MECHANICAL CHARACTERIZATION OF POLYMERS AND COMPOSITES WITH A SERVOHYDRAULIC HIGH-SPEED TENSILE TESTER

This study is concerned with the measurement of the mechanical behaviour of polymers and composites at intermediate strain rates. It illustrates with two examples, the application of a high speed servohydraulic testing machine and a newly designed optical extensometer. In the first part of the study, the dynamic nature of high speed tensile testing with servohydraulic apparatus is discussed, and a damping technique is proposed. In the second part, this technique has been applied to the measurement of the tensile properties of annealed and unannealed neat PEEK at strain rates between 3 x 10(-2) and 2.4 x 10(2) s-1. Both materials show increased yield stress and drawing stress with increasing strain rate. However, annealed specimens have been shown to exhibit superior mechanical properties. In the third part, mode I delamination tests have been performed on unidirectional IM6/PEEK composites at nominal strain rates between 1 x 10(-6) and 8 x 10(-1) s-1. At the higher velocities the analysis is performed by means of FFT filtering. A moderate reduction in interlaminar fracture toughness was found with increasing loading rate.