Investigation On Dynamic Behavior Of Cellular Titanium Subjected To Impact Loading

As a new type of structural engineering material,cellular titanium with regular pores can be used widely in military and civilian and other fields with its high specific strength,strong design ability,excellent energy absorption performance.The studies of this kind of materials have become one of the hottest research filed nowadays.Working as an energy absorbing and cushioning material,it's inevitable to withstand impact loading with dramatically changes,such as collision,explosion,impacting and other dynamic loads.Therefore,it has a great value of theoretical and practical using to study the dynamic properties of cellular titanium.In this thesis,a new type of cellular titanium material with regularly distributed cylindrical pores was prepared using TA2 as the matrix material.By combining experimental research with numerical simulation and theoretical analysis,the stress-strain relation,compression properties,strain rate effect and energy absorption abilities of cellular titanium with different porosities are studied,and the results can provide some theoretical reference for engineering application.The major work of this thesis is summarized as follows:1.By using electronic universal material testing machine and a Split-Hopkinson pressure bar system,the quasi-static mechanical behavior and the dynamic properties of cellular titanium with different porosities are studied.The influence of strain rates and porosities on stress-strain relation and yield strength of cellular titanium is analyzed and compared,and the relevant empirical formula is given;The compressive deformation mechanism of cellular titanium with regular pores under strain rate10^-32?10³ s^-1is discussed;the phenomenological constitutive model of cellular titanium based on experimental results is built,and fits well the experimental curves.2.The dynamic mechanical properties of cellular titanium with different porosities under different impacting velocities are investigated using one-stage light gas gun.The stress-time relationship of shock wave propagation in cellular titanium samples is obtained and the peak stress attenuation properties is discussed.The Hugoniot relation of cellular titanium is calculated and the corresponding high pressure equation of state is given.The Lagrangian method is used to simulate the dynamic constitutive curves of different Lagrangian position in cellular samples.The deformation of pores in cellular samples is analyzed by using optical microscope cross-section photos,and the deformation mechanism under strain rate10⁴¹0⁵ s^-1 is discussed.3.Numerical analysis is used to study the stress-strain relation and energy absorption of cellular titanium with different porosities.The representative volume element is used to build a numerical model according to the cellular titanium samples used in the experiments,and the stress-strain curves under dynamic loading are obtained,which are compared with the experimental results to validate the verification of numerical results.The stress-strain curves of different porosities under different strain rates loading are obtained,and the corresponding energy absorption properties are discussed.The total energy absorption volume schemes and the energy absorption efficiency schemes are given,the porosities effect,strain rate effect and pore size effect is analyzed separately.4.The consititutive modle of cellular titanium is built by combining the macroscopic properties of the matrix material and the microscopic analysis of pores.Based on the modified KHL model which considering the work hardening,strain rate,porosity and temperature effect of the matrix material,and combining with traditional Gurson model,a new dynamic constitutive model of cellular titanium is built.The expression of dynamic constitutive model in condition of axial compression is given,and so is the porosity evolution law.Effect of crack on porosity is considered in a modified dynamic constitutive form.The prediction curves of dynamic constitutive model are compared with experimental curves and numerical curves,the results show a good agreement in accuracy and tendency.