Mechanical Properties and Fatigue Behavior of 2D and 3D Woven PMC Airframe Structures at Elevated Temperature

Abstract

The tension-tension fatigue behavior of newly developed polymer matrix composites (PMCs) was studied. The PMCs investigated in this effort consisted of an NRPE (a hightemperature polyimide) matrix reinforced with carbon fibers. Two PMCs consisting of the aforementioned matrix with different fiber architectures were studied: one reinforced with a 2D woven fiber fabric and another reinforced with a non-crimp 3D orthogonal woven fiber fabric. For both material systems (3D PMC and 2D PMC), material properties were investigated for both on-axis [0/90°] and off-axis [±45°] fiber orientations. Tensile properties were evaluated at (1) room temperature and (2) with one side of the specimen at 329 °C and the other side exposed to ambient air. Tension-tension fatigue tests were conducted at elevated temperature at a frequency of 1.0 Hz with a ratio of minimum stress to maximum stress of R=0.05. Fatigue run-out for this effort was defined as 2×10 cycles. Elevated temperature had little effect on the tensile properties of both material systems with the 0/90° fiber orientation; however, specimens with the ±45° fiber orientation exhibited a significant increase in failure strain at elevated temperature. The ultimate tensile strength (UTS) of both PMCs with the ±45° fiber orientation decreased slightly at elevated temperature. The 3D PMC did not not exhibit an increase in tensile strength and stiffness compared to the 2D PMC. However, the 2D PMC with ±45° fiber orientation produced significantly greater failure strain. The 2D PMC showed slightly better fatigue resistance than the 3D PMC with the 0/90° fiber orientation. For the ±45° fiber orientation, the fatigue limit for the 2D PMC was approximately two times greater than that for the 3D PMC. Microstructural investigation of tested specimens revealed delamination in the 2D PMC. However, the 3D PMC offered improved delamination resistance.