A new cure kinetics model to simulate thermomechanical behavior of polymeric sealants for automotive applications

Accurate prediction of the cure level of thermoset polymers is essential to simulate the thermomechanical behavior of polymeric thermoset sealants, which is strongly dependent on cure level. Conventional cure kinetics models, however, fail to accurately predict the cure levels of thermoset sealants subjected to a complex temperature program. Herein, we propose a new cure kinetics model that greatly enhances cure level predictability by considering temperature derivatives. The validity of our model was verified by simulating the thermomechanical behavior of a polymeric sealant using a user material subroutine (UMAT) of ABAQUS software. Experimental results from an appropriately designed thermomechanical test were compared with simulation results obtained from the UMAT.

A Unified Abaqus Implementation of the Phase Field Fracture Method Using Only a User Material Subroutine

We present a simple and robust implementation of the phase field fracture method in Abaqus. Unlike previous works, only a user material (UMAT) subroutine is used. This is achieved by exploiting the analogy between the phase field balance equation and heat transfer, which avoids the need for a user element mesh and enables taking advantage of Abaqus’ in-built features. A unified theoretical framework and its implementation are presented, suitable for any arbitrary choice of crack density function and fracture driving force. Specifically, the framework is exemplified with the so-called AT1, AT2 and phase field-cohesive zone models (PF-CZM). Both staggered and monolithic solution schemes are handled. We demonstrate the potential and robustness of this new implementation by addressing several paradigmatic 2D and 3D boundary value problems. The numerical examples show how the current implementation can be used to reproduce numerical and experimental results from the literature, and efficiently capture advanced features such as complex crack trajectories, crack nucleation from arbitrary sites and contact problems. The code developed is made freely available.

Coupled Thermomechanical Responses of Zirconium Alloy System Claddings under Neutron Irradiation

Zirconium (Zr) alloy is a promising fuel cladding material used widely in nuclear reactors. Usually, it is in service for a long time under the effects of neutron radiation with high temperature and high pressure, which results in thermomechanical coupling behavior during the service process. Focusing on the UO2/Zr fuel elements, the macroscopic thermomechanical coupling responses of pure Zr, Zr-Sn, and Zr-Nb binary system alloys, as well as Zr-Sn-Nb ternary system alloy as cladding materials, were studied under neutron irradiation. As a heat source, the thermal conductivity and thermal expansion coefficient models of the UO2 core were established, and an irradiation growth model of a pure Zr and Zr alloy multisystem was built. Based on the user material subroutine (UMAT) with ABAQUS, the current theoretical model was implemented into the finite element framework, and the consequent thermomechanical coupling behavior under irradiation was calculated. The distribution of temperature, the stress field of the fuel cladding, and their evolution over time were analyzed. It was found that the stress and displacement of the cladding were sensitive to alloying elements due to irradiated growth.

Development and application of hyperelastic model for diaphragm considering the influence of temperature

The basic mechanical properties of a diaphragm under various temperatures in hot diaphragm preforming of composites are obtained by uniaxial tensile tests. A constitutive model considering the influence of temperature is accordingly developed to characterize its large deformation behavior. Model parameters are obtained by nonlinear fitting experiment data. The constitutive model is implemented in ABAQUS through the user material subroutine UHYPER. The developed constitutive model is verified by simulating the covering deformation of the diaphragm over a C-type mold. Finally, as an application of the developed hyperelastic model, an optimal design of a support bar in the hot diaphragm preforming process is implemented. The constitutive model lays a solid foundation for the finite element simulation and process optimization of the hot diaphragm forming (HDF) of carbon composites.

On Finite Element Implementation of Polyconvex Incompressible Hyperelasticity: Theory, Coding and Applications

This work concerns mainly the finite element (FE) implementation of polyconvex incompressible hyperelastic models. A user material subroutine (UMAT) has been developed and can be utilized to define the aforementioned material behaviors in the FE system ABAQUS. The subroutine is written using a novel strategy in order to maximally simplify the relations for the analytical material Jacobian (MJ). The UMAT code is attached in the appendix. The developed subroutine allows to significantly decrease the time of computations and to avoid possible convergence difficulties. The structure of the code enables modifications which may lead to a rheological, damage or growth models, for instance.

Anisotropic Nonlinear Elastic Model of Concrete and Secondary Development in ABAQUS

In order to solve the convergence problem of concrete constitutive in the softening phase, an anisotropic nonlinear elastic constitutive model (ANECM) was proposed, which was developed based on the uniaxial concrete constitutive relation in the Chinese code for design of concrete structures (GB 50010-2010). The user material subroutine (UMAT) based on ANECM is developed in ABAQUS software. The above UMAT is applied to analyze a simulation model in ABAQUS software. The result shows that compared to the default plastic-damage concrete constitutive in ABAQUS, ANECM is an effective and appropriate model to simulate the performance of concrete and it has improved the convergence problem.

