Method for measuring multi-axis strain of thin-walled tube under internal pressure axial composite load

Abstract

The invention provides a method for measuring the multi-axis strain of a thin-walled tube under an internal pressure axial composite load. The method comprises the steps that a standard test mark is made on the surface of the thin-walled tube as the reference of image processing; a CCD camera is used to display the image of the standard test mark on the measured thin-walled tube in the process of an axial fatigue and internal pressure composite test in real time; the distance between the axis direction and the circumferential direction of the mark are determined; the distance between two adjacent furthest edges between two axial strain marks and the change of the distance between two adjacent furthest edges between two circumferential strain marks are used to calculate strain measurement values; variable values are output to a host computer, and are displayed and stored; the digital signal of axial and circumferential strain measurement values is converted into an analog signal, and the signal is output; and a common interface is provided for a general mechanical test device. The method provided by the invention has the advantages of flexible test range adjustment and good dynamic response characteristic, is suitable for real-time acquisition of axial and circumferential strain of various metal and non-metallic thin-walled tubes, and can be used for high temperature low-cycle and high-cycle fatigue tests of metal materials and non-metallic materials.

Description

technical field [0001] The invention relates to a method for measuring multiaxial strain of a thin-walled tube. In particular, it relates to a multi-axial strain measurement method for thin-walled pipes under internal pressure and axial compound loads. Background technique [0002] Thin-walled tubes are widely used in chemical industry, nuclear power and other fields, and it is necessary to study their mechanical properties. However, it is difficult to measure the deformation of thin-walled pipes. At present, two uniaxial strain gauges or strain rosettes are usually used to measure the axial deformation and circumferential deformation of thin-walled tubes. However, the strain gauge measurement method has the following disadvantages: 1) The measurement accuracy of the strain gauge is subject to many factors: such as the sticking position, the quality of the adhesive glue, the stability of the supply bridge voltage, the signal amplifier circuit, etc., especially when testing...

AI Technical Summary

Problems solved by technology

However, the strain gauge measurement method has the following disadvantages: 1) The measurement accuracy of the strain gauge is subject to many factors: such as the sticking position, the quality of the adhesive glue, the stability of the supply bridge voltage, the signal amplifier circuit, etc., especially when testing thin-walled tubes , it is difficult to ensure the repeatability of the measurement; 2) The maximum deformation of the strain gauge is usually 2%, which makes it unable to be applied to the large deformation measurement of the thin-walled tube; 3) The actual use of the strain gauge is cumbersome and needs to be The surface of the test sample can only be pasted after grinding and polishing, which will affect the performance of the test sample to a certain extent; 4) When the thin-walled tube is subjected to complex cyclic external forces, the strain gauge is prone to fall off, especially when the diameter of the thin-walled tube is small, the strain gauge The gauge is very easy to fail; 5) The strain gauge is not suitable for high temperature test occasions

High-temperature strain gauges are extremely expensive, and high requirements are placed on adhesives, sensitive grids, wires, etc. during use, resulting in less use of strain gauges in high-temperature tests

Therefore, it is necessary to develop a new strain test method for thin-walled tubes, which can solve the problems of poor test repeatability, small measurement range, cumbersome steps, and short service life of strain gauges. The mechanical properties and fatigue properties of thin-walled tubes lay the foundation for experiments

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