Method for measuring plastic strain ratio in metal tensile test process

Abstract

The invention relates to a method for measuring a plastic strain ratio in a metal tensile test process. The method comprises the following steps: arranging speckle points in a scale distance area on the surface of a metal sample to prepare a to-be-measured tensile sample; performing a tensile test on the tensile sample to obtain an image in an initial state as a first image and an image in a uniform plastic deformation stage as a second image; performing correlation matching on gray fields of the first image and the second image to obtain displacement fields of all pixel points of the first image; performing differential calculation on the displacement field to obtain displacement fields of all pixel points of the first image; carrying out differential calculation on the displacement fields to obtain real plastic strains in length and width directions in the scale distance area; and acquiring a plastic strain ratio of the metal sample according to the principle of volume constancy in the stretching process. The method has advantages of having a non-contact mode, low influence on the mechanical performance of the sample, high precision, and reliable result and the like; and a novelconcept and way are provide for accurately measuring the plastic strain ratio (r value) in the metal tensile test process.

Description

technical field [0001] The invention relates to a method for measuring the plastic strain ratio in the metal tensile test process, belonging to the technical field of material mechanics. Background technique [0002] Plastic strain ratio (r value) is an important mechanical parameter to measure the formability of metal sheets, reflecting the ability of metal sheets to resist thinning or thickening when they are subjected to tension or compression in a certain plane. A larger r value indicates that the material is easily deformed in the width direction during stretch forming to resist thinning in the thickness direction, and thickness reduction is one of the main reasons for material fracture during the stamping process. [0003] Since the plastic strain ratio (r value) characterizes the ratio of the true plastic strain in the width direction and the true plastic strain in the thickness direction of the material under uniaxial tension, the deformation of the length is easier ...

AI Technical Summary

Problems solved by technology

In the actual measurement of the plastic strain ratio (r value), contact measurement is often used, that is, the extensometer is installed at both ends of the gauge length of the sample, and the elongation of the sample is measured by the deformation of the extensometer. Although the extensometer The use of the extensometer can improve the measurement accuracy, but it will inevitably affect its mechanical properties when it is in direct contact with the sample, and the change in the width direction cannot be measured by the extensometer, and it needs to rely on traditional measurement tools such as vernier calipers, which leads to the measurement accuracy. There is a certain error

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