Dynamic fracture experiment of laminated glass and its considerations.

Square plates of laminated glass, whose interlayer is the polyvinyl butyral, are impacted transversely by a circular steel ball. The impact critical energies Uc and Up, which are the energy to initiate a crack in the outerlayer glasses and penetration energy of the ball, are measured by changing the dropping height of the ball. The static bending strength and Uc are dependent on the total thickness T of glass in the laminated glass. But, Up is independent of T and dependent on the thickness of the interlayer. In the laminated glass, the crack initiates from the glass of the impact side, and the next cracks initiate from the glass of the side on the reverse of the impact side. The penetration fracture of the laminated glasses consists of three steps. The first step is until initial cracks initiate in the outerlayer glasses, the second step is the bending fracture of the laminated glass, and the third step is the fracture due to shearing of the interlayer.