Experimental Investigation of Dynamically Loaded Bolted Joints in Carbon Fibre Composite Structures

Abstract

This paper reports on recent experimental work to investigate the response of bolted carbon fibre composite joints and structures when subjected to constant dynamic loading rates between 0.1 m/s and 10 m/s. Single fastener joints were tested in both the bearing (shear) and pull-through (normal) loading directions. It was found that the joints exhibited only minor loading rate dependence when loaded in the pull-through direction but there was a significant change in failure mode when the joints were loaded in bearing at or above 1 m/s. Below 1 m/s loading rate the failure mode consisted of initial bolt bearing followed by bolt failure. At a loading rate of 1 m/s and above the bolt failed in a 'tearing' mode that absorbed significantly more energy than the low rate tests. A simple composite structure was created to investigate the effect of loading rate on a more complex joint arrangement. The structure was loaded in two different modes and at constant dynamic loading rates between 0.1 m/s and 10 m/s. For the structure investigated and the loading modes considered, only minor loading rate effects were observed, even when the dominant contribution to joint loads came from bearing. It was observed that the load realignment present in the structural tests allowed the joints to fail in a mode that was not bearing dominant, and hence the loading rate sensitivity was not expressed.

Static and high-rate loading of single and multi-bolt carbon–epoxy aircraft fuselage joints

“…These findings are in agreement with Pearce et al [3], where below 1 m/s, limited bearing damage preceded bolt failure, but at 1 m/s and above, joints eventually failed in a cleavage mode with more bearing damage in the laminate. In the study of Heimbs et al [27] net-tension failure occurred in both the quasi-static and 2 m/s test on a two-bolt joint, but this changed to a bearing and fastener pull-through failure at 10 m/s.…”

“…As in [3], the dynamic loading rate was quantified by the far field velocity of the applied load. Quasi-static tests were carried out according to ASTM D5961/D5961M [29].…”

“…Consequently, greater energy was absorbed in the higher speed tests. [3,25] and Li et al [24]. The single-bolt, single-lap shear joint displayed bearing failure followed by fastener pull-through for all loading rates, with a similar load-displacement response at all rates.…”

“…Pearce et al [3,25] carried out tests at loading velocities of up to 10 m/s on bolted carbon-epoxy joints. Singlebolt joints were loaded in bearing and pull-through, and a more complex multi-bolt structure was the subject of dynamic impact tests.…”

“…The chosen dynamic loading velocities of 5 m/s and 10 m/s are representative of joint loading seen close to the impact site in low energy impact events and further away from the impact site in high energy events such as bird strike or gear-up landing [3]. Ultimate joint strength and energy absorption are the main focus as these are of primary importance in quantifying joint performance in such situations [24].…”