Key Engineering Materials Vols. 326-328

Abstract: The quasi-static tests on the endplate bolted connections of the new structure system consisting of SCC beam and CCSHRC column are briefly introduced in this paper. Meanwhile, the 3-D solid finite element models of the connections with pre-existing cracks in the lower flange’s high stress fields are set up by ANSYS. The material nonlinearities of concrete, steel and bars, together with the contact between the endplate and column surface are all considered in the model. With the transverse load applied on top of columns, the fracture parameters are calculated by APDL. The results indicate that the opening mode crack will happen mainly. When the pre-existing crack length is 2.50mm and the inter-storey drift is less than 6mm, the stress intensity factor values agree well with the converting values derived from J-integral and the crack tip fields are in elastic state. The J values are highly influenced by the pre-existing crack length, while seldom influenced by the concrete compression strength. Moreover, the J-integral have the trend to sharply increase when the pre-existing crack length is larger than 0.61mm, and the pre-existing crack will grow during loading when its length is larger than 1.35mm.

Abstract: The most common mode of the gear failure is tooth breakage, which is usually produced by bending fatigue failure. It is important to manufacture the gears which can withstand the applied stresses in view of safety and economic requirements. In this study, fatigue test and analysis were performed to evaluate the bending fatigue strength of an automotive bevel gear. Test fixtures of the double tooth concept were considered to obtain reliable fatigue test results. Fatigue life of automotive bevel gear was evaluated by Weibull analysis. To compare the test results and to verify the fatigue analysis procedures, fatigue analyses were carried out. The results of fatigue analysis show that fatigue life and crack initiation sites were well agreed with test results. The random loading of bevel gear under the real driving conditions was defined here, and then the fatigue analysis under random loading was also performed.

Abstract: The interior stress field of the surface crack specimen subjected to a uniform tensile load has been successfully analyzed by the 3-D local hybrid method. In this study, it was examined whether the 3-D local hybrid method was applicable to the specimen subjected to the bending load. It has been understood that the decision of the optimal size of the local model is indispensable in the improvement of accuracy from the previous research. Then, the width and thickness of the local model were changed widely, and analyses were carried out to find the optimal hybrid local model size. Moreover, it was examined how to decide the optimal size of the hybrid local model with various crack length and aspect ratio of the specimen. The optimal size of the hybrid local model was examined from the comparison with the J integral of the whole model.

Abstract: Fatigue strength assessments with two types of load carrying fillet weldment under out-of-plane bending load have been carried out by using both hot spot stress and structural stress methods. Basis for the derivation of structural stress method is discussed in detail. Finite element analyses using shell elements models have been performed for the fatigue strength assessment of weldments. As a result of the fatigue strength evaluation for load carrying transverse fillet weldment, hot spot stress method is found to be consistent with structural stress method as well as measurement. Hot spot stress, however, estimated for the load carrying longitudinal fillet weldment exhibit large variation with respect to mesh size and element type while the calculated structural stress for the longitudinal fillet weldment is relatively independent of mesh size. The fatigue life estimation according to structural stress has been introduced with the master S-N curve.

Abstract: Detection of delamination of a thermally sprayed coating on an SUS304 substrate was carried out nondestructively using electronic speckle pattern interferometry (ESPI) method in both static and cyclic tests at T=298 K and 873 K. Results showed that the surface strain of the coating becomes smaller than that of the substrate when delamination occurs from the interface of the substrate. Two parameters of critical strain of ε c and ε f, which correspond respectively for the static test and the cyclic test, are introduced to evaluate the existence of delamination according to the ε- σ s and ε-N curve. It is considered possible to evaluate the occurrence of delamination in cyclic tests using the static critical strain of ε c, instead of ε f.

Abstract: In this paper, the optical method of caustics is developed to apply in dynamic fracture problems of orthotropic materials. The initial curve and the caustics formulas about mode-I crack are derived first from the distribution of stress field to determine the dynamic stress intensity factor (SIF). Meanwhile, dynamic caustics experiments are performed to study the dynamic fracture process of orthotropic materials, during which the dynamic fracture toughness and the velocity of crack propagation are calculated directly from the series of caustics patterns. Moreover, typical mesoanalysis of fracture section are done by a scanning electron microscope (SEM), revealing the fracture mechanism of fiber reinforced material.

Abstract: In this research, corrosion fatigue crack initiation tests using 13 Cr stainless steel were conducted in synthetic seawater to investigate the corrosion fatigue crack initiation life (Nc). In addition, a corrosion fatigue crack initiation and propagation model was suggested also. Until now, corrosion fatigue crack initiation life was treated ambiguously. The important point of this model is the suggestion of the moment of the corrosion fatigue crack initiation life at which the critical size of the corrosion pit changes to the crack. As the crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM were conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the following were obtained. In the case without a clear stress concentration point which seems to fall into a corrosion fatigue crack initiation, as the meaning to define the number of cycles, at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and its propagation starts in earnest, as the reasonable and universal corrosion fatigue crack initiation life (Nc) has been clarified.

Abstract: For developing fatigue design curve of cast stainless steel that is used in piping material of nuclear power plants, a low-cycle fatigue test rig was built. It is capable of performing tests in pressurized high temperature water environment of PWR. Cylindrical solid fatigue specimens of CF8M were used for the strain-controlled environmental fatigue tests. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitude at 0.04%/s strain rates. The disparity between target length and measured length of specimens was corrected by using finite element method. The corrected test results showed similar fatigue life trend with other previous results.

Abstract: This paper deals with the creep-fatigue defect growth behavior at the defect front of a high temperature cylindrical structure subjected to a cyclic axial tensile loading and a thermal loading in the LMR(Liquid Metal Reactor) structures. The defect growth evaluation was carried out per the France RCC-MR A16 guide and UK R5 code and their results were compared. The creepfatigue structural test to confirm the evaulated results was carried out with a induction heater. The defect front was investigated at every 100th cycle of a testing by using the metallurgical inspection technique with an optical microscope. From these results, we showed that the creep-fatigue defect behavior of a high temperature structure can be predicted with a conservatism by following the RCC-MR A16 guide and the R5 code.

Abstract: Fatigue damage plays an increasingly important role in the design of various safety critical components that are exposed simultaneously to thermal and mechanical loads. Non-isothermal conditions, as these are to be found in turbine components, rocket engines, but also in high-speed machining tools makes the understanding even more complex. As the nature of those loading histories is mostly multiaxial, design engineers are interested in material models, which take into account the complexity of stress state and temperature history as well. The experimental validations of those models require specially designed test set-ups. The basic concepts of experimental techniques to perform non-isothermal, uniaxial fatigue tests will be described in general. Test systems, capable to simulate non-isothermal multiaxial stress states are presented. A new miniaturised electrothermalmechanical test rig, which allows testing of small specimens under complex thermomechanical loading conditions, will be discussed.