A clamping surface and its use in stress testing fixtures and medical locking structures and testing methods

Abstract

The application discloses a clamping surface used for cooperating with another opposite clamping surface to clamp a clamped piece, wherein the clamping surface is provided with a clamping structure, the clamping structure comprises a plurality of clamping units, and the plurality of clamping units are arranged on the clamping surface according to a preset rule; the surface of the clamping structure in contact with the clamped piece is a smooth surface; when the clamping surface and the opposite clamping surface clamp the clamped piece, the clamped piece is continuously deformed along the undulating profile of the clamping structure. The application can significantly reduce stress concentration at the clamping position and improve anti-slippage stability on the premise that the surface integrity of the clamped piece is not damaged, thereby reducing clamping fracture and improving the reliability and repeatability of testing and locking.

Description

Technical Field

[0001] This invention relates to the field of clamping and locking structure technology, and more particularly to a clamping surface for clamping slender parts and its application in stress and strain testing fixtures and medical locking structures, and to a method for testing the stress and strain of shape memory alloys based on the clamping surface. Background Technology

[0002] Slender, sheet-like, or small-scale components (such as wires, rods, sheets, strips, and their combinations) often require reliable clamping, locking, or positioning in industrial testing, precision assembly, and medical device applications. Functional materials, such as shape memory alloys (e.g., nickel-titanium alloys), are widely used in material performance evaluation and medical device structural components due to their superelasticity, shape memory effect, corrosion resistance, and good biocompatibility. Whether it's clamping and fixing the ends of specimens during stress-strain mechanical testing, connecting and fixing medical components in medical locking structures, or in other assembly and use processes requiring "clamping / locking / limiting / positioning / connection," a common interface is involved: the force and contact between the clamping surface (or locking contact surface) and the clamped component. The design of this interface directly determines the anti-slip capability, stress concentration level, surface damage risk, and long-term reliability and repeatability.

[0003] In the prior art, common clamping / locking methods include: achieving frictional locking by increasing the normal clamping force; setting knurling, teeth, serrations, sharp edges or hard particles on the contact surface to improve the coefficient of friction; or forming a clamping effect by local compression (such as screw end face compression, wedge compression, chuck clamping, etc.).

[0004] Existing clamping / locking interfaces generally suffer from the dilemma of balancing "reliable fixation" and "low damage": On the one hand, to prevent slippage and loosening of components under tension, torsion, vibration, or cyclic loading, large clamping forces are often required, or rough / sharp contact surfaces such as knurling or toothing are used. This approach easily leads to point / line contact and edge effects, causing local stress concentration, indentation, and microcrack initiation, which in turn leads to early failure, reduced fatigue life, and drift in positioning / measurement accuracy. At the same time, this type of solution is quite sensitive to component size and surface condition, assembly torque / clamping force, and process consistency, resulting in insufficient adaptability and repeatability.

[0005] Therefore, there is an urgent need for a clamping / locking contact surface structure that can provide reliable anti-slip capability without relying on sharp and rough engagement, and can achieve distributed contact and reduce stress concentration through a more reasonable geometric contact method. This would make it suitable for various application scenarios, including mechanical testing fixtures and medical locking structures, thereby improving the stability, reliability and repeatability of clamping / locking. Summary of the Invention

[0006] This invention aims to provide a clamping surface and its application and testing method. By achieving geometric engagement and dispersed contact through a smooth, undulating peak-valley structure, it addresses the stress concentration, slippage, and premature fracture problems caused by traditional "point contact / sharp tooth engagement," thereby improving the reliability of material testing and the stability of medical locking.

[0007] The present invention provides a clamping surface for cooperating with another opposing clamping surface to clamp a clamped part. The clamping surface is provided with a clamping structure, which includes a plurality of clamping units arranged on the clamping surface according to a preset rule. The surface of the clamping structure that contacts the clamped part is a smooth surface. When the clamping surface clamps the clamped part with the opposing clamping surface, the clamped part undergoes continuous deformation along the undulating contour of the clamping structure.

[0008] Furthermore, the clamping unit includes peaks and valleys spaced apart; when the opposing clamping surfaces approach each other, the peaks contact the clamped part first.

[0009] Furthermore, the edges of the clamping surface are chamfered.

[0010] Furthermore, the clamping structures on the first clamping surface and the second clamping surface used to clamp the clamped parts have the same dimensions and structure.

[0011] Furthermore, when the first clamping surface and the second clamping surface, which are used to clamp the clamped part together, clamp the clamped part, the peaks of the first clamping surface and the peaks of the second clamping surface are staggered.

[0012] Furthermore, when the first clamping surface and the second clamping surface, which are used to clamp the clamped part together, clamp the clamped part, the peak of the first clamping surface corresponds to the valley of the second clamping surface.

[0013] Furthermore, the peaks and valleys connect end to end, forming a smooth, wavy surface.

[0014] Furthermore, the clamping unit has a circular arc cross-section, and multiple clamping units with circular arc cross-sections are arranged at intervals to form a clamping structure.

[0015] Furthermore, the cross-sectional shape of the clamping unit is a triangular wave with rounded corners or a sawtooth wave with rounded corners, and multiple clamping units with cross-sectional shapes are arranged at intervals to form a clamping structure.

[0016] Furthermore, the clamping unit has a trapezoidal cross-sectional shape with rounded corners, and multiple clamping units with the same cross-sectional shape are arranged at intervals to form a clamping structure.

[0017] Furthermore, the extension direction of the clamping unit is parallel to the horizontal direction.

[0018] Furthermore, the extension direction of the clamping unit is inclined relative to the horizontal direction, and the range of the inclination angle is greater than 0° and less than or equal to 70°.

[0019] Furthermore, the distance between the point where the clamping structure first contacts the surface of the clamped part and the point where the clamping structure is furthest from the first contact point is defined as the nodal depth; the total nodal depth formed by the first clamping surface and the second clamping surface used to clamp the clamped part is d, and the ratio of the total nodal depth d to the width Dt of the narrowest part of the clamped part is in the range of 3%≤d / Dt≤30%.

[0020] Furthermore, the equivalent radius of the surface that first contacts the clamped part in the clamping structure is defined as Re; the ratio of the equivalent radius Re to the width Dt of the narrowest part of the clamped part is 0.1≤Re / Dt≤2.

[0021] Furthermore, the interval between adjacent clamping units is defined as p; the ratio of the interval p to the width Dt of the narrowest part of the clamped part is 0.2≤p / Dt≤5.

[0022] Furthermore, the clamping surface is configured to be disposed on the locking contact surface of the clamping block of the stress-strain testing fixture or the medical locking structure for clamping and locking the clamped part.

