Papers by Author: Mauricio Torres

Abstract: The present work lies in the framework of designing polymeric fibre reinforced materials to be used in nanosatellite structures (CubeSat). In the design of any structural system for a space mission the balance between mass, stiffness and strength must be taken into account, also the used materials have to be appropriated for the space environmental conditions. The CubeSat are exposed to high radiation levels (because of the sun irradiance), and so, the accurate determination of the thermal and radiation properties are a key issue for the materials design used in such applications. This work reports the thermal and radiation performance of a biphasic epoxy resin system incorporating two types of ceramic nanoparticles: zinc oxide and graphene, chosen as potential fillers to improve the thermal properties of the epoxy system. Materials are exposed to Gamma and UV radiation at rates of 1 kGy and 10 kGy and characterized after exposure. Different characterization techniques (Thermogravimetric analysis - TGA, Scanning Electron Microscopy - SEM and Colorimetry) are performed to determine thermal properties and possible material degradation after radiation exposure. The influence of the different nanofiller in the thermal and radiation response of the epoxy system are discussed. Thermal properties found are also added to the Finite Element Analysis of a CubeSat composite structure to estimate more accurately its performance under the thermal load and service conditions during satellite life cycle.

Abstract: Aircraft composite structures are mostly joined by mechanical fasteners like bolts, pins or screws. However, the effect of the presence of holes in the remaining strength of the composite structures is still being studied extensively. In this work, epoxy/glass laminates with drilled holes of different sizes were tensile tested and from these results, the residual strength was plotted. Strength vs. hole’s diameter at different fiber orientation was obtained. The fracture path and failure mechanism were identified by fractographic examination. The Point Stress Criterion (PSC) was used, in order to establish the stress intensification due to the presence of a drilled hole. A numerical model by Finite Element Method was carried out to verify the experimental results and the analytic failure predictions. A reduction of 50% in laminate strength was observed when diameter-width ratio was 0.12. The principal fracture mechanism observed in composite laminates was interface breakup. FEM results and analytic results by PSC show accuracy of 90% for predicting the damage in drilled composites.