Development of Shock Tube Testing

Finnish shelter legislation was issued 1958. It required to build blast proof shelters into every bigger building housing citizens. Products were needed to make these shelters as well as method to test blast resistance. Temet with VTT Technical Reseach Centre started to develop this testing method. First version was based on master thesis. 

During Second World War and in the beginning of cold war era a lot was tested on the area of blast protection and blast wave was studied. Since then lot of knowledge has disappeared from the world Finland being one the few places where it has been preserved. Generally, efforts in explosions have been placed on destructive side, not on the protective.

Compressing high initial pressure e.g. 50 bar, is dangerous and needs experience and methods to do safely. So that all the equipment/test setup will hold that pressure and smaller pieces don’t detach from the test rig becoming fragment. However, the main challenge is the controlled release of pressure. To achieve needed amount of repeatability, it has needed thousands of shots.

In one occasion many years ago, product was not well enough attached and blast impulse was higher than anticipated. The product flew through the wall.

The testing has some challenges. One mentionable is vibration. Vibration of test setup and sensors is high when stored energy is suddenly released creating blast wave. Knowledge is needed to interpret the data and methods to have reliable test readings which lead to correct conclusions. Another challenge is the size of the product. The bigger the product is, more initial pressure/stored energy is needed as pressure wave should hit larger area with uniform loading.

Entering into the industrial protection at the turn of the century brought a new challenge - long durations and variability in pressure – time loading curves. Main risk in industrial protection is gas explosion. It differentiates from conventional weapon explosion. When earlier interest was on shooting certain peak overpressure values, now the interest shifted to the shape of the loading curve. On 2014 Temet innovated new method improving control over the resulting shape. The work continues enabling Temet to bring advanced products into the market.