MULTISCALE DAMAGE IN CO-CURED COMPOSITES—PERSPECTIVES FROM EXPERIMENTS AND MODELLING

2021 ◽  
Author(s):  
NITHYA SUBRAMANIAN ◽  
CHIARA BISAGNI
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Experimental Testing ◽  
Void Formation ◽  
Md Simulations ◽  
Interface Fracture ◽  
Damage Initiation ◽  
Mode I Fracture Toughness ◽  
Modelling Strategies ◽  
Critical Regions

Bonded and co-cured composites are popular alternatives to structures joined with mechanical fasteners in aircraft but the complex and coupled damage mechanisms in the co-cured/bonded region are poorly understood, thus making the evaluation of their strength and durability difficult with current modelling strategies. This study explores the potential of interleaf inclusion in failure-prone, critical regions of co-cured composite specimens in improving the joint strength and interface fracture toughness and strives to advance the understanding of damage initiation in the co-cured region using an atomistic model. A two-pronged approach is pursued here with bench-scale experimental testing and molecular modelling in this study. Experiments are performed for mode I fracture toughness with double cantilever beam (DCB) on composite laminates with an epoxy interleaf layer. Two epoxy resins and three methods for interleaf inclusion are explored in this study; we supplement the results from DCB testing with insights from confocal microscopy on the crack tip and the interleaf layer pre- and post-testing. Molecular dynamic (MD) simulations capture the cohesive interactions at the threephase interface containing the carbon fiber, the prepreg epoxy, and the interleaf epoxy. Results highlight that an interleaf layer made from partially-cured and filmed epoxy, further consolidated in the composite lay-up is the most effective way to suppress void formation, improve dispersion, and maximize cohesive interactions at the interface of co-cured composites.

Effect of fixation stitches on out-of-plane response of textile non-crimp fabric composites

2018 ◽  
Vol 48 (7) ◽  
pp. 1151-1166 ◽  
Author(s):  
Somen K Bhudolia ◽  
Kenneth KC Kam ◽  
Pavel Perrotey ◽  
Sunil C Joshi
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Peak Load ◽  
Experimental Studies ◽  
Critical Energy ◽  
Critical Energy Release Rate ◽  
Mode I Fracture Toughness ◽  
Out Of Plane ◽  
Static Indentation ◽  
Sem Investigation

Non-crimp fabrics are fabric tapes stitched to an adjacent orthogonal fabric with no associated crimp. In the current research, the effect of fixation polyester stitches in improving through-the-thickness properties of non-crimp fabric composite laminates is investigated. Detailed experimental studies on interlaminar fracture toughness and static indentation properties of stitched and unstitched thin ply carbon fibre epoxy composites have been conducted. About 23% higher peak load and 37% higher energy absorption were noticed during static indentation tests for the stitched ply composites. A detailed SEM investigation has shown that the stitch-stitch interaction ‘within a bi-angle ply’ and ‘between the bi-angle ply’ plays a significant role in reducing the delamination extent. The critical energy release rate during Mode I fracture toughness of stitched composites was found to be 26.5% higher and SEM investigation depicted that the stitches promote the intra-laminar delamination and enhance the toughness of the composite.

Experimental and statistical analysis of carbon fiber/epoxy composites interleaved with nylon 6,6 nonwoven fabric interlayers

2020 ◽  
Vol 54 (27) ◽  
pp. 4173-4184
Author(s):  
Bertan Beylergil ◽  
Metin Tanoğlu ◽  
Engin Aktaş
Keyword(s):  
Fracture Toughness ◽  
Carbon Fiber ◽  
Composite Laminates ◽  
Nonwoven Fabric ◽  
Epoxy Composites ◽  
Nonwoven Fabrics ◽  
Mode I Fracture Toughness ◽  
Weight Density ◽  
Nylon 6,6 ◽  
Carbon Fiber Epoxy

