Thanate Ratanawilai

This research studied the effects of cold metal transfer (CMT) repair welding with varying heat inputs on the mechanical properties and corrosion resistance of friction stir welded AA6082-T6 aluminum alloy joints. The original friction stir welding (FSW) joint and repaired joints by CMT were investigated by metallurgical characterization, microhardness tests, tensile tests, three-point bending tests, and electrochemical corrosion tests. The results indicated that CMT repair welding affected the mechanical properties. Notably, the CMT-155 showed the best performance, retaining 97.7% of the original FSW joint’s tensile strength. The location of the fracture after tensile tests changed from the thermo-mechanical affected zone of the FSW joint to the heat affected zone (HAZ) of the CMT repair joint. The microhardness in the weld metal (WM) and HAZ of the CMT repaired joints was lower than that of the base metal (BM). The CMT-155 and CMT-160 had higher hardness than the CMT-150. The highest bending strengths for both face bend and root bend were found in the repaired joint using 155 A. Electrochemical corrosion results of the WM in CMT repaired joints exhibited lower corrosion resistance compared to the stir zone of FSW joint and the BM. Corrosion rates increased with higher CMT welding currents.

Wood-Plastic Composites (WPCs) are commonly used in furniture and structural applications. However, forming-based fabrication limits the production of complex shapes. Therefore, post-machining operations, such as hole machining, are required for WPCs, and achieving high machining quality remains challenging owing to the unique properties and layered structures of materials. Therefore, the novelty of this study lies in assessing the machinability of Abrasive WaterJet (AWJ) cutting as an effective non-traditional machining method for hole fabrication in single-layer and three-layer WPCs, comparing its performance with WaterJet (WJ) cutting and conventional drilling. The effects of water pressure, traverse speed, abrasive mass flow rate, and hole diameter on the roundness and machined surface quality were investigated experimentally. The results show that AWJ successfully produced through-cut holes in both WPC structures, whereas pure WJ achieved complete cuts mainly at 350 MPa water pressure due to insufficient cutting energy at lower pressure to surpass the material’s hardness. According to response optimization, the proposed AWJ parameters are an abrasive mass flow rate of 6.67 g/s, a water pressure of 350 MPa, and a traverse speed of 30 mm/s, yielding a high desirability index of 0.848. A regression model was developed to predict roundness, and its validation revealed a small difference of 3.19% between the predicted and actual values. Compared to traditional hole drilling, AWJ offers shorter processing times and greater flexibility in hole size without requiring tool changes, although it results in larger hole roundness quality, which remains acceptable for clearance-fit applications. These findings highlight the potential of AWJ as an attractive option for machining WPCs.

Seashell waste bio-filler in polymeric material composites sustainably improves insulating performance. This study focuses on polyurethane foam composites (PUFc) reinforced with seashell waste powders and the effects of shell type, particle size, and filler loading on physical and mechanical properties and thermal conduction. Oyster, green mussel, and cockle shells were processed into 20, 40, and 80 mesh sizes and integrated into PUF at 10 to 30 wt% using the closed-mold method. Material characterization results shown by X-ray fluorescence analysis revealed calcium carbonate contents of 91 to 96 wt% in all shells. PUF with 20 wt% fillers, at 40 mesh, increased density, hardness, tensile strength, and compressive strength compared with neat PUF. The optimal formulation, oyster shell density (191 kg/m³), and cockle shell achieved a hardness of 86.7 Shore A. Tensile and compressive strengths were 1580 and 1352 kPa, respectively. Thermal conductivity slightly increased with filler additions. The optimal formulation of 20 wt% at 40 mesh oyster shell was 0.0472 mW/mK. However, water absorption increased with increasing filler content and particle size. Scanning electron microscopy-energy dispersive X-ray microstructural observations indicated improved filler dispersion and preserved closed-cell morphology at 20 wt%, 40-mesh filler loadings, values supporting the suitability of seashell-reinforced PUF as a sustainable building insulation material.

