Dynamic characterization of brittle fracture is possible by relating the instantaneous stress-intensity factorK(t) to the velocity of propagation of the crack. High-speed photographic systems are employed with photoelastic methods to obtain a sequence of isochromatic-fringe patterns representing the state of stress associated with the propagating crack. Methods for determiningK(t) from these isochromatic patterns are reviewed.

Dynamic photoelastic studies of fracture

Current understanding of dynamic fracture mechanisms and the methods of modeling are reviewed critically. Experimental methods used in dynamic fracture investigations and key experimental observations are reviewed. This is followed by a critical review of the dynamic fracture models. Mechanistic and phenomenological models as well as discrete and continuum models and their ability to reproduce experimental results are discussed.

Dynamic Fracture of Nominally Brittle Materials

Dynamic fracture toughness of Homalite-100 determined by T. Kobayashi and Dally are compared with those previously obtained by the authors where similarities in the two results for single-edged-notch specimens of various configurations are noted. Dynamic fracture toughness of Araldite B obtained by Kalthoff, Beinert and Winkler and those of Homalite-100 obtained by the authors are then compared and, again, similarities in the two results and, in particular, the scatters in experimental data for wedge-loaded DCB specimens of different sizes are found. All three teams of investigators used static near-field solution to compute the dynamic stress-intensity factors from recored dynamic isochromatics or dynamic caustics. Errors generated through this use of static near-field solutions, as well as through the use of larger isochromatic lobes, are thus discussed.

Dynamic fracture toughness of Homalite-100: Dynamic fracture toughness of Homalite-100 determined by T. Kobayashi and Dally, as well as those of Araldite B by Kalthoff, Beinert and Winkler, are compared with those of the authors' previous results. Errors generated through the use of static near-field crack-tip stresses for evaluating dynamic stress-intensity factor are also discussed

Two-parameter methods of fracture analysis for determining the stress-intensity factor from photoelastic isochromatic-fringe data were critically reviewed. The methods of Irwin, Bradley and Kobayashi, and Smith were developed in detail and differences in the three approaches were noted. Theoretical fringe loops were generated for a crack of length 2a in a semi-infinite plate with biaxial loading. These fringe loops were used to compare the three analysis methods and to determine the accuracy of each method.

A critical review of methods for determining stress-intensity factors from isochromatic fringes

The enrichment of the extended finite element method (XFEM) by meshfree approximations is studied. The XFEM allows for modeling arbitrary discontinuities, but with low order elements the accuracy often needs improvement. Here, the meshfree approximation is used as an enrichment in a cluster of nodes about the crack tip to improve accuracy. Several numerical examples show that this leads to more accuracy for stress intensity factors computations, and to the capability to capture the branching point of a propagating crack from the stresses.

Dynamic fracture with meshfree enriched XFEM

: Fracture dynamics of Homalite-100 plates is discussed in the context of linear theory of fracture mechanics. Dynamic photoelasticity is used for dynamic analysis and finite element method is used for static analysis. Static and dynamic strain energy release rates and kinetic energy release rates for constant velocity, accelerating and decelerating cracks are determined for tension loaded and impacted pretensioned plates. (Author)

W B Bradley

Papers

Fracture dynamics of homalite-100 sheets