Crack initiation and propagation in laminated composite materials

Abstract

PVB laminated glass is a kind of typical laminated composite material and its crack characteristics are of great interest to vehicle manufacturers, safety engineers, and accident investigators. Because crack morphology on laminated windshield contains important information on energy mitigation, pedestrian protection, and accident reconstruction. In this chapter, we investigated the propagation characteristics for both radial and circular cracks in PVB laminated glasses by theoretical constitutive equations analysis, numerical simulation, experiments, and tests of impact. A damage-modified nonlinear viscoelastic constitutive relations model of PVB laminated glass were developed and implemented into FEA software to simulate the pedestrian head impact with vehicle windshield. Results showed that shear stress, compressive stress, and tensile stress were main causes of plastic deformation, radial cracks, and circumferential cracks for the laminated glass subject to impactor. In addition, the extended finite element method (XFEM) was adopted to study the multiple crack propagation in brittle plates. The effects of various impact conditions and sensitivity to initial flaw were discussed. For experiment analysis, crack branching was investigated and an explicit expression describing the crack velocity and number of crack branching is proposed under quasi-static Split Hopkinson Pressure Bar (SHPB) compression experiments. And the radial crack propagation behavior of PVB laminated glass subjected to dynamic out of - plane loading was investigated. The steady-state cracking speed of PVB laminated glass was lower pure glass, and it increased with higher impactor speed and mass. The supported glass layer would always initiate before the loaded layer and the final morphologies of radial cracks on both sides are completely overlapped. Two different mechanisms of crack propagation on different glass layers explained the phenomenon above. Then further parametric dynamic experiments study on two dominant factors, i.e., impact velocity and PVB thickness are investigated: Firstly, a semiphysical model describing the relationship between the maximum cracking velocity and influential factors was established; Then the Weibull statistical model was suggested considering various factors to describe the macroscopic crack pattern in this chapter; Finally, the relation between radial crack velocity and crack numbers on the backing glass layer and the relation between the crack length and the capability of energy absorption on the impacted glass layer were proposed.