Ahmad Kamal Ariffin

Multi objective optimization of foam-filled circular tubes for quasi-static and dynamic responses

FUEL CONSUMPTION AND SAFETY ARE CURRENTLY KEY ASPECTS IN AUTO-MOBILE DESIGN. THE FOAM-FILLED THIN-WALLED ALUMINIUM TUBE REPRE-SENTS A POTENTIALLY EFFECTIVE MATERIAL FOR USE IN THE AUTOMOTIVE INDUSTRY, DUE TO ITS ENERGY ABSORPTION CAPABILITY AND LIGHT WEIGHT. MULTI-OBJECTIVE CRASHWORTHINESS DESIGN OPTIMIZATION FOR FOAM-FILLED DOUBLE CYLINDRICAL TUBES IS PRESENTED IN THIS PAPER. THE DOUBLE STRUCTURES WERE IMPACTED BY A RIGID WALL SIMULATING QUASI-STATIC AND DYNAMIC LOADINGS. THE OPTIMAL PARAMETERS UNDER CONSIDERATION WERE THE MINIMUM PEAK CRUSHING FORCE AND MAXIMUM SPECIFIC ENERGY ABSORPTION, USING THE NON-DOMINATED SORTING GENETIC ALGORITHM-II (NSGA-II) TECHNIQUE. RADIAL BASIS FUNCTIONS (RBF) AND D-OPTIMAL WERE ADOPTED TO DETERMINE THE MORE COMPLEX CRASHWORTHINESS FUNCTIONAL OBJECTIVES. THE COMPARISON WAS CARRIED OUT BY FINITE ELEMENT ANALYSIS OF THE IMPACT CRASHWORTHINESS CHARACTERISTICS IN TUBES UNDER STATIC AND DYNAMIC LOADS. FINALLY, THE OPTIMUM CRASHWORTHINESS PERFORMANCE OF EMPTY AND FOAM-FILLED DOUBLE TUBES WAS INVESTIGATED AND COMPARED TO THE TRADITIONAL SINGLE FOAM-FILLED TUBE. CONSEQUENTLY, THE RESULTS INDICATE THAT THE FOAM-FILLED DOUBLE ALUMINIUM CIRCULAR TUBE CAN BE RECOMMENDED FOR CRASHWORTHY STRUCTURES.

An experimental investigation on the response of woven natural silk fiber/epoxy sandwich composite panels under low velocity impact

This paper presents results of dynamic deformation behavior of woven natural silk/epoxy sandwich composite panels. The specimens were prepared in configurations of reinforced woven natural silk fiber (RWNSF)/Epoxy/Foam, RWNSF/Epoxy/Coremat; RWNSF/Epoxy/Honeycomb and reinforced RWNSF/Epoxy (control material) using hand-lay-up method. Each of the three core material was sandwiched between reinforced woven natural silk fiber/Epoxy composite facesheet. Drop weight impact test was carried out under 32 J impact energy. Degree of damages inflicted on the contact surface, through thickness and rear surface were analyzed, sandwich composites performed better than the reinforced (control material). Failure mechanism involved interlaminar matrix cracking, layer debonding, delamination and fibre breakage.

Incorporating feedforward neural network within finite element analysis for L-bending springback prediction

A generalised neural network has been implemented in the finite element simulation.The trained data is applicable to different finite element simulation.The method improves the springback prediction as compared to the experimental data. The use of the latest nonlinear recovery in finite element (FE) analysis for obtaining an accurate springback prediction has become more complicated and requires complex computational programming in order to develop a constitutive model. Thus, the purpose of this paper is to apply an alternative method that is capable of facilitating the modelling of nonlinear recovery with acceptable accuracy. By using the artificial neural network (ANN), the experimental results of monotonic loading, unloading, and reloading can be processed through a back propagation network that is able to detect a pattern and do a direct mapping of elastically-driven change after the plastic forming. FE analysis procedures were carried out for the springback prediction of sheet metal based on an L-bending experiment. The findings of the FE analysis show an improvement in the accuracy of the predictions when compared to the measured data.

Thermal–mechanical model of warm powder compaction process

Abstract A coupled mechanical and thermal analysis of powder during the warm compaction process has been investigated. This paper presents the development of the numerical model to generate a green compact through uniaxial die compaction. The powder is considered to be the rate independent thermo-elastoplastic material. The constitutive laws are derived based on a continuum approach and the governing equations are developed where the thermal strain is taken into account together with elastic and plastic strains. The Elliptical Cap failure criterion is considered to model the yielding of the material during the process. A large displacement based finite element approach is used considering an updated Lagrangian strategy. The non-linear systems of equations are solved employing the staggered-incremental-iterative solution strategy.

Mode III Stress Intensity Factors of Surface Crack in Round Bars

This study presents a numerical investigation on the stress intensity factors (SIF), K of surface cracks in round bars that were obtained under pure torsion loadings or mode III. ANSYS finite element analysis (FEA) was used to determine the SIFs along the crack front of surface cracks embedded in the solid circular bars. 20-node isoparametric singular elements were used around the crack tip by shifting the mid-side node ¼-position close to a crack tip. Different crack aspect ratio, a/b were used ranging between 0.0 to 1.2 and relative crack depth, a/D were ranged between 0.1 to 0.6. Mode I SIF, KI obtained under bending moment was used to validate the proposed model and it was assumed this proposed model validated for analyzing mode III problems. It was found that, the mode II SIF, FII and mode III SIF, FIII were dependent on the crack geometries and the sites of crack growth were also dependent on a/b and a/D.

