• Title/Summary/Keyword: Fatigue Curve

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Crack growth behavior of fatigue surface crack initiated from a small surface defect (작은 表面缺陷에서 發생.成長하는 表面疲勞균열의 成長特性에 관한 硏究)

  • 서창민;권오헌;이정주
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.191-197
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    • 1987
  • It has been well known that the fracture mechanics can be applied to large through crack growth. But the growth rate of small surface cracks initiated from a small defect under rotary bending fatigue tests can not be treated as a function of stress intensity factor range. In this paper, to investigate the growth behavior of surface small fatigue cracks in the view-point of both fracture mechanics and strength of materials, the fatigue test has been carried out on two kinds of plain carbon steels with a small surface defect. Applying the concept of the cyclic strain intensity factor range .DELTA. $K_{\epsilon}$/$_{t}$ to the analysis of small surface fatigue crack growth, it is found that the relationship between cyclic strain intensity factor range and crack growth rate shows linear relation on logarithmic coordinates regardless of defect sizes and two kinds of carbon steels.s.s.

Detection of Fatigue Damage in Aluminum Thin Plates with Rivet Holes by Acoustic Emission (리벳 구멍을 가진 알루미늄 박판구조의 피로손상 탐지를 위한 음향방출의 활용)

  • Kim, Jung-Chan;Kim, Sung-Jin;Kwon, Oh-Yang
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.3
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    • pp.246-253
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    • 2003
  • The initiation and growth of short fatigue cracks in the simulated aircraft structure with a series of rivet holes was detected by acoustic emission (AE). The location and the size of short tracks were determined by AE source location techniques and the measurement with traveling microscope. AE events increased intermittently with the initiation and growth of short cracks to form a stepwise increment curve of cumulative AE events. For the precise determination of AE source locations, a region-of-interest (ROI) was set around the rivet holes based on the plastic zone size in fracture mechanics. Since the signal-to-noise ratio (SNR) was very low at this early stage of fatigue cracks, the accuracy of source location was also enhanced by the wavelet transform do-noising. In practice, the majority of AE signals detected within the ROI appeared to be noise from various origins. The results showed that the effort of structural geometry and SNR should be closely taken into consideration for the accurate evaluation of fatigue damage in the structure.

Electrical properties of $Pb(Zr_xTi_{1-x})O_3$ferroelectric thin films prepared by sol-gel processing (Sol-gel법에 의한 $Pb(Zr_xTi_{1-x})O_3$ 강유전 박막의 전기특성)

  • 백동수;박창엽
    • Electrical & Electronic Materials
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    • v.9 no.2
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    • pp.132-137
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    • 1996
  • Pb(Zr$_{x}$Ti$_{1-x}$ )O$_{3}$ solutions prepared by sol-gel processing with different Zr/Ti ratio were coated on Pt/SiO$_{2}$/Si substrates using spin coating method. Coated films were annealed by rapid thermal annealing at 650.deg. C for 20sec to fabricate Pb(Zr, Ti)O$_{3}$ ferroelectric thin films. Electrical properties of the films such as dielectric constant and loss, ferroelectric hysteresis, fatigue, switching time, and leakage current were measured. Hysteresis of the films with different Zr/Ti ratio yield Pr ranging 10-21.mu.C/cm$^{2}$, E$_{c}$ ranging 37.5-137.5kV/cm. Hysteresis curve was changed from square-type to slim type according to increasing Zr contents. Switching time was faster than 180ns, and leakage current was about 20.mu.A/cm$^{2}$. The film underwent above 10$^{8}$ cycles of reversed polarization showed fatigue with increased coercive field and decreased remnant polarization.tion.

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Fatigue Life Estimation Using the Multi-Axial Multi-Point Load Counting Method under Variable Amplitude Loading (가변진폭하중하에서 다축-다점 하중 Counting method를 이용한 피로수명평가)

  • Lee, W.S.;Lee, H.W.
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.6
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    • pp.22-27
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    • 1997
  • In general, the load which acts on the structure is almost independent of time in many locations. In this case. It is difficult to estimate the life with the service load history, because the structure is on the multi- axial and multi-point loading states. In this study, the service load of the excavator which is widely used in industry field was calculated using measured cylinder pressures and displacements. The fatigue life was estimated using the multi-axial and multi-point load counting method. Service load history of 4 pin joint which act independently each other is yielded by mult-axial and multi-point load counting method. The stress spectrum is yielded by superposition of the results of FEM stress analysis applied unit load. Palm- gren-Miner's cumulative Damage is 0.000804 for Von Mises equivalent stress sequence by one side fillet weld S-N curve. This result agress with Bench test results. As a result of this study, the fatigue life esti- mation using the multi-axial and multi-axial and multi-point load counting method is useful.

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A study on the fatigue and fracture characteristics of localized nuclear reactor vessel material (국산 원자로용기 재료의 피로 및 파괴특성 연구)

  • Jeong, Sun-Eok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.10
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    • pp.1626-1635
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    • 1997
  • It is important to ensure the reliability of the first localized reactor vessel steel. To satisfy with this purpose, a study on the impact/hardness, low cycle fatigue(LCF), crack growth rate(da/dN) and fracture toughness( ) of base material(BM) and weld metal(WM) were performed under room temperature air and corrosion conditions. A summary of the results is as folows : (1) Charpy impact absorbed energy of BM was the highest value, heat affected zoon(HAZ) and the lowest, WM. The hardness of BM was similar to HAZ. (2) Coefficients of Manson equation using the monotonic tensile test data were obtained for the present material. (3) The effects of stress ratio and ambient (120.deg. C and NaCl) condition on da/dN were investigated, da/dN with NaCl condition expressed the highest value. (4) The results of Charpy V-notch impact test had good correlation with $K_{IC}$ characteristics and the lowest curve of $K_{IC}$ for BM was derived, more researches about WM and HAZ are required hereafter.

