• Title/Summary/Keyword: Crack-Tip

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A Study on Crack Retardation Behavior by Single Overload (단일 과대하중에 의한 균열지연거동에 관한 연구)

  • 송삼홍;권윤기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.2
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    • pp.451-462
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    • 1995
  • Single overload tests performed to examine the crack retardation behavior for the specimen thickness and overload ratios. Delayed crack length was tend to increase in small thickness and big overload ratio but was difference between delayed crack length and plastic zone size that expected in specimen thickness. So retardation behavior that estimated in plastic zone size, was not sufficient. Crack tip branching and striation distribution, secondary mechanisms that effected in retardation behavior, was examined by experiment and finite element analysis. Crack tip branching was affected by micro structure, and appeared the more complicatedly according to increasing damage by overload and decreasing crack driving force in base line stress level. And crack tip branching the branching angle decreased crack driving force in the crack tip. And a characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force.

The Behavior of Fatigue Crack Propagation by Position of Indentations (압흔가공위치에 따른 피로균열 전파거동)

  • 송삼홍;최진호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.04b
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    • pp.28-32
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    • 1995
  • This effective way for repairing a fatigue crack is making indetations around fatigue crack tip. In this paper, we performed fatigue test to investigate the optimal position of the indentations, and observed crack opening behavior at the same time. The indentation positions of specimens were on the crack tip, front and back of the crack tip. The results of the experiment showed taht it was veryeffective way to increase fatigue life that making indentations on the crack tip, and it was the optimal position that making indentations on the crack tip.

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Evaluationof Growing Crack-Tip Singularity in A533B Steel by Image Processing Technique (화상처리법을 이용한 A533B강의 진전균열특이장 평가)

  • Pyo, Chang-Ryul;Kim, Yeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.124-132
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    • 1997
  • This paper describes an experimental and numerical study on growing ductile crack-tip behaviors. The hybrid experimental and numerical method by means of a computer image processign technique, was applied to the analysis of both base metal and weld metal CT specimens. In the weld metal specimen, the initial crack-tip was placed in front of fusion line, and the crack orientation was perpendicular to it. Finite element analysis of crack growth behaviors in both base and weld matal specimens made of A533B Class 1 steel were also performed to examine the effects of weldment on near crack-tip fields. a series of experimental studies on crack-tip behaviors have clearly shown the qualitative effects of material properties, especially a hardening exponent. The experimental and numerical results have also shown that weldment does not affect displacement and strain fields near a crack-tip while a stress field is influenced by the difference between yield stresses of both base and weld metals.

A Study on Parameters Affected the Fatigue Crack Growth in Steel Structure Members( II ) -The Effect of Surface Residual Stress for Crack Closure- (강구조 부재의 피로균열성장에 미치는 제인자에 관한 연구( II ) -표면잔류응력이 균열닫힘에 미치는 영향-)

  • Choi, Young Jae;Kyung, Kab Soo
    • Journal of Korean Society of Steel Construction
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    • v.8 no.3 s.28
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    • pp.3-11
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    • 1996
  • To investigate the effect of fatigue crack growth due to the surface residual stress, it is measured the residual stress distribution by x-ray diffraction at the crack tip each constant crack growth in the notch specimens, and quantitively assessed the effect of crack closure caused to the distribution of compressive stress at the crack tip from evaluating crack openning stress using the finite element analysis. It is concluded that the degree of the residual stress distribution at the crack tip is decreased with increasing the crack length. From the fact that it is similar to the crack openning stress ratio, it is found that the compressive residual stress distribution and size is related to the crack closure effect and surface residual stress field with propagating crack in the notch specimens depends on the stress intensity factor range at the crack tip.

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Experimental Behaviors of the Constraint Effects A2 Depending on Displacement at Various Measuring Positions near Crack Front for STS 316L CT Specimen (균열선단 변위측정위치에 따른 STS 316L의 구속효과 A2 거동)

  • Han, Min-Su;Jang, Seok-Ki
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.4
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    • pp.533-538
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    • 2009
  • The magnitude of constraint effect $A_2$ values on the non-linear elastic plastic fracture toughness was experimentally estimated by using displacement at various measuring positions near crack tip. Constraint effect $A_2$ value was dependent on specimen configuration and on the measured displacement near crack front. The crack tip opening displacement in the vicinity of the crack tip front should be estimated within plastic region when appropriately constraint effect was calculated. It was found that the magnitude of constrain effect |$A_2$| is below 8.0 at the crack tip. But an appropriate location to measure the effective constraint effects $A_2$ at the critical value of J that crack initiation is characterizable by is r = 2mm and ${\theta}=90^{\circ}$ away from original crack tip, and the constraint effect |$A_2$| estimated is 5.3.

