Bearing Strenght of Thin ply Carbon fiber Laminates

Sammanfattning: The lighter an object is the easier it is to send into space. This principle is what drives the never ending hunt for lighter structures in the space industry. One way to reduce weight is to replace existing materials with lighter ones. Polymer matrix composites are such materials, as their density is lower than both steel and aluminium. The company RUAG Space produces a payload separating system that operates by clamping the payload using a clamp band to the rocket and releasing the payload by releasing the tension in the band. The current band is made in aluminium but RUAG seeks to build them using carbon fiber reinforced epoxy instead. Earlier projects have shown that carbon fiber fulfills the basic requirements, but has insufficient bearing strength to handle the loads at the bolted joints to the release mechanism. Research suggests that making the individual layers of carbon fiber thinner will increase the bearing strength and so in this project test specimen have been manufactured using thick and thin carbon fiber layers. These specimen were then subjected to bearing loads and the response was observed. The result showed that the ultimate bearing strength only increased a small amount with thin plies, but the onset of damage came at 47% higher stress levels compared to thick plies, suggesting a more brittle behavior. Since the onset of damage is the most important factor for RUAG the use of thin plies produced very positive results and could be a viable solution to increase the bearing strength in the clamp band.