Railway systems play a crucial role for transporting goods andpassengers. When derailments occur, cranes need a stable base to lift traincars, often relying on wooden sleepers arranged in cribbing structures.However, wood is heavy, susceptible to rot, and raises environmental issues.This study introduces a sustainable alternative through sandwich compositestructures featuring hybrid face sheets composed of recycled plastics (rHDPE,rLDPE, rPE) and wood flour from both softwood and hardwood. Ten differentmaterial ratios were prepared using twin-screw extrusion and compressionmolding to assess their mechanical properties. The optimal performing blendconsisted of 70% recycled plastic and 30% softwood flour, showing superiorstrength, surface hardness, and water resistance. The softwood plasticcomposite sheets exhibit higher flexural and compressive strength comparedto materials made from hardwood flour, suggesting that the type of woodflour used influences the overall strength of the composites. Additionally,using rHDPE as the core material further improves the mechanical properties.The sandwich structure with an HDPE plastic core layer showed superiorperformance in terms of parallel compression, bending resistance, and surfacehardness when compared to structures with core layers made of other typesof plastics. When compared to conventional wood, the newly developedcomposite material is lighter in weight, more durable, and exhibits much lowerwater absorption. This innovative material provides an eco-friendly andeffective substitute for traditional wooden sleepers, promoting a moresustainable and robust railway infrastructure.

While the field of plant fibre composites is experiencing rapid growth in research and development, there are still essential considerations that must be addressed before these materials can be adopted by industries for structural applications. One of the primary concerns revolves around their durability. This study aims to assess how moisture affects the static and fatigue behaviour of a rubberwood/recycled polypropylene composite. The specimens were exposed to a humid environment at 23 °C in water immersion for 30 days. Quasi-static and tension-tension fatigue tests were carried out. Results show that exposure to moisture has caused a significant decrease in their initial quasi-static strength and stiffness. The fatigue strength, on the other hand, has been enhanced. The fatigue strength coefficient decreases by more than half after ageing, suggesting a less pronounced decrease in maximum stress as the number of cycles increases. The fatigue hysteresis loop and evolution of the secant modulus of non-aged composite show more pronounced fatigue damage when compared to the aged composite.

An additive manufacturing (AM) has become very popular due to its simplicity in producing complicated products using just one process due to the layer-by-layer addition of material, which makes it possible for more complicated products to be created. The constraint of Fused Filament Fabrication (FFF) printed components with inadequate mechanical qualities has prevented AM from being widely adopted by numerous industries. The mechanical and thermal qualities of FFF printed components which is a pure polymer could be enhanced by reinforcing the wood fiber into the polymer. In this study, the twin-screw extruder was used to produce the wood plastic composites (WPCs) filaments, which were made with ABS (Acrylonitrile Butadiene Styrene) as the matrix material and 1-3wt% rubberwood fiber (RWF) for reinforcement. The effects of the extrusion parameter, such as the volume fraction of RWF and the temperature of the extrusion process, on the 3D-printed WPCs samples were investigated. The experimental results of 3D-printed WPC sample were found that the highest compressive strength value is 24.3 MPa, obtained from the rubberwood 1wt% at the extrusion temperature 218 °C whereas the pure ABS filaments obtaining from the commercial and extrusion process gave the values of 28.9 and 14.5 MPa, respectively. The highest value of tensile strength is 8.4 MPa with the rubberwood 2wt% and temperature 198 °C whereas the pure ABS filaments obtaining from the commercial and extrusion process gave the values of 10.9 and 7.4 MPa, respectively. The morphological analysis of the 3D-printed WPC sample was observed to exhibit an effect of printing process. The result showed that an increasing temperature of extrusion process increases both tensile and compressive strengths of the samples whereas an increasing amount of fiber increases the tensile strength but decreased the compressive strength. Analysis of variance demonstrated linear factor and 2-way interaction factor of the extrusion parameter influence on compression and tensile strength significantly. The rubberwood 2wt% and the temperature 218 °C was suggested to achieve the suitable condition for extrusion process for the 3D-printed WPC sample. In addition, the discussions were supported with the thermal properties achieved from Thermogravimetric analysis and Differential Scanning Calorimetry.