R. Villavicencio

Numerical plastic response and failure of a pre-notched transversely impacted beam

In this paper, numerical simulations of drop weight impact tests examining the plastic response and failure of clamped pre-notched beams struck transversely by a mass with a hemispherical indenter are presented. The simulations aim at proposing techniques for defining the material and restraints on finite element models which analyse the structural crashworthiness of ships in collision and grounding scenarios. The mesh size and the critical failure strain are predicted by numerical simulations of the tensile tests used to obtain the mechanical properties of the material. The experimental boundary conditions are modelled in order to represent the axial displacements at the supports and the reacting forces developed during the impact. The beams are studied in terms of their force–displacement response during the impact event, which gives good agreement between experimental and numerical results. The shape of the failure modes is well predicted by the finite element model when a finer mesh is used. Comments on the stress and strain distribution at the impact point and the energy partitioning during the impact are included.

Numerical simulation of transversely impacted, clamped circular aluminium plates

This paper presents experimental and numerical results of a series of drop weight impact tests examining the dynamic response of fully clamped aluminium 5083/H111 circular plates struck laterally at the centre by a mass with a spherical indenter. The impact velocity varied from 1.0 to 6.0 m/s. The plates showed no visible damage at the very low incident energies but suffered both indentation and global deformation as incident energy was increased. The numerical modelling was performed using the LS-DYNA non-linear, dynamic finite element software. Both shell and solid element models of progressively refined mesh sizes were used and the results compared with the experimental data. The numerical calculations used can accurately predict the response of deflections, forces and absorbed energies, even for the models with coarse meshes. However, finer meshes and solid elements were required to obtain a satisfactorily accurate prediction of the deformed shape.

Influence of the neutral axis displacement on the residual strength of a damaged tanker double-bottom structure

The paper presents a method to estimate the displacement of the neutral axis during the loading of a damaged ship hull subjected to bending moment. The method uses the load–end shortening relationship obtained from numerical residual strength calculations of the double-bottom structure with a fixed location of the neutral axis and establishes the force equilibrium over the whole transverse section of the ship. The set of the estimated locations of the neutral axes allows defining the new load condition to induce the bending moment on the double bottom at a higher strain rate. The new residual strength is compared with previous numerical calculations of the intact and damaged double bottom in which the bending moment is induced considering that the neutral axis is fixed during the entire simulation. The comparison shows a small reduction in the capacity of the double-bottom structure when the bending moment is caused by the new load condition.

Plastic Response and Failure Prediction of Stiffened Plates Punched by a Wedge

Experimental tests have been performed to examine the response of small-scale stiffened plates laterally punched by a wedge. The specimens are supported at two opposite edges and the indenter is located at the mid-span. In the unsupported edges, the ends of the stiffeners are either connected to transverse stiffeners or remain free. The obtained force-displacement responses show a good agreement with the simulations performed by the LS-DYNA finite element solver. The finite element model includes defining the experimental boundary condition so as to simulate small axial displacements of the specimen at the supports. The strain hardening of the material is defined using experimental data of quasi-static tension tests and the critical failure strain is evaluated using tensile test simulations. The results show that the response of the specimens is highly sensitive to the amount of restraint provided at the supports. In addition, simplified calculations are proposed to evaluate the contribution of each structural component on the energy absorbed by the stiffened plate specimens.Copyright

Influence of Striker Shape on the Crack Initiation and Propagation on Laterally Impacted Thin Aluminium Plates

Experimental and numerical results of drop weight impact tests are presented, examining the plastic response and the crack initiation and propagation of small-scale clamped rectangular aluminium plates laterally impacted by different indenter shapes. The experiments are conducted using a fully instrumented impact testing machine. The shape of the deformation of the specimens and the process of initiation and propagation of the material fracture is presented. The obtained force-displacement responses show a good agreement with the simulations performed by the LS-DYNA finite element solver. The strain hardening of the material is defined using experimental data of quasi-static tensile tests and the critical failure strain is evaluated measuring the thickness and the width at fracture of the tensile test pieces. The results show that the absorbed energy to perforate the specimens is highly sensitive to the shape of the striker. Thus, the crack propagation for each striker type is analysed in terms of the force-displacement response. The failure modes are described by the matrix of the infinitesimal strain tensors and the shape of the deformation of the failing elements.© 2013 ASME

Numerical Investigation on the Plastic Response of a Small-Scale Laterally Impacted Tanker Double Hull Structure

Numerical simulations are presented, on the dynamic response of a one-tenth scaled tanker double hull structure struck laterally by a knife edge indenter. The small stiffeners of the full-scale prototype are smeared in the small-scale model by increasing the thicknesses of the corresponding plates. The dynamic response is evaluated at an impact velocity of 7.22 m/s and the impact point is chosen between two frames to assure damage to the outer shell plating and stringers. The simulations are performed by LS-DYNA finite element solver. They aim at evaluating the influence of strain hardening and strain rate hardening on the global impact response of the structure, following different models proposed in the literature. Moreover, the numerical model is scaled to its full-scale prototype, summarizing the governing scaling laws for collision analysis and evaluating the effect of the material strain rate on the plastic response of large scaled numerical models.Copyright