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HTW-50 solid wire CO2 gas-shielded arc spot welding and resistance spot welding techniques were utilized to fabricate multiple sets of HRB400E hot-rolled ribbed seismic reinforcement cross-spot welded test specimens. These specimens were subjected to unidirectional tensile testing to investigate the impact of cross-spot welding on the mechanical properties of the steel bars. Chemical composition analysis and hardness testing were conducted on the brittle fracture test specimens using a metallurgical microscope, scanning electron microscope, and Rockwell hardness tester, among other related equipment. The brittle fracture mechanism of the cross-welded test specimens was subsequently examined from both macroscopic and microscopic perspectives. The results indicate that cross-spot welding of large-diameter rebars does not affect their strength. However, 80% of the test specimens exhibited brittle fractures that occurred at the weld point. Moreover, the elongation of the brittle fracture specimens was lower than the standard value, indicating a need for improved toughness. In comparison to CO2 gas-shielded arc spot welding, resistance spot welding had a lesser impact on the elongation of the steel bars and demonstrated greater stability. The test specimens exhibited fractures primarily at the welded area, where only a minimal amount of toughness was observed. Disintegration steps and river-like patterns were also observed at the weld, suggesting a mechanism of disintegration fracture. Additionally, tempered martensite was detected in the heat-affected zone, rendering the bars brittle, and making them prone to fracture at the weld. [ABSTRACT FROM AUTHOR]

Polyetheretherketone (PEEK) is the leading high-performance thermoplastic biomaterial that can be processed through material extrusion (ME) additive manufacturing (AM), also known as three-dimensional (3D) printing, for patient-specific load-bearing implant manufacture. Considering the importance of cyclic loading for load-bearing implant design, this work addresses the high-cycle fatigue behaviour of 3D-printed PEEK. In this work, printed PEEK specimens are cyclically loaded under stress-controlled tension–tension using different stress levels between 75% and 95% of printed PEEK's tensile strength. The experimental results are used to document 3D-printed PEEK's fatigue behaviour using Basquin's power law, which was compared with previous fatigue research on bulk PEEK and other 3D-printing materials. As a pioneering study on its fatigue behaviour, the results from this work show that 3D-printed PEEK exhibits an above-average fatigue strength of 65 MPa, corresponding to about 75% of its tensile strength. Fracture surface analysis suggests that a transition can occur from ductile to brittle fracture with maximum stresses between 85% and 95% of the tensile strength. Evidence of crack propagation features on fracture surfaces under scanning electron microscope (SEM) observation suggests crack initiation in void defects created by printing deposition that propagates longitudinally through line bonding interfaces along layers. Considering this, 3D-printed PEEK's fatigue behaviour can be strongly related to printing conditions. Further research on the fatigue behaviour of 3D-printed PEEK is necessary to support its use in load-bearing implant applications. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to determine the effect of different friction stir welding (FSW) parameters on mechanical and metallurgical characteristics of aviation-grade AA8090 alloy joints. Design/methodology/approach: Response surface methodology with central composite design is used to design experiments. The mechanical and microstructure characteristics of the weld joints have been studied through a standardized method, and the influence of threaded pins on the joint microstructure has also been assessed. Findings: From a desirability strategy, the optimum parameters setting of the friction stir welding was the tool rotational speed (TRS) of 800, 1,100 and 1,400 rpm; tool traverse speed (TTS) of 20, 30 and 40 mm/min; and tilt angle 1°, 2° and 3° with different tool pin profiles, i.e. cylindrical threaded (CT), square threaded and triangular threaded (TT), for achieving the maximum tensile strength, yield strength (YTS) and % elongation as an output parameter. The TRS speed was the highest weld joint characteristics influencing parameter. Peak tensile strength (378 MPa), percentage elongation (10.1) and YTS (308 MPa) were observed for the optimized parametric value of TRS-1,400, TTS-40 mm/min and TA (3°) along with CT pin profile. Microstructure study of the welded surface was achieved by using scanning electron microscope of output parameters. When the tool rotation speed, tool transverse speed, tilt angle and tool profile are set to moderately optimal levels, a mixed mode of ductile and brittle fracture has been seen during the microstructure analysis of the welded joint. This has been aided by the material's plastic deformation and the small cracks surrounding the weld zone. Originality/value: From the reported literature, it has been observed that limited work has been reported on aviation-grade AA8090 alloys. Further thermal behavior of welded joints has also been observed in this experimental work. [ABSTRACT FROM AUTHOR]

