Sherif Rashed

Effect of low transformation temperature weld filler metal on welding residual stress

Abstract The effect of weld filler metal austenite to acicular ferrite transformation temperature on the residual stresses that arise during the gas metal arc welding of a low carbon steel has been examined using a finite element model. It was found that the stress levels in the weld can be tailored by the appropriate selection of the filler metal and compressive, near zero or tensile residual stresses produced. Reasonable agreement was obtained between the model and the stresses measured using neutron diffraction both in welds using conventional and low transformation temperature filler metal.

Buckling and Ultimate Strength Interaction in Plates and Stiffened Panels under Combined Inplane Biaxial and Shearing Forces

Abstract The main portion of a ships structure is usually composed of stiffened plates. Between girders and floors, stiffeners are furnished to plates usually in the longitudinal direction. Under various loads applied to a ship, such as those due to cargo, buoyancy and waves, these stiffened plates are subjected to combined inplane and lateral loads. Imperfections due to fabrication exist mainly in the form of initial deflection and residual stresses. The behaviour of perfectly flat plates is, however, an important reference in design. In this paper, buckling, ultimate and fully plastic strength interaction relationships for rectangular perfectly flat plates and uniaxially stiffened plates subjected to inplane biaxial and shearing forces are derived and expressed in explicit forms based on the results of theoretical investigations of the non-linear behaviour of plates and stiffened plates. The accuracy of these interaction relationships is confirmed through comparison with the results of other analysis methods. With the aid of these interaction relationships, buckling load, ultimate strength andlor fully plastic strength of such perfectly fat plates and uniaxially stiffened plates subjected to inplane loads may be predicted by hand calculation.

An incremental galerkin method for plates and stiffened plates

Abstract In order to perform a detailed analysis of large deflection behavior of a rectangular plate or stiffened plate, an efficient semi-analytical method is developed. First, incremental forms of the governing differential equations of plates and stiffened plates with initial deflection are derived. These equations are linearized and may be easily solved. Secondly, these equations are solved for each load increment by the Galerkin method with a special consideration of simply supported boundaries. A procedure of equilibrium correction at intermediate load steps is presented such that good accuracy of the solution may be maintained with larger load steps. This method is successfully applied to plates with initial deflection subjected to in-plane as well as out-of-plane loads to obtain the whole histories of the behavior of these plates. Application of this method to stiffened plates with initial deflection is also presented. Comparisons of results obtained by this method with those obtained by other methods are made and the validity of the method is demonstrated. This incremental version of the Galerkin method is found to be extremely advantageous in certain types of plate and stiffened plate problems. These types are identified and the efficiency of the method is demonstrated.

An Improved ISUM Rectangular Plate Element : Taking Account of Post-Ultimate Strength Behavior

Abstract In the framework of the Idealized Structural Unit Method (ISUM), a rectangular plate element has been developed. This element takes account of buckling, post-buckling behavior and ultimate strength of the plate. After ultimate strength, the element predicts a constant carrying capacity in contrast with the decreasing carrying capacity of actual plates after they reach their ultimate strength. In the ultimate strength analysis of redundant structures, such as ships, highly loaded plate panels may reach their ultimate strength and exhibit considerable plastic deformation, thus losing a portion of their carrying capacity, before the whole structure reaches its ultimate strength. In this paper, an improved element is presented in which the effectiveness of the plate after buckling is expressed as a function of the total strain, and a new concept of strain hardening is introduced in evaluating the post-ultimate strength elastic-plastic stiffness matrix. In this way, after the element reaches its ultimate strength, the reduction of plate strength with the increase of in-plane displacement can be evaluated. Comparison of the results of analysis by this improved element with those from the Finite Element Method indicates improved accuracy of the new element in practical use.

A practical method for prediction of distortion produced on large thin plate structures during welding assembly

Fusion welding processes are widely used to assemble large thin plate structures such as ships, automobiles, and passenger trains because of their high productivity. However, welding-induced distortion often inevitably occurs during the assembly process. Welding distortion not only reduces the fabrication accuracy of a welded structure but also decreases productivity due to correction works. If welding distortion can be predicted using a practical method beforehand, the prediction will be helpful for taking appropriate measures to control the dimensional accuracy. In this study, an elastic finite element method to predict the distortion accumulated in large and complex structures during the welding assembly process from cutting through straightening is developed based on inherent strain theory and interface element.

