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Briggs, Timothy M.

Publications and source records attributed to Briggs, Timothy M..

Quantitative validation of carbon-fiber laminate low velocity impact simulations

Simulations of low velocity impact with a flat cylindrical indenter upon a carbon fiber fabric reinforced polymer laminate are rigorously validated. Comparison of the impact energy absorption between the model and experiment is used as the validation metric. Additionally, non-destructive evaluation, including ultrasonic scans and three-dimensional computed tomography, provide qualitative validation of the models. The simulations include delamination, matrix cracks and fiber breaks. An orthotropic damage and failure constitutive model, capable of predicting progressive damage and failure, is developed in conjunction and described. An ensemble of simulations incorporating model parameter uncertainties is used to predict a response distribution which is then compared to experimental output using appropriate statistical methods. Lastly, the model form errors are exposed and corrected for use in an additional blind validation analysis. The result is a quantifiable confidence in material characterization and model physics when simulating low velocity impact in structures of interest.

36 MATERIALS SCIENCE↗

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↗

Developing a Multiscale Test Approach for Characterizing Polymer Composites

A systematic series of experimental characterization efforts have been applied to a novel advanced fiber reinforced nanocomposite material composed of carbon fiber doped with carbon nanotubes in a thermoplastic polymer. A novel depositional process has been developed and refined in order to obtain homogeneous and isotropic dispersion of the CNTs onto the interfacial surface of interest. Fracture mechanics characterization efforts under Mode I and Mode II loading have been investigated to quantify critical strain energy release rate values and study the complex fracture processes. Finite element simulations have complimented the fracture analysis in order to elucidate mechanisms at work during the precipitation and propagation. Thermal analytical responses have been measured using differential scanning calorimetry and thermal gravimetric analysis, while temperature dependent viscoelastic properties have been characterized through variable amplitude dynamic mechanical analysis. Significant increases in the energy absorption characteristics during deformation and fracture behavior have been directly measured for this CNT enhanced material system. This CNT modified CFRP material shows extreme promise for improving interply adhesion and inhibiting delamination.

36 MATERIALS SCIENCE↗