Fatigue strength of laser-welded foam-filled steel sandwich beams

International Journal of Fatigue, 1997

The present paper addresses the fatigue characteristics of two cellular foam core materials as used in load carrying sandwich structures. The fatigue loading studied is a constant shear stress which corresponds to the main type of loading that the core in a sandwich structure exhibits. Based on results from testing stress-life curves are presented for a number of stress ratios (R) and are fitted to a simple two-parameter Weibull function. The influence of the R-value is emphasized and standard Haigh diagrams are constructed. It is seen that the fatigue behaviour of the core materials investigated herein well can be described in manners similar to that of classical metal fatigue. A thorough investigation is performed on the behaviour of fatigue crack formation and growth.

Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2010

This is the last of three companion papers which examine the elastic buckling and collapse of laser-welded a sandwich panels with an adhesively bonded core and uni-directional vertical webs. By evaluation of the buckling stress in the first two papers it has been found that the buckling stress in compression parallel and normal to the webs typically reaches the proportional limit of the face plate and web material well before elastic buckling occurs. Hence, this paper presents an extension of the buckling model into the elasto-plastic regime, with the aim to determine the ultimate (local) strength of the sandwich and to allow experimental verification of the results. Using tangent modulus theory to 'plasticise' the elastic buckling model, the ultimate strength is evaluated for a sandwich configuration with high-strength steel face plates and a broad range of core moduli. The critical load predicted by the inelastic buckling model agrees well with non-linear finite element results and experimental values obtained from compression testing.

International Journal of Fatigue, 2001

Sandwich beams with aluminium face sheets and an aluminium alloy foam core are tested in cyclic four point bend, and S-N fatigue curves are determined for the failure modes of face fatigue, core shear and core indentation. The operative failure mode is dictated by the relative fatigue strength of face sheets to core, and upon the geometry of the sandwich beams. Simple analytical models are developed to predict the fatigue strength for each of the competing failure modes, and a design map is produced to display the fatigue strength and mode of failure as a function of sandwich beam geometry.

Materials Today: Proceedings, 2019

This study is to investigate the microstructure and the mechanical properties (hardness, strength, fatigue resistance) of laser welded double-lap joints from two different steels, ultra-high strength abrasion resistant steel (AR400) and low strength structural (S355 MC) steels. The laser welding was conducted at two different energy density 170 and 958 J/mm 2 and constant power 3 kW. The morphology and the microstructure of the cross-section lap joints have examined by optical microscopy. The shear strength and the fatigue resistance of the double-lap joints were evaluated by uniaxial tensile tests and fully reversed tension-compression strain-controlled fatigue tests, respectively. Whereas the hardness of the welded lap joints of UHS steel has been decreased due to the tempered martensite formation. The microstructure of the laser welded lap joints of LS steel shows martensite formation in the fusion zone. Hence, the hardness has been significantly increased to 300 Hv. The shear strengths of the welded lap joints have significantly influenced by the laser power density. Significant improvement in the strength could be observed in the strength of the lap joints of UHS steel at energy density 958 J/mm 2. Fatigue cracking along steels sheets boundaries that intersect the weld zone in the welded lap joints and the crack propagation towards the weld zone observed to be the fatigue-induced microstructural features in the lap joints welded by laser.

The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2007

This work deals with the study of two innovative joint techniques for aluminum composites: bonding with structural adhesives and hybrid laser-arc welding. The research objective is the mechanical behaviour of the roof of a railway carriage made by aluminum foam sandwich (AFS) panels, which are bonded or welded one to the other and to the vertical rod. As well known, bonding with structural adhesive is a less expensive joining technology, that does not affect the material characteristics and results in a better distribution of stresses. So, the aim of the experimental analysis is to investigate and validate the use of this technique. Several static and fatigue test on the components were executed and the results achieved for the welded components and the bonded ones were compared. At the beginning static tensile tests were performed submitting the adhesive to shear stresses, in order to reproduce the real loading condition on the component. Then, fatigue test were done on welded components to plot fatigue curves.