[0023] Furthermore, a method for testing the stress and strain of shape memory alloys, using the clamping surface of any one of claims 1 to 10, is characterized by comprising the following steps: S1: placing the clamped part in the clamping area of ​​the clamping surface, so that the clamped part spans multiple clamping units; S2: applying a lateral constraint force to the clamped part, so that the clamped part is locked axially; S3: while maintaining the locked state, applying an axial load to the clamped part, and collecting the mechanical response data of the clamped part.

[0024] Furthermore, in step S2, applying a lateral constraint force to the clamped part includes driving the first clamping surface and the second clamping surface to move closer to each other, so that the peak of the clamping unit on one side of the clamping surface is embedded in the valley of the clamping unit on the other side of the clamping surface, thereby causing the clamped part to undergo continuous bending deformation along the undulating contour formed by the clamping unit.

[0025] Furthermore, before step S3, a preloading step is included: applying a preset initial load to the clamped part until the monitored load value reaches a preset threshold to eliminate the initial relaxation of the clamped part in the clamping area, and marking this state as the zero point of strain measurement.

[0026] Furthermore, in step S3, the axial load applied to the clamped part adopts a displacement control mode, which specifically includes: driving the tensioning device to move at a constant strain rate, the strain rate being configured to maintain quasi-static conditions during the test process to minimize temperature fluctuations caused by the latent heat of phase transformation of the shape memory alloy; real-time monitoring of the stress-strain response of the clamped part, and when a stress plateau characteristic is detected, identifying the plateau as phase transformation stress.

[0027] Furthermore, the loading process in step S3 includes a loading-unloading cycle, specifically including: loading stage: stretching the clamped part to the target strain exceeding its austenitic-martensite phase transformation endpoint; unloading stage: releasing the load in the opposite direction at the same strain rate until the stress returns to zero; collecting the mechanical response data of the clamped part includes recording the complete hyperelastic hysteresis loop, and calculating the dissipated energy and residual strain based on the hysteresis loop.

[0028] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0029] The smooth, undulating complementary / interlocking structure transforms the traditional V-type or knurled clamping "point contact / sharp tooth engagement" mode into a "surface contact + geometric bending" shape-locking mechanism. Utilizing the winch effect, the lateral clamping force is converted into cumulative frictional resistance distributed along the axial direction. This improves anti-slip capability while eliminating stress singularities at the contact interface, reducing the risk of shearing and peeling of the oxide / plating layer on the wire surface, preventing the induction of phase transformation nucleation sites in the clamping area, and inhibiting premature nucleation of the phase transformation front in the clamping area. This ensures that the stress-strain curve reflects the true phase transformation plateau characteristics of the material, reducing gripping fractures and improving the integrity and accuracy of test data. In medical locking structures, higher anti-slip capability can be achieved at lower locking forces / torques, and the risk of sudden local indentation and early fatigue failure can be reduced. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the clamping engagement between the clamping surface and the clamped part according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of a clamping surface structure with a limiting plane according to an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram of a clamping surface structure with peaks and valleys according to an embodiment of the present invention.

[0033] Figure 4 This is a schematic diagram of a clamping surface structure with different relative positions of the valley to the limiting plane according to an embodiment of the present invention.

[0034] Figure 5 This is a schematic diagram of the complementary meshing of peaks and valleys on two opposing clamping surfaces according to an embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram of the clamping engagement of a clamping structure provided on one side according to an embodiment of the present invention.

[0036] Figure 7 This is a schematic diagram of a clamping fit with asymmetrical clamping structure parameters on both sides according to an embodiment of the present invention.

[0037] Figure 8 This is a schematic diagram of the clamping structure of the present invention, which has a wavy, smooth curved surface in cross section.

[0038] Figure 9 This is a schematic diagram of the clamping structure of the present invention, which has a cross-section of side-by-side circular arc-shaped undulating surfaces.

[0039] Figure 10 This is a schematic diagram of the clamping structure of the present invention, which has a triangular wave cross-section with rounded corners.

[0040] Figure 11 This is a schematic diagram of the clamping structure of the present invention, which has a sawtooth wave cross-section with rounded corners.

[0041] Figure 12 This is a schematic diagram of the clamping structure of the present invention, which has a trapezoidal cross section (with chamfered / rounded corner transition).

[0042] Figure 13 This is a schematic diagram showing the clamping units of the present invention arranged along the axial direction of the clamped part.

[0043] Figure 14 This is a schematic diagram showing the clamping units of the present invention arranged at an axial angle relative to the clamped part.

[0044] Figure 15 This is a schematic diagram illustrating the definition of key dimensional parameters of the clamping structure of the present invention.

[0045] Explanation of reference numerals in the attached figures:

[0046] 1. First clamping block (corresponding to the first clamping surface); 2. Second clamping block (corresponding to the second clamping surface); 3. Clamped part; 4. Clamping unit; 41. Peak; 42. Valley. Detailed Implementation

[0047] To make the objectives, features, and advantages of this invention more apparent and understandable, specific embodiments of the invention are described in detail below with reference to the accompanying drawings. The following embodiments are used to explain the principles of this invention; those skilled in the art can make modifications or substitutions without departing from the concept of this invention, and all such modifications or substitutions should fall within the protection scope of this invention.

[0048] The clamping surface provided by this invention can be used for clamping, locking, and mechanical testing of slender components such as shape memory alloy wires, and is particularly suitable for precision mechanical property testing and constitutive behavior characterization of hyperelastic materials such as nickel-titanium alloys. Simultaneously, the clamping surface of this invention can also serve as the contact clamping surface for medical locking structures, used for locking and preventing slippage of medical components such as connecting rods, steel wires / cables, and sutures.

[0049] In one embodiment of the present invention, a stress-strain testing fixture is provided, comprising a first clamping block 1 and a second clamping block 2 disposed opposite to each other. Both the first clamping block 1 and the second clamping block 2 have opposing clamping surfaces (which can be understood as two opposing clamping surfaces) for clamping a clamped component 3 (e.g., medical-grade nickel-titanium alloy wire or titanium alloy connecting rod). Under the action of an external force, the pair of clamping blocks move closer together until they abut, thereby clamping the clamped component 3.

[0050] A clamping structure is provided on the clamping surface. The clamping structure includes several clamping units 4, which are arranged on the clamping surface according to a preset rule. The clamping structure is used to clamp the clamped part 3, and the cross-section of the part of the clamping structure that first contacts the clamped part is set as a smooth curved surface to avoid local cutting and stress concentration caused by sharp teeth / edges.

