Laminate beam theory based design analysis of the sandwich End Notch Flexure (ENF) test specimen is presented. The analysis is specifically considering specimens with honeycomb core, prone to in-plane compression failure of the core, other undesirable failure modes such as face indentation and core shear failure are analyzed. In addition, crack stability and energy dissipation due to frictional sliding between the crack surfaces are analyzed. Parametric analysis of ENF specimens with a range of face and core thickness, is presented to guide the design. In-plane compression failure of the core, but shorten the range of crack lengths were stable growth occurs. A thicker face will also increase the critical load for crack propagation and by so elevate the risk for indentation and core shear failures. Increased core density is beneficial for preventing indentation and core shear failures, but may increase the risk for in-plane compression failure of the core. The thickness of the core does not strongly influence the critical load for crack propagation. A thicker core increases frictional energy loss, but reduces the risk for core shear failure. A thicker core, however, makes the ENF specimen more prone to in-plane compression failure. ENF sandwich specimens with foam and honeycomb core were tested. The test results support the design analysis.