Young Suck Chai

New analysis on the fiber push-out problem with interface roughness and thermal residual stresses

An improved analysis considering the effects of interface roughness and thermal residual stresses in both radial and axial directions is developed for the single fiber push-out test. The roughness of the interface, which has a significant effect on the fiber sliding behavior, is expressed by a Fourier series expansion that has good convergence and can handle general shapes of roughness. The interfacial shear stress that plays an important role in interfacial debonding is very much affected by the axial thermal residual stress in the bonded region, which can induce a two-way debonding mechanism. It has been found that both residual stress and interface roughness have pronounced effects on the stress transfer across the interface and interfacial debonding behaviour.

High-temperature Oxidation Behavior of Zircaloy-4 and Zirlo in Steam Ambient

The oxidation characteristics for Zircaloy-4 and Zirlo in the temperature range of 700-1200°C under steam supply condition were investigated by using a modified thermo-gravimetric analyzer. The specimens were oxidized for 3600 s at each temperature and then quenched in a furnace. The oxidation rate constants were measured from the weight gains to evaluate the oxidation behavior in Zircaloy-4 and Zirlo. The weight gain rates of Zirlo were lower than those of Zircaloy-4, leading to the low rate constants. The different oxidation behaviors between both cladding materials were considered to be due to the difference in their chemical compositions.

12Finite Element Analysis of an Automobile Clutch System

A pressure plate, a component of the clutch system, was analyzed by two-dimensional and three-dimensional finite element method under three major load conditions of thermal loading due to temperature distribution, centrifugal force and contact pressure of diaphragm spring. The results show that the effects of thermal loading and contact pressure of diaphragm spring are important, which suggests the direction of design improvement. A hub plate was also analyzed with finite element modeling. A stress concentration occurs around the fillet region around the window in the plate where the fracture analysis is executed to find the stress intensity factors. These results will be used as the fundamental data for design improvement of the shapes of pressure plates and hub plates.

Simplified simulation of fretting wear using the method of dimensionality reduction

We study the problem of wear of a rotationally symmetric profile subjected to oscillations with small amplitude. Under these conditions, sliding occurs at the boundary of the contact area while the inner parts of the contact area may still stick. In a recent paper, Dimaki with colleagues proposed a numerically exact simulation procedure based on the method of dimensionality reduction (MDR). This drastically reduced the simulation time compared with conventional finite element simulations. The proposed simulation procedure requires carrying out the direct and the inverse MDR transformations in each time step. This is the main time consuming operation in the proposed method. However, solutions obtained with this method showed a remarkable simplicity of the development of wear profiles in the MDR space. In the present paper, we utilize these results to formulate an approximate model, in which the wear is simulated directly in the one-dimensional space without using integral transformations. This speeds up the simulations of wear by further several orders of magnitude.

Finite Element Analysis and Optimal Design of Automobile Clutch Diaphragm Spring

A diaphragm spring is an important component of a clutch assembly, characteristics of which depends largely on that of a diaphragm spring. A diaphragm spring is subject to high stress concentration in driving condition, which frequently causes cracks and fracture around finger area. In this paper, behavior of a diaphragm spring is analysed by finite element method to calculate sensitivity of design parameters, which is used to perform optimal design of diaphragm spring shape. As an object function, hoop stresses are taken and minimized to improve durability. Characteristics of the diaphragm is used as equality constraint to maintain the original design purpose and sequential linear programming(SLP) is utilized as an optimization tool. With optimized design, it is verified that concentrated stress is decreased maintaining release load characteristic.

Evaluation of Fretting Fatigue Life for Steam Generator Tubes in Nuclear Power Plants

Studies on the strength and fatigue life of machines and structures have been conducted in accordance with the development of modern industries. In particular, fine and repetitive cyclic damage occurring in contact regions has been known to have an impact on fretting fatigue fractures. INCONEL alloy 600, 690 and INCOLOY alloy 800 are iron-nickel-chromium alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. These alloy are used extensively in the nuclear power plants industry, the chemical industry, the heat-treating industry and the electronic industry. In this paper, the effect of fretting damage on fatigue behavior for INCONEL alloy 600, 690 and INCOLOY alloy 800 were studied. Also, various kinds of mechanical tests such as tension and plain fatigue tests are performed. The objective of this study is to guarantee reliability of the facility applied in a power plant by comparing three materials in respect to fretting fatigue.

