The Evaluaiton Of Damage For Materials And Compenents Based On Mesoscopic Structure

Damage refers to the process of deterioration or failure of materials and components during service due to the defects of materials or components which is caused by environment,load and other factors.The gradual accumulation of damage can affect the reliability and safety of the whole structure.Therefore,it is significant for the study on damage of materials and components.At present,with the continuous progress of research method and experiment facility,the material damage research becomes more and more thorough,and the meso-damage methods based on the evolution of internal structures of materials have become the main direction of the damage mechanics research.However,there are relatively rare reports about the impact of the meso-structure of materials and components on its mechanical properties,and also,there are few researches on the quantitative relationship between defects and mechanical properties.Therefore,in this paper,based on the mesoscopic structure of materials and components,combined with the finite element method,the damage was studied though both sides of the evolution of internal structure and the mechanical properties.The following main works were carried out in this paper:1.A series of experiments were performed for 6061 aluminum alloy under different cycles of asymmetrical stress cyclic loading.Then,the 3D-model was reconstructed by using internal tomography of working segments,which was obtained by XCT scanning test.Furthermore,combined with ABAQUS FEA software,the damage was evaluated for 6061 aluminum alloy.The results show that the geometric defects occurred on the surface and inside of the component during cyclic loading;The concentrated effect of stress mainly occurred at the location of defects;The damage variable represented by young's modulus increased with the number of cyclic loadings,however,the range of damage variable was relatively small.2.Based on in situ X-ray scanning test during asymmetrical stress cyclic loading experiment,combination with FEA method,the fatigue damage was studied for 7020 aluminum alloy welded joint.It is found that the failure of welded component was mainly caused by residual geometric defects like cracks and holes in the weld toe;The damage variable characterized by young's modulus was more obvious throughout the whole cyclic loading process,so it can describe the evolution of damage reasonably,furthermore,this kind of damage variable can be achieved by the finite element method easily.3.Uniaxial tensile test and finite element simulation were carried out on the 3D printed PLA specimen contained with different kinds of inner holes.The results show that compared with the specimen without hole,there were a certain improvement on the tensile strength for the components with inner hole,and with the increase of the hole volume,the influence of the spherical hole on the tensile strength was greater than that of the ellipsoidal hole under the same volume;However,the holes could decrease the ductility of the component;Due to the particularity of 3D printing path,orthotropic constitutive model can describe the deformation behavior of 3D printed components with inner holes better.