Papers by Keyword: Thermal Stress Intensity Factor

Abstract: Structural durability is the main focus of solid oxide fuel cells (SOFCs) development which is affected by the thermal stress caused by considerable CTE mismatch between components and thermal gradient. In this paper we investigate the thermal stress intensity factor for mode I, mode II and mode III of positive electrode-electrolyte-negative electrode (PEN) at room temperature and steady stage for an initial crack size of 10 μm. A commercial finite element analysis (FEA) was used to find the highly stressed regions in PENs and calculate the thermal stress intensity factors. The stress distributions are calculated at uniform room temperature and at steady stage with a non-uniform temperature profile. The thermal stress intensity factors are calculated for various principal directions at the location having the greatest maximum principal stress at room temperature and steady stage. The critical stress regions are identified based on the maximum principal stress at room temperature and steady stage. The maximum principal stress is of 53.45 MPa and 45.12 MPa in principal direction of-43.97° and-42.37° at room temperature and steady stage, respectively. The mixed-mode stress intensity factor including mode I, mode II, and mode III is calculated due to multi-axial thermal stresses. However, the stress intensity factor for mode I have a highest value compared to those for modes II and III. The principal direction has an effect on the thermal stress intensity factor for the critical region with the greatest maximum principal stress. All the calculated stress intensity factors in the present study are less than the corresponding fracture toughness given in the literature, ensuring the structural integrity for the given planar SOFC stack.

Abstract: In this study, the distribution of the thermal residual stresses due to the adhesive curing in elliptical and circular bonded composite repairs is analyzed using the finite element method. The computation of these stresses comprises all components of the structures: cracked plate, composite patch and adhesive layer. In addition, the influence of these residual stresses on the repair performance is highlighted by analyzing their effect on the stress intensity factor at the crack tip. The obtained results show that the normal thermal stresses in the plate and the patch are significant.. The presence of the thermal stresses increases the stress intensity factor at the crack tip which reduce the repair efficiency.

Abstract: In this paper, the thermal shock induced cracking behavior of a segmented coating on the outer surface of a hollow cylinder has been investigated. The driving force for the propagation of multiple segmentation crack, represented by the Thermal Stress Intensity Factor (TSIF), was determined by combination of the principle of superposition and the finite element method. The maximum TSIF has been shown to occur neither at the beginning nor at the steady state of thermal transients, but at an intermediate instant. As the spacing between multiple segmentation cracks decreases, the magnitude of TSIF first plateaus, and then decreases sharply. This quantitative mechanistic result rationalizes the experimental observations that a segmented coating can exhibit much higher thermal shock resistance than an intact counterpart, if only the segmentation crack spacing is narrow enough. Some other parameters affecting TSIF, such as segmentation crack depth and convection severity, were also discussed.