The composite-aluminum hybrid bolted structures are widely used in aircraft. Due to low molding accuracy of composite components, gaps always occur between components during assembly. In this case, the bolt connection can cause a complex strain and stress state of component. It may adversely affect the mechanical properties or cause local damage of the structure. A simplified model of the composite-aluminum assembly structure was established in this paper. Then, the influence of forced assembly, liquid shim, and peelable fiberglass shim on the strain and stress state of the composite-aluminum hybrid bolted structure was studied. A bolt connection experimental device was designed to apply a preload to the specimen. The strain field on the specimen surface was measured using the 3D-DIC strain measurement system. The finite element model was established to study the interlaminar stress and damage state of composite laminates. It is found that the strain of specimen in the -direction is mainly affected by the bending deformation, while the strain in the -direction is mainly affected by the compression of bolt head. For composite laminates, the strain value in the -direction can be reduced by 8.31%-70.97% with shims. As for the strain value in the -direction, the liquid shim can only reduce it up to 23.93%when the gap is large. In addition, the liquid shim and peelable fiberglass shim cannot reduce the stress value of all interlaminar elements, but it can make the stress distribution more uniform and improve the stress state of the interlaminar element when the shim was more than 0.8 mm.

中文翻译：

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间隙和垫片对铝复合螺栓复合结构应变和应力状态的影响

复合铝混合螺栓结构广泛用于飞机。由于复合部件的成型精度低，因此在组装过程中总是在部件之间出现间隙。在这种情况下，螺栓连接会导致复杂的应变和应力状态。它可能会对机械性能产生不利影响，或导致结构的局部损坏。建立了复合铝装配结构的简化模型。然后，研究了强制组装，液体垫片和可剥离玻璃纤维垫片对复合铝混合螺栓结构的应变和应力状态的影响。设计了螺栓连接实验装置以对样品施加预紧力。使用3D-DIC应变测量系统测量样品表面的应变场。建立了有限元模型来研究层合板的层间应力和损伤状态。发现样品中的应变-方向主要受弯曲变形的影响，而-方向上的应变主要受螺栓头的压缩影响。对于复合层压板，带垫片可将-方向的应变值降低8.31％-70.97％。至于-方向上的应变值，当间隙较大时，液体垫片只能将其降低至23.93％。另外，液体垫片和可剥离玻璃纤维垫片不能降低所有层间元件的应力值，但是当垫片大于0.8mm时，它可以使应力分布更加均匀并改善层间元件的应力状态。