Further studies on dynamic crack branching (original) (raw)
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Further Studies on Dynamic Crack Curving
The elasto-dynamic stress field surrounding rapidly propagating cracks in thin polycarbonate, double edged crack tension specimens were analyzed by dynamic photoelasticity using a 16-spark gap Cranz-Schardin cam.era system. Crack curving was observed in rwo slarted double edged crack specimens and in two offset parallel double edged crack specimens. In another test, the crack ran straight between two symmetrically located twin cracks. Re.sults of these five tests were used to verify the dynamic crack curving criterion by Ramuiu et al. in which a reference distance of ro=1/128/pi*[K1/sigmaox*V(c,cl,c2)]** 2 from the crack tip is incorporated into the maximum circumferential stress or minimum strain energy density criteria. The critical material property for crack curving in this thin polycarbonate sheet was found to be about rc= 0.5 nim.
Mechanics of crack curving and branching ? a dynamic fracture analysis
International Journal of Fracture, 1985
-On presente un c r i t e r e de courbure de f i s s u r e fond& sur sa s t a b i l i t i ! d i r e c t i o n n e l l e a i n s i qu'un c r i t e r e de r a m i f i c a t i o n necessi t a n t un f a c t e u r dynamique d ' i n t e n s i t@ de c o n t r a i n t e de r a m i f i c a t i o n e t l e c r i t e r e de courbure.
Dynamic Crack Branching—A Photoelastic Evaluation
Fracture Mechanics: Fifteenth Symposium, 1984
The research reported in this technical report was made possible through support extended to the Department of Mechanical Engineering, University of Washington, by the Office of Naval Research under Contract N00014-76-C-0060 NR 064-478. Reproduction in whole or in part is permitted for any purpose of the United States Government.
An experimental investigation of dynamic crack propagation
Engineering Fracture Mechanics, 1983
The dynamic fracture behavior of polymethylmethacrylate (PMMA) has been investigated. The specimens were in the form of rectangular sheets with sharp notches. The elastodynamic crack tip stress field and the crack velocity were determined by the use of resistance strain gauges. An analytic expression for the dynamic crack tip stress field was used to evaluate the dynamic stress intensity factors, and the dynamic arrest toughness was also determined. The dynamic response of the stresses at the notch tip at varying loading rates was considered and some "hysteresis" fracture phenomena were observed.
Theory of dynamic crack branching in brittle materials
International Journal of Fracture, 2007
The problem of dynamic symmetric branching of a tensile crack propagating in a brittle material is studied within Linear Elastic Fracture Mechanics theory. The Griffith energy criterion and the principle of local symmetry provide necessary conditions for the onset of dynamic branching instability and for the subsequent paths of the branches. The theory predicts a critical velocity for branching and a well defined shape described by a branching angle and a curvature of the side branches. The model rests on a scenario of crack branching based on reasonable assumptions and on exact dynamic results for the anti-plane branching problem. Our results reproduce within a simplified 2D continuum mechanics approach the main experimental features of the branching instability of fast cracks in brittle materials.
Dynamic crack curving—A photoelastic evaluation
Experimental Mechanics, 1983
A dynamic-crack-curving criterion, which is valid under pure Mode i or combined Modes 1 and II ioadings and which is based on either the maximum circumferential stress or minimum strain-energy-densitY factor at a reference distance of ro from the crack tip, is verified with dynamic-photoelastir, experiments. Directional stability of a Mode I crack propaga-1 . Kx.2 2 tion is attained when ro = ~-(~--) V6 (c,cl,c2)>r~, where r~ = 1.3 mm for Homalite-lO0 used in the dynamicphotoetastic experiments.
Dynamic crack curving and branching under biaxial loading
Experimental Mechanics, 1987
A 16-spark-gap camera was used to record the dynamic photoelastic patterns of ten centrally cracked, Homalite-100 specimens which fractured under ten initial biaxial-stress ratios ranging from 3.7 to 0, some of which do not exist in normal fracture specimens. The dynamic photoelastic patterns of curved cracks were used to verify the previously developed dynamic-crack-curving criterion. Cracks which immediately curved upon propagation in three specimens under abnormally high initial biaxial loading were used to verify the static counterpart of the dynamic-crack-curving criterion under these extreme loading conditions. A previously developed dynamic-crack-branching criterion was also verified by four dynamic photoelastic results involving cracks which eventually branched under the lower initial biaxial loading.
Crack branching and arrest in environmental cracking of polyethylene
Journal of Materials Science, 1986
At intermediate K values a region where the crack speed is constant, that is, independent of K, is observed in detergent cracking of low density polyethylene. This region is terminated at high K by one of two processes: in thin specimens the crack arrests, and in thick specimens it branches. The mechanism of crack branching involves the crack front twisting and then the initiation of a new crack at the centre of the specimen. A model has been proposed to explain this mechanism and also the fact that crack arrest or branching occur at approximately the same K value. After branching the cracks continue to propagate at constant speed along paths where K, ~ 0 and if the specimen is wide enough, can branch again.