【国外标准】 Standard Test Method for Constant Torque Thermal Cycling of Cylindrical Shape Memory Alloy Specimens

4.1 Constant torque thermal cycling tests determine the effect of shear stress on the transformation properties such as transformation temperatures, actuation shear strain and residual shear strain of a shape memory alloy. This test is done to provide data for the characterization selection of shape memory alloy materials, quality control, design allowables and actuator design (1-3).5 The tests should be used for one thermal cycle but may be used for repeated thermal cycles as agreed upon between supplier and customer.4.2 Measurement of the specimen's motion closely parallels many shape memory actuator applications and provides a result that is applicable to the function of the material.4.3 This test method may be used for cylindrical specimens such as wire, round tube or bar forms. Thus, it is able to provide an assessment of the product in its semi-finished form.4.4 This test method provides a simple method for determining transformation temperatures by heating and cooling specimens through their full thermal transformation under torque.4.5 This test method may also be used to evaluate partial transformation cycles as set by the LCT and UCT and agreed upon between the user and customer. Examples of partial and full transformation thermal cycles are provided in Fig. 2.FIG. 2 Effects of Shear Stress and Upper Cycle Temperature on Test ResultsNOTE 1: A) UCT sufficient for complete Austenitic transformation. B) UCT not sufficient for complete Austenitic transformation. “τ” is the applied shear stress.4.6 This test method can be used on trained and processed material in a semi-finished form to measure Two Way Shape Memory Effect (TWSME) by comparing the shear strain at the LCT and UCT with a torque set such that the corresponding shear stress shall not exceed 7 MPa. For determining TWSME in this manner it is suggested that a full transformation cycle be performed in accordance with 5.7.4.7 This test method is useful for quality control, specification acceptance, and research.4.8 Transformation temperatures derived from this test method may not agree with those obtained by other test methods due to the effects of shear strain and shear stress on the transformation.4.9 Components such as springs, specimens with non-circular cross-sections or other semi-finished parts can be tested using this method as agreed upon by the customer and supplier. Test parameters and results shall be determined with respect to torque and rotation measured at the ends of the active region of the specimen.1.1 This test method will define procedures for thermomechanical cycling of shape memory alloys (SMA) material and components with circular cross-sections under constant torque. This test method will measure the transformation properties such as transformation temperatures, actuation shear strain and residual shear strain, when a shape memory alloy is thermally cycled through the phase transformation under a constant applied torque. This test is done to provide data for the characterization selection of shape memory alloy materials, quality control, design allowables and actuator design.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.