A unified direct method for ratchet and fatigue analysis of structures subjected to arbitrary cyclic thermal-mechanical load histories

Multiscale analysis of thermomechanical stresses in double wall transpiration cooling systems for gas turbine blades

“…A decision on the optimal 𝑡 𝑐 /𝑡 ℎ ratio requires further analysis in the creep-plastic regime, in order to determine the inelastic cyclic strain range, 𝛥𝜀, experienced in the vicinity of a feature and then relate this to the number of cycles for fatigue crack initiation, 𝑁 𝑓 , based on an empirical Coffin-Manson relationship [13]. An accurate evaluation of 𝛥𝜀 can be performed through traditional inelastic FE cycle-by-cycle analysis [13] or by modern, intelligent methods that determine the structural cyclic state directly [53]. Simultaneously, however, the elastic stress solutions presented here can be readily used in computationally efficient Neuber type schemes (local strain approach) [13] to determine 𝛥𝜀 and thus predict 𝑁 𝑓 for the critical locations of the double wall system, over a range of loading and geometric combinations.…”

“…However, the actual problem here is more complex as it additionally involves two interacting plates with holes and a temperature mismatch, a temperature dependent yield strength, significant creep in the hot wall and the traction (CF loading) also cycling with time. In this case, the ratchet boundaries can be determined numerically through modern schemes, such as the Linear Matching Method [53], which uses the elastic stress field solutions into search algorithms for the residual stress field and iterative algorithms based on shakedown theorems [59]. Nevertheless, geometric and material model idealisations can be used to simultaneously obtain analytical expressions for the ratchet boundary, by using directly the analytical elastic solutions presented here within classical [60] and extended [61] shakedown theorems.…”

Ratchetting and Creep Failure in Twin-Wall Turbine Blades Experiencing Severe Thermal and Centrifugal Loading

“…The analysis of Section 4 can be extended to account for stresses and strains in two directions (Fig 1b), as well as hole effects [32,37]. It also provides a useful reference for developing direct numerical methods for ratchet boundary determination [38] and, generally, structural integrity assessment [24].…”

“…They also provide a framework for interpreting simulations using more elaborate material models, such as those developed to model material ratchetting. It is further noted that the analytical route employed here offers physical insights that are difficult to gain through direct/numerical methods and does not rely on assumptions for the determination of reverse plasticity-ratchet (PR) boundaries, as for example the assumption of constant ratchet strain along the PR boundary, currently used by direct methods [24,25].…”

Designing against severe stresses at compound cooling holes of double wall transpiration cooled engine components

“…additive manufacturing [45], will enable the implementation of such ideas. The results of the present paper also: (a) indicate the pathways for modifying geometric features towards optimal mechanical performance; (b) reduce the range of geometries that needs to be analysed in the plasticity-creep range, including complex temperature fields and cyclic thermomechanical loading conditions; (c) provide the thermoelastic stress range at critical locations, which can be associated with shakedown and ratcheting limits [46][47][48][49][50] and can also be readily used in fatigue life calculations based on Neuber type local strain approaches [51][52][53]; and (d) establish a strong foundation for exploring more detailed phenomena related to the directional [54,55] and temperature dependence [56] of material properties, as well as evaluating crystallographic slip failure mechanisms [57,58].…”