Impact damage resistance of several laminated material systems

The impact damage resistance of several laminated materials systems (AS4/3501-6, IM7G/X8553-50, and A3705H/3501-6 graphite/epoxy, and wet layup glass/epoxy) was studied by conducting impact tests, measuring the force-time response, and determining the damage caused by different impactor velocities. Various laminate configurations were utilized to better understand the role of stacking sequence and fiber orientation. The results indicate that force is a key parameter in the assessment of impact damage resistance, particularly the force needed to cause incipient damage. Incipient damage is generally in the form of matrix cracks in laminates made from unidirectional tape. This is followed by delamination at the interface with the cracked ply. This damage mode does not change when the material system is changed, although the force at which the damage occurs is affected. Furthermore, ply angle does not change the damage modes that occur, although it does affect the extent of the damage. However, the form of the material, that is, fabric vs unidirectional ply, does affect the damage that occurs. By its woven nature, fabric naturally inhibits the formation of long matrix cracks. This also restricts the amount of delamination that occurs. This in turn results in fiber breaks occurring as the energy dissipated by delamination in other configurations must be dissipated by another mechanism, fiber breakage, in this case. A discussion of the results in terms of the assessment of damage resistance is provided. Needs to provide better understanding are identified.