## 5 Results
### Stress Distributions at the 0/45 Interface near the Hole under Different Clamp-Up Load  
Generally, the plies elastic properties will have a momentous effect on the interlaminar stresses. However, for the laminate with tightened bolts, bolt clamp-up load seems to play a more important role for interlaminar stress distributions in the laminates near the bolt head, than in the ply properties. To further understand the clamp-up load \(F_{0}\) effect on the stress distribution around Position I and Position III, numerical calculation was performed at different clamping forces. The interlaminar stress distributions in the 0/45 interface at Position I and Position III are only given in this subsection, due to the 0/45 interface exhibiting a high magnitude of the interlaminar shear stress in this position. The variation of the interlaminar stresses around Position I at the 0/45 interface are presented in Figure 9, and the interlaminar stresses around Position III at the 0/45 interface are shown in Figure 10.  
As seen in Figure 9,  
* The interlaminar normal stress \(\sigma_{z}\) rises with increased clamp-up load in all regions of Position I at the 0/45 interface (Figure 9a). In addition, \(\sigma_{z}\) also shows interlaminar compressive stress at Position I for the case of \(F_{0}\) = 6000 N.
* A higher clamping force results in lower interlaminar shear stresses for most of the region around Position I (Figure 9b,c). This area is in the region around \(-80^{\circ}<\theta<-10^{\circ}\) and \(10^{\circ}<\theta<55^{\circ}\). For the other areas around the hole, such as the region near \(\theta=0^{\circ}\), the interlaminar shear stresses almost become zero, regardless of the kind of bolt clamp-up load mentioned in this paper.  
It should be noted that the above two stress distribution phenomena are conductive to the improvement of the hole edge strength.  
Correspondingly, for the interlaminar stresses around Position III at the 0/45 interface as depicted in Figure 10:  
Figure 9: Stress distributions in 0/45 interface at Position I at different clamping forces: (**a**) \(\sigma_{z}\); (**b**) \(\tau_{xz}\) ; (**c**) \(\tau_{yz}\).  
* For the clamping force \(F_{0}=10\) N, both the interlaminar normal and shear stresses are almost zero in most areas at Position III, except \(\tau_{xz}\) in region \(-50^{\circ}<\theta<45^{\circ}\). This is consistent with the results obtained in Section 5.1.
* With the increase in clamp-up load, both interlaminar normal stress (Figure 10a) and interlaminar shear stresses (Figure 10b,c) increase in most of the circular region. This is different from the interlaminar stress distributions in the laminate at Position I. At Position III, the phenomenon of the interlaminar shear stress reduction does not appear with the increase in clamp-up load. In contrast, shear stress increases with the increase of the clamping force.  
As a result, the bolt clamp-up load cannot ameliorate the interlaminar stress distributions at the interface near Position II.  
The resulting phenomenon in this subsection can be summarized as follows: First, increasing the clamping force can reduce the magnitude of the interlaminar shear stresses in most regions around the hole. Thus, improvements can be made in the ability of the hole edge of the laminate to resist delamination. Second, the bolt clamp-up force cannot improve the interlaminar stress distribution near Position II. The former is consistent with the understanding of Reference [43]. For the latter, this paper will further analyze its causation.