Continuous failure analysis of the mixture material plate bolt

Microscopically, after the load exceeds the FPF (first layer failure) envelope, the crack begins to form along the fibers of some unidirectional layers and expands inside the matrix and at the fiber-matrix interface. According to Stephen W. Tsai, these cracks lead to local stress concentration, which will cause damage or fracture of adjacent layers, and the effective stiffness of the laminate will decrease, but it will not be too obvious <8>. In addition, Cai also pointed out that as long as the layer is still buried in the laminate, it continues to contribute to the stiffness of the laminate. The laminate containing transverse cracks in the laminate is not the same as removing the layer completely from the laminate. For this reason, the second degradation method considers that the amount of material stiffness degradation is different for the corresponding tensile failure and compression failure, and more stiffness will be retained when the material undergoes compression failure. Specific stiffness degradation method.

The stiffness degradation method used in this paper requires a total of five field variables to describe, except for the variables that reflect the four failure modes of matrix failure, fiber matrix shear failure, fiber tension and fiber compression failure, the fifth field variable expression (3) The failure parameter d in the description describes the nonlinear shear constitutive relationship of the material.

In this paper, the failure rule is added by the USDFLD module in ABAQUS to realize the above failure judgment and stiffness degradation algorithm. In the process of numerical simulation, as the load increases, the stiffness degradation of the failed unit will cause large deformation of the mesh. When the calculation fails to converge due to the excessive distortion of the mesh, the program automatically exits and observes the load-displacement obtained at this time. The curve, the load has begun to decline, at this time the ultimate load and failure mode of the structure can be obtained from the load-displacement curve.

Numerical calculations The three sets of laminates were calculated using the calculation method described above. The layup material was T300-QY8911, laminate size and layup parameters. According to the research results of the literature <2, 3>, the closer the bolt hole is, the larger the deviation between the numerical simulation and the experimental value. Since the local damage of the hole edge has made the stress distribution tend to be uniform, the analysis results according to the elastic theory in the edge region often have a large error with the experimental value. In addition, it can be clearly seen from the test photographs given that the bolted joint is completely different from the broken joint of the pin joint. Due to the lateral pressure of the gasket, the crushing area is often outside the bolt washer for the crushing damage. According to the results of this test, the connection strength is calculated by the method of not degrading the stiffness of the cells in the gasket.

The numerical calculation results are compared with the experimental results. The maximum load of the test machine used in this experiment is 100KN, and the loading speed is 2mm/min. To eliminate the influence of humidity and temperature on the joint strength of the laminate, the normal laminate (non-hygroscopic) is used at normal temperature. In the experiment, the average value of each group was taken. The test values ​​of groups 1, 2 and 3 were 4839kg, 4421kg and 3412kg respectively. The results of numerical simulation and experiment were compared.

It can be seen from the comparison between the calculated value and the experimental value that different stiffness degradation methods have a certain influence on the calculation of the ultimate strength of the laminate. The second stiffness degradation method has a smaller error between the calculated value and the experimental value. It is believed that the second stiffness degradation method can obtain more accurate extrusion strength calculation results, and this method can be applied to engineering practice.

Conclusion 1) By comparing the calculated value with the experimental value, it is proved that the proposed damage hypothesis and the stiffness degradation method can describe the failure process of the joint more accurately, and the calculated laminate plate has high precision of extrusion strength. This method can be applied to Engineering practice.

2) Different stiffness degradation methods have a certain influence on the numerical simulation of the failure process of the joint and the final ultimate strength calculation. For single-layer boards, the stiffness degradation should be retained in the compression failure mode, while the material stiffness can be reduced to zero for the tensile failure mode. That is, different stiffness degradation methods for compression and tensile failure can effectively improve the accuracy of numerical simulation.

3) Through the numerical simulation and experimental analysis of the three sets of laminates, it is shown that the D/t value has a great influence on the extrusion strength of the laminate.

Round Led Shower

Round Led Shower,LED Rain Shower Head,Round Led Overhead Shower,Plastic Round Led Shower

KaiPing HuiPu Shower Metalwork Industrial CO,LTD , https://www.hp-shower.com