Kengo Kuwaki

FEM Stress Analyses of the Contact Stress Distributions at the Bearing Surfaces in Bolted Joints Using Hexagon Bolts With Flanges

In designing bolted joints, it is important to understand the contact stress distribution and permanent set at the bearing surface in the case of high initial axial tension. They are investigated using elasto-plastic FEM for hexagon bolts with flange. It is found that the difference in the contact stress distribution is large between elastic FEM and elasto-plastic FEM. Effects of the flange thickness and the flange slope angle on the contact stress distribution and permanent set are examined, and it is shown that they are substantially influential. In the experiments, hollow cylindrical specimens are compressed by the bolts with flange and permanent sets are measured at the bearing surface. The permanent sets are compared with permanent sets obtained from the elasto-plastic FEM and they are in a fairly good agreement. In addition, the equivalent length for the hexagon bolt with flange is proposed.Copyright

FEM Contact Stress Analysis at the Bearing Surfaces in Bolted Joints With Washer Under Tensile Loadings

High strength bolts with washers are utilized widely for high reliability. The usage of the high strength bolts enables higher bolt preload, thus the contact stress at the bearing surfaces increase. When a bolted joint is under external axial load W, the axial bolt force increases by Ft and the contact stress increases at the bearing surface. This may cause the plastic deformation and a decrease in the axial bolt force. Consequently, it is important to determine the initial axial bolt force (bolt preload) considering external load. In this paper, The characteristics of hollow cylindrical bolted joints with plain washers under external tensile loadings are analyzed using elasto-plastic FEM such as the contact stress distributions, plastic displacement (permanent set) at the bearing surfaces and the load factor Φ = (Ft/W). The effect of thickness of the plain washers on the contact stress distributions and the plastic displacements are clarified. It is found that the effect of the plain washer specified in JIS B 1256 is small on the contact stress distributions and the plastic displacements. Also, the effect of the external load on the changes in the contact stress distributions and the plastic displacements at the bearing surfaces using the values of load factor is observed to be small. The prediction for the reduction in axial bolt force was compared with the experiment. As a result, it was found that a higher bolt preload shows a small reduction in axial bolt force.Copyright

The Load Factor and Permanent Set at the Bearing Surfaces in Hollow Cylindrical Bolted Joints Under External Axial Loads

High strength bolts are utilized widely for high reliability and to reduce the weight of the bolted joints. The usage of the high strength bolts may increase the contact stress at the bearing surfaces. When a bolted joint is under external axial load W, the axial bolt force increases by Ft and the contact stress increases at the bearing surface. This may cause the plastic deformation and a decrease in the axial bolt force. Consequently, it is important to determine the initial axial bolt force (bolt preload) considering external load. In this paper, (load factor) Φ = (Ft/W) is investigated by axi-symmetrical theory of elasticity, FEM analysis and experiments. The results obtained from these methods showed in a fairly good agreement. Then the contact stress distributions and the plastic displacement distributions under external loads were studied for three different initial axial forces by elasto-plastic FEM analyses. The prediction for the reduction in axial bolt force, which is obtained by multiplying the setting factor by the mean plastic displacement, was compared with the experiment. As a result, it was found that a higher bolt preload shows a small reduction in axial bolt force.Copyright

FEM Stress Analysis of the Characteristics of Bolted Joints Under External Loadings (In the Case Where Two Hollow Cylinders Are Clamped)

In designing bolted joints, it is necessary to know the stress distributions in bolted joints. Recently, high strength bolts have been used with a higher bolt preload. As the results, the permanent set occurs sometimes at the bearing surfaces of clamped parts in a bolted joint. In addition, when an external load is applied to the bolted joint, the permanent set can be extended at the bearing surfaces. As the permanent set increases, the reduction in the bolt preload increases. Thus, it is important to estimate the reduction in the bolt preload from the reliability stand point. However, no study on the permanent set at the bearing surface under the external loading has been carried out. In this study, the stress distribution and the extension of the permanent set at the bearing surface of the bolted joint under the external tensile loading are examined using finite element Method (FEM), where two hollow cylinders are clamped with a hexagon bolt and a nut. The spring constants for the hexagon bolt and the clamped parts are analyzed using an axi-symmetrical theory of elasticity. Using the obtained results, an increment in the axial bolt force and the reduction in the bolt preload are estimated. For verification of the FEM stress analysis, the load factor of hexagon bolt was measured. The FEM results of the load factor (the increment in the axial bolt force) and the axial bolt force are in a fairly good agreement with the experimental results and the reduction of the axial bolt force. Finally, discussion is made on the appreciate bolt preload.Copyright

FEM Stress Analysis of Mechanical Behaviors in Bolted Joints Under External Loadings

In designing bolted joints, it is necessary to know the stress-changes in bolt loads and the stress distribution at the interfaces between clamped parts when external load is applied to the joints. The ratio of variation of bolt load to external load is called the load factor. The load factors have been studied. However, the load factors for bolted joints using bolt with flange have not been studied. In the present paper the mechanical behaviors of bolted joints in which bolt with flange are used such as the load factor and the contact stress distributions at the bearing surfaces are analyzed using Finite Element Method calculations in the case where the clamped parts are two hollow cylinders. The effects of factor such as flange slope angle on the value of the load factor, the contact stress distribution and permanent set at the bearing surfaces are examined. Variation of permanent set at the bearing surface when the external load is applied has not studied. In the experiments, to examine the load factor for the joints using a bolt/nut with flange, the variations of bolt load under the external loading were measured. The calculated results of the load factor show a fairy good agreement with the measured results. In addition, engineering formula for calculating the spring constant of bolt and nut with flanges are proposed.Copyright