Adiabatic decohesion in a thermoplastic craze thickening at constant or increasing rate

Leevers, P. S.; Godart, Marie-Aude

doi:10.1016/j.jmps.2008.02.001

Cited by 11 publications

(9 citation statements)

References 36 publications

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“…The interfacial shear stress distribution is very important for evaluation of the interfacial shear strength (Agrawal and Raj 1989;Chen et al 2000;Wang and Qiao 2004;Leevers and Godart 2008). Combining Eqs.…”

Section: Interfacial Shear Stress and Frictional Spring Coefficientmentioning

confidence: 99%

An explicit elastic solution for a brittle film with periodic cracks

2008

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A two-dimensional explicit elastic solution is derived for a brittle film bonded to a ductile substrate through either a frictional interface or a fully bonded interface, in which periodically distributed discontinuities are formed within the film due to the applied tensile stress in the substrate and consideration of a "weak form stress boundary condition" at the crack surface. This solution is applied to calculate the energy release rate of three-dimensional channeling cracks. Fracture toughness and nominal tensile strength of the film are obtained through the relation between crack spacing and tensile strain in the substrate. Comparisons of this solution with finite element simulations show that the proposed model provides an accurate solution for the film/substrate system with a frictional interface; whereas for a fully bonded interface it produces a good prediction only when the substrate is not overly compliant or when the crack spacing is large compared with the thickness of the film. If the section is idealized as infinitely long, this solution in terms of the energy release rate recovers Beuth's exact solution for a fully cracked film bonded to a semi-infinite substrate. Interfacial shear stress and the edge effect on the energy release rate of an asymmetric crack are analyzed. Fracture toughness and crack spacing are calculated and are in good agreement with available experiments.

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Section: Interfacial Shear Stress and Frictional Spring Coefficientmentioning

confidence: 99%

An explicit elastic solution for a brittle film with periodic cracks

2008

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“…Considering Figure 7 , it becomes clear why an improvement of fracture initiation properties due to rubber toughening of rate-sensitive plastics is ineffective at very high impact speeds (e.g., S4 tests). As G Ic ( v ) is possibly reduced to a minimum value [ 12 ], the fundamental rapid fracture resistance of different pipe grades during S4 testing at 16 m/s load speed can be considered to be primarily dependent on the dynamic crack propagation resistance G Id (

) after crack initiation.…”

Section: Resultsmentioning

confidence: 99%

Structure-Property Relationships of Polyamide 12 Grades Exposed to Rapid Crack Extension

et al. 2021

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Thermoplastic materials have established a reputation for long-term reliability in low-pressure gas and water distribution pipe systems. However, occasional Slow Crack Growth (SCG) and Rapid Crack Propagation (RCP) failures still occur. SCG may initiate only a small leak, but it has the potential to trigger RCP, which is much rarer but more catastrophic and destructive. RCP can create a long, straight or meandering axial crack path at speeds of up to hundreds of meters per second. It is driven by internal (residual) and external (pressure) loads and resisted by molecular and morphological characteristics of the polymer. The safe installation and operation of a pipe throughout its service lifetime therefore requires knowledge of its resistance to RCP, particularly when using new materials. In this context, the RCP resistance of five different polyamide (PA) 12 grades was investigated using the ISO 13477 Small-Scale Steady State (S4) test. Since these grades differed not only in molecular weight but also in their use of additives (impact modifiers and pigments), structure-property relationships could be deduced from S4 test results. A new method is proposed for correlating these results more efficiently to evaluate each grade using the crack arrest lengths from individual S4 test specimens.

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“…Although only the numerical implementation of the adiabatic decohesion model can give results when the relative craze density ρ * is finite, analytical solutions can be derived when ρ * = 0 and used as a reference. Analytical solutions for the impact reloading phase on a monolayer specimen have been fully described by Leevers and Godart (2007) and those during the skin retraction phase are derived in Appendix B. The computed and analytical results are compared in Fig.…”

Section: Modelmentioning

confidence: 99%

“…Finally, the values of the parameters need to have the order of magnitude determined according to Leevers and Godart (2007): λ F should lie between 10 and 20, β cannot exceed 0.9 and s c should lie between 0.01 and 0.16 µm. In order to get the best agreement with the experimental traces with the chosen cohesive stress, the parameters were chosen so that the final displacement was the lowest, i.e.…”

Section: Cohesive Stressmentioning

confidence: 99%

Effect of skin fracture on failure of a bilayer polymer structure

Godart

Leevers

2007

Int J Fract

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A thin skin of low tensile failure strain, if bonded to the tensile surface of an unnotched impact bend specimen of much tougher material, can change the global failure mode from ductile to brittle. A novel model of this well-known effect is developed and applied to results from impact tests on a tough core of polyamidepolyethylene blend, with a single skin of brittle EVOH. At a fixed crosshead speed, notched specimens of the blend become brittle at a relatively low temperature T bt . Un-notched bilayer specimens continue to show skin fracture up to a considerably higher temperature T fs ; above this temperature they do not fail at all but below T bt they too fail in a brittle manner. Within the temperature range from T fs down to T bt there is a transition from crack arrest, either at the skin/core interface or further into the core where a crack would not normally propagate, to brittle fracture. This brittle fracture temperature is predicted by modelling the process as a three-phase impact event. In the first phase, the striker bends the bilayer quasi-statically. The second phase begins with instantaneous fracture of the skin at its failure strain. The skin ends retract at finite speed, and a craze grows in the adjacent core material to accommodate the local strain singularity. The last phase is a striker-driven impact event similar to that in a notched bend specimen of the core material, except that the crack-tip craze already bears the adiabatic temperature distribution generated while it was driven open by skin retraction. The criterion for craze decohesion, and hence for a crack jump, is the same adiabatic decohesion criterion which accounts for the speed-dependence of impact fracture in notched monolayer specimens. Applied computationally, this model predicts whether a bilayer structure fails in a brittle way or whether cracks initiated in the skin are arrested, either temporarily or permanently, at the skin/core interface.

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Adiabatic decohesion in a thermoplastic craze thickening at constant or increasing rate

Cited by 11 publications

References 36 publications

An explicit elastic solution for a brittle film with periodic cracks

An explicit elastic solution for a brittle film with periodic cracks

Structure-Property Relationships of Polyamide 12 Grades Exposed to Rapid Crack Extension

Effect of skin fracture on failure of a bilayer polymer structure

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