• 한국자동차공학회논문집
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• 제20권6호
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• pp.100-106
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• 2012

Recently, the demand to acquire and improve durability performance has steadily risen in rubber components design. In design process of a rubber component, an analytical prediction is the most effective way to improve fatigue life. Existing methods of analytical estimation have mainly used an equation for fatigue life obtained from fatigue test data. However, such formula is rarely used due to costs and time required for fatigue testing, as well as randomness of rubber materials. In this paper, we describe fatigue life estimation of rubber component using only the results from a relatively simple tearing test. We estimated fatigue life of the Janggu type fatigue specimen and the automotive motor mount, and evaluated reliability of the proposed method by comparing the estimated values with actual test results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1708-1711
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• 2007

This paper presents high cycle fatigue properties of an Al-3%Ti thin film, used in a RF (radio-frequency) MEMS switch for a mobile phone and also describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film developed by authors. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile and fatigue tests were performed to obtain mechanical and fatigue properties. The specimen was made with dimensions of $1000{\mu}m$ long, $1.0{\mu}m$ thickness, and 3 kinds of width, 50, 100 and $150{\mu}m$. High cycle fatigue tests for each width were also performed, from which the fatigue strength coefficient and the fatigue strength exponent were found to be 193MPa and .0.02319 for $50{\mu}m$, 181MPa and -0.02001 for $100{\mu}m$, and 164MPa and -0.01322 for $150{\mu}m$, respectively. We found that the narrower specimen is, the longer fatigue life of Al-3%Ti is and the wider specimen is, the more susceptible to stress level fatigue life of Al-3%Ti was.

• Journal of Welding and Joining
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• 제21권3호
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• pp.92-98
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• 2003

This paper describes the numerical prediction of the thermal fatigue life of a $\mu$BGA(Micro Ball Grid Array) solder joint. Finite element analysis(FEA) was employed to simulate thermal cycling loading for solder joint reliability. Strain values, along with the result of mechanical fatigue tests for solder alloys were then used to predict the solder joint fatigue life using the Coffin-Manson equation. The results show that Sn-3.5mass%Ag solder had the longest thermal fatigue life in low cycle fatigue. Also a practical correlation for the prediction of the thermal fatigue life was suggested by using the dimensionless variable ${\gamma}$, which was possible to use several lead free solder alloys for prediction of thermal fatigue life. Furthermore, when the contact angle of the ball and chip has 50 degrees, solder joint has longest fatigue life.

• 한국생산제조학회지
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• 제19권3호
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• pp.359-364
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• 2010

The objective of this study is to propose an effective method for measurement and analysis of fatigue crack. A technique that can measure the statue of fatigue crack propagation fast and correctly for enhancing safety of constructions and securing reliability is necessary. Moreover, the crack propagation behavior characteristics evaluation technique has to be developed using this technique. In this paper, fatigue crack was caused via the fatigue experiment with repeated load on the CT specimen that is made up of STS304. Fatigue crack propagation was measured by tracing the position of the maximum temperature according to the cycles using infrared thermography. The crack growth characteristics was evaluated by applying the moment values on the measuring area to the measured value. As a result of this study, the possibility that the infrared thermography could be applied to measure the fatigue crack was identified. Moreover, it was identified that fatigue crack propagation have a relationship with the moment value of construction.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2004년도 ISMP Pb-free solders and the PCB technologies related to Pb-free solders
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• pp.1-26
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• 2004

The implementation of Pb-free solder technology is making good progress in electronic industry. Further understanding on fundamental issues on Pb-free solders/processes is required to reduce reliability risk factors of Pb-free solder joints. Several reliability issues including thermal fatigue, impact reliability, IMC growth, spalling, void formation are reviewed for Pb-free solder joints. Several applications of Pb-free technology are discussed, such as Pb-free, CBGA, CuCGA, flip chips, and wafer bumping by IMS.

