Fracture mechanics of glass panels subjected to low velocity missile impact

The windborne debris during severe windstorms often slams into glass windows, resulting in the property damage and personal injury. Depending on its mass and stiffness, the debris is generally classified as small hard missiles and large soft missiles. The former consists of small pieces of rock, tar and roof gravel while the latter consists of pieces of wood from collapsed house roofs and trees. Laminated glass can help prevent breaching of the building glass windows and thereby maintain the integrity of the building envelope. In such cases, the outer glass ply is sacrificed and the polymer interlayer and the inside glass ply are kept intact.; The stresses in laminated glass impacted by a 2.05 kg wooden cylinder are calculated using the finite element method. The effects of geometry, material properties and loading parameters on the maximum principal stress in the inside glass ply are presented. A finite element code based on the strain energy release rate criterion has been developed for predicting the failure mode of monolithic and laminated glass under small hard missile impacts. The results show that for a thick glass plate, the fracture initiates just outside the missile-glass contact region following the Hertzian contact theory. For thin plates, however, the cracks initiate on the surface opposite to the impact site governed by flexural stress. This method is then extended to study the fracture behavior of laminated glass panels subjected to large soft missile impact. For this case, it is shown that the cracks may initiate at the bottom surface of either plies depending on the end-shape of the missile, the thickness of the outside glass ply and the polymer interlayer.