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  • Open Access


    Micromechanical Viscoelastic Analysis of Flax Fiber Reinforced Bio-Based Polyurethane Composites

    Nassibeh Hosseini1, Samad Javid1, Ali Amiri1, Chad Ulven1,*, Dean C. Webster2, Ghodrat Karami1

    Journal of Renewable Materials, Vol.3, No.3, pp. 205-215, 2015, DOI:10.7569/JRM.2015.634112

    Abstract In this study, a novel, bio-based polyol was used in the formulation of a polyurethane (PU) matrix for a composite material where fl ax fi ber was used as the reinforcement. The viscoelastic properties of the matrix and fl ax fi ber were determined by a linear viscoelastic model through experimentation and the results were used as input for the material properties in the computational model. A fi nite element micromechanical model of a representative volume element (RVE) in terms of repeating unit cells (RUC) was developed to predict the mechanical properties of composites. Six… More >

  • Open Access


    Stress Relaxation and Sensitivity Weight for Bi-Directional Evolutionary Structural Optimization to Improve the Computational Efficiency and Stabilization on Stress-Based Topology Optimization

    Chao Ma, Yunkai Gao*, Yuexing Duan, Zhe Liu

    CMES-Computer Modeling in Engineering & Sciences, Vol.126, No.2, pp. 715-738, 2021, DOI:10.32604/cmes.2021.011187

    Abstract Stress-based topology optimization is one of the most concerns of structural optimization and receives much attention in a wide range of engineering designs. To solve the inherent issues of stress-based topology optimization, many schemes are added to the conventional bi-directional evolutionary structural optimization (BESO) method in the previous studies. However, these schemes degrade the generality of BESO and increase the computational cost. This study proposes an improved topology optimization method for the continuum structures considering stress minimization in the framework of the conventional BESO method. A global stress measure constructed by p-norm function is treated as… More >

  • Open Access


    Relaxation of Residual Stress under Fatigue Load Described in Terms of Cyclic-Plastic Deformation Model

    S. Kwofie1

    Structural Durability & Health Monitoring, Vol.8, No.4, pp. 295-306, 2012, DOI:10.32604/sdhm.2012.008.295

    Abstract Fatigue life of components may be enhanced by mechanical surface treatments, such as shot penning, which induce compressive residual stresses in the component's surface. Under cyclic/fatigue loads, however, relaxation of the residual stress may occur thus, reducing the optimum benefit of the surface treatment. For health monitoring / life prediction under such conditions it is important to be able to assess stress relaxation in real-time. However, the phenomenon of cyclic relaxation of residual stress is not well understood and its tracking during component operation is a technical challenge. By means of cyclic plastic deformation model More >

  • Open Access


    Shear Deformation Kinematics During Cartilage Articulation: Effect of Lubrication, Degeneration, and Stress Relaxation

    Benjamin L. Wong*, Won C. Bae*, Kenneth R. Gratz*, Robert L. Sah∗,†

    Molecular & Cellular Biomechanics, Vol.5, No.3, pp. 197-206, 2008, DOI:10.3970/mcb.2008.005.197

    Abstract During joint articulation, the biomechanical behavior of cartilage not only facilitates load-bearing and low-friction, but also provides regulatory cues to chondrocytes. Elucidation of cartilage kinematics under combined compression and shearing conditions clarifies these cues in health and disease. The objectives of this study were to elucidate the effects of lubricant, tissue degeneration, and stress relaxation duration on cartilage shear kinematics during articulation. Human osteochondral cores with normal and mildly degenerate surface structures were isolated. Paired blocks from each core were apposed, compressed, allowed to stress relax for 5 or 60 min, and shear tested with… More >

  • Open Access


    Modeling of Nonlinear Rate Sensitivity by Using an Overstress Model


    CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.3, pp. 351-364, 2001, DOI:10.3970/cmes.2001.002.351

    Abstract Negative, zero or positive rate sensitivity of the flow stress can be observed in metals and alloys over a certain range of strain, strain rate and temperature. It is believed that negative rate sensitivity is an essential feature of dynamic strain aging, of which the Portevin-Le Chatelier effect is one other manifestation. The viscoplasticity theory based on overstress (VBO), one of the unified state variable theories, is generalized to model zero (rate independence) and negative as well as positive rate sensitivity in a consistent way. The present model does not have the stress rate term… More >

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