• 제목/요약/키워드: Fatigue design criterion

검색결과 57건 처리시간 0.024초

Homogenization based continuum damage mechanics model for monotonic and cyclic damage evolution in 3D composites

  • Jain, Jayesh R.;Ghosh, Somnath
    • Interaction and multiscale mechanics
    • /
    • 제1권2호
    • /
    • pp.279-301
    • /
    • 2008
  • This paper develops a 3D homogenization based continuum damage mechanics (HCDM) model for fiber reinforced composites undergoing micromechanical damage under monotonic and cyclic loading. Micromechanical damage in a representative volume element (RVE) of the material occurs by fiber-matrix interfacial debonding, which is incorporated in the model through a hysteretic bilinear cohesive zone model. The proposed model expresses a damage evolution surface in the strain space in the principal damage coordinate system or PDCS. PDCS enables the model to account for the effect of non-proportional load history. The loading/unloading criterion during cyclic loading is based on the scalar product of the strain increment and the normal to the damage surface in strain space. The material constitutive law involves a fourth order orthotropic tensor with stiffness characterized as a macroscopic internal variable. Three dimensional damage in composites is accounted for through functional forms of the fourth order damage tensor in terms of components of macroscopic strain and elastic stiffness tensors. The HCDM model parameters are calibrated from homogenization of micromechanical solutions of the RVE for a few representative strain histories. The proposed model is validated by comparing results of the HCDM model with pure micromechanical analysis results followed by homogenization. Finally, the potential of HCDM model as a design tool is demonstrated through macro-micro analysis of monotonic and cyclic damage progression in composite structures.

Carbon/Epoxy 적층판의 저속충격손상에 따른 잔류강도 평가 (Evaluation of Residual Strength of Carbon/Epoxy Laminates Due to Low Velocity Impact Damage)

  • 강민성;최정훈;김상영;구재민;석창성
    • 한국정밀공학회지
    • /
    • 제27권2호
    • /
    • pp.102-108
    • /
    • 2010
  • Recently, carbon fiber reinforced plastic(CFRP) composite materials have been widely used in various fields of engineering because of its advanced properties. Also, CFRP composite materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. However CFRP composite materials are susceptible to impact damage due to their lack of through-thickness reinforcement and it causes large drops in the load-carrying capacity of a structure. Therefore, the impact damage behavior and subsequently load-carrying capacity of impacted composite materials deserve careful investigation. In this study, the residual strength and impact characteristics of plain-woven CFRP composites with impact damage are investigated under axial tensile test. By using obtained residual strength and Tan-Cheng failure criterion, residual strength of CFRP laminate with arbitrary fiber angle were evaluated.

선박용 휴대형 질소용기(11 kg, 10 L 및 50 bar)의 두께 및 외형 설계 (Design of Portable Welded-Nitrogen Vessel (11 kg, 10 L and 50 bar) for Shipbuilding)

  • 성한샘;김재열;엄태진;곽효서;이광오;김철
    • 대한기계학회논문집A
    • /
    • 제41권4호
    • /
    • pp.263-270
    • /
    • 2017
  • 조선소에서 사용되는 대형 셧오프 밸브의 개폐를 위한 용기의 경우, 저압의 고정식 대형 공기탱크가 사용되고 있는데, 이는 먼 거리에 있는 밸브에 공압을 공급해야 할 경우, 추가 배관이 필요하며 수송도중 압력 강하가 발생하는 문제점이 있다. 이에 본 논문에서는 작업자들의 편의성을 증대시키고, 공기누설로 인한 폭발 방지를 위하여 고압의 휴대형 용접식 질소용기(11 kg, 10 L 및 50 bar)의 설계를 수행하였다. 구조적으로 취약한 용접부를 최소화하기 위하여 용기의 외형을 타원형으로 설계하였으며, 기준 무게 및 용적 충족과 사용압력에 대한 구조안전성을 확립하기 위하여 용기의 두께와 장단축 비를 설계하였다. 또한 용접 잔류응력 예측을 위해 APDL(ANSYS Parametric Design Language)을 이용하여 과도 열-구조 연성해석을 수행하였으며, 내압에 의한 구조안전 및 피로수명을 검증하였다.

