• Title/Summary/Keyword: S-N curve

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Basic Characteristics of Micro-Fatigue-Cracks on the Unnotched Smooth Specimens (平활材表面 의 微小피勞균열에 관한 基礎的 特性)

  • 서창민;북천영부;결성양치
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.7 no.1
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    • pp.28-35
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    • 1983
  • Quantitative analysis have been carried out on the micro-cracks on the surface and into the depth of unnotched smooth mild steel specimen under cyclic stains by rotating bending fatigue tests. Some of the results are; (1) Cracks initiate at the early stage of fatigue life N$_{I}$/ N$_{f}$=10 to 20%, and propagate during the rest of fatigue life. (2) Coalescence of highly crowded small fatigue cracks of random distribution seems to induce the final fracture at higher stress level. (3) The curves of crack initiation and the equal crack length on the graph of stress versus number of cycles are parallel to the S-N curve. (3) The curves of crack initiation and the equal crack length on the graph of stress versus number of cycles are parallel to the S-N curve. (4) The distributions of micro-surface crack length and depth show the composite Weibull distributions which are approximated to two straight lines separated by the value of transient region between stage I and stage II crack.k.k.

Flexural Fatigue Bechavior of Steel Fiber Reinforced Concrete Structures (강섬유보강 콘크리트의 휨 피로거동에 관한 연구)

  • 장동일;채원규;손영현
    • Magazine of the Korea Concrete Institute
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    • v.4 no.1
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    • pp.81-87
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    • 1992
  • In this thesis, the fatigue tests were performed on a series of SFRC(steel fiber reinforced concrete) to investigate the fatigue behavior of SFRC varying with the steel fiber contents and the steel fiber aspect ratios. The three point loading system is used in the fatigue tests. In tl1ese tests, relations between the repeated loading cycles and the mid-span deflections, number of repeated loadmg cycles when specimen was fractured were observed. On this basis, the mid-span deflections, the elastic strain energy and inelastic strain energy of SFRC were studied. A S - N curve \vas drawn to present the fatigue strength of SFRC beam. From che test results, by increasing the steel fiber content the energy lost on the permanent deformation decreases and the energy spent on crack growth increases. But in case of SFRC with the same steel fiber content the higher the steel fiber aspect ratio is, the less the elastic strain energy is. According to S - N curve drawn by the regression analysis on the fatugue test results, the fatigue strength with 2,000,000 repeated loading cycles in SFRC with the steel fiber content is 1.0% shows about 70% on the first crack static flexural strength.

Shear-fatigue behavior of high-strength reinforced concrete beams under repeated loading

  • Kwak, Kae-Hwan;Park, Jong-Gun
    • Structural Engineering and Mechanics
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    • v.11 no.3
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    • pp.301-314
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    • 2001
  • The purpose of this experimental study is to investigate the damage mechanism due to shear-fatigue behavior of high-strength reinforced concrete beams under repeated loading. The relationship between the number of cycles and the deflection or strain, the crack growths and modes of failure with the increase of number of cycles, fatigue strength, and S-N curve were observed through a fatigue test. Based on the fatigue test results, high-strength reinforced concrete beams failed at 57-66 percent of static ultimate strength for 2 million cycles. The fatigue strength at 2 million cycles from S-N curves was shown as about 60 percent of static ultimate strength. Compared to normal-strength reinforced concrete beams, fatigue capacity of high-strength reinforced concrete beams was similar to or lower than fatigue capacity of normal-strength reinforced concrete beams. Fatigue capacity of normal-strength reinforced concrete beams improved by over 60 percent.

Efficient Piecewise-Cubic Polynomial Curve Approximation Using Uniform Metric

  • Kim, Jae-Hoon
    • Journal of information and communication convergence engineering
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    • v.6 no.3
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    • pp.320-322
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    • 2008
  • We present efficient algorithms for solving the piecewise-cubic approximation problems in the plane. Given a set D of n points in the plane, we find a piecewise-cubic polynomial curve passing through only the points of a subset S of D and approximating the other points using the uniform metric. The goal is to minimize the size of S for a given error tolerance $\varepsilon$, called the min-# problem, or to minimize the error tolerance $\varepsilon$ for a given size of S, called the min-$\varepsilon$ problem. We give algorithms with running times O($n^2$ logn) and O($n^3$) for both problems, respectively.

Fracture Probability Properties of Torsion Fatigue of STS304 Steel (STS304강의 비틀림 피로파괴 확률특성)

  • Park, Dae-Hyun;Jeong, Soon-Ug
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.201-206
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    • 2003
  • This study is test for STS304 specimen using bending and torsion state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress, the fatigue life of the test specimen was higher at high speed than low speed If summarize STS304 torsion result of fatigue test, is as following. Fatigue life prediction was available by Weibull statistics distribution, and 50% breakdown probability correlation equation was appeared as following.

