Influence of the measurement method and sample dimensions on the Young's modulus of open porous alumina foam structures

Abstract Within this study the influence of the sample shape, the cell size and the measurement method on the Young's modulus E of open cell foam alumina was investigated. The measurement methods used for the determination of E were the impulse excitation technique, the longitudinal ultrasonic measurement, the quasi-longitudinal ultrasonic measurement and the three point bending technique (3PB). The samples comprising the smallest height, yielded the highest E values for all measurement methods due to its processing, causing higher densities and homogeneity and hence leading to increased E values. Furthermore, its smaller area moment of inertia results in a higher beam deflection for a fixed force applied in 3PB. Thus, in the case of this shape, the forces involved during the 3PB tests were much lower and a smoother test could be performed and resulted in higher E values. Problems were found for the determination of E by the impulse excitation technique at large cell sizes (10 and 20 ppi). This was attributed to a reduction of the vibrating surface beneath the microphone capturing the audio signal. Ultrasonic methods performed robustly, however have to be conducted with care (e.g. Poisson's ratio assumption).