On-line monitoring of multi-parameters in thermoplastic composite structure forming based on fiber grating sensor

Automatic laying and forming technology of thermoplastic composites based on AFP (automatic fiber placement) has attracted extensive attention. It is necessary to monitor the composite structure forming process in real time, in which temperature and strain are two key parameters. The traditional technique are not suitable for the conditions of structure forming, and will be failure under the high temperature and the high pressure. In this paper, polyimide coated FBG (fiber Bragg grating) and polarization-maintaining FBG are used as sensing components to construct real-time monitoring systems. The sensor system can realize high-temperature monitoring above 400 degrees C and complex dynamic strain monitoring above 20,000 mu epsilon, and the sampling frequency reached 1000 Hz. Using this system, mold temperature is set to 40 and 120 degrees C, laying temperature is set to 250 and 380 degrees C. Laying pressure is set to 500 N, 1000 N, 1500 N and 2000 N, and laying speed is set to 3.6 m/min, 6 m/min and 12 m/min, which is divided into five kinds of experiments, a total of 10 series of 40 groups of monitoring experiments, to study the influence of temperature and strain in the thermoplastic composite forming process. Exploring a single process parameter change peak strain change rule and influence law of structure shape, proved that set up by the grating sensor system can accurately reflect the temperature of the composites molding process real-time and complex dynamic strain changes, it is concluded that the single process parameter change on the influence law of strain, and the temperature resolution of 0.1 degrees C, the strain resolution is 1 mu epsilon.