This paper presents models for predicting residual tensile strength after fatigue in unidirectional brittle fiber-reinforced ceramic composites. First, the subcritical crack growth law was employed to predict residual strength of fiber. Next, two models were proposed for residual strength of a composite. The first model, Model I, is established based on Curtin's probabilistic model that describes the relationship between strengths of the fiber and the composite. In the second model, Model II, the composite strength is directly derived from the survival probability of fiber. Thirdly, the relationship between lives of the fiber and the composite was investigated. Finally, a case study was conducted for a ceramic matrix composite (CMC) to obtain the residual strength of the CMC after static fatigue loading. It was proven that the life and the initial strength of the fiber and the composite depend on the shape parameter of fiber strength and the fiber/matrix interfacial shear stress. In contrast, the residual strength ratio of the composite was found to be almost independent of these two parameters.

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In the present study, the interaction of two non-coplanar cracks and their growth behavior in round bars was investigated using the superposition finite element method (s-version FEM, S-FEM) and a number of fatigue fracture criteria. The S-FEM, in the frame of finite element method, is a global-local overlaying method. The interactions of two static cracks were analyzed by changing the relative distance between the cracks and the crack sizes. Simulations of the experimental conditions were then performed. The fatigue crack growth simulations were based on linear elastic fracture mechanics. The crack opening level was analyzed by a single elastic-plastic analysis and then integrated into the simulation while taking plasticity-induced crack closure into consideration. The simulation results were then compared to the experimental results, which were found to be in sufficient agreement. Finally, the variation of the stress intensity factor due to the interaction of two propagating cracks was investigated.

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This paper presents the theoretical analysis of a multilayered magneto-electro-thermoelastic hollow cylinder under unsteady and uniform surface heating. We obtain the exact solution of the transient thermal stress problem of the multilayered magneto-electro-thermoelastic hollow cylinder in the plane strain state. As an illustration, we perform numerical calculations of a two-layered composite hollow cylinder made of piezoelectric and magnetostrictive materials and investigate the numerical results for temperature change, displacement, stress, and electric and magnetic potential distributions in the transient state. Furthermore, the effects of the coupling, stacking sequence and position of the interface on the stresses, electric potential and magnetic potential are investigated.

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In order to clarify the loading-frequency effect on the fatigue crack growth behavior of a low carbon steel JIS S10C in a hydrogen gas environment, fully reversed bending fatigue tests were carried out. The main results are as follows. The loading-frequency effect on the FCG revealed a complex behavior; that is, not only acceleration, but also deceleration even in the same low loading-frequency range. The slight acceleration appears in the low growth rate range in which the ductile fracture mode is predominant. The deceleration appears due to the transition behavior from a quasi-cleavage fracture mode with a higher FCGR to a ductile one with a lower FCGR. This shows that lowering the load frequency does not necessarily lead to an unpredictable fatigue crack growth.

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In the previous study, crack initiation from a free edge along an interface between Cr microdot and SiO₂/Si substrate was experimentally investigated and theoretically analyzed within the framework of fracture mechanics. Since the size of stress concentrated zone confined to a nanoscale, it was questionable whether the fracture mechanics was still valid or not. The cohesive zone model (CZM) has advantages in describing cracking behavior along an interface. However, its 3-D applicability in nanoscale components has not yet been investigated. In this study, a three-dimensional cohesive zone model of exponential type is used to extract the toughness for the crack initiation along the interface between Cr microdot and SiO₂/Si substrate with the nanoscale stress concentration. After the CZM parameters for the Cr/SiO₂ interface cracking are calibrated by an experiment, its validity is examined by other experiments. This study demonstrates the applicability of the three-dimensional CZM to the characterization of interface fracture behavior in nanoscale components.

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