• 제목/요약/키워드: Local Failure Criterion

검색결과 41건 처리시간 0.017초

감육배관 손상시험 결과를 이용한 국부손상기준 검증 (Validation of a Local Failure Criteria Using the Results of Wall-Thinned Pipe Failure Tests)

  • 김진원;이성호;박치용
    • 대한기계학회논문집A
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    • 제33권12호
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    • pp.1393-1400
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    • 2009
  • The objective of this study is to validate local failure criteria, which were proposed based on the notched-bar specimen tests combining with finite element (FE) simulations, using the results of real-scale pipe failure tests. This study conducted burst test using wall-thinned pipe specimens, which were made of 4 inch Sch.80 ASTM A106 Gr.B carbon steel pipe, under simple internal pressure at ambient temperature and performed associated FE simulations. Failure pressures were estimated by applying the failure criteria to the results of FE simulations and were compared with experimental failure pressures. It showed that the local stress based criterion, given as true ultimate tensile stress of material, accurately estimated the failure pressure of wall-thinned pipe specimens. However, the local strain based criterion, which is fracture strain of material as a function of stress tri-axiality, could not predict the failure pressure. It was confirmed that the local stress based criterion is reliably applicable to estimation of failure pressure of local wall-thinned piping components.

내압을 받는 외부 국부 감육 직관의 파손 기준 (Failure Criterion of Straight Pipe with Outer Local Wall Thinning under Internal Pressure)

  • 김수영;남기우
    • 동력기계공학회지
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    • 제18권1호
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    • pp.76-83
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    • 2014
  • This study was carried out an experimental and finite element analysis on the fracture behavior of straight pipes with local wall thinning under internal pressure. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area has an eroded ratio of d/t=0.80~0.92 and an eroded length of l=25, 50 and 102 mm. Three-dimensional elastic-plastic analyses were also carried out using the finite element method, which is able to accurately simulate failure behaviors. In regards to the relation ship between pressure and eroded ratio, the criterion that can be used safely under operating pressure and design pressure were obtained from this calculation. The results of this calculation were in relatively good agreement with that of the experiment.

소성불안정성에 의한 관재 하이드로포밍 공정에서의 터짐 불량 예측 (A Prediction of Bursting Failure in Tube Hydroforming Process Based on Plastic Instability)

  • 김상우;김정;박훈재;강범수
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2004년도 춘계학술대회 논문집
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    • pp.210-213
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    • 2004
  • Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

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네킹발생조건에 의한 관재 액압성형 공정에서의 터짐 불량 예측 (A Prediction of Bursting Failure in Tube Hydroforming Process Based on Necking Conditions)

  • 김상우;김정;박훈재;강범수
    • 소성∙가공
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    • 제13권7호
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    • pp.629-634
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    • 2004
  • Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined infernal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity for anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy Parameter, strain hardening exponent and strength coefficient on bursting Pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

파괴변형률모델에 기초한 결함이 존재하는 API X65 배관의 연성파괴 해석 (Ductile Failure Analysis of Defective API X65 Pipes Based on Stress-Modified Fracture Strain Criterion)

  • 오창균;백종현;김영표;김우식;김윤재
    • 대한기계학회논문집A
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    • 제30권9호
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    • pp.1086-1093
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    • 2006
  • A local failure criterion for the API X65 steel is applied to predict ductile failure of full-scale API X65 pipes with simulated corrosion and gouge defects under internal pressure. The local failure criterion is the stress-modified fracture strain for the API X65 steel as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the effective stress). Based on detailed FE analyses with the proposed local failure criteria, burst pressures of defective pipes are estimated and compared with experimental data. The predicted burst pressures are in good agreement with experimental data. Noting that an assessment equation against the gouge defect is not yet available, parametric study is performed, from which a simple equation is proposed to predict burst pressure fur API X65 pipes with gouge defects.

유한요소해석에 기초한 감육곡관 손상압력 평가 모델 개발 (Development of Failure Pressure Evaluation Model for Local Wall-Thinned Elbows Based on Finite Element Analysis)

  • 김진원;박종선
    • 대한기계학회논문집A
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    • 제32권12호
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    • pp.1063-1071
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    • 2008
  • This paper provides a failure pressure evaluation model for local wall-thinned elbows. In this study, parametric finite element analyses are performed on the elbows containing local wall-thinning defect at their intrados and extrados, and the failure pressures are obtained from the analysis results by applying a local failure criterion that was validated by real-scale pipe tests. An evaluation model including the effects of thinning depth, length, circumferential angle, thinning location, and elbow geometries on the failure pressure is derived based on the evaluated failure pressures. The proposed model agrees well with the results of finite element analyses and reasonably estimates the dependence of failure pressure on the wall-thinning dimensions and elbow geometries. Also, the comparison with experimental data demonstrates that the proposed evaluation model can accurately predict the failure pressure of local wall-thinned elbows.

