This paper discusses the potential of T300/V-378A graphite/bismaleimide for use in aircraft structures that are likely to be exposed to service temperatures in the 120 to 204°C (250 to 400°F) range. The microstructure of cured T300/V-378A laminates was examined to detect the presence of any process-induced defects; moisture absorption studies were conducted to characterize the hygroscopic behavior of the material; and its basic properties were generated through static tests on 16T, 16T, and [±45]4s laminates. These were followed by static tests on plain [0/±45/90]2s T300/V-378A specimens and specimens with unloaded (open and filled) and loaded holes. Tests were conducted under room temperature, dry (RTD) and elevated temperature, wet (ETW) conditions. Plain specimens and specimens with open holes were also subjected to constant-amplitude fatigue tests at minimum-to-maximum cyclic stress ratios (R) of 0.05 and −1.0.
Subsequently, the tolerance of [0/±45/90]4s T300/V-378 laminates to low-velocity impact damage by a hard object was evaluated by measuring impact energy levels corresponding to incipient (not necessarily visible) damage and through-penetration. Specimens from impact-damaged panels were then tested to obtain residual static compression strengths. Finally, multibay, hat-stiffened, flat shear panels were fabricated using the T300/V-378A material system, and were subjected to pure-shear static and fatigue tests under RTD and ETW conditions.
Results were compared with available data on T300/5208 and AS/3501-6 graphite/epoxy laminates to assess the relative merits of the T300/V-378A graphite/bismaleimide material system. In general, the RTD matrix-dominated response of T300/V-378A laminates is inferior to that of AS1/3501-6 laminates. But, the T300/V-378A laminates retain most of their RTD strengths under 177°CW (350°FW) (wet) conditions, where conventional epoxy-matrix materials suffer property losses that occur at the glass transition temperature. The V-378A bismaleimide material, therefore, provides a viable alternative to conventional epoxy-matrix materials, for applications in components that experience humid conditions and temperatures in the 120 to 205°C (250° to 400°F) range.