Small punch testing of Al-TiB2 composites fabricated by spark plasma sintering: A computational and experimental study

The Small Punch Test (SPT) method is especially useful for quantifying the mechanical properties of metallic materials in cases where the material available for testing is limited or for in service monitoring. However, the applicability of this method to metal matrix composites has not yet been fully established. In the present study, Al-TiB2 composite billets with TiB2 particle volume fractions of 5%,10% and 15% were manufactured using Spark Plasma Sintering (SPS). Thin specimens with 0.5 mm thickness were cut from the billets, and SPT experiments were conducted until failure. Well-accepted analytical techniques were utilized to determine the Al-TiB2 composite effective yield stress for all TiB2 particle volume fractions. It was shown, that standard analytical methods for characterizing the effective yield stress were adequate only for TiB2 volume fractions of up to 5%. The experimental mechanical response up to and including failure was reproduced for all Al-TiB2 compositions by finite element analysis incorporating a continuum damage mechanics approach. The computational analysis revealed that for high TiB2 volume content, the region of the SPT loading curve which is commonly associated with specimen yielding, may represent a mixture of yielded and damaged areas. Since the damage distribution in the specimen influences the specimen flexural modulus, standard analytical relations cannot be used to determine the composite yield stress and computational methods must be used. This finding may explain the inconsistent results reported in the literature with regard to the accuracy of the SPT method in determining the effective yield stress for metal matrix composites.