Microbuckle tunnelling in fibre composites

Fleck, N.A.; Zhao, Liguo

doi:10.1016/s0022-5096(99)00097-6

Cited by 8 publications

(8 citation statements)

References 38 publications

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“…A detailed post-failure inspection within the Scanning Electron Microscope (SEM) revealed that the microbuckle grew in combination with splitting of the -45° plies, see Figure 9(a), similar to the phenomenon of microbuckling tunnelling as analysed by Fleck and Zhao [38]. The kink bands in the -45° plies were observed to be inclined at β ≈ 26°.…”

Section: Mechanism Bsupporting

confidence: 55%

Failure mechanisms of a notched CFRP laminate under multi-axial loading

Tan

Deshpande

Fleck

2015

Composites Part A: Applied Science and Manufacturing

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A quasi-isotropic CFRP laminate, containing a notch or circular hole, is subjected to combined tension and shear, or compression. The measured failure strengths of the specimens are used to construct failure envelopes in stress space. Three competing failure mechanisms are observed, and for each mechanism splitting within the critical ply reduces the stress concentration from the hole or notch: (i) a tension-dominated mode, with laminate failure dictated by tensile failure of the 0 o plies, (ii) a shear-dominated mode entailing microbuckling of the-45 o plies, and (iii) microbuckling of the 0 o plies under remote compression. The net section strength (for all stress states investigated) is greater for specimens with a notch than a circular hole, and this is associated with greater split development in the load-bearing plies. The paper contributes to the literature by reporting subcritical damage modes and failure envelopes under multi-axial loading for two types of stress raiser.

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Section: Mechanism Bsupporting

confidence: 55%

Failure mechanisms of a notched CFRP laminate under multi-axial loading

Tan

Deshpande

Fleck

2015

Composites Part A: Applied Science and Manufacturing

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“…The delamination toughness is taken to be constant and independent of the mode-mix; this assumption is acceptable, as the modemix attains a steady-state value at a relatively short delamination length for all configurations investigated. This modelling strategy for the analysis of 3D crack channelling mechanisms is similar to that used in Fleck and Zhao (2000) for microbuckle tunnelling in fibre composites and in Suiker and Fleck (2004), Cox and Marshall (1996), Suiker and Fleck (2006) for crack tunnelling in layered solids. The numerical results are used in the construction of failure mechanism maps, which illustrate the sensitivity of the active fracture mechanism and corresponding critical channelling stress to the ratio of layer interface to coating toughness, and to the mismatches in stiffness and in coefficient of hygral expansion.…”

Section: Pictures Courtesy Of Matteo Rossi Doriamentioning

confidence: 99%

“…The governing equations for steady-state crack channelling and plane-strain delamination in a coatingsubstrate system under a moisture gradient can be derived from a framework similar to that employed for microbuckle tunnelling in fibre composites in Fleck and Zhao (2000) and that developed for crack tunnelling in layered solids (Cox and Marshall 1996;Fleck 2004, 2006). Accordingly, it is assumed that the channelling crack has nucleated from an initial flaw in the coating and develops as a result of a moistureinduced tensile remote stress σ ∞ 1 (y) given by Eq.…”

Section: Steady-state Crack Channelling and Plane-strain Delaminationmentioning

confidence: 99%

“…During steady-state channelling, the channelling front has a constant shape, whereby the energy release rate does not depend on the channelling length in the outof-plane direction of the crack. Hence, the energy released per unit advance of crack channelling can be calculated as the difference in the elastic strain energy W upstream and downstream of the channelling front (Hutchinson and Suo 1992;Beuth 1992;Fleck and Zhao 2000;Suiker and Fleck 2004), which equals the difference between the strain energy stored in the uncracked plane-strain solid and in the cracked plane-strain solid. For the channelling crack shown in Fig.…”

Section: Steady-state Crack Channelling and Plane-strain Delaminationmentioning

confidence: 99%

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Crack channelling mechanisms in brittle coating systems under moisture or temperature gradients