Analysis and probabilistic modeling of wind characteristics of an arch bridge using structural health monitoring data during typhoons

  • Ye, X.W.;Xi, P.S.;Su, Y.H.;Chen, B.
    • Structural Engineering and Mechanics
    • /
    • 제63권6호
    • /
    • pp.809-824
    • /
    • 2017
  • The accurate evaluation of wind characteristics and wind-induced structural responses during a typhoon is of significant importance for bridge design and safety assessment. This paper presents an expectation maximization (EM) algorithm-based angular-linear approach for probabilistic modeling of field-measured wind characteristics. The proposed method has been applied to model the wind speed and direction data during typhoons recorded by the structural health monitoring (SHM) system instrumented on the arch Jiubao Bridge located in Hangzhou, China. In the summer of 2015, three typhoons, i.e., Typhoon Chan-hom, Typhoon Soudelor and Typhoon Goni, made landfall in the east of China and then struck the Jiubao Bridge. By analyzing the wind monitoring data such as the wind speed and direction measured by three anemometers during typhoons, the wind characteristics during typhoons are derived, including the average wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, and power spectral density (PSD). An EM algorithm-based angular-linear modeling approach is proposed for modeling the joint distribution of the wind speed and direction. For the marginal distribution of the wind speed, the finite mixture of two-parameter Weibull distribution is employed, and the finite mixture of von Mises distribution is used to represent the wind direction. The parameters of each distribution model are estimated by use of the EM algorithm, and the optimal model is determined by the values of $R^2$ statistic and the Akaike's information criterion (AIC). The results indicate that the stochastic properties of the wind field around the bridge site during typhoons are effectively characterized by the proposed EM algorithm-based angular-linear modeling approach. The formulated joint distribution of the wind speed and direction can serve as a solid foundation for the purpose of accurately evaluating the typhoon-induced fatigue damage of long-span bridges.

잔류응력과 계면접합강도를 고려한 금속복합재료의 열탄소성 변형 해석 (Thermal Elasto-Plastic Deformation Analysis of Metal Matrix Composites Considering Residual Stress and Interface Bonding Strength)

  • 강충길;서영호
    • 한국정밀공학회지
    • /
    • 제16권1호통권94호
    • /
    • pp.227-237
    • /
    • 1999
  • As the interface bonding phenomenon between the matrix and the reinforcements has a large effect on the mechanical properties of MMCs, a sugestion of the strength analysis technique considering the residual stress and the interface bonding phenomenon is very important for the design of pans and the estimation of fatigue behavior. In this paper the three dimensional finite element anaysis is performed during the elasto-plastic deformation of the particulate reinforced metal matrix composites. It was analyzed with the volume fractions in view of microscale. Bonding strength. interface separation and matrix void growth between the matrix and the reinforcements will be predicted on deformation under tensile loading. An interface seperation is estimated by the fracture criterion which is a critical value of generalized plastic work per unit volume. The shape of the reinforcement is assumed to be a perfect sphere. And the type of the reinforcement distribution is assumed as FCC array. The thermal residual stress in MMCs is induced by the heat treatment. It is included at the simulation as an initial residual stress. The element birth and death method of the ANSYS program is used for the estimation of the interface bonding strength, void generation and propagation. It is assumed that the fracture in the matrix region begin to occur under the external loading when the plastic work per unit volume is equal to the critical value. The fracture strain will be defined. The experimental data of the extruded $SiC_p$>/606l Al composites are compared with the theoretical results.

