• 한국군사과학기술학회지
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• 제15권4호
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• pp.435-441
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• 2012

This paper provides simulation-based results of effect analysis of sample size and sampling periods on accuracy of reliability estimation methods using multiple comparisons with analysis of variance. Sum of squared errors in estimated reliability measures were evaluated through applying seven estimation methods for one-shot systems to simulated quantal-response data. Analysis of variance was implemented to investigate change in these errors according to variations of sample size and sampling periods for each estimation method, and then the effect analysis on accuracy in reliability estimation was performed using multiple comparisons based on sample size and sampling periods. An efficient way to allocate both sample size and sampling periods for reliability estimation tests of one-shot systems is proposed in this paper from the effect analysis results.

• Structural Engineering and Mechanics
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• 제63권1호
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• pp.1-9
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• 2017

Shot peening is a cold surface treatment employed to induce residual stress field in a metallic component beneficial for increasing its fatigue strength. The experimental investigation of parameters involved in shot peening process is very complex as well as costly. The most attractive alternative is the explicit dynamics finite element (FE) analysis capable of determining the shot peening process parameters subject to the selection of a proper material's constitutive model and numerical technique. In this study, Ansys / LS-Dyna software was used to simulate the impact of steel shots of various sizes on an aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The influence of shot velocity and size on the plastic deformation, compressive residual stress and force-time response were investigated. The results exhibited that increasing the shot velocity and size resulted in an increase in plastic deformation of the aluminium target. However, a little effect of the shot velocity and size was observed on the magnitude of target's subsurface compressive residual stress. The obtained results were close to the published ones, and the numerical models demonstrated the capability of the method to capture the pattern of residual stress and plastic deformation observed experimentally in aluminium alloys. The study can be quite helpful in determining and selecting the optimal shot peening parameters to achieve specific level of plastic deformation and compressive residual stress in the aluminium alloy parts especially compressor blades.

• 한국신뢰성학회지:신뢰성응용연구
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• 제14권3호
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• pp.162-168
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• 2014

This paper discusses the application of Bayesian techniques with test data on similar products for performing the Economical Reliability Test of new one-shot device. Using the test data on similar products, reliability test required lower sample size currently being spent in order to demonstrate a target reliability with a specified confidence level. Furthermore, lower sample size reduces cost, time and various resources on reliability test. In this paper, we use similarity as calculating weight of similar products and analyze similarity between new and similar product for comparison of the essential function.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.328-333
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• 2003

The purpose of this study is to analyze the impact of shot peening angle on residual stress distribution. From the residual stress analysis of perpendicular shot peening, it could be known that the residual stress in the case of high velocity is larger than low velocity, but the amount of shot size has little effect on the magnitude of compressive residual stress. The centroidal residual stress is not greatly affected by the inclined shot peening but mainly related to the unstable conditions of surface residual stress field. Therefore, this tendency may lead to reduce fatigue life of treated material.

• 한국기계가공학회지
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• 제12권1호
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• pp.22-27
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• 2013

A shot blasting process is to improve the surface quality of stainless steels. The process is similar to a well-known shot peening that is used to strengthen the surface via the residual stress. In the shot blasting process, it is important to decide many parameters, such as the size, incident angle and velocity of shot balls, to effectively get rid of the iron oxide on the surface of stainless steels. In this study, the simulation of the shot blasting process is carried out by a finite element software, which can help to find out the optimal design parameters to cause the delamination of the iron oxide from the stainless steel substrate. The results obtained are also compared to those of the discrete element method to verify them.

• 한국산업융합학회 논문집
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• 제26권5호
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• pp.725-731
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• 2023

In this study, the harmless crack size was evaluated using carburized, quenched-tempered SCM822H steel. The possibility of detecting cracks that reduce the fatigue limit by non-destructive inspection was evaluated. The conclusions obtained are as follows. The retained austenite of surface was reduced by SP. About 35% and 65% of the retained austenite on the surface were transformed into strain-induced martensite, increasing the hardness by 79HV and 122HV over the as-received material. The maximum compressive residual stresses introduced on the surfaces were -695 MPa and -688 MPa, respectively. The fatigue limit increased by 1.48 times and 1.67 times, respectively, compared to the as-received material. The harmless crack size of SP specimen was determined differently depending on the shot ball size.

• 대한기계학회논문집A
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• 제40권12호
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• pp.987-995
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• 2016

본 연구는 $ZrO_2$의 비커스 경도에 대한 쇼트 피닝 효과를 연구하였다. 쇼트의 크기는 ${\phi}180{\mu}m$와 ${\phi}300{\mu}m$를 사용하여 피닝하였다. 비커스경도는 압입하중 98 N과 294 N으로 측정하였다. 비커스 경도는 와이블 통계 해석을 수행하여, 볼 크기 및 압압 하중에 따르는 영향을 평가하였다. 척도 파라메터는 98 N 압입 하중 및 ${\phi}180{\mu}m$ 쇼트 볼에서 크게 나타났다. 형상 파라메터도 대체적으로 작은 쇼트 볼(180sp)이 크게 나타났다. 이것으로부터 SP처리에 의한 압축 잔류 응력은 $ZrO_2$의 기계적 성질의 향상에 좋은 방법이다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.239-241
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• 2004

Stress intensity factor of semi-circular crack front was calculated by FEM, and also allowable crack size which doesn‘t break out the fracture by SCC in residual stress field of STS materials. Allowable crack size was increased with compressive residual stress provided by shot peening on material surface, and with magnitude of compressive residual stress for depth direction.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권2호
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• pp.99-107
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• 2013

One-shot device is required to successfully perform its function only once at the moment of use. The reliability of a one-shot device should be expressed as a probability of success. In this paper, we propose a bayesian approach for estimating reliability of one-shot devices with small sample size. We employ a gamma prior to obtain the posterior distribution. Finally, we compare the accuracy of the proposed method with general maximum likelihood method.

• 한국신뢰성학회지:신뢰성응용연구
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• 제14권4호
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• pp.225-229
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• 2014

A one-shot device is defined as a product, system, weapon, or equipment that can be used only once. After use, the device is destroyed or must undergo extensive rebuild. Determining the reliability of a one-shot device poses a unique challenge to the manufacturers and users due to the destructive nature and costs of the testing. This paper presents a reliability growth prediction for a one-shot system. It is assumed that 1) test duration is discrete(i.e. trials or rounds); 2) trials are statistically independent; 3) the number of failures for a given system configuration is distributed according to a binomial distribution; and 4) the cumulative expected number of failures through any sequence of configurations is given by AMSAA model. When the system development is represented by three configurations and the number of trials and failures during configurations are given, the AMSAA model parameters and reliability at configuration 3 are estimated by using a reliability growth analysis software. Further, if the reliability growth predictions do not meet the target reliability, the sample size of an additional test is determined for achieving the target reliability.