A Continuous Ship Unloader (CSU) is a facility in which multiple buckets rotate to excavate cargo from a ship to land. It is typically designed to have a lifespan of 20 years. However, fatigue damage is likely to occur before the end of its designated lifespan. This study aims to examine the possibility of extending the component"s lifespan by evaluating the remaining useful life of L-holder, a part of CSU, that has been in use for 20 years. Fatigue load history was predicted by measuring the strain with or without strain at the L-holder part requiring periodic replacement. Through tensile and fatigue tests, the remaining life was evaluated when cracks were not present. In addition, the remaining life in the presence of cracks was evaluated through destructive toughness test and fatigue crack propagation test. Life prediction results based on test cycles were obtained. The proposed guidelines are expected to be helpful for preventing CSU accidents.

Microlattice is well known as an efficient structure having a low density which maintains mechanical properties, so microlattice is being applied to the structural design of lightweight material in many industrial fields. In this study, we proposed a core-shell microlattice structure by the conformal coating of a metal nanoparticle-polymer composite in order to enhance the mechanical properties of polymeric microlattice printed by light-based 3D printing method. Polymeric architected microlattice was fabricated using digital light printing, which enabled the printing of complex structures with good surface smoothness. Then, the polymeric microlattice was conformally coated with aluminum nanoparticle-polymer composites. To investigate the effect of the metal nanoparticle-polymer composite coating on the mechanical properties of the microlattice, we studied the compressive behavior of cubic and octet-truss microlattices. As a result, we confirmed that both compressive strength and toughness of the two types of microlattices were effectively increased by coating with aluminum nanoparticle-polymer composites.

Rolling contact fatigue (RCF) and wear caused by rolling contact between the wheel and rail are inevitable problems in railway systems. An increase in axle load or the slip ratio causes excessive wear. However, RCF and wear do not act independently, but one influences the other. Wheel and rail materials and manufacturing quality have a considerable influence on the formation of RCF and the ensuing wear. Therefore, the mechanical properties of the wheel and rail are important factors for reducing RCF and wear on the contact surface. This paper presents a comparative evaluation of the wheel and rail used in the Korean industry for high speed trains and conventional rails with respect to their fatigue and fracture behavior. A series of tests such as uniaxial tensile tests, fracture toughness tests, and fatigue crack growth tests were carried out at both room temperature and low temperatures.

Seismic load induces a reverse cyclic load that alternately applies a tensile and a compressive load to a structure. For nuclear piping material, safety is assessed in terms of fracture toughness. However, test results using a quasi-static load can’t guarantee safety if there is a seismic load. In this paper, the fracture toughness of SA312 TP304 stainless steel, which is used as the safety injection pipe of a nuclear power plant, was estimated by using reverse cyclic loads with different ratios of tensile load to compressive load. The test results using a load ratio of -1 (compressive load / tensile load) show that fracture toughness decreases to approximately 10% against a load ratio of zero. These test results show that the reverse cyclic load must be considered in planning for the safety of nuclear power plants under seismic loads.