Haris Ahmad Israr

Numerical simulation methodology for mode II delamination of quasi-isotropic quasi-homogeneous composite laminates

This work proposed a methodology to obtain the lamina and interface properties using minimal experimental works. Studies were limited to mode II delamination behavior of three quasi-isotropic quasi-homogeneous woven glass/polyester composites. It was found that the fracture toughness of 0//0, 0//45, and 45//45 laminates calculated using experimental calibration method were 0.91 N/m, 0.94 N/m, and 0.51 N/m, respectively. In addition, fiber twisting and shear cusps were observed on the delaminated surfaces of 45°-ply. Subsequently, a methodology was proposed to obtain the lamina properties for the numerical simulation without performing any additional experiment. An approach to account for the shear nonlinearity of the composite laminate due to the existence of 0°-ply was also presented. Finally, it was proposed that for reliable numerical modeling using cohesive zone model, the following parameters were recommended: penalty stiffness = 3 × 106 MPa/mm, interface shear strength = 65 MPa, mesh size = 0.5 mm, and viscosity parameter = 1 × 10−3.

Thickness-dependent non-Fickian moisture absorption in epoxy molding compounds

The objective of this research is to characterize the relationship between the moisture uptake behavior and the thickness in epoxy-based molding compounds (EMCs). Experimental results from the literature were adopted for this purpose. A thickness-dependent moisture uptake model was proposed to describe the moisture uptake behavior. In order to apply the model, a methodology to develop the fictitious Fickian curve was suggested. Subsequently, the relationships between the non-Fickian parameters and the thickness were correlated and compared. Results showed that the apparent diffusivity of the fictitious curve was sensitive to the environmental conditions but not the thickness. In addition, when combining all data, it was found that each normalized non-Fickian parameter could be described by a single equation with respect to the normalized thickness. Based on the thickness-dependent model, the moisture concentration across the thickness was further characterized. In conclusion, the model proposed in this study allows the prediction of moisture uptake behavior at various thicknesses of EMCs. This could greatly reduce the time and cost of extensive experimental works.

Mode I and mode II delamination of a chopped strand mat E-glass reinforced vinyl ester composite

ABSTRACT The objective of the present work is to investigate mode I and mode II delamination behaviour of chopped strand mat (CSM) E-glass reinforced vinyl ester (VE) composite. Double cantilever beam and end notched flexure tests were carried out to evaluate the mode I and mode II delamination, respectively. The fracture toughnesses were calculated using the experimental calibration method. Results showed that the average mode I and mode II fracture toughnesses were 185 and 2386 N m−1, respectively. Furthermore, the mode II–mode I ratio for this material was 12.9. This value was the highest when compared with other composite materials from the literature. Finally, through scanning electron micrographs, the dominant failure mechanisms were found to be matrix cracking, fibre debonding and fibre breakage. In addition, shear cusps were observed in mode II specimen, which signified the shearing between the layers.

Numerical simulations of mixed-mode II+III delamination in carbon/epoxy composite laminate

The objective of this study is to develop a reliable finite element model to simulate the mixed-mode II+III delamination behavior using six-point bending plate (6PBP) test. Two different cases were studied, which were 6PBP specimens with 60% (6PBP(60)) and 85% (6PBP(85)) of mode III component, respectively. The delamination behavior was simulated using cohesive zone modeling. Results showed good fits between the experimental and numerical force-displacement curves for both cases. In addition, it was found that there were three and one cohesive elements in the fracture process zone of 6PBP(60) and 6PBP(85) models, respectively. Furthermore, for both cases, the first damaged node in both cases was highly mode III dominated. Not only that, the mode III and mode II components in the first two damaged nodes were different. The numerical results from this study signified that the mode ratio of the 6PBP specimens was not constant.

Impact resistance of short bamboo fibre reinforced polyester concretes

Bamboo fibre is becoming more important as reinforcement in polymer composites owing to its environment sustainability and cost effectiveness. This study examines the performance of bamboo/polyester concretes under impact loading. Specimens at fibre volume fractions of 40 vol.%, 50 vol.% and 60 vol.% and 3 mm, 7 mm and 10 mm fibre lengths were fabricated. Results showed that the optimum impact resistance was attained at 50 vol.%/10 mm, with 16.6 times higher compared to neat polyester. Scanning electron micrographs revealed that the failure mechanisms include matrix cracking, fibre/matrix debonding, fibre pull-out, fibre end damage, fibre splitting and sand particles debonding. In addition, by relating the experimental results to a theoretical model, the damage zone size was found to increase with the fibre length except at 60 vol.%/10 mm, which could be due to fibre–fibre interaction. Results suggest that bamboo fibre is a good candidate to enhance the impact resistance of polyester concrete.