Method for ball-shape pressure head for determining shape memory alloy phase change property

Abstract

The utility model discloses a method using a spherical indenter for measuring the phase transition properties of shape memory alloy (SMAs). The phase transition is induced under the pressure of the spherical indenter pressed into the surface of the shape memory alloy; the load signals and the displacement signals in the unloading process are detected by a sensor at the same time, and the ht curve of the load F-displacement is obtained; the load-displacement curve obtained in the test is transformed to a corresponding nominal stress Sigmam-nominal stress Epsilonm curve according to the analysis; then properties of the transformation stress, the elastic modulus and other aspects of the SMAs can be obtained. The test method has advantages that the method is easy in operation, and the nondestructive measurement of the materials can be elementally realized; the method not only can be widely used in the measurement of the phase transition properties of various super-elastic and shape memory SMAs, but also is particularly suitable for the phase transition measurement of the SMAs films with the low thickness only up to a plurality of micrometers or the SMAs micro devices with the micrometer order typical structure size; the method has accurate and precise measured value, which can supply the reliable measurement basis of the phase transition property for the application of the SMAs in the micro-electro-mechanical system.

Description

technical field [0001] The invention belongs to the technical field of mechanical performance testing of shape memory alloy materials. Background technique [0002] Shape memory alloys (Shape Memory Alloys, SMAs for short) can exhibit unique shape memory properties or superelastic properties at different temperatures. Combined with its outstanding advantages such as high power density (output power per unit volume), large output force and output displacement, SMAs have become ideal materials for the development of MEMS drivers and sensors. Among various SMAs, nickel-titanium alloy (NiTi) is the most practical shape memory alloy with a work density as high as 2.5×10 7 J / m 3 , two orders of magnitude higher than other types of micro-actuation materials. The driver developed with high power density materials has the same output power but smaller structural size, or the same structural size but higher output power. [0003] The research on nickel-titanium alloy (NiTi) micro-...

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Problems solved by technology

Therefore, although the nanoindentation method based on the Berkovich indenter has been widely used to measure the hardness and elastic modulus of elastic or elastoplastic materials, however, due to the coupling of phase change deformation and plastic deformation during the deformation of SMAs, it cannot be used with conventional Berkovich indentation technique to measure the phase transition properties of SMAs: as figure 2 As shown, since the shape of the Berkovich indenter is a triangular pyramid with a small radius of curvature at the tip, under a small load condition, martensitic yield deformation will be induced in the center of the indentation area, and martensitic deformation will be induced in the edge area at the same time. bulk phase deformation

For this, the measured hardness will be the martensitic transformation stress σ t and the martensitic yield stress σ n Since the size of the martensitic yield region in the contact zone cannot be determined, it is impossible to further analyze the transformation characteristics such as the martensite transformation stress of SMAs

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