Experimental Evaluation of Longitudinal Splitting in Unidirectional Composites

Wolla, Jeffrey M.; Goree, James G.

doi:10.1177/002199838702100104

Cited by 24 publications

(19 citation statements)

References 13 publications

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“…7a). According to several reports [33][34][35], at tension the critical stress at which splits appear near a hole coincides with that for splitting near a crack. Splitting stress in both cases is described by linear fracture mechanics.…”

Section: The Effect Of Circular Holessupporting

confidence: 55%

“…According to WoUa and Goree [34], fractographic analysis of the fracture surface of individual fibres in a kink allows one to conclude whether the final step of a failure is a result of tension, compression or bending of the fibres. If parallel fracture lines are detected upon the facets of single fibres in a kink, it can be concluded [38] that finally a fracture of all types of fibre in a kink is caused by their bending.…”

Section: Fracturementioning

confidence: 99%

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Compression fracture of unidirectional carbon fibre-reinforced plastics

Баженов¹,

Kozey²

1991

J Mater Sci

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The effect of volume fraction and tensile strength of fibres, temperature and stress concentrators on the compression strength and fracture mode of unidirectional CFRP was studied. The cause of kinking is different for composites reinforced by low-(< 3 G Pa) and high-strength fibres. If fibre strength is high, the kink is initiated by composite splitting followed by fibre bend fracture in the tip of the split. In the case of low-strength fibres, kinking is initiated by compressive fracture of the fibres. The effect of stress concentrators on the CFRP compressive strength is described by linear fracture mechanics. In the presence of defects, fracture is a result of the emergence of splits near a hole. As the critical stress of splitting growth initiation reduces in proportion to the square root of the defect size, the Griffith criterion describes the composite compressive fracture. At elevated temperature, failure is caused by fibre buckling. The fracture band in this case is oriented perpendicular to the fibre direction. Carbon fibre compressive strength may be measured by the loop method. Bending a strand of carbon fibres glued to the elastic beam gives a fibre-controlled upper limit of the composite compressive strength.

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Section: The Effect Of Circular Holessupporting

confidence: 55%

Section: Fracturementioning

confidence: 99%

Compression fracture of unidirectional carbon fibre-reinforced plastics

Баженов¹,

Kozey²

1991

J Mater Sci

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“…The magnitudes and length scale of overloads in fibres adjacent to a cluster of contiguous breaks, combined with the strength statistics of the fibres at this characteristic length scale, determine the transverse growth of the cluster. The stress distribution at a break depends on the existence and growth of fibre/matrix debonding, which is often the precursor to longitudinal splitting [8][9][10]. While several theoretical studies have attempted to explain these phenomena [11][12][13][14][15], little has been substantiated experimentally about the constitutive behaviour and the mechanisms of debonding at the length scale of a fibre break, especially in the presence of other closely spaced fibres.…”

Section: Introductionmentioning

confidence: 99%

Experiments on shear deformation, debonding and local load transfer in a model graphite/glass/epoxy microcomposite

1991

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Recent statistical theories for the failure of polymer matrix composites depend heavily on details of the stress redistribution around fibre breaks. The magnitudes and length scales of fibre overloads as well as the extent of fibre/matrix debonding are key components in the development of longitudinal versus transverse crack propagation. While several theoretical studies have been conducted to investigate the roles of these mechanisms, little has been substantiated experimentally about the matrix constitutive behaviour and mechanisms of debonding at the length scale of a fibre break. In order to predict the growth of transverse and longitudinal cracks using the same micromechanical model, we microscopically observed the epoxy shear behaviour around a single fibre break in a three-fibre microcomposite tape. The planar specimens consisted of a single graphite fibre placed between two larger glass fibres in an epoxy matrix. The interfibre spacing was less than one fibre diameter (< 6 I~m) in order to reflect the spacing between fibres found in typical composites. The epoxy constitutive behaviour was modelled using shear-lag theory where the epoxy had elastic, plastic, and debond zones. The criteria for debonding were modified from conventional shear-lag approaches to reflect the orientational hardening in the epoxy network structure. The epoxy, which is brittle in bulk, locally underwent a shear strain of about 60% prior to debonding from the fibre.

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“…This phenomenon is shown in Figures 1 and 2, which indicates that the traditional shear-lag analytical method is not capabile of accounting for the stable longitudinal split of unidirectional composites. Wolla and Goree [14,15] also drew the same conclusions as us from their study of unidirectional composites with a center penetrating crack. It is suggested that a successful predictive method for the failure of composites must contain a suitable mathematical model into which the main damage factors are introduced, and a reasonable fracture criterion that can describe and control the distinct process of composites failure.…”

mentioning

confidence: 61%

“…A large number of experiments and numerical simulations [12][13][14][15] on the split failure of unidirectional composites with a crack or a surface notch, suggested that the reason for the disagreement between the experimental results and the numerically predicted ones may be that the effects of matrix yield, fiber bridging, and friction across longitudinal splitting surfaces are not taken account in the traditional shear-lag model. These factors cause a delay effect for split growth.…”

Section: Delay Effect Of Splitting Growthmentioning

confidence: 99%

Experimental study and numerical simulation of split growth for unidirectional composites with a surface notch

Wang

Yanning²

1996

Appl Compos Mater

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An analytical model based on the shear-lag theory has been developed to predict the failure behavior of unidirectional composites with a center surface notch under uniaxial tensile load. A delay effect on two split faces touching each other is taken account in the analytical model. The equations obtained by the analytical model are solved using a variational technique -the principle of minimum potential energy (PMPE). Combining the fracture criterion of energy release rate with the experimental data gathered from tests, we have numerically predicted longitudinal split initiation and split growth. The predicted results are in agreement witht the experimental results. The prodicted results and experimental results both apparently show two regions -the first stable split growth and the second rapid split growth.

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Experimental Evaluation of Longitudinal Splitting in Unidirectional Composites

Abstract: An experimental study was conducted to determine the fracture behavior of center- notched, unidirectional graphite/epoxy laminates when subjected to tensile loading. The actual behavior is compared to the behavior predicted by a mathematical model based on classical shear-lag assumptions.

Cited by 24 publications

References 13 publications

Compression fracture of unidirectional carbon fibre-reinforced plastics

Compression fracture of unidirectional carbon fibre-reinforced plastics

Experiments on shear deformation, debonding and local load transfer in a model graphite/glass/epoxy microcomposite

Experimental study and numerical simulation of split growth for unidirectional composites with a surface notch

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