• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.1 s.173
• /
• pp.38-51
• /
• 2000

The study on the mechanical behavior of a spot-welded specimen is largely divided into the quasi-static overload failure analysis and the fatigue failure prediction. The main issue in an overload analysis is to examine the critical loads, thereby providing a generalized overload failure criterion. As the welding spot forms a singular geometry of an external crack type, fatigue failure of spot-welded specimens can be evaluated by means of a fracture parameter. In this study, we first present the limit loads of 4 representative types of single spot-welded specimens in terms of the base metal yield strength and specimen geometries. Recasting the load vs. fatigue life relationships experimentally, obtained here, we then predict the fatigue life of spot-weld specimens with a single parameter denoted the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and loading type in a comprehensive manner. The suggested fatigue life formula for a single spot weld can play a key, role in the design and assessment of spot-welded panel structures, in that the fatigue strength of multi-spots is eventually determined by the fatigue strength of each single spot.

• Composites Research
• /
• v.17 no.4
• /
• pp.68-73
• /
• 2004

An analytical study was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates repaired with asymmetric bonded composite patch. For single-sided repairs, due to the asymmetry and the presence of out-of$.$plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from Previous studies. Therefore, for the accurate investigation of fatigue behavior, it is necessary to predict the actual crack front evolution and take it into consideration in the analysis. In this study, the fatigue analysis of single-sided repairs considering crack front shape development was conducted by implementing three-dimensional successive finite element method coupled with linear elastic fracture mechanics (LEFM) concept, which enables the growing crack front to be directly traced and modeled in a step by step way. Through conducting present analysis technique, crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations.

• Journal of the Korean Society for Precision Engineering
• /
• v.33 no.7
• /
• pp.559-564
• /
• 2016

The objectives of this paper are to develop a finite element analysis model to analyze press-fitted and bending load conditions in a press-fitted assembly, and propose a hub shape optimization method to minimize contact pressure near the shaft contact edge. Numerical asymmetric-axisymmetric finite element models have been developed to predict contact stress on press-fitted shafts. The global optimization method, genetic algorithm, local optimization method, and sequential quadratic programming were applied to a press-fitted assembly to optimize the hub contact edge geometry. The results showed that the maximum contact pressure with the optimized hub shape decreased more than 60 % compared to conventional hubs and the maximum contact stress affecting fatigue life was reduced about 47 %. Hub shape optimization can be useful to increase the load capability of press fits in terms of wear and fatigue behavior.

• Journal of Ocean Engineering and Technology
• /
• v.16 no.3
• /
• pp.54-58
• /
• 2002

This study investigates a relationship between fracture mechanics parameters (Stress Intensity Factor Range: ΔK, Maximum Stress Intensity Factor; Kmax) and X-ray parameters (residual stress:$\sigma$r half-value breadth: B) for SG365 steel at elevated temperature up to 30$0^{\circ}C$. The fatigue crack propagation test were carried out and X-ray diffraction technique according to the direction of crack length was applied to fatigue fractured surface. The residual stress on the fracture surface was found to increase at low ΔK region, to reach a maximum value at a certain value of Kmax or ΔK and then to decrease. Residual stress was independent of stress ratio by arrangement of ΔK and half value breadth were independent of the arrangement of Kmax. The equation of $\sigma$r-ΔK was established by the experimental data. therefore, fracture mechanics parameters could be estimated by the measurement of X-ray parameters.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.317-323
• /
• 2001

This study verified the relationship between fracture mechanics parameters$({\Delta}K,\;{\Delta}K_{eff},\;K_{max})$ and X-ray parameters $(\sigma_r,\;B)$ for SG365 steel at elevated temperature up to $300^{\circ}C$. The fatigue crack propagation test were carried out and X-ray diffraction technique according to crack length direction was applied to fatigue fractured surface. The residual stress on the fracture surface was found to increase low ${\Delta}K$ region, reach to a maximum value at a certain value of $K_{max}\;or\;{\Delta}K$ and then decrease. Residual stress were independent on stress ratio by arrangement of ${\Delta}K$ and half value breadth were independent by the arrangement of $K_{max}$. The equation of $\sigma_r-{\Delta}K$ was established by the experimental data. Therefore, fracture mechanics parameters could be estimated by the measurement of X-ray parameters.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.5
• /
• pp.772-778
• /
• 2001