[0051] As an optional implementation, such as Figure 1 As shown, both the first clamping block 1 and the second clamping block 2, which are arranged opposite to each other, are equipped with clamping structures. The clamping structures are composed of protruding clamping units 4, and the two adjacent clamping units transition smoothly to form an arc-shaped cross-section. The clamping units 4 can cover the clamping surfaces of the first clamping block 1 and the second clamping block 2, that is, any part of the clamping surface is a clamping unit or a part of a clamping unit. For the clamping structures located at the edge of the clamping surface, the edge portion is also smoothly designed to avoid damage to the clamped part 3 caused by sharp clamping edges.

[0052] exist Figure 1 In the fixture shown, the dimensions, shape, and arrangement of the clamping structures on the surfaces of the first and second clamping blocks can be set to be completely identical. This symmetrical and consistent setting ensures that the stress-strain test of the clamped part is not affected by the asymmetrical clamping blocks, avoiding measurement errors caused by the installation position of the clamped part or the setting position of the clamping blocks.

[0053] As another alternative implementation, such as Figure 2As shown, the ends of the first and second clamping blocks include limiting planes. Taking the first clamping block as an example, both ends of its clamping surface are planes; alternatively, only one end may be a plane. A clamping unit 4 is provided on the clamping surface of the first clamping block. The clamping unit protrudes from the limiting planes at both ends and is used to form a "biting / fitting" with the clamped part. When the clamping blocks clamp the clamped part, the protruding clamping unit contacts the clamped part and causes deformation of the part of the clamped part's surface corresponding to the clamping unit; the limiting plane abuts against the surface of the clamped part, thereby limiting the deformation depth of the clamped part's surface and preventing premature failure of the clamped part during tensile and other stress-strain tests due to excessive deformation.

[0054] Alternatively, to avoid excessive clamping deformation at the same length of the clamped part, the clamping units on the first clamping block and the second clamping block can be staggered, that is, the protruding structures corresponding to the first and second clamping blocks are staggered. This staggered arrangement further prevents the clamped part from deforming too deeply and improves clamping stability.

[0055] As another alternative implementation, such as Figure 3 As shown, in addition to the protruding end (peak) protruding from the end limiting plane, the clamping unit also includes a smooth arc-shaped connecting part disposed between the two protruding ends; the smooth arc-shaped connecting part forms a valley and is recessed into the reference plane where the end limiting plane is located. Overall, the clamping units on the clamping surface present an alternating arrangement of peaks and valleys.

[0056] By setting recessed valleys between the protruding peaks, the local stress caused by the protruding peaks during clamping deformation can be effectively accommodated and buffered, making the deformation of the clamped part surface tend to "bending and extending" rather than "local indentation", thereby avoiding local damage caused by stress concentration and improving the accuracy and reliability of stress-strain testing.

[0057] As another alternative implementation, such as Figure 4 As shown, the clamping unit includes a protruding arc surface, and the two clamping units form a smooth transition through the arc surface. Figure 4 and Figure 3 The difference is: Figure 4 The lowest point of the valley is higher than the end limiting plane. By setting the relative position between the limiting plane and the bottom of the valley of the clamping structure, the engagement depth of the clamping structure with the clamped part can be increased, further improving the clamping stability.

[0058] As another alternative implementation, such as Figure 5As shown, the clamping block structure may not have a limiting plane. In this embodiment, since there is no limiting plane, the maximum engagement depth that the clamping structure can generate on the surface of the clamped part is the peak-valley height difference. The peaks and valleys of the clamping structures of the first and second clamping blocks are staggered, specifically, the peak of the first clamping block corresponds to the valley of the second clamping block, forming a complementary meshing relationship. Through complementary meshing, excessive deformation at the same length position of the clamped part can be avoided to the greatest extent, thus preventing fracture failure; at the same time, complementary meshing generates a strong geometric interlocking effect, which allows for higher axial anti-slip capability under a smaller clamping force.

[0059] In another alternative approach, the peaks and valleys of the two clamping structures are staggered, so that the peak of one clamping structure corresponds to the transition area between the valley and peak of the other clamping structure, and the valley also corresponds to the transition area on the opposite side, thus forming an interlocking meshing relationship. During clamping, the peak partially enters the valley on the opposite side and forms dispersed, multi-segment continuous contact over multiple undulation cycles. The interlocking meshing transforms the contact from a single aligned meshing to a multi-point, multi-segment distributed contact, which helps to distribute the clamping pressure over a larger contact area, further reducing local peak contact stress and indentation depth. At the same time, the interlocking meshing makes the deformation path of the clamped part surface more tortuous, and the sliding must overcome the superposition of frictional resistance and geometric resistance, thereby improving clamping stability and providing better adaptability to assembly deviations, clamped part diameter tolerances, or changes in clamping stroke.

[0060] As another alternative implementation, such as Figure 6 As shown, only the first clamping block has a clamping structure, while the second clamping block is flat or has a certain degree of roughness. In this configuration, the first clamping block can still generate a biting / engaging force on the clamped part, preventing displacement of the clamped part during the test. This configuration is suitable for applications where the clamping force requirement is relatively low.

[0061] Alternatively, the clamping structures of the first and second clamping blocks may differ in any aspect, such as size or shape, i.e., asymmetric parameter settings may be used. For example... Figure 7 As shown, the equivalent size of the peak of the first clamping block on the left is smaller than that of the peak of the second clamping block on the right. When the force applied to the clamped part is not along the axial direction of the clamped part, but at a certain angle to the axial direction, the stress on the surfaces of the clamped part opposite to the first and second clamping blocks is different. This asymmetrical arrangement can better adapt to non-axial force application situations and improve clamping stability and testing reliability.

[0062] The cross-sectional shape of the clamping structure can be set as a smooth curved surface that changes periodically along the undulating direction. The clamping structure is composed of multiple adjacent protruding and recessed units alternating, so that the clamped part, in addition to obtaining frictional force, also forms a geometric fit under the constraint of the undulating contour during clamping, thereby suppressing relative slippage of the clamped part under axial load or vibration. The cross-sectional contour of the clamping structure preferably adopts a smooth transition structure without sharp edges, so as to improve the anti-slip capability while reducing the risk of scratches, cutting, or stress concentration on the surface of the clamped part, thereby improving clamping stability and repeatability.

