ABSTRACT
All of the above devices have been instrumented to provide both instantaneous and cumulative assessments of the impact response of materials. Not all of the above impact tests produce the same degree of information about the response of composites to an impact. Izod, Charpy, and tensile impact tests are less useful for evaluating composites because the affected impact surface is in the same plane as the surface of the part and, therefore, perpendicular to the direction of any actual impact a part may experience. Since composites are anisotropic, it is more appropriate to test them in the manner in which they are expected to perform. Instrumented free-falling balls provide a fixed level of kinetic energy to the impact site directly against the plane of the surface of a pan. The instrumented free-falling bali procedure can be used to assess the damage tolerance of composites subjected to varying levels of kinetic energy. After the ball impacts the surface it is caught before it can impact a second time. The area of impact is then examined by an ultrasonic C-scan, or x-rays to determine the extent of damage caused by the impact. Figure 2 shows the damaged area determined by an ultrasonic C-scan of a carbon fiber reinforced polyetheretherketone composite. Subsequent tensile or flexural tests are often conducted following this procedure to determine the residual strength remaining after the impact.
