Investigation On The Dynamic Mechanical Behavior And Protective Capability Of Laminate Composites Ti/Al₃Ti

With the development of aerospace industry and anti-armor technique,higher properties,such as flexibility,high performance and multi-function,are needed by the protective materials.Recently,the appearance of Ti/Al3Ti Metal/Intermetallic Laminate(MIL)composite provides a new way for the research of protective materials.The composite is composed by the alternative layers of Ti and Al3Ti,which integrates the constituent phases with dissimilar properties into novel multiphase composite material.Under the impact loading,more energy is absorbed by the laminate material due to its unique toughening mechanisms of bridge effect,brittle cracks,delamination and crack deflection.Most studies about this composite focus on its preparation and mechanical properties at low strain rates.But according to its application background,it is necessary to understand its failure process and toughening mechanisms under dynamic loading.The monothetic Al3Ti and Ti/Al3Ti MIL composites with different layer structures were fabricated using Ti and Al foils through vacuum sintering process.The residual stress produced due to the difference of thermal expansion coefficients between Ti and Al3Ti has an effect on stress distribution under external load.On the basis of uniform strain model,the residual stress distributions of Ti/Al3Ti laminate composite at different directions were presented through the established uneven strain model.The effects of residual stress on mechanical response of the MIL composites with different volume fraction of Ti were also analyzed,and the optimized volume fraction that made the best use of the material was provided then.There is an abundance of data available for titanium,but this is not the case for the matrix of Al3Ti.The quasi-static and dynamic compression tests of the synthesized Al3Ti were performed on Instron machine and Split Hopkinson Pressure Bar(SHPB)experimental system,respectively.The mechanical responses and failure modes under the strain rates among 0.0001/s to 2000/s were analyzed.The result of quasi-static compression test demonstrated that the monothetic Al3Ti was a typical brittle material,of which fracture occurred without any significant plastic deformation.In addition,the material strength changed with different loading strain rate.According to the above characteristics of Al3Ti,the JH-2 constitutive model was selected to describe the mechanical responses of Al3Ti.The JH-2 constitutive model parameters of Al3Ti were determined by the experimental data for the first time,which laid the foundation for the analysis of mechanical responses and numerical simulation of monothetic Al3Ti and Ti/Al3Ti MIL composite.The mechanical responses of the Ti/Al3Ti MIL composite under dynamic compressive load were investigated via SHPB system.The compressive strength of the laminate composite was about 1200MPa,which was closed to the strength of Al3Ti.But the failure strain of the composite was improved greatly,which was almost five times of the Al3Ti.Different with the serious smash for the Al3Ti,the Ti/Al3Ti MIL composite fractured at the angle of 45 degrees.The corresponding numerical model of the experiment was established,and the energy absorbing during the impact process of Ti/Al3Ti MIL composites with different volume fraction of Ti was calculated.The result demonstrated that the MIL composites have higher energy absorbing abilities than monolithic Al3Ti,and most energy was absorbed by the MIL composite when the volume fraction of Ti is 20%.The failure modes and mechanical responses of Ti/Al3Ti MIL composite under dynamic bending load were studied via SHPB loading three-point bending specimen.The step-like characteristic was found in its load-displacement curve,which demonstrated that the material still had damage-tolerance ability even reached the strength limit.In order to directly understand the dynamic failure process of specimen,the hybrid experimental-numerical technique has been performed to simulate the test process.The simulated load-displacement curve had a good agreement with the experimental result.The fracture works of Ti/Al3Ti MIL composite that calculated through the integration of the simulated load-displacement curves was about five times of Al3Ti due to the effects of many toughing mechanisms.The ballistic impact tests were conducted in the Ti/Al3Ti MIL composite to calculate the specific energy absorption.The failure modes of the material under severe dynamic load were investigated by finite element method,and a good agreement of residual velocity with the experiment was obtained.The effects of projectile velocity and the laminate structure,such as volume fraction of Ti and layer number,on the damage distribution and the protective performance of the Ti/Al3Ti MIL composite were then analyzed through the same method.