Effect of Gap and Shims on the Strain and Stress State of the Composite-Aluminum Hybrid Bolted Structure

Abstract

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 X -direction is mainly affected by the bending deformation, while the strain in the Y -direction is mainly affected by the compression of bolt head. For composite laminates, the strain value in the X -direction can be reduced by 8.31%-70.97% with shims. As for the strain value in the Y -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.

Duroplastic gap filling materials in preloaded bolted connections

“…This difference can be linked to a higher creep sensitivity of the MM1018 P in compliance with the results in [19]. 5) [%]…”

“…act,mean 4) µini,mean: calculated slip factors as mean values considering the initial preload when the tests started. 5) CV: Coefficient of variation for µini. | 6) µnom,mean: calculated slip factors as mean values considering the nominal preload level of Fp,C = 110 kN (M16).…”

Einsatz vom duroplastischen Spaltausgleichsmaterial DIAMANT MM1018 in vorgespannten geschraubten Verbindungen

“…B. in der Flugzeugindustrie weitverbreitet. Um das Tragverhalten solcher Verbindungen zu erfassen, werden laufend Untersuchungen durchgeführt [2–12]. Im Bereich des Stahlbaus ist jedoch der Einsatz derartiger Materialien, v. a. in Kombination mit geschraubten Verbindungen, noch nicht üblich.…”

Analytical method for assembly-induced deformation prediction of composite bolted joints with assembly gap

“…Thus, deformation computation of the assembled parts consist of bending deformation calculation and bolt head compression deformation calculation. 30 Flow chart of assembly-induced deformation prediction is shown in Figure 2. First of all, basic parameters are necessary, including parameters of the assembled parts (geometries, number of layers, single-layer thickness, ply-up, mechanical properties), parameters of the fasteners (number, space length, contact radii ratio, pressure distribution angle), parameters of the assembly gap (assembly gap size and position) and parameters of the shimming material (shimming thickness, shimming material properties).…”