  • PDF

고장력강의 구멍 확장 실험을 이용한 자동차부품 설계연구 (A Study of Automobile Product Design using Hole Expansion Testing of High Strength Steels)

  • 박병철;배경운;구선모;장승현;홍성훈;김영석
    • 소성∙가공
    • /
    • 제19권6호
    • /
    • pp.337-343
    • /
    • 2010
  • Current need of weight reduction in automotive part increases the application for high strength steel (HSS). The various types of high strength steels have been used to produce chassis part, control arms and trailing arms for weight reduction and increasing of fatigue durability such as dual phase steel (DP) and ferrite bainite steel (FB). But, DP and FB steels have proven to show inferiority in durability as well as press formability. Edge cracking occurred often in flange forming and hole expansion processes is the major failure encountered. This paper discussed the behavior of edge stretchability of high strength steel of DP and FB steels. Experimental works have been conducted to study the effect of punch clearance and burr direction on hole expansion ratio (HER). Also finite element simulation (FEM) has been preformed to clarify the mechanism of flange crack and support the experimental results on HER of DP and FB steels. It was simulated the whole process of blanking process following by hole expansion process and ductile fracture criterion named the modified Cockcroft-Latham model which was used to capture the fracture initiation. From the hole expansion tests and FEM simulation studies it was concluded that ferrite bainite steel showed better stretch-flangeability than dual phase steel. It was attributed to the lower work hardening rate of ferrite bainite steel than dual phase steel at the sheared edge.

안경테 종류에 따른 유발프리즘 (Induced Prism by the Categories of Spectacle Frames)

  • 박우정;김수운;황해영;유동식;손정식
    • 한국안광학회지
    • /
    • 제17권3호
    • /
    • pp.311-319
    • /
    • 2012
  • 목적: 안경의 조제가공에 있어서 동공중심과 교정렌즈의 광학중심이 일치하지 않으면 안경이 프리즘을 발생시켜 사위가 유발되고 유발된 사위는 안정피로를 일으키는 요인으로 작용한다. 동공의 중심과 교정렌즈 광학중심의 불일치로 인해 발생하는 유발프리즘에 대해 알아보고자 하였다. 방법: 본 연구는 총 103명을 대상으로 착용 안경렌즈의 광학중심과 동공중심의 일치 여부를 수평방향과 수직방향으로 나누어 조사하였고, 그리고 그 결과들을 안경의 구조에 따라 4개의 그룹으로 분류하였다. 프리즘유발에 안경테의 효과를 보기 위해 프리즘의 총량을 비교하였고, 측정된 프리즘 값들은 독일의 RAL-RG 915 규약과 비교하였다. 결과: 수평방향의 경우 10.7%의 실험 대상자에서는 유발프리즘을 관찰할 수 없었고, 73.8%의 실험 대상자들은 유발프리즘에 의해 영향을 받았으나 그 범위는 허용 수준 내에 있었다. 하지만 15.5%의 실험 대상자들은 허용 범위를 초과하여 프리즘에 의해 영향을 받는 것으로 나타났다. 수직방향의 경우, 23.3%의 실험 대상자들은 안경의 초기 착용시 프리즘에 의한 영향이 없었고, 54.4%의 실험 대상자들은 허용 범위 내의 극히 적은 프리즘에 영향을 받았으며, 22.3%의 실험대상자들은 허용 범위를 초과하는 프리즘 영향을 받는 것으로 나타났다. 이러한 결과는 안경조정(fitting)이 가능한 요소가 적은 그룹 A와 B에서 그룹 C와 D에 비해 보다 많은 수평, 수직 방향의 유발프리즘이 발생한 것을 보여준다. 결론: 안경 착용자의 굴절이상도가 높을수록 안경테 전조정(pre-fitting)을 통하여 동공중심과 렌즈의 광학중심점을 일치시킴으로서 수평, 수직방향 유발프리즘을 최소화시켜 안정피로를 줄일 수 있을 것이다. 따라서 시지각력을 향상시키기 위해 단안PD와 단안Oh의 정확한 설계와 적절한 안경테 조정을 통해 정확한 안경의 조제가공이 필요하다고 사료된다.