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The present paper continues the recent works reported by Liu et al. (2020) where quasi-static indentation experiments and finite element simulations were reported to investigate the plastic behaviour and failure of four stiffened aluminium-alloy plates punched by a rigid hemispherical indenter: one bare plate, one butt-welded plate, two plates with respectively one and two flat-bar stiffeners. Here specimens with the same geometry are investigated using a rigid hemi-cylindrical indenter to examine the effect of the indenter shape on the deformation and collapse modes. The experimental comparison shows the different structural deformation and failure mechanisms of welded aluminium alloy panels. The finite element analysis discusses the importance of the modelling of welded joining details, the boundary conditions and the material degradation at welded heat-affected zones and at the same time illustrates the similarities and differences between impact analyses of aluminium and steel stiffened plates. [ABSTRACT FROM AUTHOR]

Abstract Closed-form expressions to estimate the energy absorption and damage extent for severe ship collision damages were initially developed in 1999 [1, 2], and further validated with experimental data in 2016 [3]. To gain further confidence for applications within design using the proposed analytical procedure, it is evident that more detailed and comprehensive comparisons and validations with experiments and numerical simulations are necessary. The purpose of the present paper is to use the analytical approach and finite element analyses to study in depth model-scale and full-scale collision tests so that to further quantify key calculation parameters and to verify the capability and accuracy of the proposed analytical method. In total 18 experimental tests and one full-scale collision accident are evaluated. The 18 experimental energy absorption-penetration and collision force-penetration curves, and the associated finite element simulations, are compared with results obtained from the analytical calculations. It can be concluded that the analytical method gives consistently good agreement with all experiments analysed here. Finally, an application of the analytical method is demonstrated by an example where speed restrictions are determined in a port to avoid LNG cargo leakage in an event of an LNG carrier being struck by another ship. Highlights • An analytical method for ship collision damage assessments is validated with 18 experiments and one full-scale collision accident data. • It is demonstrated that a consistent good agreement with the experiments is achieved when using a common criterion for the assessment. • Comparisons of energy-penetration and collision force-penetration curves between the experimental results, the analytical calculations and the finite element simulations are also provided. • An application example for managing collision risks at busy ports to avoid potential cargo leakage in an event of an LNG carrier struck by other ships is demonstrated. [ABSTRACT FROM AUTHOR]

The paper presents an experimental and numerical analysis of the residual stresses and strains induced during the cold bending of thick steel plates. Cold bending technique is widely used in the shipbuilding and offshore industry, and thus it is important to know about the changes in the material characteristics induced during the metal fabrication process. For this purpose, firstly, three-point cold bending experiments are conducted with a relatively small indenter on the specimens cut from a thick steel plate (54 mm), and afterwards, tension tests are carried out on tensile coupons cut from the already bent specimens. Thus, the mechanical properties (engineering stress-strain curve) of the tensile coupons cut from the loaded and unloaded locations are compared so that to determine the residual stresses and strains resulting from the bending process. A numerical simulation is performed with the explicit LS-DYNA finite element solver to replicate the experimentally determined residual stresses and strains. The simulation provides information of the distribution of the residual stresses and strains along the span and through the thickness of the specimens. It is found that the local deformation underneath the indenter harms severely the structural integrity, producing large residual stresses and strains during the bending process. This work illustrates the potential use of finite element analysis to evaluate the residual stresses and strains in metal fabrication processes. [ABSTRACT FROM AUTHOR]

The paper compares two methods based on finite element simulations to assess the external dynamics and the internal mechanics in ship collisions. One method treats independently the external dynamics and the internal mechanics (decoupled method), while the other one couples their interaction (coupled method). In the decoupled method, the external dynamics are evaluated by the analytical approach of Pedersen and Zhang (1998), and the internal mechanics are assessed by simulations performed with the LS-DYNA finite element solver. In the coupled method, both the external dynamics and the internal mechanics are evaluated directly by numerical simulations that follow the model of Pill and Tabri (2011). The two methods are compared to determine the differences in predicting the deformation and rupture of the collided ship structures and to assess the relationship between the structural deformation energy of the struck ship and the energy loss of the striking ship. The objective of the paper is to verify whether the decoupled method satisfies the predictions required for design appraisal assessments. The paper also illustrates the influence of the collision angle on the mechanics of ship collisions. [ABSTRACT FROM AUTHOR]

Experimental and numerical results of drop weight impact tests are presented, examining the plastic response and the crack initiation and propagation of small-scale damped rectangular aluminum 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 are 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 by measuring the thickness and the width at fracture of the tensile test pieces. The results show that the absorbed energy to petforate the specimens is highly sensitive to the shape of the striker. Thus, the crack propagation for each striker type is analyzed 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. [ABSTRACT FROM AUTHOR]

