The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Kaixin Liu - One of the best experts on this subject based on the ideXlab platform.
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Crack propagation in viscoplastic polymers: Heat generation in near-tip zone and viscoplastic cohesive model
Applied Physics Letters, 2015Co-Authors: Yuansha Chen, Kaixin LiuAbstract: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.
Yuansha Chen - One of the best experts on this subject based on the ideXlab platform.
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Crack propagation in viscoplastic polymers: Heat generation in near-tip zone and viscoplastic cohesive model
Applied Physics Letters, 2015Co-Authors: Yuansha Chen, Kaixin LiuAbstract: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.
Guido Borino - One of the best experts on this subject based on the ideXlab platform.
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Integration of finite Displacement interface element in reference and current configurations
Meccanica, 2017Co-Authors: Francesco Parrinello, Guido BorinoAbstract:In the present paper the non-linear behaviour of a solid body with embedded cohesive interfaces is examined in a finite Displacements context. The principal target is the formulation of a two dimensional interface finite element which is referred to a local reference frame, defined by normal and tangential unit vectors to the interface middle surface. All the geometric operators, such as the interface elongation and the reference frame, are computed as function of the actual nodal Displacements. The constitutive cohesive law is defined in terms of Helmholtz free energy for unit undeformed interface surface and, in order to obtain the same nodal force vector and stiffness matrix by the two integration schemes, the cohesive law in the deformed configuration is defined in terms of Cauchy traction, as a function of Separation Displacement and of interface elongation. Explicit expression of the nodal force vector is integrated either over the reference configuration or over the current configuration, which is shown to produce the same analytical finite element operators. No differences between the integration carried out in the reference and in the current configuration are shown, provided that elongation of the interface is taken in to account.
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Mixed Mode Delamination Analysis by a Thermodynamically Consistent Cohesive Interface Model with Independent Mode I and Mode II Fracture Energies
Procedia Engineering, 2015Co-Authors: Francesco Parrinello, Giuseppe Vincenzo Marannano, Guido BorinoAbstract:Abstract In the present paper a new thermodynamically consistent cohesive interface model is proposed; it based on a predefined Helmhotz free energy with a single scalar damage variable and produces two independent fracture energies, in pure mode I and pure mode II debonding conditions. The proposed model can also take in to account the frictional effects with a smooth transition of the mechanical behaviour, from the initial cohesive one of the sound material, to the frictional one of the fully debonded interface. The cohesive-frictional behaviour is based on the mesoscale geometric interpretation of the scalar damage variable, which distinguish sound and debonded fractions of a representative surface element of the interface. The proposed formulation is defined by a damage activation function, which depends on the Separation Displacement. Traction components, damage evolution and the relevant constitutive equations are derived by following the classical Noll and Coleman procedure, and the model implicitly verify the second thermodynamic law by proving that dissipation is non-negative for any loading path. The numerical simulations of mixed mode delamination tests are performed and compared to the experimental results, for different mixed mode ratio.
H Ghonem - One of the best experts on this subject based on the ideXlab platform.
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some issues in the application of cohesive zone models for metal ceramic interfaces
International Journal of Solids and Structures, 2002Co-Authors: Namas Chandra, C Shet, H GhonemAbstract:Abstract Cohesive zone models (CZMs) are being increasingly used to simulate discrete fracture processes in a number of homogeneous and inhomogeneous material systems. The models are typically expressed as a function of normal and tangential tractions in terms of Separation distances. The forms of the functions and parameters vary from model to model. In this work, two different forms of CZMs (exponential and bilinear) are used to evaluate the response of interfaces in titanium matrix composites reinforced by silicon carbide (SCS-6) fibers. The computational results are then compared to thin slice push-out experimental data. It is observed that the bilinear CZM reproduces the macroscopic mechanical response and the failure process while the exponential form fails to do so. From the numerical simulations, the parameters that describe the bilinear CZM are determined. The sensitivity of the various cohesive zone parameters in predicting the overall interfacial mechanical response (as observed in the thin-slice push out test) is carefully examined. Many researchers have suggested that two independent parameters (the cohesive energy, and either of the cohesive strength or the Separation Displacement) are sufficient to model cohesive zones implying that the form (shape) of the traction–Separation equations is unimportant. However, it is shown in this work that in addition to the two independent parameters, the form of the traction–Separation equations for CZMs plays a very critical role in determining the macroscopic mechanical response of the composite system.
