Mohammed Yunus

Prediction of Mechanical Properties of Plasma Sprayed Thermal Barrier Coatings (TBCs) with Genetic Programming (GP)

The mechanical properties especially hardness and porosity of plasma sprayed thermal barrier coating (TBC) play a major role in deciding their lifetime and performance with respect to input process parameters such as power input of plasma jet, coating thickness, stand-off distance and type of coating. Sources of mechanical properties values are experimental measurements only, and empirical correlations are to be built up (without appropriate fitting techniques), however, these are often too complicated, expensive and time consuming and can lead to erroneous results. Genetic programming (GP) is the most common approach from various evolutionary computation methods using multivariate regression fitting for the modelling of various systems. This study presents a new model for estimating the mechanical properties of TBC using GP. On the basis of a training data set, different genetic models for mechanical properties with great accuracy were obtained during simulated evolution. The newly developed GP-based computational model provides a more accurate prediction of mechanical properties compared to the empirical correlations, and the results can then be utilized to estimate a future set of parameters based on the historical data. Keywords—Hardness, Porosity, Thermal Barrier Coatings, Plasma Spraying, Genetic Programming.

Mathematical Modelling of a Friction Stir Welding Process to Predict the Joint Strength of Two Dissimilar Aluminium Alloys Using Experimental Data and Genetic Programming

Friction stir welding (FSW) is the most popular and efficient method of solid-state joining for similar as well as dissimilar metals and alloys. It is mostly used in applications for aerospace, rail, automotive, and marine industries. Many researchers are currently working with different perspectives on this FSW process for various combinations of materials. The general input process parameters are the thickness of the plate, axial load, rotational speed, welding speed, and tilt angle. The output parameters are joint hardness, % of elongation, and impact and yield strengths. Genetic programming (GP) is a relatively new method of evolutionary computing with the principal advantage of this approach being to evaluate efficacious predictive mathematical models or equations without any prior assumption regarding the possible form of the functional relationship. This paper both defines and illustrates how GP can be applied to the FSW process to derive precise relationships between the output and input parameters in order to obtain a generalized prediction model. A GP model will assist engineers in quantifying the performance of FSW, and the results from this study can then be utilized to estimate future requirements based on the historical data to provide a robust solution. The obtained results from the GP models showed good agreement with experimental and target data at an average prediction error of 0.72%.

Experimental Investigations into the Mechanical, Tribological, and Corrosion Properties of Hybrid Polymer Matrix Composites Comprising Ceramic Reinforcement for Biomedical Applications

Hybrid polymer matrix composites (HPMC) are prominent material for the formation of biomaterial and offer various advantages such as low cost, high strength, and the fact that they are easy to manufacture. However, they are associated with low mechanical (low hardness) and tribological properties (high wear rate). The average hip joint load fluctuates between three to five times of the body weight during jumping and jogging and depends on various actions relating to body positions. Alternate bone and prosthesis material plays a critical role in attaining strength as it determines the method of load transferred to the system. The material property called modulus of elasticity is an important design variable during the selection of the geometry and design methodology. The present work is demonstrated on how to improve the properties of high-density polyethylene (HDPE) substantially by the addition of bioceramic fillers such as titanium oxide (TiO2) and alumina (Al2O3). The volume fractions of Al2O3 and TiO2 are limited to 20% and 10%, respectively. Samples were fabricated as per ASTM standards using an injection moulding machine and various properties such as mechanical (tensile, flexural, and impact), tribological (hardness, wear), and corrosion including SEM, density, and fractography analysis studied. Experimental results revealed that an injection moulding process is suitable for producing defect-free mould HPMC. HPMC comprising 70% HDPE/20% Al2O3/10% TiO2 has proved biocompatible and a substitute for biomaterial. A substantial increase in the mechanical and tribological properties and full resistance to corrosion makes HPMC suitable for use in orthopaedic applications such as human bone replacement, bone fixation plates, hip joint replacement, bone cement, and bone graft in bone surgery.