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Giang D Nguyen - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamics based Cohesive Model for discrete element Modelling of fracture in cemented materials
    International Journal of Solids and Structures, 2017
    Co-Authors: Nhu H T Nguyen, Giang D Nguyen, Jayantha Kodikara, S Arooran, Peerapong Jitsangiam
    Abstract:

    Abstract In this research, a discrete Modelling approach employing a new Cohesive Model is proposed to investigate the failure response of cemented materials. A Cohesive Model considering mixed-mode fracture is developed based on a generic thermodynamic framework for coupling damage mechanics and plasticity theory. Discrete Element Method (DEM), a well-known computational method for simulating large deformation and cracking issues, is utilised as a numerical platform to facilitate the implementation of the proposed Cohesive Model. The nature of discrete Modelling is analogous to the internal structure of cemented materials, making it more efficient compared with conventional continuum methods to characterise the failure behaviour of cemented materials. This combined Cohesive-discrete Modelling approach is then employed to simulate four experimental tests under different boundary conditions. Simulation results show excellent agreements with the experiments in terms of both macro force-displacement responses and cracking patterns, suggesting the effectiveness of the proposed Modelling approach for conducting numerical experiments and exploring the failure mechanisms in cemented materials.

  • a thermodynamics based Cohesive Model for interface debonding and friction
    International Journal of Solids and Structures, 2014
    Co-Authors: Irene Guiamatsia, Giang D Nguyen
    Abstract:

    Abstract A constitutive Model for interface debonding is proposed which is able to account for mixed-mode coupled debonding and plasticity, as well as further coupling between debonding and friction including post-delamination friction. The work is an extension of a previous Model which focuses on the coupling between mixed-mode delamination and plasticity. By distinguishing the interface into two parts, a cracked one where friction can occur and an integral one where further damage takes place, the coupling between frictional dissipation and energy loss through damage is seamlessly achieved. A simple framework for coupled dissipative processes is utilised to derive a single yield function which accurately captures the evolution of interface strength with increasing damage, for both tensile and compressive regimes. The new material Model is implemented as a user-defined interface element in the commercial package ABAQUS and is used to predict delamination under compressive loads in several test cases.

  • A thermodynamics-based Cohesive Model for interface debonding and friction
    International Journal of Solids and Structures, 2014
    Co-Authors: Irene Guiamatsia, Giang D Nguyen
    Abstract:

    Abstract not availableIrene Guiamatsia, Giang D. Nguye

Anuradha Banerjee - One of the best experts on this subject based on the ideXlab platform.

  • Simulation of fracture in a low ductility aluminum alloy using a triaxiality dependent Cohesive Model
    Engineering Fracture Mechanics, 2017
    Co-Authors: Faizan Md. Rashid, Anuradha Banerjee
    Abstract:

    Abstract In the simulation of the ductile fracture process in a low ductility aluminum alloy, the limitations of the current implementation of a stress-state dependent Cohesive Model are identified. Ductile fracture data was generated at moderate triaxiality with experiments on a range of notched bars while at high triaxiality in growth of a pre-existing mode-I crack in compact test specimens. In the corresponding finite element analysis, Cohesive elements obeying a stress-state dependent Cohesive law were introduced in the plane where material separation was expected to occur. By recognizing that the effect of Model parameters is decoupled in fracture at moderate triaxiality, a procedure is outlined to determine the unique combination of Model parameters that is shown to reproduce the experimental data for the entire range of triaxiality well. It is argued that the necessity of a plane strain core and its thickness is largely driven by the extent to which plastic deformation spreads during the growth of crack.

  • Stress-state dependent Cohesive Model for fatigue crack growth
    Frattura ed Integrità Strutturale, 2016
    Co-Authors: R. Shravan Kumar, I.s. Nijin, M. Vivek Bharadwaj, G. Rajkumar, Anuradha Banerjee
    Abstract:

    In the Cohesive framework, a stress-state dependent Cohesive Model, combined with an irreversible damage parameter has been used in simulation of fatigue crack growth initiation and continued growth. The Model is implemented as interface elements and plane strain simulations of crack initiation and growth under cyclic loading are performed. The stressstate of neighboring continuum elements is used in the traction-separation behavior of the Cohesive elements. The Model is shown to be able to reproduce the typical initiation life as well as fatigue crack growth curves. Further, the effect of the Cohesive fatigue parameter on the initiation life and crack growth rates is established. KEYWORDS. Cohesive zone Model; Fatigue; Triaxiality; Stress state.

