Investigation On The Cracking Mechanism Of Laminated Glass Under Dynamic Loading

PVB (Polyvinyl butyral) laminated glass has been widely used in automotive andconstruction industry serving as a critical safety structure material. The crack on thePVB laminated glass contains abundant accident information. In this paper, adrop-weight combined with high-speed photography experiment devices are set up toconduct out-plane impact test of PVB laminated glass panel. Results show that thefacture of the PVB laminates subject to impact loading follows such sequence:(1)Initiation of radial cracks on the backing glass layer;(2) Initiation of radial cracks onthe impacted layer;(3) Initiation of circular cracks on the impacted layer. Velocity timehistory curves of both radial and circular cracks are recorded and analyzed incombination with the theory of stress waves to understand the crack initiation andpropagation mechanism.The propagation characteristics of the radial cracks on the two glass layers arecompared. Results show that the radial cracks on the backing and impacted glass sheetsare completely overlapped, with the sequence that cracks on impacted plate appear longafter the full growth of those on backing plate. However, it is experimentally discoveredthat cracks on two glass sheets generate along the different cracking propagation paths,due to the different cracking mechanisms: the cracks on backing layer are motivated byin-plane stress concentration while the one on impacted layer are caused by stressconcentration in depth direction brought by each generated crack on backing layer asinitial flaw. Thus, a re-initiation criteria model is suggested to describe the transversecracks on impacted layer. Further, a qualitative relationship between the inter-platecracking delay and two parameters (i.e. the interlayer thickness and loading speed) isconcluded, which further confirms the new fundamental driving mechanism of in-planecracking on impacted glass plate.In addition, the propagation characteristics of the radial cracks and the circularcracks are compared as well. There exists fundamentally difference between the radialcrack and the circular crack on both the cracking law and the mechanism. The radialcracks probably result from the transmitting and reflection of the longitudinal stresswaves caused by the impact loading. While the circular cracks, which only exist on the impacted glass layer, nuclear under the influence of Rayleigh waves. A semi-physicalmodel is established describing the relationship between the maximum crackingvelocity and influential factors (i.e. the interlayer thickness and loading speed)quantitatively. The good agreement between the parametric experiment data and thefitted data proves the model to be dependable.In the end, a Weibull statistical model on the macroscopic crack pattern issuggested based on considerable quantities of repeated experiments. This study furtherexplains the in-plane cracking mechanism of the brittle layered material under dynamicloading, which provides a reference for the laminated glass design.