• International Journal of Reliability and Applications
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• 제15권2호
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• pp.125-150
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• 2014

Accelerated life tests (ALTs) are extensively used to determine the reliability of a product in a short period of time. Test units are subject to elevated stresses which yield quick failures. ALT can be carried out using constant-stress, step-stress, progressive-stress, cyclic-stress or random-stress loading and their various combinations. An ALT with linearly increasing stress is ramp-stress test. Much of the previous work on planning ALTs has focused on constant-stress, step-stress, ramp-stress schemes and their various combinations where the stress is generally increased. This paper presents an optimal design of ramp soak-stress ALT model which is based on the principle of Thermal cycling. Thermal cycling involves applying high and low temperatures repeatedly over time. The optimal plan consists in finding out relevant experimental variables, namely, stress rates and stress rate change points, by minimizing variance of reliability function with pre-specified mission time under normal operating conditions. The Burr type XII life distribution and time-censored data have been used for the purpose. Burr type XII life distribution has been found appropriate for accelerated life testing experiments. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• International Journal of Reliability and Applications
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• 제18권2호
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• pp.45-63
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• 2017

In this paper, we have formulated optimum Accelerated Life Test (ALT) plan for a parallel system with two independent components using masked data with ramp-stress loading scheme and Type-I censoring. Consider a system of two independent and non-identical components connected in parallel. Such a system fails whenever all of its components has failed. The exact component that causes the system to fail is often unknown due to cost and time constraint. For each parallel system at test, we observe its system's failure time and a set of component that includes the component actually causing the system to fail. The stress-life relationship is modelled using inverse power law, and cumulative exposure model is assumed to model the effect of changing stress. The optimal plan consists in finding out the optimum stress rate using D-optimality criterion. The method developed has been explained using a numerical example and sensitivity analysis carried out.

• 정보저장시스템학회논문집
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• 제5권2호
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• pp.82-88
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• 2009

Understanding the adhesion behavior and characteristics of toner film is required to achieve image and text printing with high quality resolution. Toner can be considered as a thin film coating on a media such as paper or polymer film. Quantitative measurement of adhesion characteristics of the thin film is important to assess the reliability of the system. In this work the main objective was to investigate the adhesion characteristic between the toner and the media by ramp loading scratch test method. The scratch test may be used to obtain quantitative information about the adhesion of the film to the substrate. In the scratch test a diamond tip was used to scratch the surface of the toner film under an increasing normal load until the toner detached or fractured. The critical load (LC) was obtained from the experimental results. Also, the relationship between the critical load and the adhesive strength of the interface between the substrate and the toner was obtained by measuring the normal and tangential forces during the scratch test. Finally, theoretical analysis of the toner scratch characteristics was performed based on Benjamin and Weaver theory, Plowing model, and Laugier model.

• 한국지반공학회지:지반
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• 제8권1호
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• pp.67-80
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• 1992

본 연구에서는 시간에 따른 공사하중의 크기 변화가 다양할 경우에, smear zone및 well resistance의 영향을 모두 고려하여 설계시에 요구되는 모래기등 영향원의 반지름(즉, 모래기둥의 설치간격)을 결정하기 위한 해석법을 제시하였다. 이를 위해 단순선형점증하중의 경우에 대해 제시된 Olson의 해석법(smear zone 및 well resistance의 영향을 모두 무시한 경우)을 변형하였으며, 아울러 제시된 해석법을 토대로 설계에 관련된 여러가지 변수가 모래기end의 설치간격에 미치는 영향을 조건별로 분석하였다.

• Structural Engineering and Mechanics
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• 제74권4호
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• pp.471-479
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• 2020

This paper aims to study the effect of the elastic nonlocality on the transient waves in a two-dimensional thermoelastic medium influenced by thermal loading due to the laser pulse. The bounding plane surface is heated by a non-Gaussian laser beam. The problem is discussed under the Eringen's nonlocal elasticity model and the Green-Naghdi (G-N) theory with and without energy dissipation. The normal mode analysis method is used to get the exact expressions for the physical quantities which illustrated graphically by comparison and discussion. The effects of nonlocality and different values of time on the displacement, the stresses, and the temperature were made numerically. All the computed results obtained have been depicted graphically and explained.

