Abstract Manufacturing defects in the sandwich structures have significant impact on their ultimate strength performance. It is essential to codify some criteria for the effects of such defects on the performance of the structure in order to investigate the quality of sandwich compo-sites and their load-bearing capabilities. By means of such criteria, one can predict the property degradation of the defected structure in comparison to a defect-free one, and assess whether the faulty part could be remained in the structures. Among all the potential defects in a sandwich structure they could be induced during the Vacuum Infusion Process (VIP), the dry area defect is the most significant and frequently occurring one. Hence, adequate tests should be conducted in order to examine the effect of dry area defect on the structure. For this purpose, a methodology is required for preparing the defected samples similar to the main structure. The current study is aimed at suggesting two accurate approaches to induce artificial defects in sandwich structures manufactured implementing the vacuum infusion process. These methods are used for making some defected samples and their responses are compared with those of the defect-free structures. All samples are subjected to the uniform inplane compression loading and their behaviors up to the fracture point are evaluated to assess the remaining strength. Infusion process.

Abstract This article presents the results of numerical investigation on modeling buckling behavior and ultimate strength of corroded multi-planar tubular joints. Finite element method was used in order to simulate the behavior of DX multi-planar tubular joints under axial compressive loading. Three different patterns were chosen for corrosion modeling. Also the effects of corrosion-related parameters such as age and depth of corrosion were evaluated. The first corrosion pattern is based on uniform reduction of wall thickness over a portion of tube length while the second pattern represents a sinusoidal reduction of thickness. The third pattern of corrosion uses average thickness and standard deviation as main parameters for defining a random corroded region. A linear criterion for predicting corrosion wastage has been used for the first and the second patterns, whereas predictions of the third pattern are determined by a nonlinear method. The results indicate differences in the ultimate strength concluded from different patterns. It was found that conventional methods are conservative in evaluating the strength of corroded tubular joints of jacket platforms. Amongst 3 methods used for modeling corrosion, the third and the second pattern had similar results. It was also shown that corrosion is ineffective in braces and increasing the number of waves for the second pattern will result in increase of joint strength. The optimum sizes of elements were defined by implementing an analysis of model sensitivity toward element size.

Abstract Parametric study of composite-steel double lap joint under tensile loading is performed using finite element modeling. The joint is such that steel is placed between a straight and a curved composite sublaminate. Three joint characteristics including maximum Von Mises stress in adhesive layer, stiffness and weight are investigated. Design curves are provided to study the influence of geometric parameters on the joint behavior to determine the joint performance. The curves illustrate sensitivity of three mentioned joint characteristics to geometric variations. Selected parameters are adhesive thickness, overlap length, composite sublaminates’ thickness and stiffness ratio. Results indicate variation of parameters may have either significant or negligible influence in the performance of the joint. Results also show that variation in geometric parameters does not make monotonous change in the performance of the joint and in some cases rate of the changes may differ. From the prepared curves it can be understood that increase in overlap length and adhesive thickness will decrease maximum Von Mises stress in adhesive layer and global stiffness of the joint. In case of sublaminate thickness decrease in the thickness of straight sublaminate leads to decrease in maximum stress in adhesive layer while the stiffness is increased. For the stiffness ratio an optimized point can be found beyond which maximum stress will increase. Global stiffness of the joint increases by increase in stiffness ratio. Changes in weight of the joints are easily calculated from the geometry and are reported in the text.

Abstract Ultimate compressive strength of welded stiffened aluminium plates under combined biaxial in-plane compression and different levels of lateral pressure is assessed herein. A numerical database of the ultimate strengths for stiffened aluminium plates is generated at first. Then, regression analysis is applied in order to derive the empirical formulations as functions of two parameters, namely the plate slenderness ratio and the column (stiffener) slenderness ratio. The formulae implicitly include the effects of initial imperfections and heat affected zone.

AbstractThis paper is focused on experimental evaluation and comparison of progressive damage behaviors in adhesively bonded single lap and double butt lap joints between aluminum and glass fiber reinforced plastic (GFRP). The effect of joint design and dissimilarity of adherents on damage evolution of adhesive bonding under tensile quasi static loading is analyzed. Bonding was created by toughened epoxy adhesive as one of the most important and widely used structural adhesives in aerospace, automobile and marine industries. Due to structural behaviour complexity of adherents and adhesive, the fracture takes place under mixed mode and the failure mechanism is characterized by the de-bonding area for the proposed joints. The results show that single lap joint could carry up to 30% more tensile load than the double butt lap joint with the same material properties while a combined failure mechanism could be observed and the most dominant ones were yielding of aluminum substrates, adhesive failure at bond-line on aluminum surface and cohesive failure of upper mat layers of composite material.

This paper presents the results of anumerical investigation into ultimate strength of locally corroded tubular member sunder axial compressive loads. A parametric finite element approach was used in order to simulatestructuralbehavior of damaged members. The results were then examined against an available experimental test. Validated models were used to derive a semi-empirical formula for predicting ultimate strength of locally damaged tubes as a function of corrosion dimensions. Geometry ofcorrosion can be defined by its depth, length, width andlocation of damage along the tube. In this study it is focused on the effect of some parameters that have not been addressed yet by other researchers, e. g. slenderness of the tubes and location of patch corrosion. It was found that location of corrosion has great effect on reduction of ultimate strength. Effect of corrosion geometry was studiedand formulated as well as tubular slenderness and it was shown that tubes with different corrosion dimensions show different behaviors under compressive loads. In cases with severe corrosion damages, the occurrence of local buckling plays an important role on reduction of ultimate strength and deformation of damaged region.

