(June 2017 – April 2018)
Link to report in repository: http://essay.utwente.nl/74854/
Solid propellant missiles (figure 1) are used in all parts of the armed forces, this means that missiles are subjected to a wide range of handling, storage and deployment conditions. Assessment of the condition of the propellant (figure 2) is done on a random sample from the batch and at the moment there is no non-destructive method to assess material properties of the ageing propellant. This means expensive weapon systems are sacrificed and conclusions about the state of the material are drawn from a small number of assessed engines.
Figure 1: Schematic drawing of a rocket with propellant engine in the back
Figure 2: Schematic cross-section of a solid propellant engine with cylindrical solid propellant (Kr)
This thesis summarizes some possibilities for vibration based non-destructive testing methods for characterizing ageing in solid propellant material and zooms in on one promising method: ultrasonic testing. The remainder of the study consists of a feasibility study on the use of ultrasound for characterizing ageing in solid propellant material.
Figure 3: Sample material
Figure 4: Reflections on interfaces of a sample with a degraded material layer
Samples of inert HTPB (hydroxyl-terminated polybutadiene) based propellant (figure 3) are accelerated aged and experiments are conducted to research the effects of ageing on the ultrasonic signal, the frequency content of the pulses and the sound velocity. Although an expected reflection of the interface between pristine and aged material (figure 4) is not observed, it is found that an increase in sound velocity is measurable, which indicates a rise in Young’s modulus of the material. This suggests that ultrasound is a promising technique for assessing the agageing of solid propellant.