• 제목/요약/키워드: Point Stress Criterion

검색결과 62건 처리시간 0.032초

노치부를 가진 Glass/Epoxy 복합재료의 노치강도 평가와 불안정 파괴조건 (The Notched Strength and Fracture Criterion in Plain Woven Glass/Epoxy Composites With a Crack)

  • 김정규;김도식
    • 한국해양공학회지
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    • 제7권2호
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    • pp.57-67
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    • 1993
  • The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.

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원공을 가진 Glass/Epoxy 복합재료의 노치강도 및 파괴조건 (Notched Strength and Fracture Criterion of Glass/Epoxy Plain Woven Composites Containing Circular Holes)

  • 김정규;김도식
    • 대한기계학회논문집
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    • 제16권7호
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    • pp.1285-1293
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    • 1992
  • 본 연구에서는 glass/epoxy 직조된 복합재료에 있어서 원공 및 판폭의 크기가 노치강도에 미치는 영향을 명확히 하고, 또한 노치강도 및 파괴조건과 위에서 언급한 특성길이와의 관계를 검토하였다.

알루미늄 합금의 접착구조물에 대한 접착강도의 평가방법 (Evaluation Method of Bonded Strength in Adhesively Bonded Structures of the Aluminum Alloys)

  • 정남용
    • 한국생산제조학회지
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    • 제8권1호
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    • pp.35-44
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    • 1999
  • In a view point of earth environmental protection and social requirement, adhesively bonded structures of aluminum alloys have become to be employed for the purpose of decreasing fuel ratio by weight reduction and to improve performance in various engineering fields such as aircrafts, automobiles, rolling stocks and so on. In spite of such wide applications in adhesively bonded structures of aluminum alloys, the quantitative fracture criterion and evolution method of its bonded strength have not been established yet. The objective of this paper is to establish fracture criterion considering stress singularity at interface edges in adhesively bonded structures of aluminum alloys. Through the analyses of boundary element method and static fracture experiments with three different types of specimens in the adhesively bonded joints of aluminum alloys, its fracture criterion was proposed and discussed about strength evolution of adhesively bonded structures.

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소결분말금속의 항복함수 (A Yield Function for Sintered Porous Metals)

  • 박종진
    • 대한기계학회논문집
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    • 제17권5호
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    • pp.1115-1122
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    • 1993
  • Several yield criteria for porous materials are compared with each other, defining the apparent yield stress as the yield stress of the porous material in simple compression. It was found that the plastic Poisson's ratio is the parameter needed to define the yield criterion, rather than the relative density. The plastic Poisson's ratio is regarded as a material characteristic that is obtained from a simple compression test. A new form of yield criterion was suggested, and it was applied to hydrostatic compression as well as uniaxial strain compression of sintered Al-2024 powder. The crossover point in the mean stress vs volume change curves of the processes was predicted. It is presented that the flow stress of the fully densed material can be obtained from that of the porous material using relations obtained from the yield criterion.

Stability condition for the evaluation of damage in three-point bending of a laminated composite

  • Allel, Mokaddem;Mohamed, Alami;Ahmed, Boutaous
    • Steel and Composite Structures
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    • 제15권2호
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    • pp.203-220
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    • 2013
  • The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.

Laminate Tensile Failure Strength Prediction using Stress Failure Criteria

  • Lee, Myoung Keon;Kim, Jae Hoon
    • 항공우주시스템공학회지
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    • 제15권6호
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    • pp.19-25
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    • 2021
  • This paper presents a method that uses the stress failure criteria to predict the tensile failure strength of open-hole laminates with stress concentrations. The composite material used in this study corresponds to a 177 ℃ cured, carbon/epoxy unidirectional tape prepreg. The results obtained by testing ten different laminates were compared and analyzed to verify the tensile strength of the open-hole laminates predicted using the proposed stress failure criteria. The findings of this study confirm that the tensile strength predictions performed using the proposed method are generally accurate, except in cases involving highly soft laminates (10% of 0° ply).