[0063] As an optional implementation method, such as Figure 8 As shown, the clamping structure has a wavy, undulating cross-section that rises and falls continuously along the undulation direction. The peak 41 and the valley 42 are connected by a continuous curvature transition section. This structure allows the contact between the clamping structure and the surface of the clamped workpiece during clamping to gradually expand from a localized area to a band-like contact (accompanied by the elastic deformation of the clamped workpiece). The contact pressure distribution is more gradual, which helps to reduce local stress concentration and reduce indentation abrupt changes. At the same time, the wavy undulation creates multiple continuous "bypassing" force paths on the surface of the clamped workpiece between the two clamping surfaces. Slippage requires crossing the geometric obstacles of multiple undulating units, so a good anti-slip effect can still be obtained without relying on simply increasing the clamping force.

[0064] When the two opposing clamping structures mesh, they can form complementary interlocking or staggered overlap: when the peak corresponds to the valley on the opposite side, the complementary interlocking of the peak and valley makes the geometric limit clearer and further improves the anti-slip capability; when the peak corresponds to the transition area on the opposite side, the staggered overlap makes the contact more dispersed and uniform, which is conducive to improving the adaptability to clamping deviation and reducing local peak contact stress.

[0065] As another alternative implementation method, such as Figure 9 As shown, the clamping structure has a cross-section of parallel circular arc-shaped undulating surfaces, composed of multiple parallel circular arc protrusions and grooves. The connection method between the arc units is not limited; it can be a smooth curved surface connection or a planar connection, etc. This structure maintains the geometric constraint function of the undulating contour while increasing the effective contact length and making the contact stress distribution more gentle, thus balancing anti-slip and surface protection. The repeated distribution of the parallel circular arc units also ensures good uniformity and repeatability of the clamping action at different clamping positions.

[0066] When the two opposing clamping structures mesh, the arc protrusion and the opposite arc groove can form a mutually supportive contact, thereby generating a certain self-centering tendency and enhancing geometric fit; when the arc protrusion and the lateral transition area of ​​the opposite arc unit form an interlocking overlap, the contact is distributed along multiple arc units, which helps to reduce local peak pressure and improve the tolerance to misalignment.

[0067] In another implementation, such as Figure 10As shown, the clamping structure has a triangular wave undulating surface with rounded corners. The undulating profile consists of rising and falling segments, forming a wedge-shaped slope between them. The peak 41 has a rounded chamfer, and the valley 42 can also have rounded corners to eliminate sharp edges. In this structure, the slope can provide a strong geometric blocking component when the clamped part tends to slip axially, so that the anti-slip capability comes more from the shape fitting than simple friction. The rounded corner transition between the peak and the valley changes the contact from sharp corner contact to smooth contact, reducing the risk of edge cutting and scratching, and reducing surface damage caused by stress concentration.

[0068] When the two opposing clamping surfaces mesh, the complementary engagement of the peaks and valleys allows the rounded peaks to enter the opposite rounded valleys and form a continuous or semi-continuous contact zone on the slope, thereby enhancing the limiting and anti-slipping capabilities. When the peaks and the opposite slopes or transition areas form staggered contact, the contact is more uniformly dispersed, thus improving clamping adaptability and reducing local overload while maintaining a high anti-slipping capability.

[0069] In another implementation, such as Figure 11 The clamping structure has a sawtooth-wave undulating surface with rounded corners. The undulating profile is asymmetrical along the undulation direction, including a steeper blocking slope on one side and a gentler guiding slope on the other. Rounded corners are provided at the tooth tips and roots to achieve a smooth transition. This structure can form a directional geometric limiting effect: when the clamped part tends to slip along the predetermined direction, the steeper blocking slope provides a stronger locking and anti-slip effect; the gentler guiding slope facilitates gradual contact and guiding positioning during clamping, reduces clamping impact and minimizes instantaneous damage to the surface of the clamped part; the rounded corner structure further suppresses scratches and tears caused by sharp tooth cutting, improving clamping repeatability. When the two opposing clamping surfaces mesh, the relative orientation of the saw teeth can achieve strong geometric resistance in both opposite directions, realizing bidirectional anti-slip; the unidirectional orientation of the saw teeth can form a stronger locking in the expected loading direction and a relatively easy disengagement in the opposite direction, thus taking into account both loading stability and ease of unclamping; the tooth tip and tooth root can form a complementary engagement to enhance geometric locking, or they can form an interlocking joint to disperse contact and reduce local stress peaks.

[0070] By selecting smooth, undulating shapes such as wavy, parallel arc, triangular wave with rounded corners, or sawtooth wave with rounded corners, the clamping structure can combine friction clamping with shape fitting without introducing sharp edge damage. This improves the anti-slip capability, clamping stability, and consistency of repeated clamping of the clamped part, while reducing the risk of damage to the surface of the clamped part.

[0071] This geometric continuity eliminates stress singularities at the contact interface. When the nickel-titanium alloy clamped parts deform and come into contact under clamping force, the smooth surface ensures that the contact pressure changes in a continuous gradient along the wave profile, rather than a step-like abrupt change. This "soft landing" contact mechanism makes it less likely for the oxide layer or coating on the wire surface to peel off due to local micro-shearing, and also avoids nucleation sites on the wire surface that would induce martensitic phase transformation due to hard contact. This ensures that the measured phase transformation behavior originates from tensile load rather than surface defects introduced by the clamp.

[0072] Furthermore, nickel-titanium alloys are extremely sensitive to stress states. During tensile testing, once the local stress reaches a critical value, the material undergoes an austenitic-to-martensite phase transformation accompanied by lattice shear deformation. Traditional hard-contact fixtures tend to generate stress concentration at the clamping edges, causing the stress at these points to exceed the critical stress for phase transformation first. This results in the transformation front nucleating from inside the fixture rather than at the gauge length. The smooth curved surface design of this invention reduces the stress level in the clamping area through a flexible transition, keeping it below the stress at the gauge length. This ensures that the SIM phase transformation is strictly limited to the gauge length range, avoiding uncontrollable phase transformations inside the fixture. Consequently, the test curve accurately reflects the material's phase transformation plateau characteristics rather than being a fixture artifact.

[0073] In other embodiments, such as Figure 12 As shown, the cross-sectional outline of the clamping structure can be a smooth curve or a trapezoid. The trapezoid includes a top surface and a bottom surface that are opposite each other, as well as a side surface that connects the top surface and the bottom surface. The top surface is used to contact the clamped part and provide support.

[0074] Optionally, a non-rounded transition is used between the top and side surfaces of the trapezoid, and between the side surface and the bottom surface: the top surface and the side surface intersect to form a first zigzag edge, and the side surface and the bottom surface intersect to form a second zigzag edge. By replacing the pointed structure of the traditional pointed clamping part with a top surface structure of a certain width, the effective contact area can be increased, the contact pressure per unit area can be reduced, and the risk of indentation, scratches, or cutting can be reduced; at the same time, the side surface provides a geometric limiting function to improve clamping stability and anti-slip capability while protecting the wire.

