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This paper reports an experimental investigation on continuous CO2 laser cutting of polymethylmethacrylate (PMMA) sheet. The influence of four process factors (laser power, cutting speed, assisting gas pressure and sheet thickness) on five process responses (kerf deviation, top heat affected zone, bottom heat affected zone, maximum surface roughness and rough area) has been investigated. The experimental plan was established based on Taguchi L18 mixed design. The kerf geometry and heat affected zones have been measured using polarising light microscopy technique, while the surface roughness was evaluated using 3D laser scanning confocal microscope. Regression models have been derived to correlate different process responses with different process factors. The cut surface could be classified into three zones: rough zone, moderate zone and soft zone. The rough area is increased by increasing gas pressure and laser power and by decreasing the sheet thickness and cutting speed. Increased kerf deviation has been observed at high cutting speed, laser power and gas pressure. High laser power and low cutting speed produced worst surface roughness and wide heat affected zone. Therefore, it is recommended to use low laser power and high cutting speed to minimize the heat affected zone and the surface roughness. However, increasing the cutting speed may result in high kerf deviation.

In this paper, an enhanced random vector functional link network (RVFL) algorithm was employed to predict kerf quality indices during CO2 laser cutting of polymethylmethacrylate (PMMA) sheets. In the proposed model, the equilibrium optimizer (EO) is used to augment the prediction capability of RVFL via selecting the optimal values of RVFL parameters. The predicting model includes four input variables: gas pressure, sheet thickness, laser power, and cutting speed, and five kerf quality indices: rough zone ratio, widths of up and down heat affected zones, maximum surface roughness, and kerf taper angle. The experiments were designed using Taguchi L18 orthogonal array. The kerf surface contains three main zones: rough, transient, and smooth zones. The results of conventional RVFL as well as modified RVFL-EO algorithms were compared with experimental ones. Seven statistical criteria were used to assess the performance of the proposed algorithms. The results indicate that the RVFL-EO model has the predicting ability to estimate the laser-cutting characteristics of PMMA sheet.

Motivated by the need to enhance the kerf quality during cutting of Poly(methyl methacrylate) (PMMA) sheets using pulsed CO2 laser beam, this study presents an experimental investigation and optimization of laser cutting parameters including cutting speed, assisted gas pressure, laser beam power, and sheet thickness. The kerf quality characteristics including the top kerf width, bottom kerf width, and kerf taper have been considered as the process responses and have been measured using polarized light microscope. The experiments were designed and planned using Taguchi L18 orthogonal array with a mixed design. The effects of different cutting parameters on the kerf characteristics have been statistically analyzed using analysis of variance technique (ANOVA). The obtained results revealed that any increase in cutting parameters will result in increasing the top and the bottom kerf widths, while increasing cutting speed or laser power results in increasing the kerf taper. Second order regression models have been developed to model different kerf characteristics as functions of the process parameters. Genetic algorithm (GA) has been used to select the optimal cutting parameters using the developed regression model as an objective function to minimize the kerf taper. A considerable improvement in kerf quality has been achieved and the obtained results have been verified using confirmation experiments. The application of the proposed approach is capable to reduce the kerf taper from 1.92° to 0.02° while maintaining the minimum kerf width at a reasonable value (less than 0.5 mm). Keywords: Laser cutting, PMMA, kerf geometry, Taguchi method, Regression analysis, Genetic algorithm

In this paper, an alternative method to predict the noise of a submersible Axial Piston Pump (APP) for different valve seat materials is presented. The proposed method is composed of an Artificial Neural Network (ANN) model trained using experimental data and integrated with a hybrid algorithm consists of Cat Swarm Optimization (CSO) and Firefly Algorithm (FA) algorithms. The hybrid CSFA algorithm is used as a subroutine in the ANN model to estimate the ANN weights. The FA is used as local operator to improve the exploitation ability of CSO. The obtained results prove the excellence of the proposed method in predicting the noise of APP considering four different valve seat materials (Polytetrafluoroethylene (PTFE), Polyetheretherketone (PEEK), Aliphatic polyamides (NYLON), and stainless steel (316 L)), five speed levels, and six system pressures. Moreover, the effects of different mechanical properties of the valve seat materials as well as operating conditions (speed and system pressure) have been investigated. Keywords: Axial piston pump, Valve seat materials, Noise prediction, Artificial neural network

