Date of Award
MS in Aerospace Engineering
The main objective of this study was to examine the effects of matrix composition of laminated woven roving S-glass epoxy composite plates which were subjected to low-velocity impact. The testing was conducted with a transverse drop-weight Instron Dynatup 9250HV machine with increasing impact energies of 50, 55, and 60 inch-lbf and a constant impactor mass of 12.57 pounds. A piezoelectric force transducer affixed to the drop-weight device, localized in the hemispherical impactor nose, yielded the complete force versus time history of the impact event. The contact force between the impactor and the composite plate, as well as the energy during impact, were analyzed as functions of time. Each laminate’s Damage Threshold Load (DTL) for the corresponding incident impact energies were also examined to determine the respective matrix composition influences. In addition, a numerical evaluation of these specimens was executed using Abaqus/Explicit, which utilized a transient dynamic Finite Element Analysis (FEA) code. The numerical transient energy during impact was used to substantiate the experimental tests.
The epoxy resin system for each specimen was mixed with either a limestone or high-density inorganic filler material, with the quantity of filler ranging between 15 and 20 percent of the total composite weight. The fillers reduced raw material costs, improved mechanical performance, and enhanced the crack resistance properties of the composites. Regardless of filler type, the static tensile tests showed that increasing the quantity of filler material resulted in a higher modulus of elasticity and shear modulus, but a lower strain-to-break. Therefore, increasing the quantity of filler produced a stiffer, more brittle material with a lower threshold of tensile deformation prior to ultimate failure. Increasing the laminate thickness also resulted in a lower average elastic modulus and modulus of rigidity.
The dynamic modal analysis showed that the specimens made with high-density filler had higher resonant frequencies for each bending mode when compared to those made with limestone. The resonances of the test samples were also modified by altering the quantity of filler material mixed in the resin system. Increasing the amount of inorganic filler resulted in a higher resonant frequency for each mode. The thicker laminates were more capable of damping energy in the form of deformation waves. The effects of laminate thickness with respect to modal frequency suggested that thicker materials are less susceptible to low magnitude vibrational issues.