A continuum constitutive model for mechanical behavior of 5052 resin epoxy containing various percentages of MWCNTs

In this article, a continuum-based constitutive model is developed to predict the mechanical behavior of 5052 resin epoxy reinforced by multiwalled carbon nanotubes (MWCNTs) based on experimentally generated data. For this purpose, MWCNTs/epoxy specimens with various percentages of functionalized and nonfunctionalized MWCNTs are prepared. The SEM graphs indicate that functionalization leads to a better bound between epoxy and MWCNTs and a higher level of dispersion. The specimens are then tested under standard ASTM D638-02 a procedure and their true plastic stress–strain curves are extracted. Investigations on experimentally generated data reveal that a wt% dependent equation which is obtained using any two series of these data can be successfully implemented for others. The equation is then implemented into a finite element software using a developed user material subroutine in which is utilized based on a particular solution algorithm. In order to verify the accuracy of the model some tensile as well as load-unload-reload tension tests are performed according to standard conditions and acceptable agreement between the numerical and experimental results are observed. Results also indicate that the proposed empirical model can precisely predict the stress–strain behavior of 5052 resin epoxy containing arbitrary wt% of MWCNTs in the range 0–1 wt%.

Remodeling of the Mandibular Bone Induced by Overdentures Supported by Different Numbers of Implants

The objective of this study was to investigate the process of mandibular bone remodeling induced by implant-supported overdentures. computed tomography (CT) images were collected from edentulous patients to reconstruct the geometry of the mandibular bone and overdentures supported by implants. Based on the theory of strain energy density (SED), bone remodeling models were established using the user material subroutine (UMAT) in abaqus. The stress distribution in the mandible and bone density change was investigated to determine the effect of implant number on the remodeling of the mandibular bone. The results indicated that the areas where high Mises stress values were observed were mainly situated around the implants. The stress was concentrated in the distal neck region of the distal-most implants. With an increased number of implants, the biting force applied on the dentures was almost all taken up by implants. The stress and bone density in peri-implant bone increased. When the stress reached the threshold of remodeling, the bone density began to decrease. In the posterior mandible area, the stress was well distributed but increased with decreased implant numbers. Changes in bone density were not observed in this area. The computational results were consistent with the clinical data. The results demonstrate that the risk of bone resorption around the distal-most implants increases with increased numbers of implants and that the occlusal force applied to overdentures should be adjusted to be distributed more in the distal areas of the mandible.

Crystallographic effects during micromachining — A finite-element model

Mechanical micromachining is a powerful and effective way for manufacturing small sized machine parts. Even though the micromachining process is similar to the traditional machining, the material behavior during the process is much different. In particular, many researchers report that the basic mechanics of the work material is affected by microstructures and their crystallographic orientations. For example, crystallographic orientations of the work material have significant influence on force response, chip formation and surface finish. In order to thoroughly understand the effect of crystallographic orientations on the micromachining process, finite-element model (FEM) simulating orthogonal cutting process of single crystallographic material was presented. For modeling the work material, rate sensitive single crystal plasticity of face-centered cubic (FCC) crystal was implemented. For the chip formation during the simulation, element deletion technique was used. The simulation model is developed using ABAQUS/explicit with user material subroutine via user material subroutine (VUMAT). Simulations showed that variation of the specific cutting energy at different crystallographic orientations of work material shows significant anisotropy. The developed FEM model can be a useful prediction tool of micromachining of crystalline materials.

Numerical Simulation of Ballistic Performance of Nanocrystalline and Nanotwinned Ultrafine Crystal Steel

Surface mechanical attrition treatment (SMAT) is an excellent method to get nanocrystalline and nanotwinned ultrafine crystalline steels from coarse-grained AISI 304 stainless steel. Due to their outstanding mechanical properties, they both appear to be relevant candidates for ballistic protection of marine engineering. Comparing their ballistic performance against coarse-grained steel, as well as identifying the effect of the hybridization with a carbon fiber–epoxy composite layer have been done by Jaime Frontan et al. Hybridization is proposed as a way to improve the nanocrystalline brittle properties in a similar way as is done with ceramics in other protection systems. Dur to the limit of experimental equipment, there are many results which are hardly got. In this paper, a numerical method with Johnson–Cook flow stress model, user material subroutine VUMAT and surface-based cohesive behaviour is presented.