Thermal and Mechanical Optimization of Structural Thermal Insulation Composites

The first objective was to investigate the literature and existing numerical that predict effective thermal conductivity (ETC) and strength and stiffness properties. Due to the lack of accurate existing models/methods, it was decided to investigate the finite element (FE) method of predicting these effective material properties. The development of three-dimensional FE models were used for designing syntactic foams for both thermal and mechanical properties. This consisted of FE thermal and stress modeling of hollow glass sphere syntactic foams with different sphere size distributions and packing geometries over a range of sphere loading from 0 to 70% by volume. Results from these FE models were compared with “closed form” analytical models from literature to demonstrate the need for FE modeling. A discussion of how the size distribution and packing of spheres affects predicted thermal and mechanical properties was presented along with how these models may be used in selection of constituent materials for syntactic foams to achieve desired thermal and mechanical properties. Syntactic foams consisting of hollow glass spheres and low-, mid-, and high-modulus matrices were modeled to predict the effective thermal conductivity, strength, and stiffness with respect to volume fractions ranging from 0 to 70%. The study was performed through three-dimensional finite element thermal and stress analysis of RVE models investigating three sphere size distributions and packing patterns under various particle-to-matrix conductivity and stiffness ratios. Three primary conclusions were drawn from this study: 1) ETC has minimal dependence on sphere size distribution, 2) RVEs of a single sphere size distribution are not adequate to predict the strength or stiffness of syntactic foams with a distribution of sphere sizes, and 3) the predicted strength of syntactic foams is highly dependent on the particle-to-matrix stiffness ratio. The results of this study may be used as a design tool in selecting constituent materials and volume fractions of these materials in developing syntactic foams with desired mechanical and thermal properties. The second objective was to complete thermal conductivity testing, which was conducted at NASA’s Kennedy Space Center. Syntactic foams developed by other researchers at SDSM&T, as part of the NASA EPSCoR STIC project, were tested to determine their ETC. The tests were performed using a variety of techniques and different pieces of testing equipment, both of which were presented in previous progress reports, and my thesis, along with the results. Comparisons were made against FE modeled data. The third objective was to decide a proper way to simultaneously model the effective laminate properties (thermal/mechanical) of a composite built up using curvilinear toe-placement. This work was started during the on-site experience at Langley Research Center and may result in a NASA tech note. • Completed on-site experiences at Johnson Space Center, Langley Research Center, Kennedy Space Center (2), and Marshall Space Flight Center. • Completed ETC and stress concentration FE analysis of low-, mid-, and high-modulus polymer/hollow glass sphere syntactic foams. • Completed journal paper to Journal of Composite Structures. • Completed master’s thesis.