• Title/Summary/Keyword: 응력 확대계수 범위

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Fracture Mechanics Applied to Fatigue Crack Growth Behavior at Elevated Temperatures (고온 피로균열 성장거동에 관한 파괴역학의 응용에 관한 연구)

  • 서창민;김영호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1552-1560
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    • 1990
  • A general form of the mathematical function in the fatigue crack growth rate law for CT specimens was determined by means of the dimensional analysis at elevated temperatures. The experimental results can be rigorously described by the combination of rate theory and fracture mechanics. The rate theory approach extends the scope of fracture mechanics through the consideration of the temperature. The fatigue crack growth rates are represented by the Arrhenius type equation. This equation explains fairly well the experimental data for Cr-Mo-V rotor steel and A517-F steel in the comparatively wide temperature regions as affected with the temperature and the stress intensity factor range interaction.

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.

An Effect of TIG Dressing on Fatigue Characteristics of Non Load-Carrying Fillet Welded Joints (TIG처리에 따른 하중비전달형 필렛용접부의 피로특성)

  • Jung, Young Hwa;Kyung, Kab Soo;Hong, Sung Wook;Kim, Ik Gyeom;Nam, Wang Hyone
    • Journal of Korean Society of Steel Construction
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    • v.12 no.5 s.48
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    • pp.617-628
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    • 2000
  • In this study, the 4-point bending test has been performed in order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strength of as-welded specimens has been satisfied the grade of fatigue strength prescribed in specifications of domestics and AASHTO & JSSC, and fatigue strength at $2{\times}106cycles$ of TIG-dressing specimens has been increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks have been occurred at several points, where the radius of curvature and flank angle in the weld bead toes are low, and grown as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has been closely related to the flank angel and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has been largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

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Short Crack Analysis by Fatigue Crack Opening Behavior (피로균열개구거동을 이용한 짧은균열의 거동 분석)

  • Song, Sam-Hong;Lee, Kyeong-Ro
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.4
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    • pp.136-144
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    • 1997
  • The characteristics of fatigue crack growth subject to out-of-plane bending fatigue are studied in terms of crack opening behavior by using pre-cracked smooth specimens. Crack opening stress is measured by an elastic compliance method which may precisely and continuously provide many date using strain gages during experiment. The results of the short crack and the long crack arranged by crack closure concept show that the effective stress gange ratio of short crack is grester than that of long crack, and ano- malous growth behavior of short crack may be elucidated by the variation of crack opening stress. When the variation of fatigue crack growth rate is arranged versus effective stress intensity factor range. Iinear relation is held also for the short crack. It shows that growth behavior of short crack can be quantitatively represent- ed by the fracture mechanics parameter using effective stress intensity factor range.

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Finite Element Analysis of Stage II Crack Growth and Branching in Fretting Fatigue (프레팅 피로에서 2단계 균열성장과 분지 유한요소해석)

  • Jung, Hyun Su;Cho, Sung-San
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.39 no.11
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    • pp.1137-1143
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    • 2015
  • The stage II fretting fatigue crack growth and branching, i.e., the process of fretting fatigue crack growth starting in an inclined direction and then changing to the normal direction, is analyzed using the finite element method. The fretting fatigue experiment data of A7075-T6 are used in the analysis. The applicability of maximum tangential stress intensity factor, maximum tangential stress intensity factor range, and maximum crack growth rate as the crack growth direction criteria is examined. It is revealed that the stage II crack growth before and after the branching cannot be simulated with a single criterion, but can be done when different criteria are applied to the two stages of crack growth. Moreover, a method to determine the crack length at which the branching occurs is proposed.

Fatigue Crack Growth Equation considered the Effect of Stress Ratio (응력비의 영향을 고려한 표면피로균열의 균열성장식)

  • 강용구;김대석
    • Journal of Ocean Engineering and Technology
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    • v.12 no.1
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    • pp.39-49
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    • 1998
  • In this work, fatigue tests by axial loading were carried out to investigate the effect of stress ratio on the growth behaviors of surface fatigue crack for SM45C steel and Al 2024-T4 alloy. The growth behaviors of surface crack have been monitored during fatigue process by measuring system attached CCTV and monitor. When the growth rates of surface crack were investigate by the concept of LEFM based on Newman-Raju's .DELTA.K, the dependence of stress ratio appears both SM45C steel and Al 2024-T4 alloy. Therefore, modified stress intensity factor range, .DELTA.K' [=(1+R)/sup n/.DELTA.K] are intorduced to eliminate the dependence of stress ratio. Using .DELTA.K', it is found that the dependence of stress ratio disappears both SM45C steel and Al 2024-T4 alloy.

