Strengthening Effects in AC8A/Al₂O₃ Short-Fiber Composites as a Function of Temperature and Strain Rate

The strengthening aspect of AC8A/Al₂O₃ short-fiber composites is examined under the framework of a modified shear lag model over the range of 298 to 723 K and 10^-3 to 10³ s^-1. The strength sustained by the composite at high temperatures is much higher than for the alloy. As the strain rate rises, the portion of strength that the composite or alloy can sustain is drastically increased. Also, the composite shows a lower strain rate sensitivity, likely to be caused by the higher tendency of fiber damage and local stress concentration. As the temperature is higher, the strain rate sensitivity becomes considerably higher. The composite strength can be theoretically calculated using the Friend and Modified Tsai-Hill formulas. By closer examination, the experimental data agree better with the prediction of the Modified Tsai-Hill 2D (min) or 2D (max) model. Nevertheless, all of the predictions give quite reasonable strength values as well as the trend as a function of temperature and strain rate. Overall, test temperature governs the strengthening efficiency. High temperatures give the best efficiency. Influence from strain rate exists, but is less significant. It is observed that the strengthening effect is more pronounced when the matrix strength is lower, such as at higher temperatures and lower strain rates. Calculations from the critical fiber volume fraction V_crit and load transfer coefficient α both show an increasing trend with increasing temperature and decreasing strain rate, also suggesting that the strengthening effect by adding short fibers into the matrix is more apparent and efficient at high temperatures and low strain rates.