A variant of conventional laser material deposition (LMD), extreme high-speed laser material deposition (German acronym: EHLA) is characterized by elevated process speeds of up to 200 m/min, increased cooling rates, and a significantly reduced heat affected zone. This study focuses on the feasibility of using EHLA to apply material onto Fe-based substrate materials with AISI 4340 as a filler material. We studied how three different build-up strategies—consisting of one, three, and five consecutive deposited layers and hence, different thermal evolutions of the build-up volume—influence the metallurgical characteristics such as microstructure, porosity, hardness, and static mechanical properties. We propose a thermo-metallurgical scheme to help understand the effects of the build-up strategy and the thermal evolution on the microstructure and hardness. The tensile strength of the build-up volume was determined and is higher than the ones of forged AISI 4340 material.

The investigation and reconstruction are fundamental to enable designers to improve the subway vehicle’s crashworthiness. In this paper, a crashworthiness study of a subway vehicle collision accident in Beijing was conducted. Based on field investigation, the full-scale detail finite-element model, has established to calculate the dynamic behaviour of the vehicle in the accident. Then, the numerical simulation assists with the field investigation to identifying the structural weakness, which leading the injury of the occupant. Finally, an enhancement design for the structural weak point was considered to improve the vehicle crashworthiness in the same accident scenario.