Study For Mechanics Properties And Failure Assessment Of Metal Honeycomb Sandwich With Defects

With the rapid development of aeronautics and astronautics, the large scale, space curved, thin-wall and high-temperature resistant alloy honeycomb sandwich structures are considered as critical parts of thermal-defending system in supersonic battle planes or cruise missiles, and attract more and more research interest in the world. Compared with the traditional ceramic-thermal-defending system, metal honeycomb sandwich structures have many advantages, such as super light weight, high toughness, shock resistance, water proofing, damp proofing, easy for mechanical connection and integral structure design. But during the process of preparation and active service, stochastic defects in different forms will be generated, which are evidently disadvantageous to the mechanical performance of the corresponding component. However, if the metal honeycomb sandwich plates with defects can meat with mechanical requirement of targets, the corresponding component can still be available during active service. On this point, this paper aims to theoretically and experimentally research the influence of three typical defects on the mechanical performance of the metal honeycomb sandwich plate, such as pulling, pressing, bending, shearing deformation. A set of complete and reliable failure evaluation method is also obtained. The outcome of this paper provides meaningful guidance for the preparation, active service and maintenance of metal honeycomb sandwich plate, as well as accumulates analysis experience in simulating the mechanical performance of metal thermal-defending system in large scale ,space cured shape and under complex heat-force coupling environment.This paper represents the background, the purpose and significance of the research firstly, and then classifies the lattice sandwich structures and porous materials used as mandrel, which are the research objects of this paper. Finally, current research situation of their mechanical performance is generally reviewed in terms of the theory analysis, experiment tests and numerical simulations.The following content introduces detailed preparation process of metal honeycomb sandwich structures. Then the possible detects generated during the preparation and active serve are summarized and classified. The formation reasons and elimination methods of each defect are also further stated. Typically, we amplify the preparation processes and detection methods of three kinds of defects in the metal honeycomb sandwich structure.As a consequence, the influence of the three typical defects on the mechanical performances of honeycomb sandwich structures is investigated by mutual authentication between experimental analysis and numerical simulations in three parts of this paper.Mechanical performance of the metal honeycomb sandwich structures is studied by conducting coplanar stretching and compressing, skewed stretching and compressing, three point bending and in-plane shear on the zero-defect metal honeycomb sandwich specimen and scanning microscopic feature of fracture surface tests. Based on the experimental results, the strength under different loading conditions and failure modes are analyzed respectively. By comparison, the experimental results are used to validate the analytic results obtained by mechanical theory. Then under the same loading condition, the mechanical performance of specimens with different dimensional mandrel connection defects is investigated by the above-mentioned tests. The relations between each mechanical parameters and dimensions of the mandrel connection defects are also worked out. Finally, curve of residual strength versus defect dimensions in the experiment data is fitted out, which provides experimental basis and reference in engineering applications.The same mechanical tests are performed on the metal honeycomb sandwich structure with surface-core connecting defect. By comparing the experimental data in groups with the test results on the zero-defect specimen, the decay rules of mechanical performance along with defect dimension increasing are presented under different loading conditions. Whether the failure mechanism is influenced by the defect dimension is concluded by observing the damage feature and deducing its mechanism. To further validate the accuracy of experimental results, FEM software (ABAQUS) is applied to analyze mechanical performances of the metal honeycomb sandwich structure in the loading process. By comparing the results with experiment results, the distribution laws and the evolutionary processes of plastic strain and internal stress can be observed evidently in the loading process. Finally, curve of structure residual strength of the metal honeycomb sandwich structure with core-surface connecting detects corresponding versus the defect dimension of experiment data is fitted out.The mechanical performance tests under the same loading conditions and numerical simulation analysis are performed on the metal honeycomb sandwich structure with penetrable defects, including three kinds of defect forms, such as crack, hole and notch. To obtain the decay laws of the mechanical performance along with sizes of penetrable defects, experimental data is summarized and compared with results obtained on zero-defect specimens. Moreover, by observing the damage feature, the failure mode can be also deduced. To validate the experimental data and accurately simulate the real failure process, FEM software is applied again for numerical simulation. In the end, curve of structure residual strength of the metal honeycomb sandwich structure with penetrable defects versus corresponding defect dimension in the experimental data is fitted out.