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This paper deals with the transient thermal stresses of a surface layered material due to the sliding contact with changing frictional coefficient. The actual frictional coefficient is given by the experimental results of the sliding-contact test on the bearing-specimen lined with white metal. The temperature and thermal stresses caused by the frictional heat generation in a coated materials are analyzed by making use of Laplace transformation and Duhamel integration. Numerical calculations are carried out for the same conditions of the examples in the sliding contact test. It became clear that the numerical results of temperature agreed well with the experimental results by choosing the proper heat transfer coefficient and the variations of temperature were similar to the change of frictional coefficient. Moreover, the thermal effects on the stress variations are considered by comparing the results of thermal stresses with the results of mechanical stresses., relation: isVersionOf: http://ci.nii.ac.jp/naid/110004997346/

This paper deals with the surface crack growth path description and the fatigue life prediction due to repeated rolling/sliding contact on the elastic half-space, accompanied by frictional heat generation and crack-face pressure. The stress intensity factors are analyzed for the surface crack which is kinked in multiple times from the inclined initial main crack. The rolling/sliding contact is simulated as a Hertzian contact pressure and a frictional load with heat generation, moving with constant velocity over the surface of the half-space. Applying the maximum energy release rate criterion to each kinked angle, the crack growth path can be described, and employing a mixed mode fatigue crack growth law, the associated fatigue life also can be predicted. The effects of frictional coefficient, slide/roll ratio and crack-face pressure on the crack growth path and associated life are considered for a high carbon-chromium bearing steel (SUJ 2).

This paper deals with the two-dimensional thermoelastic contact problem of a rolling rigid roller of specified shape, which induced of friction and heat generation in the contact region, moving with constant velocity in an elastic half-space containing a couple of subsurface cracks. In the present temperature analysis, the speed of the moving heat source is assumed to be much greater than the ratio of the thermal diffusivity and the half contact length. The problem is solved using complexvariable techniques and is reduced to singular integral equations which are solved numerically. Numerical results of stress intensity factors are obtained for the case of two short cracks which are located parallel to the surface. The variance in interference effects on the stress intensity factors with the distance between two cracks, and the effects of the frictional coefficient, the sliding/rolling ratio and the depth of the crack location on the results are considered.

Dynamic thermal stresses and cyclic crack growth behavior produced by a single and repeated thermal shocks were studied on silicon nitride. Thermal shock was applied to a square shaped bar specimen using the improved water-quenching method. It was clarified that the cyclic crack growth rates, da/dN, under the repeated thermal shock tests are represented by the following expression, da/dN=9.35×10^(K_-1.36)^. In addition, the experimentally observed maximum thermal stresses, σ_, for silicon nitride in the present study as well as those for cemented carbides and cermets in the previous report can be approximated by the expression, σ_=0.704αEΔT-57.74,where α, E, ΔT denote a linear coefficient of expansion, Young's modulus of the materials and applied temperature differences at thermal shocks, respectively. By using this expression we can directly evaluate the maximum thermal stresses induced by the thermal shocks without temperature measurements.

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The stress intensity factors of multiple radial edge cracks emanating from a circular hole have been analyzed for the case in which an infinite plate is step-functionally heated in a circular region near the hole. The stress solution can be obtained by superposing the stress disturbance due to the cracks on the transient thermal stresses due to the heat source in an infinite plate with a circular hole. The problem is reduced to multiple singular-integral equations which satisfy the boundary conditions on the crack faces. The numerical results of stress intensity factors are obtained for the case of two radial edge cracks with equal crack length. The interference effects of the locations of each crack on the stress intensity factors are considered.

The stress intensity factors of a radial edge crack emanating from a circular hole have been analyzed for an infinite plate heated by a moving circular heat source rotating at a constant angular velocity around the circular hole. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the moving heat source in an infinite plate with a circular hole. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a thermally insulated surface and a small crack. The effects of the angular velocity and the radius of rotating heat on the variations of stress intensity factors are considered.

The stress intensity factors of a small crack have been analyzed when an infinite plate is heated around the crack due to a rotating heat source changed step-functionally with time at a start point. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the rotating heat source in an infinite plate. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a uniformly distributed heat source in a circular region. The effects of the angular velocity of the heat source on the variations of stress intensity factors are considered.

The stress intensity factors of a radial edge crack emanating from a circular hole have been analyzed when an infinite plate is step-functionally heated in a circular region near the hole. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the heat source in an infinite plate with a circular hole. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a uniformly distributed heat source and a small crack. The effects of the location of the heat source on the variations of stress intensity factors are considered.

stress intensity factors of a small crack have been analyzed when an infinite plate is step-functionally heated in a circular region near the crack tip. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the heat source in an infinite plate. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a uniformly distributed heat source. The effects of the location of the heat source on the variations of stress intensity factors are considered.

Effects of microstructures and a transient temperature change on the microcracking of both cemented carbides and cermets were analyzed using a simulation method with a triangular elastic spring-lattice model. The transient temperature change was determined to fit the results of the improved thermal shock test which was proposed by Ishihara et al. The simulation results show that the initiations of a microcrack were observed at earlier stages of the transient temperature change for the models of both cemented carbides and cermets. Then, the successive occurrences of the microcracking were strongly affected by the microstructures. In the case of the large number of microcracks, the final number of microcracks for the transient calculation was different from one of a single step calculation.

Effects of the microstructures in a material on the thermal stress during thermal-shock were analyzed using a triangular spring-lattice model which was originally proposed by Sridhar et al, to analyze thermal contraction induced microcracking in single-phase ceramics. In the present study, maximum energies in a spring-lattice model were simulated for modified multi-phase polycrystalline materials with different microstructures. The simulations were carried out for variations of grain size, aspect ratio, and of physical properties of surrounding structures in the multi-phase polycrystalline structure which was observed in cermets. The results show that reductions of thermal stress were predicted by the changes of the geometry of grains and physical properties of surrounding structures.

The surface hard coating layered composite materials are more and more used in industries for the tribological and mechanical improvement. In this paper, the stress intensity factors are analyzed at the kinked interface crack tip due to the rolling-sliding contact with heat input. For the case of Al_2O_3, SiC, Stellite layered material bonded to the carbon steel substrate, the numerical calculations of the stress intensity factors are carried out, and the effects of the kinked angle, the layered thickness and the heat input strength on the results are considered.