Load‐bearing performance comparison of lap joints in oxide ceramic matrix composites

Abstract This study evaluates the load‐bearing performance of oxide ceramic matrix composites (Ox‐CMCs) reinforced with continuous fibers, which contain fiber interruptions caused by the manufacturing process. Two different lap joint designs are evaluated: stepped and overlaying lap joints. Bending, tensile, and compression tests show a lower strength of the lap joints compared to an undamaged composite. The failure of stepped lap joints is primarily attributed to the propagation of a main crack in the porous ceramic matrix, that is not bridged by any fibers. Hence, sintering temperature has a positive effect on the strength. Overlaying lap joints exhibit higher strength, especially with the sintering temperature of 1200°C, with strength increasing further with longer overlap lengths. On the other hand, higher sintering temperatures do not lead to any improvement in strength due to the superimposed effect of limited crack deflection mechanisms and decreased fiber strength. In contrast to the strength, the stiffness of all lap joints remains consistent with that of the undamaged composite. In summary, if an interruption in the fiber layers of an Ox‐CMC structural element is unavoidable, overlaying lap joints with the longest possible overlap length, that is acceptable from a structural design standpoint, is recommended to enhance strength.