Research And Development Of Materials Performance Test Equipment And Virtual Field Method To Identify Material Parameters

The testing of material properties is a very important research topic.Due to limitations of test equipment and test methods,researchers have not been able to fully evaluate the elasto-plastic properties of materials and micro-deformation damage mechanisms.As a result,failures in the actual service of materials cannot be predicted,often resulting in the loss of human life and property.To solve the above problems,this paper addresses the challenges of material performance testing from two aspects.In the first aspect,from the perspective of material performance test equipment,in order to be able to simulate the environment under actual service conditions of materials,our self-developed equipment integrates electric field,thermal field,magnetic field,and force loading modules to accurately measure the actual service life of materials.This equipment provides the basic equipment.In the second aspect,based on the material performance test method,the virtual field method is used to identify the elasto-plastic properties of the material.Compared with the traditional test method,this test method can identify all the parameters in the constitutive model of the material by analyzing a non-uniform stress and strain field created by a test.The test method has high efficiency and wide application range,and has a wide application prospect.Firstly,based on the basic theory of virtual field method,this paper deduces the physical model of uniaxial tensile test and determines the corresponding virtual field.Secondly,the main functional modules of the self-developed equipment are introduced in detail;the functional relationship between the output displacement error of the equipment system and the loading force is determined;the high-precision cantilever bending loading trajectory is planned,and two problems are proposed for the system coordinate system.A variety of solutions were developed and corresponding verification tests were carried out.Halogen lamp heating,heating on a constant temperature table,and Ohmic heating were compared and studied.The uniformity of the heating temperature distribution and the influence on the DIC acquisition pattern were experimentally studied;a high temperature speckle was built.The test system,using Blu-ray band-pass filtering,effectively improved the effect of thermal radiation on the DIC acquisition image and increased the system test temperature limit from450°C to 678°C.Based on self-developed equipment,relevant experimental studies were conducted.First,the DIC technique measures the tensile test strain of the standard,and studies the influence of the position of the fracture relative to the gauge section and the variable gauge length on the result of measuring strain.The results show that the position of the fracture relative to the gauge section varies.The mechanism behind it is necking.With respect to the influence of gauge length measurement,for measuring the strain at the elastic stage,when the gauge length is less than 10mm,the gauge length has a significant effect on the variable measurement result,and when the gauge length is greater than 10mm,the measurement is performed.And the effect of elastic strain on the gauge length is no longer sensitive.For measuring the strain at the plastic stage,the measured strain value gradually decreases with increasing gauge length.Using the improved high temperature DIC test system,the coefficient of thermal expansion of Q215 was measured to verify the reliability of the measurement results of the improved high temperature DIC test system.In addition,the thermal noise of the high temperature DIC system was also tested.The results show that the displacement noise level is1 0^-4and the strain noise level is1 0^-5 in the normal temperature state,and1 0^-3 in the high temperature state.The strain noise is1 0^-4.The virtual field method was used to identify the elastic modulus,Poisson's ratio,plasticity parameters of bilinear hardening model,power law hardening model and Voce hardening model for isotropic materials.The noise and model loading boundary were also used to identify the virtual field method.The results show that the virtual field method is not sensitive to the boundary conditions,and the error caused by the noise on the elastic modulus measurement result is 0.4%.Through comparison with other literatures,we found that when the noise level is1 0^-4,it is recognized by the virtual field method.The error caused by the elastic modulus E and Poisson's ratio is about 0.4%-0.7%,which has good consistency.