Applied Mechanics and Materials Vols. 465-466

Abstract: Electromagnetic Interference (EMI) issue is gaining more attention as the result of proliferation of electrical and electronic devices. In order to reduce the exposure to EMI, shielding and absorbing materials are often applied. This paper discussed the process of forming the nickel-zinc ferrite as one of the absorbing material by mixing the nickel nitrate, zinc nitrate and iron (III) nitrate together. X-ray diffraction, scanning electron microscopy, and dielectric measurement are carried out to reveal the characteristic of the specimen. The sintering temperature determines the formation of a pure spinal nickel-zinc ferrite and grain size.

Abstract: Steel is a mostly challenging metal to semisolid process because of the high temperatures implicated and the prospective for surface oxidation. Slurry processing experiment was performed with AISI D2 cold work tool steel to identify the evolution of globular microstructures via Direct Partial Re-Melting Method (DPRM). Samples were heated in an argon atmosphere up to 1330°C which corresponded to about 38% of liquid fraction and held for 5 minutes. The typical microstructure after DPRM consists of globular grains (average grain size about 50μm) while the remaining interspaces were filled by precipitated eutectic carbides on the grain boundaries and lamellar network. Based on the requirements of thixoformability, the current work confirms the suitability of the AISI D2 cold work tool steel as a candidate material for semi-solid forming.

Abstract: Due to the disadvantageous of solid state in CaCu₃Mn₄O₁₂ ceramic processing, the sol gel synthesis has been extensively studied to produce fine size of powder and better homogeneity at low processing temperature. This paper provides a summary to prove that the single phase of CaCu₃Mn₄O₁₂ ceramic with high purity and characteristic is actually can be produced via sol gel synthesis at relative low temperature under pressureless sintering process. The stoichiometric CaCu₃Mn₄O₁₂ powders were successfully prepared by the citric gel method with molar ratio of [citrates/metallic io; 1:2. The precursor gel formed was calcined and sintered at range 400 °C to 800 °C. A single-phase CaCu₃Mn₄O₁₂ fairly well densified at relative low temperature under atmospheric sintering condition. Analysis has been done under XRD and FESEM. Result shown formation of CaCu₃Mn₄O₁₂ started at 500 °C and was formed completely at 700 °C for 18h. FESEM results turned out that CaCu₃Mn₄O₁₂ powder particle is submicron in size and highly agglomerates due to high calcinations temperature. Varying in sintering parameter is actually exhibit differences in phase formation, grain size and magnetic behavior.

Abstract: The evaluation of 0.1 to 1.0% of Ce addition effect on fluidity has been investigated. The fluidity of LM6 has decreased with the Ce addition. The effect of Ce can be shown very clearly with a high amount of 1% wt of Ce. The fluidity length of the composites is shorter than that of the LM6 base material. In spiral mold, the fluidity length is shortened when the weight percentage of Ce content is increased in the base metal LM6. Optical microscope images showed that the 1.0 % of Ce additive led to modification of silica morphology which reduced the fluidity length to 28%. The partial modification of silica can be observed clearly in small amount of Ce but it does not have large affect on the fluidity length.

Abstract: Hydroxyapatite (HA) is a biomaterial with excellent biocompatibility. However, the brittleness and low fracture toughness of HA have limited its biomedical applications. As such, HA has been incorporated with zirconia (ZrO2) to enhance its mechanical strength. However, ZrO2 addition decreases the phase stability of HA. HA decomposition is not favored because it decreases the mechanical strength of HA/ZrO2. In this paper, the effect of sintering on HA decomposition is reviewed. Experimental results show that hot isostatic pressing of HA/ZrO2 is one of the most effective methods to suppress HA decomposition, yielding the highest relative density compared with other sintering methods.

