16, July 2018

ESA Open Invitation to Tender AO9489
Open Date: 06/07/2018
Closing Date: 06/09/2018 13:00:00

Status: ISSUED
Reference Nr.: 18.133.12
Prog. Ref.: Technology Developme
Budget Ref.: E/0901-01 – Technology Developme
Tender Type: C
Price Range: 200-500 KEURO
Products: Orbital Transportation & Re-entry Systems / Structures / Tanks / Propellant Tanks
Techology Domains: Structures / Launchers, Reentry Vehicles, Planetary Vehicles / Advanced Tank Design and Verification Technologies
Establishment: ESTEC
Directorate: Directorate of Tech, Eng. & Quality
Department: Mechanical Engineering Department
Division: Structure and Mechanisms Division
Contract Officer: van Hilten, Linda
Industrial Policy Measure: N/A – Not apply
Last Update Date: 06/07/2018
Update Reason: Tender issue

Composite overwrapped pressure vessels (COPV) are critical elements (both for safety and mission success) of many space missions. Rupture of such pressure vessels filled with gas at high pressure may result in loss of life or loss of mission and creation of a large amount of space debris due to release of a high amount of energy. This mandates a high level of design reliability.Stress-rupture (or static fatigue) is a sudden failure mode of the composite overwrap that can occur at normal operating pressures and temperatures, i.e. at stress levels below ultimate strength for an extended time. The failure mechanism is complex, not well understood, and difficult to accurately predict due to scatter or detect prior to failure.Many such pressure vessels undergo a significant pressure drop shortly after launch, which reduces the risk of stress rupture. However, in case of reusable systems, or systems that start operation after long delay (e.g. interplanetary missions) the time at or near design pressure can become very long. The stress at design pressure can be as high as 67% of ultimate strength (UTS) (for burst factor (BF) of 1.5). Stress rupture failures have been observed in accelerated test programs at NASA JSC for both Kevlar and carbon overwrapped COPVs. NASA stress rupture test programs are currently under way that should provide additional data availability in 2016, but not all of such test data may become available in Europe due to export restrictions, and the data may not address directly material systems used in Europe. Until test data is available, NASA recommends that the carbon fiber strain remain at or below 50% of the UTS (i.e. burst factor around 2.0!). Applicable pressure vessel standards and range safety requirements (esp. in USA) request that stress rupture risk be mitigated, without providing a clear methodology for compliance. Previous guidelines indicated that at 67% of UTS may in the worst case result in failure after 65 hours, for 10E6 hours lifetime the sustained stress may have to be below 58% of UTS (BF>1.7)The following tasks are included:- To evaluate the of the state-of-art in stress rupture descriptive models (several exist), including scaling laws, and related test data (including e.g. experience in hydrogen storage industry).- To evaluate the state-of-art in stress rupture testing, from strand/sample to sub-scale to full-scale vessel, real-time or accelerated.- To perform accelerated tests on simple specimens, applying well-defined stress levels (e.g. rings, simple sub-scale vessels with representative fibre pattern). Using a number of fibre-resin combinations relevant for European COPV.- To define recommended design and verification method to mitigate the risk of stress rupture. Make recommendations for further testing (e.g. full-scale, longer duration) if necessary for ESA missions.

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