The paper presents a simplified analytical method to examine the energy absorbing mechanisms of small-scale stiffened plate specimens, quasi-statically punched at the mid-span by a rigid indenter with a knife or a flat edge shape. To validate this method, experiments and numerical simulations are conducted on specimens scaled from a tanker side panel limited by one span between the web frames and the stringers. Therefore, the paper provides practical information to estimate the extent of structural damage within ship side panels during collision accidents. The experimentally obtained force–displacement responses and shapes of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The numerical results manage to describe the process of initiation and propagation of the material fracture in the side panel specimens and provide detailed information of the energy dissipated by each structural component and its contribution to total energy during the entire deformation process. The analytical method derives expressions to estimate the relation between the plastic deformation and the energy dissipation of the stiffened plates. Both the plate and the stiffener elements dissipate the energy through rotation of the plastic hinges at the applied load and the support and the membrane tension over the plastically deformed region between the loading and the supports. The proposed simplified expressions give a good agreement with the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents finite element simulations of a small-scale stiffened plate specimen quasi-statically punched at the mid-span by a rigid indenter, in order to examine its energy absorbing mechanisms and fracture. The specimen, scaled from a tanker side panel, is limited by one span between the web frames and the stringers. The paper provides practical information to estimate the extent of structural damage within ship side panels during collision accidents. Moreover, the results of this investigation should have relevance to evaluate grounding scenarios in which the bottom sustains local penetration. This is possible since the structural arrangement of the double hull and the double bottom of tanker vessels is very similar. The experimentally obtained force–displacement response and shape of the deformation show good agreement with the simulations performed by the explicit LS-DYNA finite element solver. The numerical analysis includes aspects of particular relevance to the behaviour of ship structures subjected to accidental loads which could give rise to difficulties in interpreting finite element calculations. In particular, the paper comments on the material nonlinearities, the importance of specifying the precise boundary conditions and the joining details of the structure. The considerable practical importance of these aspects has been the focus of attention in previous publications of the authors which evaluate the experimental-numerical impact response of simple ship structural components, such as beams and plates. Therefore, this paper uses the definitions proposed in those references to evaluate its applicability in the scaled tanker side panel, as an example of a more complex ship structure. [Copyright &y& Elsevier]

Abstract: Experimental drop weight impact tests have been performed to examine the dynamic plastic response and failure of clamped pre-notched beams struck transversely by a mass with a spherical indenter. The laboratory results are compared with numerical simulations. The machined notches are 2.0 and 4.0mm in depth, and the beams are impacted at the mid-span and at one-quarter from the support. The experiments are conducted using a fully instrumented impact testing machine. The obtained force–displacement responses show a good agreement with the simulations performed by the LS-DYNA finite element solver. The simulations aim at proposing techniques for defining the material characteristics and the boundary conditions of numerical models that analyse the large inelastic deformation and failure of ship structural components subjected to impact loading. The finite element model includes 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 the quasi-static tension tests and the strain rate sensitivity is evaluated using standard coefficients of the Cowper–Symonds constitutive model. The Cowper–Symonds model is also selected to estimate the dynamic critical failure strain by the use of the quasi-static failure strain predicted by numerical simulations of the tensile tests. Although the dynamic properties of the material should determine the response of the impacted specimens, the results show that the plastic response until failure is highly sensitive to the amount of restraint provided at the supports. [Copyright &y& Elsevier]

Experimental and numerical results of drop weight impact test are presented on the plas-tic behavior and fracture of rectangular plates stuck laterally by a mass with a hemi-spherical indent er. Six specimens were tested in order to study the influence of the impact velocity and the diameter of the indenter. The impact scenarios could represent abnormal actions on marine structures, such as ship collision and grounding or dropped objects on deck structures. The tests are conducted on a fully instrumented impact tester machine. The obtained force-displacement response is compared with numerical simulations, performed by the LS-DYNA finite element solver. The simulations aim at proposing techniques for defining the material and restraints on finite element models which analyze the crashworthiness of marine structures. 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 modeled in order to represent the reacting forces developed during the impact. The results show that the critical impact energy until failure is strongly sensitive to the diameter of the striker. The shape of the failure modes is well predicted by the finite element models when a relatively fine mesh is used. Comments on the process of initiation and propagation of fracture are presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, numerical results of a drop weight impact test examining the dynamic response of a clamped steel beams struck transversely at the centre by a mass with a rectangular indenter are presented. The numerical simulation showed that the results are very sensitive to the way in which the supports are modelled and thus this paper studies the modelling of the structural supports used to clamp the specimen beam in the experiment. The first approach simplifies the structural support as boundary condition on the nodes; the second model represents the entire support as the real approximation; the last approach uses simplified support plate model acting with the beam to simulate the experimental set up. The complete force–displacement curve is used to compare the plastic deformation of the impacted beams, thus the best approximation is selected for further calculations. The finite element model was performed using the LS-DYNA non-linear, dynamic finite element software. The numerical calculations can predict accurately the response of deflections, forces and absorbed energies, when proper boundary conditions are applied, in this case with shell elements representing the support plates. [Copyright &y& Elsevier]

The paper evaluates the response of an aluminium stiffened panel of a fast displacement craft under bow flare slamming loads by using three finite element methods: (1) a linear static analysis to calculate the structural elastic deformation and stress under the design load; (2) an independent analysis of the slamming load and the elastic structural response (a decoupled method); (3) a method that couples their interaction (a fully coupled method). These methods are compared to analyse the hydroelastic effect when predicting the structural loading and response. Similar results are obtained by the three methods and the linear static analysis based on design load evaluates with accuracy the local structural deformation and stress. The primary objective of the present work is to investigate the strength and safety of bow-flared structures when designing high-speed and fast displacement aluminium crafts subjected to slamming pressure loads. The influence of spray rail on the bow-flared slamming pressures and the effect of boundary conditions on the elastic structural responses are discussed. • The strength of bow-flared structures is assessed for high-speed aluminium crafts subjected to slamming pressure loads. • The response of an aluminium stiffened panel of a fast craft under bow flare slamming is assessed by 3 FEMs. • The slamming load is evaluated for a 2D rigid section, and the response are assessed by linear elastic analysis. • In the fully coupled method, the structural deformation and 3D hydrodynamic pressures are evaluated at each time step. [ABSTRACT FROM AUTHOR]