The characterization of carbon/epoxy 2D triaxial braid composites is a critical area of research for aerospace components, including jet engine fan blade containment. These materials exhibit high strength to stiffness, high damage tolerance, and a favorable impact response. This is due, in part, to the material behaving like a structure once damage occurs because of the mechanical interlocking and large unit cell of the fabric architecture. This, in turn, complicates the results and interpretation of coupon based mechanical testing because the desired uniaxial stress state is unavoidably lost within the material after the onset of damage. Though this same process will likely occur in structures, it has been shown in standard coupons that the existence of free edges can lead to premature initiation of local damage that leads to early failure. Therefore, many different methods will be needed to obtain reliable mechanical response data for use in models and structural design. The goal of this research is to attempt to bridge part of the gap between coupon level testing and structural component tests.
An in depth examination of tension, compression, and shear coupon test methods for generating stiffness, strength, and non-linear material response parameters has been performed. Additionally, the use of tubular specimens under various load conditions assisted in validation of alternate coupon geometries, as well as evaluating the utility of current cross-ply laminate test standards. Also, damage mechanisms, as they relate to global response, are considered.
The particular materials of interest (similar to braid architectures used in jet engine containment structures) have a large unit cell size which requires the use of relatively large tube specimens. To meet the “to failure” load requirements of these specimens, a custom high load, multiaxial test frame was designed, machined, and constructed. Control and data acquisition was achieved using National Instruments cDAQ hardware and custom NI Labview VI’s. The NI Labview control software includes a simple user interface with modules focused on test setup, monitoring, fault alert, and several other features. Development of tube grip fixtures and test specimen design has also been performed.
Committee: Wieslaw K. Binienda, Dr. (Advisor); Robert Goldberg, Dr. (Committee Member); Craig Menzemer, Dr. (Committee Member); Gregory Morscher, Dr. (Committee Member); Anil Patnaik, Dr. (Committee Member); Sasa Dordevic, Dr. (Committee Member)