Laser surface treatment of grey cast iron by high power diode laser

AbstractA grey cast iron surface was heat treated by a 1kW diode laser to improve the hardness and wear resistance of the surface. Based on a temperature measurement and control system, different levels of surface temperature and scan speed were investigated for single and multi-pass hardening processes. A homogeneous hardened zone with hardness 700–800 HV0.3 was obtained in cross section regardless to the process temperature and scan speed during single pass laser hardening. Considering the process productivity, the optimal combination of high temperature and high scan speed was used to identify the process condition to be used in the multi-pass laser hardening. The selected parameters were then applied in large surface treatment to investigate the effect of the overlapping procedure on the surface properties. Different overlapping lengths were investigated to produce a large hardened area with uniform hardening depth and hardness

Residual Stress Analyses in a Pipe Welding Simulation: 3D Pipe Versus Axi-symmetric Models

AbstractThis paper numerically studied the residual stress in a butt-welded steel pipe. A comparison of 3D pipe and axi-symmetric finite element model under the condition of same welding simulation parameters was carried out. The results showed that axi- symmetric model share similar residual stress distribution with 3D model in the condition of same heat source shape parameters. However, the stress values of the two concerned models were quite different. Meanwhile the scale of welding pool for 3D model was almost twice bigger than that of axi-symmetric model. Both welding experiment and simulation results of 3D model showed that peak temperature of welding pool along the welding path increased during the welding process, and welding pool width and depth also increased with the moving of heat source

Sampling-based Fast Gradient Rescaling Method for Highly Transferable Adversarial Attacks

Deep neural networks are known to be vulnerable to adversarial examples crafted by adding human-imperceptible perturbations to the benign input. After achieving nearly 100% attack success rates in white-box setting, more focus is shifted to black-box attacks, of which the transferability of adversarial examples has gained significant attention. In either case, the common gradient-based methods generally use the sign function to generate perturbations on the gradient update, that offers a roughly correct direction and has gained great success. But little work pays attention to its possible limitation. In this work, we observe that the deviation between the original gradient and the generated noise may lead to inaccurate gradient update estimation and suboptimal solutions for adversarial transferability. To this end, we propose a Sampling-based Fast Gradient Rescaling Method (S-FGRM). Specifically, we use data rescaling to substitute the sign function without extra computational cost. We further propose a Depth First Sampling method to eliminate the fluctuation of rescaling and stabilize the gradient update. Our method could be used in any gradient-based attacks and is extensible to be integrated with various input transformation or ensemble methods to further improve the adversarial transferability. Extensive experiments on the standard ImageNet dataset show that our method could significantly boost the transferability of gradient-based attacks and outperform the state-of-the-art baselines.Comment: 10 pages, 6 figures, 7 tables. arXiv admin note: substantial text overlap with arXiv:2204.0288

Does a specific MR imaging protocol with a supine-lying subject replicate tarsal kinematics seen during upright standing?

Magnetic resonance (MR) imaging is becoming increasingly important in the study of foot biomechanics. Specific devices have been constructed to load and position the foot while the subject is lying supine in the scanner. The present study examines the efficacy of such a newly developed device in replicating tarsal kinematics seen during the more commonly studied standing loading conditions. The results showed that although knee flexion and the externally applied load were carefully controlled, subtalar and talo-navicular joint rotations while lying during MR imaging and when standing (measured opto-electrically with markers attached to intracortical pins) did not match, nor were they systematically shifted. Thus, the proposed MR protocol cannot replicate tarsal kinematics seen during upright standing. It is concluded that specific foot loading conditions have to be considered when tarsal kinematics are evaluated. Improved replication of tarsal kinematics in different postures should comprehensively consider muscle activity, a fixed hip position, and a well-defined point of load applicatio