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Friction stir welding (FSW) was developed initially for welding aluminium alloys which were difficult to weld using conventional welding techniques, and a remarkable success was accomplished in these alloys and other wide range of metals. Then, this technique has been applied without any modifications for welding polymeric materials. As a result, conventional FSW of polymeric materials did not achieve satisfactory joint strength due to the huge differences between the properties of metals and thermoplastic materials. As a consequence, several modifications, developments and patents have been introduced to harmonise this technique with thermoplastic materials. This work aims to present the problems associated with the application of conventional FSW of polymers and the methods that have been developed to overcome these issues and make comparisons between them.

Simultaneous investigation of kerf quality and fume emissions during laser cutting process is essential to achieve efficient and hygienic cutting process. In this study, an experimental investigation on process factors of CO2 laser cutting (CLC) of polyvinyl chloride (PVC) sheets has been carried out followed by an optimization study to enhance the kerf geometry and reduce the emitted harmful fumes. Laser power, transverse cutting speed, and sheet thickness have been considered as the process factors. The kerf geometry has been measured using optical microscope. The emitted fumes are considered to be proportional to the generated kerf volume. An L9 experimental design plan was designed using Taguchi method, and the results were evaluated using analysis of variance (ANOVA). Second-order regression models have been developed to correlate the input parameters to the process responses. Genetic algorithm (GA) was implemented to obtain the optimum process parameters that should be used to minimize the kerf volume and consequently the emitted fumes. A significant decrease in kerf volume has been obtained using the optimum process parameters. Confirmation experiments have been conducted to verify the accuracy of the proposed approach. The proposed optimization method shows a considerable decrease in the kerf volume and the emitted fumes, especially for large sheet thicknesses. The emitted fumes can be reduced by about 39% and 61% for sheet thickness of 7 mm and 10 mm, respectively, by applying the optimum cutting parameters obtained from this study.

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.

In fracture toughness tests, a number of notched specimens with identical artificial pre-cracks are essential to obtain accurate fracture parameters. The test results are critically depending on the initiation stage quality. Any slight variance in pre-cracks front shape, length and orientation could significantly affects the test results; therefore, producing identical pre-cracks is a critical issue to obtain accurate results. The pre-cracking technique should be selected carefully to fulfil controllably and repeatability requirements of the standard pre-cracks for a certain material while preserving the induced residual stresses at the crack tip at a minimal value. The notching and pre-cracking standards for metallic material have been well specified in ASTM E399. However, the case is more cumbersome for polymeric materials due their viscoelastic nature. ASTM D5045, ISO 13586:2000 and ASTM D6068 specified different procedures to prepare a sharp pre-crack for polymeric materials. Many pre-cracking techniques have been proposed in literature. The present work introduces an overview of the pre-cracking techniques for polymeric materials.

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.

Ibrahim S. El-Deeb and Ezzat A. Showaib ABSTRACT Reverse engineering is the process of reconstructing a computer model for physical object based on 3D data point captured from the surface of the object. This work presents a low end and extremely cost effective technique for representing the free form surfaces of physical objects in a CAD model. An analogue signal was used to acquire the free form surface data unlike conventional methods like laser scanners or Coordinate Measurement Machines (CMM). The surface was scanned using a Linear Variable Differential Transducer, (LVDT) as position sensor for measuring the data from the surface of the object. The analogue signal was acquired through a data acquisition system in a continuous fashion to PC. Solid works CAD/CAM software was used to obtain the free form surface from the acquired 3D data using spline technique. A dedicated system was constructed to collect data using vertical milling machine. The benefit of this scanning technique is the ability to scan the target free form surface of the physical object in the following aspect: cost effective scanning technique, low end acceptable accuracy, speed and ease of calibration. Special software was built to minimize the data acquired during the scanning operation for reducing modeling time. KEYWORDS 3D digitizing; reverse engineering; surface modeling; line scan For More Details: https://wireilla.com/engg/ijmech/papers/1212ijmech03.pdf

