The contact area at the interface of a bolted joint was investigated analytically, experimentally and numerically. Consideration was restricted to an ideal two-plate model for which the interface was perfectly flat. The two plates made circularcontact under uniform axisymmetric normal loading. These investigations included the effect of important system parameters such as plate thickness, material properties and loading radius. In me analytical study, a two-plate model with an infinite radius,which had no center (bolt) hole, was mathematically analyzed. The normal stress distribution at the interface was used to predict the contact radius. Two alternative assumptions were considered. 1) continuous contact (no separation) at the interface, 2)discontinuous contact (separation beyond the contact region) at the interface. The continuous model was solved by a Hinkel transform and the discontinuous model by a Hankel transform and singular integral formulation.In the experimental study, a visualization technique using monochromatic light was carried out with a bolted joint which consisted of a transparent polycarbonate plate and a metal plate so that direct calibration of the contact radius was possible. Allthe test plates had rrirror4ixe surface finishes.In the numerical study, the finite element method was applied to two different two-plate models: one without a hole and the other with a hole.The results showed that the discontinuous model produced much closer agreement with the two-plate model with a hole than the continuous model, which produced a large discrepancy. The results also show that the effect of the bolt hole appeared to beinsignificant. The physical behavior of the contact radius of a bolted joint can be well explained from the mathematical equation of the discontinuous model. The contact radii obtained from Part 1 were implemented in the study of the thermal contactresistance described in the companion paper.
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