Quasi-static behaviour of composite joints with countersunk composite and metal fasteners

https://doi.org/10.1016/S1359-8368(01)00013-0Get rights and content

Abstract

An experimental study of the quasi-static behaviour of composite joints has been carried out. Composite plates were joined by six fasteners of three different types: composite, titanium Torque-set, and titanium Huck-comp. Specimens were quasi-statically tested to obtain results of the joint tensile and compressive strength. Strain gauge and extensometer measurements were used to investigate the static behaviour of the joints. Strain gauge measurements were carried out to analyse strain distribution and load transfer between bolt rows. Extensometer measurements were done in order to observe bolt-movement behaviour. Generally, composite joints with titanium fasteners have a higher quasi-static strength than that with composite fasteners.

Section snippets

Background

Advanced composite materials have been used extensively in the aircraft industry for manufacturing of both primary and secondary structures. Mechanical fastening along with adhesive gluing are common joining techniques for assembling structural components in aircraft. However, in comparison with adhesive technique, joining by mechanical fasteners offers several advantages: no special requirement is needed for the surface treatment, the joined members may be disassembled without being damaged,

Specimen preparation

Composite plates were manufactured from carbon fibre/epoxy material system (HTA7/6376) with quasi-isotropic layups [±45/0/90)3]s and [(±45/0/90)6]s for the outer and middle plates, respectively. The nominal ply thickness was 0.13 mm. The thickness of the composite laminates was 3.12 and 6.24 mm for the outer and middle plates, respectively. Elastic modulus of the composite plates in load direction, Ex, was equal to 51 GPa. The composite plates were joined by six fasteners of three different types:

Quasi-static tensile tests

One specimen of each type was quasi-statically tested to obtain the ultimate tensile strength data. Failure was considered to have occurred when the specimen could not withstand any additional increase in load. The ultimate static strength is defined as the peak failure load divided by the nominal cross-section area of the laminate. The ultimate strain was calculated using the ultimate static stress and the longitudinal elastic modulus of the composite plates. The tensile test results are

Conclusions

This paper has presented experimental results of quasi-static tests of multi-row composite joints with three countersunk fastener systems. From the experimental study, the following conclusions can be drawn:

  • The highest quasi-static strength was obtained for specimens with titanium fasteners. The specimens displayed the same static strength since the failure mode was net-section, which is not greatly affected by fastener type.

  • Composite bolts demonstrated lower mechanical strength to support

Acknowledgements

The authors wish to thank Saab Military Aircraft (SMA) and FMV for financial support during the project, NFFP 336+345 and HU4431. Special thanks go to Dr Tonny Nyman at SMA for designing the specimens.

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