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Fatigue Crack Propagation Analysis by P-Version of Finite Element Method (P-version 유한요소법에 의한 피로균열해석)

  • 우광성;이채규
    • Computational Structural Engineering
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    • v.5 no.3
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    • pp.97-103
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    • 1992
  • Since many design problems in the railroad, aerospace and machine structures involve considerations of the effect of cyclic loading, manufacturing and quality control processes much fully account for fatigue of critical components. Due to the sensitivity of the Paris law, it is very important to calculate .DELTA.K numerically to minimize the error of predicted fatigue life in cycles. However, it is shown that the p-version of FEM based on LEFM analysis is far better suited for computing the stress intensity factors than the conventional h-version. To demonstrate the proficiency of the proposed scheme, the welded T-joint with crack problems of box car body bolster assembly and a crack problem emanating from a circular hole in finite strip have been solved.

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A Model Estimating the Ratigue Crack Growth in Aluminum Alloy A5083-O Considering the Effect of Stress ratio (응력비의 영향을 고려한 알루미늄합금 A5083-O의 피로균열전파 특성 예측모델)

  • 조상명;김종호;김영식
    • Journal of Welding and Joining
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    • v.12 no.3
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    • pp.82-89
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    • 1994
  • In this paper the effect of stress ratio on the fatigue crack growth rate of aluminum alloy A5083-O was examined. The fatigue tests were carried out using CCT (center cracked tension) specimens and CT(compact tension) specimens which were subjected to 0.5 and -1.0 stress ratio respectively. The obtained results are as follows; 1) The $\DeltaK_{th}$ as the function of stress ratio R was introduced in evaluating the fatigue crack growth rate of A5083-O. 2) A new model evaluating the effect of stress ratio on the fatigue crack growth rate was developed over the region of low and high propagation rate.

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A Study on the Fatigue Characteristics of Transverse Butt-Welded Joints containing Blowholes (블로우홀을 가진 횡방향 맞대기 용접부의 피로특성에 관한 연구)

  • Chang, Dong Il;Kyung, Kab Soo;Cho, Kwang Hyun;Hong, Sung Wook
    • Journal of Korean Society of Steel Construction
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    • v.11 no.4 s.41
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    • pp.339-350
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    • 1999
  • In this study, blowholes, a kind of solid defects, were intentionally introduced in transverse butt-welded joints which are widely used for the connection of main members in steel structures to evaluate the fatigue characteristics of these joints with blowholes according to the difference of the size and shape of blowholes, and a series of tests were performed. Static test results proved that the static strength of these joints with blowholes was not affected by their size and shape. From the fatigue test results on these joints with blowholes, the size and shape of blowholes inside the weld metals were strongly affected in fatigue strength, and we suggested the relationship between fatigue strength and their size and shape quantitatively. Also, Using the relationship of fatigue crack growth rate and stress intensity factor range, the fatigue life of transverse butt-welded joints with blowholes can be estimated properly.

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The Effect of Defect Location Near a Circular Hole Notch on the Relationship Between Crack Growth Rate (da/dN) and Stress Intensity Factor Range (δK) - Comparative Studies of Fatigue Behavior in the Case of Monolithic Al Alloy vs. Al/GFRP Laminate - (원공노치 인근에 발생한 결함의 위치변화가 균열성장률(da/dN) 및 응력확대계수범위(δK)의 관계에 미치는 영향 - 단일재 알루미늄과 Al/GFRP 적층재의 피로거동 비교 -)

  • Kim, Cheol-Woong;Ko, Young-Ho;Lee, Gun-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.3 s.258
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    • pp.344-354
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    • 2007
  • The objective of this study is to investigate the effect of arbitrarily located defect around the circular hole in the aircraft structural material such as Al/GFRP laminates and monolithic Al alloy sheet under cyclic bending moment. The fatigue behavior of these materials may be different due to the defect location. Material flaws in the from of pre-existing defects can severely affect the fatigue crack initiation and propagation behavior. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic Al alloy and Al/GFRP laminates under cyclic bending moment. The fatigue behavior i.e., the stress concentration factor($K_t$), the crack initiation life($N_i$), the relationship between crack length(a) and cycles(N), the relationship between crack growth rate(da/dN) and stress intensity factor range(${\Dalta}K$) near a circular hole are considered. Especially, the defects location at ${\theta}_1=0^{\circ}\;and\;{\theta}_2=30^{\circ}$ was strongly effective in stress concentration factor($K_t$) and crack initiation life($N_i$). The test results indicated the features of different fatigue crack propagation behavior and the different growing delamination shape according to each location of defect around the circular hole in Al/GFRP laminates.