Multi-scale digital image correlation for detection and quantification of matrix cracks in carbon fiber composite laminates in the absence and presence of voids controlled by the cure cycle

Journal of Composite Materials

Gorbatikh

Verpoest

2018

Self Cite

596

305

Voids, the most studied type of manufacturing defects, form very often in processing of fiber-reinforced composites. Due to their considerable influence on physical and thermomechanical properties of composites, they have been extensively studied, with the focus on three research tracks: void formation, characteristics, and mechanical effects. Investigation of voids in composites started around half a century ago and is still an active research field in composites community. This is because of remaining unknowns and uncertainties about voids as well as difficulties in their suppression in modern manufacturing techniques like out-of-autoclave curing and parts with high complexity, further complicated by increased viscosity of modified resins. Finally, this is because of the increasing interest in realization of more accurate void rejection limits that would tolerate some voidage. The current study reviews the research on formation, characterization, and mechanical effects of voids, which has been conducted over the past five decades. Investigation and control of void formation, using experimental and modeling approaches, in liquid composite molding as well as in prepreg composite processing are surveyed. Techniques for void characterization with their advantages and disadvantages are described. Finally, the effect of voids on a broad range of mechanical properties, including inter-laminar shear, tensile, compressive, and flexural strength as well as fracture toughness and fatigue life, is appraised. Both experimental and simulation approaches and results, concerning voids' effects, are reviewed.

Section: Ply Structurementioning

confidence: 99%

Voids in fiber-reinforced polymer composites: A review on their formation, characteristics, and effects on mechanical performance

Journal of Composite Materials

Gorbatikh

Verpoest

2018

Self Cite

596

305

“…Damage development with regard to the defects in this material was studied in [32,35], where the effect of voids on matrix cracking evolution in cross-ply laminates was experimentally and numerically investigated.…”

Section: Composite Laminatesmentioning

confidence: 99%

Detailed characterization of voids in multidirectional carbon fiber/epoxy composite laminates using X-ray micro-computed tomography

Composites Part A: Applied Science and Manufacturing

Straumit

Gorbatikh

2019

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We employ X-ray micro-computed tomography to generate an extensive dataset of voids' characteristics in carbon/epoxy laminates with different stacking sequences. The voids are deliberately induced by modifying the cure cycle. The three-dimensional images with voids are segmented and quantified using an in-house software package, VoxTex. The characteristics of voids, i.e. shape, size parameters, orientation, and spatial location distribution, are obtained. The majority of voids have slightly flattened cross-sections. The voids prefer to localize in the inner plies of the laminate, rather than in the outer ones. Near the laminate mid-thickness, they become more elongated. The stacking sequence affects the size and shape of voids. The planar location of voids is not random and tends to create a pattern, corresponding to the the ply orientations in the laminate. The data is reported in detail, ready to use, for example, as input for modeling studies of similar composites with voids. Response to Reviewers: The response to the reviewer's comments is provided in a separate MS Word file, which is uploaded along with the submission.

“…The strain concentration factor around a real-shape void was calculated numerically in [9] and correlated with the global strain to crack initiation. The initiation of cracks from voids in a cross-ply carbon/epoxy laminate was confirmed by a micro-scale in-situ analysis performed inside an electron microscope in [18], where the combined effect of voids and matrix cure degree on evolution of transverse cracking was investigated, using digital image correlation, also at the meso-and macro-scales.…”

mentioning

confidence: 81%

“…The maximum crack density predicted in all the models converges to ~5 cracks/mm, which is the limitation of A multi-scale experimental study on the effect of voids on the evolution of transverse cracking was performed in [18], where voidy carbon/epoxy cross-ply laminates were produced with the same cure conditions as that mentioned in Section 2.2. It was found that the chosen cure parameters led to not only the voids but also an incomplete cure of the matrix.…”

Section: Effect Of Voids On Transverse Crackingmentioning

confidence: 99%

The effect of voids on matrix cracking in composite laminates as revealed by combined computations at the micro- and meso-scales

Composites Part A: Applied Science and Manufacturing

Petrov

Straumit

et al. 2019

Self Cite

Voids are an important type of manufacturing defects in fiber-reinforced composites. Matrix cracking is sensitive to the presence of voids. Although this cracking occurs at the ply scale, its dynamics is strongly affected by ply's microstructure, in particular, fiber distribution, fiber content, and the presence of voids. In the current study, a computational approach to simulate the influence of intra-laminar voids on cracking in composite laminates is developed. The approach combines finite element models of two scales: a micro-scale model, where the fibers and voids are modeled explicitly, and a meso-scale model, where the cracking phenomenon is captured on the ply scale. The micro-scale model, incorporating plasticity and damage in the matrix, provides input for the meso-scale model, which simulates the progressive cracking by means of the extended finite element method. The methodology is applied to investigate the effect of voids on the density of transverse cracks in cross-ply laminates in function of the quasi-static tensile load. Different sizes and contents of voids, which are chosen based on experimental micro-computed tomography data, are simulated. The numerical experiments show that the presence of voids leads to earlier start of the cracking, with the crack density evolution less sensitive to voids.