Papers by Author: Li Li Wang

Abstract: At high strain rates, the dynamic response of concrete, a heterogeneous material with damage, was experimentally studied under (1) one-dimensional strain state at high pressures from 1 to 4 GPa by using a one-stage gas gun and (2) one-dimensional-stress state by using the SHPB technique. The main results are given and discussed. The results indicate that the effects of strain rate, stress-state and damage evolution should be considered in studies on the nonlinear impact behavior of concretes. A damage-modified visco-elastic model (ZWT model) is proposed for concrete C30.

Abstract: The dynamic mechanical behavior of C30 concrete under a wide range of strain rates from 10-4s-1 up to 102s-1 is studied. According to Johnson-Cook’s strength model, the strain rate coefficients and related material constants of C30 concrete subjected to large strains, high strain rates and high pressures are determined experimentally: C=0.34*10-1, A=1.05, B=1.65, N=0.76, TC =3.162MPa, fc’=39.2MPa. The damage evolution for C30 concrete is a rate-dependent process, which can be formulated to a rate-dependent damage evolution law in a simple form for engineering application. When ε > ε th, ( ) 1 D th D = K ε&α − ε −ε . The corresponding dynamic coefficients of C30 concrete are also obtained from impact experimental results: KD=530.2, a=0.83. Due to a<1, the damage evolution corresponds to an impact toughening process that coincide well with the dynamic experimental results for C30 concrete.

Abstract: In the framework of percolation theory, a simple void-coalescence model combined with the constitutive relations for describing the stress relaxation and material softening during the void-coalescence process, name as the percolation-relaxation (P-R) model, is proposed to describe the dynamic tensile spallation of ductile metals. A critical damage is introduced and coupled into the model to identify the onset of the void coalescence. Mesoscopically, the critical damage corresponds to the critical intervoid ligament distance (ILD), indicating the start of transition from the void-growth to the void-coalescence.

Abstract: A new dynamical measurement technique that combines PVDF film piezoelectric gages with resistor strain gages in conventional SHPB is developed to study the dynamical mechanical behavior of low-impedance aluminum foam. The average value of the stresses measured by PVDF gages from the front face and the back face of the specimen at each time is taken as the effective stress history of the specimen. This effective stress history is combined with the measured axial strain history in the specimen by eliminating time t. Then the initial part of the stress-strain relationship of the material can be determined reliably. From its slope, the dynamical Young’s modulus of low-impedance aluminum foam can be determined. For the aluminum foam with a density of 1.2×103 Kg/cm3 at a given strain rate (ε& =814/s), we get: E =1.15 GPa, G=0.44GPa.