Experimental failure analysis of mechanically fastened joints with clearance in composite laminates under preload

A failure investigation was performed to determine the failure mode and bearing strength of mechanically fastened bolted-joints in glass fiber reinforced epoxy laminated composite plates, experimentally. Two different geometrical parameters those are the edge distance-to-hole diameter ratio (E/D) and plate width-to-hole diameter ratio (W/D) were considered. For this purpose, E/D ratio was selected from 1 to 5, whereas W/D ratio was chosen from 2 to 5. Due to determining material parameters effect, laminated plates were stacked as three different group which are [0°/0°/45°/−45°]s, [0°/0°/45°/45°]s and [0°/0°/30°/30°]s, symmetrically. In addition, the preload moments were applied as 0, 3 and 6 nm, since an important target of this study is to observe the changing of failure mechanism under various preloads. The experiments were also performed under a clearance, for this reason the diameters of the bolt and the circular bolt hole were fixed 5 and 6 mm, respectively. Results showed that failure modes and bearing strengths were considerable affected by the increasing of preloads. Furthermore, when the material and geometrical parameters of composite bolted-joints were changed, the failure behavior and the values of bearing strengths were fully influenced from this changing.