PSI - Issue 68

Masoomeh Farrokhtar et al. / Procedia Structural Integrity 68 (2025) 592–595 Masoomeh Farrokhtar et al. / Structural Integrity Procedia 00 (2025) 000–000

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by the heat treatment. Rather repetitive ductile responses were obtained at lower temperature, otherwise the metal is stronger but more brittle and the results are more scattered. The load-displacement curve shown in Fig. 2 refers to a composite filament (316L-Al 2 O 3 ) sintered at 1350°. The first peak in the graph corresponds to the development of a main crack that crosses the sample depth at one of the load application positions. However, the resistance is not completely lost and this event is followed by a rather ductile response, clearly due to the contribution of the metal core. The formation of additional cracks is also observed during the experiment, but the overall trend of the graph is not significantly altered. These results have been interpreted with the aid of a numerical model of the performed tests. The transferability to the composite of the mechanical characteristics exhibited by the individual components was specifically investigated. 3. Numerical Simulations Fig. 3 represents the main elements of the numerical model implemented in the commercial code Abaqus to simulate the 4PBT. The ceramic shell and the metal core have been modelled independently, and then connected to reproduce either perfectly bonded or frictionless contact conditions.

Fig. 3. Schematic of the simulation model

A linear elastic constitutive model has been introduced for the ceramic, while fracture is simulated by the presence of a thin cohesive layer placed at the load application points (one or both). The cohesive elements are characterized by the tensile strength estimated from the homogeneous samples, and are removed beyond a critical separation value, as shown in Fig. 4.

Fig. 4. Simulation of the fracture process

The numerical investigation permits to understand the role and influence of the uncertainty sources. In particular, the results of the simulations performed on the steel-alumina system evidence that: - the overall strength and ductility are significantly influenced by the diameter of the metal core and, therefore, by the injection pressure; - the produced composite elements are characterized by weak metal-ceramic interfaces; in fact, the maximum load computed under the assumption of perfect bonding is much higher than that obtained experimentally in all cases; - the core metal properties differ from those of the homogeneous samples sintered at high temperature.