V.J. Papazoglou

Numerical Analysis of Thermal Stresses During Welding Including Phase Transformation Effects

The problem of determining temperature distributions, transient thermal strains, and residual stresses during butt welding thick plates with the multipass GMAW process is solved using the finite element method. First, a nonlinear heat transfer analysis is performed taking into account the temperature dependence of the material properties, and convection and radiation surface heat losses. This is followed by a thermo-elastic-plastic stress analysis that incorporates phase transformation strains. Finally, the theoretical predictions are compared with experimentally obtained data showing good correlation.

DEEP WATER MOORING DYNAMICS

The dynamics of mooring lines for deep water applications with submerged buoys attached to them are studied both experimentally and numerically. First, the theoretical background is outlined. The experimental set-up, as well as the data acquisition procedures, are then detailed. This is followed by a presentation of the obtained results and their comparison with numerical predictions using both time and frequency domain computer codes. Very good correlation is obtained. Finally, the beneficial effects of buoys in reducing the mooring line dynamic tension is shown, provided that proper selection of their size, number and location is performed.

Buckling of unsymmetric laminates under linearly varying, biaxial in-plane loads, combined with shear

Classical lamination theory in conjunction with the Rayleigh-Ritz method is used for the determination of the critical buckling load of simply supported, unsymmetric cross-ply and antisymmetric angle-ply laminates, under linearly varying in-plane biaxial loads, combined with shear. The algorithms that produce each element of both the stiffness and load matrices in the final generalized eigenvalue problem are obtained. No limitation in the number of terms of the displacement field expansion considered exists. The validity of the presented method is evaluated by comparing its results with those of other investigators. Finally, a parametric study for both types of laminates is given, changing parameters such as the form of the applied load, the E1E2 ratio and the angle of fiber orientation.

Numerical modeling of composite laminated cylinders in compression using a novel imperfections modeling method

The present study presents the finite element modeling procedure of two composite laminated cylinders exhibiting initial geometric imperfections. Using as input a set of experimental measurements of the cylinder geometry, the application of the skinning method leads to the analytical representation of the cylinder imperfect internal, external and middle surfaces. A finite element mesh is then easily constructed over these surfaces. The results of the analysis are in very good agreement with the experimental strains and buckling load measurements and are used to estimate the knockdown effect of the imperfections on the cylinder buckling behaviour. They are also compared to results obtained by other simpler finite element models, in an effort to evaluate the accuracy of various modeling simplifications.

Three-dimensional effects on the natural vibrations of cracked timoshenko beams in water

Abstract An efficient and quick numerical method for the computation of the vertical natural vibrations of a Timoshenko beam in water is given. The method is based on one-dimensional Timoshenko beam finite elements for the structural part and on fluid boundary elements for the fluid part, in both coupled and uncoupled versions. Various boundary conditions, including the free-free case, can be taken into account. The longitudinal correction factor J (for three-dimensional and end-effects) is computed and compared with other published values. It is found that the J values remain almost the same for Euler-Bernoulli and Timoshenko beams of the same geometry, material and boundary conditions. The J values were also computed for a Timoshenko beam with a transverse crack and compared with those found for the uncracked beam. The results obtained were almost identical.

The effect of geometric imperfections on the buckling behaviour of composite laminated cylinders under external hydrostatic pressure

Using a new FE modelling procedure for the accurate representation of a geometrically imperfect cylinder, the present study investigates the effect of the initial imperfection magnitude on the cylinder buckling load, when it is loaded by external hydrostatic pressure. The buckling behaviour of a carbon/epoxy filament wound cylinder is initially studied and the modelling procedure is validated through a comparison between calculated and experimental results. Various FE models are developed and evaluated, with increasing degree of complexity. The method is then applied to a cylinder with different end supports, to assess how the boundary conditions together with the imperfections affect the buckling behaviour. Finally, the effect of imperfection magnitude is investigated, leading to the calculation of knockdown factors as low as 0.6.

Large deflection dynamic response of composite laminated plates under in-plane loads

An analytical solution is presented for the dynamic buckling behaviour of a laminate subjected to time-dependent uniformly distributed normal and shear in-plane loads based on the Classical Lamination Theory and accounting for moderately large deflections. The assumed load-time variation is either linear or of a pulse type. The Galerkin method is applied and the obtained nonlinear differential equations are solved numerically by the Runge-Kutta method. The parametric study performed revealed three distinct phases in the undamped centre deflection time-history of a laminate. No significant deformations are produced in phase I, while the subsequent phase II reflects the dynamic buckling behaviour, exhibiting a rapid increase of the deformations. These magnitudes follow an oscillating motion in phase III, analogous to the loading condition under consideration. Relatively large initial imperfection values change completely the response of the laminate, by eliminating both the characteristic dynamic buckling phase II and the oscillations of phase III.

Mechanical behaviour of bimodulus laminated plates

Abstract A new analytical method for the prediction of the mechanical behaviour of laminates consisting of layers having different properties in tension and compression is proposed in this paper. As a case study, bending of simply supported, multilayered, unsymmetric, specially orthotropic laminates under various types of lateral loads is considered. The underlying bending theory used is a higher-order shear deformation theory. With the proposed method, laminates having more than two layers, not necessarily in an antisymmetric stacking sequence, can be analyzed. The validity of the new method is confirmed by comparing its results with the ones of other simpler theories. Finally, as an example, deflections, strains and stresses are calculated for a five-layer, unsymmetric, specially-orthotropic laminate.

Large deflection dynamic response of composite laminated plates under lateral loads

A very effective analytical tool for the nonlinear large deflection response of simply supported laminated plates under the action of various types of time dependent lateral loads is presented. The solution, based on the Classical Lamination Theory and accounting for moderately large deflections, is obtained by applying the Galerkin procedure. Several numerical results are presented, including a convergence study, comparisons with other published results, and parametric studies. The relationship between duration of load application and lowest plate natural period that leads to a minimum response after load removal is investigated.

Dynamics of fractured Timoshenko beams moving in wavy fluids

Abstract The fail-safe criterion is applied to floating ship-like structures moving forward in waves. The proposed model utilizes thick-walled Timoshenko beam structures excited by waves. The response to wave excitation is evaluated numerically, including both hydrodynamic and structural damping. Added mass and damping terms appear on both sides of the global equations describing vibrations excited by waves. A coupled direct method has been adopted for the evaluation of the corresponding terms. The nominal stress near the crack, needed as input to the Paris equation for the evaluation of the cycles required to failure, is computed assuming known values for the stress intensity factor. The resulting fail-safe diagrams indicate the effect of various parameters of the problem.