A higher bolt preload is desirable for higher integrity of bolted joints. However, the bearing surface in the joints could be permanently deformed under a higher preload and the bolt preload decreases with an increase of permanent deformation. Various materials are used as clamped parts, so the permanent plastic deformation should be examined for each material clamped parts. In addition, the critical contact stresses should be examined for various clamped materials. In the previous paper, it was found that the relationship between the contact stress when the plastic deformation initiated, and the compressive proof stress of the clamped parts is linear. However, this conclusion was due to the specific bolt shape and dimensions. In the present paper, the effects of shape and dimensions of bolt head on the contact stress and deformation are examined. This applies to normal and undercut type bolts with sloped bearing surfaces. FEM calculations were used and the clamped part materials were steel and aluminum alloy. Also, a new contact area ratio at the bearing surface is defined and investigated because the nominal contact area is different from the actual contact area when the bolt bearing surface is sloped. Finally, discussion is made on an appropriate contact area, and critical contact stress at the bearing surface as well as suitable bolt shape and bolt head dimensions.

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