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The present study focuses on buckling and collapse behaviors of cracked steel panel by accounting for the crack opening/closure. A rectangular panel with a transverse through crack to the loading direction is selected to better understand the typical mechanical characteristics of a panel subjected to a sequence of tensile to compressive loading. When a tensile load is applied to the cracked panel, a through crack gradually opened and yielding occurs around the crack tip. When a compressive load is applied after the tensile load, the crack gradually closed and elastic/elasto-plastic buckling occur. A shell-solid mixed finite element (FE) model is adopted to effectively analyze the crack opening/closure. Shell FEs are employed in the rectangular panel (shell model), while solid FEs are partially adopted around the crack (solid model). Double nodes and contact condition are imposed on the crack face. The shell and solid models are joined together with a rigid body element (RBE). The buckling and collapse behaviors of the panel models under a sequence of tensile to compressive loading is critically examined, as well as its local behavior, i.e., crack opening displacement (COD) varying displacement amplitude, panel aspect ratio and panel thickness. The results show that the crack opening/closure strongly affect the buckling and collapse behaviors of the cracked panel.

The external loads and structural ultimate strength are two important aspects for the safety of ship hull girder. It may collapse in case the structural capacity is less than the external forces in extreme seas. In the present research, progressive collapse test is performed to investigate the collapse mechanism of ship structure in waves. External load with time history and corresponding structural collapse behavior are measured and discussed to demonstrate the interaction of fluid and structures.

The dynamic buckling of the main deck grillage would result in the total collapse of the ship hull subjected to a far-filed underwater explosion. This dynamic buckling is mainly due to the dynamic moment of the ship hull when the ship hull experiences a sudden movement under impact load from the explosion. In order to investigate the ultimate strength of a typical deck grillage under quasi-static and dynamic in-plane compressive load, a structure model, in which the real constrained condition of the deck grillage was taken into consideration, was designed and manufactured. The quasi-static ultimate strength and damage mode of the deck grillage under in-plane compressive load was experimentally investigated. The Finite Element Method (FEM) was employed to predict the ultimate strength of the deck grillage subjected to quasi-static in-plane compressive load, and was validated by comparing the results from experimental tests and numerical simulations. In addition, the numerical simulations of dynamic buckling of the same model under in-plane impact load was performed, in which the influences of the load amplitude and the frequency of dynamic impact load, as well as the initial stress and deflection induced by wave load on the ultimate strength and failure mode were investigated. The results show that the dynamic buckling mode is quite different from the failure mode of the structure subjected to quasi-static in-plane compressive load. The displacements of deck edge in the vertical direction and the axial displacements are getting larger with the decrease of impact frequency. Besides, it is found that the dynamic buckling strength roughly linearly decreased with the increase of initial proportion of the static ultimate strength P0. The conclusions drawn from the researches of this paper would help better designing of the ship structure under impact loads.

A single wave of extreme height can damage ship structures in the ocean by generating buckling midship, thus destabilizing the ship girder and causing rupture. The probability of such an extreme wave is low in reality. On the one hand, it is very costly to recreate a real ship test for the study of extreme wave conditions. On the other hand, it is difficult to carry out tests on a scale model in tank waves, because such waves are too small to damage the ship model. In this paper, a hydroelasto-buckling experiment is performed on a ship model to study the dynamic ultimate strength of the ship and dynamic course of collapse of the structure. Thus far, no method of simulation has been proposed to study this problem because the dynamic ultimate strength of the ship involves strong coupling between the nonlinearity in the ship structure and waves. Here, a hydroelasto-buckling ship model is first designed, and a test programme is determined. A buckling hinge that can collapse under the load of the tank wave is used to connect two ship girders with a hinge joint. Then, a number of single tank waves are generated by changing their wave patterns to simulate an extreme ocean wave. The dynamic rotation angle, bottom water press and acceleration at midship are measured in the experiment. Importantly, the relationship between structural response and wave patterns is analyzed. The structural response involves encountering the VBM/rotation deformation induced by the wave load and whipping the VBM/rotation deformation induced by natural structural oscillations. It is found that the ultimate strength of the ship girder can be generated by both encountering waves and the structural flutter response caused by changing wave height. Lastly, the midship water pressure and acceleration are also analyzed to discuss the influence of a large deformation of the ship structure on the fluid load. Some conclusions are presented in the paper.

The combination damage induced by mechanical interference, in reality, is more likely to happen. In this paper, numerical models on pipes with combined dent and metal loss in terms of a notch are developed and validated through tests (diameter-to-thickness ratio D / t of test pipes around 21), capable of predicting the residual ultimate strength of pipes in terms of bending moment ( M c r ) and critical curvature ( κ c r ). The effect of residual stress is explored, assuming a linear distribution in the pipe hoop direction. Investigations of damaged pipes with different D / t (15–50) are carried out. Through changing damage parameters in the combinations, i.e. dent depth ( d d ) or metal loss depth ( d m ), the corresponding effects of damage are clarified. Results show that the combined dent and notch damage is a more severe type of damage on pipe strength compared with other damage types (excluding fracture). The dent in combined damage plays a more dominant role on the pipe residual strength. Empirical formulas are proposed to predict residual ultimate strength of damaged metallic pipes ( D / t around 21) with combined dent and metal loss under bending moment, which can be used for practical purposes. The application domain can be expanded to pipes with D / t up to 30 based on simulations.

Numerical investigation is conducted in this paper on both intact and dented seamless metallic pipelines (diameter-to-thickness ratio D/t around 21), deploying nonlinear finite element method (FEM). A full numerical model is developed, capable of predicting the residual ultimate strength of pipes in terms of bending capacity (Mcr) and critical curvature (κcr). The simulation results are validated through test results by using the measured material properties and specimen geometry. An extensive parametric investigation is conducted on the influences of material anisotropy, initial imperfection, friction of the test set-up and dent parameters. It is found that the structural response is quite sensitive to the frictions that have been introduced by the test configuration. For a pipe with a considerable dent size, the effect of manufacturing induced initial imperfection is insignificant and can be neglected in the FEM simulation. The material yield stress in the pipe longitudinal direction dominates the bending capacity of structures. In the end, formulas are proposed to predict the residual ultimate strength of dented metallic pipes under pure bending moment, which can be used for practical purposes. A satisfying fit is obtained through the comparison between the formulas and FEM methods.

The ultimate strength of metallic pipelines will be inevitably affected when they have suffered from structural damage after mechanical interference. The present experiments aim to investigate the residual ultimate bending strength of metallic pipes with structural damage based on large-scale pipe tests. Artificial damage, such as a dent, metal loss, a crack, and combinations thereof, is introduced to the pipe surface in advance. Four-point bending tests are performed to investigate the structural behavior of metallic pipes in terms of bending moment–curvature diagrams, failure modes, bending capacity, and critical bending curvatures. Test results show that the occurrence of structural damage on the pipe compression side reduces the bending capacity significantly. Only a slight effect has been observed for pipes with damage on the tensile side as long as no fracture failure appears. The possible causes that have introduced experimental errors are presented and discussed. The test data obtained in this paper can be used to further quantify damage effects on bending capacity of seamless pipes with similar D/t ratios. The comparison results in this paper can facilitate the structural integrity design as well as the maintenance of damaged pipes when mechanical interference happens during the service life of pipelines.