Abstract
The hybrid CMC and superalloy bolted joints have exhibited great potential to be used as thermostructural components of reusable space transportation systems, given the respective strengths of these two materials. In the high temperature excursion of the hybrid joints with the aircrafts and space vehicles, the substantial difference in thermal expansion coefficients of CMC and superalloy materials will induce complex superposition of initial assembly stress, thermal stress, and tensile stress around fastening area, which might lead to unknown failure behavior of joint structure. To address this concern, a finite element model embedded with progressive damage analysis was established to simulate the thermostructural behavior and high-temperature tensile performance of single-lap, single-bolt C/SiC composite and superalloy joint, by using the ABAQUS software. It was found that the initial stiffness of the CMC/superalloy hybrid bolted joints decreases with the rise of applied temperature under all bolt-hole clearance levels. However, the load-bearing capacity varies significantly with the initial clearance level and exposed temperature for the studied joint. The thermal expansion mismatch generated between the CMC and superalloy materials led to significant changes in the assembly preload and bolt-hole clearance as the high-temperature load is applied to the joint. The evolution in the thermostructural behavior upon temperature was then correlated with the variations in stiffness and failure load of the joints. The provided new findings are valuable for structural design and practical application of the hybrid CMC/superalloy bolted joints at high temperatures in next-generation aircrafts.
Highlights
Continuous fiber-reinforced ceramic matrix composites (CMC) are one of the most important key technologies in the development of reusable space transportation systems, e.g., FOTON 9 and FOTON-M2 [1, 2], EXPRESS [2], and SHEFEX [3] missions, due to their high specific stiffness and strength, low thermal expansion coefficient, nonbrittle failure nature, and excellent environmental stability at elevated temperatures [4,5,6,7]
The hybrid CMC and superalloy joints are often assembled at room
For the neat-fit joint, when the imposed temperature loads were higher than 450°C, damage occurred around hole edges of the CMC plate, which led to premature failure of the joint structure before applying tensile load
Summary
Continuous fiber-reinforced ceramic matrix composites (CMC) are one of the most important key technologies in the development of reusable space transportation systems, e.g., FOTON 9 and FOTON-M2 [1, 2], EXPRESS [2], and SHEFEX [3] missions, due to their high specific stiffness and strength, low thermal expansion coefficient, nonbrittle failure nature, and excellent environmental stability at elevated temperatures [4,5,6,7]. The thermal expansion coefficients of CMC and superalloy materials usually differ 2-3 times, causing significant thermal mismatch effect This effect will induce complex thermal stress and strain distributions at a hole-edge area and change assembly parameters of the joint [7], which might lead to unknown failure behavior of joint structure. To address the above deficiencies in open literatures, a 3D finite element model coupled with progressive damage analysis is firstly carried out to predict tensile performance and failure behavior of single-lap, single-bolt hybrid CMC/superalloy joint. The preload loosening and variation of bolt-hole clearance caused by thermal expansion mismatch of the CMC and superalloy materials at high-temperature loading were evaluated, and their resultant influence on high-temperature tensile behavior and damage mechanisms will be discussed for the studied hybrid bolted joint.
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