On the failure criterion of aluminum and steel plates subjected to low-velocity impact by a spherical indenter

• A failure criterion is proposed to characterise aluminium or steel plated structures.
• It considers the critical deflection, force and absorbed energy of plates laterally impacted.
• The proposed expressions are compared with numerical results validated with drop weight tests.
• The tests show that the critical deflections are similar for both the aluminium and the steel plates.
• However differences are observed in the critical forces and energies.

An analytical failure criterion is proposed to characterise ship plated structures manufactured with aluminium or steel materials subjected to low impact velocities. The criterion considers the critical deflection, force and absorbed energy of plates laterally impacted by a hemispherical indenter, and assumes that failure occurs at the presence of necking. The proposed expressions are compared with numerical results validated with drop weight experiments conducted on small-scaled rectangular aluminium and steel plates of the same bending stiffness. Thus, the impact tests and simulations could describe the behaviour of stiffness-equivalent shipbuilding materials subjected to rapidly varying loads. In addition, the criterion uses quasi-static theoretical formulae, including the plate thickness and the material power law coefficients to assess the deformation characteristics and the plate localisation. The experimental results show that the critical deflections are similar for both the aluminium and the steel plates, although differences are observed in the critical forces and energies. Even though the numerical simulations use most definitions reported in previous works, the emphasis is put on the material characterisation, where the fracture strain is obtained by measuring the tensile test pieces of the materials and using simplified equations to define the equivalent strain. The proposed criterion's theoretical expressions give a good agreement with the numerical results. The criterion shows that the absorbing capabilities of the plates are improved by increasing the strength coefficient of the material and the plate thickness, while other material coefficients could be omitted. It is also demonstrated that the critical defection increases and the force decreases with the strain hardening exponent. Moreover, the specific energy absorption of the material is used to evaluate the impact characteristics of the material.