[0075] Alternatively, such as Figure 12 As shown, chamfered or rounded transitions are provided between the top and side surfaces, and between the side and bottom surfaces, to reduce the sharpness of the folded edges, further reduce local stress concentration, and improve the smoothness and fault tolerance of the clamping process.

[0076] In some embodiments, the clamp includes a first clamping block and a second clamping block disposed opposite to each other. The first clamping block has a first clamping surface, and the second clamping block has a second clamping surface opposite to the first clamping surface. The first clamping surface and the second clamping surface cooperate to clamp the wire. To balance clamping stability and protection of the wire surface, in some embodiments, the clamping structure cross-sectional shapes of the first clamping surface and the second clamping surface are set to be different, so that the two clamping surfaces form different contact patterns and cooperate with each other during the clamping process, thereby suppressing relative slippage or minor displacement of the wire and reducing local stress concentration.

[0077] In some embodiments, the clamping structure of the first clamping surface can be configured as a wavy, undulating surface. This provides a more continuous supporting contact and disperses contact pressure, thereby achieving a gentler clamping and reducing the probability of indentations or scratches on the wire surface. The clamping structure of the second clamping surface can be configured as a circular bump array surface. This circular bump array surface forms point-like limiting contacts through multiple discrete bumps, thereby enhancing the wire's anti-slip capability. The combination of these two different surface properties ensures both stability and protection of the wire surface during clamping.

[0078] In other embodiments, the clamping structure of the first clamping surface can be configured as a wavy undulating surface, and the clamping structure of the second clamping surface can be configured as a fine tooth or sawtooth textured surface; wherein, the wavy undulating surface is used to disperse clamping pressure and reduce local stress concentration, and the fine tooth or sawtooth textured surface is used to provide stronger geometric limiting effect to suppress axial slippage or creep of the wire in the clamping state, thereby improving clamping reliability.

[0079] In other embodiments, the clamping structure of the first clamping surface can be configured as a planar or slightly roughened surface, and the clamping structure of the second clamping surface can be configured as a circular convex dot array surface; the planar or slightly roughened surface is used to provide relatively uniform and gentle basic contact, and the circular convex dot array surface is used to provide point-like limiting and anti-slip function, thereby improving anti-slip performance while reducing the risk of surface damage.

[0080] In other embodiments, the clamping structure of the first clamping surface can be set as a planar or slightly rough surface, and the clamping structure of the second clamping surface can be set as a wavy undulating surface; when the surface properties of the two sides are inconsistent, the effective contact area can be increased and the force distribution can be improved while maintaining the clamping gentleness, thereby improving the clamping stability and reducing the local damage to the wire caused by the clamping effect.

[0081] In other embodiments, the clamping structure of the first clamping surface can be configured as a grooved surface, and the clamping structure of the second clamping surface can be configured as a circular bump array surface or a fine textured surface; the grooved surface is used to guide the wire and suppress lateral movement or deviation, and the circular bump array surface or fine textured surface is used to provide limiting and anti-slip function. The cooperation of both sides can simultaneously improve the centering stability and anti-displacement capability.

[0082] It should be understood that the above are only some example combinations of clamping structures with inconsistent cross-sectional shapes on the two opposing clamping surfaces. The clamping structures of the first clamping surface and the second clamping surface can also be selected with different cross-sectional shapes, and a synergistic clamping effect can be achieved through the differentiated configuration of the cross-sectional properties on both sides.

[0083] In one embodiment, such as Figure 13 As shown, the clamping units are arranged along the stretching direction of the clamped part. In this embodiment, the clamping units are specifically arranged along the stretching direction of the clamped part, which means that the wave undulation path (crest and trough lines) is perpendicular to the direction of the tensile force; more precisely, the wave propagation direction is perpendicular to the axis of the clamped part. This arrangement ensures that the clamped part undergoes multiple bends along the axial path during the stress process, forcing the wire to overcome the bending deformation energy and the frictional force along the wave surface before sliding can occur, thereby maximizing the axial frictional resistance and ensuring clamping stability during large strain stretching.

[0084] In addition to the vertical arrangement described above, the clamping units can also be arranged at an angle to the stretching direction of the clamped component, so that the wave propagation direction forms a preset angle α with the wire axis. The angle α can be greater than 0° and less than or equal to 70°. In this non-vertical arrangement, the contact between the clamped component and the wave surface no longer occurs mainly along a single transverse section, but forms an inclined extended contact path along the clamping surface, increasing the effective contact length corresponding to the wire axis, thereby increasing the contact area (contact length) and improving clamping stability; at the same time, the contact pressure is dispersed along a longer path, which helps to reduce local pressure peaks and improve the consistency of repeated clamping.

[0085] The preset angle α is used to strike a balance between "contact length enhancement" and "anti-slip geometric restraint capability": when α is small and close to 0°, the increase in extended contact length is not significant; when α is large and close to 90°, the wave propagation direction tends to be parallel to the wire axis, and the undulating structure of the clamping surface more closely forms a continuous guide groove / longitudinal texture in the axial direction, making the clamped part more likely to slip or creep relative to each other in this direction, resulting in weakened resistance to axial slippage and possible force bias, which is not conducive to the consistency of repeated clamping. Therefore, setting α to 0° to 70° (excluding 0°) can significantly increase the effective contact length and disperse contact pressure while maintaining sufficient geometric restraint components, thus balancing the increase in contact area and anti-slip capability.

[0086] In one implementation, the wave propagation directions of the two opposing clamping structures adopt the same tilt angle (same-direction oblique placement) to obtain a more continuous extended contact path; in another implementation, the wave propagation directions of the two opposing clamping structures adopt opposite tilt angles (cross-oblique placement), so that the wire forms an interlaced contact path on both clamping surfaces, thereby further improving the anti-rotation and anti-lateral displacement capabilities.

[0087] Taking the clamped component as a wire as an example, the undulation amplitude of the wavy smooth surface is characterized by the node depth d. The node depth d is defined as: the distance between the point where the clamping structure first contacts the surface of the clamped component and the point where the clamping structure is furthest from the point of first contact.

[0088] For example Figure 1 , Figure 5 For the clamping block shown without a limiting plane, the nodal depth d is the distance from the peak to the valley along the normal direction of the clamping surface;

[0089] For example Figures 2-4 For the clamping block with a limiting plane shown, the node depth d is the distance from the top of the protrusion or peak to the limiting plane along the normal direction of the clamping surface.

