The formation of a liquid plug inside a human airway, known as airway closure, is computationally studied by considering the elastoviscoplastic (EVP) properties of the pulmonary mucus covering the ...airway walls for a range of liquid film thicknesses and Laplace numbers. The airway is modeled as a rigid tube lined with a single layer of an EVP liquid. The Saramito–Herschel–Bulkley (Saramito-HB) model is coupled with an Isotropic Kinematic Hardening model (Saramito-HB-IKH) to allow energy dissipation at low strain rates. The rheological model is fitted to the experimental data under healthy and cystic fibrosis (CF) conditions. Yielded/unyielded regions and stresses on the airway wall are examined throughout the closure process. Yielding is found to begin near the closure in the Saramito-HB model, whereas it occurs noticeably earlier in the Saramito-HB-IKH model. The kinematic hardening is seen to have a notable effect on the closure time, especially for the CF case, with the effect being more pronounced at low Laplace numbers and initial film thicknesses. Finally, standalone effects of rheological properties on wall stresses are examined considering their physiological values as baseline.
•Kinematic hardening captures non-Newtonian behavior of pulmonary mucus accurately.•Kinematic hardening yields earlier airway closure especially at low Laplace numbers.•The mucus yield stress is a prominent factor for airway closure time.•Post closure relaxation of stresses is particularly affected by polymeric viscosity.
The present study intends to characterize ratcheting response of several steel alloys subject to asymmetric loading cycles through coupling the Ahmadzadeh‐Varvani kinematic hardening rule with ...isotropic hardening rules of Lee and Zavrel, Chaboche, and Kang. The Ahmadzadeh‐Varvani kinematic hardening rule was developed to address ratcheting progress over asymmetric stress cycles with relatively a simple framework and less number of coefficients. Inclusion of isotropic hardening rules to the framework improved ratcheting response of materials mainly over the first stage of ratcheting. Lee and Zavrel model (ISO‐I) developed an exponential function to account for accumulated plastic strain as yield surface is expanded over stage I and early stage II of ratcheting. Isotropic models by Chaboche (ISO‐II) and Kang (ISO‐III) encountered yield surface evolution in the framework by introducing an internal variable that takes into account the prior maximum plastic strain range. The choice of isotropic hardening model coupled to the kinematic hardening model is highly influenced by material softening/hardening response.
A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an ...infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress–strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media.
Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.
•Distinct behavioral characteristics of HSD were investigated based on loading type.•Focusing on real-world applications, the impact of different variables was evaluated.•Damage and cracks were found ...to be evenly distributed over the height of the strips.•A hysteretic model using a combined isotropic–kinematic hardening rule was proposed.•The hysteresis loop and dissipated energy were well predicted by the proposed model.
An hourglass-shaped strip damper (HSD) was proposed to improve on the conventional slit damper. The damper has non-uniform strips which have a smaller cross-sectional area close to the middle height. To find the structural capacities of HSD subjected to monotonic and cyclic loadings, experimental tests were carried out in this study. Test parameters were loading rate, material strength, and the number of damper plates. The results showed substantial load–resistance capacity under monotonic loadings, and excellent ductility and energy dissipation were exhibited under cyclic loadings, with even distribution of damage over the entire height of strips. Based on the test results, a simple hysteretic model using a combined isotropic–kinematic hardening rule was also proposed. The comparison demonstrated that it represents the tested cyclic load–displacement hysteresis well. It is expected that the proposed model can be successfully used to predict the behavior of HSD in real-world applications.
We present a generalised phase field-based formulation for predicting fatigue crack growth in metals. The theoretical framework aims at covering a wide range of material behaviour. Different fatigue ...degradation functions are considered and their influence is benchmarked against experiments. The phase field constitutive theory accommodates the so-called AT1, AT2 and phase field-cohesive zone (PF-CZM) models. In regards to material deformation, both non-linear kinematic and isotropic hardening are considered, as well as the combination of the two. Moreover, a monolithic solution scheme based on quasi-Newton algorithms is presented and shown to significantly outperform staggered approaches. The potential of the computational framework is demonstrated by investigating several 2D and 3D boundary value problems of particular interest. Constitutive and numerical choices are compared and insight is gained into their differences and similarities. The framework enables predicting fatigue crack growth in arbitrary geometries and for materials exhibiting complex (cyclic) deformation and damage responses. The finite element code developed is made freely available at www.empaneda.com/codes.
•We present a generalised, phase field-based fatigue model for elasto-plastic solids.•Cyclic deformation is modelled by a combined non-linear kinematic/isotropic hardening law.•Three classes of phase field models are considered: AT1, AT2 and PF-CZM.•A quasi-Newton algorithm is used to enable a robust and efficient monolithic scheme.•The potential of the model is showcased with paradigmatic 2D and 3D case studies.
