CALCULATION OF 3-D SURFACE CRACK STRESS INTENSITY FACTOR BASED ON APDL AND UIDL

In engineering,cracks are usually regarded as semi-elliptical surface cracks. It is not easy to establish a complete finite element model of a semi-elliptical surface crack,thus a quarter of the crack model is generally used to calculate the stress intensity factor by finite element method. This paper adopts APDL and UIDL technologies for secondary development of ANSYS software,establishes a complete model of semi-elliptical surface crack by simple interface operation with the method of model block processing. Using this method,the stress intensity factors of the central semi-elliptical crack and the oblique semielliptical crack were solved respectively. The results are basically consistent with the theoretical solution and the results in the literature,which shows that it is accurate and reliable to use the complete crack model established by this method to calculate the stress intensity factor. The combined development modeling function can be used to solve the stress intensity factors in complex structures under complex loads,and has important value for practical application of engineering

Tribological Property of Al₃BC₃ Ceramic: A Lightweight Material

Lightweight materials with a density less than 3 g/cm3 as potential tribo-materials for tribological applications (e.g., space tribology) are always desired. Al3BC3 ceramic, a kind of ternary material, is one of the lightweight materials. In this study, dense Al3BC3 ceramic is prepared via a reactive hot-pressing process in a vacuum furnace. Its tribological properties are investigated in two unlubricated conditions (one is at elevated temperature up to 700 °C in air, and another is in a vacuum chamber of back pressures from 105 Pa to 10−2 Pa at room temperature) and lubricated conditions (i.e., water and ethanol as low-viscosity fluids). At 400 °C and lower temperatures in air, as well as in vacuum, the tribological property of Al3BC3 ceramic is poor due to the fracture of grains and formation of a mechanically mixed layer. The beneficial influence of adsorbed gas species on reducing friction is very limited. Due to the formation of lubricious tribo-oxide at 600 °C and 700 °C, the friction coefficient is reduced from ca. 0.9 at room temperature and 400 °C to ca. 0.4. In the presence of low-viscosity fluids, a high friction coefficient and wear but a polished surface are observed in water, while a low friction coefficient and wear occur in ethanol. A lubricious carbide-derived carbon (CDC) coating on top of Al3BC3 ceramic through high-temperature chlorination can be fabricated and the wear resistance of CDC can be improved by adjusting the chlorination parameters. The above results suggest that Al3BC3 ceramic is a potential lubricating material for some tribological applications

Two-photon imaging of formaldehyde in live cells and animals utilizing a lysosome-targetable and acidic pH-activatable fluorescent probe

A two-photon fluorescent probe presented lysosomal targetability and an acidic pH-activatable response toward formaldehyde, and was applied to visualize formaldehyde in living systems.</p