Cold welding under vacuum and launch conditions
It is the aim of AAC to provide engineers with data on adhesion force: in worst case this force needs to be overcome by the opening mechanism. This helps in design of mechanisms and reduces risk in failure during final model testing. It offers on one hand determination of cold welding on bare metal contacts and on the other hand life-times of anti-adhesion coatings. AAC has created on basis of an ESA- agreed test procedure (STM-279) data on several typical combinations of space materials and coatings.
Testing is offered for customers in 3 ways:
- Consultancy and testing of candidate materials according to customer specificaitons
- “Launch-test” fretting in 3 steps (Air-LowVacuum-HighVacuum) to proof under launch conditions
- Assessment of contact material combination to cold welding (determination of adhesion forces or life time of coatings) in comparison to existing data (STM-279).
Cold welding due to fretting (“Fretting Test Facility”)
The fretting facility enables the measurement of the adhesion force between two materials in cyclic closed contacts which are subjected to fretting. This means that pin and disc are oscillated in their contact plane with small amplitudes (50 µm). “Cyclic contact” means that the contact between the pin and the disc is closed and opened for several (thousand) cycles.
After closing the contact, fretting is applied for a selectable duration. After stopping fretting, the contact is opened and at each opening the adhesion force, i.e. the force necessary to separate both in vertical direction, is measured. High resolutions down to 50 mN can be achieved. The test provides the tendency to cold welding by a plot of the adhesion force as function of cycles.
Cold welding due to impact (“Impact Test Facility”)
This facility is similar to the fretting test device, however it enables to close the contact with an impact. It also enables ultra high vacuum down to 5.10-8mbar.