Integrated Analysis of Mechanical Thinning and Thermal Subsidence in Engineering Materials and Systems

Abstract

Structural degradation of engineering materials via the intertwined processes of mechanical thinning and thermal subsidence has become a chronic and, in reality, often underestimated problem over a broad spectrum of industrial applications, including aeronautical structures and subsea pipelines, onshore and offshore infrastructure and energy conversion systems. Mechanical thinning: the progressive loss of cross-sectional material due to plastic deformation, abrasion, or controlled manufacturing processes, which changes load-bearing capacity and stress distribution in a manner that is not always reflected in conventional safety margins. Superimposed on thermal subsidence, which in this context is the thermally induced vertical movement and volumetric contraction of material systems under constant or a varying load in terms of temperature, the damage accretion may proceed with rates generally much larger than either of these mechanisms would yield in the absence of the other. In this paper, an analytical and numerical framework has been integrated in the characterization of the interaction between these two degradation echanisms in metallic alloys and composite structures of engineering interest. Based on finite element simulations that have been validated using experimental data obtained through tensile coupons and profilometric thinning measurements, thermocouple-measured subsidence experiments, we can determine quantitative relations between thinning severity indices, magnitude of thermal gradients, and the development of concurrent failure modes such local buckling, creep-assisted cracking, and interfacial delamination. A parametric study of carbon steel (ASTM A36), aluminium alloy (6061-T6) and a unidirectional carbon-fibre reinforced polymer (CFRP) laminate indicates that thermal cycling between, at least, -40°C and 250°C expedites the subsidence-induced displacement by a factor of up to 34 in pre-thinned specimens as compared to nominal geometry controls. The findings carry direct implications for inspection scheduling, remaining useful life (RUL) estimation, and structural health monitoring protocols, and they challenge the adequacy of standards that treat thinning and thermal effects as independently additive degradation factors.