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  • Open Access


    Automated X-ray Defect Inspection on Occluded BGA Balls Using Hybrid Algorithm

    Ki-Yeol Eom1, Byungseok Min2,*

    CMC-Computers, Materials & Continua, Vol.75, No.3, pp. 6337-6350, 2023, DOI:10.32604/cmc.2023.035336

    Abstract Automated X-ray defect inspection of occluded objects has been an essential topic in semiconductors, autonomous vehicles, and artificial intelligence devices. However, there are few solutions to segment occluded objects in the X-ray inspection efficiently. In particular, in the Ball Grid Array inspection of X-ray images, it is difficult to accurately segment the regions of occluded solder balls and detect defects inside solder balls. In this paper, we present a novel automatic inspection algorithm that segments solder balls, and detects defects fast and efficiently when solder balls are occluded. The proposed algorithm consists of two stages. In the first stage, the… More >

  • Open Access


    Multiresolution Isogeometric Topology Optimisation Using Moving Morphable Voids

    Bingxiao Du1, Yong Zhao1, *, Wen Yao2, Xuan Wang3, Senlin Huo1

    CMES-Computer Modeling in Engineering & Sciences, Vol.122, No.3, pp. 1119-1140, 2020, DOI:10.32604/cmes.2020.08859

    Abstract A general and new explicit isogeometric topology optimisation approach with moving morphable voids (MMV) is proposed. In this approach, a novel multiresolution scheme with two distinct discretisation levels is developed to obtain high-resolution designs with a relatively low computational cost. Ersatz material model based on Greville abscissae collocation scheme is utilised to represent both the Young’s modulus of the material and the density field. Two benchmark examples are tested to illustrate the effectiveness of the proposed method. Numerical results show that high-resolution designs can be obtained with relatively low computational cost, and the optimisation can be significantly improved without introducing… More >

  • Open Access


    The Effect of Initial Defects on Overall Mechanical Properties of Concrete Material

    Yunfa Zhang1, Xiaozhou Xia1, *, Zhenjie Wu1, Qing Zhang1

    CMC-Computers, Materials & Continua, Vol.62, No.1, pp. 413-442, 2020, DOI:10.32604/cmc.2020.04660

    Abstract Considering the fact that the initial defects, like the imperfect interfacial transition zones (ITZ) and the micro voids in mortar matrix, weaken the mechanical properties of concrete, this study develops corresponding constitutive models for ITZ and matrix, and simulates the concrete failure with finite element methods. Specifically, an elastic-damage traction-separation model for ITZ is constructed, and an anisotropic plastic-damage model distinguishing the strength-difference under tension and compression for mortar matrix is proposed as well. In this anisotropic plastic-damage model, the weakening effect of micro voids is reflected by introducing initial isotropic damage, the distinct characteristic of tension and compression which… More >

  • Open Access


    SGBEM Voronoi Cells (SVCs), with Embedded Arbitrary-Shaped Inclusions, Voids, and/or Cracks, for Micromechanical Modeling of Heterogeneous Materials

    Leiting Dong1,2, Satya N. Atluri1,3

    CMC-Computers, Materials & Continua, Vol.33, No.2, pp. 111-154, 2013, DOI:10.3970/cmc.2013.033.111

    Abstract In this study, SGBEM Voronoi Cells (SVCs), with each cell representing a grain of the material at the micro-level, are developed for direct micromechanical numerical modeling of heterogeneous composites. Each SVC can consist of either a (each with a different) homogenous isotropic matrix, and can include micro-inhomogeneities such as inclusions, voids of a different material, and cracks. These inclusions and voids in each SVC can be arbitrarily-shaped, such as circular, elliptical, polygonal, etc., for 2D problems. Further, the cracks in each SVC can be fully-embedded, edge, branching, or intersecting types, with arbitrary curved shapes. By rearranging the weakly-singular boundary integral… More >

  • Open Access


    Effect of Gravitational Field and Temperature Dependent Properties on Two-Temperature Thermoelastic Medium with Voids under G-N Theory

    Mohamed I. A. Othman1, Magda E. M. Zidan1, Mohamed I. M. Hilal1

    CMC-Computers, Materials & Continua, Vol.40, No.3, pp. 179-201, 2014, DOI:10.3970/cmc.2014.040.179

    Abstract This investigation is aimed to study the two dimensional problem of thermoelastic medium with voids under the effect of the gravity. The modulus of elasticity is taken as a linear function of the reference temperature and employing the two-temperature generalized thermoelasticity. The problem is studied in the context of Green-Naghdi (G-N) theory of types II and III. The normal mode analysis method is used to obtain the exact expressions for the physical quantities which have been shown graphically by comparison between two types of the (G-N) theory in the presence and the absence of the gravity, the temperature dependent properties… More >

  • Open Access


    Microscopic Model Containing Micro-Voids for Analysis of Cement Mortar Damage Fracture Process

