edge blade 102 that is rigidly attached to the first contact device mount 228.
[0064] The flexure assembly 216 further includes an upper flexure arm 260 and a lower flexure arm 262, although it is possible for the flexure assembly 216 to include a single flexure arm. As shown, the second contact device mount 230 is coupled to the support mount 236 by flexure arms 260 and 262 that are spaced apart from and aligned with one another, with the upper flexure arm 260 located directly above the lower flexure arm 262. Both the upper flexure arm 260 and the lower flexure arm 262 are coupled at a front end to the second contact device mount 230 and at a rear end to the rear support mount 236. The upper flexure arm 260 is spaced apart from the lower flexure arm 262 and is positioned or located above and aligned with the lower flexure arm 262. In the illustrated embodiment, the longitudinal axis 260A along the centerline of the upper flexure arm 260 is substantially aligned with the longitudinal axis 262A along the centerline of the lower flexure arm 262. Preferably, the longitudinal axes 260A and 262A are also substantially aligned with the centerlines of the knife edge blades 202 and 204. In one embodiment, the second contact device mount 230, the rear support mount 236, the upper flexure arm 260 and the lower flexure arm 262 may all be made of the same unitary material.
[0065] The upper flexure arm 260 and the lower flexure arm 262 allow the second knife edge blade 204 to move in response to compression or extension of the test sample, as well as to handle moments caused by contact or shear forces at the contact surfaces 206 and 208 of the knife edge blades 202 and 204. The upper flexure arm 260 includes a first flexure strap 264, a second flexure strap 266, and a rigid interconnect 268 connecting the first flexure strap 264 to the second flexure strap 266. The lower flexure arm 262 includes a first flexure strap 270, a second flexure strap 272, and a rigid interconnect 274 connecting the first flexure strap 270 to the second flexure strap 272. 21 shows the upper flexure arm 260 and the lower flexure arm 262 as having two flexure straps connected together by a rigid interconnect, other variations are possible, including a single flexure strap, or three or more flexure straps with interconnects. One purpose of the length of each of the upper flexure arm 260 and the lower flexure arm 262 is to position the rear assembly, which provides both the contact and lifting forces to the extensometer structure 214, far enough away from the contact surfaces 206 and 208. In this way, ease of assembly for the operator is achieved. Additionally, the flexure assembly 216 includes thin flexure straps 264, 266, 270 and 272, which makes the assembly as lightweight as possible by eliminating excess joints that are held together using heavy mechanical fasteners.
[0066] In some embodiments, one or more strain sensor gauges are provided on the flexure arms 260 and 262, not shown in FIG. 21, to sense the movement of the second knife edge blade 204 relative to the first knife edge blade 102 or the movement of the second contact device mount 230 relative to the first contact device mount 228. Such configurations of strain sensor gauges are discussed above and shown in FIGS. 8-15. In other embodiments, other forms of sensors sense the movement of the blade 104 relative to the blade 102. For example, sensors based on changes in capacitance, inductance or resistance may be used. Similarly, optically based sensors may be used if desired. Such sensing devices are well known. The aspects disclosed herein are not dependent on the type of sensor or sensing device used, but in embodiments in which strain sensor gauges are used, the positioning of those strain sensor gauges and the corresponding sensing circuitry used is important.
[0067] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.
Claims
1. 1. An extensometer structure comprising:
1. A flexure assembly comprising: A support mount; a first contact device mount rigidly secured to the support mount; a second contact device mount coupled to the support mount by an upper flexure arm and a lower flexure arm, the upper flexure arm being spaced apart from the lower flexure arm and positioned directly above and in alignment with the lower flexure arm; Equipped with the second contact device mount is configured to move vertically relative to the first contact device mount; Flexure Assembly, The extensometer structure comprises:
2. 2. The extensometer structure of claim 1, further comprising a first contact probe having a contact surface and fastened to the first contact device mount, and a second contact probe having a contact surface and fastened to the second contact device mount, the second contact probe configured to move vertically in a manner substantially parallel to the first contact probe.
3. 3. The extensometer structure of claim 2, wherein the first and second contact probes include a first elongated rod and a second elongated rod, the first elongated rod mounted to the first contact device mount and extending from a contact surface along an underside of the first contact device mount and an underside of the support mount and terminating at a proximal end, and the second elongated rod mounted to the second contact device mount and extending from a contact surface between the upper and lower flexure arms through a slot in the second contact device mount, through a slot in the support mount, to a proximal end.
4. 3. The extensometer structure of claim 2, wherein the first and second contact probes include a first knife edge blade and a second knife edge blade, the first knife edge blade being attached to a front end and underside of a first contact device mount by a blade mount, and the second knife edge blade being clamped in a slot recessed from a front side of the second contact device mount.
