Search Results

Fatigue strength of steel sheet adhesive joints was investigated. From the results of the fatigue tests, it was obtained that the fatigue strength of the tensile-shear adhesive joints was much higher than that of the T-type tension adhesive joints. Stress distributions on adhesive layer have been analyzed by theoretical analysis method. All of the data obtained by the fatigue tests fell almost on one S/N curve, in spite of the differences of joints type and plate thickness, if the equivalent stress(Mises stress) range of the adhesive layer at the periphery of the end of the jointed part obtained by theoretical analysis was taken as the ordinate of S/N curve.

In automobile frame work, box members formed by spot welding two thin walled members of hat section together, or by welding a flat plate to one hat member are widely used as members. (The former are called double hat members, and the latter single hat members.) When such members are subjected to repeated torsion, cracks would occur at the spot weld point. This is due to a large shearing force transmitted through the weld point. Since fatigue strength is directly required in the aspect of design, many studies are being made in this connection. Considering that the basis of fatigue strength is primarily the stress distribution around the weld point, its problem must be clarified by all means. In this report, then, the stress distribution of welding flanges was theoretically analyzed as a plane stress problem and a bending problem of plates by the theory of elasticity and obtained by superposition of these solutions.

A method of fatigue life estimation for the spot-welds of vehicle body structures by means of Finite Element Analysis (FEA) was studied. 6 general forces applied to a nugget of spot-weld under multiaxial loads were determined and the Nominal Structural Stress (σns) was calculated from them. It was confirmed that fatigue strength of the spot-welds under various multiaxial loads could be estimated universally by using σns. Based on the theory of elasticity of plates, stress of spot-weld nugget was analyzed. The theoretical equations for determining the principal stress at the nugget edge from6 general forces acting on a nugget were derived. And the principal stress was defined as the σns. The value of σns was determined by FEM that used a solid model and compared with the theoretical calculation value. They agreed quite well. Fatigue tests of DC specimens under various multiaxial loads (shear plus cross tension and tensile shear plus torsion) were conducted.

In this paper, a new theory to obtain the nominal structural stress to the cross tension and the bending moment is described and, the method of the fatigue life estimation for the spot welding structure is proposed using this theory. Proposed method can do away with D value decision problem that is the current problem in D.Radaj's method for fatigue life estimation. Moreover, a nominal structural stress that is the fatigue strength evaluation parameter can be estimated in accuracy good, because the deformation around the nugget to which it pays attention in the spot welding structure is introduced into the analysis.

The main operations for the manufacturing of auto parts are the cutting of the flange and the stamping. In order to perform accurate fatigue calculation it is necessary to have the material properties for each point of the structure. Usually, only the fatigue curve obtained on the flat sheet with polished edges is used because it represents the basic metal behaviour. The real edge quality decreases the fatigue limit while the hardening induced by the stamping increases it. To take these effects into account allows a better fatigue calculation of the structural part.

In this paper the fatigue life of welded steel sheet structures is predicted by using FE-Fatigue, which is one of fatigue analysis software tools on the market, and these predicted results are evaluated by reference to corresponding experimental results. Also, we try to predict these structures by using two fatigue life prediction theories established by the JSAE fatigue and reliability committee to compare prediction results. It was confirmed that spot welds fatigue life predictions agree qualitatively with corresponding experimental results and arc welds fatigue life predictions are in good agreement with corresponding experimental results in cases where the SN curve database is modified appropriately.

Fatigue strength of adhesive bonded box beams with longitudinal partition was investigate. From results of the fatigue tests, it was seen that the fatigue strength of bonded beams was higher than that of spot welded beams. Fatigue strength of bonded beams was independent of plate thickness and partition. The flexural rigidity of the box beams in the plane of partition can increase without decrease of torsional rigidity and torsional fatigue strength, if the partition is jointed by adhesive bonding instead of spot welding.

Torsional fatigue tests of: spot-welded box-section beams were conducted to explain fatigue fracture phenomena, and a technique to predict fatigue life of spot welds in beams was developed. When a torsional moment acts on box-section beams that are hat beams with their flanges spot-welded to form closed sections, shearing force is transmitted through the spot welds. Based on theoretical analysis of stress distribution in the vicinity of spot welds and using strain values measured on the outer surface of spot welds, fatigue life of beams was successfully predicted. A technique to predict fatigue life of beams was developed by computing the load acting on spot welds in a beam and using fatigue strength data of a single-point spot-welded joint of the same load coponent.

For the purpose of changing the stress concentration controlling its fatigue strength. An “ELLIPTICAL” spot weld was investigated by the analytical method, the finite element analysis of the stress distribution around the spot weld and related fatigue experiments. The stress around the specimen with a flat elliptical spot weld can be lower than that a circular spot with the same area. Therefor, flat spot weld can be used for reduction of the stress concentration. Using the maximum stress, all of experimental S-N data for the spot welded specimens with various sizes and various radius ratios fell nearly into one scatter band.

A method of fatigue life prediction of spot welded joint under multi-axial loads has been developed by fatigue life estimation working groups in the committee on fatigue strength and structural reliability of JSAE. This method is based on the concept of nominal structural stress ( σ ns) proposed by Radaj and Rupp, and improved so that D value is not involved in stress calculation. The result of fatigue life estimation of actual vehicle with nominal structural stress which was calculated through newly developed method had very good correlation with the result of multi-axial loads fatigue test carried out with test piece including high strength steel.