U档案编号：NO．57 目击地点：波兰，奥伯莱

备注：“2004年1月29日，在我去幼儿园接6岁的孩子放学回家的路上看到天空中有个东西，我抓过车上的一次性相机透过挡风玻璃拍下了一张，我又跳下车拍了第二张，然后物体就不见了。我一共拍了两张照片。对我来说它可能是UFO，或者还可能有其他解释？     

Dynamic Response Analysis of Bird Strike on Aircraft Windshield Based on Damage-modified Nonlinear Viscoelastic Constitutive Relation

Damage-modified nonlinear viscoelastic constitutive equation and failure criterion are introduced and the three-dimensional incremental forms are deduced based on the updated Lagrangian approach. A simple tensile test model and a split Hopkinson pressure bar model are built to verify the accuracy of the subroutine implemented within the non-linear finite element program LS-DYNA. A numerical model of bird strike on windshield is established to study the responses of windshield under three different bird velocities at three sites. The bird is represented by a cylinder with a hemisphere at each end and the contact-impact coupling algorithm is used in this study. It is found that the implemented subroutine can properly describe the mechanical behavior of polymethyl methacrylate under low and high strain rates and large deformation, and can be used validly.