On the measurement of dynamic fracture toughnesses - a review of recent work

The influence of dynamic effects on test procedures for measuring the crack arrest toughness and the impact fracture toughness is analyzed. It is shown that these dynamic effects can be significant: for cracks at arrest the stress condition is still dynamic and not static although the crack velocity has become zero. Dynamic effects become small only for small crack velocities or small crack jumps or for specially designed specimens. It is shown that the stress intensity factor history for cracks under impact loading cannot be adequately derived from instrumented impact data via static evaluation procedures. Only for large times to failure, resulting for small impact velocities and/or ductile material behavior do static approaches represent acceptable approximations. Reliable crack arrest and impact fracture toughness data can only be obtained by evaluation procedures which take the dynamic effects into account, e.g. by utilizing the reduced dynamic effects crack arrest test specimen or by applying the concept of impact response curves. 36 ref.--AA