Final report for biaxial testing of composite joint at elevated temperature
Publish date: 2017-03-03
Report number: FOI-R--4400--SE
Pages: 92
Written in: English
Keywords:
- Bolted joint
- Composite
- Biaxial loading
- Fatigue
- Spectrum loading
Abstract
We consider a hybrid joint in a structure between a composite plate and an aluminium plate which is heated to an elevated temperature. To simulate this load case on a non-expensive composite specimen a small test object was designed. A biaxial test rig which can be used in an ordinary load frame was designed. In the vertical load frame both grip displacement and force are measured with the sensors on the load frame. In the horizontal direction force and hydraulic cylinder movement are measured. Specimens were fatigue loaded at constant amplitude. Specimens were also spectrum fatigue loaded with three different load sequences which are based on modified short Falstaff spectrum. Addition of biaxial load will reduce fatigue life for constant amplitude loading. For biaxial loading an effective stress is calculated from the resulting force on a fastener. Using effective stress might be a conservative method for predicting constant amplitude fatigue life. The scatter in fatigue life for spectrum loaded specimens is very large. Miner´s rule prediction of spectrum fatigue life works for specimens with biaxial loading but not for specimens without biaxial loading. For spectrum loaded specimens there is no fatigue life reduction when a biaxial load is added. The testing suggest that the addition of some overloads only have a small effect on the fatigue life as long as static failure does not occur.