Trenton M. Ricks

A Multiscale Modeling Methodology for Metal Matrix Composites Including Fiber Strength Stochastics

A multiscale modeling methodology was developed that incorporates a statistical distribution of fiber strengths into coupled micromechanics / finite element analyses. A parametric study using the NASA Micromechanics Analysis Code with the Generalized Method of Cells was performed to assess the effect of variable fiber strengths on global composite failure at the repeating unit cell level. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a metal matrix composite tensile dogbone specimen. A statistical distribution of fiber strengths based upon a two parameter Weibull cumulative distribution function was assigned to individual repeating unit cells corresponding to element integration points within ABAQUS. Multiple analyses were performed to quantify the effect of randomly varying fiber strengths on the temperature-dependent composite stress-strain response and local failure. By including a random distribution of fiber strength in micromechanical calculations that feed into a global finite element framework, distributed failure occurs in the specimen more consistent with experimental observation.

On the Viability of Energy Harvesting Piezoelectric Devices for Supplemental Power Generation in Uninhabited Aircraft Systems

In this work, a global air vehicle finite element model employing empirically determined cyclic loads is used to assess the viability of energy harvesting piezoelectric devices for supplemental power generation in lightweight uninhabited aircraft systems (UASs) where the “Owl” all-composite ultralight UAS is used as a candidate proof-of-concept platform. The Owl was developed at the Mississippi State University Raspet Flight Research Laboratory as part of the U.S. Army Space Missile Defense Command High Performance Materials/Processes (HIPERMAP) Program. In the HIPERMAP flight test program, straintime histories were recorded at key locations throughout the wing and fuselage. These measured strains were used in the investigation of practical implementation of energy harvesting piezoelectric materials within the Owl UAS with the intent of harvesting electrical power from structural oscillations of the wings during operation. The total power generated was determined from a 80 KIAS 4G pullup maneuver, where piezoelectric patches were simulated in the span-wise direction along the inner surfaces of the upper and lower skins of both wings. The energy harvesting capability of the Owl UAS was insufficient due to the small oscillation frequency and low strain magnitudes of the wing during flight. Nevertheless, such energy harvesting devices remain promising for microscale UASs where power requirements are lower and the oscilation frequency of the wings is higher.

The Effect of Scale Dependent Discretization on the Progressive Failure of Composite Materials Using Multiscale Analyses

A multiscale modeling methodology, which incorporates a statistical distribution of fiber strengths into coupled micromechanics/ finite element analyses, is applied to unidirectional polymer matrix composites (PMCs) to analyze the effect of mesh discretization both at the micro- and macroscales on the predicted ultimate tensile (UTS) strength and failure behavior. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a PMC tensile specimen that initiates at the repeating unit cell (RUC) level. Three different finite element mesh densities were employed and each coupled with an appropriate RUC. Multiple simulations were performed in order to assess the effect of a statistical distribution of fiber strengths on the bulk composite failure and predicted strength. The coupled effects of both the micro- and macroscale discretizations were found to have a noticeable effect on the predicted UTS and computational efficiency of the simulations.

Solution of the Nonlinear High-Fidelity Generalized Method of Cells Micromechanics Relations via Order-Reduction Techniques

The High-Fidelity Generalized Method of Cells (HFGMC) is one technique, distinct from traditional finite-element approaches, for accurately simulating nonlinear composite material behavior. In this work, the HFGMC global system of equations for doubly periodic repeating unit cells with nonlinear constituents has been reduced in size through the novel application of a Petrov-Galerkin Proper Orthogonal Decomposition order-reduction scheme in order to improve its computational efficiency. Order-reduced models of an E-glass/Nylon 12 composite led to a 4.8–6.3x speedup in the equation assembly/solution runtime while maintaining model accuracy. This corresponded to a 21–38% reduction in total runtime. The significant difference in assembly/solution and total runtimes was attributed to the evaluation of integration point inelastic field quantities; this step was identical between the unreduced and order-reduced models. Nonetheless, order-reduced techniques offer the potential to significantly improve the computational efficiency of multiscale calculations.

Order-Reduced Solution of the Nonlinear High-Fidelity Generalized Method of Cells Micromechanics Relations

The High-Fidelity Generalized Method of Cells (HFGMC) is one technique for accurately simulating nonlinear composite material behavior. The HFGMC uses a higher-order approximation for the subcell displacement field that allows for a more accurate determination of the subcell stress/strain fields at the cost of some computational efficiency. In order to reduce computational costs associated with the solution of the ensuing system of simultaneous equations, the HFGMC global system of equations for doubly-periodic repeating unit cells with nonlinear constituents was reduced in size through the use of a Petrov-Galerkin-based Proper Orthogonal Decomposition order-reduction scheme. A number of cases were presented that address the computational feasibility of using order-reduction techniques to solve solid mechanics problems involving complex microstructures.