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Some issues in the application of cohesive zone models for metal–ceramic interfaces
International Journal of Solids and Structures, 2002Co-Authors: Namas Chandra, C Shet, H GhonemAbstract:Abstract Cohesive zone models (CZMs) are being increasingly used to simulate discrete fracture processes in a number of homogeneous and inhomogeneous material systems. The models are typically expressed as a function of normal and tangential tractions in terms of Separation distances. The forms of the functions and parameters vary from model to model. In this work, two different forms of CZMs (exponential and bilinear) are used to evaluate the response of interfaces in titanium matrix composites reinforced by silicon carbide (SCS-6) fibers. The computational results are then compared to thin slice push-out experimental data. It is observed that the bilinear CZM reproduces the macroscopic mechanical response and the failure process while the exponential form fails to do so. From the numerical simulations, the parameters that describe the bilinear CZM are determined. The sensitivity of the various cohesive zone parameters in predicting the overall interfacial mechanical response (as observed in the thin-slice push out test) is carefully examined. Many researchers have suggested that two independent parameters (the cohesive energy, and either of the cohesive strength or the Separation Displacement) are sufficient to model cohesive zones implying that the form (shape) of the traction–Separation equations is unimportant. However, it is shown in this work that in addition to the two independent parameters, the form of the traction–Separation equations for CZMs plays a very critical role in determining the macroscopic mechanical response of the composite system.
Eric R. Mueller - One of the best experts on this subject based on the ideXlab platform.
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optimized measurements of unmanned air vehicle mass moment of inertia with a bifilar pendulum
AIAA Guidance Navigation and Control Conference and Exhibit, 2009Co-Authors: Matt R. Jardin, Eric R. MuellerAbstract:A bifilar (two-wire) pendulum is a torsional pendulum consisting of a test object suspended by two thin parallel wires. The pendulum oscillates about the vertical axis. The restoring torque of the bifilar pendulum is provided by the gravitational force as rotations from the rest state cause the test object to raise slightly. The mass moment of inertia is computed using dynamic modeling, measurements of the oscillation period, and the physical dimensions of the bifilar pendulum such as the length and Separation Displacement of the pendulum wires. A simulation technique is described that improves estimates of the mass moment of inertia by considering the nonlinear effects of damping and large angular Displacements. An analysis of the error variance of mass moment of inertia measurements is also described. The resulting expression for the error variance is used to optimize the physical parameters of the bifilar pendulum to obtain the moment of inertia measurement with the minimum error variance. Monte Carlo simulations were used to validate the parameter optimization technique. Experimental results are presented for a uniform-density test object for which the moment of inertia is straightforward to compute from geometric considerations. Results are also presented for a small unmanned air vehicle, which was the intended application for this moment of inertia measurement technique.
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Optimized Measurements of UAV Mass Moment of Inertia with a Bifilar Pendulum
AIAA Guidance Navigation and Control Conference and Exhibit, 2007Co-Authors: Matt R. Jardin, Eric R. MuellerAbstract:A bifilar (two-wire) pendulum is a torsional pendulum consisting of a test object suspended by two thin parallel wires. The pendulum oscillates about the vertical axis. The restoring torque of the bifilar pendulum is provided by the gravitational force as rotations from the rest state cause the test object to raise slightly. The mass moment of inertia is computed using dynamic modeling, measurements of the oscillation period, and the physical dimensions of the bifilar pendulum such as the length and Separation Displacement of the pendulum wires. A simulation technique is described that improves estimates of the mass moment of inertia by considering the nonlinear effects of damping and large angular Displacements. An analysis of the error variance of mass moment of inertia measurements is also described. The resulting expression for the error variance is used to optimize the physical parameters of the bifilar pendulum to obtain the moment of inertia measurement with the minimum error variance. Monte Carlo simulations were used to validate the parameter optimization technique. Experimental results are presented for a uniform-density test object for which the moment of inertia is straightforward to compute from geometric considerations. Results are also presented for a small unmanned air vehicle, which was the intended application for this moment of inertia measurement technique.
