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  • Open Access

    ARTICLE

    DEVELOPMENT OF A 10 KW MICROWAVE APPLICATOR FOR THERMAL CRACKING OF LIGNITE BRIQUETTES

    Benjamin Lepersa,∗, Thomas Seitza, Guido Linka, John Jelonneka,b, Mark Zinkc

    Frontiers in Heat and Mass Transfer, Vol.6, pp. 1-6, 2015, DOI:10.5098/hmt.6.20

    Abstract A compact 10 kW microwave applicator operating at 2.45 GHz for fast volumetric heating and thermal cracking of lignite briquettes has been successfully designed and tested. In this paper, the applicator design and construction are presented together with a sequentially coupled electromagnetic, thermal-fluid and mechanical Comsol model. In a first step, this model allows us to calculate the power density inside the lignite material and the temperature distribution in the applicator for different water flow rates. In a second step, the total stress due to the thermal dilatation, the internal pressure inside the ceramic and More >

  • Open Access

    ARTICLE

    Modeling of Hydro-Viscoelastic State of Deformable and Saturated Product During Convective Drying

    R. Lamloumi1,2, L. Hassini1, G. L. Lecomte-Nana2, M. A. Elcafsi1, D. Smith2

    CMC-Computers, Materials & Continua, Vol.43, No.3, pp. 137-152, 2014, DOI:10.3970/cmc.2014.043.137

    Abstract A mathematical model was developed to simulate in 2D the spatiotemporal evolution of the moisture content, the temperature and the mechanical stress within a deformable and saturated product during convective drying. A comprehensive hydro-thermal model had been merged with a Maxwell model with two branches, assuming a viscoelastic material, a plane deformation and an isotropic hydric-shrinkage of the sample. A long sample of clay mixture with a square section was chosen as an application case. The transport and equilibrium properties of the product required for the modeling were determined from previous experiments which were independent More >

  • Open Access

    ARTICLE

    Analysis on Flexural Behavior of UHPFRC Beams based on Tensile Stress-Crack Opening Relationship

    Jung Soo Lee1, Sung Yong Park2, Keunhee Cho2, Jeong-Rae Cho2, Seung Hee Kwon1,3

    CMC-Computers, Materials & Continua, Vol.41, No.2, pp. 85-110, 2014, DOI:10.3970/cmc.2014.041.085

    Abstract The objective of this study is to investigate the differences between the tensile stress-crack opening relationships of the small size notched beam and the real size beam which were made of two ultra-high performance fiber reinforced concretes (UHPFRCs) having different volume fractions and lengths of fibers. The stress-crack opening relationships of two UHPFRCs were first obtained from the inverse analysis for the small size notched beam tests. In addition, the three types of real size beams were manufactured for each mix: (1) plain beam, (2) beam with tensile reinforcement, and (3) beam with both tensile More >

  • Open Access

    ARTICLE

    An Integrated Model for Tension Stiffening and Reinforcement Corrosion of RC Flexural Members

    Smitha Gopinath1,2, J. Rajasankar1, Nagesh R.Iyer1, A.Rama Chandra Murthy1

    CMC-Computers, Materials & Continua, Vol.33, No.1, pp. 87-110, 2013, DOI:10.3970/cmc.2013.033.087

    Abstract An integrated model is proposed to describe tension stiffening in reinforced concrete (RC) flexural members that are undergoing uniform corrosion of reinforcement. The tension stiffening model is taken as base to incorporate the effects of reinforcement corrosion. The model is developed in two steps. In the first step, tension stiffening of concrete is modelled using an exponential stress-strain curve defined as function of a decay parameter. Modular ratio and reinforcement ratio are considered in the definition of the decay parameter. In the second step, the effects of uniform corrosion of reinforcement are integrated with the… More >

  • Open Access

    ARTICLE

    Prediction of Interfacial Cracking due to Differential Drying Shrinkage of Concrete in Precast Shell Pier Cap

    Kyong Pil Jang1, Je kuk Son2, Seung Hee Kwon1,3

    CMC-Computers, Materials & Continua, Vol.38, No.3, pp. 155-173, 2013, DOI:10.3970/cmc.2013.038.155

    Abstract In a precast shell pier cap, cracking at the interface between the precast shell and the cast-in-place concrete may happen due to differences between the drying shrinkage of the inner and the outer concrete. The objective of this study is to establish a prediction method for interfacial cracking that will consider the real mechanism of differential drying shrinkage and creep. The main parameters used in the analysis were determined from experiments for a concrete mix that is applied to the manufacturing of pier caps. The variation of internal relative humidity over time was first calculated More >