[0090] Additionally, define the clamped part dimension Dt, where Dt is the narrowest part of the clamped part during clamping: for wire-type clamped parts, its diameter is Dt; for rectangular cross-section clamped parts, its short side distance is Dt.

[0091] For implementations with a clamping structure on only one side, the following condition must be met: 3% ≤ d / Dt ≤ 30%;

[0092] For a clamp with clamping structures on both sides, the wave depth formed by the first clamping block is d1, the wave depth formed by the second clamping block is d2, and the total undulation depth of the two opposing clamping surfaces when the wire is clamped satisfies 3%≤(d1+d2) / Dt≤30%.

[0093] When (d1+d2) / Dt is above the lower limit, the amplitude of wave fluctuations increases, the geometric envelope and degree of circumduction of the clamped part in the clamping area are enhanced, the winch effect is more obvious, and higher axial anti-slip capability and improved clamping stability can be obtained with a smaller clamping force. When (d1+d2) / Dt is below the upper limit, the degree of clamping of the clamped part is reduced, the contact pressure distribution is more gentle, which helps to reduce the risk of surface indentation and scratches, and improves the adaptability to diameter tolerances and clamping deviations.

[0094] In some embodiments, the peak in contact with the clamped part is formed by a smooth, convex curved surface, the curvature of which is represented by the equivalent radius Re. The equivalent radius Re is defined as the equivalent arc radius of the peak contact profile within a preset range; Re and Dt satisfy 0.1≤Re / Dt≤2. The smaller Re is, the sharper the peak, making it easier to form stronger geometric restraint and higher local friction contribution under the same clamping force, thus improving anti-slip capability; when Re / Dt is above the lower limit, the sharpness of the peak is limited, the peak value of local contact pressure is reduced, which helps to reduce the risk of wire surface indentation, microcrack initiation and wear, and improves the consistency of repeated clamping; when Re / Dt is below the upper limit, the peak still maintains sufficient curvature change to provide effective geometric fit, avoiding the peak from being too rounded and slipping.

[0095] Furthermore, medical-grade nickel-titanium alloy wires are often covered with a dense titanium dioxide (TiO2) oxide layer (black or blue) with self-lubricating properties. This oxide layer is hard and insulating, which can easily cause slippage and unstable electrical measurement signals. In this embodiment, the Re / Dt ratio is limited to below 2, which endows the peak with the ability to "pierce / break through" the micron-sized oxide layer. This makes it easier for the peak to penetrate the insulating oxide layer and establish a metal-to-metal contact with the nickel-titanium metal substrate. While providing mechanical micro-anchoring, it also provides a lower-noise electrical connection path for temperature sensors and resistance monitoring in the temperature control system, improving the signal-to-noise ratio of microvolt-level signal measurements.

[0096] In some embodiments, the periodic distribution of the wavy smooth surface is characterized by the crest interval p. The crest interval p is defined as the distance between the tops of two adjacent peaks along the wire axis. The crest interval p and the wire diameter Dt satisfy a preset proportional relationship: 0.2 ≤ p / Dt ≤ 5. When p / Dt is above the lower limit, the number of crests per unit clamping length decreases, the contact becomes gentler, and the bending frequency of the wire in the clamping area decreases, which helps to reduce wear points under fretting conditions and reduce sensitivity to processing consistency. When p / Dt is below the upper limit, the number of crests per unit clamping length increases, the number of geometric limit points increases, and the wire slippage path becomes more tortuous, which can increase the friction path length and improve anti-slip capability and positioning repeatability.

[0097] Meanwhile, nickel-titanium alloys exhibit significant superelasticity, with recoverable strain exceeding 8%. According to Poisson's ratio principle, under such enormous axial tension, the radial diameter of the wire will significantly shrink (Necking down). If the crest interval p is not properly selected to accommodate this dynamic diameter change, it will lead to a decrease in clamping force in the later stages of the test. The range of p values ​​set in this embodiment provides ample "breathing space" for the radial shrinkage and expansion (during unloading and springback) of the wire. Especially during temperature-dependent testing, the wire will experience dimensional fluctuations due to thermal expansion and contraction. The wide troughs ensure that the wire will not get stuck at the bottom due to thermal expansion, nor will it detach from contact due to Poisson's contraction, thus maintaining a stable geometric constraint state. In some embodiments, d, Re, and p are selected synergistically to form a continuous, smooth, and multi-segmented contact path within the clamping area. This allows the normal clamping force to be gradually converted into axial frictional resistance along the wave profile, improving anti-slip capability while reducing the risk of stress concentration at the clamp opening, thereby reducing the probability of clamping breakage and improving the completeness and accuracy of tensile test data.

[0098] As an optional implementation, this embodiment provides an array-type flat-top boss clamping surface structure. Unlike a wave-shaped design, the clamping units are arranged in a grid pattern along the length and / or width of the clamping surface, and each clamping unit has a clearly defined top surface and sidewalls. The top surface is parallel to the clamping reference surface, and the sidewalls are centrally symmetrically distributed, so that their projection on the clamping surface is rectangular or rhomboid (similar to a truncated pyramid or flat-top tooth structure).

[0099] In terms of technical effectiveness, this design is an improvement on traditional knurled clamps. Traditional sharp-tooth clamps penetrate deeply into the material surface, creating a severe stress concentration point. This embodiment, by setting a top surface, transforms point contact into micro-area contact. While providing sufficient mechanical interlocking force to pierce the hard oxide layer (TiO2) on the nickel-titanium alloy surface, it effectively limits the penetration depth, avoiding deep cuts in the base material. This achieves a better balance between "anti-slip" and "anti-fracture," making it particularly suitable for samples with thick surface oxide layers and requiring high friction.

[0100] As a further optional implementation, the dimensions of the flat-top boss structure are limited: the included angle between a pair of symmetrical sidewalls along the top surface is set to 90°; the clamping unit projection is a square with a side length of 1 mm; and the nodal depth is controlled within 0.3 mm. The low height of 0.3 mm constitutes a "shallow engagement" strategy, which is sufficient to provide tangential resistance to overcome slippage on the nickel-titanium wire surface, but not enough to cause deep plastic damage. The 1 mm² square projection, combined with the 90° sidewalls, constructs a high-density friction array, so that the clamping pressure is evenly distributed on multiple micro-platforms, significantly reducing local Hertzian contact stress. Although it may be slightly inferior to corrugated clamps in terms of non-destructive performance under ultra-large strain, it has better anti-slip performance when dealing with extremely smooth, high-hardness, or specially coated wires, and the processing cost is relatively lower, providing another option for different testing needs.

