Sensors for Cure Monitoring of Composite Materials

Monitoring and control of the integrity and properties of materials at all stages of structural life, from cradle to retirement, is a growing NDE field. A typical system consists of a sensor, data acquisition, processing and control setup with a host personal computer. For composites, the stage of cure is the only time when an adequate actuation can easily affect the cause of unacceptable characteristics or possibly eliminate the formation of defects. Real-time monitoring of the cure process of plastic-reinforced composites can prevent overbleeding, minimize trapped volatiles, alert of vacuum leak, indicate cure rate and optimize the material properties. For many years, the process of curing composites has been an empirical science and has evolved through a trial-and-error approach. In recent years, significant progress has been made towards understanding the process as a result of data accumulation and progress in mathematical modelling of the composite cure process. Computer science is increasingly applied to support the process analysis using artificial intelligence and knowledge base systems

Tooling design and microwave curing technologies for the manufacturing of fiber-reinforced polymer composites in aerospace applications

The increasing demand for high-performance and quality polymer composite materials has led to international research effort on pursuing advanced tooling design and new processing technologies to satisfy the highly specialized requirements of composite components used in the aerospace industry. This paper reports the problems in the fabrication of advanced composite materials identified through literature survey, and an investigation carried out by the authors about the composite manufacturing status in China’s aerospace industry. Current tooling design technologies use tooling materials which cannot match the thermal expansion coefficient of composite parts, and hardly consider the calibration of tooling surface. Current autoclave curing technologies cannot ensure high accuracy of large composite materials because of the wide range of temperature gradients and long curing cycles. It has been identified that microwave curing has the potential to solve those problems. The proposed technologies for the manufacturing of fiber-reinforced polymer composite materials include the design of tooling using anisotropy composite materials with characteristics for compensating part deformation during forming process, and vacuum-pressure microwave curing technology. Those technologies are mainly for ensuring the high accuracy of anisotropic composite parts in aerospace applications with large size (both in length and thickness) and complex shapes. Experiments have been carried out in this on-going research project and the results have been verified with engineering applications in one of the project collaborating companies

Carbon fibres reinforced composites. Electrical impedance analysis: a gateway to smartness

International audienceFor more than 7 years, our research work is focussed upon the electrical behavior of carbon fiber reinforced composites. Effectively carbon/polymeric matrix laminates can be considered as an electrically conductive network (i.e. carbon fibers) embedded in an insulating medium (i.e. the polymeric matrix). Consequently, from an electrical point of view laminated composites have been modelled owing to combinations of electrical resistances (i.e. fibers themselves and the contact points between the fibers) and capacitances (i.e. polymeric matrix). During their manufacturing, composite material such as thermoset matrix composites for instance, undergo various changes in their physical (including electrical and mechanical) properties and in their geometrical characteristics. In fact, in the case of manufacturing processes such as oven curing (vacuum bag), autoclave curing or heating plate press, beside the chemo-rheological changes, the laminated parts are the place of a compaction phenomenon inducing changes in fiber volume fraction and thicknesses. The idea developed in this paper is that since the carbon/polymeric matrix laminate can be considered as an electrical network, it can then be view and used as a sensor for following the material state during the manufacturing process enabling thus defects to be detected and this without any additional sensing material or device