Abstract: The development of high-performance materials made from natural resources are increasing worldwide in recent years. Natural fibres offer both cost savings and reduction in density when compared to Kevlar fibres. However, the strength of natural fibres is not as great as Kevlar. The following preliminary research investigated the use of Kevlar fibres in kenaf composites as a possible to improve the impact properties. The impact properties of Kevlar reinforced in kenaf composites was studied by using DYNATUP 9250 drop weight machine. According to the standard ASTM D638 Kevlar fibres in different weight percentage of 10,15,20 and 25 wt% were reinforced with kenaf/epoxy composites by using hand lay-up combined with cold-press method. It is clearly observed that the impact strength and hardness were increased with the addition of weight percentage of woven Kevlar in the kenaf composites. The highest energy was recorded at 12.76 J by hybrid composite in combination of 2Kevlar/Kenaf/2Kevlar. The microstructure observation of impacted hybrid samples indicated that the delamination area was increased with the increasing of the impact energy.

Abstract: This study investigated the influence of electrospun polyurethane mats containing different contents of carbon nanotubes (CNTs) stacked in between basalt fabric layers to form a composite laminate. The composite laminate was fabricated using a vacuum-assisted resin transfer molding (VARTM) process. Flexural test were carried out to investigate the strength and stiffness of composites for each configuration, while the failure characteristics were observed using a field emission scanning electron microscopy (FESEM) analysis. The results showed that flexural strength and stiffness of the hybrid composites with increasing CNT content in polyurethane (PU) nanofiber were increased by 6.5% and 17.3%, respectively. Furthermore, the addition of surfactants for the dispersion of CNTs in nanofibers significantly improved the flexural property of the composite interply basalt fabric-CNT/PU laminates. This study proved that the use of multi-scale reinforcement fillers with good and homogeneous dispersion increased the mechanical performance of the composite.

Abstract: All-ceramic dental crown restoration is popular because it results in better aesthetic quality than metal alloy restoration. Ceramics also show superior biocompatibility and inertness to human biological systems. However, clinical experience indicates that all-ceramic crowns are not as durable as their porcelain-fused-to-metal counterparts, particularly on molar teeth. New ceramic biomaterials that combine durability with excellent aesthetic qualities have been developed. In this study, several promising bioceramics for dental crown applications are evaluated and compared. The evaluated parameters include strength of the material, survival rate in clinical performance, and aesthetic quality.

Abstract: Mechanical failure of a structure or a machine during the regular working conditions are often related to the fatigue damage. As a consequence, the structural integrity monitoring of a system has always been a laborious task in the field of engineering. Since the strain measurement is one of the most important predictors of fatigue life, a precise strain measurement method is therefore required. There are many strain measurement methods in fatigue analysis; namely strain gauge, brittle coating method, photoelastic-coating and other optical strain measurement methods. However, various advantages and disadvantages have been found in each of the method mentioned above. Hence, there is always a need to develop a precise and yet informative strain measurement method in mechanical testing. The objective of this study is to develop the first-order shape functions for fatigue test using the Digital Image Correlation technique. In this study, sub-pixel accuracy image correlation algorithm was developed by using MATLAB whereby the positions of the points were precisely selected by using the fine-tuned function. As a result, the first-order shape functions were determined by retrieving the information that is stored in the affine transformation matrix. The works presented in this paper were mainly focused on the development of the algorithms, together with the results and the discussions for the validation exercises. In conclusion, a good agreement was achieved and the newly developed algorithm was proven to be accurate.

Abstract: Titanium has been widely used in many field of application due to the low density, sensitive to corrosion, high mechanical strength and ease of fabrication. It also has been widely used as structural materials in variety of industrial fields such as aeronautical, energy and chemical industry. Plating of metal on titanium is complex and difficult because titanium always reacts with air to form oxide. It is difficult to obtain good adhesive property on the titanium surface. Thus, to plate metal on the titanium, oxide layer must be eliminated by using an intermediate pre-treatment. However, this process involves several steps and even then the level of addition between the plated metal and the titanium is poor. This paper presents the results of the thickness and morphology of plated sample with the effects of the rate of deposition. The level adhesion of the nickel coating was determined qualitatively by using adhesion testing while morphology and thickness of Ni plated was studied using scanning electron microscopy (SEM) and field emissionscanning electron microscopy (FESEM). The results show by increasing the solution movement, it has been possible to obtain higher rate of plating and Ni deposits with higher hardness and finer grain structures. By using high speed electroplating and by maintaining a narrow gap between the anode and the cathode, it has been possible to electrodeposit Ni directly on Ti without any pre-treatment or even without any traditional cleaning before plating.