An experimental and numerical investigation into the damage mechanisms in notched composites

Hallett, Stephen R.; Green, Ben G.; Jiang, Wenguang; Wisnom, Michael R

doi:10.1016/j.compositesa.2009.02.021

Cited by 325 publications

(206 citation statements)

References 29 publications

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“…Criterion B is also very close to the Weibull longitudinal tensile strength of a small representative volume of 1 mm 3 [16], consistent with failure occurring in a similarly small volume surrounding the symmetry plane of the specimens. In a plane stress condition or when σ 2 = 0, Criteria A and B are equivalent.…”

Section: Discussionmentioning

confidence: 61%

“…The very high compressive strength obtained in the present study is Another interesting point is that, when a best fit line is drawn through the experimental points in Figure 2 and extrapolated to the y-axis, it shows an expected fibre-direction strength of a 0° lamina of about 3200 MPa. This value is close to the tensile strength of 3131 MPa for 1 mm 3 of IM7/8552, derived from scaled unidirectional tests based on Weibull strength-volume scaling [16]. The lower value of 2724 MPa reported in the manufacturer datasheet [14] is probably due to the test specimen size effect or an underestimate of the true strength due to the effect of stress concentrations at the tabs.…”

Section: Resultsmentioning

confidence: 72%

“…The combination of stresses in Equations (1) and (2) and the Weibull tensile strength of a small representative volume, 1 mm 3 , for IM7/8552 [16] are also plotted as straight lines for comparison.…”

Section: Fe Results and Failure Criterionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 72%

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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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“…Applying a two-parameter Weibull distribution, the probability of survival, P(s), of a volume V subject to a stress ơ is described in Equation 3 [2]. According to Equation 3, the strength ơ1 and ơ2 of two specimens of volumes V1 and V2 respectively can be related by assuming equal probabilities of survival as shown in Equation 4.…”

Section: Size Effectsmentioning

confidence: 99%

“…Open-hole quasi-isotropic specimens have been extensively tested to study strength scaling. For example, Green et al [3] and Hallett et al [4] studied scaled open-hole [45/90/-45/0]4s laminates concluding that the scaling was due to the sub-critical damage around the hole.…”

Section: Introductionmentioning

confidence: 99%

An experimental investigation into size effects in quasi-isotropic carbon/epoxy laminates with sharp and blunt notches

Wisnom

Mahadik

et al. 2014

Composites Science and Technology

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Delamination and Reliability Issues in Packaged Devices

Lei

Kumar

2014

Adhesion in Microelectronics

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An experimental and numerical investigation into the damage mechanisms in notched composites

Cited by 325 publications

References 29 publications

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

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

An experimental investigation into size effects in quasi-isotropic carbon/epoxy laminates with sharp and blunt notches

Delamination and Reliability Issues in Packaged Devices

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