By the SHS reaction of mechanically alloyed Al-Ti powders set on Cu surface, thick and homogeneous Al3Ti layer free from unreacted elements was prepared in order to improve the wear properties of Cu. The surface layer was chemically binded with base metal by the formatin of three reaction layers. To prepare the MA powders for SHS reaction, it was comfirmed that MA time should be optimized because too short length of MA leads to the existance of unreacted elements. Furthermore, too long length of MA decreases the heat of reaction due to the formation of Al super saturated solid solution during MA.
A model to describe the change in the properties of the inelastic deformation and the fracture of reactor pressure vessel steels due to neutron irradiation, i.e., irradiation embrittlement, in the ductile region is developed. First, constitutive equations for unirradiated elastic-viscoplastic-damaged materials are developed within the irreversible thermodynamics theory. To take into account the effect of hydrostatic pressure on the growth of microvoids, suitable dissipation potential is used. Then, the effect of irradiation on the material behavior is incorporated into the proposed model as function of neutron fluence Φ taking into account the interactin of irradiation induced defects and movable dislocations. Especially for the effect on damage strain threshold pD, the mechanism of void nucleation due to stress concentration responsible for pile-up of dislocations at the inclusions in the material is proposed under unirradiated condition, then the effect of irradiation on that mechanism is considered. To demonstrate the validity of this model, it is applied to the case of uniaxial tensile loading of a low alloy steel A533B cl. 1 for the pressure vessel use of light-water reactors at 260°C. The resulting model can describe the increase of yield stress, ultimate tensile strength and the decrease of total elongation, strain hardening and strain rate dependence of yield stress due to neutron irradiation.
The objective of this study is to clarify crush phenomena of the hexagonal honeycomb core of aluminum alloy under the dynamic loading. The impact collapse test of the core was performed by the Hopkinson-bar method. The FEM program for the dynamic plastic buckling analysis was developed based on the iterative method that has been proposed by authors. The effect of load point speed on the collapse configuration, the buckling strength and the energy absorption capacity were discussed with the experimental results and the FEM calculation. The dynamic collapse configuration is different from the quasi-static one, but the dynamic buckling load and the energy absorption capacity are comparable to the quasi-static ones.
Interlaminar fracture toughness was investigated in CFRP laminates with ionomer interleaf of the thickness of 200μm. Ethylene based ionomer resin used in this study has high bonding strength with base composite. EPMA analysis revealed that the tough interphase layers where ionomer was mixed with epoxy resin were formed at the interfaces between ionomer layer and prepreg layer. Mode I fracture toughness tests were carried out using double cantilever beam specimens. The fracture toughness of ionomer interleaved CFRP was much higher than that of base CFRP. This high level of the toughness was kept constant with the increase of the crack length. Microscopic observation showed that the crack path was at the ionomer/tough interphase interface or inside the interphase region. Thus, the large plastic deformation of the ionomer resin mainly affected the great increase of the fracture toughness. Furthermore, bridged ionomer layers also affected the increase of the fracture toughness.
Static fatigue strength of sintered silicon nitride in multi-axial stress field is studied using shoulder fillet disks at 1000°C. Strength under step up loading is also studied using specimens that survived static fatigue test over 106 seconds. In case of static fatigue test, the strength can be evaluated by slow crack growth (SCG) theory. Under step up loading, the strength increases with total exposing time at high temperature. Fracture origin observation reveals that the percentage of fracture originated from surface defects decreases from 55% to 10%. These results imply that increase in strength under step up loading is associated with the crack healing in surface defects.
Behaviors of fatigue crack propagation in Si3N4 at 1300°C in air were investigated. The results of fatigue tests showed that a cyclic fatigue crack initiated from a precrack introduced by the indentation method when the precrack was above 150μm in length, but from inherent flaws when the length of precrack was below 150μm. The fatigue process at 1300°C was predominantly time dependent in the present testing condition. The crack growth rate for short crack was higher than that for long through thickness crack. Difference of crack growth behavior between short and long cracks will certainly result from difference in stress shielding effect due to bridging.
The effect of coating material on the high-cycle fatigue strength of a Ni-base superalloy, IN738LC, was studied at room temperature and 800°C. Through the work specific attention was paid to understand not only the fatigue lives themselves but also the interaction between the coatings, the substrate and the diffusion zone. The IN738LC specimens with three kinds of protective coatings were prepared and specified: one was the IN738LC with CoCrAlY alloy overlay coating of 230μm in thickness, the second was the IN738LC with CoNiCrAlY alloy overlay coating of 230μm in thickness, and the third was the combined coatings in which the aluminide coating of about 10mm in thickness was conducted on the CoNiCrAlY overlay coated IN738LC. The CoNiCrAlY and CoCrAlY alloy coatings, and the aluminide coating, were performed by high velocity oxygen fuel (HVOF) spraying, and chemical vapor deposition (CVD) technique, respectively. It was shown that there was a significant effect of the coating material on the fatigue lives of the protective coatings. The fatigue test results also indicated that the fatigue strength at room, or, low temperature should be as important as that at high temperature. The effect of long term isothermal aging on the fatigue lives of the protective coatings was also studied and clarified, investigating the inward and outward diffusion of main alloy elements between the substrate and the coatings.