    Jichang Wang, Xiaoming Guo*, Xiaoxiao Sun

    The International Conference on Computational & Experimental Engineering and Sciences, Vol.21, No.4, pp. 79-79, 2019, DOI:10.32604/icces.2019.05248

    Abstract Cement mortar is an important component of many composite materials and one of the most widely used materials in engineering construction. At microscopic level, cement mortar can be regarded as a multiphase material composed of fine aggregates, cement paste, and a great many of initial defects, the form of which are micro-cracks and micro-voids. The macroscopic properties of cement mortar will be influenced by mechanical properties of different constituents and complex internal structures. The microscopic model containing micro-voids is established by the method of secondary development. The process of cement mortar damage fracture is studied. The fracture toughness of fine… More >

  • Open Access


    Development of 3D Trefftz Voronoi Cells with Ellipsoidal Voids &/or Elastic/Rigid Inclusions for Micromechanical Modeling of Heterogeneous Materials

    Leiting Dong1, Satya N. Atluri11

    CMC-Computers, Materials & Continua, Vol.30, No.1, pp. 39-82, 2012, DOI:10.3970/cmc.2012.030.039

    Abstract In this paper, as an extension to the authors's work in [Dong and Atluri (2011a,b, 2012a,b,c)], three-dimensional Trefftz Voronoi Cells (TVCs) with ellipsoidal voids/inclusions are developed for micromechanical modeling of heterogeneous materials. Several types of TVCs are developed, depending on the types of heterogeneity in each Voronoi Cell(VC). Each TVC can include alternatively an ellipsoidal void, an ellipsoidal elastic inclusion, or an ellipsoidal rigid inclusion. In all of these cases, an inter-VC compatible displacement field is assumed at each surface of the polyhedral VC, with Barycentric coordinates as nodal shape functions. The Trefftz trial displacement fields in each VC are… More >

  • Open Access


    Development of 3D T-Trefftz Voronoi Cell Finite Elements with/without Spherical Voids &/or Elastic/Rigid Inclusions for Micromechanical Modeling of Heterogeneous Materials

    L. Dong1, S. N. Atluri1

    CMC-Computers, Materials & Continua, Vol.29, No.2, pp. 169-212, 2012, DOI:10.3970/cmc.2012.029.169

    Abstract In this paper, three-dimensionalT-Trefftz Voronoi Cell Finite Elements (VCFEM-TTs) are developed for micromechanical modeling of heterogeneous materials. Several types of VCFEMs are developed, depending on the types of heterogeneity in each element. Each VCFEM can include alternatively a spherical void, a spherical elastic inclusion, a spherical rigid inclusion, or no voids/inclusions at all.In all of these cases, an inter-element compatible displacement field is assumed at each surface of the polyhedral element, with Barycentric coordinates as nodal shape functions.The T-Trefftz trial displacement fields in each element are expressed in terms of the Papkovich-Neuber solution. Spherical harmonics are used as the Papkovich-Neuber… More >

  • Open Access


    Scaled Boundary Finite Element Method for Thermoelasticity in Voided Materials

    Jan Sladek1, Vladimir Sladek1, Peter Stanak1

    CMES-Computer Modeling in Engineering & Sciences, Vol.106, No.4, pp. 229-262, 2015, DOI:10.3970/cmes.2015.106.229

    Abstract The scaled boundary finite element method (SBFEM) is presented to study thermoelastic problems in materials with voids. The SBFEM combines the main advantages of the finite element method (FEM) and the boundary element method (BEM). In this method, only the boundary is discretized with elements leading to a reduction of spatial dimension by one. It reduces computational efforts in mesh generation and CPU. In contrast to the BEM, no fundamental solution is required, which permits to analyze general boundary value problems, where the conventional BEM cannot be applied due to missing fundamental solution. The computational homogenization technique is applied for… More >

  • Open Access


    T-Trefftz Voronoi Cell Finite Elements with Elastic/Rigid Inclusions or Voids for Micromechanical Analysis of Composite and Porous Materials

    L. Dong1, S. N. Atluri2

    CMES-Computer Modeling in Engineering & Sciences, Vol.83, No.2, pp. 183-220, 2012, DOI:10.32604/cmes.2012.083.183

    Abstract In this paper, we develop T-Trefftz Voronoi Cell Finite Elements (VCF -EM-TTs) for micromechanical modeling of composite and porous materials. In addition to a homogenous matrix in each polygon-shaped element, three types of arbitrarily-shaped heterogeneities are considered in each element: an elastic inclusion, a rigid inclusion, or a void. In all of these three cases, an inter-element compatible displacement field is assumed along the element outer-boundary, and interior displacement fields in the matrix as well as in the inclusion are independently assumed as T-Trefftz trial functions. Characteristic lengths are used for each element to scale the T-Trefftz trial functions, in… More >

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