• Title, Summary, Keyword: Length-Scale-Dependent Failure

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Particle Size-Dependent Failure Analysis of Particle-Reinforced Metal Matrix Composites using Dislocation Punched Zone Modeling (전위 펀치 영역 모델링에 의한 입자 강화 금속지지 복합재의 입자 크기 의존 파손 해석)

  • Suh, Yeong Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.3
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    • pp.275-282
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    • 2014
  • Particle-reinforced metal matrix composites exhibit a strengthening effect due to the particle size-dependent length scale that arises from the strain gradient, and thus from the geometrically necessary dislocations between the particles and matrix that result from their CTE(Coefficient of Thermal Expansion) and elastic-plastic mismatches. In this study, the influence of the size-dependent length scale on the particle-matrix interface failure and ductile failure in the matrix was examined using finite-element punch zone modeling whereby an augmented strength was assigned around the particle. The failure behavior was observed by a parametric study, while varying the interface failure properties such as the interface strength and debonding energy with different particle sizes and volume fractions. It is shown that the two failure modes (interface failure and ductile failure in the matrix) interact with each other and are closely related to the particle size-dependent length scale; in other words, the composite with the smaller particles, which is surrounded by a denser dislocation than that with the larger particles, retards the initiation and growth of the interface and matrix failures, and also leads to a smaller amount of decrease in the flow stress during failure.

Hierarchical Finite-Element Modeling of SiCp/Al2124-T4 Composites with Dislocation Plasticity and Size-Dependent Failure (전위 소성과 크기 종속 파손을 고려한 SiCp/Al2124-T4 복합재의 계층적 유한요소 모델링)

  • Suh, Yeong-Sung;Kim, Yong-Bae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.2
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    • pp.187-194
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    • 2012
  • The strength of particle-reinforced metal matrix composites is, in general, known to be increased by the geometrically necessary dislocations punched around a particle that form during cooling after consolidation because of coefficient of thermal expansion (CTE) mismatch between the particle and the matrix. An additional strength increase may also be observed, since another type of geometrically necessary dislocation can be formed during extensive deformation as a result of the strain gradient plasticity due to the elastic-plastic mismatch between the particle and the matrix. In this paper, the magnitudes of these two types of dislocations are calculated based on the dislocation plasticity. The dislocations are then converted to the respective strengths and allocated hierarchically to the matrix around the particle in the axisymmetric finite-element unit cell model. The proposed method is shown to be very effective by performing finite-element strength analysis of $SiC_p$/Al2124-T4 composites that included ductile failure in the matrix and particlematrix decohesion. The predicted results for different particle sizes and volume fractions show that the length scale effect of the particle size obviously affects the strength and failure behavior of the particle-reinforced metal matrix composites.

Fatigue Failure Behavior of Pipe Bends with Local Wall-Thinning Under Cyclic Bending Condition (반복굽힘 조건에서 감육 곡관의 피로손상 거동)

  • Yoon, Min-Soo;Kim, Jin-Weon;Kim, Jong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.10
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    • pp.1227-1234
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    • 2012
  • In this study, fatigue tests were carried out using real-scale pipe bend specimens with wall-thinning defects under a cyclic bending load together with a constant internal pressure of 10 MPa. The wall-thinning defect was located at the extrados and the intrados of the pipe bend specimens. A fully reversed cyclic in-plane bending displacement was applied to the specimens. For the pipe bends with wall thinning at the extrados, an axial crack occurred at the crown of the pipe bend rather than at the extrados where the defect was located. In addition, the fatigue life was longer than that of a sound pipe bend predicted from the design fatigue curve in ASME Sec.III, and it was less dependent on the axial length of the wall-thinning defect. For the pipe bends with wall thinning at the intrados, a circumferential crack occurred at the intrados. In this case, the fatigue life was much shorter than that of a sound pipe bend predicted from the design fatigue curve, and it clearly decreased with decreasing axial length of the wall-thinning defect.