Harry Ku

An evaluation of fracture toughness of vinyl ester composites cured under microwave conditions

The shrinkage of vinyl ester particulate composites has been reduced by curing the resins under microwave conditions. The reduction in the shrinkage of the resins by microwaves will enable the manufacture of large vinyl ester composite items possible (H.S. Ku, G. Van Erp, J.A.R. Ball, and S. Ayers, Shrinkage Reduction of Thermoset Fibre Composites during Hardening using Microwaves Irradiation for Curing, Proceedings, Second World Engineering Congress, Kuching, Malaysia, 2002a, 22-25 July, p 177-182; H.S. Ku, Risks Involved in Curing Vinyl Ester Resins Using Microwaves Irradiation. J. Mater. Synth. Proces. 2002b, 10(2), p 97-106; S.H. Ku, Curing Vinyl Ester Particle Reinforced Composites Using Microwaves. J. Comp. Mater., (2003a), 37(22), p 2027-2042; S.H. Ku and E. Siores, Shrinkage Reduction of Thermoset Matrix Particle Reinforced Composites During Hardening Using Microwaves Irradiation, Trans. Hong Kong Inst. Eng., 2004, 11(3), p 29-34). In tensile tests, the yield strengths of samples cured under microwave conditions obtained are within 5% of those obtained by ambient curing; it is also found that with 180xa0W microwave power, the tensile strengths obtained for all duration of exposure to microwaves are also within the 5% of those obtained by ambient curing. While, with 360xa0W microwave power, the tensile strengths obtained for all duration of exposure to microwaves are 5% higher than those obtained by ambient curing. Whereas, with 540xa0W microwave power, the tensile strengths obtained for most samples are 5% below those obtained by ambient curing (H. Ku, V.C. Puttgunta, and M. Trada, Young’s Modulus of Vinyl Ester Composites Cured by Microwave Irradiation: Preliminary Results, J. Electromagnet. Waves Appl., 2007, 20(14), p. 1911-1924). This project, using 33% by weight fly ash reinforced vinyl ester composite [VE/FLYSH (33%)], is to further investigate the difference in fracture toughness between microwave cured vinyl ester particulate composites and those cured under ambient conditions. Higher power microwaves, 540 and 720xa0W with shorter duration of exposure are used to cure the composites. Short-bar method of fracture toughness measurement was used to perform the tests. Plastic (PVC) re-usable molds were designed and manufactured for producing the test samples. The results show that the fracture toughness of specimens cured by microwave conditions are generally higher than those cured under ambient conditions, provided the power level and duration of microwave irradiation are properly and optimally selected.

Yield and tensile strength of vinyl ester composites cured by microwaves

In the previous investigation, it was found that the difference in Youngs modulus, ultimate tensile strength and yield strength between microwave cured vinyl ester particulate composites and those cured under ambient conditions is minimal provided low power microwaves are combined with short duration of exposure. The results also show that microwave cured composite samples will result in smaller shrinkage with the similar values of mechanical properties mentioned above than those samples cured under ambient conditions [1]. The reduction in the shrinkage of the resins by microwaves will enable the manufacture of large vinyl ester composite items possible. This research with more data collected is to confirm the earlier results. The values of mechanical properties considered in the two studies are very near and reliable.

Tensile tests of glass powder reinforced epoxy composites: pilot study

Epoxy resin was filled with glass powder to optimize the strength and of the composite for structural applications by a research centre in the University of Southern Queensland (USQ). In order to reduce costs, the centre wishes to fill as much glass microspheres as possible subject to maintaining sufficient strength and fracture toughness of the composites in structural applications. This project varies the percentage by weight of the glass powder in the composites. After casting the composites to the moulds, they were cured at ambient conditions for 24 hours. They were then post-cured in a conventional oven and subjected to tensile tests. It was found that the best percentage of glass powder by weight that can be added to the epoxy resin to give an optimum yield and tensile strengths as well as Young modulus and cost was five percent. It was also found that the fractured surfaces examined under scanning electron microscope were correlated with the fracture toughness. The contribution of the study was that if tensile properties were the most important factors to be considered in the applications of the composites, glass powder is not a suitable filler. It is also hoped that the discussion and results in this work would not only contribute towards the development of glass powder reinforced epoxy composites with better material properties, but also useful for the investigations of tensile properties in other composites.

Tensile properties of nanoclay reinforced epoxy composites

Kinetic epoxy resin was filled with nanoclay to increase tensile properties of the composite for civil and structural. This project manufactured samples with different percentages by weight of nanoclay in the composites in steps of 1 wt %, which were then post-cured in an oven. The samples were then subjected to tensile tests. The results showed that the composite with 3 wt % of nanoclay produced the highest yield and tensile strengths. However, the Young’s modulus increased with increasing nanoparticulate loading. It is hoped that the discussion and results in this work would not only contribute towards the further development of nanoclay reinforced epoxy composites with enhanced material properties, but also provide useful information for the studies of fracture toughness, tensile properties and flexural properties of other composites.

Flexural Properties of Epoxy Composites Filled with Glass Powder: Preliminary Results

Epoxy resin was filled with glass powder with a view to increasing strength of the composite for structural applications by a research Centre on composites, University of Southern Queensland (USQ). In order to reduce costs, the Centre wishes to fill as much glass powder as possible subject to maintaining sufficient strength of the composites in structural applications. This project varies the percentage by weight of the glass powder in the composites which are then subjected to flexural tests. The results show that composite with 25 % by weight of the glass powder produces the highest flexural strength and Young’s modulus combined with a reasonable fluidity for casting; the highest flexural strain was achieved when the percentage by weight of glass powder is 10 %.