In this study, corrosion fatigue characteristics of 12Cr alloy steel were investigated in 3.5wt.% NaCl solution of 150$^{\circ}C$ and 4.5bar. Behavior of corrosion fatigue cracks was measured by the indirect compliance method and compared with the results in distilled water and in air. 1) 12Cr alloy steel was susceptible to temperature. Its susceptibility was increased as the temperature was increased. 2) The crack growth characteristics of 12Cr alloy steel in distilled water were similar to 3.5wt.% NaCl solution. 3) The temperature of solution affects to the crack growth characteristics of 12Cr alloy steel. In corrosion solutions of 4.5bar, 150$^{\circ}C$, fracture surfaces of corrosion fatigue crack growth at a/W=0.3 was showed the trans-granular fracture suface. As the crack grew up, it was changed to inter-granular type. In condition of high temperature, The crack growth behaviors of 12Cr alloy steel were remarkable.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.3
• /
• pp.61-69
• /
• 1997

A simple and relatively new experimental method is proposed to estimate the plane stress fracture toughness by using compact tension (CT) specimen. The anti-buckling plates (fabricated to prevent the buckling caused by the 45 plastic yielding around crack tip under the plane stress condition) help to determine the relatively accurate plane stress fracture toughness of two stainless steels (SS304 and SS316). The fatigue crack propagation behavior of two stainless steels under two different loading conditions such as 10Hz and 5Hz frequency fatigue loadings was investigated by using image analysis technique (IAT) which renders several technical advantages over various conventional measuring methods. It was found that the IAT could be used to estimate fatigue crack lengths more effectively. Furthermore, it was suggested that we might control the measuring time interval for fatigue crack propagation by nearly automatically controlled technical process with the help of IAT.

• Journal of the Korean Ceramic Society
• /
• v.36 no.1
• /
• pp.15-20
• /
• 1999

Elevated temperature static fatigue behavior of silicon has been investigated by stress intensity/life test method. Static fatigue crack growth rate increase with the increase of temperature. Such tendency is found to be mainly related to the decrease of fracture toughness with the increase of temperature. That is, when static fatigue crack growth rate, da/dt is expressed by da/dt=AK1m, a constant A is a function of fracture toughness Kc and the exponent m is a constant which is independent of temperature or Kc. However, in the case of high temperature that glass phase is softened, the crack growth rate is found to be deviated from the above relation. This reason is, thus, discussed.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.3
• /
• pp.100-106
• /
• 1990

Microcracking of type 304 stainless steel at $593^{\circ}C(1,100^{\circ}F)$ has been studied, in particular, initiation, growth, and coalescence of fatigue and creep microcracks on smooth specimens and small notch specimens via surface replicas and photomicrographs. Quantitative information, such as, initiation period, growth, and coalescence behavior, statistical distributions of crack length, density of cracks, distribution patterns and crack growth properties, were obtained. From this study, the fracture process, fatigue life, and creep life prediction characterized by the growth of surface microcracks have been analysed by a new approach unifying the conventional approaches based on the final fracture of materials with the fracture mechanics approach. Knowledge of these parameters is critical for the application of fracture mechanics to fatigue and creep life assessment, and the damage evaluation of structures at elevated temperature.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.256-261
• /
• 2007

The purpose of this study is to investigate the effect of shot peening on the fatigue strength and fatigue life of two kinds of aluminum alloys. The fatigue strength behavior of aluminum alloys were estimated by the stress ratio and shot velocities. The fatigue life and strength increased with increasing the test shot velocity. However, at the shot velocity range between 50m/s and 70m/s, the compressive residual stress phenomena were observed in test conditions of different shot velocity. The optimal shot velocity is acquired by considering the peak values of the compressive residual stress, dislocations, brittle striation, slip, and fisheye on the fracture surface of test specimen. It was observed from the SEM observation on the deformed specimen that the brittle striation, fisheye were showed in the intergranular fracture structure boundaries at the this velocities. Therefore, fatigue strength and fatigue life would be considered that shot velocity has close relationship with the compressive residual stress.