Splitting initiation and propagation in notched unidirectional graphite/epoxy composites under tension-tension cyclic loading

Daken, Hatem H.; Mar, James W.

doi:10.1016/0263-8223(85)90002-9

Cited by 13 publications

(7 citation statements)

References 3 publications

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“…The Tsai-Wu failure criterion is adopted to initiate the onset of matrix cracking [56] in the form of longitudinal splitting in the fiber direction at hole edges ( Figure 19) driven by local shear stresses C-. After initiation, the cracks continue to propagate along the fiber direction ( Figure 20), in agreement with experimental observations [57,58]. At both initiation and propagation stages, the coarse mesh model over predicts the high stress region around the crack fronts.…”

Section: End Notch Flexure (Enf) and Mixed-mode Bending (Mmb) Testssupporting

confidence: 85%

Adaptive floating node method for modelling cohesive fracture of composite materials

Lü

Chen

Tan

et al. 2018

Engineering Fracture Mechanics

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The cohesive element has been widely employed to model delamination and matrix cracking in composite materials. However, an extremely fine mesh along the potential crack path is required to achieve accurate predictions of stresses within the cohesive zone. A sufficient number of cohesive elements must be present within the cohesive zone ahead of the crack tip, resulting in very high computational cost and time for application to practical composite structures. To mitigate this problem, an adaptive floating node method (A-FNM) with potential to reduce model size and computational effort is proposed. An element with adaptive partitioning capabilities is designed such that it can be formulated as a master element, a refined element and a coarsened element, depending on the damage state in the progressive damage process. A relatively coarse overall mesh may be used initially, and by transforming the element configurations adaptively, the local refinement and coarsening schemes are applied in the analysis. The localized stress gradient ahead of the crack front within the refinement zone is captured by the refined elements. The refinement and coarsening operations are performed at the elemental level with fixed nodal connectivity, so that global successive remeshing in adaptive mesh refinement (AMR) techniques is avoided; this is the key difference between AMR and A-FNM. It is demonstrated that, without loss of accuracy, the present method simplifies the modelling procedure and reduces computational cost. KEYWORDSA. Adaptive modelling; B. Fracture; C. Finite element method; D. Floating node method. © 2018 Manuscript version made available under CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/

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Section: End Notch Flexure (Enf) and Mixed-mode Bending (Mmb) Testssupporting

confidence: 85%

Adaptive floating node method for modelling cohesive fracture of composite materials

Lü

Chen

Tan

et al. 2018

Engineering Fracture Mechanics

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“…The propagation of 0° ply splits is largely caused by shear stresses. There are many combinations by which these splits can initiate as defined by Daken and Mar [24]. The failure mode changes from brittle when testing un-fatigued specimens in quasi-static loading, to pull-out after 1x10 6 cycles as fatigue loading had caused sufficient damage in the outer sub-laminates prior to residual strength tests.…”

Section: Second Sub-laminate Configurationmentioning

confidence: 99%

An investigation into the damage development and residual strengths of open-hole specimens in fatigue

Nixon-Pearson

Hallett

2015

Composites Part A: Applied Science and Manufacturing

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An extensive experimental program was carried out to investigate and understand the sequence of damage development throughout the life of open-hole composite laminates loaded in tension-tension fatigue. Quasiisotropic carbon/epoxy laminates, with stacking sequence [45 2 /90 2 /-45 2 /0 2 ] S , [45/90/-45/0] 2S and [45/90/-45/0] 4S were examined. These were selected on the basis that under quasi-static loading the [45 2 /90 2 /-45 2 /0 2 ] S configuration exhibited a delamination dominated mode of failure whilst the [45/90/-45/0] 2S and [45/90/-45/0] 4S configurations showed a fibre dominated failure mode, previously described as "pull-out" and "brittle" respectively. Specimens were fatigue loaded to 1x10 6 cycles or catastrophic failure, which ever occurred first. A number of tests were interrupted at various points as the stiffness dropped with increasing cycles, which were inspected using X-ray Computed Tomography (CT) scanning. A static residual strength program was carried out for run-out specimens of each configuration.

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“…Interlaminar stresses at the free edge degrades the compressive strength leading to delaminations. Daken and Mar [12] investigated the development of splitting in notched unidirectional specimens under tension-tension cyclic loading. Splitting was found to relieve stress concentrations at the notch and developed at cyclic loads well below the static splitting stress, suggesting a degradation of properties with cyclic loading.…”

Section: Generaleffectsmentioning

confidence: 99%

Damage Accumulation in Graphite/Epoxy Laminates Due to Cyclic Gradient Stress Fields

Lagacé

Bonello

1993

Journal of Reinforced Plastics and Composites

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The progression of damage in gradient stress fields under cyclic loading was studied in simply-supported graphite/epoxy beam-columns. Three layups, [454/-454/(0/90)412s, [±45/0/904]4s, and [(452/-452/0)2/905]2s, were chosen to be consistent with data collected in a previous study with static loading. Specimens were loaded statically until predetermined characteristic damage levels were obtained, after which cyclic loading began. Cyclic tests were run in load control at an R ratio of ten and a frequency of 1.5 Hz. At specific intervals, cyclic loading was stopped, a static test measuring the load and the corresponding center deflection was performed, and edge replicas of the specimen's sides were taken. Cyclic loading was then resumed until the next interval or final failure. Damage histories were pieced together for each laminate type under different maximum cyclic load levels. The damage of these specimens varied both along the length and through the thickness of the specimens with two modes of damage present. Damage due to the static loading occurred on the tension side of the specimen and was controlled by matrix cracks. Delaminations initiated and grew in areas of crack saturation. Damage due to the cyclic loading also occurred on the compression side of the specimens and was controlled by delaminations which initiated and grew independently of matrix cracks, leading to sublaminate buckling. These compression side delaminations did not initiate in static tests to failure. Increasing the maximum cyclic load changed the relative growth of the two modes of damage, thus changing the failure mode. The stiffness of the specimens increased slightly with cyclic loading but steadily declined thereafter. Stiffness degradation was less than 6% until just prior to failure. Because cyclic loading revealed critical damage modes not found with static loading, cyclic loading should be used when ascertaining all possible damage modes. Using higher cyclic load levels to reduce testing time can hide critical damage modes with the potential of overestimating cyclic lifetime.

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Splitting initiation and propagation in notched unidirectional graphite/epoxy composites under tension-tension cyclic loading

Cited by 13 publications

References 3 publications

Adaptive floating node method for modelling cohesive fracture of composite materials

Adaptive floating node method for modelling cohesive fracture of composite materials

An investigation into the damage development and residual strengths of open-hole specimens in fatigue

Damage Accumulation in Graphite/Epoxy Laminates Due to Cyclic Gradient Stress Fields

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