Hideo Kashiwaya

Prediction of fatigue crack growth rate in welding residual stress field

Abstract Fatigue life prediction of welded joints is investigated by paying attention to a fatigue crack that initiates at the weld metal and propagates perpendicular to the weld line. Experiments have been conducted by using a C-Mn-Si steel and an austenitic stainless steel. The welded and unwelded specimens have been tested under constant and variable amplitude load with stress ratio R

Slow crack growth and acoustic emission characteristics in COD test

0 for investigating the effect of residual stresses on fatigue crack growth. The experimental results indicate that the crack growth rates are equivalent by use of the effective stress intensity range, based on the measurements of crack opening ratio. The effect of residual stress is equivalent to the stress ratio within the experiments. These results make it possible to predict the fatigue crack growth rates on the basis of data obtained from base materials. The proposed method based on the effective sress intensity range is sound enough for practical use.

Approximate formulae for estimating the j-integral of a circumferentially cracked round bar under tension or torsion

Abstract Brittle material fractures at a critical value of stress intensity factor or crack opening displacement (COD) without any prior crack growth. In the ductile materials, however unstable fracture initiation may be preceded by a period of slow crack growth from the notch tip. Such slow crack growth may be an essential prelude to unstable fast fracture and thus COD at the start of slow crack growth can also be regarded as a critical value of the fracture characteristics. We have tried to apply the acoustic emission techniques to the COD test. Acoustic emission techniques can be used to detect the onset of slow crack growth and to obtain a relation between COD and AE characteristics in the COD test.

Improved ultrasonic testing by phased array technique and its application

Abstract The approximate formulae for estimating the J contour integral by the use of a single load-displacement curve were newly derived for the circumferentially cracked round bar subjected to tensile (Mode I) or torsional (Mode II) loading, by paying attention to the elastic-plastic deformation behavior which is characterized by full yielding (net section of specimen is in yield) or general yielding (gross section of specimen is in yield). As application examples, elastic-plastic fracture toughness tests were performed at room temperature on Ni-Cr-Mo-V forged steel. The ductile crack growth resistance curves under the Mode I or the Mode III loading were measured with the multi-specimen method, and the fracture behaviors of each mode were examined.

Proportional extrapolation techniques for determining stress intensity factors

Abstract The phased array ultrasonic testing method is available for beam steering and focusing, and then the focused beam divergence angle can be narrowed and the sound level can be intensified at the focused region. In the present study, two examples of phased array application which are the linear scanning mode operation and the sector scanning mode operation, were conducted in order to establish the availability of this technique as an actual NDT technique. As the result of the experiments, it was recognized that both types of scanning mode had the capability for defect detection and successful estimation of the defect size. Furthermore, it was well realized that the real time B-scope display without mechanical scanning was effective to reduce the operating time of inspection.

Computerised defect sizing using ALOK analysis in shrunk-on wheel of turbine rotor

Abstract Proportional extrapolation techniques were proposed to compute simply and accurately stress intensity factors using the numerical computation method. They are based on procedures in which the effects of element division near the crack tip on stresses and displacements are corrected by comparison with a standard problem. Corrected results are only accurate in the limit as r → 0 ( r = distance from crack tip). A few crack problems were analysed by the boundary element method, and the proportional extrapolation techniques were applied to determine the crack tip stress intensity factors. A special strain gauge pattern was developed for applying the proportional extrapolation technique. The stress intensity factors of two-dimensional crack problems were analysed experimentally using the strain gauge.

Ductile fracture analysis of carbon steel pipe with a circumferential through-wall crack

Abstract A computerised defect evaluation system using an advanced ultrasonic technique for shrunk-on wheels of a turbine rotor has been developed. The flaw image was reconstructed by a modified ALOK method with attention to the tip diffraction echoes of stress corrosion cracking (SCC). The results of the application of this system to the mock-up wheel with artificial slits and real SCC cracks show that this system is very useful for crack sizing and locating.

Near-Threshold Fatigue Crack Growth of Austenitic Stainless Steels at Liquid Helium Temperature

Abstract It is necessary to make clear the pipe fracture conditions based on elastic-plastic fracture mechanics to assess the leak before break situation of carbon steel pipes for LWR plants. The aim of the present work is to discuss the effects of pipe size, initial crack length and fracture toughness on the estimated fracture load and mode of carbon steel pipes with a circumferential through-wall crack. As an analytical method, the R6-Rev.3 approach was applied to the pipe fracture analyses considering its simplicity in the application. The results indicate that the net-section collapse attainment becomes difficult with increasing diameter and decreasing thickness of carbon steel pipes. The degree of the net-section collapse attainment decreases with increasing crack length up to some critical size and then increases. The predicted fracture load is more sensitive to the materials J– R curve than to the elastic-plastic fracture toughness J IC . And a simple limit load analysis based on the yield stress is appropriate to evaluate the fracture load, as long as a proper margin was included.

Hot Isostatic Pressing and Sintering Behavior of Yttrium Oxide Dispersed Tungsten

When designing superconducting magnets for nuclear fusion equipment or superconducting generators, consideration must be made of the difficulties of in-service inspections arising from structural complications. Through paying proper consideration, it is necessary to evaluate the remaining service life by means of fatigue crack growth analyses based on preliminarily assumed initial flaws.

Blast erosion properties of thermal sprayed metal coatings.

Densification of tungsten with various yttrium oxide additions was investigated and the effect of capsule-free and encapsuled HIP treatment on density and bending strength at room and elevated temperature was examined. The sintered density of tungsten was greatly improved by addition of the yttrium oxide and a relative density above 99% was obtained by even in the case of capsule-free HIP treatment. Also, the bending strength was much improved and improved homogeneity could be obtained by HIP treatment. Significant difference were not found between capsule-free and encapsuled HIP treated tungsten with yttrium oxide. It was clear that dense and homogeneous tungsten components can be produced by HIP treatment without encapsulation through the addition of small amount of yttrium oxide.