Al-Cu alloy has broad application prospects in the field of aerospace due to its excellent performance. In this paper, deposits with different Cu contents were prepared by the wire arc additive manufacturing (WAAM) process, and the effects of Cu content on the microstructure and mechanical properties were investigated. The microstructure of Al-Cu alloy was investigated by metallography, scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), and transmission electron microscope (TEM). The results show that both the number and size of the precipitated θ phases (Al2Cu) in the as-deposited material increase with the increase of Cu content. After the T4 treatment, the solid solution amount of Cu in the matrix showed a trend of first increasing and then remaining stable. When the content of Cu was greater than 5.65%, as the Cu content increased, the number and size of the remaining θ phases both increased. In the peak ageing state, the amount of precipitated θ' phase showed a trend of increasing and then remaining stable. After the T6 treatment, the mechanical properties showed a trend of first increasing and then decreasing with the increase of the content of Cu. When the Cu content was 5.65%, the deposit achieved the best mechanical properties, and the anisotropy of the mechanical properties disappeared. The tensile strength, yield strength, and elongation reached 538 MPa, 478 MPa, and 10.5%, respectively. When the content of Cu was greater than 5.65%, the anisotropy of mechanical properties was obvious, and the fracture mode of the vertical specimen changed from ductile fracture to brittle fracture. [ABSTRACT FROM AUTHOR]

Nanoparticle incorporation in polymeric matrices to generate polymer nanocomposite with the intention of maximizing the "nano-effect" derived from the nanoparticles and minimizing the drawbacks of the polymer is an emerging field of research. In this study, low-density polyethylene (LDPE) was mixed with varying concentrations of montmorillonite (MMT) nanoclays to create a polymer nanocomposite with desirable characteristics. Composite sheets with nanoclays contents of (0, 1, 2, 3, and 4 wt%) were prepared for hardness, tensile-fractography, thermal conductivity, and tensile testing (elongation and stress-at-break). The results showed that, according to scanning electron microscope (SEM) study, LDPE has a low flexibility temperature and is prone to corrosion. For larger MMT filler loadings (>3% wt), tensile-fractography showed nanoclays particle micro-aggregation. The pure LDPE sample fracture's tensile-fractography showed plastic deformation. MMT/LDPE samples with 3% wt hard MMT filler have brittle fractures without appreciable plastic deformation. Thermal conductivity test results show that LDPE/MMT composite thermal conductivity decreased with increasing clay concentration. The thermal conductivity values were reduced from a value of 0.13 W/m.K to a value of 0.039 W/m.K when reinforced with 0% wt to 3% wt filler loading, respectively. With 4% wt filler loading, LDPE/MMT composites had the highest shore hardness at 47.4. Yet, tensile tests indicated that increasing clay content improved the composite's characteristics. At modest loading percentages (1-2 wt%), tensile results were excellent. Furthermore, the elongation at break of the unadulterated LDPE was reduced by 20% and 30% after introducing 1% wt and 2% wt of MMT as reinforcement additives, respectively. Hence, MMT clay can improve the mechanical properties and thermal insulation of LDPE polymer matrix. [ABSTRACT FROM AUTHOR]

HIPS-g-MAH compatibilizer and the other three compatibilizers were prepared and added to the polyamide 66/polyphenylene oxide (PA66/PPO) alloy. The FT-IR spectra showed that the maleic anhydride (MAH) had successfully undergone grafting on the high impact polystyrene (HIPS). The effect of the MAH ratio in the HIPS-g-MAH compatibilizer, the HIPS-g-MAH compatibilizer weight ratio, and the PA66/PPO ratio on the mechanical properties of PA66/PPO alloy was systematically studied. The results showed that the PA66/PPO alloy possessed the optimal mechanical properties when the HIPS-g-MAH compatibilizer weight ratio was 7% and the MAH ratio in HIPS-g-MAH compatibilizer ranged 4% ~ 8%. The fracture morphologies of PA66/PPO alloy with different HIPS-g-MAH compatibilizer weight ratios were characterized by scanning electron microscope (SEM). The PA66/PPO alloy without HIPS-g-MAH compatibilizer showed a typical brittle fracture. The mechanical properties of PA66/PPO alloys with the HIPS-g-MAH compatibilizer were improved. In addition, the crystallization temperature of PA66/PPO alloy decreased with the increase in the HIPS-g-MAH compatibilizer weight ratio. The PA66/PPO ratio also played an essential role in the PA66/PPO alloy properties. The coefficient of friction and wear rate both increased with the increase in the PPO ratio. [ABSTRACT FROM AUTHOR]