Dielectric properties of sawdust reinforced epoxy composites post-cured in microwaves:

This study focuses on the measurement and evaluation of dielectric properties of composite materials with a view to benefiting these relevant industries. Previously published have been the mechanical and thermal properties of sawdust reinforced epoxy composites. The properties of a dielectric material can be controlled through the introduction of various fillers. This study was primarily undertaken to determine the effect of sawdust on the dielectric properties of the composites. The original contribution of this paper states that samples post-cured in microwaves have higher dielectric constant values but lower loss tangent values than their counterparts post-cured in an oven. For all percentages by weight of sawdust, the glass transition temperature for the microwave-cured samples was lower and the composite was softer; the opposite was true for the oven-cured sample. In addition, the storage modulus of all samples post-cured in microwaves is also lower than their counterparts. This is in line with the fact that it is a softer material and has lower storage modulus and lower glass transition temperature.

Modelling of tensile properties glass powder/epoxy composites post-cured in an oven and in microwaves

This paper discusses a simplified approach to analyse the mechanical properties of randomly distributed particulate composites. Mechanical properties of glass powder–filled vinyl ester resins were experimentally investigated. The analytical results were compared with experimental results and a very good correlation was found. Further, the experimental results and the predictions showed that the strength of the composites is less than the strength of the matrix material, for all three composites tested.

Flexural properties of sawdust-reinforced epoxy composites post-cured in microwaves

Epoxy resin was filled with sawdust to optimize the flexural properties of the composite for structural applications. In order to reduce costs, it will be necessary to fill as much sawdust as possible subject to maintaining sufficient strength of the composites in civil and structural applications. This project varies the percentage by weight of the sawdust in the composites. The sawdust particles were sieved into three different sizes, which were <425u2009µm, 425–600u2009µm and 600–1180u2009µm, respectively. Palm oil was also added to the composites of epoxy resin and sawdust as a plasticizer to improve the flexibility of the composites. After casting the composites to the moulds, they were cured at ambient conditions for 24u2009h. They were then post-cured in a conventional oven or microwave irradiation and subjected to flexural tests. It was found that the best percentage of sawdust, with particle size of <425u2009µm, and of palm oil, by weight that can be added to epoxy resin to give an optimum flexural modulus and flexural strength, as well as cost was 15% and 5%, respectively. The contribution of the study was that if flexural modulus was the most important factor to be considered in the applications of the composites, sawdust is a suitable filler. However, if the most sought after properties were the flexural strength then sawdust is not a suitable filler.

A pilot study on the relationship between mechanical and electrical loss tangents of glass powder reinforced epoxy composites post-cured in microwaves

The mechanical and thermal properties of hollow glass powder reinforced epoxy resin composites have been measured and evaluated in earlier studies. This basic but critical and important data have caused interests in the relevant industry in Australia. This study is therefore carried out to measure and evaluate the dielectric properties of the composites with a view to benefit the relevant industry. The relationship between the dielectric and thermal properties will also be studied and correlated. The original contributions of this paper are that samples post-cured in conventional ovens have higher electrical as well as mechanical loss tangent values than their counterparts cured in microwaves only. The storage modulus of all samples post-cured conventionally is higher than its counterpart. This is in line with the fact that they are softer material with lower glass transition temperatures. For all percentages by weight of glass powder, the glass transition temperature for the microwave cured sample was higher and the composite was stiffer; the opposite was true for the conventionally cured samples.

Assessing Heat-Treatment Effects on Bovine Cortical Bones by Nanoindentation

Among different sterilization methods, heat-treatment of bone is recognized as one of the simple and practical methods to lower the human immunodeficiency virus (HIV) infection and overcome the risks of rejection and disease transfer from allograft and xenograft during bone transplantation. In order to best characterize the micro-structural mechanical property of bone after heat treatment, the nanoindentation technique was applied in this study to measure the localized elastic modulus and hardness for interstitial lamellae and osteons lamellae of bovine cortical bones at temperature 23°C (room temperature-pristine specimen), 37°C, 90°C, 120°C and 160°C, respectively. The elastic modulus (E) and hardness (H) of interstitial lamellae obtained higher values as compared with osteons lamellae which show that interstitial lamellae are more stiff and mineralized than osteons. Moreover, as a specimen pre-heat treated at 90°C, the E and H values of interstitial lamellae and osteons were closed to a pristine specimen. For a specimen pre-heat treated at 120°C, both interstitial lamellae and osteons obtained an increase in E and H values. As a specimen pre-heat treated at 160°C, the interstitial lamellae and osteons obtained a slight decrease in E and H values. These findings are correlated to results reported by other researchers [1, 2] that calcified collagen molecules starts to degenerate at about 120°C and complete at 160°C. Interestingly, when a specimen was pre-heat treated at 37°C, both interstitial lamellae and osteons obtained significant decreases in E values of 57% and 40%, respectively as compared to the pristine specimen; while in H values, there was a decrease of 27.4% and 15%, respectively. Thus, this paper will investigate the mechanical properties of bovine cortical bones under various temperature ranges by nanoindentation technique.