Chen Danian

An interrupted tensile testing at high strain rates for pure copper bars

A high-speed tensile facility (HSTF) invented by us was applied to interrupting the tests for pure copper specimen bars controlled locally at different levels of elongation. It was realized to isolate and identify the different stages of the dynamic fracture process of the pure copper specimen bar under impact tension. The results of scanning electron microscopical (SEM) investigation of the recovered pure copper specimens show that the void evolution near the surface of the minimum cross-section of the necking area is more severe than that at the middle of the necking area, which may be connected with the findings discussed by Alves and Jones [J. Mech. Phys. Solids 47, 643 (1999)]. The constitutive models in a certain range of strain determined from the tensile split Hopkinson bar optimized by us were employed and adjusted in numerically simulating the large deformation of the pure copper specimen in the interrupted tensile tests on HSTF. The dependence of the instability strain of thermoviscoplastic mat...

Study on constitutive relations and spall models for oxygen-free high-conductivity copper under planar shock tests

It is indicated that the constitutive relations for shear modulus G as functions of thermodynamic state were not given in the Johnson-Cook model and the Zerilli-Armstrong model while the constitutive relations for yield strength Y as functions of strain and strain rate were not given in the Wallace model and the Straub model. Seven constitutive models are constructed based on Y∕G=constant and on G∕B=constant (B-bulk modulus), respectively. The variations of longitudinal stress, transverse stress, and yield strength of oxygen-free high-conductive (OFHC) copper with time under planar shock loading are obtained using the manganin stress gauges and compared with the predicted results by the constructed seven constitutive models. It seems that the pressure, density, temperature, and plastic strain dependence of the yield strength for OFHC copper subjected to planar shock loading is essential to the constitutive description. Planar spall tests for OFHC copper are also performed and the void coalescence-based spall model presented by the authors are applied to numerical simulations of planar spall tests including tests given by Seaman et al. [Phys. Rep. 147, 253 (1987)]. The Steinberg-Cochran-Guinan constitutive model is proved appropriate to the planar shock loading and is adopted in the numerical simulations of planar spall tests.It is indicated that the constitutive relations for shear modulus G as functions of thermodynamic state were not given in the Johnson-Cook model and the Zerilli-Armstrong model while the constitutive relations for yield strength Y as functions of strain and strain rate were not given in the Wallace model and the Straub model. Seven constitutive models are constructed based on Y∕G=constant and on G∕B=constant (B-bulk modulus), respectively. The variations of longitudinal stress, transverse stress, and yield strength of oxygen-free high-conductive (OFHC) copper with time under planar shock loading are obtained using the manganin stress gauges and compared with the predicted results by the constructed seven constitutive models. It seems that the pressure, density, temperature, and plastic strain dependence of the yield strength for OFHC copper subjected to planar shock loading is essential to the constitutive description. Planar spall tests for OFHC copper are also performed and the void coalescence-based sp...

Sound Velocity and Release Behaviour of Shock-Compressed LY12 Al

A velocity interferometer system for any reflector (VISAR) is used to measure the sound velocity of LY12 Al shock-compressed to peak pressures of 20, 32, 55 and 71 GPa. Unloading wave velocities from these pressures are obtained from the observed particle velocity profiles at the LY12 Al/LiF window interface; and the longitudinal, bulk and shear sound velocities at the initial Hugoniot state are well determined. The histories of stress, strain, density or volume, and particle velocity along the release paths are calculated by the impedance-matching method based on the unloading sound velocity data. It is revealed that the release behaviour of shocked LY12 Al departures obviously from the elastic perfectly-plastic response.

A dynamic investigation of observable void growth and coalescence in pure copper sheets

A combined experimental, theoretical, and numerical investigation of dynamic growth and coalescence of drilled voids in pure copper sheets was performed to visualize void growth and coalescence in a controlled matter. The dynamic constitutive model of the pure copper determined from the first tension loading in the optimized tensile split Hopkinson bar (TSHB) tests for pure copper sheets was adjusted in numerically simulating the large deformation of pure copper sheets generated by the multi-tension loading in the TSHB tests and recorded by a high speed camera. The dynamic growth, coalescence, and evolution post coalescence of drilled simplest cluster voids in pure copper sheets subjected to the multi-tension loading in the TSHB tests were recorded by the high speed camera and simulated by using the adjusted constitutive model of the pure copper and the different criteria for void coalescence. Based on Bandstra’s work [J. P. Bandstra et al. Mater. Sci. Eng. A 249, 46 (1998); J. P. Bandstra and D. A. Koss,...

A Novel Impact Tension Testing for OFHC Copper Bars under Local Strain Controlled

A novel high-speed tensile facility (HSTF) with special fixture is applied to research the dynamic failure characteristics of oxygen-free high-conductivity (OFHC) copper bars at different levels of strain. The experimental tests are numerically simulated involving void evolution. It is indicated that the localized strains at necking region computed with the adjusted Johnson—Cook model and the Zerilli—Armstrong model are consistent with the experimental results.

Measurement of Critical Impact Velocity of Copper in Tension

Critical impact velocity (CIV) of oxygen-free high-conductivity (OFHC) copper is experimentally measured with a novel facility in a gas gun system. The results are compared with the theoretical predictions using the typical constitutive relations, and the measured CIV value is much lower than the predictions. The difference of physical mechanisms in experiment and in theoretical calculation is discussed. It is suggested that the reduction of CIV in experiment would be related with the damage evolution in tensile copper that needs to be considered in the computation model.

Mechanical Yielding and Strength Behaviour of OFHC Copper in Planar Shock Waves

It is necessary to study the validation of strength models under planar shock loading in view of the fact that strength models for metals obtained at moderate strain rates are often used in the numerical simulations of shock wave phenomena. The variations of longitudinal stress, transverse stress and yield strength of oxygen-free high conductance (OFHC) copper with time under planar shock loading are obtained by using the manganin stress gauges and compared with the predicted results by the constructed seven constitutive models based on Y/G=constant and on G/B=constant (Y the yield strength, G the shear modulus, B the bulk modulus), respectively. It seems that the pressure, density, temperature and plastic strain dependence of the yield strength for OFHC copper under planar shock loading is essential to the constitutive description.