Device and method for measuring volume expansion characteristics of material under tensile load

Abstract

The invention discloses a device and a method for measuring the volume expansion characteristic of a material under a tensile load. The device comprises a stretching rod, a compensation rod, a reference cavity, a differential pressure gauge and a micrometer caliper. Screws of the stretching rod, the compensation rod and the micrometer caliper respectively extend into a test cavity through specificmounting seats, the stretching rod and the compensation rod are the same in material size specification and are fixedly connected in the test cavity, and the moving directions are opposite in the stretching process. The measurement process is divided into three stages of background curve measurement, total curve measurement and data comprehensive processing. In the background curve determinationstage, a background curve representing the relationship between volume change data and displacement data caused by device factors in the stretching process is obtained through calibration and stretching test under the condition of no sample; in the total curve determination stage, a total curve representing the relationship between total volume change data and displacement data in the stretching process is obtained through calibration and stretching test after sample installation; in the data comprehensive processing stage, the inflection point of the force curve is used for determining starting point displacement in the stretching process, and a volume expansion characteristic curve is obtained in combination with the background curve and the total curve.

Description

technical field [0001] The invention belongs to the technical field of material testing, and in particular relates to a measuring device and a measuring method for volume expansion characteristics of materials under tensile load. Background technique [0002] Tensile testing is a test to determine the properties of a material under an axial tensile load. Using the data obtained from the tensile test, in addition to determining the tensile properties such as the elastic limit, elongation, elastic modulus, and tensile strength of the material, other specific properties can also be tested with special equipment. The volume expansion property is one of them. This characteristic generally refers to the characteristic that the volume of a material sample changes (increases or decreases) under tensile load conditions. The general method to obtain the volume expansion characteristics of materials under tensile load is to use a special volume change measurement device to simultaneo...

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Problems solved by technology

[0006] In the above-mentioned gas dilatometer / measuring device, there are the following problems: First, a key prerequisite for effective and reliable measurement is that the relationship between the gas volume change and the differential pressure change obtained by using the volume calibration system is calibrated. - When the amount of gas substance in the combined cavity of the compensation cavity remains unchanged, it can continue to be established during the measurement process, and then used to convert the volume change from the differential pressure measurement result

However, in the process of opening the test chamber and the sample chamber, replacing the calibration steel rod with the material sample to be tested, and then sealing the sample chamber and the test chamber, it is impossible to avoid the influence of gas flow, small changes in air pressure, and small changes in the tightening degree of fastening bolts on the gas in the chamber. Due to the change of the value, the calibration relationship cannot continue to be established during the measurement process; secondly, due to the limitations of the manufacturing process, assembly process and other environmental factors, it is difficult to ensure that the volume compensation rod can accurately align the stretching rod at any time during the stretching process. Compensate for the volume change of the gas in the chamber caused by moving out of the test chamber; finally, based on the experience of the test personnel, it is impossible to accurately determine the time and displacement point of the sample starting to stretch

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