FAILURE ANALYSIS OF A SEMICONDUCTOR PACKAGING LEADFRAME USING THE SIGNAL PROCESSING APPROACH

This paper presents a durability analysis of two types of copper leadframe, i.e. the un-oxidised leadframe and the oxidised leadframe. Both leadframe types were used in the fabrication process of a Quad Flat No-Lead (QFN) package, which can be said as a recent type of the 3D stacked die semiconductor package. This study involved the durability test and analysis on QFN packages when these packages were subjected under constant cyclic loadings. In order to perform the cyclic test, the procedure of the three-point cyclic bending test has been employed on the packages. In addition, a strain gauge which was connected to the dynamic data acquisition system was used for each tested QFN package for determining the response of the captured cyclic strain signal. It has been found that the variable amplitude pattern of signal response has been obtained during the constant cyclic test. The obtained response signals for both type of leadframe were then analysed using the approaches of signal processing technique, which is relatively new in this field. The collected response signal were analysed using the normal statistical methods, the Power Spectrum Density (PSD) calculation and also the time-frequency localization analysis. From the detail signal analysis, it has been found that the un-oxidised leadframe showed a lower range of strain response compared to the oxidised leadframe, indicating higher lifetime. As a result, this finding lead to the durability conclusion, for which the un-oxidised leadframe has more durability effects and it also has higher lifetime compared to the oxidised leadframe. Finally, a micro-crack phenomenon at the epoxy interface between the die and the leadframe was also observed for the QFN package with the oxidised leadframe.

Simulation of the Ill-Posed Problem of Reinforced Concrete Corrosion Detection Using Boundary Element Method

Many studies have suggested that the corrosion detection of reinforced concrete (RC) based on electrical potential on concrete surface was an ill-posed problem, and thus it may present an inaccurate interpretation of corrosion. However, it is difficult to prove the ill-posed problem of the RC corrosion detection by experiment. One promising technique is using a numerical method. The objective of this study is to simulate the ill-posed problem of RC corrosion detection based on electrical potential on a concrete surface using the Boundary Element Method (BEM). BEM simulates electrical potential within a concrete domain. In order to simulate the electrical potential, the domain is assumed to be governed by Laplace’s equation. The boundary conditions for the corrosion area and the noncorrosion area of rebar were selected from its polarization curve. A rectangular reinforced concrete model with a single rebar was chosen to be simulated using BEM. The numerical simulation results using BEM showed that the same electrical potential distribution on the concrete surface could be generated from different combinations of parameters. Corresponding to such a phenomenon, this problem can be categorized as an ill-posed problem since it has many solutions. Therefore, BEM successfully simulates the ill-posed problem of reinforced concrete corrosion detection.

K-means clustering and neural network for evaluating sound level vibration in vehicle cabin

One of the characteristics that may influence customers in vehicle purchasing is the level of comfort of the vehicle’s sound vibration in the vehicle cabin. The basic principle suggests that the sound vibration discomfort level is affected by a few factors which are mainly based on magnitudes, frequencies, directions and also the exposed periods. Normally, the phenomenon of sound vibration disrupts the performance of the driver by affecting the driver’s vision and also inducing a certain degree of stress due to the sound and vibration to which the driver and his or her passengers are exposed. The sound vibration is generally contributed by a few sources originated from the transmission of the vehicle’s engine, tire interactions with the road surface and also the exposure of vehicle’s body vibration during the movement. The objective of this study is to propose an approach that clusters the level of sound and vibration into a few categories and classifies them into those categories without implementing the subjective test that normally involves human assessment. The study has observed the changes of the sound quality and the level of vibration at particular points in the vehicle cabin over the changes of engine speeds. In reference to the results, the study has successfully provided a technical procedure in order to cluster, and also to classify, the level of sound vibration by taking into account the correlation between experienced noise and exposed vibration in the vehicle cabin.

CORROSION RISK ASSESSMENT OF PUBLIC BUILDINGS AFFECTED BY THE 2004 TSUNAMI IN BANDA ACEH

Banda Aceh region has a coastal environment and frequent earthquakes. The 2004 Sumatra tsunami caused many buildings to collapse and became submerged by seawater in the region. Thus, the buildings might become susceptible to corrosion, which will reduce their strength. Consequently, sudden failure might happen when even a small earthquake occurs. This study reports a corrosion risk assessment for some reinforced concrete (RC) public buildings in Banda Aceh region in order to understand how the tsunami has influenced the corrosion risk level. The assessment was performed by using half-cell potential mapping technique. Six buildings were chosen: three existing buildings, two newly constructed buildings in the tsunami-affected area and one building located outside that area. The assessments were carried out from 2009 until mid of 2010. The assessment results indicated that the corrosion risk to the existing buildings were at intermediate to severe level. In addition, newly developed buildings were at intermediate level, while outside building was still at low levels. Those findings showed that the RC buildings around the tsunami-affected area, either existing or new buildings, had become corrosive. Therefore, it is important to conduct regular corrosion assessments to prevent early failure due to the coexistence of rebar corrosion and earthquake.

Crushing Behavior of Hybrid Foam-Filled Pultruded Composite under Quasi-Static Oblique Loading

In this present paper, the two square cross-section pultruded composite tubes E-glass reinforced polyester unfilled and polyurethane hybrid foam-filled subjected to oblique load are investigated and examined experimentally. The oblique angles were varied from 5 to 20 with an increment of every 5 degree. The bottom base platen of clamped specimen was adjusted inclination angle of loading direction with respect to the tube axis. During the experimental observation, three characteristic crushing stages were identified as initial peak load stage, progressive crushing stage and compaction zone stage. The pultruded composite tube wall-thicknesses of at 3 mm were examined, and the effects of crushing behaviors and failure modes were analyzed and discussed. Results showed that the tube’s energy absorption capability was affected significantly by varying of oblique loading. It is also found that as the filling polyurethane foam into pultruded E-glass reinforced polyester composite square tube increases the amount of specific absorbed energy than the empty tubes.