Tubular offshore structures are commonly assembled using welded joints, creating areas of stress concentration and potential fatigue failure. This study focuses on tubular T, Y and K joints, a common offshore structural component. Finite element modeling is used to predict stress concentration factors (Kt) for various loading conditions on the T, Y and K joints. The goal is to calculate Kt values and compare them to existing theoretical solutions from literature. Additionally, the influence of different loading modes (tension, bending) on the Kt values is investigated. By using advanced modeling techniques, this work aims to provide new insight into the behavior of tubular T, Y and K joints connections under realistic offshore loading conditions. The results can help improve design standards and fatigue life predictions for these critical structural joints.

Since the late 80’s the Structural Analysis Research Group of the Instituto Superior Técnico (IST) has been involved in the development of non-conventional finite element formulations in order to overcome some of the limitations associated with the use of the CFE method and to develop high performance numerical tools for the analysis of structural engineering problems. Several alternative models for the linear and non-linear structural analysis have been developed using hybrid and mixed models techniques. These works are summarized in this paper, in which their past and future applications of this formulation in non-linear analysis of structures are fully detailed.

Modeling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. This paper presents an application of the finite element method to the analysis of crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental data. In the present study, the crack growth simulation has been numerically simulated by using the finite element source code program using Visual FORTRAN language. This code includes the mesh generator based on the advancing front method as well as all the pre and post process for the crack growth simulation under linear elastic fracture mechanics theory. The maximum circumferential stress criterion has been used for prediction of the crack growth in isotropic materials under mixed-mode loading. Furthermore, the equivalent domain integral method has been used for calculating the stress intensity factors values during crack growth. The crack grows when the stress intensity factor exceeds the fracture toughness of the material in the case of static loading. Verification of the predicted crack path is validated with relevant experimental data and numerical results obtained by other researchers with a good agreement.

In the present study, the flexural behavior of concrete beams reinforced with longitudinal rebars made of glass fiber reinforced polymer composites (GFRP), is studied using finite element method. For this purpose, a number of concrete beams with square sections are modeled in ABAQUS. In all of the beams, four GFRP rebars with diameter of 12 mm, and 10 steel rebars with diameter of 8 mm are vertically used to prevent creating shear cracks in the beams. The beam no. 1 is without transverse rebar, beam no. 2 has a row of transverse rebar, which is placed at the bottom and in the plane of vertical rebars. Beam no. 3 has a row of transverse rebars that is placed at the top and in the plane of vertical rebars; and the beam no. 4 has two rows of transverse rebar at the top and bottom of the beam in the plane of vertical rebars. The beams are gradually loaded under up to 6 ton, and the amounts of displacement and strain at the middle of beams are compared together. The obtained results reveal that the force-displacement diagram of reinforced beams with composite rebars are almost linear until ultimate phase, and in all of the beams, adding transverse rebar leads to less deflection in the middle of the beam under an identical loading. Moreover, the load bearing capacity of beams containing transverse rebars, were higher than the other beams.

Zirconia/ veneer bi-layered components are extensively used in dental restoration technology to improve resistance of tooth’s surface from decay. The direction of the fracture propagation at the interface of zirconia and veneer is investigated in this paper. Finite element analysis is performed on a bi-material four point bend specimen in different geometries, and the fracture initiation angle is obtained using maximum tangential stress (MTS) criterion. The effect of specimen geometry on the fracture initiation angle is discussed. Because an interface crack may propagate through interface or kink into one of the materials, some comments are given to determine under which condition “interface de-bounding” will be happened.

An analytical and numerical solution is developed for a transient heat conduction equation in which a plane slab is heated by a bimodal distribution beam over the upper surface. In laser heat treatment of steel few methods are used to produce a wider and nearly uniform average irradiance profile. This may be achieved by a bimodal (TEM11) shaped laser beam. In this paper, Green function method is employed to derive an analytical solution for thermal field distribution induced by laser forming process. Then 3-D finite element modeling of a slab in the ANSYS code is used to model the thermal field of laser forming with bimodal beam distribution. The results show that bimodal beam is useful for obtaining a uniform heat intensity distribution.

This paper presents an approach of linking finite element method with artificial neural network to predict J-Integral parameter in desirable airfoil condition. Finite Element (FE) and Artificial Neural Network (ANN) have been employed for the purpose. In other words, a prediction of finite element results has been done using ANN. Ultimately results of two methods have been compared for different cases. Wing fracture is a well-known problem of the planes which depends on various parameters. The J-integral is a vital parameter in evaluations of structure fracture phenomena. On the other hand residual stresses play an influential role in fracture formation. In the current work, effect of residual stresses and crack depth on J-Integral has been investigated in a standard NACA0012-34 airfoil. As will be seen, residual stresses and crack depth influence J-Integral values. It also will be shown that predictions of ANN method are in a good agreement with those obtained by finite element method.

Buckling is one of the most complicated concepts in mechanical engineering. Buckling often happens by compressive loads on thin structures. Thermal gradient between two ends of a column may cause a deflection in it. This will add an extra deformation to the one provided by compressive loads on the column. This phenomenon occurs when two ends of the column are at different temperatures, which can be seen at various structures. Because of the considered temperature gradients, the critical load of the column will decrease. In the current paper, various columns are modeled and the effect of thermal gradient and compressive load and other parameters on the Bi-material columns are studied. In other words, influences of compressive load and temperature gradient on critical load of Bi-material columns with interface crack are investigated. Effect of change in each parameter on critical load of column and crack opening was investigated. First, the thermal gradient was only applied to the model and in the next step; only the effect of mechanical loading was studied. Furthermore, artificial neural network (ANN) was used to extend the results to a bigger range of temperature conditions through the columns. Based on the results, ANN and finite element results are in a good agreement and the thermal effects may have a significant role in buckling of the column.

Generation of residual stress and structure deformation are the most important problems in the process of structure welding. Residual stresses inside and around the welded joints are harmful for integrity and proper functioning of the welded part. Tensile residual stresses near the weld zone may cause in developing brittle fracture, reduction of fatigue life or crack propagation caused by corrosion stresses. Welding residual stresses may even reach the yield stress of the part and can affect the thermal or mechanical working properties of it. Different thermal and mechanical approaches have been developed in the past in order to reduce these residual effects. Thus, both radiative and convective heat transfer methods have important roles in distribution of residual stresses during the welding process. In this study, convection and radiation effects on distribution of residual stress inside a welded part have been investigated for three different cases. In the first case, convection heat transfer was ignored and only effect of radiation on residual stress distribution was considered. In the second case, just the convection heat transfer applied on the model during the welding process. In another case, effects of radiation and convection heat transfer methods were investigated, simultaneously. Results of the current study showed that both radiative and convective heat transfer mechanisms have a significant share on distribution of residual stresses inside the welded part. It was also shown that the share of convection is greater than that of radiation heat transfer method.