Fatigue strength assessment of laser stake‐welded web‐core steel sandwich panels

Abstract

This paper investigates the fatigue strength assessment of web‐core steel sandwich panels. The production of these structures is made possible by laser stake welding. The investigation in this study considered two series of panels, one being an empty steel structure and the other filled with in situ polyurethane foam in order to increase the panel stiffness. Both series were tested under cyclic bending loading condition (R = 0) until one of the panel joints failed completely. A 3D panel bending response was analysed using finite element method. The J‐integral values at the panel joints were obtained by means of plane strain finite element analysis and by using displacements from 3D panel response. The influence of the weld geometry on the J‐integral value was investigated. It was found that the J‐integral value is similar in the cases of the average and critical geometry. The contact between the joint plates is possible in some cases, but its influence proved to be insignificant for the fatigue strength assessment. The study further shows that by using the average geometry, the J‐integral approach was able to identify the critical panel joints and present the fatigue strength results from both panel series in a narrow scatterband. The fatigue strength at two million cycles obtained for the panels within this study was in agreement with the laser stake welds and other steel joint types from previous studies. However, the slope of the panels fatigue resistance curve was found to be shallower than in the case of joints.

Fatigue strength assessment of laser stake-welded T-joints using local approaches

“…Regardless of the loading condition, one of the notch tips is more stressed and therefore critical from the fatigue point of view because this notch determines the fatigue strength of the joint [6]. The utilisation of local approaches requires accurate stress and strain fields around the critical notch tip and thus the response of the joint needs to be obtained by accounting precise notch depths [6,[11][12][13].…”

“…A systematic comparison of the above-mentioned stress and energy-based concepts showed that they can be used for the fatigue strength assessment of thick T-joints (t > 5 mm) [11]. Later, the J-integral was used for thin joints [6] and also for panels under different loading conditions [12,13]. However, the applicability of other approaches in studies [6,12,13] was not investigated further.…”

“…Later, the J-integral was used for thin joints [6] and also for panels under different loading conditions [12,13]. However, the applicability of other approaches in studies [6,12,13] was not investigated further. It was observed that the J-integral-based fatigue resistance curves can have slope values between 4 and 8, depending on the loading condition [12].…”

Geometrical parameters influence on the stiffness of steel sandwich plates with web-core

“…(3) the experimental result has a good repeatability and reliability. So according to the equations (1) and (2), it is calculated that the bending stiffness is 2.92×10 5 Nm  , and the shear stiffness is 8.12×10 5 N/m .…”

“…The joint connects a vertical core plate called the web plate to the horizontal face plates that are located far from the mid-plane of the cross-section of the panel. The so-called sandwich effect is achieved by the coupled response of the connected web and face plates [5]. The design and production aspects of web-core panels in the shipbuilding industry have been explored by many authors [6][7][8] and in civil engineering [9][10][11].…”