Introduction to the re-elastic deformation stage of metal tensile testing machine

MentionedTension testerProblems with the tensile speed test performed. During the elastic deformation stage, the deformation amount of the metal is very small and the tensile load increases rapidly. At this time, if the tensile test is performed with the beam displacement control, then the speed is too fast and the entire elastic section will be rushed over quickly. Taking ordinary steel with an elastic modulus of 200Gpa as an example, if the material with a gauge distance of 50mm is subjected to tensile tests in the elastic section at a speed of 10mm/min, then the actual stress rate is 200000N/mm2S-1×10mm/min×1min/60S×1/50mm=666N/mm2S-1 The yield strength of ordinary steel is less than 600Mpa, so it takes only 1 second to pull the sample to yield.Jinan Hengsi Shanda Instrument Co., Ltd.This speed is obviously too fast. Therefore, in the elastic section, stress rate control or load control is generally used. After the sample of material with better plasticity passes through the elastic section, the load does not increase much, and the deformation increases very quickly. Therefore, in order to prevent the tensile speed from being too fast, strain control or beam displacement control is generally used. Therefore, it is recommended in GB228-2002, "In the elastic range and up to the upper yield strength, the separation rate of the test machine chuck should be kept as constant as possible and within the specified stress rate range (material elastic modulus E/(N/mm2) <150,000, the stress rate control range is 2-20 (N/mm2) •s-1, material elastic modulus E/(N/mm2) ≥150,000, and stress rate control range is 6-60 (N/mm2) •s-1 =. If the yield strength is measured only, the strain rate during the yield length of the sample should be between 0.00025/s and 0.0025/s. The strain rate within the parallel length should be kept as constant as possible.

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