A Study on Estimation of Fatigue Life of Aged Continuous Welded Rail using the Field Test (현장측정을 통한 노후 레일의 피로수명 평가에 관한 연구)

  • Kong, Sun-Yong;Sung, Deok-Yong;Kim, Jun-Hyung;Park, Yong-Gul
    • Proceedings of the KSR Conference
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    • 2007.11a
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    • pp.352-364
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    • 2007
  • It is essential to reduce track maintenance costs and to extend the periodic replacements of continuous welded rails based on accumulated passing tonnage. As recently train load decrease and rail joints wear down less, the periodic replacements of continuous welded rails can be extended. There are many kinds of rail damage like squat, head-check and corrugation. These can be taken nondestructive or naked eye test. So the periodic replacements of continuous welded rails based on accumulated passing tonnage were examine with focusing on a crack of rail bottom of continuous welded rail. Therefore, this study measure dynamic response of track by metro train load, it compute impact coefficient and track spring coefficient for estimating a condition of actual track system. Also, it is converted the measured stress waveform into stress frequency histogram by the rain-flow counting methods, and then the equivalence of stress is calculated. As apply s-n curve of a new welded rail, accumulated fatigue damage ratio of laid rail and remaining service lives is estimated. This study suggest a plan of the periodic replacements of continuous welded rails based on accumulated passing tonnage classified by the types of track system.

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FATIGUE SIMULATION OF POWER TRAIN COMPONENTS DURING THE DESIGN PROCESS

  • Steiner, W.;Steinwender, G.;Unger, B.
    • International Journal of Automotive Technology
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    • v.2 no.1
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    • pp.9-16
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    • 2001
  • The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

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The Influence of Temperature on Low Cycle Fatigue Behavior of Prior Cold Worked 316L Stainless Steel (I) - Monotonic and Cyclic Behavior - (냉간 가공된 316L 스테인리스강의 저주기 피로 거동에 미치는 온도의 영향 (I) - 인장 및 반복 거동 -)

  • Hong, Seong-Gu;Yoon, Sam-Son;Lee, Soon-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.4
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    • pp.333-342
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    • 2004
  • Tensile and low cycle fatigue (LCF) tests on prior cold worked 316L stainless steel were carried out at various temperatures from room temperature to 650$^{\circ}C$. At all test temperatures, cold worked material showed the tendency of higher strength and lower ductility compared with those of solution treated material. The embrittlement of material occurred in the temperature region from 300$^{\circ}C$ to 600$^{\circ}C$ due to dynamic strain aging. Following initial cyclic hardening for a few cycles, cycling softening was observed to dominate until failure occurred during LCF deformation, and the cyclic softening behavior strongly depended on temperature and strain amplitude. Non-Masing behavior was observed at all test temperatures and hysteresis energy curve method was employed to describe the stress-strain hysteresis loops at half$.$life. The prediction shows a good agreement with the experimental results.

A Study on the Elastic Plastic Fracture Analysis for Carbon Steel with a Fatigue Crack (탄소강의 피로균열에 대한 탄소성파괴 해석에 관한 연구)

  • Lee, Jong-Hyung;Jeong, Hyung-Sik;Yoo, Duck-Sang;Kim, Young-Moon
    • Journal of the Korean Society of Industry Convergence
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    • v.9 no.2
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    • pp.117-122
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    • 2006
  • This paper is to provide some of the analysis procedures of the FAD(Failure Assessment Diagram), which is applied th the safety test of the atomic pressure vessels and other structures. Harrison proposed R-6 Diagram, and Bloom developed the method of DPFAD(Deformation Plasticty Failure Assessment Diagram). Analysis of J-integration of the plastic materials give the failure test curve for the materials with serious work hardening effect. J value was obtained form both FEM(Finite Element Mothod) and the experiment using compact type specimen for J=JIC, and the results were compared. In this study, the results of analysis using DPFAD and the factors affecting DPFAD in Static fatigue and fracture were reviewed. It was shown that the concept of DPFAD can be applied to test the safety of the structures.

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EFFECT OF COMPRESSIVE RESIDUAL STRESS FOR CORROSION PROPERTY OF SUP-9 STEEL USING AS SUSPENSION MATERIAL

  • Park, K.D.;Ki, W.T.;Shin, Y.J.;Ryu, H.J.
    • International Journal of Automotive Technology
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    • v.8 no.3
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    • pp.343-349
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    • 2007
  • One of the useful technologies for light-weightening of components required in the automobile and machine industry is to use high strength materials. To improve material properties, the carbonizing treatment, nitrifying treatment, and shot-peening method are representatively applied. However, the shot-peening method is generally used to remove surface defect on steel and to improve the fatigue strength of the surface. Benefits of shot-peening are increasing resistance against fatigue, stress corrosion cracking, fretting, galling, erosion and closing of pores. In this paper, the effect of shot-peening on the corrosion of SUP-9 steel immersed in a 3.5% NaCl solution and corrosion characteristics from heat treatment during the shot peening process has been investigated. The immersion test was performed on four kinds of specimens. Corrosion potential, the polarization curve, residual stress etc. Were analyzed from the experimental results.