• 한국운동역학회지
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• 제25권2호
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• pp.191-198
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• 2015

Objective : The purpose of this study was to conduct biomechanical analysis of varying backpack loads on the lower limb movements during downhill walking over $-20^{\circ}$ ramp. Method : Thirteen male university students (age: $23.5{\pm}2.1yrs$, height: $175.7{\pm}4.6cm$, weight: $651.9{\pm}55.5N$) who have no musculoskeletal disorder were recruited as the subjects. Each subject walked over $20^{\circ}$ ramp with four different backpack weights (0%, 10%, 20% and 30% of body weight) in random order at a speed of $1.0{\pm}0.1m/s$. Five digital camcorders and two force plates were used to obtain 3-d data and kinetics of the lower extremity. For each trial being analyzed, five critical instants were identified from the video recordings. Ground reaction force, loading rate, decay rate, and resultant joint moment of the ankle and the knee were determined by the inverse dynamics analysis. For each dependent variable, one-way ANOVA with repeated measures was used to determine whether there were significant differences among four different backpack weight conditions (p<.05). When a significant difference was found, post hoc analyses were performed using the contrast procedure. Results : The results of this study showed that the medio-lateral GRFs at RHC in 20% and 30% body weight were significantly greater than the corresponding value in 0% of body weight. A consistent increase in the vertical GRFs as backpack loads increased was observed. The valgus joint movement of the knee at RTO in 30% body weight was significantly greater than the corresponding values in 0% and 10% body weight. The increased valgus moment of 30% body weight observed in this phase was associated with decelerating and stabilizing effects on the knee joint. The results also showed that the extension and valgus joint moments of the knee were systematically affected by the backpack load during downhill walking. Conclusion : Since downhill walking while carrying heavy external loads in a backpack may lead to excessive knee joint moment, damage can occur to the joint structures such as joint capsule and ligaments. Therefore, excessive repetitions of downhill walking should be avoided if the lower extremity is subjected to abnormally high levels of load over an extended period of time.

• 대한토목학회논문집
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• 제37권1호
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• pp.125-132
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• 2017

부산항 신항은 항만의 대형화 및 하역장비의 현대화와 상해, 싱가포르 등 경쟁항만과의 중심항만 선점 필요성 등 세계해운항만 여건 변화에 대응하기 위해 물류중심항만(Hub Port)으로 건설을 목표로 추진되고 있다. 현재 북컨테이너 부두 및 남컨테이너 부두 등 23선석 운영 중에 있으며, 장래 서컨테이너 부두, 남컨테이너 부두 등에 2020년까지 45선석 규모로 확장될 계획이다. 또한 기 준공된 북컨 외에 웅동지구 1,2단계, 서컨 1,2단계, 남컨 항만배후부지 등 항만배후단지 개발이 동시에 추진되고 있다. 따라서 이러한 개발계획을 반영한 장래 교통수요를 예측하여 부산 신항의 교통체계의 문제점을 도출하였다. 부산항 신항의 교통체계 문제점은 부산항 신항 제2배후도로와 연계되는 남북축 도로의 주요교차로의 교통혼잡이 발생하고, 장래 증가될 교통량 대비 신항로(북컨 임항도로)의 용량이 부족할 것으로 예상되었다. 또한 부산항 신항 제1진입도로와 국도2호선이 직접 연결되지 않아 신항북로 등으로 우회교통량이 발생하는 문제점이 있는 것으로 파악되었다. 이에 본 연구에서는 부산항 신항의 원활한 교통처리를 위한 3가지 교통체계 개선방안을 제시하였다. 첫째, 첫째, 부산 신항 제2배후도로와 연계되는 서"컨"남북간 교통축에 대한 주요교차로 운영 및 부교차로의 우회전 진입,진출만 허용하는 방안, 둘째, 존 보도 및 중앙분리대 공간을 활용한 신항로(북"컨"임항도로) 차로 확장방안, 셋째, 부산항 신항 제1진입도로에서 지방도 1042호선 직결 진출입램프 설치하여 국도2호선 방면 연계방안이다. 이러한 개선방안의 효과를 측정하기 위해 Micro Simulation Package인 Vissim을 사용하여 분석하였다.