Key Engineering Materials Vols. 462-463

Abstract: Almost all the phenomena occurring around us are the coupled phenomena. In the field of numerical analysis, it is difficult to perform coupled analysis. Because, there are a lot of problems and these problems make coupled analysis difficult, so we have to resolve these problems to perform analyses with considering the coupling effect. At present, as the popularity of numerical analysis rising along advancement in computer performance, demand of numerical analyses with incorporating coupling effects will further increase. In this research, we propose a new fluid-structure coupled analysis method using SUPG/PSPG stabilized FEM and Enriched Free Mesh Method to eliminate a lot of problems occurring in the process of coupled analysis. As the feature of our proposed method, linear triangular elements are only used in the analysis.

Abstract: The effect of heat treatment on tensile and creep properties of nickel-base superalloy, Inconel 718 in room and at high temperature was investigated. Solution treatment was applied on the as-received material at 980oC for 1 hour before water quenched followed by double aging treatments at 720oC and 621oC for 8 hours, respectively and then cooled in air. The tensile strength at elevated temperatures of 550oC and 650oC were slightly deteriorated for heat treated and as-received materials. Beside strength, significant difference was observed in the elongation. The elongation of heat treated samples drastically reduced to 4 to 5% only compared to that of the as received materials which exhibited more than 30% elongation. The significant increased in tensile strength is suspected due to the present of γ’, γ” and δ precipitates which pinned the movement of grain boundary and sliding. However, the present of these precipitates caused the material to become harder and brittle. Moreover, the increase in load from 70% to 90% UTS and in temperature significantly accelerated the creep rate.

Abstract: The corrosion of four Fe-Cr alloys (Cr: 9, 12, 20, and 25%) with different Cr contents were subjected to cyclic oxidation furnace in Ar-10%O2 atmosphere at 950oC for 120 h. The samples after oxidation were investigated by using X-ray diffraction (XRD), optical metallography and SEM/EDS. The results indicated that increasing Cr content reduced the oxidation rate and the scale cracking. Alloys with less Cr content occurred breakaway oxidation due to formation of Fe-rich oxide scale. However, a thin protective chromia scale was observed on alloys with Cr > 20%. The corrosion behaviour on Fe-Cr alloy was then discussed based on experimental observation.

Abstract: This study presents a mesh generation technique considering the measurement accuracy of the potential on an inverse analysis using the boundary element analysis. We evaluate the effects of the distance between layered rebar and corrosion size on measured potential distribution on the concrete surface, and then propose a technique to select reasonable and efficient size of boundary element. A numerical simulation demonstrates the validity and efficiency of the proposed technique.

Abstract: This study evaluates effects of the diffusion layer thickness and the share stress on metal surface for the polarization curve under flow field on metal corrosion. We measure the polarization curves under the different diffusion boundary layer thickness and the wall share stress. Metal surface conditions are observed from microscopic and macroscopic view points to evaluate tendencty of corrosion and shape of corrosion product.

Abstract: In this paper, combination of a boundary element formulation and genetic algorithm (GA) was developed and used for analyzing of cathodic protection systems of buried pipe-lines structures. It is very important to maintain the effectiveness of the cathodic protection system for pipeline structure, in order to lengthen the lifetime of the system. However, nowadays the evaluation of the effectiveness of the system only could be performed after the system applying in the field. This study was conducted to combine 2D boundary element method (BEM) and GA in order to evaluate the effectiveness of the cathodic protection system for pipe-lines structure using ribbon sacrificial anode. Two factors i.e. the soil conductivity and the distance between pipe-lines and anode, were analyzed by using the proposed method. In this method, the potential in the domain was modeled by Laplace’s equation. The anode and cathode areas were represented by polarization curves of different metals. Boundary element method was applied to solve the Laplace’s equation to obtain any potential and current density in the whole surface of the pipe. The pipe and anode were modeled into 2D model. The numerical analysis result shows that the optimum distance between pipe-lines and anode can be determined by combining BEM and GA.