The Bounding Surface (BS) plasticity model for metals is modified according to the proposition introduced in the works of Burlet and Cailletaud (1986) and Delobelle (1993) for the kinematic hardening ...of a classical Armstrong/Frederick (AF) model, called the BCD modification from the initials of the foregoing authors. The BCD modification was introduced in the relative kinematic hardening between Yield Surface (YS) and BS, unlike its introduction in the absolute and single kinematic hardening of YS for an AF model, hence, achieving two objectives: first, maintaining the inherent feature of BS for decoupling plastic modulus and direction of kinematic hardening, and, second, allowing a flexibility as to the relative kinematic hardening direction without altering the value of the plastic modulus, a property of BCD modification. In addition, the introduced BCD modification for the BS is significantly modified itself, by introducing a properly varying modification parameter instead of the fixed one used in the original works. This simple feature of the novel BCD modification provides a dramatically improved capability to simulate multiaxial ratcheting (MR), because it affects directly the changing flow rule direction, due to the relative kinematic hardening, during complex multiaxial loading, without sacrificing accurate simulations under uniaxial ratcheting (UR) since the plastic modulus is not affected. An additional significant contribution to successful UR simulations is provided by the free-to-choose kinematic hardening of the BS, since the BCD modification is applied only to the relative kinematic hardening between BS and YS. The new model, named SANIMETAL-BCD, is shown to yield superior or equal simulations of UR and very complex MR experimental data for three Carbon Steel specimens, in comparison with other models, within a much simpler constitutive framework. Shortcomings and future necessary improvements are discussed in details.
•The multiaxial formulation of a modified bounding surface plasticity is presented.•A novel BCD modification is presented.•The new model, named SANIMETAL-BCD is validated against uniaxial and multiaxial ratcheting experiments.•A discussion about the model’s capabilities and limitations is finally presented.
This paper evaluates the performance of four Ohno–Wang type constitutive models in predicting ratcheting responses of medium carbon steel S45C for a set of axial/torsional loading paths. Suggestions ...are also made for further modification. The four models are the Ohno–Wang model, the McDowell model, the Jiang–Sehitoglu model and the AbdelKarim–Ohno model. It is shown that the Ohno–Wang model and the McDowell model overestimate the multiaxial ratcheting. Whereas, the Jiang–Sehitoglu model yields good predictions for most loading conditions used in this study with an appropriate modification of the dynamic recovery term. The AbdelKarim–Ohno model gives acceptable predictions for all considered multiaxial conditions when used with an evolution function for
μ
i
, but gives poor predictions of uniaxial ratcheting if the parameter
μ
i
is determined from a multiaxial ratcheting response. A new modified Ohno–Wang hardening rule is proposed for better adaptability under diverse situations by multiplying a factor to the dynamic recovery term, which is dependent on noncoaxiality of the plastic strain rate and back stress. This new model predicts ratcheting strain reasonably well for the test cases.
•A peridynamic plasticity model with various hardenings is proposed for cyclic load.•Equivalent plastic stretch is used as internal variable for different hardenings.•The modified kinematic hardening ...is based on a scalar-valued internal variable.•Numerical method is proposed to solve the elasto-plastic peridynamic equations.•The results of peridynamic model are in good agreement with corresponding FEM ones.
In this study, an elastoplastic model based on ordinary state-based peridynamic theory is presented. The von Mises yield criteria is used to describe plastic yielding and the equivalent plastic stretch is utilized as internal variable for the general form of isotropic hardening, the modified form of kinematic hardening and the mixed of isotropic and kinematic hardening. Like classical approach to plasticity, a plastic flow rule is proposed based on the yield function. The proposed plastic model is described in the thermodynamic framework and it is shown that the proposed plastic flow and hardening of the peridynamic model are satisfied the requirements of the second law of thermodynamics. The proposed plastic model is rate-independent and the quasi-static analysis is considered. A numerical approach is proposed for the elastoplastic model and Newton Raphson algorithm is used to solve the nonlinear peridynamic equations. The numerical validation of proposed peridynamic models are done by comparing the results of 2-D peridynamic models under cyclic loading with the results of finite element methods based on the classical local continuum mechanic assumptions. The numerical results show that the proposed PD elastoplastic model can predict plastic yielding and linear/nonlinear hardening of materials beyond initial yield stress accurately. Moreover, it is observed that the presented method it is capable of modeling the kinematic hardening and Bauschinger effect in cyclic loading too.
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