Key Engineering Materials Vol. 796

Abstract: Drill string failure is a prevalent and costly problem to the oil and gas industry. This paper proposes a method for remaining useful life prediction of drill string components subjected to fatigue under combined loadings, namely axial stress, bending moment, and torsion. To accomplish this, fuzzy systems are used to model the dimensionless stress intensity factor, β of different API graded drill pipes. Based on the gathered database of the dimensionless stress intensity factor for various crack types, the parameter is numerically estimated using Adaptive Neuro-Fuzzy Inference System in MATLAB. The fuzzy model is then incorporated into the available crack growth models (Paris Law & Walker’s Law) to quantitatively evaluate the number of cycles as the crack propagates from its initial size to its critical size. The nonlinear crack propagation model is solved by Euler’s Method. Finally, a parametric study is performed in order to identify the influence of load magnitudes, the variation of loadings, crack shape, and geometrical parameters on the fatigue life. The ANFIS model developed has a mean square error (MSE) of 8.3e-4, root mean square error (RMSE) of 0.0288 and R-squared error of 0.9807, thus indicating the model is highly reliable. The increase in the magnitude of stress, mean stress ratio (R) and environmental constants reduces the number of cycles to failure, thus indicating shorter RUL.

Abstract: Molecular dynamics (MD) is a computer simulation method for studying the physical movements of atoms and molecules at nanoscale. It allows interaction between the atoms and molecules for a fixed period, giving an understanding of the system as they dynamically begin to evolve. The paths of the atoms and molecules are determined by numerically solving Newton's equations of motion for a system of interacting atoms, where interatomic potentials or molecular mechanics force fields are used to calculate forces and potential energies between the atoms. In this study, the basic parameters used in MD simulations are briefly discussed. An MD simulation of the friction stir processing (FSP) of aluminium alloy 6061-T6 was carried out to explain the invisible thermodynamic microscopic details which occurred during the process. However, the aim of the MD simulation is not to predict precisely the process, but to predict the average thermodynamic behavior of the process if conducted in a practical state. This is to further enhance the understanding of the FSP process. The results obtained from the MD simulation prove that it may be possible to adequately represent the MD simulation of the FSP of an aluminium alloy.

Abstract: Curved surfaces have been widely used in engineering applications such as friction stir welding (FSW), 5 axis CNC machining, and other processes. Therefore, the development of the finite element modelling of the complicated geometries has created a need to determine efficient tool paths. Previous finite element models modelled the single point movement of the tool. However, in industrial applications such as aerospace, mould and die, etc. the movement of the tool is complex. Proper determination of the tool path can lead to substantial savings of the process time, improvement of the workpiece surface quality and the improvement of the tool life, thereby leading to overall cost reduction and higher productivity. This paper presents a new approach for the determination of efficient tool paths in finite element modelling by using ABAQUS^® software. VDISP user defined subroutine is used in order to define the complex curved movement of the tool. The results indicate that the method is appropriate for modelling of the tool path, and the tool always has a perpendicular position to the surface. Therefore, the method can be suitable for increasing the application of the finite element modelling in various industries.

Abstract: Welding process is an efficient joining process of metals that is achieved by gas metal arc welding (GMAW) process. Localized heating during welding process can result in distortion of the welded plate. The estimation of magnitude and distribution of distortion are important to maintain the quality of products. Finite element method is implemented to investigate the distortions behavior of thin steel plate, cold rolled (SPCC) material in lap joint using GMAW process. A three-dimensional, two-step thermomechanical finite element model study was applied to analyze and evaluate distortion behavior in lap joint. The result of distortion from finite element analysis (FEA) was compared to experimental data to validate the accuracy of the method.

Abstract: Surface finish is coating layer plated on a bare copper board of printed circuit board (PCB). Among PCB surface finishes, Electroless Nickel/Immersion Gold (ENIG) finish is a top choice among electronic packaging manufacturer due to its excellent properties for PCB. However, the use of gold element in ENIG is very high cost and the black pad issue have not been resolved. Thus, by introducing an Electroless Nickel/Immersion Silver (ENImAg) as alternative surface finish hopefully can reduce the cost and offer better properties. The aim of this study is to investigate the effect of bismuth on interfacial reaction during reflow soldering between Sn-2.5Ag (SA25), Sn-3.4Ag-4.8Bi (SAB3448) and ENIMAG surface finish. Solder balls with sizes of 500μm diameters were used. The characteristics of intermetallic compound (IMC) were analyzed by using scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After reflow soldering, the result revealed that only the irregular circle-shape of (Cu,Ni)₆Sn₅ IMC layer was formed at the interface and change to an irregular rod-like shape meanwhile the irregular needle-shape (Ni,Cu)₃Sn₄ was appeared after aging treatment. The result also indicated that, the grain size and thickness of IMC for SAB3448 is smaller and thinner compared to the SA25. The IMC thickness is proportional to the aging duration and IMC morphology for both solder are became thicker, larger and coarser after isothermal aging. No bismuth particle has been detected on SAB3448 solder during top surface examination. In addition, the Bi has been observed can reduce the grain size and the growth rate of IMC. Keywords: ENIMAG, reflow soldering, lead-free solder, intermetallic compound, bismuth