Acetal is known for its fatigue resistance, however, it is also susceptible to degradation at high temperatures. Commercial resins therefore contain complex stabilizer systems that, although present in relatively small amounts, provide thermal stability both for processing and subsequent in-service aging. The present study was undertaken to determine how sensitive the fatigue resistance of an acetal copolymer was to changes in stabilizer concentration. Blends containing a series of increasing stabilizer levels were investigated and compared to the commercial material. Fatigue resistance was assessed using accelerated fatigue crack propagation rate measurements for injection molded plaques. Results demonstrate that the fatigue resistance is dependent upon the amount of stabilizer and in fact suggest that a critical level of stabilizer is needed to provide adequate fatigue resistance in the molded part. It is also shown that room temperature aging further aggravates the poor fatigue resistance of samples with low stabilizer levels. Moreover, the results from this study demonstrate that the varying concentrations of heat stabilizer affect even short term mechanical properties such as tensile modulus, strength, and elongation to fail. In addition, fracture toughness tests clearly distinguish the various materials. The short term mechanical tests provide added support that a critical concentration of stabilizer exists.

A method to determine viscoelastic changes in medium density polyethylene (MDPE) pipe specimens associated with the crack tip during fatigue crack initiation (FCI) and propagation (FCP) experiments is described. The load-displacement curves are analyzed to obtain the phase angle, δ. Changes in δ are related to the number of cycles of crack initiation of three different MDPE copolymers: hexene (H), butene (B), and methyl pentene (MP) copolymers. These changes are related to craze formation and growth at the notch tip, leading to crack initiation and to the irreversible work, Wi, expended on them. Within a given material, step wise increments in δ distinguish the onset of crack initiation and the brittle-to-ductile transition in crack growth. The magnitudes of tan δ and Wi are noted to be in quantitative agreement with the resistance of the three copolymers to FCI and brittle propagation that rank in the order: isobutyl (MP) > ethyl (B) > butyl (H). Similar crystallinity of the three copolymers insinuates a hypothesis that variance in the nature of chain entanglements associated with the respective branch type might be accountable for the observed differences in viscoelastic character. The final stage of failure by ductile tearing is dominated by large scale plastic flow that seemingly overshadows the material differences governing time dependent brittle fracture.

Kinetics parameters of craze evolution preceding fatigue crack initiation (FCI) in mediumdensity polyethylene (MDPE) pipe materials were determined and analysed within fracture mechanics theory. A single craze initially preceded the notch tip, a root craze, which subsequently became accompanied by a few side crazes. Crack initiation transpired after the craze-zone growth had reached its fully developed configuration. The length of the root craze of the fully developed zone was found to be equal to the length of the first discontinuous crack band on the fracture surface. The growth of the root-craze length and the crack-tip opening displacement (CTOD) followed a power law over the major portion (94%) of the FCI time. Measurable rupture of the craze material was only noted within the final portion of the FCI time and was associated with exponential increase of the CTOD. The Dugdale/Barenblatt model overestimated the craze length by 30% and underestimated the CTOD by 50% which was hypothesized to be due to multiple crazing at the notch tip.

Purpose To evaluate the effect of dentin desensitization using casein phosphopeptide amorphous calcium phosphate paste; CPP-ACP, with and without deproteinization (10% sodium hypochlorite), on dentin permeability of two types of self-etch adhesives and a total-etch one. Materials and methods 90 freshly extracted, sound human molars were sectioned into 1 mm thick dentin disks, and randomly divided into three equal groups (S1, S2, and S3); 30 specimens each, according to the dentin surface treatment, as follows: (S1) adhesive system {AS} only, (S2) CPP-ACP + AS, (S3) 10% NaOCl + CPP-ACP + AS. Each group was further divided into 3 divisions (D1, D2, and D3), 10 specimens each, according to the tested adhesive system (Solobond M, Clearfill SE and Futurabond DC) respectively. Dentin surfaces were treated Dentin permeability was measured at base line and after dentin treatment and storage under simulated pulpal pressure for 10 min. Results CPP-ACP treatment significantly decreased the permeability of (S2D2) and (S2D3), but didn't affect (S2D1). The combined NaOCl and CPP-ACP treatment decreased the permeability of the three tested adhesives significantly. Clinical significance: The combined application of 10% sodium hypochlorite and CPP-ACP paste may be recommended to improve the dentinal permeability before using dental adhesive systems.

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.