ANALYSIS OF FIRING AND FABRICATION STRESSES AND FAILURE IN CERAMIC-LINED CANNON TUBES

Four aspects of service loading of ceramic lined cannons are considered, based upon recent work with ceramics under cannon thermomechanical loads and upon experience with cannons made from more conventional materials. First, candidate ceramics are evaluated by comparing models of thermal compressive firing stress with their measured compressive strength at elevated temperatures. The strength of each of the ceramics exceeds typical near-bore firing stress, with SiAlON having more margin between high temperature strength and near-bore firing stress than SiC and Si(3)N(4). Second, an upper bound analysis is performed of the shear failure of a typical ceramic "island" created by thermal cracks and subjected to further compressive firing stress. The analysis shows that failure of cracked ceramic islands is possible. Third, a generic design concept of a thin ceramic liner is considered, supported by a thicker, intermediate, shrink-fitted, steel liner, and further supported by a shrink-fitted steel or tension-wrapped carbon fiber/epoxy jacket. Radial and hoop fabrication and firing stresses are calculated and axial fabrication stresses are estimated for typical cannon steel and composite properties, showing radial crushing of composites to be a concern. Fourth, a fracture mechanics analysis is used to calculate the cannon firing pressure at which a thermal crack would grow to full depth of the ceramic liner. The low fracture toughness of SiC is a limitation.