Experimental study on erosion characteristics of char layer of EPDM composite by cold flow

Char layer erosion due to gas flow is an important part of the ablation process for insulation materials used in solid rocket motors (SRMs) or rocket ramjets. However, the current understanding of the erosion pattern is very limited. This paper reports on an experimental study on the erosion characteristics of the char layer of ethylene propylene diene monomer (EPDM) composite. First, the charring samples were prepared using a special ablation motor. A cold flow erosion test device was then developed, and the erosion experiments on the charring samples under cold airflow conditions were conducted. The experimental results show that under a pressure of 0.5 MPa, when the airflow velocity is lower than or equal to 180 m/s, the char layer erosion is largely in the form of wear; when the airflow velocity reaches 200 m/s, the large pieces of the char layer are peeled off; when the airflow velocity reaches 230 m/s, the entire char layer is peeled off. The tensile and shear strength of the char layer under cold conditions were tested using a simple method. It was found that the shear stress of the airflow when the char layer is peeled off is significantly lower than the shear strength of the char layer. The failure of the char layer is not only due to the pure shear force of the airflow. The local cracking, warping, and delamination not only reduce the char layer strength, but also enhance the destructive force of the airflow. This was the main cause of the char layer erosion due to airflow.