Akihiro Matsuda

Strength and Fracture Characteristics of SUS304/AL-Alloy Scarf Adhesive Joint with Various Adhesive Thicknesses

In this study, strength and fracture toughness of epoxy adhesively bonded scarf joints of dissimilar adherends, namely SUS304 stainless steel and YH75 aluminium alloy are examined on several scarf angles and various bond thicknesses under uniaxial tensile loading. Scarf angles, θ = 45°, 60° and 75° are employed. The bond thickness, t between dissimilar metals is controlled to be ranged between 0.1 mm to 1.2 mm. Finite element (FE) analysis is also executed to investigate the stress distributions in the scarf joints by ANSYS 11 code. From analytical solutions, stress singularity exists most pronouncedly at the steel/adhesive interface corner of joints having 45° to 75° scarf angle. This is not only in agreement with the FE analyses results but also confirmed by fracture surfaces observation wherein the fracture has always been initiated at this point. The strength of scarf joints increases as the bond thickness decreases. Interface corner toughness, Hc approach can be applied when predicting the failure stress of scarf joints. Besides, for scarf joints with an interfacial crack, the fracture toughness, Jc values are independent of bond thickness and less sensitive to adherends. Moreover, Jc increases as mode mixity increases.

Stress and Strain Locus of Perforated Plate in Inelastic Deformation—Strain-Controlled Loading Case

Plastic strain of structures having stress concentration is estimated by using the simplified method or the finite element elastic solutions. As the simplified methods used in codes and standards, we can cite Neuber’s formula in the work by American Society of Mechanical Engineers (1995, “Boiler and Pressure Vessel Code,” ASME-Code, Section 3, Division 1, Subsection NH) and by Neuber (1961, “Theory of Stress Concentration for Shear Strained Prismatic Bodies With Arbitrary Nonlinear Stress-Strain Law,” ASME, J. Appl. Mech., 28 , pp.544–550) and elastic follow-up procedure in the work by Japan Society of Mechanical Engineers [2005, “Rules on Design and Construction for Nuclear Power Plants, 2005, Division 2: Fast Breeder Reactor” (in Japanese)]. Also, we will cite stress redistribution locus (SRL) method recently proposed as the other simplified method in the work by Shimakawa [2002, “Creep-Fatigue Life Evaluation Based on Stress Redistribution Locus (SRL) Method,” JPVRC Symposium 2002, JPVRC/EPERC/JPVRC Joint Workshop sponsored by JPVRC, Tokyo, Japan, pp. 87–95] ad by High Pressure Institute of Japan [2005, “Creep-Fatigue Life Evaluation Scheme for Ferritic Component at Elevated Temperature,” HPIS C 107 TR 2005 (in Japanese)]. In the present paper, inelastic finite element analysis of perforated plate, whose stress concentration is about 2.2–2.5, is carried out, and stress and strain locus in inelastic range by the detailed finite element solutions is investigated to compare accuracy of the simplified methods. As strain-controlled loading conditions, monotonic loading, cyclic loading, and cyclic loading having hold time in tension under strain-controlled loading are assumed. The inelastic strain affects significantly life evaluation of fatigue and creep-fatigue failure modes, and the stress and strain locus is discussed from the detailed inelastic finite element solutions.

Crack Initiation/Propagation of Perforated Plate Under Displacement-Controlled Fatigue Test at Elevated Temperature

In structures having stress concentration under cyclic loading, a small crack initiates and it grows and propagates. The present paper shows the experimental results of the perforated plate having the different diameters and the prescribed different strain amplitude. In the specimens having a circular hole, a crack initiates at the hole side having the most severe stress concentration in the specimen, and then the other crack also starts to initiate at the opposite hole side. Growth of both cracks is observed from the photographs taken at each cycle to study the relation between crack growth and load decrease. The feature of crack growth initiating from multiple origins will be discussed for fatigue test. The crack initiation is evaluated by referring to the accumulation law using the simplified estimation scheme, and the crack growth is evaluated by referring the increment of J-Integral. The agreement for crack initiation and propagation with these test results will be discussed.Copyright

J Integral in Elasto-Plasticity by Path Integral Method and Virtual Crack Extension Method in 2-Dimensional Problem

This paper shows the two calculation method of J Integral in elastic-plastic behavior of central crack in 2-dimensional problem. The analysis of the J integral and the increment of J for a plate with a central crack under cyclic fatigue loadings are carried out by using path integration based on the numerical results of Finite Element (FE) analysis. The J integral is calculated by both elastic analysis and elasto-plastic analysis. The accuracy of numerical results for the increment of J is proved by comparison with the simplified method results. In this study, we also analyzed the J-integral using the virtual crack extension method based on the finite element method. Analysis model is a two-dimensional flat plate with a central crack, and by changing the crack length in the different FE analysis, the fundamental feature of J-integral by the virtual crack extension method under cyclic fatigue analysis is discussed.Copyright

Stress and Strain Locus of Perforated Plate in Inelastic Deformation: Strain-Controlled Loading Case