[0101] In some embodiments, the aforementioned clamping surfaces can be integrated into the locking structure of an orthopedic / spinal internal fixation system, serving as clamping surfaces for connecting rods (such as spinal system connecting rods, rods clamped by transverse connectors / cross links, etc.) or contact surfaces for locking blocks. By creating a smooth, undulating peak-valve structure on the relative clamping surfaces and forming complementary or staggered engagement, higher anti-slip capability can be achieved under lower locking force or lower locking torque conditions, and the contact pressure is distributed to a larger continuous contact area, thereby reducing local stress concentration and indentation abrupt changes in the clamping area of ​​the rods, and reducing the risk of early fatigue failure due to fretting wear or notch effects.

[0102] In some embodiments, the aforementioned clamping surface can be used as the clamping and locking interface for trauma orthopedic wire or cable fixation systems (e.g., cerclage wires, cables, and their locking / crimping sleeves). The smooth, undulating contact profile allows the wire or cable to form a continuous, curved contact path in the locking area. Slippage requires overcoming both frictional and geometrical engagement resistance, thereby improving locking reliability. Simultaneously, the smooth, continuous transition of the surface morphology reduces the cutting and stress concentration caused by traditional sharp-edge compression or toothed engagement, decreasing the risk of crack initiation and premature breakage of the wire / cable at the locking position.

[0103] In some embodiments, the aforementioned clamping surface can be used as a locking and clamping interface for sutures, suture tapes, or traction threads in sports medicine and soft tissue repair devices. Compared to sharp, toothed surfaces, smooth, undulating surfaces can provide anti-slip locking capabilities while reducing cutting damage to fibrous materials and localized stress concentration, thereby improving the stability and durability of the lock.

[0104] In some embodiments, the aforementioned clamping surfaces can also be used in the manufacturing, assembly, or inspection tooling related to minimally invasive devices, such as for non-destructive clamping, positioning, or mechanical testing of slender components like guidewire cores and stent wires, in order to improve clamping stability, avoid slippage, reduce the risk of damage to the coating / oxide layer on the surface of slender components, and reduce premature failure of the clamping area.

[0105] As an optional implementation, this embodiment relates to a specific processing technology for the clamping surface. In this embodiment, regardless of whether the clamping unit adopts the aforementioned wavy or trapezoidal cross-section, its final contact surface can be optionally an electrical discharge machining (EDM) surface. Technically, EDM removes material through electrical discharge, naturally forming a uniform, non-directional micro-patterned texture (MatteFinish) on the metal surface. This micro-texture differs from traditional mechanical grinding textures; it significantly increases the surface's micro-roughness and coefficient of friction, and has no specific slip direction. For nickel-titanium alloy oxide layers with self-lubricating properties, the EDM surface can provide excellent micro-grip, further preventing slippage by the macro-clamping unit. Furthermore, the hardened layer formed by EDM can improve the wear resistance of the clamping surface, preventing failure under repeated scratching by high-hardness nickel-titanium wire, thereby extending the clamp's service life and ensuring the consistency of long-term test data.

[0106] This invention also provides a method for testing the stress and strain of shape memory alloys, which uses a stress and strain testing fixture formed by the aforementioned clamping surfaces. The testing process includes:

[0107] Step S1: Place the workpiece to be clamped in the clamping area of ​​the fixture. The operator must ensure that the workpiece spans multiple clamping units of the first and / or second clamping blocks axially to maximize the effective clamping length.

[0108] Step S2: Apply lateral constraint force to the clamped part to achieve axial locking. The locking mechanism differs from traditional planar clamping; instead, it drives the first and second clamping blocks closer together, causing the peak of the clamping unit on one side to embed into the valley of the clamping unit on the other side, forcing the clamped part to undergo continuous bending deformation along the undulating contour formed by the clamping units. This "wave-like" path guidance utilizes the Capstan Effect to transform the lateral constraint force perpendicular to the wire surface into cumulative frictional resistance distributed axially. Since nickel-titanium alloy surfaces are often covered with a hard and easily slippery oxide layer, simple friction is insufficient to resist large strain tension; this method introduces geometric bending, requiring the wire to overcome bending deformation energy to achieve relative sliding, thereby establishing a stable form-closure without damaging the wire surface integrity, solving the problems of slippage or breakage common in traditional clamps.

[0109] Step S3: While maintaining the locked state, apply an axial load to the clamped part and collect the mechanical response data of the clamped part.

[0110] Before the formal loading in step S3, a pre-loading step can be introduced. Since nickel-titanium alloy wire is typically supplied in coiled form, there may be minute geometric gaps or non-straightness when it is loaded into the corrugated clamp. Directly starting the test will cause a non-linear "toe region" in the initial stage of the stress-strain curve, affecting the accuracy of the elastic modulus calculation. Therefore, a preset initial load (e.g., 5 N to 10 N or a stress value below 5% of the material's elastic limit) can be applied to the clamped part and continued until the monitored load value stably reaches the preset threshold. This step eliminates the initial slack in the clamping area and the structural gaps caused by the corrugated bending, ensuring that the wire is in a taut state before testing. This state is marked as the zero-strain point to ensure that subsequent displacement data reflects the tensile deformation of the material rather than the mechanical adjustment displacement of the clamping system.

[0111] In step S3, applying an axial load to the clamped part preferably uses a displacement control mode, and a constant strain rate is set. Nickel-titanium alloys are sensitive to strain rate; they release latent heat during stress-induced martensitic transformation (exothermic) and absorb latent heat during reverse transformation. Excessive tensile speed can cause the internal heat of the specimen to rise due to insufficient heat dissipation. According to the Clausius-Clapeyron relation, increased temperature significantly raises the phase transformation stress plateau, causing the measured data to deviate from the true properties under isothermal conditions. Therefore, the strain rate is configured to maintain quasi-static conditions during the test (e.g., a low rate conforming to ASTM F2516 recommendations) to minimize temperature fluctuations caused by latent heat of phase transformation, making the test as close to an isothermal process as possible. The system monitors the stress-strain response in real time. When the stress is observed to change very little or remain constant with increasing strain, the plateau is identified as a transformation stress to obtain high-fidelity constitutive parameters.