Thermoplastic interleaving is a promising technique to improve delamination resistance of laminated composites. In this study, plain-weave carbon fiber/epoxy composites were interleaved with nylon 6,6 nonwoven fabrics with an areal weight density of 17 gsm. The carbon fiber/epoxy composite laminates with/without nylon 6,6 nonwoven fabric interlayers were manufactured by VARTM technique. Double cantilever beam fracture toughness tests were carried out on the prepared composite test specimens in accordance with ASTM 5528 standard. The experimental test data were statistically analyzed by two-parameter Weibull distribution. The results showed that the initiation and propagation fracture toughness Mode-I fracture toughness of carbon fiber/epoxy composites could be improved by about 34 and 156% (corresponding to a reliability level of 0.50) with the incorporation of nylon 6,6 interlayers in the interlaminar region, respectively. The results also revealed that the percent increase in the propagation fracture toughness value was 67 and 41% at reliability levels of 0.90 and 0.95, respectively.

The Interlaminar Toughening Effect of Hybrid PES/E51 Films on Carbon Fiber/ Epoxy Composite

2020 ◽  
Vol 984 ◽  
pp. 131-136
Author(s):  
Chao Cheng ◽  
Hui Zhang ◽  
Ze Yu Sun ◽  
Yong Liu ◽  
Mu Huo Yu
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Phase Inversion ◽  
Hybrid Film ◽  
Epoxy Composite ◽  
Interlaminar Fracture Toughness ◽  
Resin Infusion ◽  
Mode I Fracture Toughness ◽  
Carbon Fiber Epoxy ◽  
Opposite Tendency

In this study, E51 was appended as an additive to the PES casting solution and hybrid PES/E51 films with different E51 content were produced by phase inversion approach, applied as interleaves to improve the interlaminar fracture toughness of CF/EP composite laminates prepared by vacuum assistant resin infusion process (VARI). The time that the hybrid film dissloved into the epoxy resin depended on the content of E51 in the film, moreover, it was observed that Mode I fracture toughness of the hybrid film modified composite reduced with the addition of E51 compared with the pure PES film interleaved composite, however, the tensile properties showed the opposite tendency. The reason was the reduction in the thickness of the interlayer resin illustrated by cross-section morphologies of all types of laminates.

scholarly journals Application of discrete damage mechanics for determination of the crack density in composite laminates

2020 ◽  
Vol 310 ◽  
pp. 00002
Author(s):  
Milan Žmindák ◽  
Eva Kormaníková ◽  
Pavol Novák ◽  
Josef Soukup ◽  
Kamila Kotrasová
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Composite Structures ◽  
Damage Mechanics ◽  
Crack Density ◽  
Matrix Cracking ◽  
Mapping Algorithm ◽  
Damage Initiation ◽  
Return Mapping

The finite element method (FEM) is one of the most widely and most popular numerical methods for analyzing damage of composite structures, In this paper discrete damage mechanics (DDM) is used to predict inter-laminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the laminate. ANSYS commercial software is used for analysis of layered plate composite structure reinforced with long unidirectional fibers with Carbon/Epoxy material. Because ANSYS does not have a built-in capability for calculating crack density, we have to use plagin. A methodology for determination of the fracture toughness is based on fitting DDM model and these data are obtained from literature. Also, prediction of modulus vs. applied strain is contrasted with ply discount results and the effect of in situ correction of strength is highlighted. Evaluation of matrix cracking detected in lamina has been solved using return mapping algorithm.

