The Welding Institute (TWI) is a research and technology organisation, with a specialty in welding. With headquarters six miles south of Cambridge, Cambridgeshire, England, since 1946, and with facilities across the UK and around the world. TWI works across all industry sectors and in all aspects of manufacturing, fabrication and whole-life integrity management technologies.TWI services include consultancy, technical advice, research and investigation for industrial member companies and public funding bodies. It also offers training and examination services in NDT, welding and inspection across the globe.Employing over 800 staff, TWI serves 700 Industrial Member companies across 4500 sites in 80 countries. The formation in 1922 of its professional institution, The Welding Institute, and the later establishment of the British Welding Research Association (BWRA) in 1946 provided the basis of the company group as it is today. The Welding Institute currently has a separate membership of over 6000 individuals.Friction stir welding was invented by TWI in 1991.
Composite materials are increasingly utilized in industries such as automotive and aerospace due to their lightweight nature and high strength-to-weight ratio. Understanding how strain rate affects the mechanical and crashworthiness properties of CFRP composites is essential for accurate impact simulations and improved safety performance. This study examines the strain rate sensitivity of CFRP composites through mechanical testing and finite element analysis (FEA). Experimental results confirm that compressive strength increases by 100%–200% under dynamic loading, while stiffness decreases by up to 22% at a strain rate of 50 s−1, consistent with trends observed in previous studies. A sled test simulation using LS-Dyna demonstrated that the CFRP crash box sustained an average strain rate of 46.5 s−1, aligning with realistic impact conditions. Incorporating strain rate–dependent material properties into the FEA model significantly improved correlation with experimental crashworthiness data, reducing discrepancies in peak acceleration, mean acceleration, and displacement by 6.5%, 5.9%, and 6.3%, respectively. These findings reinforce the necessity of accounting for strain rate effects in crash simulations and composite structure design, ensuring more accurate predictions of impact performance and structural integrity in safety-critical applications.
This work aimed to (i) understand conventional and pulse gas tungsten arc welding (GTAW) of AZ31B, and (ii) explore high frequency welding (100 Hz-150 0 Hz). GTA welding with alternating current (AC) and direct current electrode positive (DCEP) polarities yielded crack-free partial penetration welds for 6 mm thick AZ31B alloy sheet. Welding under direct current electrode negative (DCEN) polarity with identical parameters as that for AC and DCEP resulted in full penetration welds that had microcracks. Defect-free full-penetration welds could be accomplished with pulse GTA welding using DCEN polarity at a pulse frequency of 1 Hz with a pulse duration ratio of 1:1. The resultant DCEN P 1:1 weld metal had a microstructure finer than the conventional DCEN weld. Welds produced with pulse duration ratios of 1:2 and 1:4 lacked penetration but had a much finer microstructures because of the lower heat input. The arc constriction by the high frequency pulsing in the ActivArc (R)-High frequency (AA-HF) mode welding was responsible for deeper penetration. Welds produced under DCEN pulsing and AA-HF conditions had hardness higher than conventional DCEN, DCEP and AC GTA welds, attributed to the finer microstructure. AA-HF GTA welding produced defect free deeper penetration welds with good microstructural features/ mechanical properties and also gave an advantage of 50% enhanced productivity when welded at 1500 Hz. (c) 2024 China Ordnance Society. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
To understand the influence mechanism of post weld heat treatment (PWHT) on the strength and toughness of the deposited metal in ultra-high strength steel welding, gas metal arc welding (GMAW) was employed on the deposited metal, followed by testing and analysis of its microstructure and properties. The results indicate that the as-welded deposited metal consists of martensite and 3 % residual austenite, exhibiting significant dendritic micro-segregation. The segregation zone primarily comprises fine martensite and residual austenite. Following PWHT, the martensite in the deposited metal transforms into tempered martensite, and the residual austenite content decreases to 0.2 %, accompanied by the precipitation of a substantial amount of MoWC2. The yield strength and average impact energy at room temperature for the deposited metal in the as-welded condition are measured at 1090 MPa and 46.67 J, respectively. After PWHT, these values increase to 1330 MPa and decrease to 32.33 J, respectively. Furthermore, the particles within the dimples of shear zone of the deposited metal impact fracture in the as-welded condition and the PWHT condition are identified as residual austenite and MoWC2, respectively. Based on four strengthening mechanisms, the calculated yield strength of the deposited metal aligns closely with the measured values. The primary strengthening mechanisms for deposited metal in the as-welded condition include fine crystal strengthening and dislocation strengthening, while those for deposited metal in the PWHT condition encompass fine crystal strengthening, dislocation strengthening, and second phase strengthening.
This study investigates the mechanical and low-cycle fatigue (LCF) behaviour of ZrO2-coated Al-7075-T6 alloy under subzero temperature conditions (-60 degrees C). Tensile and LCF tests were conducted in accordance with ASTM E08 and E606 standards at both room and subzero temperatures, with strain-controlled fatigue tests performed at various strain amplitudes (Delta epsilon t/2= 0.65 %, 0.75 %, 0.85 %, and 0.95 %). The LCF performance of both coated and uncoated specimens were evaluated through hysteresis loop analysis, plastic strain life curves, plastic strain energy density, cyclic stress-strain responses, and Basquin-Coffin-Manson relationship curves. The microstructural changes in the fatigue-fractured surfaces were examined using Optical Emission Microscopy (OEM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). The results showed that the ZrO2 coating significantly enhanced the fatigue life of Al-7075-T6 under subzero conditions. This was attributed to the thermal barrier effect of the coating, which mitigated strain localization, reduced dislocation activity, and suppressed microcrack initiation. SEM analysis revealed the fracture morphologies at both room and subzero temperatures, including ductile-to-brittle transitions at low temperatures. XRD analysis showed variations in crystalline size and microstrain in the fractured surfaces, further supporting the enhanced fatigue performance of the ZrO2coated specimens. These findings emphasize the role of ZrO2 coatings in improving the mechanical and fatigue resistance of Al-7075-T6 alloy, offering a promising solution for enhancing the durability of lightweight alloys in aerospace and other extreme environmental applications.
Dissimilar joints between titanium (Ti) and nickel (Ni) alloys are increasingly sought after in different advance applications. Specifically, the combination of Ti6Al4V and Nitinol offers potential benefits in aerospace, energy sectors and biomedical devices where titanium's strength and Nitinol's shape memory properties can be leveraged. This study explores the feasibility of joining dissimilar Ti6Al4V and Nitinol alloys via Electron Beam Welding (EBW) and Laser Beam Welding (LBW) without an interlayer. Both the welding techniques produced stable joints. A comparative analysis reveals that EBW and LBW exhibit distinct microstructural evolution and mechanical properties. EBW samples showed a higher Ultimate Tensile Strength (UTS) of 160 +/- 5 MPa, corresponding to a joint efficiency of similar to 27% with respect to the Nitinol (weaker material) base alloy strength, compared to 120 +/- 5 MPa for LBW samples, which exhibited a joint efficiency of similar to 20%. Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis detected Ti2Ni and NiTi intermetallic compounds (IMCs), with a relatively higher concentration of Ti2Ni in LBW samples. Ti2Ni layer was formed at the titanium alloy interface during EBW, but at the nickel alloy interface during LBW. Tensile tests indicated that the fracture happened at areas of high concentration of Ti2Ni in EBW and LBW joints. This comprehensive study highlights the potential of EBW and LBW for dissimilar titanium-nickel alloy joints without an interlayer and offers insights that can be used in future research via optimized welding parameters and interlayer when necessary.
