Detailed introduction to the static deformation measurement process of the test machine

The accuracy of deformation measurements is also mutually restricted by the relevant environment. For example: high-resolution non-contact extensometers are used to measure carbon fiber deformation and glass fiber wire deformation due to the characteristics of the sample; special devices are required to measure tensile and compression deformation in high-temperature sample environments. There are many links involved in deformation measurement in practical applications, including many microscopic and some macroscopic large deformations. Here I am just expressing my own experience, hoping to attract everyone to discuss material deformation testing.

Early domestic dial-typeTesting machine(Whether it is mechanical or hydraulic) Although the measurement of test force has poor discrimination, low accuracy and narrow range, it basically meets the measurement of tensile strength, yield strength, and elongation after break of some metal materials. However, the way in which mechanical transmission draws curves is impossible to accurately record the elastic segments of metal materials, so it is inaccurate or impossible to obtain the values ​​of the series of Young's modulus, specified non-proportional extension strength, force elongation, residual elongation, and yield point elongation.

So, what is the significance of accurate measurement of deformation? What are the main factors affecting the measurement of deformation? Inspection and testing work serves production needs. When we understand the actual production needs, we will have a deep understanding of some parameters defined in GB/T 228-2002, and these parameters basically have clear requirements for the measurement of sample deformation. The forming of a car body requires multiple stampings. So how to determine that the thin steel plate of the car can still have the corresponding strength after multiple stampings? How to determine whether the plane and arc surface parts do not crack during stamping and the strength meets the requirements? The n-value and r-value test methods specified in the standard clearly gave answers. The accuracy of the n and r values ​​depends on the accurate measurement of the axial deformation and radial deformation of the sample. In engineering, such as steel structure bridges and high-rise buildings, there are very strict requirements for safety, so when it comes to steel and rock foundation materials, there are clear regulations on the deformation of materials and structures under the bearing. SpecificallyUniversal testing machineIn the field of testing, steel strength, specified non-proportional extension strength, specified total extension strength; compressive strength and compressive elastic modulus of rock are parameters that must be tested in quantitative terms, and the determination of these parameters has specific requirements for the measurement of sample deformation.