Key Engineering Materials Vol. 1032

Abstract: The understanding of crack growth and therefore failure of components in geothermal energy production could lower maintenance costs tremendously. During in-situ corrosion fatigue experiments of high alloyed steel in geothermal brine the electrochemical potential was measured as well as temperature, frequency and pH of the surrounding geothermal brine. The decline of the electrochemical potential is in good agreement with estimated increasing linear crack propagation velocity. During initial crack propagation the electrochemical potential is in good agreement with the stress amplitude applied revealing that a steeper decline of potential indicates faster crack propagation. However, towards the end of propagation, this potential becomes independent of the stress amplitude.

Abstract: The FEM analysis evaluated how varying tightening loads affect diaphragm fatigue life at the position where fretting fatigue is most critical. Increasing body-side tightening load significantly shortened fatigue life, while increasing piece-side load slightly extended it. Under high body-side load, the beneficial effect of greater piece-side load became more noticeable. These findings indicate differing impacts from each side, with the body-side load having a stronger influence. An optimal tightening load balance may exist to maximize fatigue life.

Abstract: Molecular dynamics (MD) simulation was used to explore how models of W-He respond to irradiation induced damage. Displacement cascades up to 10 keV recoil energy were simulated for W-Σ17 and W-Σ17-He models. The pre-existing He bubbles within and around the grain boundary region have a major effect on the number and distribution of surviving Frenkel pairs. Frenkel pairs increased as the energy of the primary knock-on atom (PKA) increased across all models. Models containing pre-existing He bubbles showed a significant reduction in the number of surviving vacancies/SIAs compared to those without He bubbles. A large portion of point defects accumulate at the grain boundary which acts as a sink for defects during the recrystallization phase. The presence of He bubbles within or near the grain boundary region facilitates the defects generation, absorbs residual point defects, and form clusters. When He bubbles are located around the grain boundary, the number of surviving vacancies/SIAs decreased by 23% to 60% compared to models without He bubbles. However, for models with He bubbles located within the grain boundary structure, a much more extensive reduction occurred compared to models without He bubbles, which is between the range of 76% to 92%.

Abstract: Firefighter protective clothing is a crucial piece of equipment for firefighters during firefighting operations. However, the current firefighting clothing, when exposed to high temperatures around 100°C, provide only about 10 minutes of protection, which is insufficient. To enhance the protective performance of firefighter clothing, the most effective approach is to incorporate a cooling source, which can then transfer its cooling energy to the suit via a circulating medium, helping to regulate the body's temperature. Water is the most commonly used circulating medium, but it significantly increases the weight of the clothing. To address the issue of balancing the weight of the cooling system and its protective effectiveness, this paper proposes using air inside the firefighting clothing as the circulating medium. This would enhance the internal heat transfer through convection. In this study, a seven-layer geometric model is constructed using finite element software. The model includes the external air layer, outer layer, waterproof and breathable layer, thermal insulation layer, comfort layer, internal air layer, and skin layer. The temperature distribution and changes on the outer surface, inner surface, and human body surface of the suit are analyzed. The material of the firefighting clothing is modeled as a porous medium, while organic silica gel is used to simulate human skin. A wet air convection heat transfer model is developed to assess its thermal protection performance. The model's reliability is verified through experimental validation. The model is then used to examine the impact of external air temperature and internal air layer thickness on the thermal protection performance of the firefighting clothing. It was found that the internal air layer significantly influenced the thermal protection: The thermal protection of the suits with air convection was significantly improved compared to the thermal protection of the suits without air convection. when the external temperature increased from 50°C to 100°C, the surface temperature of the human body rose by only 2.24°C. However, when the internal air layer thickness was reduced from 10 mm to 2 mm, the human body surface temperature increased by 4.21°C, and thermal comfort decreased, though it still did not exceed the thermal safety limit.

Abstract: The marine atmospheric environment exposure test of BL-60 basalt composites was carried out in Hainan test station. The effects of marine atmospheric environment on the aging behavior of composites were studied by macro and micro morphology, moisture absorption rate, bending strength, linear expansion coefficient, glass transition temperature and infrared spectrum. The results show that the moisture absorption of the composite matrix plays a dominant role in the initial stage of exposure to the marine atmospheric environment ( 0.25 years ). With the extension of the test time ( ≥0.5 years ), the surface epoxy resin is aged and the basalt fiber is exposed. The intensity of the resin characteristic peak is obviously weakened, and the resin pulverization and shedding are greater than the moisture absorption effect. After one year of exposure to the marine atmospheric environment, the basalt fiber is almost completely exposed to the surface and exhibits a uniform cross-woven structure, and the resin characteristic peaks all disappear. After exposure to marine atmospheric environment for 1.5 years, the glass transition temperature of the composites decreased from 116.9 °C to 82.79 °C, the linear expansion coefficient decreased from 49.65 μm/(m·°C) to 31.43 μm/(m·°C), and the bending strength decreased from 570 MPa to 513 MPa. The experimental results show that the marine atmospheric environment causes aging damage to the hygroscopicity, macro and micro morphology and chemical structure of BL-60 basalt composites, which leads to the decrease of thermal and bending properties.