Modelling the interaction between matrix cracks and delamination damage in scaled quasi-isotropic specimens

Hallett, Stephen R.; Jiang, Wenguang; Khan, B; Wisnom, Michael R

doi:10.1016/j.compscitech.2007.05.038

Cited by 157 publications

(98 citation statements)

References 16 publications

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“…The large variation in strengths which are all below this value is due to the differences in delamination behaviour of the different laminates. This is particularly striking because the stacking sequence was selected to minimize the risk of edge delamination after analysis of all 12 possible symmetric quasi-isotropic stacking sequences with eight plies by finite-element strain energy-release rate calculations [31].…”

Section: (B) Effect Of Thickness On Unnotched Tensile Strengthmentioning

confidence: 99%

The role of delamination in failure of fibre-reinforced composites

Wisnom

2012

Phil. Trans. R. Soc. A.

228

119

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The mechanisms by which delamination contributes to the failure of fibre-reinforced composites are reviewed. Through-thickness failure owing to interlaminar stresses is considered first, and the effect of delamination in impact and compression after impact. The way in which in-plane failure can occur by delamination and matrix cracks joining up to produce a fracture surface without the need to break fibres is considered next. Examples of quasi-isotropic laminates loaded at different off-axis angles, and with different numbers and thicknesses of ply blocks show large differences in unnotched tensile strength controlled by delamination from the free edge. Similar mechanisms determine the strength of notched specimens and give rise to the hole size effect, whereby tensile strength increases with decreasing hole diameter owing to increased delamination and splitting. Open hole tension and over-height compact tension tests with constant inplane dimensions show a transition in failure mode with increasing ply block thickness from fibre-dominated fracture to complete delamination. In all these cases, the critical factor controlling strength is the relative propensity to delaminate.

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Section: (B) Effect Of Thickness On Unnotched Tensile Strengthmentioning

confidence: 99%

The role of delamination in failure of fibre-reinforced composites

Wisnom

2012

Phil. Trans. R. Soc. A.

228

119

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“…The unidirectional ply elastic properties for IM7/8552 carbon/epoxy are as given in Section 2.3 and the coefficients of thermal expansion are α 1 = 0 (index 1 refer to fibre direction), α 2 = α 3 = 3×10 -5 °C -1 [18]. The steel elastic properties E = 200 GPa and ν = 0.3 are used for the indenter.…”

Section: Finite Element (Fe) Modelmentioning

confidence: 99%

Effect of high through-thickness compressive stress on fibre direction tensile strength of carbon/epoxy composite laminates

Gan

Wisnom

Hallett

2014

Composites Science and Technology

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The fibre-direction tensile strength of carbon/epoxy laminates under the influence of throughthickness compressive stresses has been experimentally investigated. In a unidirectional (UD) laminate, the through-thickness compressive stresses will cause premature longitudinal fibresplitting, masking the effect of transverse stresses on the fibre-direction strength. Here a cross-ply laminate has been used. With the addition of 90° plies preventing the 0° fibres from splitting, it effectively allows the dependence of fibre-direction tensile strength on high through-thickness stresses to be studied. The severity of the through-thickness loads has been varied using cylindrical indenters of different radii, up to the loads near the through-thickness compressive failure stress of the cross-ply laminate. The results show that there is a linear decrease in fibre-direction strength with the mean through-thickness stress. In all the test cases, the specimens failed in a catastrophic brittle manner, with scanning electron micrography showing primarily a fibre tensile fracture mode. The detailed stress state in the specimens has been calculated via finite element analysis. Two failure criteria are proposed, which can be used as conservative design criteria concerning fibre-dominated failures in multiaxial load scenarios. IntroductionWith the increasing use of composite materials replacing metals in aerospace applications, the need to consider complex load conditions is also increasing. Highly localised throughthickness stresses can often be seen in components where localised contact conditions exist, such as in bolted joints. These stresses may interact with co-existing primary in-plane tensile loading in the fibre-direction, leading to earlier failure. when he studied through-thickness compressive loading on unidirectional and cross-plied carbon/epoxy AS4/8552 laminates. The through-thickness stresses that interact with the unidirectional composite fibre direction strength found in the literature are mostly in the form of hydrostatic pressure, at most up to moderate values of ~700 MPa. The current study is a detailed expansion of initial results presented in [12]. In this work, a biaxial test method is developed to apply highly localised through-thickness compressive stress (locally as high as -1700 MPa, as calculated by linear elastic finite element analysis) on a simple cross-plied carbon/epoxy tensile test specimen.The high through-thickness compressive strength of a cross-plied laminate allows the interaction between a broad range of through-thickness compression and in-plane tensile strength to be examined. Multiple experimental load cases are presented and finite element models have been used to study the stresses within the specimens so that a simple failure criterion can be proposed for engineering design purposes. Experimental Specimen preparation and rig setupThe material under consideration is Hexcel's carbon epoxy pre-preg system, IM7/8552 with a nominal ply thickness of 0.125 mm. Four identical panels wi...

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“…Eventually, transverse cracking is succeeded by more catastrophic damage mechanisms like interlamina delamination, fiber breakage, pull-out and bridging associated with macroscopic laminate fracture. 11,47,61 The average behavior of numerous coupon level laminates exhibiting progressive microdamage and transverse cracking was successfully modeled in Refs. 2 and 54 using ST. A similar formulation will be used in this work, in conjunction with the FEM, to model more complicated laminates.…”

Section: Iia Dual-isv Formulation Of St To Model Progressive Microdmentioning

confidence: 99%

“…5,[34][35][36][37][38][39] Moreover, micromechanics models can be tied to the continuum scale using multiscale methods in which the RUC is homogenized to give the effective response of the continuum. [40][41][42][43][44][45] Commonly used techniques for introducing interlamina damage into a composite simulation include the virtual crack closure technique (VCCT), cohesive zone model (CZM) 10,[46][47][48] and discrete cohesive zone model (DCZM). [49][50][51][52] Additionally, multiscale methods can also be used to simulate interlamina effects.…”

Section: Nasa Sti Program In Profilementioning

confidence: 99%