During the training flight, the CFI initiated a simulated engine power failure. The student pilot trimmed the airplane for 65 knots and maneuvered to a nearby grass runway. During the landing roll, the airplane hit a “hole or obstacle” and the airplane bounced. The CFI applied power and aborted the landing. After returning to the departure airport, structural damage and skin deformation was discovered to the aft fuselage. The operator reported damage to longerons and an aft bulkhead. The operator reported no mechanical malfunctions or failures with the airplane.