Mechanical Properties And Failure Mechanism Of Ti/Cu Laminated Composite

With the rapid development of modern science and technology,the requiments for material are extremely strict and high.The idea of laminated metal composite materials is derived from the shell structure in nature.Due to the unique mechanical property,laminated material has been a hot area of research topic for several years.The failure of material is a complex process,which contains damage initiation,crack propagation and ultimately complete destruction.Note that,the laminated structure has a unique inhibitory effect on crack propagation.This paper focuses on the mechanical properties and failure mechanism of laminated metal composite under static loading.Ti/Cu laminated composite which acquires advantages of both Ti and Cu,as a new type of electrode material,has a fairly bright application prospect in electrolytic extraction and electrochemical industry.The contents of the present thesis mainly include: Ⅰ)preparation and characterization of Ti/Cu laminated composite;Ⅱ)tensile test at room temperature and the pre-notched three-point bending test;Ⅲ)failure behavior based on finite element method.The main works of this thesis are as follows:(1)The microstructure of the Ti/Cu laminated composite was observed by optical microscope(OM),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS).The results show that the interface was well bonded without obvious cracks,pores,delamination or large melting zone.The heat affected zone is small and the interface is straight.At the interface,there are less intermetallic compounds comparing with other welding methods and the width of the mixing region is about 50μm.Metallurgical and mechanical bonding occurred during the preparation of Ti layer and Cu layer.(2)The mechanical properties of Ti/Cu laminated composite were studied by microhardness analysis,tensile test and the pre-notched three-point bending test.The results show that the hardness of each component is higher than that of the raw material and the hardness at the interface is between two sides.The process of tensile test exhibited a typical stress-strain curve of homogeneous metals but the ultimate tensile strength is much higher than the theoretical strength of the titanium-copper composite based on the mixing rule;The crack trajectory in the three-point bending test was a typical curve that can be observed in laminated composite.(3)The deformation and failure mechanism of Ti/Cu laminated composite under tensile and bending loads were studied.The results show that in the tensile test,the failure of Ti/Cu laminated composite is due to the coupling effect of multi-direction stress.The main strengthening mechanism is work hardening and interface protection effect,which was caused by underwater explosive welding.In the pre-notched three-point bending test,the fracture of Ti/Cu laminated composite is the results of multiple damage effect and failure effect.A unique failure pattern of wave propagation trajectory is formed in the Ti/Cu laminated composite.In addition to the internal toughening mechanism of grain refinement,different external toughening mechanisms can be acquired by different types of loads.(4)The failure behaviors of Ti/Cu laminated composite under tensile and bending loads were analyzed by finite element method.The complex stress state change can be simulated by Johnson-Cook constitutive model during tensile process of Ti/Cu laminated composite.The numerical simulation result can reflect the failure mechanism of the actual experiment during tensile test.The effects of different interface strengths were analyzed on the crack propagation and bearing capacity of Ti/Cu laminated composite.The method of XFEM-CZM coupling was used to realize simulation of crack growth and interface debonding.The crack propagation process under bending load was explained,which was consistent with the failure mechanism in the experiment.