King Jye Wong

Impact behavior of short and continuous fiber-reinforced polyester composites

In this study, the impact strengths of E-glass, coir, oil palm as well as E-glass/coir and E-glass/oil palm hybrid polyester composites were studied. All types of composites were reinforced with fiber volume fractions of 30%, 40%, and 50% and fiber lengths 3, 7, and 10 mm. Composite laminates reinforced with longitudinal and transverse coir fiber mats were also studied. The number of fiber mats varied from 1, 2, 3, and 4 layers for non-spaced fiber mats and 2, 3, and 4 layers for 1.5 mm spaced fiber mats. Besides, coir—polyester composite with addition of sand filler was studied as well, with 40%, 50%, and 60% of volume fractions and fiber lengths of 3, 7, and 10 mm. Results show that impact strength improves with fiber content and fiber length. In addition, longitudinal fiber mats always exhibit better impact toughness compared to transverse fiber mats. Impact strength is improved with the number of fiber layers but worsened by the fiber spacing. As for coir/polyester concrete, low fiber content and fiber length improve the impact strength. The fractured surfaces were inspected under scanning electron microscope to investigate the fracture mechanisms in each type of composites.

Effects of fillers on the fracture behaviour of particulate polyester composites

In the current work, the fracture toughness of sand-particle- and wood-flake-reinforced polyester composites was studied under a linear elastic fracture mechanics approach. The effects of the particulate volume fraction (0–60 vol %) were studied. Scanning electron microscopy was used to observe the damage features on the composite surface. Results showed that sand-particle- and fine-wood-flake-reinforced polymer composites exhibited better results at 40 vol % than at other particulate volume fractions. Meanwhile, coarse-wood-flake-reinforced polymer composites showed higher properties at 30 vol % than at other particulate volume fractions. Observation of the composite surface after tests showed that sand particles have poor interfacial adhesion compared with wood flakes.

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.

Application of cohesive-zone models to delamination behaviour of composite material

The parameters of cohesive elements have to be chosen correctly in the simulation of composite delamination by finite element method: such as interface strength, interface stiffness and shape of cohesive law. The purpose of this work is to investigate their influence on the accuracy of the results obtained. A three-dimensional cohesive-zone model has been established using Ls-dyna to simulate Double-Cantilever-Beam mode I (DCB) and Edge-Notched-Flexure mode II (ENF) tests. The influence of these parameters of cohesive element on the maximum load and the slope of load-displacement curve have been discussed by comparing experimental and numerical results. Four traction-separation laws: bilinear, linear-parabolic, exponential and trapezoidal were considered associated with a large variation of the interface strength and of the initial interface stiffness.

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.

Fracture behaviour of glass fibre-reinforced polyester composite

Fracture toughness and critical energy release rate of polyester-reinforced glass fibres were investigated using linear elastic fracture mechanics approach. The effect of fibre volume fraction of chopped strand mat glass fibres in the matrix on the composite properties was considered. Finite-element analysis using FRANC2D/L was adopted for further verification. The results showed a dramatic increase in the values of fracture toughness and critical energy release rate with increasing fibre content. 60% vf of glass fibres enhanced the fracture toughness and critical energy release rate properties of neat polyester by ∼ 22-fold and 1200-fold, respectively. The numerical results showed an agreement with experimental ones.

An Investigation on Tensile, Compression and Flexural Properties of Natural Fibre Reinforced Polyester Composites

[Abstract]: In the present work, effects of two types of natural fibres on mechanical properties of polyester composites were investigated at different volume fraction of fibre. Tensile, compression, and flexural properties of oil palm bunch and oil palm fruit fibres reinforced polyester composite were presented. In addition, tensile strength of the composites was calculated theoretically. Scanning electron microscope was used to observe the fracture mechanism of the specimens. Single fiber pull-out tests were carried out to determine the interfacial shear strength between polyester resin and oil palm fibres. As results, it was found that both type of oil palm fibres enhanced the mechanical performance of polyester composite. Improved tensile strength was evidence at higher volume fraction (≈41%).when polyester reinforced with oil palm fruit fibres, i.e. 2.5 folds improvement in the tensile strength. Further, experimental tensile strength of oil palm bunch/polyester composites was found to have less variation with the theoretical results compared to oil palm fruit/polyester composites. Flexural strength of polyester was worsened with oil palm fibres at all of fibre volume fraction.

Interfacial shear strength characterisation of alkali treated bamboo bundle – polyester composites using an improved technique

ABSTRACT This study examined the influences of alkali concentration on the interfacial characteristics of bamboo–polyester. Pull-out tests were carried out using a newly designed jig to minimise the fibre breakage during clamping. Bamboo bundles were embedded at 3, 5, 7 and 10 mm and alkali concentrations ranged from 0, 1, 3, 5 to 7 wt-%. The attenuated total reflectance-Fourier transform infrared spectroscopy spectra revealed hemicelluloses was observed at ∼1030 cm−1. The pull-out results showed that interfacial characteristics were not influenced by the embedded length. Furthermore, the highest apparent interfacial shear strength was attained at 3 wt-% concentration, with approximately three times higher compared to the untreated one. A comparison with data from the literature showed that both untreated and treated bamboo/polyester composites have the weakest interfacial bonding. Scanning electron micrographs revealed that alkali treatment has resulted in interface enhancement through chemical modification, mechanical interlocking and frictional contact.

Moisture Absorption Effects on the Resistance to Interlaminar Fracture of Woven Glass/Epoxy Composite Laminates

The influence of moisture absorption on the interlaminar fracture behaviour of 8/8 harness satin weave glass/epoxy composite was investigated. Two series of specimens with 0°/0° and 90°/90° predominant interfaces immersed in water for different duration were tested under double cantilever beam (DCB mode I), single leg bending (SLB mode I + II) and end notched flexural (ENF mode II) loadings. In general, the apparent flexural modulus: E, and the fracture toughness: G C, decrease with increasing moisture content. This effect is more remarkable if mode II participation is bigger. The value of G C measured on 90°/90° specimens reveals higher than that on 0°/0° ones, but the variation in G C is inversed under ENF loading. The experimental results have been correlated with a criterion previously proposed by the first author expressed by: \( G_{TC} = G_{IC} + (G_{IIC} - G_{IC} )\left( {\frac{{G_{II} }}{{G_{I} + G_{II} }}} \right)^{m}.\) A good agreement is shown with m = 2/3 at all moisture contents and interfaces. Regarding the R-curves under DCB loading, water absorption leads to a higher rate of increment in the resistance in the early crack growth. However, the maximum of the resistance to the crack growth decreases with the moisture content.

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.