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Engineering Design Fundamentals and Single Flat Joint Characteristics 241

obtained from the related researches, e.g., those of Kirsanova, Boothroyd
et al., and Burdekin et al., the following characteristic behavior can be
revealed.

1. The shear stiffness increases with normal preload and also the
improvement of the surface finish.
2. The tangential deflection consists of the elastic deflection and
microslip, showing a considerable residual displacement after unload-
ing of the first loading cycle.
3. The hysteresis loop decreases its area with the increase of normal pre-
load and repeated number of loading cycles.
4. The hysteresis loop encompasses gradually wider area with increas-
ing tangential force under constant normal preload, as shown in
Fig. 6-18, simultaneously maintaining constant slope of loops.
5. The joint deflection in tangential direction is, in most cases, compa-
rable with that in normal direction. In addition, the load-deflection
curve shows an opposite trend to that subjected to normal loading:
the incremental tangential stiffness is maximum at the commence-
ment of loading, whereas the incremental normal stiffness increases
continuously with loading.

Tangential force
P h

P hs

Slope K pa

X
Displacement

Figure 6-18 Hysteresis loops with increasing tangential loads
under constant normal preload (courtesy of Boothroyd).