A.A. Saad

Thermal-mechanical fatigue simulation of a P91 steel in a temperature range of 400–600°C

Abstract This paper deals with the identification of material constants to simulate the effect of cyclic mechanical loading and temperatures. A Chaboche viscoplasticity model was used in this study to model the thermal-mechanical behaviour of a P91 martensitic steel. A fully-reversed cyclic mechanical testing programme was conducted isothermally between 400 and 600°C with a strain amplitude of 0.5%, to identify the model constants using a thermo-mechanical fatigue (TMF) test machine. Thermo-mechanical tests of P91 steel were conducted for two temperature ranges of 400 – 500°C and 400 – 600°C. From the test results, it can be seen that the P91 steel exhibits cyclic softening throughout the life of the specimens, for both isothermal and thermal-mechanical loading and this effect can be modelled by the set of viscoplasticity constants obtained. Finite element simulations of the test specimens show good comparison to isothermal and TMF experimental data.

SAC-xTiO2 nano-reinforced lead-free solder joint characterizations in ultra-fine package assembly

Purpose This paper aims to investigate the characteristics of ultra-fine lead-free solder joints reinforced with TiO2 nanoparticles in an electronic assembly. Design/methodology/approach This study focused on the microstructure and quality of solder joints. Various percentages of TiO2 nanoparticles were mixed with a lead-free Sn-3.5Ag-0.7Cu solder paste. This new form of nano-reinforced lead-free solder paste was used to assemble a miniature package consisting of an ultra-fine capacitor on a printed circuit board by means of a reflow soldering process. The microstructure and the fillet height were investigated using a focused ion beam, a high-resolution transmission electron microscope system equipped with an energy dispersive X-ray spectrometer (EDS), and a field emission scanning electron microscope coupled with an EDS and X-ray diffraction machine. Findings The experimental results revealed that the intermetallic compound with the lowest thickness was produced by the nano-reinforced solder with a TiO2 content of 0.05 Wt.%. Increasing the TiO2 content to 0.15 Wt.% led to an improvement in the fillet height. The characteristics of the solder joint fulfilled the reliability requirements of the IPC standards. Practical implications This study provides engineers with a profound understanding of the characteristics of ultra-fine nano-reinforced solder joint packages in the microelectronics industry. Originality/value The findings are expected to provide proper guidelines and references with regard to the manufacture of miniaturized electronic packages. This study also explored the effects of TiO2 on the microstructure and the fillet height of ultra-fine capacitors.

Numerical simulation of self-alignment of chip resistor components for different silver content during reflow soldering

Abstract Three-dimensional simulation and experimental investigation of self-alignment phenomena during the reflow soldering process were presented. The multiphase flow model was developed using ANSYS Fluent to investigate the self-alignment effect of laminar melted lead-free solder during the reflow phase on board. User-defined function with c-code was integrated into the model, Volume of Fluid (VOF) method was applied to the melt front tracking, and solidification model was used for the phase change solder material. The material used in the study was SAC 105, SAC 305 and SAC 405. The specific heat, latent heat, solidus temperature, liquidus temperature of the lead-free solder and geometrical data for model input was determined experimentally. The model was validated experimentally. The self-alignment capability of different lead-free solder was presented. It has been observed that higher silver content solder (SAC 405) have higher self-alignment capability during reflow soldering compare to SAC 305 and SAC 105. Moreover, all cases show self-alignment in perpendicular to the longer sides of chip resistor travelled more towards the central position. The experimental and simulation results are in good conformity and can be extended for different cases.

Multiaxial Viscoplasticity Modelling of Power Plant Steel

The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant. A time-dependent plasticity model can be used to simulate the component response under cyclic thermo-mechanical loading. This paper is concerned with the modelling of thermo-mechanical behaviour of power plant steel under various loading conditions. Fully-reversed, strain-controlled tests were conducted on a parent material of P91 steel at high temperatures in order to determine material constants. A unified, Chaboche viscoplasticity model, was used to model the TMF behaviour of the steel. The multiaxial form of the Chaboche constitutive equations have been implemented in the finite element software and validated by comparing to experimental data. Simulation results have been compared with the results of anisothermal cyclic testing in order to validate the performance of the model in cyclic temperature conditions. The model’s performance under multiaxial stress conditions was investigated by testing and simulating the notched bar specimen under load-controlled conditions.

Investigation on the Fretting Wear of a Coated Substrate with Interlayer

The fretting wear of coated SCMV (high-strength alloy steel) substrate with interlayer is studied with the focus on stresses associated with the coating failure under gross sliding condition. The analysis is simulated using finite element based method for a given number of cycles of worn half cylinder-on-flat geometry. The effect of interlayer stiffness on the stress distributions in the coating is studied. The maximum tensile stress at the trailing edge and the maximum compressive stress at the leading edge are reducing with increasing interlayer stiffness. The maximum shear stress at the coating-interlayer interface is predicted to have negligible effect with the change of interlayer stiffness. All the stresses are generally predicted to reduce with cycle. In general, stiffer interlayer will reduce the risk of coating failure.