모사시편 시험을 통한 감육결함 국부손상기준 개발 (Development of Local Failure Criteria for Well Thinning Defect by Simulated Specimen Tests)

  • 김진원;김도형;박치용;이성호
    • 대한기계학회논문집A
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    • 제31권3호
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    • pp.304-312
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    • 2007
  • The objective of this study is to develop a local failure criterion for a wall thinning defect of piping components. For this purpose, a series of tensile tests was performed using several types of simulated specimens with different stress states, including smooth round bar, notched round bar (five different notch radii), and grooved plate (three different groove radii). In addition, finite element (FE) simulations were performed on the simulated specimen tests and the results were compared with the test results. From the comparisons, the equivalent stress and strain corresponding to maximum load and final failure of notched specimens were proposed as failure criteria under tensile load. The criteria were verified by employing them to the estimation of failure of grooved plate specimens that simulate the wall thinning defect. It showed that the proposed criteria accurately estimate the maximum load and final failure of grooved plate specimen tests.

A set of failure variables for analyzing stability of slopes and tunnels

  • Kim, Jun-Mo;Lee, Sungho;Park, Jai-Yong;Kihm, Jung-Hwi;Park, Sangho
    • Geomechanics and Engineering
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    • 제20권3호
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    • pp.175-189
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    • 2020
  • A set of relatively simple five local shear and tension failure variables is presented and then implemented into a generalized poroelastic hydromechanical numerical model to analyze failure potential and stability of variably saturated geologic media. These five local shear and tension failure variables are formulated from geometrical relationships between the Mohr circle and the Mohr-Coulomb failure criterion superimposed with the tension cutoff, which approximate together the Mohr effective stress failure envelope. Finally, fully coupled groundwater flow and land deformation in two variably saturated geologic media, which are associated with a slope (Case 1) and a tunnel (Case 2), respectively, and their failure potential and stability are simulated using the resultant hydromechanical numerical model. The numerical simulation results of both cases show that shear and tension failure potential and stability of variably saturated geologic media can be analyzed numerically simply and efficiently and even better by using the five local shear and tension failure variables as a set than by using the conventional factors of safety against shear and tension failures only.

Modeling of progressive collapse of a multi-storey structure using a spring-mass-damper system

  • Yuan, Weifeng;Tan, Kang Hai
    • Structural Engineering and Mechanics
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    • 제37권1호
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    • pp.79-93
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    • 2011
  • A simple mechanical model is proposed to demonstrate qualitatively the pancake progressive collapse of multi-storey structures. The impact between two collapsed storeys is simulated using a simple algorithm that builds on virtual mass-spring-damper system. To analyze various collapse modes, columns and beams are considered separately. Parametric studies show that the process of progressive collapse involves a large number of complex mechanisms. However, the proposed model provides a simple numerical tool to assess the overall behavior of collapse arising from a few initiating causes. Unique features, such as beam-to-beam connection failure criterion, and beam-to-column connection failure criterion are incorporated into the program. Besides, the criterion of local failure of structural members can also be easily incorporated into the proposed model.

Study on mechanism of macro failure and micro fracture of local nearly horizontal stratum in super-large section and deep buried tunnel

  • Li, Shu-cai;Wang, Jian-hua;Chen, Wei-zhong;Li, Li-ping;Zhang, Qian-qing;He, Peng
    • Geomechanics and Engineering
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    • 제11권2호
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    • pp.253-267
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    • 2016
  • The stability of surrounding rock will be poor when the tunnel is excavated through nearly horizontal stratum. In this paper, the instability mechanism of local nearly horizontal stratum in super-large section and deep buried tunnel is revealed by the analysis of the macro failure and micro fracture. A structural model is proposed to explain the mechanics of surrounding rock collapse under the action of stress redistribution and shed light on the macroscopic analytical approach of the stability of surrounding rock. Then, some highly effective formulas applied in the tunnel engineering are developed according to the theory of mixed-mode micro fracture. And well-documented field case is made to demonstrate the effectiveness and accuracy of the proposed analytical methods of mixed-mode fracture. Meanwhile, in order to make the more accurate judgment about yield failure of rock mass, a series of comprehensive failure criteria are formed. In addition, the relationship between the nonlinear failure criterion and $K_I$ and $K_{II}$ of micro fracture is established to make the surrounding rock failure criterion more comprehensive and accurate. Further, the influence of the parameters related to the tension-shear mixed-mode fracture and compression-shear mixed-mode fracture on the propagation of rock crack is analyzed. Results show that ${\sigma}_3$ changes linearly with the change of ${\sigma}_1$. And the change rate is related to ${\beta}$, angle between the cracks and ${\sigma}_1$. The proposed simple analytical approach is economical and efficient, and suitable for the analysis of local nearly horizontal stratum in super-large section and deep buried tunnel.