Welding in the World

For bridge deck applications, laser-welded corrugated core steel sandwich panels with dual weld lines per crest and trough have been shown to be highly material-and economically efficient. The nature of welding induces a variation in the geometric properties of the joint that connects the core to the faces. The geometric properties of the joint are the weld width, weld misalignment, and plate gap between the core and the faces. This paper aims to investigate the impact of the variation of the production-dependent geometric properties of the joint on the fatigue-relevant stresses. A secondary aim of this paper is to investigate the impact of contact between the core and the faces on the weld region stresses. Within this paper, the production of four sandwich panels is documented and the manufacturing-dependent geometric properties of their joints are quantified. In order to investigate the impact of the natural variation of the parameters, a parametric study based on finite element analyses is executed. The result of the parametric study shows, among several other findings, that misalignment of the weld line in relation to the core direction can lead to considerable increases in stresses, determinant for the fatigue life of the panel.

Jelovica, J., Romanoff, J. and Remes, H., “Influence of general corrosion on buckling strength of laser-welded web-core sandwich plates”, Journal of Constructional Steel Research, Vol.101, 2014, p. 342-350.

The strength of a web-core steel sandwich plate is potentially reduced in a corrosive environment. This study is dedicated to the influence of a reduction in the thickness of the plates as a result of general corrosion on sandwich plate buckling strength and first-fibre failure. Two scenarios are investigated in which corrosion reduces the thickness of (a) the outer sides of the face plates and (b) all surfaces, including the core. The laser weld between the face sheets and the core is assumed to be intact. The assumptions are made on the basis of earlier experimental findings. Critical buckling and geometric non-linear analysis are carried out with the finite element method, with the kinematics being represented using two approaches: (1) equivalent single-layer with first-order shear deformation theory, and (2) a three-dimensional model of the actual geometry of the structure, modelled using shell and connector elements. The former is used to identify the effect of corrosion on the stiffness coefficients and, consequently, the buckling strength. The latter is used for verification and for stress prediction during post-buckling. A rapid decrease in the buckling strength was found for corrosion affecting the outer sides of the sandwich plate. The decrease in the buckling strength doubled in the case of the diffusion of moisture (water) into the core. The shear-induced secondary bending of the faces was found to affect the first-fibre yield.

2011

Thin-Walled Structures, 2007

The purpose of this paper is to describe experiments carried out on laser stake welded T-joints of web-core steel sandwich structures. A special test setup was developed to measure the shear-induced rotation at the T-joint. The ratio of the shear force to rotation angle gave the joint stiffness. This stiffness was measured for specimens with two different face-plate thicknesses. The influence of weld thickness, root gap and occurrence of contact were further investigated with finite element simulations. Finally, the shear stiffness of the sandwich structure transverse to the web plate direction was determined using the experimentally obtained average joint stiffness value. The validation of the shear stiffness was carried out by considering a beam in four-point bending. The agreement between calculated deflection and stress and experimental results was found to be good. r

2004

Numerical modelling and dynamic analysis of laser-welded sandwich panels are carried out using the broken line sandwich finite elements. To homogenize material properties of complex sandwich core with evenly spaced vertical webs and low-density core material, two approaches have been applied. The first is connected with the rule of mixture and the second – with a calculation of equivalent stiffnesses. In order to describe the rheological behaviour of viscoelastic core materials under dynamic loading, the complex modulus representation is used. Dynamic characteristics of laser-welded sandwich panels are evaluated by the method of complex eigenvalues and from the resonant peaks of the frequency response function. To estimate correctness of the methodology developed, the ANSYS solutions for empty I-core steel sandwich beams and frequency response experimental measurements for different types of laser-welded sandwich beams with longitudinal and transverse webs and foam materials have be...