Preparation and thermodynamic analysis of the porous functionally graded bolted joint

Abstract

Ceramic-metal functionally graded materials (FGMs) have been extensively used in aerospace engineering where high strength and excellent heat insulation materials are desired. In this paper, the thermodynamic behavior of the Thermal Protection System (TPS) used bolted joints made up of porous ZrO2/(ZrO2+Ni) FGMs is investigated by finite-element (FE) modeling. The bolted joint is subjected to reentry heating corresponding to the Access to Space Vehicle. Thermodynamic simulations are carried out to yield the transient response of the porous ZrO2/(ZrO2+Ni) functionally graded bolted joint (FGBJ).The effects of the preload on the thermomechanical behavior and service reliability of the bolted joint are numerically analyzed in detail by ABAQUS codes. It is found that the preload relaxation of the bolted joint occurs at elevated temperature, and the preload has significant influence on service reliability of the bolted joint under transient thermomechanical circumstances. With the increase of the preload, stress concentration which occurs at the root of the first thread of the bolt increases rapidly and predominates in service reliability. Proper preload is thus defined to balance the service reliability and tightness of the bolted joint. Further studies show that the shape of the nut has a great effect on the stress concentration of the thread, the optimized nut is designed to reduce the stress concentration of the thread, and thus the reliability of the bolted joint is also improved.

A study on fabrication of silicon nitride-based advanced ceramic composite materials via spark plasma sintering

“…36,37 Also, it is found by researchers that porosity can greatly affect the thermal conductivity, which has been deliberately utilized to design thermal resistance of ceramics. [38][39][40] Researchers have fabricated Si 3 N 4 ceramic materials using different additives, and it is confirmed that the function of different sintering aids is different in the preparation of Si 3 N 4 ceramics. For instance, to improve thermal conductivity, rare earth oxides like Y 2 O 3 and Yb 2 O 3 can be chosen as sintering aids.…”