5. Discussion and conclusions
Numerical calculations are performed for an aluminum plate with the following mechanical properties: Y= 414 MPa, E= 69 GPa, ν= 0.33 [8] and an elastic inclusion (for example, steel bolt). It follows from the stress analysis that the maximum allowable pressure is p ¼ p max ¼ 2= ffiffiffi 3 p . This value corresponds to the hole size α= 0.3376 which implies that for α≤0.3376, the plate never reaches its limit load carrying capacity (full plasticization), that is, some region of the plate near the outer radius will always be in the elastic state. For bolted structures, it means that the minimum distance between centers of bolts should be at least 2.96 times the bolt diameter (b = 2.96a). Hence, the analytical modeling of interference-fit structures presumes roughly α≤0.33. Meanwhile, in general fastener-hole applications, geometrical ratio α goes up to 1, and for αN0.3376, the plate reaches its limit load carrying capacity determined directly from the stress analysis for specific loads p max ≤2= ffiffiffi 3 p . However, to establish actual boundaries of external loading, a ductile failure criterion should be supplied based on the consideration of strains. One of the suitable criteria for interference-fit structures and elastic-perfectly-plastic material is so-called the decohesive carrying capacity criterion [29]. According to this criterion, the decohesion of the material may occur as a result of local infinite increase in radial strains, so a continuous deformation process terminates which automatically leads to the limit of serviceability of the structure. The review of papers dealing with problems of decohesive carrying capacity is given by Szuwalski [27] within elastic-perfectly-plastic material. For similar (to considered here) engineering problems, this criterion has been applied to a disk with rigid inclusion under various types of loading, namely, uniform tension at infinity [29], tension and in-plane torsion [30], tension and out-of-plane bending [31], and to a variable-thickness annular disk subjected to internal and external radial loading [32]. In most of these studies [29–31], at the moment of decohesion, radial strains increase infinitely at a disk/inclusion interface, and in [32]—at a particular location inside the disk.
