Papers by Author: Ian J. Davies

Abstract: This paper presents a study on the effect of alkali treatment of Oil Palm Kernel Shell (OPKS) on the mechanical properties ofpolyester composite. The dosage of NaOH in this study is limited to 5wt% concentration.The experiments on mechanical properties investigate the tensile strength, the flexural strength and theflextural modulus of untreated, cold alkali treated and hot alkali treated OPKS reinforced polyester composite. It is found that the alkali treatment improves the mechanical properties of the composite. However, the improvement due tothe hot alkali treatment is significant compared to the cold alkali treatment. The morphology of OPKS and the fracture surface of OPKS composites were investigated using scanning electron microscopy (SEM), showing a rough surface and good interfacial adhesion between OPKS as filler and polyester as a matrix.

Abstract: The effect of surface modified Si-Al-C® fibre with carbon interface (SA/C fibre) addition on the densification of silicon carbide (SiC) composite was examined. An acid treatment (H2SO4 and HNO3) was carried out at 50°C for 3 h in order to add COO- group to the surface of SA/C fibre and to enhance the dispersibility of SA/C fibre in the SiC powder due to the mixing operation in the polar solvent. Commercially available ultrafine SiC powder (specific surface area: 47.5 m2∙g-1) was mixed with acid-treated SA/C fibre and sintering aid (4.8 mass% Al4C3 and 1.2 mass% B4C) in the presence of acetone. The relative density of the SiC composite with non-acid-treated SA/C fibre addition hot-pressed at 1800°C for 1 h in Ar atmosphere under a pressure of 62 MPa was 98.4%, whereas that of the SiC composite with acid-treated SA/C fibre addition increased to 98.7%. Furthermore, the fracture toughness increased from 5.6 MPa∙m1/2 to 7.0 MPa∙m1/2 for the acid-treated SA/C fibre addition.

Abstract: The fabrication conditions of dense silicon carbide (SiC) composites containing chopped Tyranno Si-Al-C (SA) fiber were examined in this work; SiC compacts containing SA fiber (mean lengths: 214, 394 and 706 m) were hot-pressed at 1800°C for 30 min under a pressure of 31 MPa in Ar atmosphere. The fracture toughness of SiC composites with 40 mass% of SA fiber addition (sintering aid: 5 mol% Al4C3) increased from 2.8 up to 4.7 MPa•m1/2 as the fiber length increased from 214 to 706 m. The enhanced fracture toughness of the SiC composites was attributed to the lowering of fiber orientation angle (i.e., the angle between the fiber length and direction perpendicular to the hot-pressing direction) to 5° with increasing fiber length. The fracture toughness of SiC composites could be further enhanced through the incorporation of SA fibers with a carbon interface (thickness: 100 nm) into the SiC matrix. The fracture toughness of SiC composite containing 40 mass% of these fibers attained 6.0 MPa•m1/2. The thermal conductivity of SiC composites increased with fiber length from 30.5 W•m-1•K-1 to 45.5 W•m-1•K-1; with no significant influence being noted for the case of fibers with a carbon interface.

Abstract: The flexural behaviour of 6-ply unidirectional hybrid fibre-reinforced polymer (FRP) matrix composites containing a mixture of E-glass and S2-glass fibres was investigated. A high performance epoxy system comprising of Kinetix® R240 epoxy resin (combined with Kinetix® H160 epoxy hardener) was utilised for the composite matrix. Flexural testing was conducted in accordance with Procedure A of the ASTM D790-03 test standard on a universal testing machine equipped with a three-point bend test rig. In addition to varying the stacking configurations of the composite prepregs, the influence of span-to-depth ratio on the flexural properties and failure mechanisms was also studied. The failure mechanisms of the resulting fractured specimens were characterised using optical microscopy and compared with those noted by the authors in previous work.

Abstract: The microstructure (i.e., fibre volume fraction, void content, and fibre misalignment) of unidirectional carbon fibre-reinforced polymer (CFRP) composites was optimised by controlling several parameters during manufacture, namely: (i) compressive pressure (0.25~1.25 MPa, in steps of 0.25 MPa), (ii) vacuum pressure (−0.15, −0.20, −0.30, −0.45, and −0.65 MPa), and (iii) holding temperature (100~140 oC, in steps of 10 oC), applied during autoclave curing with the holding time being 30 minutes for all specimens. Optical micrographs captured from cross-sectional, through-the thickness areas, and in-plane areas of the resulting composites were evaluated and analysed in order to describe their microstructural characteristics.

Abstract: Epoxy composites reinforced with recycled cellulose fibre (RCF) have been synthesized and characterized. The reinforcement by RCF has resulted in a significant increase in the strain at break, fracture toughness and impact toughness but moderate increase in flexural strength and flexural modulus. The effect of seawater soaking on the flexural and impact properties has also been investigated. The micromechanisms of toughening and crack-tip failure processes are identified and discussed in the light of observed microstructures from in-situ and ex-situ fracture.

Abstract: Structure-property relationships in bovine cortical bone have been characterised using grazing-incidence synchrotron radiation diffraction, Vickers indentation and mechanical testing. Depth profiling results indicated the existence of distinct gradual changes in crystal disorder, phase abundance, and texture of hydroxyapatite whilst the crystallite size was depth-independent.

Abstract: The phosphoryl oligosaccharides of calcium (POC), extracted from potato starch, are composed of phosphorus oligosaccharides and calcium ions. Ultrafine calcium phosphate particles, whose main phase was hydroxyapatite (Ca10(PO4)6(OH)2: HAp), could be prepared through the hydrothermal treatment of POC solution at a temperature between 110 and 130°C; X-ray diffraction indicated the crystallinity of HAp in the resulting powder to be poor and similar to that of living bone. The present HAp powder was regarded to be calcium deficient carbonate apatite with the OH- group being partly substituted by a carbonate (CO3 2-) group. The solubility of the resulting powder in dilute hydrochloric acid was higher compared to that of commercially available HAp, suggesting excellent bioabsorbability for the present powder.

Abstract: Structure-property relationships in baby and adult teeth have been characterised using grazing-incidence synchrotron radiation diffraction and Vickers indentation. Similarities and differences between both types of teeth have been highlighted and discussed. Depth profiling results indicated the existence of contrasting but distinct gradual changes in crystal disorder, phase abundance, crystallite size and hardness within the baby and adult canine enamel, thus confirming the graded nature of human teeth. When compared to the adult tooth, the baby enamel is softer, more prone to fracture, but has larger hydroxyapatite grains.