Although construction and demolition wastes (CDW) has been recycled widely in many industrial countries, such application is still limited in many under development countries. Efficient recycling and more possible applications for different parts of the crushed CDW materials provided more added values to these environmentally harmful wastes and hence encourage their recycling efforts. The main objective of this study is to propose sustainable construction utilizations of common CDW materials usually found in developing countries. The influence of two different crushing techniques, on various particles size’s properties of the recycled CDW samples, was investigated. In addition, performance of some construction materials, made of different particle sizes of the recycled CDW, was studied. Coarse particles of crushed CDW were used as coarse aggregates for concrete and the fine particles were proposed for producing cement bricks. On the other hand, very fine particles were assessed as pozzolanic materials or as mineral filers for asphalt. Jaw technique was found more efficient, to recycle the investigated CDW materials, than hammer technique. On the other hand, proposed optimum construction applications, for different particle sizes of the recycled materials, were ranked based on the performance of the proposed construction materials. Keywords: Construction and demolition wastes, Crushing techniques, Pozzolanic activity, Crushed concrete, Crushed clay bricks, Crushed tiles, Cement bricks, Asphalt filler, Cement brick, Aggregate

Performance of polymer reinforced with continuous long natural and man-made fibers was extensively investigated in literature. However, using yarns made of short discrete natural fibers needs to be investigated as a source of sustainable reinforcement for composites. In this study, long yarns made of short flax and jute fibers were selected to reinforce polyester bars. Infusion technique was implemented to produce natural yarns reinforced polyester (NYRP) bars having various fiber volume fraction ratios. Microscopic images showed good fibers distribution and resin-fibers impregnation across the of NYRP bars. In addition, polyester bars reinforced with selected natural yarns lead to remarkable enhancement of their tensile strength, stiffness and ductility. Moreover, concrete slabs reinforced with surface treated NYRP bars performed compatibly until failure. Despite low stiffness of the produced NYRP bars, their use for reinforcing normal and lightweight concrete slabs enhanced their ductility and toughness as well as increased their flexural capacity up to six-fold.

Vibration welding technique has been widely used to weld molded surfaces parts produced by injection or compression molding techniques. However, the majority of early studies used machined surfaces to eliminate the complication associated with molded surfaces. Different process parameters such as the welding pressure, frequency, and amplitude have been investigated to determine their optimal values that maximize the welding strength. However, some other parameters such as joint design and the welding interface preparation were leftover for real application test or for technology transfer studies. Most of molded parts from semi-crystalline materials and their composites usually have skin layer that was exposed to thermal history differs from that of the core. Moreover, the amount and the orientation of fibers in the skin layer differ from that of core and shell regions. Therefore, this work investigates and explores the effect of the molded surfaces with skin on tensile strength of vibration welded butt joints made from polybutylene terephthalate reinforced with 30% glass fiber (PBT GF30). The effect of fibers orientation on the welded joint strength has been also investigated.

Attractive properties of TRIP-type bainitic ferrite (TBF) steel ascribe to its unique microstructure of lath structure bainitic ferrite matrix and interlath retained austenite films. This work is concerned with obtaining ultra high-strength hot forged TBF steel with high elongation and excellent strength-elongation balance. The effect of austempering temperature on the microstructure along with its retained austenite characteristics and tensile properties of a hot forged TBF steel was studied. A detailed investigation correlating the steel structure and its tensile properties was carried out. Tensile strength ranging from 1058 to 1552 MPa was achieved when the hot forged steel was austempered at (325 - 475 °C). Ultra high tensile strength of 1058 MPa, large total elongation of 29% and excellent strength-elongation balance of 30 GPa % were attained when the steel was austempered at 425 °C. The large total elongation of this steel is mainly due to the uniform fine lath structure matrix and the pronounced TRIP effect of a large amount of retained austenite films which prevents a rapid decrease of strain hardening rate at low strain and leads to a relatively high strain hardening at high strain level. Rapid transformation of blocky retained austenite at low strain in the hot forged TBF steel austempered at higher temperatures results in a rapid increase of initial strain hardening. In addition, the coarse microstructure that contains large blocks of retained austenite / martensite and the insufficient numbers of bainitic ferrite lathes and retained austenite films deteriorate the total elongation and the strength-elongation balance of the TBF austempered at 475 °C.