Plastic strain of structures having stress concentration is estimated by using the simplified method or the finite element elastic solutions. As the simplified methods used in codes and standards, we can cite Neuber’s formula and elastic follow-up procedure. Also we will cite stress redistribution locus (abbreviated as SRL) method recently proposed as the other simplified method. In the present paper, inelastic finite element analysis of perforated plate, whose stress concentration is about 2.2∼2.5, is carried out, and stress and strain locus in inelastic range by the detailed finite element solutions is investigated to compare accuracy of the simplified methods. As strain-controlled loading conditions, monotonic loading, cyclic loading and cyclic loading having hold time in tension are assumed. The inelastic strain affects significantly life evaluation of fatigue and creep-fatigue, and the stress and strain locus is discussed from the detailed inelastic finite element solutions.Copyright

Simulation of Mechanical Characteristics of Tennis Racket String Bed Considering String Pattern

The effect of string pattern on the mechanical characteristics of a tennis racket were simulated numerically. A numerical simulation program to evaluate deformation of the string bed of a tennis racket was developed using the finite element method. The formulation of a numerical simulation code is described in this paper. The applicability of the developed simulation program was investigated by comparing experimental results of loading tests on string bed specimens, for which the distance between strings was 12 mm. The out-of-plane stiffness and sliding characteristics of strings of an actual racket were simulated using the developed simulation code.

Estimation of Crack Growth Rate by J-Integral Range for Type SUS304 Stainless Steel Plate in Creep-Fatigue Tests at High Temperature

In structures having stress concentration under cyclic loading, a small crack initiates and it grows and propagates. Evaluating crack growth is important to estimate the remaining life of cracked components.The present paper shows the estimation of crack growth rate under creep-fatigue loading with some patterns of strain holding times.Creep-fatigue tests of the perforated plate having initial crack were conducted with the different strain holding time under strain-controlled loading at 550°C. The crack growth was observed from the photographs taken at each cycle. The crack growth per one cycle of creep-fatigue loading was evaluated by the creep-fatigue crack propagation law which used increment J-integral range. Comparing the crack growth rates of experimental with those of predicted, the crack growth rates were predicted by using increment J-integral range with the accuracy was factor of 2.Copyright

Manufacture Trial of Tensile and Compressive Creep Test Machine Both for Plate-Type Specimen and Round-Bar Specimen

This paper shows the concepts for creep test machine. Designed creep machine can be used for tensile dead loading or compressive dead loading for the specimens of plate-type and round-bar types. Applied temperature is up to 1000°C. The developed creep test machine can be applied under the action of dead loading, so that long time measurement is possible. The firm measurement stock shelf is used as the framework of keeping right angle maintenance. The obtained creep test machine is also expected to have the rigidity of long term use. The necessary devises are for general purpose to reduce the cost.Copyright

Inelastic FE Analysis for J-Integral of Center-Cracked Plate in Creep-Fatigue Range

In order to estimate crack growth rate, it is necessary to use increments of the J-integral for both of time-independent fatigue process and time-dependent creep process. Many researchers and methodologies use C* to characterize creep crack growth and ΔJ or ΔK for fatigue crack growth, suggested are the following Refs.[1,2] This paper shows the fundamental features of J-integral in elastic, plastic and creep range. The path dependency is studied for center-cracked plate by using path integral from the large path to the small path near crack tip. The inelastic FE analysis is carried out for creep-fatigue loading, where the tensile strain is held constant to receive creep damage, and this paper shows the J-integral according to the loading histories. Also discussed are effects of the strain rate in fatigue process to affect the successive creep behavior.Copyright

Safety Evaluation of Nuclear Plant Fire Using CFD Analysis

In this paper, investigations of the safety of electrical cables in nuclear plant fire were described by CFD analysis and by flammability tests of power and control cables. For CFD analysis, thermal configurations of a nuclear power plant room in a fire accident was calculated by the Fire Dynamics Simulator (FDS). For flammability tests of cables, the cone-calorimeter test machine was modified to use the cable tray type specimen. The modified cone-calorimeter test machine is able to test the flammability of cables and insulation resistance from room temperature to 800°C.In the flammability test, electric power and control cables of the polyethylene sheathed cables which had been applied to the nuclear plants were adopt.The cable specimens of which length were 600mm, were fixed on a cable tray specimen. The temperature of the cable specimens was raised to from 200 to 570°C using the cone-type electrical heater. During the tests, electrical resistance and temperature was measured to evaluate safety of insulation resistance of cables.As results, the destruction of the insulation resistance of a polyethylene sheathed control cable was observed in the examinations, temperatures of which were 400°C and 500°C.In the numerical simulation using Fire Dynamics Simulator (FDS), an electrical switchgear room in nuclear plants was supposed as an evaluation model. As the fire source, fire in motor control cabinet in the switchgear room on nearby cable tray was applied to CFD analysis. From the results of numerical simulations, the heat configuration and temperature in the switchgear room was evaluated and radiation heat from fire to the cable trays was calculated.Considering these results given by flammability tests of electrical cables and CFD analysis, the safety of a switchgear room in nuclear plants was shown.Copyright