Materials--Compression testing

This research focuses on deformation constraints of honeycomb core cells in a sandwich imposed by bonds to the face sheets. Specifically, the influence of one-sided core constraints on the bending stiffness of a single-face honeycomb core sandwich is examined. To characterize the unconstrained in-plane compressive response of honeycomb core, a range of honeycomb cores was experimentally examined. Cores with a thin cell wall displayed extensive bending deformation of inclined cell walls while cores with thicker walls failed by a shear-type instability of the cells indicated by tilting of vertical cell wall segments. The modulus and compressive strength of the core were compared to the predictions from unit cell models. The results show that geometrical imperfections such as deviation from the intended cell wall angle cause in-plane anisotropy and have strong influence on modulus and strength of the core. Modulus and strength were in reasonable agreement with predictions from unit cell models for cell wall modulus and strength between 5-12 GPa and 72-171 MPa for the set of cores examined.

Laboratory experiments were conducted to observe, document and evaluate the mechanical behavior of Fiber Reinforced Concrete after being submitted to five different environments for 8 months. The specimens were molded and reinforced with synthetic fibers with a composition similar to that used for dry-cast concrete. Four different types of fibers with different composition were used. The fibers were mixed with the concrete to create the samples and the samples were exposed to different environmental conditions. Some of these environments were meant to increase degradation of the interface fiber-concrete to simulate longevity and imitate harsh environments or marine conditions. The environments consisted of: a high humidity locker (laboratory conditions), submerged in the Intracoastal Waterway in a barge (SeaTech), a wet/dry cycle in seawater immersion simulating a splash/tidal zone, low pH wet/dry seawater immersion cycle and samples submerged in calcium hydroxide solution. The latter three were in an elevated temperature tank (87-95°F) to increase degradation process. The specimens were monitored weekly and the environments were controlled. Then, specimens were evaluated using different mechanical testing as the Indirect Tensile (IDT) test method, compressive strength according to ASTM standards. Results of testing were documented and observed in this study for further understanding of mechanical properties of Fiber Reinforced concrete. Forensic observation of fiber distribution after the IDT tests were also performed.