| Ceramic composite materials possess both low toughness and low impact resistance. However, the incorporation of ceramic whiskers into the microstructure of ceramic matrix has been shown to produce a ceramic composite with improved toughness and greater strength. This dissertation studies both experimentally and theoretically the dynamic behavior of SiC{dollar}rmsb{lcub}w{rcub}Alsb2Osb3{dollar} ceramic composites under low velocity impact loading. The main objective of this study is to determine the effects of local-contact loading and dynamic flexural stresses on impact resistance, failure modes, and toughening mechanisms of whisker reinforced composites. To accomplish this objective, (1) several samples of this composite material were designed and fabricated using different SiC whisker volume fractions, and then tested at low-velocity impact; (2) the static and dynamic mechanical properties of this composite were determined, and the damage caused by low velocity impact loading was quantified and assessed. A theoretical solution to the transverse impact problem of whisker-reinforced ceramic composite plates by striking these plates with solid projectiles, at low impact velocity was formulated, and its predictions are compared to impact test results. Test results of this study show that under low-velocity, transverse impact the local-contact tensile stresses in {dollar}rm Alsb2Osb3/SiCsb{lcub}w{rcub}{dollar} composites didn't reach critical values that would initiate fractures around the contact area in any tested specimen, and that all fractures were caused by dynamic flexural stresses. In addition, correlations between impact test results and these composites' material properties are also included in this dissertation. This study's test results indicate that the {dollar}rm Alsb2Osb3/SiCsb{lcub}w{rcub}{dollar} composite which possesses the highest bending strength, highest fracture toughness, highest theoretical density percentage, and lowest Young's modulus should be the most (low-velocity) impact resistant. |
