The detailed structure of delamination fracture surfaces in graphite/epoxy laminates

Johannesson, T.; Sjöblom, Peter; Seldén, R.

doi:10.1007/bf01120026

Cited by 67 publications

(28 citation statements)

References 3 publications

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“…From similar observations 15,38,42,43,44 of the cusp angle changing with the mode of loading and the results of the present study, it seems likely that the cusp angle can be used to determine the fracture mode with confidence as was done by Gilchrist et al 45 in the investigation of failure modes in composite I-beams. Also the cusp angles appear to be independent of the actual material system which supports the theory for microcrack formation.…”

Section: Discussionsupporting

confidence: 63%

“…Another suggestion for the delamination process was presented by Johannesson et al 38 . Fibres initially debond, probably due to stress concentrations at the interface, angled cracks are subsequently formed in the resin perpendicular to the major principal stress, and finally, the debonded regions and slant cracks are linked together by microscopic cracks propagating from the broken interfaces into the resin.…”

Section: Fracture Toughnessmentioning

confidence: 99%

“…Using the theory of cusp formation suggested by several authors 15,36,38,39 as being due to the coalescence of brittle microcracks in the resin, an expression for the angle at which cusps are inclined to the fracture surface can be derived from the stress state, shown in Fig. 4, of a small interlaminar resin element just ahead of the crack tip.…”

Section: Cusp Anglementioning

confidence: 99%

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Mixed-Mode Delamination of Multidirectional Carbon Fiber/Epoxy Laminates

Svensson¹,

Gikhrist

1998

Mech. of Adv. Mat. & Structures

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SUMMARYScanning electron microscopy was used to identify fractographic features that are characteristic of different modes of interlaminar fracture. The cusp angle and the amount of fibre pull-out on the fracture surface can be used to characterise the different loading modes.A large amount of fibre pull-out is the dominant feature of a mode I fracture whilst in mode II large cusp angles and many cusps are the main characteristics. The amount of fibre pullout, and subsequently broken fibres, per unit area was investigated and found to vary in proportion to the degree of mode I loading. Such methods can be used to analyse failure and the propagation of delamination in structural components. The energy associated with cusp formation constitutes a large proportion of the mode II fracture toughness component whilst the amount of fibre pull-out and fracture has a considerable influence on the mode I fracture component. The cusp angle was seen to provide a quantitative measure of the fracture surface roughness. A failure criterion which takes the fracture surface appearance into account was evaluated. The cusp angle was subsequently used to modify this failure criterion. As a consequence, this provided an improved agreement with the experimental data.2

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Section: Discussionsupporting

confidence: 63%

Section: Fracture Toughnessmentioning

confidence: 99%

Section: Cusp Anglementioning

confidence: 99%

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Mixed-Mode Delamination of Multidirectional Carbon Fiber/Epoxy Laminates

Svensson¹,

Gikhrist

1998

Mech. of Adv. Mat. & Structures

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“…This angle would decrease with an increasing amount of Mode I loading and for pure Mode I no cusps would form [26]. Experimental evidence supports this qualitatively [6,[26][27][28] and lately also quantitatively [7]. Cusp angles significantly greater than 45° have been observed.…”

Section: Mode IIsupporting

confidence: 57%

Interlaminar Fracture of Commingled GF/PET Composite Laminates

Svensson¹,

Shishoo

Gilchrist

1998

Journal of Composite Materials

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The Mode I, Mode II and mixed mode (Mode I:II ratios of 4:1, 1:1 and 1:4) fracture behavior of novel textile glass fiber reinforced polyethylene terephthalate (GF/PET) laminates has been investigated. The laminates were manufactured by compression molding two different fabrics produced by weaving and warp knitting commingled GF/PET yarns. The initiation fracture toughnesses of the woven laminates in pure Mode I and Mode II were slightly higher than those of the warp knitted laminates. For the mixed modes, the difference between the fracture toughnesses of the two materials was smaller. An extensive scanning electron microscopy (SEM) investigation of the fracture surfaces was conducted to identify any characteristic failure mechanisms. The main fractographic features of the Mode I dominated failures were a brittle matrix failure and large amounts of fiber pull-out. As the Mode II loading component increased, the amount of fiber pull-out was reduced and the matrix had a more sheared appearance. A relatively large amount of cusps were found in pure Mode II and mixed mode I:II=1:4; such features are seldom seen in thermoplastic matrix composites. A general mixed mode failure criterion, which accounts for the appearance of the fracture surface, was evaluated and was seen to give a good fit to the experimental fracture toughness values.

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“…8. The formation of cusps has been attributed to a brittle failure of the matrix [17][18][19][20][21] and can be described as the coalescence of brittle microcracks which form perpendicular to the resolved principal stresses just ahead of the crack tip, as shown schematically in Fig. 9.…”

Section: Fracturementioning

confidence: 99%

Fracture and fatigue performance of textile commingled yarn composites

Gilchrist

Svensson²,

Shishoo

1998

Journal of Materials Science

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The response to mechanical loads of commingled warp knitted and woven glass fibre reinforced polyethylene terephthalate (GF/PET) laminates has been characterised. The mechanical properties of the two materials were determined under tension, in-plane shear and flexure. The flexural fatigue properties were determined for the woven laminates by means of three point bending tests with a loading ratio of R=0.1 at stress levels of 50-90% of the ultimate static strength. The Mode I, Mode II and mixed mode (Mode I:II ratios 4:1, 1:1 and 1:4) interlaminar fracture toughnesses of the laminates were determined by means of the double cantilever beam (DCB) and mixed mode bending (MMB) tests respectively. The main fractographic features, as determined by an scanning electron microscopy (SEM) examination, of the Mode I dominated failures were a brittle matrix failure and larger amounts of fibre pullout. As the Mode II loading component increased, the amount of fibre pull-out was reduced and the features of the matrix appeared to be more sheared. Cusps were found on the fracture surfaces of specimens tested in pure Mode II and mixed mode I:II=1:4. Cusps are normally not found in thermoplastic matrix composites.

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The detailed structure of delamination fracture surfaces in graphite/epoxy laminates

Cited by 67 publications

References 3 publications

Mixed-Mode Delamination of Multidirectional Carbon Fiber/Epoxy Laminates

Mixed-Mode Delamination of Multidirectional Carbon Fiber/Epoxy Laminates

Interlaminar Fracture of Commingled GF/PET Composite Laminates

Fracture and fatigue performance of textile commingled yarn composites

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