Structural Effects of Spatially Non-Uniform Evolution of Material Parameters Under Cyclic Thermo-Mechanical Loading

Abstract

Metallic thermal protection structures of reusable high-speed vehicles experience aerodynamic heating, high-temperature hold, and cooling in each flight mission, and the hot and cold faces accumulate different temperature and plasticity histories; after multiple missions, the elastic modulus, yield strength, cyclic hardening parameters, and thermal conductivity no longer vary only with mission count, but form a spatial field varying jointly with position and mission count. This paper establishes a mission-to-mission, spatially local property update method: each mission solves the thermo-mechanical response with the current property field. At the end of the mission, the thermal exposure and plasticity accumulation at each integration point are extracted, and the material properties are updated through an evolution relation driven by the dual histories, for use in the next mission; the method is embedded in a non-isothermal Chaboche–Perzyna viscoplasticity program. Under a unified mission profile, a thin plate, a perforated plate, and a thick plate are computed for 50 missions each, that is, 50 thermo-mechanical loading cycles in sequence, with pointwise update (Case C) as the reference and no evolution (Case A) and uniform update (Case B) as comparisons. The results show that ignoring evolution gives higher structural stresses than the evolution-tracking case, with the peak-stress deviation not exceeding about 7% for the reference parameter set over the 50 missions (thin plate 4.2%, perforated plate 6.8%, thick plate less than 0.1%). Assessing the strength margin with the current, degraded strength rather than the peak stress alone shows that ignoring evolution reduces the margin by 12.2% of the reference margin in both the thin plate and the perforated plate, so that the treatment is conservative for these two structures, but only slightly so; the thick plate is marginally non-conservative, by a negligible amount. Ignoring evolution continuously underestimates the damage accumulation, with the maximum accumulated equivalent plastic strain underestimated by about 11.6% at the thin-plate hot face and about 6.0% at the perforated-plate hole edge, biasing life assessment toward the non-conservative side. At mission 50, uniform update deviates by only 0.4% in the thin plate with a mild degradation distribution, and by no more than 1% in the perforated plate with concentrated degradation; over the whole 50-mission window, the largest deviations are about 1.5% and 1.6%, respectively. The evolution parameters are assumed rather than calibrated, so the quantitative results are a sensitivity study rather than experimentally validated predictions.