[0112] Step S3, the loading process, can be designed as a complete "load-unload cycle" to characterize the full picture of hyperelasticity. During the loading phase, the clamped component is stretched to a target strain (e.g., 6%–8%) exceeding its austenitic-martensite phase transformation endpoint to ensure the complete phase transformation plateau is recorded. Subsequently, during the unloading phase, the load is released in reverse at the same strain rate until the stress returns to zero. Data acquisition records a complete hyperelastic hysteresis loop; the area enclosed by the loop represents the dissipated energy per cycle, used to evaluate the material's damping characteristics and fatigue resistance. By analyzing the residual strain at the end of unloading, it is possible to assess whether the clamp caused plastic slippage in the specimen and the material's shape memory recovery capability. Through this cyclic test, this method can provide a complete set of mechanical spectra, including phase transformation stress, modulus, dissipated energy, and recovery rate, meeting the needs of in-depth material performance evaluation in medical device development.

[0113] The technical features in the above embodiments can be combined arbitrarily, and as long as there is no contradiction, they should all be considered to fall within the scope of this specification. The above embodiments are merely several implementations of the present invention and do not constitute a limitation on the scope of protection of the present invention; the scope of protection of the present invention is determined by the claims.

[0114] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A clamping surface for engaging with another opposing clamping surface to clamp a clamped part, characterized in that: The clamping surface is provided with a clamping structure, the clamping structure includes a plurality of clamping units, and the plurality of clamping units are arranged on the clamping surface according to a preset rule; The surface of the clamping structure that contacts the clamped part is a smooth surface; When the clamping surface clamps the clamped part with the opposite clamping surface, the clamped part undergoes continuous deformation along the undulating contour of the clamping structure.

2. The clamping surface according to claim 1, characterized in that: The clamping unit includes peaks and valleys spaced apart; when the opposing clamping surfaces approach each other, the peaks first contact the clamped part.

3. The clamping surface according to claim 2, characterized in that: The edges of the clamping surface are chamfered.

4. The clamping surface according to claim 3, characterized in that: The clamping structures on the first clamping surface and the second clamping surface used to clamp the clamped part have the same dimensions and structure.

5. The clamping surface according to claim 4, characterized in that: When the first clamping surface and the second clamping surface, which are used to clamp the clamped part together, clamp the clamped part, the peaks of the first clamping surface and the peaks of the second clamping surface are staggered.

6. The clamping surface according to claim 4, characterized in that: When the first clamping surface and the second clamping surface, which are used to clamp the clamped part together, clamp the clamped part, the peak of the first clamping surface corresponds to the valley of the second clamping surface.

7. The clamping surface according to claim 2, characterized in that: The peaks and valleys are connected end to end, forming a smooth, wavy surface.

8. The clamping surface according to claim 1, characterized in that: The clamping unit has a circular arc cross-section, and multiple clamping units with circular arc cross-sections are arranged at intervals to form the clamping structure.

9. The clamping surface according to claim 1, characterized in that: The clamping unit has a cross-sectional shape of triangular wave with rounded corners or sawtooth wave with rounded corners, and multiple clamping units with the cross-sectional shape are arranged at intervals to form the clamping structure.

10. The clamping surface according to claim 1, characterized in that: The clamping unit has a trapezoidal cross-sectional shape with rounded corners, and multiple clamping units with the cross-sectional shape are arranged at intervals to form the clamping structure.

11. The clamping surface according to any one of claims 1 to 10, characterized in that: The clamping unit extends in a direction parallel to the horizontal direction.

12. The clamping surface according to any one of claims 1 to 10, characterized in that: The clamping unit is inclined relative to the horizontal direction in its extension direction, and the inclination angle is greater than 0° and less than or equal to 70°.

13. The clamping surface according to claim 1, characterized in that: The distance between the point where the clamping structure first contacts the surface of the clamped part and the point where the clamping structure is furthest from the first contact point is defined as the node depth. The total depth of the nodal formed by the first clamping surface and the second clamping surface used to clamp the clamped part is d, and the ratio of the total nodal depth d to the width Dt of the narrowest part of the clamped part is in the range of 3%≤d / Dt≤30%.

14. The clamping surface according to claim 1, characterized in that: The equivalent radius of the surface in the clamping structure that first contacts the clamped part is defined as Re; The ratio of the equivalent radius Re to the width Dt of the narrowest part of the clamped part is in the range of 0.1≤Re / Dt≤2.

15. The clamping surface according to claim 1, characterized in that: Define the interval between adjacent clamping units as p; The ratio of the interval p to the width Dt of the narrowest part of the clamped part is in the range of 0.2≤p / Dt≤5.

16. The clamping surface according to any one of claims 1 to 10, characterized in that: The clamping surface is configured to be disposed on the locking contact surface of the clamping block of the stress-strain testing fixture or the medical locking structure for clamping and locking the clamped part.

17. A method for testing the stress and strain of shape memory alloys, using the clamping surface as described in any one of claims 1 to 10, characterized in that, Includes the following steps: S1: Place the clamped part in the clamping area of ​​the clamping surface, so that the clamped part spans multiple clamping units; S2: Apply a lateral constraint force to the clamped part to lock it axially; S3: While keeping the clamped part locked, apply an axial load to the clamped part and collect the mechanical response data of the clamped part.

18. The method for testing the stress and strain of shape memory alloys according to claim 17, characterized in that: In step S2, applying lateral constraint force to the clamped part includes driving the first clamping surface and the second clamping surface to move closer to each other, so that the peak of the clamping unit on one side of the clamping surface is embedded in the valley of the clamping unit on the other side of the clamping surface, thereby causing the clamped part to undergo continuous bending deformation along the undulating contour formed by the clamping unit.

19. The method for testing the stress and strain of shape memory alloys according to claim 17, characterized in that: Before step S3, a preloading step is also included: applying a preset initial load to the clamped part until the monitored load value reaches a preset threshold to eliminate the initial relaxation of the clamped part in the clamping area, and marking this state as the zero point of strain measurement.

20. The method for testing the stress and strain of shape memory alloys according to claim 17, characterized in that: In step S3, applying an axial load to the clamped part using a displacement control mode specifically includes: driving the tensioning device to move at a constant strain rate, wherein the strain rate is configured to maintain quasi-static conditions during the test process to minimize temperature fluctuations caused by the latent heat of phase transformation of the shape memory alloy; and monitoring the stress-strain response of the clamped part in real time, identifying the stress plateau as phase transformation stress when a stress plateau characteristic is detected.

21. The method for testing the stress and strain of shape memory alloys according to claim 20, characterized in that: The loading process in step S3 includes a load-unload loop, specifically including: Loading phase: The clamped part is stretched to a target strain exceeding its austenite-martensite phase transformation end point; Unloading phase: The load is released in the opposite direction at the same strain rate until the stress returns to zero; The acquisition of mechanical response data of the clamped component includes recording a complete hyperelastic hysteresis loop and calculating dissipated energy and residual strain based on the hysteresis loop.

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