Microstructural Evolution of Inconel 690 Alloy for Steam Generator Tubes

Inconel 690 alloy is a Ni-Cr-Fe austenite solid solution alloy with a wide range of applications such as steam generator tubes in nuclear power plant due to its good mechanical properties and corrosion resistance. In this study, the effects of heat treatment on the microstructural properties of Inconel 690 alloy were investigated. Inconel 690 alloy was annealed at solid solution temperature of 1150°C for 20 min, and cooled down to 800°C with different cooling rates, and then aged at 800°C for 100 min in vacuum, and then cooled down to room temperature by water quenching. The optical microscopy, scanning electron microscopy, and transmission electron microscopy results indicated that in case of the cooling rate of 0.5°C/min, discontinuous carbides along the grain boundaries were formed and when the cooling rate was 10°C/min, continuous carbides were formed. In both cases, many annealing twins were also formed. These results can help to improve the understanding of microstructural properties of Inconel 690 alloy.

The Evaluation of Fretting Fatigue Life for Inconel 600 and 690 Alloy

The initial crack under fretting condition occurs at lower stress amplitude and at lower cycles of cyclic loading than that under plain fatigue condition. INCONEL alloy 600 and 690 are high–chromium nickel alloy having excellent resistance to many corrosive aqueous media and high-temperature atmospheres. In this paper, the effect of fretting damage on fatigue behavior for INCONEL alloy 600 and 690 were studied. Also, various kinds of mechanical tests such as hardness, tension and plain fatigue tests are performed. Fretting fatigue tests were carried out with flat-flat contact configuration using a bridge type contact pad and plate type specimen. Through these experiments, it is found that the fretting fatigue strength decreased about 40~70% compared to the plain fatigue strength in two materials. In fretting fatigue, the wear debris is observed on the contact surface, and the oblique micro-cracks at an earlier stage are initiated. These results can be used as basic data in a structural integrity evaluation of heat and corrosion resisting alloy considering fretting damages.

Interfacial crack propagation under various mode-mixes

Initiation and propagation of interfacial crack along bimaterial interface are considered in this study. A biaxial loading device for a single specimen is used for obtaining a wide range of mode-mixities. The specimen is an edge-cracked bimaterial strip of glass and epoxy; the biaxial loading device, being capable of controlling displacements in two perpendicular directions, is developed. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mixed modes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. The behavior of interfacial crack propagation analyzed as a function of mode-mix shows that initial crack propagation is delayed with increase of mode-mixity, and its velocity is increased with positive mode-mixity but decreased with negative case. However, it is found that crack propagation is less accelerated with positive mode-mixity than the negative mode-mixity, which may be caused by contact and/or effects of friction between far field and near-tip field along the interfacial crack.

THREE DIMENSIONAL FINITE ELEMENT SIMULATION OF THE FRETTING WEAR PROBLEMS

The structural integrity of steam generators in nuclear power plants is very much dependent upon the fretting wear characteristics of Inconel 690 U-tubes. In this study, a finite element analysis was used to investigate fretting wear on the secondary side of the steam generator, which arises from flow-induced vibrations (FIV) between the U-tubes and supports or foreign objects. Two-dimensional and three-dimensional finite element analyses were adopted to investigate the fretting wear problems. The purpose of the two-dimensional analysis, which simulated the contact between a punch and a plate, was to demonstrate the validity of using finite element analysis to analyze fretting wear problems. This was achieved by controlling the value of the wear constant and the number of cycles. The two-dimensional solutions obtained from this study were in good agreement with previous results reported by Stromberg. In the three-dimensional finite element analysis, a quarterly symmetric model was used to simulate tubes contacting at right angles. The results of the analyses showed donut-shaped wear along the contacting boundary, which is a typical feature of fretting wear.