  • Open Access

    ARTICLE

    A Higher Order Synergistic Damage Model for Prediction of Stiffness Changes due to Ply Cracking in Composite Laminates

    Chandra Veer Singh1,*

    CMC-Computers, Materials & Continua, Vol.34, No.3, pp. 227-249, 2013, DOI:10.3970/cmc.2013.034.227

    Abstract A non-linear damage model is developed for the prediction of stiffness degradation in composite laminates due to transverse matrix cracking. The model follows the framework of a recently developed synergistic damage mechanics (SDM) approach which combines the strengths of micro-damage mechanics and continuum damage mechanics (CDM) through the so-called constraint parameters. A common limitation of the current CDM and SDM models has been the tendency to over-predict stiffness changes at high crack densities due to linearity inherent in their stiffness-damage relationships. The present paper extends this SDM approach by including higher order damage terms in More >

  • Open Access

    ARTICLE

    Studies on Chloride Induced Corrosion of Reinforcement Steel in Cracked Concrete

    Sangoju Bhaskar1, Ravindra Gettu2, B.H. Bharatkumar1, M. Neelamegam1

    Structural Durability & Health Monitoring, Vol.7, No.4, pp. 231-252, 2011, DOI:10.3970/sdhm.2011.007.231

    Abstract The durability of reinforced concrete (RC) exposed to severe environments depends largely on its ability to resist the penetration of aggressive compounds. This paper deals with the corrosion of reinforcement bars (rebars) in cracked concrete exposed to chlorides. A simple U-shaped specimen was used in the study, with a high yield strength deformed bar of 12 mm diameter placed at with 20 mm clear cover. Concrete specimens with three water to cement ratios (w/c) and pre-cracks exposed to chlorides were studied for quality assessment and quantifying the corrosion damage in terms of gravimetric weight loss. More >

  • Open Access

    ARTICLE

    Fatigue Resistance and Cracking Mechanisms in an Aircraft AISI 4340 Steel with Surface Affected by Electro-Erosive and Water Jet Cutting

    I. Černý1,2, D. Mikulová1

    Structural Durability & Health Monitoring, Vol.6, No.1, pp. 43-52, 2010, DOI:10.3970/sdhm.2010.006.043

    Abstract Alternative methods of material machining like electro-erosive or water jet cutting, respectively, represent modern technologies, which are perspective to be used as final end-to-shape operations due to their possibilities of automatization and cutting precision. The paper contains results of an investigation of resistance of an aircraft AISI 4340 steel against fatigue loading performed using specimens loaded by three point bending at ambient temperature and standard laboratory conditions. Results of fatigue tests of specimens with surface after electro-erosive and water jet cutting, respectively, are presented, whereas in the latter case, areas of water jet incidence and… More >

  • Open Access

    ARTICLE

    3D Higher-OrderX-FEM Model for the Simulation of Cohesive Cracks in Cementitious Materials Considering Hygro-Mechanical Couplings

    C. Becker1, S. Jox2, G. Meschke3

    CMES-Computer Modeling in Engineering & Sciences, Vol.57, No.3, pp. 245-278, 2010, DOI:10.3970/cmes.2010.057.245

    Abstract A three-dimensional numerical model based on the Extended Finite Element Method (X-FEM) is presented for the simulation of cohesive cracks in cementitious materials, such as concrete, in a hygro-mechanical framework. Enhancement functions for the small scale resolution of the displacement jump across cracks in the context of the X-FEM is used in conjunction with a higher order family of hierarchical shape functions for the representation of the large scale displacement field of the investigated structure. Besides the theoretical and computational formulation in a multiphase context, aspects of the implementation, such as integration and crack tracking More >

  • Open Access

    ARTICLE

    Numerical Study of PVB Laminated Windshield Cracking Upon Human Head Impact

    Jun Xu1,2, Yibing Li1, Xi Chen2,3, Yuan Yan2,3, Dongyun Ge4,1, Bohan Liu1

    CMC-Computers, Materials & Continua, Vol.18, No.2, pp. 183-212, 2010, DOI:10.3970/cmc.2010.018.183

    Abstract The crack pattern in a PVB laminated windshield upon head impact is of considerable interest because it contains important information on energy mitigation, pedestrian protection, and accident reconstruction. We carry out a systematic numerical study based on the extended finite element method (XFEM), to investigate the effects of various material and system variables, including the impact speed, effective head mass, PVB interlayer material thickness and property, windshield curvature, aspect ratio and size, boundary constraint, impact angle and off-center impact, on the parameters characterizing the resulting crack pattern, i.e. the crack length, crack angle and circumferential More >

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