Monday  |  Salon 11  |  10:00 AM–10:20 AM

#15794, A Stochastic Fiber Breakage Model for Stress-rupture Failure of Unidirectional Continuous Fiber Composites with Temperature and Non-linear Matrix Creep Effects

Stress rupture is a time-dependent failure mode occurring in unidirectional fiber composites under high tensile loads sustained over long times (e.g., many years), resulting in highly variable lifetimes and often with explosive consequences. Stress-rupture is of particular concern in such structures as composite overwrapped pressure vessels (COPVs), and tension members in infrastructure applications (suspended roofs, post-tensioned bridge cables). At the micromechanical level, stress rupture begins with the failure of individual fibers at random flaws, followed by local load-transfer to intact neighbors through shear stresses in the matrix. Over time, the matrix creeps in shear, which causes lengthening of overload zones around previous fiber breaks, resulting in even more fiber breaks, and eventually, formation clusters of fiber breaks, one of which eventually grows to a catastrophically unstable size.
Most previous models are direct extensions of classic stochastic breakdown models for a single fiber, and do not reflect such micromechanical activity, particularly in terms of the creep behavior of the matrix. These models may be adequate for modeling composite stress rupture under a constant load, however, they of highly questionable accuracy under more complex loading profiles, such as a constant load in service that follows a brief ‘proof test’ where they invariably predict an improved reliability of proof-test survivors. In our previous work relevant to carbon fiber/epoxy composite structures we showed that damage occurs nonetheless in the form of a large number of fiber breaks that would not otherwise occur, and in many important circumstances the net effect is reduced reliability over time, if the proof stress is too high.
The current paper continues our previous work by revising the model for matrix creep to include temperature effects into the non-linear matrix creep. Connections are made to the model by Miyano, which is not based in micromechanics.

Amy Engelbrecht-Wiggans   Rochester Institute of Technology
Stuart Phoenix   Cornell University