BIAXIAL BEARING BYPASS TESTING OF GRAPHITE/EPOXY PLATES/

Bolted graphite/epoxy plates were subjected to in-plane biaxial loadin g. Cruciform shape samples were used. Testing was performed on a biaxi al machine developed and built at Concordia University. The bolt hole was constrained using a rigid structure. Four arms of the cruciform sa mples were independently loaded. Equal and opposite lateral loads were applied along one direction (y). Along the other direction (x), load is applied on one arm (right arm of the cruciform), while the opposite arm (left arm of the cruciform) was held fixed in the grip without ap plied load. This was possible because the bolt hole at the center of t he cruciform sample was held fixed. This opposite arm measured whichev er load that was bypassed around the constrained hole (called bypass l oad). Acoustic emission was used to measure the onset of failure. The applied load in the x direction at the onset of failure is called the joint strength. Subsequent to the onset of failure, the bypass load in creased significantly. Also after onset of failure, the bypass load on reloading was larger than the bypass load on previous loading. Result s obtained showed that the existence of lateral loads (load along the y direction) had significant effect on the joint strength. Increasing the lateral load decreased the joint strength. These results show that data obtained using uniaxial test are nonconservative.