평균수직응력에 민감한 모재를 가진 기공체의 구성식과 기공생성모델 (A Constitutive Law for Porous Solids with Pressure-Sensitive Matrices and a Void Nucleation Model)

  • 정현용
    • 대한기계학회논문집A
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    • 제24권2호
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    • pp.472-480
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    • 2000
  • A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion was obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stresses for a spherical thick-walled shell and by fitting the finite element results of a voided cube. The macroscopic yield criterion is valid for negative mean normal stresses as well as for positive mean normal stresses. From the yield criterion, a plastic potential function for the porous solids was derived either for plastic normality flow or for plastic non-normality flow of pressure- sensitive matrices. In addition, the elastic relation, an evolution equation of the plastic flow stress of the matrices and an evolution equation of the void volume fraction were presented to complete a set of constitutive relations. The set of constitutive relations was implemented into a finite element code ABAQUS to analyze the material behavior of rubber-toughened epoxies. The cavitation and the deformation behavior were analyzed around a crack tip under three-point bending and around notch tips under four-point bending. In the numerical analyses, the cavitation of rubber particles was considered via a stress-controlled nucleation model. The numerical results indicate that a reasonable cavitation zone can be obtained with void nucleation controlled by the macroscopic mean normal stress, and a plastic zone is smaller around a notch tip under compression than under tension. These numerical results agree well with corresponding experimental results on the cavitation and plastic zones.

탄소성 구성 방정식을 이용한 삼차원 브레이드 복합재료의 역학적 해석 (Mechanical Analysis of 3D Circular Braided Glass Fiber Reinforced Composites Using Elastic-Plastic Constitutive Equations)

  • 류한선;이명규;김지훈;정관수
    • 한국복합재료학회:학술대회논문집
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    • 한국복합재료학회 2004년도 추계학술발표대회 논문집
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    • pp.147-150
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    • 2004
  • In order to describe the mechanical behavior of highly anisotropic and asymmetric materials such as fiber­reinforced composites, the elastic-plastic constitutive equations were used here based on the recently developed yield criterion and hardening laws. As for the yield criterion, modified Drucker-Prager yield surface was used to represent the orthotropic and asymetric properties of composite materials, while the anisotropic evolution of back­stress was accounted for the hardening behavior. Experimental procedures to obtain the material parameters of the hardening laws and yield surface are presented for 3D Circular Braided Glass Fiber Reinforced Composites. For verification purpose, comparisons of finite element simulations using the elastic-plastic constitutive equations, anisotropic elastic constitutive equations and experiments were performed for the three point bending tests. The results of finite element simulations showed good agreements with experiments, especially for the elastic-plastic constitutive equations with yield criterion considering anisotropy as well as asymmetry and anisotropic back stress evolution rule.

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Measurement of the mixed mode fracture strength of green sandstone using three-point bending specimens

  • Li, Yifan;Dong, Shiming;Pavier, Martyn J.
    • Geomechanics and Engineering
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    • 제20권1호
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    • pp.9-18
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    • 2020
  • Three-point bending specimens have been used to investigate the mixed mode fracture of green sandstone. Dimensionless stress intensity factors and T-stresses were calculated first by using the finite element method for various crack lengths, crack angles and span to length ratios. It is shown that three-point bending specimens can provide the whole range of mode mixities from pure mode I to pure mode II, provided suitable values are chosen for the crack angle and span to length ratio. The fracture test results were also used to compare with predictions of different criteria. These comparisons show that modified criteria including the influence of the T-stress agree better with experiment than the conventional criteria but that no one criterion matches perfectly the test results.

Glass/Epoxy 복합재료의 피로강도평가 및 피로수명예측 (The Fatigue Strength and the Fatigue Life Prediction in Plain Woven Glass/Epoxy Composite Plates)

  • 김정규;김도식
    • 대한기계학회논문집
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    • 제17권10호
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    • pp.2475-2482
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    • 1993
  • The effects of the hole size(2R) and the specimen width(W) on the fatigue strength and the fatigue life in plain woven glass/epoxy composite plates are experimentally investigated under constant amplitude tensile fatigue loading. It is shown in this study that the notch sensitivity under fatigue loading is lower than that under static loading. It can be explained by the fact that the stress concentration is relaxed by the damage developed at the boundary of circular hole. To predict the fatigue strength at a specific cycle, the modified point stress criterion represented as a function of the geometry of the specimen(2R and W) is applied. It is found that the model used in the prediction of the notched tensile strength predicts the fatigue strength with reasonable accuracy. A model for predicting the fatigue life in the notched specimen, based on the S-$N_f$, curve in the smooth specimen, is suggested.