A 81-mm mortar barrel that is at least 50% lighter than the current steel barrel used in the M252 mortar system would prove to be advantageous for the army. The desire for the weight reduction was based on the army’s vision of the future combat systems. The current barrel has a maximum rated pressure of 109 MPa (15,800 psi) and is capable of sustained fire rates of 15 rounds per minute. The concept of sheathing a steel liner with a lightweight material to meet the weight saving goal while satisfying the performance requirements was investigated. The perceived need for lightweight mortars led to the study of composite materials. Composites are increasingly being used because of their lightweight, high strength to stiffness ratio and high durability under severe loading environments.
High temperatures around 550oC (1022oF) are produced in the mortar barrel during firing. Very few resins are now available that are susceptible to working temperatures of as high as 350oC (662oF). A thermal barrier material was introduced between the steel liner and the composite sheath to reduce the transmission of high temperatures to the sheath, hence reducing the working temperature of the resin. Viable materials for the barrel were investigated and identified. 4340 steel was considered for the liner material, Nextel 610/Sialyte composite for the thermal barrier material and IM7/cyanate ester composite for the sheath material. The lightweight composite mortar barrel was modeled and analyzed using the finite element analysis software ABAQUS.
Finite element analysis was conducted on the mortar barrel to determine the integrity of the design against the maximum expected pressure and temperature loads. The failure strength analysis determined that the design was susceptible to the rated loads. The weight of the composite mortar barrel was evaluated to be 5.3 Kg (11.68 lb) while the weight of the current steel barrel is 12.4 Kg (27.4 lb). The composite mortar barrel design achieved a potential weight reduction of 57% compared to that of the current steel barrel.
