Narrow Gap MAG Welding and Joint Performance Analysis of 25Cr2NiMo1V Thick Plate

The narrow gap MAG welding system was used to successfully weld the 50mm thick butt joint of 25Cr2NiMo1V rotor steel. After 15-layer bead welding, heat treatment is performed on the welded joint. Compare the changes in the microstructure, tensile strength and impact energy of the welded joints and the heat-treated joints at 580°C (20h). The results show that after the heat treatment of the structure, the side lath ferrite in the coarse-grained region grows up, and the eutectoid ferrite grows up in the fine-grained region first. The strength of the welded joint is about 605MPa, and the fracture is characterized by ductile fracture. After heat treatment at 580°C (20h), the strength is about 543MPa, the fracture is characterized by ductile fracture, and there are also a large number of discontinuous small surface platforms, and the characteristic of brittle fracture appears slightly. The impact energy of the weld center of the welded joint is about 141J, the fusion line area is about 113J, and the toughness of the fusion line is slightly lower than that of the weld center. After heat treatment, the impact energy at the center of the weld is about 183J, the fusion line area is about 95J, the toughness of the weld center increases, and the toughness of the fusion line decreases.

Effects of shear-thickening polymer on force attenuation capacities in hip protectors

Many elderly people use hip protectors to prevent hip fractures from sideways falls. These hip protectors absorb or shunt away the energy applied to the greater trochanter. Herein, shear-thickening polymer (STP)-based hip protectors composed of STP and polyurethane foam are studied. The purpose of this study was to identify the main factor that reduces the impact force directly applied to the femoral neck region and to determine the optimal thickness of STP in hip protectors. Seven hip protectors of different thicknesses were prepared, and two sets of free-fall mechanical tests with a low impact energy of 25.1 J and moderate impact energy of 44.1 J were conducted for each hip protector. When the thickness of STP exceeded 8 mm, the resultant peak force tended to plateau under both impact conditions, and the force attenuation capacity decreased even under low impact energy conditions. Thus, a hip protector with a 6 mm or 8 mm STP and 5 mm foam was recommended. The STP was the key factor affecting force attenuation capacity, not the polyurethane foam. However, the foam also played an important role in helping the STP function and improving compliance for users.

Effect of Fibre Orientation on Impact Damage Resistance of S2/FM94 Glass Fibre Composites for Aerospace Applications: An Experimental Evaluation and Numerical Validation

This study aims to investigate the influence of fibre orientation and varied incident energy levels on the impact-induced damage of S2/FM94, a kind of aerospace glass fibre epoxy/composite regularly used in aircraft components and often subjected to low-velocity impact loadings. Effects of varying parameters on the impact resistance behaviour and damage modes are evaluated experimentally and numerically. Laminates fabricated with four different fibre orientations 0/90/+45/−458s, 0/90/90/08s, +45/−4516s, and 032 were impacted using three energy levels. Experimental results showed that plates with unidirectional fibre orientation failed due to shear stresses, while no penetration occurred for the 0/90/90/08s and +45/−4516s plates due to the energy transfer back to the plate at the point of maximum displacement. The impact energy and resulting damage were modelled using Abaqus/Explicit. The Finite Element (FE) results could accurately predict the maximum impact load on the plates with an accuracy of 0.52% to 13%. The FE model was also able to predict the onset of damage initiation, evolution, and the subsequent reduction of the strength of the impacted laminates. The results obtained on the relationship of fibre geometry and varying incident impact energy on the impact damage modes can provide design guidance of S2/FM94 glass composites for aerospace applications where impact toughness is critical.

Effect of Aluminum on Microstructure and Mechanical Properties of Weld Metal of Q960 Steel

High-strength low-alloy (HSLA) steel is used in important steel structural members because of its strength and plastic toughness. Q960 steel is HSLA steel obtained by adding an appropriate amount of alloy elements and quenching and tempering treatment on the basis of ordinary low-carbon steel. This kind of steel has strong hardenability due to the alloy elements added. Cold cracks, embrittlement and softening of the heat-affected zone easily occur after welding. In particular, the low-temperature impact toughness cannot meet the requirements and limits its use. In this paper, self-shielded welding is used to adjust the content of aluminum in flux-cored wire. The relationship between weld metal (WM) microstructure and strength and properties was studied by tensile test and impact test, and the influence mechanism of Al content on weld metal microstructure and properties was analyzed. The results show that when the content of Al is 0.21%, the impact energy at 0 °C~−60 °C is the best, the tensile strength can reach 1035 MPA and the number of pores is small. The size of inclusions in WM is mostly less than 1.0 μm Al2O3 spherical oxide. It can become the center of acicular ferrite (AF) and increase the nucleation probability. However, with the increase of Al content, large irregular AlN inclusions are produced, which reduces the tensile strength and impact energy of the welded joint.

Dynamic Model of Impact Energy Absorption by a Conveyor Belt in Interaction with the Support System

Measurements of the dynamic load of conveyor belts of identical strengths were used to evaluate and compare the data for belts with and without a support system. The goal was to identify the effects of the support system in terms of a relative amount of impact energy absorbed by a conveyor belt. A dynamic model was designed based on selected parameters of the impact process. Damage to conveyor belts, caused by the absorption of impact energy, was evaluated using the applied methods of mathematical statistics.