On crack path stability in a layered material

Gunnars, Jens; Ståhle, Per; Wang, T.C.

doi:10.1007/s004660050207

Cited by 13 publications

(8 citation statements)

References 13 publications

(13 reference statements)

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“…Gunnars et al 12 performed the same type of experiments to study the path of non‐branching cracks growing towards an interface between the PC and a stiffer substrate. (Results from the study are also presented in Gunnars et al 13 ) They found that cracks did not follow straight paths, but deflected gradually avoiding the interface. Several of the tests in their study gave branched cracks, but these were disregarded.…”

Section: Introductionmentioning

confidence: 52%

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Dissolution driven crack branching in polycarbonate

Hejman

Bjerkén

2010

Fatigue &Amp; Fracture of Engineering Materials &Amp; Structures

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A B S T R A C T Stress corrosion, in the form of chemically assisted crack growth, in polycarbonate is examined with focus on crack branching characteristics. Cracks with finite width are observed; this is to be expected for dissolution driven cracking. The cracks branched repeatedly and crack widths before and after branching are measured. Both symmetric and asymmetric branching is found. The dissolution rate is assumed to be a linear function of the strain along the crack surface. In the literature, it is proposed that the crack width is proportional to the square of the mode I stress intensity factor. Energy considerations lead to that the sum of branch widths must equal the width of the unbranched crack. The results from this study correspond fairly well with this assumption. The branching angle is found to be 32 • ± 12 • , which is in line with results for sharp cracks reported in the literature. The mean growth direction of the branches is found to deviate slightly from the expected straight. No significant correlation between angles and crack widths is found. The scatter in results is mainly addressed to the inherent perturbation sensitivity of stress corrosion cracking. Also numerically simulations of crack branching is performed. These results show promising agreement with the experiments.

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Section: Introductionmentioning

confidence: 52%

“…Broberg, 23 meaning that a crack will follow a path where K II = 0. In numerical analysis of the experimental results, Gunnars et al , 12,13 also found that dissolution driven SC cracks grow predominantly along a mode I path. In this study, it is observed that the cracks always divide into two branches.…”

Section: Theoretical Considerationsmentioning

confidence: 91%

Dissolution driven crack branching in polycarbonate

Hejman

Bjerkén

2010

Fatigue &Amp; Fracture of Engineering Materials &Amp; Structures

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“…8. Gunnars et al (1997) presented another definition of directional instability by divergence of the initially adjacent crack trajectories as common in nonlinear dynamics. A crack path is directionally unstable, if a small path deviation d 0 at the arc length s 0 leads to greater path deviation d at a sufficiently large arc length s, such that…”

Section: Definition Of Global Directional Stabilitymentioning

confidence: 98%

Crack paths and the problem of global directional stability

Pham

Bahr

et al. 2006

Int J Fract

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Crack paths of original Griffith crack and edge crack under biaxial remote mode-I loading after different local disturbances are calculated by using integro-differential equations of first-order perturbation and numerical simulation with FEM respectively.Considering the asymptotic behaviour for large crack lengths the problem of global directional stability is reinvestigated extending the work by Melin. For the Griffith crack, correct power functions for the asymptotic path with one or both crack tips growing have been determined. The wellknown critical stress biaxiality ratio R c = 1 for the global directional stability has been obtained independently whether the crack is disturbed by local imperfections in geometry or in loading. For an edge crack the calculated critical stress biaxiality ratio for the global directional stability R c = 0.616, also irrespective of the local disturbances, corresponds to a positive T-stress and is considerably smaller than the value R > 0.95 estimated by Melin (2002). In general, cracks need not propagate asymptotically in the direction perpendicular to the largest principal stress (without crack). This is found to be due to the effect of the boundaries.Considering the initial crack growth exclusively, it is shown that the solution for crack path prediction in series expansion form as derived by Cotterell and Rice (1980) for traction-free crack faces (after correction of a misprint) is exact in the two first terms in all cases. Thus, for small crack growth the Cotterell and Rice solution is universal with respect to all loading and geometrical situations.

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“…Polycarbonate is also chosen because it has proven usable in similar studies. Gunnars et al (1994Gunnars et al ( , 1997 used this material combination to study non-branching crack propagation directions.…”

Section: Materials and Preparationmentioning

confidence: 99%

Environmentally assisted initiation and growth of multiple surface cracks

Hejman

Bjerkén

2010

International Journal of Solids and Structures

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a b s t r a c tThe initial stages of stress corrosion on an amorphous polymer is investigated. This is done by exposing stressed specimens of polycarbonate to an acetone and water solution. The surface develops two distinct features of degradation that appear on different length scales when subjected to tensile stress. Small pits form on the surface and make it rough. These pits are in the order of micrometers, and are found to be randomly distributed. They occur even without load and seem to slightly increase in number with increasing stress. In the millimeter domain, visible to the bare eye, surface cracks are formed transverse to the direction of loading. The occurrence of cracks is seen to have a positive stress threshold value, exceeding which, a linear increase of number of cracks with stress is found. The manners in which the cracks grow and coalesce on the surface are examined. It is seen that they do not meet crack tip to crack tip. Instead, they avoid each other initially and coalesce crack tip to crack side. The results are discussed in the light of mechanical considerations. A stress analysis for a few configurations of meeting cracks supports the experimental observations. With assumptions of stress corrosion crack growth and coalescence, a simulation of cracks growing from randomly distributed initiation sites is performed. Similar crack patterns as obtained in the experiments are found.

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On crack path stability in a layered material

Cited by 13 publications

References 13 publications

Dissolution driven crack branching in polycarbonate

Dissolution driven crack branching in polycarbonate

Crack paths and the problem of global directional stability

Environmentally assisted initiation and growth of multiple surface cracks

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