In order to characterize the “Repeating-division type” cracking pattern which is often observed in brittle coating on a ductile substrate under increasing biaxial tensile stress, the bulge tests were carried out on steel disks with WC-Co coating which were prepared by high-velocity flame spraying. Moreover, an elastic analysis was applied to the division process of coating to derive a relation among the crack interval, the tensile stress and strain of substrate at the division, coating and substrate thickness and material's constants. The characteristics of the division process calculated from the analytical equation agree qualitatively well with the experimental results that the crack interval decreases with an increase in tensile stress and the crack interval is large when the coating thickness is large at the same stress.
In the present study, we have developed a system for evaluating numerous formulas of three-dimensional (3D) stress intensity factors (SIFs) found in literature. In general, this kind of system has to be flexible in extending its functions, and easy for ordinary engineers to use. In addition, it is important to keep system compact by sharing common functions among various cracks and structure geometries. To meet those requests, the present system has been fully designed based on an object-oriented programming approach, and built in a personal computer using one of object-oriented languages Visual C++. Its first version contains about 50 different formulas of 3D-SIFs.
X-ray fractography is a technique for estimating the loading conditions at fractures from the information obtained by X-ray stress analysis on fatigue fractured surfaces. This technique was applied to a rotating bending fatigue fractured surface. The specimens were actual size “Shinkansen (Bullet train)” axles bench tested at the Railway Technology Research Institute. The axles are 209 or 210mm in diameter, induction hardened 0.38% carbon steel (JIS S38C) with semi-elliptical artificial flaws. Fatigue fracture was caused mainly by rotating bending stress, and the effect of torsional stress was very slight. The residual stress at the fatigue fractured surface was tensile at the initial crack propagation region, increased to a tensile maximum value, then decreased to a compressive maximum value and increased again toward zero near the final fractured area. The results were compared to the residual stress distribution on fatigue fractured surfaces of CCT specimens under a tension-compression fatigue load of stress ratio R=-1. The general tendencies of residual stress distributions on both fatigue fractured surfaces agree well qualitatively.
The X-ray stress measurement for a coarse grained TiAl intermetallic compound was carried out to measure residual stress on various surfaces. It is, however, difficult to decide peak positions accurately because of spotty diffraction rings due to coarse grains and low P/B diffraction profiles obtained from worked surfaces. In the present study, an X-ray stress measurement method using an imaging plate (IP) and a conventional X-ray stress measurement method were applied to these surfaces. The results obtained are; (1) The X-ray stress measurement using the IP, adopted a software oscillation method and an X-Y plane oscillation method, was effective to obtain accurate residual stress values from the coarse grained TiAl intermetallic compound. (2) The conventional method was more useful for low P/B diffraction profiles than the method using the IP. (3) By applying a suitable X-ray stress measurement method to each surface, residual stress values were able to be obtained quantitatively.
When CFRP lamina is applied for the reinforcement of concrete structures, the lamina has a possibility to delaminate from the surface of concrete. The delamination must be detected and be repaired as soon as possible for the reliability of structures. In pursuit of this, an intelligent structure was proposed in this paper. Both sensor and actuator are required to detect and to repair the delamination, respectively. As the intelligent structure, optical fiber was used to detect the delamination of CFRP as a sensor. Epoxy resin adhesive in a capsule was used to repair the delamination as an actuator. In the first paper, characteristics of both sensor and actuator were investigated. The brightness of transmitted light in the optical fiber was decreased at bended point caused by delamination of CFRP. On the other hand, the capsuled epoxy resin has been spreaded widely into delaminated interface. As a result, it was recognized that the proposed sensor and actuator can be used to detect and repair the delamination of CFRP.
An intelligent structure of concrete reinforced by CFRP which can detect and repair the delamination of CFRP from the surface of concrete has been proposed and the performance has been evaluated in this paper. In order to investigate the effect of repair, three-point bending test has been performed on the test piece. When the optical fiber sensor detects the delamination during the test, the processor judges the damage to be repaired. The embedded Ni-Cr wire is heated to release the epoxy resin in the capsule, it spreads into the delamination to adhere the damage. The result of three-point bending test after repair showed better performance than that of a specimen of non-repaired. In case the repair was delayed, however, reasonable repairing cannot be expected. Therefore, delamination must be detected and repaired in the early stage of fracture. As a result, it was recognized that the delamination of CFRP on mortar concrete can be repaired with the proposed system.