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

Abstract

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.

Thermal decohesion model validity for polycrystalline advanced ceramics

“…It was shown (Kalthoff, 1985) that the dynamic effects at the crack tip were significantly smaller than the load measured at the striker contact point. This means that expensive instrumentation of the specimen was necessary and the load-time trace from the crack-tip strain gauge must be used for high rate tests (Carolan et al, 2010).…”

A combined experimental–numerical investigation of fracture of polycrystalline cubic boron nitride

“…[20] showed that the dynamic effects at the crack tip were significantly smaller than the load measured at the striker contact point. It follows then, that there exists a unique relationship between the dynamic fracture toughness of the material and the time to fracture initiation.…”

Effect of loading wedge length on the propagation of stress pulse in Hopkinson bar apparatus

“…However, the Hopkinson bar loading experimental technique that can be used to study various dynamic fracture properties of materials under a stress-intensity factor rate ∼ 10 6 MPa m 1/2 s −1 are still being developed [2][3][4][5][6][7][8]. The one-bar (one incident loading bar)/three-point bending (3PB) impact setup [9][10][11][12][13][14][15][16] is currently the most popular setup used to determine the dynamic fracture toughness of materials under stress wave loading, since this loading configuration has some advantages: (1) the loading rate acquired in such one-bar/3PB loaded fracture test is higher than that in Charpy impact test [17][18][19][20][21][22][23][24][25][26]; (2) the dynamic response of fracture specimen can be determined via *Corresponding author: tel. : +86 451 82569890; e-mail address: fengchunjiang@hrbeu.edu.cn strain signals recorded by the strain gauges mounted on the loading bar; and (3) a relatively large fracture specimen can be used for measuring the valid plane strain fracture toughness [1,[27][28].…”