5. The extensometer structure of claim 1 , wherein the flexure assembly further comprises at least one over-travel stop.
6. 6. The extensometer structure of claim 5, wherein the at least one over-travel stop includes a first over-travel stop mounted to the first contact device mount, the first over-travel stop having a first flange, the first flange having a free end that moves within a first groove recessed in the second contact device mount, and a second over-travel stop mounted to the first contact device mount, the second flange having a free end that moves within a second groove recessed in the second contact device mount, the first over-travel stop and the second over-travel stop providing limited travel of the second contact device mount relative to the first contact device mount.
7. 7. The extensometer structure of claim 1, wherein the upper flexure arm comprises a first flexure strap, a second flexure strap, and a rigid interconnect coupling the first flexure strap to the second flexure strap, and the lower flexure arm comprises a first flexure strap, a second flexure strap, and a rigid interconnect coupling the first flexure strap to the second flexure strap.
8. 8. The extensometer structure of claim 1, further comprising one or more sensors configured to sense movement of a second contact device mount relative to the first contact device mount, wherein in a first embodiment the one or more sensors include four strain gauge sensors, a first and a second strain gauge sensor positioned on the upper flexure arm and a third and a fourth strain gauge sensor positioned on the lower flexure arm, and in a second embodiment the one or more sensors include eight strain gauge sensors, a first, a second, a third and a fourth strain gauge sensor positioned on an upper and lower surface of the upper flexure arm and a fifth, a sixth, a seventh and an eighth strain gauge sensor positioned on an upper and lower surface of the lower flexure arm.
9. 1. An extensometer structure comprising: a first contact probe having a contact surface; a second contact probe having a contact surface and movably connected to the first contact probe; 1. A flexure assembly comprising: A support mount; a first contact device mount rigidly secured to the support mount and configured to support the first contact probe, the first contact probe being attached to the first contact device mount; a second contact device mount coupled to the support mount by an upper flexure arm and a lower flexure arm, the second contact probe being attached to the second contact device mount; Equipped with the second contact device mount is configured to move vertically relative to the first contact device mount, and the second contact probe is configured to move vertically relative to the first contact probe. a flexure assembly; The extensometer structure comprises:
10. 10. The extensometer structure of claim 9, wherein the first and second contact probes include a first and second elongated rod, the first elongated rod mounted to the first contact device mount and extending from the contact surface of the first elongated rod along an underside of the first contact device mount and an underside of the support mount and terminating at a proximal end, and the second elongated rod mounted to the second contact device mount and extending from the contact surface of the second elongated rod between the upper and lower flexure arms through a slot in the second contact device mount, through a slot in the support mount, to a proximal end.
11. 11. The extensometer structure of claim 9 or 10, wherein the flexure assembly further comprises at least one over-travel stop.
12. 12. The extensometer structure of claim 9, wherein the upper flexure arm is spaced apart from the lower flexure arm and positioned directly above and in alignment with the lower flexure arm, and in one embodiment the upper flexure arm comprises a first flexure strap, a second flexure strap, and an interconnect coupling the first flexure strap to the second flexure strap, and the lower flexure arm comprises a first flexure strap, a second flexure strap, and an interconnect coupling the first flexure strap to the second flexure strap.
13. 1. An extensometer assembly comprising:
1. An extensometer structure comprising: a first elongated rod extending from the contact surface to a proximal end; a second elongated rod extending from the contact surface to a proximal end; and a flexure assembly having at least one flexure arm, the flexure assembly including: a support mount; a first contact device mount rigidly secured to the support mount; and a second contact device mount coupled to the support mount by the at least one flexure arm, the first elongated rod being attached to the first contact device mount and the second elongated rod being attached to the second contact device mount; an extensometer structure comprising: a hold-down system coupled to the proximal end of the first elongated rod and the proximal end of the second elongated rod to provide lifting and contact forces of the first elongated rod and the second elongated rod to a test sample; 1. An extensometer assembly comprising:
14. 14. The extensometer assembly of claim 13, wherein the at least one flexure arm includes an upper flexure arm and a lower flexure arm, the upper flexure arm being spaced apart from and aligned with the lower flexure arm.
15. 15. The extensometer assembly of claim 14, wherein the first elongated rod extends from the contact surface of the first elongated rod along an underside of a first contact device mount and an underside of the support mount and terminates at the proximal end of the first elongated rod, and the second elongated rod extends from the contact surface of the second elongated rod between the upper and lower flexure arms, through a slot in the second contact device mount, through a slot in the support mount, to the proximal end of the second elongated rod.