Electrical-thermal interaction study of electrical busway using finite element analysis

This paper presents an approach for determining temperature distribution on a 2200A busway model. Solidwork software was used in order to create 3D modeling of busway model. This paper proposes a simulation model developed by coupling the multiphysics between electrical analysis and thermal analysis. The coupling was done by using ANSYS Workbench and ANSYS Maxwell. Basically, the electrical analysis is performed onwards busway model in order to get the value of ohmic loss which is heat loss from the conductors in the busway. The ohmic loss results will be imported to thermal analysis in order to get the temperature result as well as temperature distribution. First, the direct current loading of the busbar, which neglect the alternating current effects, was considered. Second, the alternating current loading of busbar was used instead of direct current loading. The model of the second approach gives much more accurate result in term of temperature difference. The presented model was validated against temperature measurement on real size busway under electrical loading. The obtained results show that a very good agreement between computed and experimental data. Once the verification of the model is done, the busway configurations setup behavior is studied. Increasing number of feeder affects thermal stress concentration on busway joint.This paper presents an approach for determining temperature distribution on a 2200A busway model. Solidwork software was used in order to create 3D modeling of busway model. This paper proposes a simulation model developed by coupling the multiphysics between electrical analysis and thermal analysis. The coupling was done by using ANSYS Workbench and ANSYS Maxwell. Basically, the electrical analysis is performed onwards busway model in order to get the value of ohmic loss which is heat loss from the conductors in the busway. The ohmic loss results will be imported to thermal analysis in order to get the temperature result as well as temperature distribution. First, the direct current loading of the busbar, which neglect the alternating current effects, was considered. Second, the alternating current loading of busbar was used instead of direct current loading. The model of the second approach gives much more accurate result in term of temperature difference. The presented model was validated against tempe...

Investigation on the Fretting Wear of a Coated Substrate: Interlayer Stress Behaviour

The effect of surface modification due to fretting wear behaviour of coated SCMV (High Strength Alloy Steel) with interlayer is investigated by simulation using ABAQUS Software on a cylinder on flat contact configuration under gross sliding conditions. The effect of interlayer stiffness and the surface modification are analysed with the focus on the interlayer stress failures and its associated stresses behaviour. Tangential stress and shear stress are predicted to reduce with the increase of numbers of wear cycles due to the effect of contact conforming. Stresses in the interlayer are predicted to increase with the interlayer stiffness due to the function of the interlayer as the load bearer.

Prediction of wind induced noise over bodies and small cavity

The problem with wind induced noise exists in any electronic device used in the outdoor that incorporates microphone components mounted underneath small opened cavities within its body. Due to the complexity nature of the problem, efforts in trying to experimentally understand the flow induced noise problem has lengthened product development cycle time. In this paper, a CFD approach using the SST k-omega turbulence model were utilized as an initial model to assist in understanding the phenomenon. Several instances of experimentation using actual prototype models were conducted for the correlation study. The experimentally perceived noise from the output of the microphone was found to be fundamentally correlated to the numerical analysis as evidenced from the flow velocity vectors, profiles, and vortex core inside the cavity region. It is also shown that by following the principle of nonlinear theory of cavity resonances and Rossiter’s Theory, the understanding of the phenomenon can be further strengthened...

Investigation on the Stress Behaviour of Coating-Substrate Interface under Contact Loading

This study is intended to predict the stress behavior of thick hard coating at the interface with the changes of coating stiffness and thickness to the substrate of Ti-6Al-4V and SCMV. The elastic mismatch between the coating and the substrate is presented in the value of Dundurs parameter α. The prediction is done using simple geometry of a cylinder-on-flat model in 2D analysis subjected to normal and tangential loading. Tangential stress distribution along the coating-substrate interface is then obtained from the FE modelling after a finite sliding of the cylinder. It is predicted that the maximum tangential stress value predicted at the interface which relates to coating fracture failure is increasing as stiffer coating is used on compliant substrate (i.e. increasing α values). The location of the maximum tangential stress predicted also changes from the trailing edge to the center of contact with increasing α values. Effect of changes of coating thickness on the predicted maximum tangential stress value is more significant for high positive α values. Risk of coating fracture at the interface is therefore predicted to increase with the increase of coating thickness and stiffness.

Investigation on the Interaction between Plasticity Response and Fretting Wear under Gross Sliding Condition

The fretting wear behavior of Ti-6Al-4V is studied with the focus on cyclic plasticity effect under gross sliding condition. The analysis is simulated using finite element based method with a new surface profile model represently a given number of cycles using a cylinder-on-flat geometry. The effect of cyclic plasticity on the stresses and plastic strain distribution is studied. The maximum tangential stress is predicted at the trailing edge while the maximum compressive tangential stress is predicted at the leading edge of contact area. Plasticity in shear component is significant compare to tangential component and predicted at 0th and 3000th cycles only. It is found that important to include plasticity that remains from previous cycle for better prediction of fretting wear.