A Modified Two-Parameter Solution for Crack-Tip Field in Bending Dominated Specimens

  • Jang Seok-Ki;Zhu Xian Kui
    • Journal of Advanced Marine Engineering and Technology
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    • v.30 no.4
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    • pp.494-504
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    • 2006
  • It is well known that the two-parameter $J-A_2$ solution can well characterize the crack-tip fields and quantify the crack-tip constraint for different flawed geometries in variety of loading conditions. However, this solution fails to do so for bending dominated specimens or geometries at large deformation because of the influence of significant global bending stress on the crack-tip field. To solve this issue, a modified $J-A_2$ solution is developed in this paper by introducing an additional term to address the global bending influence. Using the $J_2$ flow theory of plasticity and within the small-strain framework detailed finite element analyses are carried out for the single edge notched bend (SENB) specimen with a deep crack in A533B steel at different deformation levels ranging from small-scale Yielding to large-scale Yielding conditions. The numerical results of the crack-tip stress field are then compared with those determined from the $J-A_2$ solution and from the modified $J-A_2$ solution at the same level of applied loading Results indicate that the modified $J-A_2$ solution largely improves the $J-A_2$ solution, and match very well with the numerical results in the region of interest at all deformation levels. Therefore, the proposed solution can effectively describe the crack-tip field and the constraint for bending dominated specimens or geometries.

Evaluation of the Plastic Region Using Recrystallization Heat Treatment for Constraint Effect with STS 316L (STS 316L의 재결정 열처리법을 이용한 구속효과 평가)

  • Han, Min-Su;Jang, Seok-Ki
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.4
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    • pp.539-544
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    • 2009
  • The constraint effect $A_2$ has to be evaluated within plastic region near crack tip front using opening displacement. Plastic boundary and stress or strain conditions in the vicinity of the crack tip using recrystallization heat treatment was represented. It was found that the plastic deformation boundary by recrystallization heat treatment method was the true strain of ${\epsilon}t$ = 0.05mm/mm. With the estimation of constraint effects $A_2$, the region of proper displacement measurement point near crack tip was between 0mm and 1mm distance toward direction of crack propagation, and was between 1mm to 3mm distance toward direction of load line.

Numerical Analysis of Stress Field around Crack Tip under Impact Load (충격하중에 의해 크랙 주위에 형성되는 응력장에 관한 수치해석적 연구)

  • Hwang, Gap-Woon;Cho, Kyu-Zong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.2
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    • pp.450-460
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    • 1996
  • To investigate the effect of stress wave propagation for crack tip, impact responses of two-dimensional plates with oblique cracks are investigated by a numerical method. In the numerical analysis, the finite element method is used in space domain discretization and the Newmark constant acceleration algorithm is used in time integration. According to the numerical results from the impact response analysis. it is found that the stress fields are bisected at the crack surface and the parts of stress intensity are moved along the crack face. The crack tip stress fields are yaried rapidly. The magnitude of crack tip stress fields are converted to dynamic stress intensity factor. Dynamic sress intensity factor appears when the stress wave has reached at the crack tip and the aspect of change of dynamic stress intensity factor is shown to be the same as the part of the flow of stress intensity.

A Study on the Microscopic Model for Fatigue Crack Closure Behavior (피로균열 개폐구거동의 미시적 모델에 관한 연구)

  • O, Se-Uk;Gang, Sang-Hun
    • Journal of Ocean Engineering and Technology
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    • v.4 no.1
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    • pp.81-87
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    • 1990
  • Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.

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A Study on the Microscopic Model for Fatigue Crack Closure Behavior (피로균열 개폐구거동의 미시적 모델에 관한 연구)

  • O, Se-Uk;Gang, Sang-Hun
    • Journal of Ocean Engineering and Technology
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    • v.4 no.1
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    • pp.87-87
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    • 1990
  • Fatigue crack closure levels based on the behavior of residual displacements on crack surfaces, are determined analytically according to the microscopic crack closure mechanisms, i.e., whether the first contact of crack surfaces takes place at the very crack tip or on the surfaces near the tip. The comparative analysis on the two models is carried out empirically by the constant amplitude fatigue tests on 2024-T3 aluminum alloy plate, and it shows that under negative stress ratio, the case of the first contact at crack tip gives better agreement with the experimental results than the other.