Impact testing of polymeric foam using Hopkinson bars and digital image analysis

This paper has investigated the impact testing method on the polymeric foams using digital image correlation. Accurate average stress-strain relations can be obtained when soft large diameter polymeric pressure bars and appropriate data processing are used. However, as there is generally no homogeneous strain and stress fields for polymeric foam, an optical displacement field observation is essential. In contrast with quasi-static tests where the digital image correlation (DIC) measurement is commonly used, technical difficulties still remain for an use under impact conditions such as synchronization and measuring accuracy due to rather poor quality images obtained from high speed camera. In the present paper, an accurate synchronization method based on direct displacement measurement from DIC is proposed and the feasibility of a calibration method using DIC on pressure bar ends is discussed. The relevance of the present method for establishing mechanical response of polymeric foam is also demonstrated.