Development of an internal shock tube imaging procedure for the analysis of structural behavior of NBC protection components during air blast loading

NBC (nuclear, biological or chemical) protection components installed in the outer shell of protective structures must be capable to withstand blast waves. In order to experimentally investigate their re-sistance and functionality, specimens are subjected to blast loading in shock tubes. By means of highly dynamic pressure measurements, the load profile is verified and for certain components perfor-mance can be determined in terms of pressure leakage. Until now, damage analysis was limited to post-load functional tests and visual examination outside the shock tube. Structural behavior during the blast loading process could not be captured. For this purpose, a high-speed camera imaging procedure was developed specifically for shock tube testing. Recording the whole blast loading process up- and downstream of the specimen provides im-portant information for analyzing its oscillation, and deflection as well as for the detection of design flaws. The method was developed in three steps. First, air-blast safety valves were filmed from outside the shock tube at a frame rate of up to 30’000 frames per second (FSP). Subsequently, a periscope-like device was built into the measuring section of the shock tube to record component behavior in-situ from a downstream position. Finally, building upon the knowledge gained in both preceding steps, the system was optimized for its application in the driven section (upstream of the specimen), where pres-sures up to 40 bar are expected. Additional challenges such as mechanical resistance of the peri-scopic inserts, minimizing their gas dynamic impact or adequate illumination had to be resolved. Future work will seek to optimize the system by reducing effects on the flow field inside the tube as well as avoiding camera movements during blast loading.