Dimensional design of miniaturized flat specimens and its influence on creep behavior

Purpose – This study is devoted to miniaturized creep testing for in situ performance assessment of high-temperature components. It seeks to systematically elucidate how the geometric parameters of flat mini-specimens—gauge-length ratio l/d, fillet-radius ratio R/d and thickness ratio t/d—influence stress concentration, creep deformation, life and damage evolution, and to establish a practically applicable recommended design window for specimen dimensions. Design/methodology/approach – Flat mini-specimens were designed using l/d, R/d and t/d as non-dimensional geometric parameters. A three-dimensional finite element model incorporating the Kachanov–Rabotnov creep damage formulation was constructed to perform elastic and creep simulations. Mesh-convergence studies were used to determine the element type and local mesh refinement. On this basis, the stress concentration factor, creep life, core equivalent creep strain, displacements of the gauge section and gripping ends, and the time-dependent migration of the maximum-damage location were systematically evaluated. Findings – The results show that the stress concentration factor is mainly governed by R/d, is only slightly sensitive to t/d, and is essentially insensitive to l/d. Stress, creep strain and damage are all concentrated in the central region of the gauge section, so the total displacement can be well approximated by the gauge-section displacement. When l/d = 2–3, the creep life approaches that of the reference specimen and the stress state is close to quasi-uniaxial, whereas at l/d = 1 the geometric effect becomes particularly pronounced. At l/d = 1, the location of maximum damage remains in the specimen core, while with increasing l/d the maximum-damage location migrates from the region near the fillet towards the core; this damage offset can be mitigated by increasing R/d and t/d. Originality/value – This work establishes a dimensional assessment framework for miniaturized flat creep specimens by combining the K–R creep damage model with three-dimensional finite element analysis including the grips. The individual and coupled influences of l/d, R/d and t/d on creep behavior are quantitatively examined. A damage-migration metric based on the movement of the maximum-damage location is proposed, and dimension-design recommendations are provided that can be directly used for in situ extraction of high-temperature components and creep characterization with limited material volume.