The Effect of the Secondary Bending Moment on the Fracture Strength Evaluation of the Laser Welded Joints from a Web Core Sandwich Structure

Abstract

During the last period the interest on the sandwich structures has became more favorable due to the strength to weight ratio. In the same manner, in ship building field the lightweight structures became more and more attractive. With increasing the usage fields has increased the need to study the behavior of these structures. In general all the sandwich structures loaded in bending shows an effect of the secondary bending moment. In the case of web core sandwich panels used in ship structures has been observed a pronounced effect of the secondary bending moment on laser welded joints. Considering this, the paper presents an analysis of the fracture strength of laser welded joints of a web core sandwich structure, due to the effect of secondary bending moment. In the first part, the paper analytical formulation of the secondary bending moments and their effect on welded joints. This effect is explained on the basis of angle α defined in the paper and which depends on the thickness of the face plate, the thickness of the web plate and respectively the height. The paper continues with a numerical analysis of the stress and strain state from a web core sandwich beam and where also it is analyzed the effect of the secondary bending moment on the fracture strength of laser welded joints. Based on the carried out study it was observed that for high thickness of the web plate the effect of secondary bending moments is the overloading of the welded joints, instead for small thickness of the web plate the effect of the secondary bending moments can be of the unloading the welded joints. However, a small thickness of the web plate can affect the rigidity of the structure. Therefore, based on this study was proposed a solution to reduce the secondary bending moment without reducing the stiffness of the sandwich panel. The analysis conducted in this paper can be a design criterion for the web core sandwich structures.