Optimization and prediction of tribological behaviour of filled polytetrafluoroethylene composites using Taguchi Deng and hybrid support vector regression models.

This study presents optimization and prediction of tribological behaviour of filled polytetrafluoroethylene (PTFE) composites using hybrid Taguchi and support vector regression (SVR) models. To achieve the optimization, Taguchi Deng was employed considering multiple responses and process parameters relevant to the tribological behaviour. Coefficient of friction (µ) and specific wear rate (Ks) were measured using pin-on-disc tribometer. In this study, load, grit size, distance and speed were the process parameters. An L27 orthogonal array was applied for the Taguchi experimental design. A set of optimal parameters were obtained using the Deng approach for multiple responses of µ and KS. Analysis of variance was performed to study the effect of individual parameters on the multiple responses. To predict µ and Ks, SVR was coupled with novel Harris Hawks' optimization (HHO) and swarm particle optimization (PSO) forming SVR-HHO and SVR-PSO models respectively, were employed. Four model evaluation metrics were used to appraise the prediction accuracy of the models. Validation results revealed enhancement under optimal test conditions. Hybrid SVR models indicated superior prediction accuracy to single SVR model. Furthermore, SVR-HHO outperformed SVR-PSO model. It was found that Taguchi Deng, SVR-PSO and SVR-HHO models led to optimization and prediction with low cost and superior accuracy.

Mechanical strength variability of deformed reinforcing steel bars for concrete structures in Ethiopia.

The paper presents statistical analysis of mechanical strength and linear density properties of deformed reinforcing Grade 60 steel bars. Two different lots of samples are identified based on test years for the years 2015-2017 as Lot 1 and 2018-2020 as Lot 2. Yield strength (YS), tensile strength (TS), elongation, mass per length and characteristic ratio of TS and YS are analyzed for rebar diameters of 8, 10, 12 and 16 mm considering both lots. Mechanical and linear density properties are compared statistically using range, mean, standard deviation, coefficient of variance, skewness and kurtosis of the recorded sets of values. Moreover, the results of YS, TS and elongation are analyzed separately by one-way analysis of variance for both lots. The result shows that the aggregate mean values of YS, TS and elongation for Lot 1 and Lot 2 are 593.1 MPa, 701.1 MPa, 14.78%; and 572.5 MPa, 673.8 MPa, 15.47%, respectively. Even though there is a slight decrement in values of YS and TS and increment in elongation from Lot 1 to Lot 2, both lots exceeded values recommended by ASTM A615 standard. Furthermore, with 95% confidence interval, one-way analysis of variance showed that the aggregate data of rebars are dissimilar in terms of YS, TS and percentage elongation with figures showing decrement from Lot 1 to Lot 2.