In this study, vibration behavior of orthotropic cylindrical shells with variable thickness is investigated. Based on linear shell theory and applying energy method and using spline functions, free vibration relations are derived for shell with variable thickness and curvature. Frequency parameter and mode shapes are found after solving the frequency Eigenvalue equation. Effects of variable thickness along axial and circumferential directions of the shell on its frequency parameter are studied and compared against each other. Shell thickness is assumed to be varied in a parabolic profile along both directions. Also, frequency parameters for both circular and parabolic curvatures along circumferential direction are investigated and results are compared together. In addition, effect of variable thickness on the mode shapes is studied.

The post-buckling behavior of composite ships' stiffened plate panels has been studied. In this study, the average strain- average stress curves for these panels are derived using progressive failure method as well as nonlinear finite element method. The boundary conditions are appropriate for the continuous plate panels used in shipbuilding. The effects of the aspect ratio, initial geometrical imperfection and stiffener size on the post-buckling of these stiffened panels are evaluated

A novel ship concept design is significantly an "adhoc" process. In the preliminary design stage of novel vessels, it is very important to be able to develop an initial estimate of the effects of stiffness and mass distribution on the longitudinal flexural natural frequencies due to different general arrangements in still water at zero speed to satisfy design specifications. For new emerging designs, this estimate has to be made based on a model test. The experiments should also be planned so that scales effects and other features that are not present in full scale case, are minimized. A model with a length of 1.5 meter has been selected. The model was cut into four segments longitudinally and connected by a backbone beam with three elastic hinges joining the four segments. Wet vibration tests were conducted on the model, showed significant influences on the flexural natural frequencies through variations in stiffness and different mass distributions. The whipping frequency was calculated with four degrees of freedom theoretical model to compare with the experimental results. The theoretical model shows a good agreement with the experimental results.

Optimisation of stacking sequence for composite panels under slamming impact loads using a genetic algorithm method is studied in this paper. For this purpose, slamming load is assumed to have a uniform distribution with a triangular-pulse type of intensity function. In order to perform optimisation based on a genetic algorithm, a special code is written in MATLAB software environment. The optimiser is coupled with the commercial software ANSYS in order to analyse the composite panel under study and calculate the central deflection. After validation, different cases of stacking sequence optimisation are investigated for a variety of composite panels. The investigations include symmetric as well as asymmetric conditions of stacking sequence. Results obtained from these analyses reveal the fact that the adopted approach based on a genetic algorithm is highly capable of performing such optimisations.

Dynamic response and free vibration analysis of stiffened shells having parabolic curvatures, with applications to ships and other similar structures are the main focus of this study. The energy approach is employed to the determination of equivalent orthotropic shell parameters of parabolic stiffened shells. The unstiffened equivalent shell has proper accuracy in predicting free vibration characteristics as well as dynamic response of the main stiffened shell. Reducing the governing equation difficulties with suitable precision in free vibration and dynamic response analyses is the most advantage of replacement of stiffened shells with their unstiffened equivalences.

This paper presents the results of an investigation into the post-buckling behaviour and ultimate strength of imperfect pitted steel plates used in ship and other marine-related structures. A series of elastic-plastic large deflection finite element analyses is performed on pitted steel plates. The effects of pitting corrosion on one side of the plates are introduced into the finite element models. The effects on plate compressive strength as a result of parametric variation of the pitting corrosion geometry are evaluated. A proposal on the effective thickness is concluded in order to estimate the ultimate strength and explore the post-buckling behaviour of pitted steel plates under uniaxial compression.

This paper presents the vibration analysis of stiffened plates, using both conventional and super finite element methods. Mindlin plate and Timoshenko beam theories are utilized so as to formulate the plate and stiffeners, respectively. Eccentricity of the stiffeners is considered and they are not limited to be placed on nodal lines. Therefore, any configuration of plate and stiffeners can be modeled. Numerical examples are proposed to study the accuracy and convergence characteristics of the super elements. Effects of various parameters such as the boundary conditions of the plate, along with orientation, eccentricity, dimensions and number of the stiffeners on free vibration characteristics of stiffened panels are studied.

This paper describes an extended formulation for the coupled beam method (CBM). The method is originally developed for elastic bending response analysis of passenger ships with large multi-deck superstructures. The extension is mainly performed to enable the available method in order to study elastic bending behaviour of ships fitted with superstructures of any sizes and locations. Finite element method (FEM) is applied for solving the equilibrium equations. Both hull and superstructure of the ship are modelled using beam elements. The connection between beam elements representing hull and superstructure is made using specially developed spring box elements. The accuracy of the extended method is demonstrated using an available experimental result. Then, two simplified structures, one representing a ship with a short superstructure and the other one representing a ship with a long superstructure, are analysed in order to validate the extended coupled beam method against the finite element method. In spite of some existing simplifications in the extended formulation, it is very effective in the early stages of ship structural design owing to its advantageous capability of rapid estimation of the longitudinal stress distributions along the height of ships at different stations.

The main targets of this research are mainly divided in to two parts: (1) identifying the effects of parabolic curvature on the buckling strength and behaviour of stiffened plates under in-plane compression, (2) generating practical graphs for extracting eigenvalue buckling stress of parabolic curved stiffened plate to dimensionless parameters. A parametric model for study of the problem is created. The model includes different parameters related to plate, stiffeners and also parabolic curvature. Three distinct sensitivity cases are assumed. In each sensitivity case, many different models are analysed and their buckling strengths are obtained using a finite element commercial program (ANSYS). Buckling strength and behaviour of all models with different ratios of parabolic curvature are compared to each other.