Hierarchical analysis of the degradation of fibre-reinforced polymers under the presence of void imperfections

Liebig, Wilfried V.; Schulte, Karl; Fiedler, Bodo

doi:10.1098/rsta.2015.0279

Cited by 10 publications

(9 citation statements)

References 22 publications

(40 reference statements)

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“…Therefore, to estimate the compressive strength, the critical number of affected fibers by voids needs to be determined through a probabilistic approach, in addition to the void content. Although in contrast to the approach presented by Hapke et al, 270 the methodology investigated by Liebig et al 218,227,242 shows information also about failure initiation, it is still not representative of the compressive failure in real composites. This can be attributed to the lower fiber volume fraction, larger fiber diameter ($70 mm), and larger size of voids (up to 3500 mm length and 800 mm height) compared with typical composites.…”

Section: Compressive Propertiesmentioning

confidence: 84%

“…In a further study, 242 the authors showed that DIC indicates also minimum and maximum strains in the summit and in the middle of the void, respectively. The high strain alongside the void was linked to the fiber deflection into the void, which accompanies the non-linear deformation of the matrix.…”

Section: Compressive Propertiesmentioning

confidence: 92%

“…placing foreign objects such as polytetrafluoroethylene (PTFE) filaments in the lay-up, 224 5. assigning poor LCM parameters, 172,223,230,232,233 6. following inadequate degassing prior to infusion, 219,223,231 and 7. injecting air before consolidation. 218,227,241,242 Analytical, statistical, and more recently numerical methodologies have been employed in the studies on voids' effects, while experimental works provide the largest contribution to this field. Many studies correlated the degradation of mechanical properties with the void content increase, and some of them 92,146,154,155,222,225,239,243 reported a critical void content, below which the voidage has a negligible effect on the performance.…”

Section: Effect Of Voids On Mechanical Propertiesmentioning

confidence: 99%

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

Mehdikhani

Gorbatikh

Verpoest

2018

Journal of Composite Materials

541

305

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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.

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Section: Compressive Propertiesmentioning

confidence: 84%

Section: Compressive Propertiesmentioning

confidence: 92%

Section: Effect Of Voids On Mechanical Propertiesmentioning

confidence: 99%

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

Mehdikhani

Gorbatikh

Verpoest

2018

Journal of Composite Materials

541

305

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“…Initiation of kink-bands is facilitated at defects, e.g., voids [ 9 , 10 ] or local fibre misalignment [ 11 ]. Despite these flaws, the laminate properties and stacking sequence play an important role in damage initiation and propagation and the resulting mechanical properties under compressive loading.…”

Section: Introductionmentioning

confidence: 99%

Compression Fracture of CFRP Laminates Containing Stress Intensifications

Leopold

Schütt²,

Liebig

et al. 2017

Materials

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Abstract:For brittle fracture behaviour of carbon fibre reinforced plastics (CFRP) under compression, several approaches exist, which describe different mechanisms during failure, especially at stress intensifications. The failure process is not only initiated by the buckling fibres, but a shear driven fibre compressive failure beneficiaries or initiates the formation of fibres into a kink-band. Starting from this kink-band further damage can be detected, which leads to the final failure. The subject of this work is an experimental investigation on the influence of ply thickness and stacking sequence in quasi-isotropic CFRP laminates containing stress intensifications under compression loading. Different effects that influence the compression failure and the role the stacking sequence has on damage development and the resulting compressive strength are identified and discussed. The influence of stress intensifications is investigated in detail at a hole in open hole compression (OHC) tests. A proposed interrupted test approach allows identifying the mechanisms of damage initiation and propagation from the free edge of the hole by causing a distinct damage state and examine it at a precise instant of time during fracture process. Compression after impact (CAI) tests are executed in order to compare the OHC results to a different type of stress intensifications. Unnotched compression tests are carried out for comparison as a reference. With this approach, a more detailed description of the failure mechanisms during the sudden compression failure of CFRP is achieved. By microscopic examination of single plies from various specimens, the different effects that influence the compression failure are identified. First damage of fibres occurs always in 0°-ply. Fibre shear failure leads to local microbuckling and the formation and growth of a kink-band as final failure mechanisms. The formation of a kink-band and finally steady state kinking is shifted to higher compressive strains with decreasing ply thickness. Final failure mode in laminates with stress intensification depends on ply thickness. In thick or inner plies, damage initiates as shear failure and fibre buckling into the drilled hole. The kink-band orientation angle is changing with increasing strain. In outer or thin plies shear failure of single fibres is observed as first damage and the kink-band orientation angle is constant until final failure. Decreasing ply thickness increases the unnotched compressive strength. When stress intensifications are present, the position of the 0°-layer is critical for stability under compression and is thus more important than the ply thickness. Central 0°-layers show best results for OHC and CAI strength due to higher bending stiffness and better supporting effect of the adjacent layers.

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“…The analytical model of Argon [18] that assumes rigid-plastic microbuckling and the extension from Budiansky [19,20,21], which considers elastic-plastic microbuckling, describe the initiation and propagation of a kink-band with an orientation angle β, the kink-band width, and the inclination angle of the fibres. Initiation of fibre microbuckling and a kink-band is facilitated at defects, e.g., local fibre misalignment [22,23,24,25] or voids [26,27] and can be described for the latter case with an analytical model [28]. It was shown by Bazhenov et al [29] that the fibre diameter is relevant for compressive strength, especially if flaws such as voids are present.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Analytical Approaches Predicting the Compressive Strength of Fibre Reinforced Polymers

et al. 2018

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Common analytical models to predict the unidirectional compressive strength of fibre reinforced polymers are analysed in terms of their accuracy. Several tests were performed to determine parameters for the models and the compressive strength of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). The analytical models are validated for composites with glass and carbon fibres by using the same epoxy matrix system in order to examine whether different fibre types are taken into account. The variation in fibre diameter is smaller for CFRP. The experimental results show that CFRP has about 50% higher compressive strength than GFRP. The models exhibit significantly different results. In general, the analytical models are more precise for CFRP. Only one fibre kinking model’s prediction is in good agreement with the experimental results. This is in contrast to previous findings, where a combined modes model achieves the best prediction accuracy. However, in the original form, the combined modes model is not able to predict the compressive strength for GFRP and was adapted to address this issue. The fibre volume fraction is found to determine the dominating failure mechanisms under compression and thus has a high influence on the prediction accuracy of the various models.

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Hierarchical analysis of the degradation of fibre-reinforced polymers under the presence of void imperfections

Cited by 10 publications

References 22 publications

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

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

Compression Fracture of CFRP Laminates Containing Stress Intensifications

Comparison of Analytical Approaches Predicting the Compressive Strength of Fibre Reinforced Polymers

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