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랜덤하중하의 피로균열진전 데이터를 이용한 △Keff 평가법의 정량적 평가
구자석(Ja-Suk Koo),송지호(Ji-Ho Song),강재윤(Jae-Youn Kang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
Methods for estimation of the effective stress intensity factor range (△Keff) are evaluated for narrow and wide band random loading crack growth test data of 2024-T351 aluminum alloy. Three methods of determining Kop, visual measurement, ASTM offset compliance method, and the neural network method proposed by Kang and Song, and three methods of estimating △Keff, conventional, the 2/PI0 and 2/PI methods proposed by Donald and Paris, are compared in a quantitative manner by using the results of fatigue crack growth life prediction under random loading. For all Kop determination methods discussed, the 2/PI0 and 2/PI methods of estimating △Keff provide better results than conventional method for narrow and wide band random loading data.
자동차용 고장력강 DP590의 인장 및 저되풀이수 피로물성 평가
구자석(Ja-Suk Koo),최재석(Jae-Seock Choi),전태룡(Tae-Ryong Jeon),허용학(Yong-Hak Huh),이해무(Hae-Moo Lee) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_2
Tensile and low cycle fatigue properties of high strength steel DP590 used for automotive chassis parts are evaluated. Test specimens are made of DP590 plate after painting and baking process. Load cell calibration, extensometer calibration and specimen alignment are performed to enhance the accuracy and precision. In addition, the guiding apparatus is made in order to prevent buckling when compression loading is present. When DP590 replaces SAPH370, the fatigue life of the lower control arm increases by 2 or 3 times.
설계 인자 영향도 분석을 통한 자동차용 스틸 휠의 동적 선회 내구 성능 육성 연구
신헌(Hun Shin),구자석(Ja Suk Koo),진재걸(Jae Gul Jin),강창존(Chang Jon Kang) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
In automotive engineering, road wheels are critical components to support total vehicle weight. In order to prevent fatigue failure of the wheel working under severe cyclic loading, it is necessary to estimate the fatigue life and improve the fatigue strength. Conventional drop center wheels made of steel are widely used in the automotive industry by providing significant weight and cost savings. But it is difficult to achieve required fatigue strength for the wheel with restrictions on the weight which are becoming strong for the OEM’s. This paper describes the stress calculation in the disc hat by simulating the cornering fatigue test which is one of the traditional durability tests for the wheel prototype verification using finite-element analysis. To investigate the disc design aspects of the fatigue strength, the parametric study of the disc design parameters influencing on the cornering fatigue strength of the wheel was carried out by design of experiments. Based on the results, models for durability improvement and weight reduction were proposed.
이순욱(Soon-Wook Lee),구자석(Ja-Suk Koo),송민수(Min-Soo Song) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
Under driving condition, A vehicle experiences various kinds of loads, which brings on the buckling and fracture of suspension systems. Lower control arm (LCA), which consists of 2 bush joints and 1 ball joint connection, is the one of the most important parts in the suspension system. The bush joints absorb the impact load and reduce the vibration from the road. When analyzing the LCA behavior, it is important to understand the material properties and boundary conditions of bushing systems correctly, because of the nonlinearity characteristics of the rubber. In this paper, in order to predict the large scale deformation of the LCA more precisely, three factors are newly suggested, that is, coupling of bush stiffness between translation and rotation, bush extraction force and maximum rotation angle of ball joint. LCA stiffness is estimated by CAE and component test. Analysis and test results are almost same and the validity of considering three factors in LCA analysis is verified.
강재윤(Jae-Youn Kang),송지호(Ji-Ho Song),구자석(Ja-Suk Koo) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
For determination of crack opening load, a modified ASTM compliance offset method called the normalized ASTM offset method is proposed, which utilizes the relative compliance offset normalized by the maximum offset obtained by the ASTM offset method. The normalized ASTM offset method is evaluated in a quantitative manner for the conventional estimation and also for the 2/π(2/PI) estimation method proposed by Paris et al. The normalized ASTM offset method improves remarkably correlation of crack growth rate stress ratio effects, in comparison with the ASTM offset method. Quantitative evaluation results indicate that the normalized ASTM offset method is very promising as a precise, simple and practical K<SUB>op</SUB> determination method alternative to the ASTM method. method is recommended.