Abstract: In the last decade, failure of microelectronic devices has become a prominent field of research all across the world. The results of this of failure analysis allow an engineer to choose package geometries and materials which reduce the risk of failure. This paper is meant to relate the stress effect on material properties during Quad Flat No-Leads (QFN) stacked-die packages manufacturing processes. To achieve the study, the finite element technique was used to perform an extensive structural analysis on a QFN package design once it was verified by related experiments. A QFN unit was developed in three dimensional geometry with various materials be will simulated in order to determine the location of failure. The induced stress results were also measured in the maximum value, indicating the low modulus and coefficient of thermal expansion (CTE) in the packaging material were important for reducing high stress during the manufacturing stages. However, numerical simulation demonstrated that the stress developments increased exponentially when the die attach temperature increased. Therefore, the induced stress can be relieved by having high die attach process temperature with an adequate bonding force and time. It was vital to control the induced stress in package materials during die attachment process for ensuring the reliability level of QFN packages.

Abstract: Over the years the methods for checking bonding quality during volume production still remains the same. These inspection methods like ball shear to test the first bond quality and wire pull to test the second bond integrity and quality have proven to be acceptable and achievable for many current industrial needs. However, driven by the relentless pursuit of dimensional reduction in wire bonding technology which calls for reduction in wire diameter, these conventional methods may not be sufficient. The interaction between machine, bonding tools, materials and the different categories of failure modes and mechanism during this quality test has become much more sensitive. The intent of this paper is to study and define the different categories of failure modes during 2nd bond test for ultra fine gold wire from 15 micron diameter up to 50 micron diameter. Therefore, lifted stitch or lifted 2nd bond which is a failure description known to be a ‘reject’ before can be re-visited. Analysis found that the two different test locations revealed that test location B or placing the hook as near possible to the leads where the 2nd bond was bonded is the better method to test the 2nd bond strength and performance as compared to the earlier bond pull method (location A).

Abstract: A material’s sound absorbing properties can be described as a sound absorption coefficient in a particular frequency range. Porous absorbers are the most commonly used sound absorbing materials, however they do not have good absorption properties at low and mid frequencies. In order to increase the absorption properties at low and mid frequencies, porous absorber should have larger thickness and size. By using perforated plates backing with porous absorber, it is possible to gain higher noise absorption at low and mid frequencies. This study was conducted to investigate the effect of perforation size ratio, mass, air gap and holes diameter of perforated plates as backing plate for porous absorber. Coconut fibres were used as backing medium for perforated plates. Perforated plates were fabricated using two different materials; aluminium and zinc plates with perforation size ratio of 0.10, 0.15 and 0.22 at thickness of 1 mm. The holes diameters of the perforated plates are 2 mm, 3 mm, and 4 mm, respectively. The tests samples were tested at the acoustic lab of the Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia according to ASTM E 1050-98 international standards for noise absorption coefficient. The data presented the perforated plates backing with coconut fibers have perforation ratio less to 0.22 showed the significant absorption at 800 Hz – 1800 Hz frequency range. The perforated plates backing with coconut fibers that their holes diameters are 4 mm also showed a good absorption at 600 Hz – 1800 Hz frequency range. However, perforated plates backing with coconut fibers showed a decreasing absorption coefficient at frequencies more than 1800 Hz.

Abstract: An asymptotic analysis for singular stress fields around an interface-edge of dissimilar power-law hardening materials joint has been presented under plane strain condition and J2 deformation plasticity theory. Both the balance of force and the continuity of displacement are satisfied on the interface. In the higher order approximation, the nonlinear effective stress term was expanded by Taylor series. An iteration method is proposed for the determination of singular fields around interface edge. Multiple stress singular terms exist for in the higher order approximation. The order of stress singularity has a dependency with the combination of hardening exponents, .