Modeling of biaxial flexure tests of transport amphorae with the finite element method: Fracture strength, deformation and stress distribution

The measurement of mechanical behavior of ceramics provides essential information about the mechanical performance of ceramic vessels produced from these materials. In the present case study fragments of Hellenistic and Roman transport amphorae from the Southeast Aegean islands of Kos and Rhodes were investigated. In terms of material properties the flexural strength is of particular interest as it reflects the performance under typical mechanical loading emerging during use of these vessels. Flexural strength can be determined either in uniaxial tests, for example by three-point-bending, or more realistically, in a biaxial flexure test, for example loading with a sphere on a ring-supported ceramic disk. For the present case study ceramic disks, prepared from actual amphora wall fragments, were tested and load-displacement curves were recorded until final fracture. The flexural strength was calculated based on the maximum load at initial fracture. In order to further investigate the recorded curves in terms of elastic as well as plastic deformation and stress distribution, a three-dimensional numerical model of the biaxial flexure test was generated and evaluated using the finite element method (FEM). By adjusting the simulated behavior to the experimentally determined curves, an estimation of material properties was attempted. This approach is useful for the development of numerical models of contact loads in amphora assemblages, simulating for example storage in a cargo ship, in order to test different vessel shapes for their performance.