  • Constraint Effects Using a Stress-state Dependent Cohesive Model☆
    Procedia Materials Science, 2014
    Co-Authors: Nishant Kanhurkar, Faizan Md. Rashid, Anuradha Banerjee
    Abstract:

    Abstract In the present work, constraint effects on growth curves of a mode-I crack are determined using a triaxiality dependent Cohesive Model. Plane strain elastic-plastic analysis based on the modified boundary layer formulation is performed and for Modeling the fracture process, the Cohesive parameters and the mechanical properties for a mild steel are taken from literature. From the analysis, the resistance curves for a range of constraint parameter are obtained. A discussion is developed on the effectiveness of the triaxiality dependent Model in capturing the well-known effect of constraint and also on the effect of the two Model parameters on the resistance curves.

  • Implementation and validation of a triaxiality dependent Cohesive Model: experiments and simulations
    International Journal of Fracture, 2013
    Co-Authors: Faizan Md. Rashid, Anuradha Banerjee
    Abstract:

    A recently formulated triaxiality dependent Cohesive Model for plane strain is implemented and its versatility is tested in simulation of ductile fracture of mild steel at different states of stress. The triaxiality dependent Model was implemented as linear displacement formulation based elements whose constitutive behaviour was dependent on the stress-state of the neighbouring continuum element. By comparing the experimental data and predictions of corresponding plane strain simulations, the Model parameters are estimated. The Model is shown to be effective in reproducing characteristic features of the macroscopic response of both pre-cracked as well as geometries without a preexisting nominal defect. Since the Model parameters are held constant for simulations at different stress-states, they are effectively material constants.

  • Cohesive Model in Prediction of Multi-Axial Fatigue
    Volume 12: Processing and Engineering Applications of Novel Materials, 2010
    Co-Authors: Deepak K Jha, Anuradha Banerjee
    Abstract:

    A fatigue failure Model for life assessment of a structure that incorporates the stress-state dependence and irreversible nature of fatigue damage is presented. In the frame work of Cohesive zone Model, a stress state dependent traction separation law for plane strain is taken to represent an undamaged ferritic steel. The evolution of damage has two additional fatigue parameters: a stress and a length parameter. Initially a parametric study is done to show that the Model is able to reproduce a typical uniaxial fatigue response to stress based cyclic load, that of a stress-life curve and reduction in life due to positive mean stress. The effect of the Cohesive fatigue parameters on the characteristics of the stress-life curve is then established. The Model is further applied for a range of sinusoidally varying in-phase stress states which are characterised by a fixed bi-axiality ratio. The initiation and growth of damage is shown to be more rapid for higher bi-axiality. Except for stress amplitudes in which the lower bi-axiality case has conditions close to monotonic failure, the effect of bi-axiality is shown to be detrimental to the life expectancy of the material as observed in available experimental literature.© 2010 ASME

Kaixin Liu - One of the best experts on this subject based on the ideXlab platform.

  • Crack propagation in viscoplastic polymers: Heat generation in near-tip zone and viscoplastic Cohesive Model
    Applied Physics Letters, 2015
    Co-Authors: Yuansha Chen, Kaixin Liu
    Abstract:

    We develop a precise experimental method to measure the full-field heat-generating process near moving (mode I) crack tips in polycarbonate films and present the experimental image of crack tip structure in viscoplastic polymers. A viscoplastic Cohesive Model is constructed to analyze the mechanical state and temperature increase in near-tip zone during steady crack propagation. The Cohesive stress in this Model is uniquely characterized by viscoplastic constitutive equation instead of traction-separation displacement relationship or constant yield stress, which greatly differs from previous Models. Our proposed Model's prediction of temperature increase agrees well with the experimental result.

Ahmed Elmarakbi - One of the best experts on this subject based on the ideXlab platform.