Improved fracture toughness of carbon fiber fabric/epoxy composite laminates using polyether sulfone fibers

2018 ◽  
Vol 31 (8) ◽  
pp. 996-1005
Author(s):  
Wenjian Zheng ◽  
Zhengjun Yao ◽  
Haiyan Lin ◽  
Jintang Zhou ◽  
Haishuo Cai ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Carbon Fiber ◽  
Composite Laminates ◽  
Composite Structures ◽  
Secondary Phase ◽  
Average Value ◽  
Mode I Fracture Toughness ◽  
Polyether Sulfone ◽  
The Matrix ◽  
Carbon Fiber Epoxy

This study demonstrated that the addition of dissolvable polyether sulfone fibers to the interlaminar area of carbon fiber/epoxy composites can effectively increase the toughness with very high accuracy. Resin film infusion (RFI) is used to fabricate composite structures. RFI was applied to obtain polyether sulfone as an interleaf of chopped fibers between fabric piles of carbon fibers. The thermoplastic polyether sulfone fiber dissolved in the epoxy when it was cured at a high temperature. A phase-separated morphology with a polyether sulfone-rich secondary phase was formed during the curing process. Experimental results indicated that G Ic, which is the average value of Mode-I fracture toughness, was increased fivefold with the addition of 10 wt% polyether sulfone fiber (with respect to the gross content of the matrix). No detrimental effects were observed in other characteristics such as thermal stability, Young’s modulus, and tensile strength. In addition, the thermal and mechanical characteristics of neat epoxy–polyether sulfone blends were analyzed for comparison.

Experimental Investigation of Interlaminar Fracture Toughness of CFRP Composites with Different Stitching Patterns

2005 ◽  
Vol 297-300 ◽  
pp. 189-194 ◽  
Author(s):  
Hong Ping Zhao ◽  
Robert Kwok Yiu Li ◽  
Xi Qiao Feng
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Test Method ◽  
Mode I ◽  
Interlaminar Fracture Toughness ◽  
Interlaminar Fracture ◽  
Reinforced Plastics ◽  
Mode I Fracture Toughness ◽  
Straight Line ◽  
Delamination Resistance

Through-thickness stitching is one of the most effective techniques to improve the delamination resistance of composite laminates. The effects of two different stitching patterns on the mode-I interlaminar fracture toughness of unidirectional carbon fiber reinforced plastics (CFRP) are examined experimentally in the present paper by using the double cantilever beam (DCB) test method. It is found that the zigzag stitching pattern results in a better toughening effect than the straight line pattern, and that the stitching density also has a considerable influence on the mode-I fracture toughness.

scholarly journals Modification of Carbon Fibre/Epoxy Composites by Polyvinyl Alcohol (PVA) Based Electrospun Nanofibres

2016 ◽  
Vol 25 (3) ◽  
pp. 096369351602500 ◽  
Author(s):  
Bertan Beylergi̇l ◽  
Metin Tanoğlu ◽  
Engin Aktaş
Keyword(s):  
Fracture Toughness ◽  
Polyvinyl Alcohol ◽  
Carbon Fibre ◽  
Composite Laminates ◽  
Mechanical Performance ◽  
Epoxy Composite ◽  
Epoxy Composites ◽  
Mode I ◽  
Mode I Fracture Toughness ◽  
Electrospun Nanofibres

In this study, the effects of modifying interlaminar region of unidirectional carbon fibre/epoxy composites by the incorporation of electrospun polyvinyl alcohol (PVA) nanofibres were investigated. PVA nanofibres were directly deposited onto the carbon fabrics by electrospinning method to improve mechanical performance of those composites. The features of the electrospun nanofibres were characterized by microscopy techniques. The unidirectional carbon fibre/epoxy composite laminates with/without PVA nanofibre interlayers were manufactured by vacuum-infusion technique in a [0]4 configuration. Tensile, three-point bending, compression, Charpy-impact and Mode-I fracture toughness tests (Double Cantilever Beam (DCB)) were carried out in accordance with ASTM standards to evaluate mechanical performance of the composites. Scanning electron microscopy (SEM) observations were made on the specimens to evaluate microstructural features. It was observed that the carbon fabrics were successfully coated with a thin layer of PVA nanofibres by electrospinning technique. The results showed that PVA nanofibres improve the mechanical properties of unidirectional carbon/epoxy composite laminates when subjected to in-plane loading. On the other hand, PVA nanofibres slightly reduced the mode-I fracture toughness values although they led to more stable crack propagation.

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