Evolution Analysis Of Mechanical Properties Of Polycrystalline Beryllium Under Cyclic Loading At Room Temperature,Based On Damage Mechanics

Evolution of mechanical properties of polycrystalline beryllium at room temperature were studied,based on uniaxial tensile tests with unload/reload cycles.It includes:research on evolution of elastic modulus;research on evolution of dissipation energy,recovery energy and other parts energy,respectively;building damage evolution model of polycrystalline beryllium according to the theory of elastic modulus,the theory of cumulative dissipative energy and model of damage energy dissipation rate,respectively;analyzing compositions of the recovery deformation and its evolution law in unloading processes.The results show that:(1)Values of elastic modulus,dissipation energy and recovery energy vary monotonically with the deformation increasing,respectively(elastic modulus deceasing,while recovery energy and dissipation energy increasing);the change process is divided into two parts,corresponding to yield stage and strengthening stage,respectively.In yield stage,each mechanical quantities mentioned above display the more significant trend of change.(2)As the fracture taking place,the damage variable defined by the theory of cumulative dissipative energy displays a higher value consistency—fluctuation range of the fracture critical value is about ±%,by contrast,the value fluctuation of damage variable in the classical form,defined by elastic modulus,is from-12%to 11%,the value fluctuation of residual elastic modulus is about ±5%,the value fluctuation of tensile strength is from-18%to 17%,and the value fluctuation of elongation is from-24%to 21%,respectively.So it may be more suitable and reasonable to choose the damage variable result from the theory of cumulative dissipative energy as the failure condition.(3)Recovery effect can be divided into two parts:elastic recovery and inelastic recovery.Values of the inelastic recovery deformation increase monotonically with the plastic deformation increasing,so do each kind of recovery energy(energy of elastic recovery,inelastic recovery and total recovery)with corresponding recovery deformation(deformation of elastic recovery,inelastic recovery and total recovery).There is a power function relationship between inelastic recovery deformation and plastic deformation,and each kind of recovery energy is approximately piecewise-linear with corresponding recovery deformation,respectively.