  • numerical simulation of damages in frp laminated structures under transverse quasi static or low velocity impact loads
    2013
    Co-Authors: Ahmed Elmarakbi, Hisao Fukunaga, Yaolu Liu, Satoshi Atobe, Tomonori Watanabe
    Abstract:

    This chapter addresses the numerical Modelling and simulations of the occurrence and propagation of damages in fibre reinforced plastic (FRP) laminated structures under transverse quasi‐static or low‐velocity impact loadings. The focus of the chapter is on the key issue of numerical Modelling of delamination using Cohesive elements, which is a conventional difficulty due to numerical instability in the simulation process. To overcome this numerical instability, several recent achievements of effective numerical approaches are proposed and reported here. The chapter describes three kinds of techniques to improve the stability and accuracy and to decrease the computational cost of the traditional Cohesive Model. These techniques include: (i) artificial damping technique for the explicit time integration scheme, (ii) move‐limit technique, and (iii) a new adaptive Cohesive Model and its extension into rate‐dependent problems. A low‐velocity impact example is used to show the effectiveness of the adaptive Cohesive Model.

  • a new Cohesive Model for simulating delamination propagation in composite laminates under transverse loads
    Mechanics of Materials, 2008
    Co-Authors: Yutaka Zemba, Hisao Fukunaga, Tomonaga Okabe, Cheng Yan, Ahmed Elmarakbi
    Abstract:

    In this paper, we propose a new Cohesive Model to stably and accurately simulate the delamination propagations in composite laminates under quasi-static and low-velocity impact transverse loads using comparatively coarse meshes. In this Model, a pre-softening zone ahead of the existing traditional softening zone is proposed. In this pre-softening zone, the initial stiffnesses and the interface strengths at the integration points of Cohesive elements are gradually reduced as the corresponding effective relative displacements at these points increase. However, the onset displacement corresponding to the onset damage is not changed in this Model. Moreover, the fracture toughness of materials for determining the final displacement of complete decohesion is kept constant. This Cohesive Model is implemented in the explicit time integration scheme combined with a powerful three-dimensional (3D) hybrid finite element for evaluating the delamination propagations on interfaces in composite laminates. A DCB problem is employed to analyze the characteristics of the present Cohesive Model. In order to reduce the computational cost for dealing with more complex problems, a stress-based criterion is also adopted in our numerical Model for evaluating various in-plane damages, such as matrix cracks, fiber breakage, etc. Finally, two experimental examples are employed to illustrate the validity of the present approach.

  • A New Rate-Dependent Cohesive Model for Simulating Dynamic Composite Delamination
    2007
    Co-Authors: Ahmed Elmarakbi, Ning Hu, Hisao Fukunaga
    Abstract:

    A new eight-node adaptive rate-dependent Cohesive element is proposed in this paper. In this Model, a pre-softening zone is proposed ahead of the existing softening zone. In this pre-softening zone, the initial stiffness and the interface strength are gradually decreased. The onset displacement corresponding to the onset damage is not changed in the proposed Model. In addition, the critical energy release rate of the materials is kept constant. Moreover, the constitutive equation of the new Cohesive Model is developed to be depended on the opening velocity of the displacement jump. The traction based Model includes a Cohesive zone viscosity parameter (η) to vary the degree of rate dependence and to adjust the maximum traction. The new Cohesive element is implemented in LS-DYNA as a user defined material subroutine (UMAT) designed for solid elements. The numerical simulation results of DCB in Mode-I is presented to illustrate the validity of the new Model. It is shown that the proposed Model brings stable simulations and can be widely used in quasi-static, dynamic and impact problems.

Irene Guiamatsia - One of the best experts on this subject based on the ideXlab platform.

  • a thermodynamics based Cohesive Model for interface debonding and friction
    International Journal of Solids and Structures, 2014
    Co-Authors: Irene Guiamatsia, Giang D Nguyen
    Abstract:

    Abstract A constitutive Model for interface debonding is proposed which is able to account for mixed-mode coupled debonding and plasticity, as well as further coupling between debonding and friction including post-delamination friction. The work is an extension of a previous Model which focuses on the coupling between mixed-mode delamination and plasticity. By distinguishing the interface into two parts, a cracked one where friction can occur and an integral one where further damage takes place, the coupling between frictional dissipation and energy loss through damage is seamlessly achieved. A simple framework for coupled dissipative processes is utilised to derive a single yield function which accurately captures the evolution of interface strength with increasing damage, for both tensile and compressive regimes. The new material Model is implemented as a user-defined interface element in the commercial package ABAQUS and is used to predict delamination under compressive loads in several test cases.

  • A thermodynamics-based Cohesive Model for interface debonding and friction
    International Journal of Solids and Structures, 2014
    Co-Authors: Irene Guiamatsia, Giang D Nguyen
    Abstract:

    Abstract not availableIrene Guiamatsia, Giang D. Nguye