A Density-Dependent Modified Doraivelu Model for the Cold Compaction of Poly (Ether Ketone Ketone) Powders

The cold compaction of poly (ether ketone ketone) (PEKK) powder was studied by experiments and simulations based on the modified Doraivelu model. Although this model can successfully predict the compaction behavior of metal powders, discussion of the prediction of polymer powders is lacking. Based on the mechanical theory of metal plasticity, the modified Doraivelu model was established by introducing the material parameters m and n. The modified model can predict the compaction density of PEKK powder during cold compaction. A sub-increment method for this constitutive model was then established and implemented into a finite-element model by using the user-defined material subroutine UMAT in ABAQUS/Standard. Consequently, the material parameters of the modified Doraivelu model were identified by an inverse method using the experimental data and simulation results. It was found that when m = 0, n = 4, and the initial relative density was 0.4485, the simulation results were the closest to the experimental ones.

Numerical Tensile Damage Procedure Analysis of Angle-Ply Laminate Using Multi-Scale RVEs with Smear Crack Models

This paper reported the tensile failure strengths and damage procedure of composite laminate manufactured from the toughened-epoxy T800 prepreg at multi-scale levels. According to the exterior and interior distinction of each layer in laminate, the macro/mesoscale representative volume element (macro-RVE, meso-RVE) was first constructed, respectively. Then the micro-scale representative volume element (micro-RVE) with a hexagonal fiber-packed pattern in the interior zone of each layer in the laminate was finally determined on the principle of the same fiber volume fraction between the composite laminate and multi-scale RVEs. In the multi-RVEs analysis, the mechanical failure strengths of each scale model were transmitted from the last-scale model’s homogenization, such as the meso-RVE from micro-RVE and the macro-RVE from meso-RVE. Based on our previous report, the innovative multi-scale damage and post-damage models on the concept of the smear crack were improved fully and incorporated by user-defined material subroutines (UMATs), such as in the addition of multiple cracks co-coupled, which makes it predict the element damage procedure. The averaged mechanical responses with damage mechanism of multi-scale RVEs under tensile, compressive, or shear loadings were obtained wholly by the homogenization method. The macroscale tensile damage initiation and propagation procedure were analyzed in detail including their global/local responses, being extended to comparison with experimental results.

Characterization of Mechanical Heterogeneity in Dissimilar Metal Welded Joints

Dissimilar metal welded joints (DMWJs) possess significant localized mechanical heterogeneity. Using finite element software ABAQUS with the User-defined Material (UMAT) subroutine, this study proposed a constitutive equation that may be used to express the heterogeneous mechanical properties of the heat-affected and fusion zones at the interfaces in DMWJs. By eliminating sudden stress changes at the material interfaces, the proposed approach provides a more realistic and accurate characterization of the mechanical heterogeneity in the local regions of DMWJs than existing methods. As such, the proposed approach enables the structural integrity of DMWJs to be analyzed in greater detail.

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.

Anisotropic and strain rate-dependent mechanical properties and constitutive modeling of the cancellous bone from piglet cervical vertebrae

BACKGROUND AND OBJECTIVE

Characterizing the mechanical properties of the cancellous bone from the cervical vertebrae of child or child surrogate is important for the development of spine finite element models and the investigation of injury mechanism, however, there is currently no public data available as far as we know.

METHODS

Compression tests were conducted on the specimens from the cervical vertebrae of 8-week-old piglets (child surrogates) in axial and radial directions at the strain rates of 0.01, 0.1, 1 and 10/s. The influences of directionality and strain rate on the mechanical properties of the vertebral cancellous bone were statistically investigated. The typical transversely isotropic model, which was added a strain rate item and a plasticity item, was implemented into LS-DYNA finite element code. Based on the material subroutine code, simulation was conducted on the vertebral tissue under compression in axial and radial directions at different strain rates.

RESULTS

The mechanical properties of the cancellous bone of cervical vertebrae were obtained and most of the stress-strain curves showed major linear elastic stage and short plastic stage before fracture. Significant anisotropic behavior was observed for the vertebral tissue in axial and radial directions. The elastic modulus, ultimate stress,yield stress, and ultimate strain of the speimens in axial direction was obtained, with on average, 2.5 ± 0.6 times, 2.1 ± 0.15 times, and 2.1 ± 0.1 times higher and 0.86 ± 0.076 times lower respecitvely, than those in radial direction. In addition, with the strain rate varying from 0.01/s to 10/s, the mechanical parameters, like elastic modulus, yield and ultimte stresses exhibited significant strain rate effect, however, no significant difference was found for the ultimate strain.

CONCLUSIONS

The cervical vertebrae showed significant anisotropic and strain rate-dependent behaviors. The self-developed subroutine codes based on the strain rate-dependent transversely isotropic elastic and plastic constitutive model can simulate the behaviors well.

Source codes and simulation data for the finite element implementation of the conventional and localizing gradient damage methods in ABAQUS

This data article presents the source codes and obtained simulation data for running numerical fracture simulation in the commercial finite element package, ABAQUS. The computational models implemented through these source codes pertain to the conventional and localizing gradient damage method which are used for the modelling of the fracture phenomena in the components and structures. For a detailed description refer to "A comparative study and ABAQUS Implementation of Conventional and Localizing Gradient Enhanced Damage Models [1]". The implementation is carried out using a feature in the ABAQUS software called the user defined subroutines. The subroutines are a set of coded files which are used to implement any newly developed computational models depicting actual physical phenomena which are not already available in any commercial software. The user subroutines used in this implementations are UEL and UMAT. The present implementation is very user friendly in the sense that the user needs to just type a couple of commands in the ABAQUS command application to run the simulations. Moreover, the ability of the ABAQUS to run large scale simulations using a very sparse amount of computational resources enables researchers and engineers with limited resources to take advantage of a very advanced computational fracture simulation technique.