A numerical investigation on determining the failure strength of a powder compact in unconfined compression testing by considering the compressible character of the specimen

• Unconfined compression testing of a powder compact was simulated.
• The current area was determined for compressible and incompressible specimens.
• The failure strength was underestimated by the incompressibility assumption.
• The degree of underestimation increased when the hardening curve increased slowly.
• It was also magnified with the cap aspect ratio of the powder compact.

The effect of the compressible character of a powder compact on the determined failure strength in unconfined compression testing is investigated numerically. The modified Drucker–Prager cap constitutive model (an elastic–plastic-work hardening model) is employed for a spray-dried Al2O3 powder compact. When the failure strength is obtained from the current cross sectional area determined solely by the axial strain based on the assumption of incompressibility of the specimen, it underestimates the failure strength of the compressible specimen significantly. The degree of underestimation is magnified if the powder compact possesses a more slowly increasing hardening curve and/or a larger cap aspect ratio. Based on these findings, we suggest that the compressible character of the specimen be taken into account, especially for a powder compact with a slowly increasing hardening curve and/or with a large cap aspect ratio; the current cross sectional area of the specimen needs to be determined by measuring not only the axial strain but also the radial strain of the specimen.

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