Reduction of Welding Distortion for an Improved Assembly Process for Hatch Coaming Production

The alignment between the hatch coaming top surface and hatch cover is essential to maintain hatch cover water tightness and smooth mechanical operation. An improved assembly process for hatch coaming production is proposed, in which the complete hatch coaming is assembled on the shop floor and then lifted as one part, fitted, and welded to the deck. When this complete hatch coaming is assembled to a ship deck, an irregularly distributed gap is usually found between the lower side of the hatch coaming and the deck. Fitting and welding distortion, in particular longitudinal and transverse shrinkage, influence the dimensional accuracy and consequently the production schedule. In this research, welding pass sequence of a fillet welded joint is improved using thermal elastic plastic analysis and welding distortion of the hatch coaming top surface is predicted using elastic analysis. First, three specimens with different gaps that model the welded joint between the hatch coaming and deck were welded and the changed distance between the measuring equipment and the flange was measured. A three-dimensional thermal elastic plastic finite element analysis was carried out for the same specimens and the computed welding distortion was shown to have good agreement with the measurements. As a result of the possible significant influence of welding pass sequence on transverse shrinkage of a fillet welded joint, the influence of welding pass sequence is studied using the computational approach and improved welding pass sequences are proposed to reduce transverse shrinkage. Finally, elastic analysis using inherent longitudinal and transverse shrinkage deformations evaluated by thermal elastic plastic analysis is used to predict welding distortion of the hatch coaming. In this elastic analysis, the influence of different gaps at different locations between the hatch coaming and the deck is considered.

FE Analysis of Buckling Behavior Caused by Welding in Thin Plates of High Tensile Strength Steel

Abstract The target of this study was to investigate buckling behavior during the entire welding process which consists of the heating and the cooling processes. For thin plate structures made of high tensile strength steel, not only residual buckling during or after cooling down but also transient buckling during heating may occur. The thermal elastic plastic FE analysis to investigate welding-induced buckling during the entire welding process is presented. Because of the high yield stress of high tensile strength steel, larger longitudinal compressive thermal stress is produced near the welding line compared with that in the case of carbon steel. Therefore, the plate may buckle due to thermal expansion, before the material nears yielding. During cooling down, the longitudinal compressive thermal stress close to the welding line disappears, and longitudinal tensile residual stress is produced due to contraction. Meanwhile, longitudinal compressive residual stress occurs far from the welding line to balance the tensile stress close to the welding line. This distribution of longitudinal residual stress would change the deformed dish shape of transient buckling into a saddle buckling type when the stress exceeds the critical buckling condition.

FEM Analysis of Joint Interface Formation in Magnetic Pressure Seam Welding

The magnetic pressure seam welding is one of the candidate methods to join thin sheet smart and multifunctional materials. In this research, to examine the mechanism of magnetic pressure welding from a dynamic viewpoint, numerical simulation of the impact was carried out by using a commercial Euler-Lagrange coupling software MSC.Dytran (MSC.Software) as a first step of the computational studies, where the joint between Fe and Al was employed according to the previous experimental researches. From the serial numerical results, it was found that the increase of temperature at the joint interface was not enough to melt Al or Fe in the range of collision velocity and angle studied in this report. Also, it was revealed that the very large mean stress occurred at the interface which could be considered as the pressure at joint interface and Al moved with high velocity along the interface. Moreover, it was found that there were two patterns of plastic strain distribution near the joint interface depending on the collision velocity and collision angle. Finally, it can be concluded that the plastic strain pattern might be related to the success of magnetic pressure seam welding.

Buckling and Ultimate Strength Interactions of Plates and Stiffened Plates under Combined Loads (1 st Report)

The main portion of a ship structure is usually composed of stiffened plates. Between girders and floors, stiffeners are furnished to plates in one direction, usually the longitudinal direction. Under various loads applied to a ship, such as those due to waves, these stiffened plates are subjected to combined in-plane and lateral loads.In this report, buckling, ultimate and fully plastic strength interaction relations of plates and unidirectional stiffened plates subjected to in-plane biaxial and shearing forces, are derived and expressed in explicit forms based on the result of theoretical investigation of the nonlinear behaviour of plates and stiffened plates.The accuracy of the interaction relations is confirmed comparing with the result of analysis by other methods.With the aid of these interaction relations, buckling load and ultimate strength, or fully plastic strength of this type of stiffened plates subjected to in-plane loads may be predicted by hand calculation.