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Fracture Probability Properties of Pure and Cantilever Bending Fatigue of STS304 Steel (STS304강의 순수 및 외팔보형 굽힘 피로에 대한 파괴확률 특성)

  • Roh, Sung-Kuk;Park, Dae-Hyun;Jeong, Soon-Uk
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.199-204
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    • 2001
  • Big accidents of flyings, vessel, subways, gas equipments, buildings and bridge happens frenquently. Therefore many people are suffering harm of property. The destruction cause of macaine components is almost accused by fatigue. This study is test for STS304 specimen using pure and cantilever bending state. Rounded specimen and notched specimen including fracture surface investigation was comparatively experimented, fatigue life according to degree of surface finishing was examined. Fatigue fracture probability of notched canilever specimens were predicted by P-S-N curve, median rank and Weibull distribution. And at the relation with the rotational speed and stress, the fatigue life of the test specimen was higher at high speed than low speed.

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Fatigue Characteristic of HIPS(HR-1360) Materials (HIPS(HR-1360) 재료의 피로 특성 평가)

  • Park, Jae-Sil;Seok, Chang-Sung;Lee, Jong-Gyu;Lee, Jae-Hyuk
    • Proceedings of the KSME Conference
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    • 2000.11a
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    • pp.129-134
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    • 2000
  • Recently, HIPS(High Impact Polystyrene) materials are spot-lighted as office equipment, home electronics, electronics appliances housing, packing containers, etc. But its using are occur to problem caused by fatigue fracture. However, its strength is larged affected by environmental conditions. So, in this paper it tried to analyze the effect of temperature by tensile test and fatigue test. It was observed that yield strength and ultimate strength, fatigue life of same stress decreased relatively with increase temperature. Further, this paper predict S-N curve using the result of tensile test and micro vickers hardness test. For this purpose, the management in the engineering department is able to design the fatigue life of HIPS(HR-1360) materials.

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Improvement of Fatigue-Proof Characteristics of Link Members Under Impact Loadings by a Spring-Actuated Mechanism (스프링구동 메커니즘의 충격 하중을 받는 링크부재의 내피로 특성 향상)

  • 안길영;박상후;이부윤;김원진;오일성
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.4
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    • pp.158-164
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    • 2003
  • The air circuit breaker (ACB) with the spring-actuated mechanism was studied to improve the fatigue-proof characteristics of its link. The low-cycle fatigue fracture phenomenon occurred on the critical link, called h-link, of ACB from the repeated rapid closing and opening operations. To analyze the cause of failure, dynamic FE-analysis on the b-link part of ACB was performed considering tile velocity and acceleration of the links per time as boundary conditions, which were obtained by using ADAMS. Also, the S-N curve obtained by experiments was used to investigate requirement on the fatigue-proof characteristics. Then, to reduce the maximum tensile stress on the h-link, three types of h-link were examined and one of them was selected.

Fatigue Strength Assessment of the Cruciform Fillet Welded Joint Using Hot-spot Stress Approach (Hot-spot 응력을 이용한 십자형 필렛 용접재의 피로강도 평가)

  • Seok, Chang-Sung;Kim, Dae-Jin;Koo, Jae-Mean;Seo, Jung-Won;Goo, Byeong-Choon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.11 s.242
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    • pp.1488-1493
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    • 2005
  • In this study, fatigue tests to obtain S-N curves and FE analyses to obtain structural stress concentration factors were conducted for the two types of cruciform fillet welded joints, that is, load-carrying and non load-carrying types. Then we changed the obtained S-N curve of load carrying joint to that based on hot spot stress. As a result, the S-N curve of load carrying joint based on hot-spot stress was almost exactly coincided with that of non load-carrying joint based on nominal stress. So we have conducted that the fatigue strength of a welded joint with different geometry from the non stress distribution along the expected crack path.

Modified S-N Curve Method to Estimate Fatigue life of Welded Joints (수정 S-N곡선법을 이용한 용접연결부의 피로수명 추정)

  • Yang, Park-Dal-Chi;Kim, Mi-Kyeong
    • Journal of Ocean Engineering and Technology
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    • v.26 no.2
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    • pp.26-32
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    • 2012
  • In this paper, the effects of irregular bead shapes on fatigue life were investigated. A modified S-N curve method was used to estimate the fatigue life, which considered the inherent multiaxiality caused by the geometrical feature produced by the welding process. The point method of the critical distance method was used to determine the fatigue effective stress. Three types of fillet joint models were tested in the fatigue experiments. For each model, real bead shapes were collected using a 3D laser scanner, and finite element analyses were performed. The results of the analyses with actual bead shapes were compared with those using an idealized bead shape model. The results of the present analytical methods showed good agreement with the experimental results.