The overarching objective of this project is to establish the needs and develop a breadboard demonstration of an in-situ health monitoring technique for Carbon Fibre Overwrapped Pressure Vessels (COPVs) for both high pressure and low pressure (hazardous) propellants.
The overarching objective is broken down into a list of specific objectives:
- To identify the requirements for health monitoring of composites in terms of the level of sensitivity, accuracy, robustness to damage (of the sensors and / or data capture system) and reliability of the system that would allow a significant reduction in the thickness (and therefore mass) of the composite overwrap, and reliability in terms of preventing false positive failure modes.
- To collect information on potential sensors and sensor systems, and create a short list of candidate technologies that could be utilized.
- To design the selected sensor / sensor system into a breadboard demonstrator, with the appropriate performance in terms of representativity of a “flight tank” and available sensors.
- To demonstrate the maturity and feasibility of the designed concept.
To design selected sensor system / systems into breadboard demonstrator several issues must be resolved:
- selection of sensor with appropriate parameters
- design of the sensor network topology
- specification of data acquisition parameters
- development of signal processing algorithms
This work is done using surrogate specimen with the same or very similar material properties as the COPV’s overwrap. Then, the sensor system design is incorporated into overall conceptual design and tested for the application in the COPV.
The main benefits of the monitoring COPV by structure health systems are:
- Reduction of risk of fatal failure. Critical and hard to investigate systems/subsystems/part are under permanent control. Thus, its health is always known and proper action can be performed if any non-standard event occurs.
- Performance optimization through prognostics-driven control.
- Reduced maintenance cost. Maintenance is done only if it is required by the state of the structure. Further, maintenance action can be done in time when extent of the damage is relatively small and repair of the structure is less expensive.
- Reduced unexpected downtimes thanks to on condition based and predictive maintenance which further benefits in increased vessels availability and readiness.
- Optimization of design. Information and data collected by SHM system can be advantageously exploited by vessel manufacturer. Engineers can consider it to optimize vessels’ design with regard to experience from operation and maintenance.
The selected sensor / sensor system is designed into the demonstrator. The design includes: selection of appropriate type of sensors, design of the sensors distribution on/into the pressure tank and adjustment of the signal acquisition parameters.
Honeywell provides its experience and capabilities in development of SHM systems based on ultrasonic guided waves using small and low weight PZT actuators / sensors. It means:
- Design and manufacturing of PZT actuator on flexible strips.
- Signal collection using up to 64 channel system for interrogation PZT actuator.
- Various methods for the PZT elements installation (PZT bonding on the surface, integration between tank lining and overwrap, embedding PZT).
CTU is responsible for research on optical fibres and FBG sensors:
- Strain measurement using the surface-mounted or integrated FBG sensors.
- FBG sensors integration into the composite by the hand layup moulding, prepreg / autoclave moulding, filament winding.
- Two types of FBG interrogators (double-channel, up to 70 Hz, single channel, up to 600 Hz)
- Fibre optic sensing system for structure defects monitoring.
The work is divided into three phases in sequential order:
- State of the art (finishing April 2013)
- Assessment of COPV design with respect to specification for health monitoring
- Survey of current and potential sensor capabilities and their detailed trade-off
- Design and development of a breadboard demonstrator for the selected sensor systems (finishing November 2013)
- Manufacturing the demonstrator and reporting results of designed performance tests (finishing August 2014)
The outputs of the three phases cover all technical notes and hardware required in the state of work.
The project was completed.
All the defined research objectives were met. The breadboard demonstrator proved feasibility of the proposed manufacturing process and a series of impact tests verified detection capabilities of the sensors network. It was demonstrated that both invetigated SHM technologies (FBG and PZT) are able to detect structural defects on the tested composite overwrap.