2020

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Crack channelling is predicted in a brittle coating-substrate system that is subjected to a moisture or temperature gradient in the thickness direction. Competing failure scenarios are identified, and are distinguished by the degree to which the coating-substrate interface delaminates, and whether this delamination is finite or unlimited in nature. Failure mechanism maps are constructed, and illustrate the sensitivity of the active crack channelling mechanism and associated channelling stress to the ratio of coating toughness to interfacial toughness, to the mismatch in elastic modulus and to the mismatch in coefficient of hygral or thermal expansion. The effect of the ratio of coating to substrate thickness upon the failure mechanism and channelling stress is also explored. Closed-form expressions for the steady-state delamination stress are derived, and are used to determine the transition value of moisture state that leads to unlimited delamination. Although the results are applicable to coating-substrate systems in a wide range of applications, the study focusses on the prediction of cracking in historical paintings due to indoor climate fluctuations, with the objective of helping museums developing strategies for the preservation of art objects. For this specific application, crack channelling with delamination needs to be avoided under all circumstances, as it may induce flaking of paint material. In historical paintings, the substrate thickness is typically more than ten times larger than the thickness of the paint layer; for such a system, the failure maps constructed from the numerical simulations indicate that paint delamination is absent if the delamination toughness is larger than approximately half of the mode I toughness of the paint layer. Further, the transition between crack channelling with and without delamination appears to be relatively insensitive to the mismatch in the elastic modulus of the substrate and paint layer. The failure maps developed in this work may provide a useful tool for museum conservators to identify the allowable indoor humidity and temperature fluctuations for which crack channelling with delamination is prevented in historical paintings.

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“…Depending on the notch geometry and material properties of the constituents (matrix, reinforcements, and interfaces), damage at the notch tip can occur by: (i) matrix cracking, (ii) splitting along the fibre direction, (iii) cracking transverse to fibre direction (Zok 2006; Ashby et al. 1985), (iv) fibre pull-out or microbuckling, or (v) interface cracking and/or debonding (Fleck and Zhao 2000; Soboyejo 2002; Heredia et al. 1994; Green et al.…”

Section: Introductionmentioning

confidence: 99%

Notch sensitivity of orthotropic solids: interaction of tensile and shear damage zones

2018

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The macroscopic tensile strength of a panel containing a centre-crack or a centre-hole is predicted, assuming the simultaneous activation of multiple cohesive zones. The panel is made from an orthotropic elastic solid, and the stress raiser has both a tensile cohesive zone ahead of its tip, and shear cohesive zones in an orthogonal direction in order to represent two simultaneous damage mechanisms. These cohesive zones allow for two modes of fracture: (i) crack extension by penetration, and (ii) splitting in an orthogonal direction. The sensitivity of macroscopic tensile strength and failure mode to the degree of orthotropy is explored. The role of notch acuity and notch size are assessed by comparing the response of the pre-crack to that of the circular hole. This study reveals the role of the relative strength and relative toughness of competing damage modes in dictating the macroscopic strength of a notched panel made from an orthotropic elastic solid. Universal failure mechanism maps are constructed for the pre-crack and hole for a wide range of material orthotropies. The maps are useful for predicting whether failure is by penetration or kinking. Case studies are developed to compare the predictions with observations taken from the literature for selected orthotropic solids. It is found that synergistic strengthening occurs: when failure is by crack penetration ahead of the stress raiser, the presence of shear plastic zones leads to an enhancement of macroscopic strength. In contrast, when failure is by crack kinking, the presence of a tensile plastic zone ahead of the stress raiser has only a mild effect upon the macroscopic strength.

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Microbuckle tunnelling in fibre composites

Cited by 8 publications

References 38 publications

Failure mechanisms of a notched CFRP laminate under multi-axial loading

Failure mechanisms of a notched CFRP laminate under multi-axial loading

Crack channelling mechanisms in brittle coating systems under moisture or temperature gradients

Notch sensitivity of orthotropic solids: interaction of tensile and shear damage zones

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