• 한국생산제조학회지
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• 제7권5호
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• pp.66-71
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• 1998

It is required the superior materials for the parts of machines or structures, which could be endurable in severe load and environment. According to advancement of casting technology, nodular graphite cast iron is used as suitable for such condition. But nodular graphite cast iron is scattering of fatigue strength and low reliability. Therefore in this study, the effect of matrix structure and number of nodular graphite on the initiation of fatigue crack and fatigue strength. It was found that the material which has relatively high ferrite volume fraction was more easily cracked than other materials and fatigue limit was low. The material which has not found pinhole on the surface, the crack was initiated in graphite went through ferrite and propagated into through graphite, but separated graphite and ferrite grain boundary and combined with other cracks to fro large one.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권4호
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• pp.241-247
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• 2015

Purpose : The demand for higher fuel economy vehicles has helped develop fuel-efficient vehicles such as a CVVL called continuous variable valve lift. Existing CVVL has been applying DC type motor to control intake valve, but recently some car parts manufacturers have been developing a BLDC type CVVL motor for improvements of endurance performance. The purpose of this study is to find the potential failure mechanism of the CVVL BLDC moto in early stage of development based on the design properties and design the accelerated life test model. Methods : CVVL BLDC is consist of brushs, coil, magnetic, PCB, bearing and so on. Each component has a latent failure mechanism caused by temperature, humidity, vibration. By analysis result of the failure mechanism, thermal fatigue is the most important factor of a durability of CVVL BLDC motor. So, we designed a new accelerated life test model for guarantee of the CVVL BLDC motor. Results : A crack occurred on via hole in test using the conditions we designed, so we did change the design to avoid this failure. The via hole dimension is changed a little larger, as a result we achieve improvements in reliability of the CVVL BLDC motor. By applying various kinds and extreme level of stresses, we can find the operating limits of products. Conclusion : In thesis, We analyzed the failure mechanism of CVVL BLDC and designed an accelerated life test method to give a guarantee for reliability. Based on the test results, we could improve the reliability of developments by change of design.

• 한국도로학회논문집
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• 제5권1호
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• pp.1-10
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• 2003

도로포장 설계의 목적은 다른 토목구조물의 설계와 마찬가지로 정해진 신뢰성 수준에서 가장 경제적인 설계를 얻는데 있다 할 것이다. 미국과 유럽의 선진국가들의 설계법들은 전혀 상이한 신뢰성 수준을 갖는 설계결과들을 생산하는 설계법을 지양해가면서 세월을 두고 변천하여 균등한 신뢰성 수준을 보장할 수 있는 LRFD양식을 채용하는 방향으로 발전되었다. 현재, LRFD 양식은 콘크리트 구조, 목구조, 강구조 및 교량설계기준에 적용되어 있다 본 논문에서 저자는 역학-경험적 포장설계법에 적용될 신뢰성 모듈의 한 대안으로 신뢰성이론을 사용하여 LRFD 양식을 개발하고자 하는 과정을 예시하였다. AASHTO 86설계법에 따라 동일한 신뢰성 수준을 갖도록 설계된 10개의 포장단면이 피로균열과 같은 역학적 포장손상 측면에서 볼 때 균등한 구조적 신뢰성을 보여주지 못하며 LRFD 양식을 사용함으로서 그러한 균등한 신뢰성을 확보할 수 있다는 사실이 본 논문을 통해 예시되고 있다.

• 대한기계학회논문집A
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• 제34권8호
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• pp.1045-1050
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• 2010

고무부품의 신뢰성을 확보하기 위해서는 피로수명예측 및 평가기술 개발이 중요하다 하겠다. 최근에 고무부품에 대한 고성능, 고신뢰성을 위해 설계, 해석 및 평가기술이 요구되고 있으나, 지금까지는 경험과 시행착오적인 방법으로 개발되고 있는 실정이다. 따라서, 본 연구에서는 고무소재에 대해 배합조건, 기계적 특성, 열화 및 피로수명 등을 포함하는 고무소재 물성 데이터베이스를 구축하고, 고무부품의 특성해석 결과를 데이터베이스와 연계하여 고무부품의 피로해석 모델을 개발하였으며, 실제 피로시험 결과를 통하여 개발된 모델의 타당성을 검증하였다.

• Elastomers and Composites
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• 제47권3호
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• pp.188-193
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• 2012

고무부품의 신뢰성을 확보하기 위해서는 피로수명예측 및 평가기술 개발이 중요하다 하겠다. 최근에 고무부품에 대한 고 성능, 고 신뢰성을 위해 설계, 해석 및 평가기술이 요구되고 있으나, 지금까지는 경험과 시행착오적인 방법으로 개발되고 있는 실정이다. 따라서, 본 연구에서는 고무소재에 대해 배합조건, 기계적 특성, 열화 및 피로수명 등을 포함하는 고무소재 물성 데이터베이스를 구축하고, 고무부품의 특성해석 결과를 데이터베이스와 연계하여 고무부품의 피로해석 모델을 개발하였으며, 실제 피로시험 결과를 통하여 개발된 모델의 타당성을 검증하였다.