Volume No. 6 Issue No.: 3A Page No.: 869-873 Jan-Mar 12




K.M. Pandey* and P. Bose

Department of Mechanical Engineering, National Institute of Technology, Silchar, Assam (INDIA)


Received on : November 25, 2011




Out of various mode of failure of rocket motor, material failure is the main cause of concern. This may be due to either the micro cracks present in the material or caused during manufacturing process. Ultimate tensile strength and thickness of the material are the parameters responsible for structural failure. The fracture strength of a classical brittle material is inversely proportional to the square root of the crack length. Stress intensity factor of the material when reaches its critical value called critical stress intensity factor, it fails as brittle fracture. It is a material property and the controlling factor to select suitable material for rocket motor. It decreases with the increase of material thickness. A thin plate sample of steel SAE 4130 having a central crack has been considered. The sample is stressed under tensile load in plane stress condition in universal testing machine. On reaching a particular stress, the crack begins to propagate and the same is analysed using Feddersen approach. Crack generated due to circumferential stress developed in the rocket motor tube as result of maximum propellant gas pressure should be less than half the thickness of the material. Under this condition it can be predicted that no structural failure would occur. The paper also suggests the criteria for safe design to withstand the severe conditions through which a rocket motor undergoes. The sample being the actual material certain data has been suitably modified however, keeping the working principle intact.


Keywords : Failure, Rocket Motor, Analysis, Tensile Strength, Stress intensity factor, Linear elastic fracture mechanics, Crack