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Brown, Arthur A.

Publications and source records attributed to Brown, Arthur A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A thermal-mechanical finite element workflow for directed energy deposition additive manufacturing process modeling

This work proposes a finite element (FE) analysis workflow to simulate directed energy deposition (DED) additive manufacturing at a macroscopic length scale (i.e. part length scale) and to predict thermal conditions during manufacturing, as well as distortions, strength and residual stresses at the completion of manufacturing. The proposed analysis method incorporates a multi-step FE workflow to elucidate the thermal and mechanical responses in laser engineered net shaping (LENS) manufacturing. For each time step, a thermal element activation scheme captures the material deposition process. Then, activated elements and their associated geometry are analyzed first thermally for heat flow due to radiation, convection, and conduction, and then mechanically for the resulting stresses, displacements, and material property evolution. Finally, simulations agree with experimentally measured in situ thermal measurements for simple cylindrical build geometries, as well as general trends of local hardness distribution and plastic strain accumulation (represented by relative distribution of geometrically necessary dislocations).

42 ENGINEERING↗
DOE OSTI2016

Sandia fracture challenge 2: Sandia California's modeling approach

The second Sandia Fracture Challenge illustrates that predicting the ductile fracture of Ti-6Al-4V subjected to moderate and elevated rates of loading requires thermomechanical coupling, elasto-thermo-poro-viscoplastic constitutive models with the physics of anisotropy and regularized numerical methods for crack initiation and propagation. We detail our initial approach with an emphasis on iterative calibration and systematically increasing complexity to accommodate anisotropy in the context of an isotropic material model. Blind predictions illustrate strengths and weaknesses of our initial approach. We then revisit our findings to illustrate the importance of including anisotropy in the failure process. Furthermore, mesh-independent solutions of continuum damage models having both isotropic and anisotropic yields surfaces are obtained through nonlocality and localization elements.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Verification and Validation of Carbon-Fiber Laminate Low Velocity Impact Simulations.

Presented is a model verification and validation effort using low - velocity impact (LVI) of carbon fiber reinforced polymer laminate experiments. A flat cylindrical indenter impacts the laminate with enough energy to produce delamination, matrix cracks and fiber breaks. Included in the experimental efforts are ultrasonic scans of the damage for qualitative validation of the models. However, the primary quantitative metrics of validation are the force time history measured through the instrumented indenter and initial and final velocities. The simulations, whi ch are run on Sandia's Sierra finite element codes , consist of all physics and material parameters of importance as determined by a sensitivity analysis conducted on the LVI simulation. A novel orthotropic damage and failure constitutive model that is cap able of predicting progressive composite damage and failure is described in detail and material properties are measured, estimated from micromechanics or optimized through calibration. A thorough verification and calibration to the accompanying experiment s are presented. Specia l emphasis is given to the four - point bend experiment. For all simulations of interest, the mesh and material behavior is verified through extensive convergence studies. An ensemble of simulations incorporating model parameter unc ertainties is used to predict a response distribution which is then compared to experimental output. The result is a quantifiable confidence in material characterization and model physics when simulating this phenomenon in structures of interest.

English, Shawn Allen↗
DOE OSTI2013

A micro to macro approach to polymer matrix composites damage modeling : final LDRD report.

Capabilities are developed, verified and validated to generate constitutive responses using material and geometric measurements with representative volume elements (RVE). The geometrically accurate RVEs are used for determining elastic properties and damage initiation and propagation analysis. Finite element modeling of the meso-structure over the distribution of characterizing measurements is automated and various boundary conditions are applied. Plain and harness weave composites are investigated. Continuum yarn damage, softening behavior and an elastic-plastic matrix are combined with known materials and geometries in order to estimate the macroscopic response as characterized by a set of orthotropic material parameters. Damage mechanics and coupling effects are investigated and macroscopic material models are demonstrated and discussed. Prediction of the elastic, damage, and failure behavior of woven composites will aid in macroscopic constitutive characterization for modeling and optimizing advanced composite systems.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Modeling Interfacial Fracture in Sierra

This report summarizes computational efforts to model interfacial fracture using cohesive zone models in the SIERRA/SolidMechanics (SIERRA/SM) finite element code. Cohesive surface elements were used to model crack initiation and propagation along predefined paths. Mesh convergence was observed with SIERRA/SM for numerous geometries. As the funding for this project came from the Advanced Simulation and Computing Verification and Validation (ASC V&V) focus area, considerable effort was spent performing verification and validation. Code verification was performed to compare code predictions to analytical solutions for simple three-element simulations as well as a higher-fidelity simulation of a double-cantilever beam. Parameter identification was conducted with Dakota using experimental results on asymmetric double-cantilever beam (ADCB) and end-notched-flexure (ENF) experiments conducted under Campaign-6 funding. Discretization convergence studies were also performed with respect to mesh size and time step and an optimization study was completed for mode II delamination using the ENF geometry. Throughout this verification process, numerous SIERRA/SM bugs were found and reported, all of which have been fixed, leading to over a 10-fold increase in convergence rates. Finally, mixed-mode flexure experiments were performed for validation. One of the unexplained issues encountered was material property variability for ostensibly the same composite material. Since the variability is not fully understood, it is difficult to accurately assess uncertainty when performing predictions.

Brown, Arthur A.↗
DOE OSTI2013

A 3D Orthotropic Elastic Continuum Damage Material Model

A three dimensional orthotropic elastic constitutive model with continuum damage is implemented for polymer matrix composite lamina. Damage evolves based on a quadratic homogeneous function of thermodynamic forces in the orthotropic planes. A small strain formulation is used to assess damage. In order to account for large deformations, a Kirchhoff material formulation is implemented and coded for numerical simulation in Sandia’s Sierra Finite Element code suite. The theoretical formulation is described in detail. An example of material parameter determination is given and an example is presented.

36 MATERIALS SCIENCE↗