The production of large and complex parts using fiber composite materials is costly due to the frequent formation of voids, porosity and waste products. By embedding different types of sensors and monitoring the process in real time, the amount of wastage can be significantly reduced. This work focuses on developing a knowledge-based method to improve and ensure complete impregnation of the fibers before initiation of the resin cure. Piezoresistive and capacitive pressure sensors were embedded in fiber composite laminates to measure the real-time the pressure values inside the laminate. A change of pressure indicates resin infusion. The sensors were placed in the laminate and the resin was infused by vacuum. The embedded piezoresistive pressure sensors were able to track the vacuum pressure in the fiber composite laminate setup, as well as the arrival of the resin at the sensor. The pressure increase due to closing the resin inlet was also measured. In contrast, the capacitive type of sensor was found to be inappropriate for measuring these quantities. The following study demonstrates real-time monitoring of pressure changes inside the fiber composite laminate, which validate the use of Darcy’s law in porous media to control the resin flow during infusion.
For producing Carbon Fiber Reinforced Plastics (CFRP) with desired mechanical and physical properties, it is essential to monitor the polymerization process. Therefore, sensors will be embedded in the composite in order to monitor temperature, pressure and/or curing index online. Inlays are foreign-objects in CFRP and behave as a wound in the composite. The composite may resist to foreign-objects. The impact of embedding sensors (inlays) on homogeneity and structural integrity of CFRP is not known yet. The aim of this study is to investigate the influence of embedding inlay on the mechanical properties of CFRP. Inlays of different materials from thick and rigid (silicon with different thicknesses) to soft and flexible (Polyimide and SU8) were embedded in the CFRP composite. These inlays are considered as embedded sensors for online monitoring. The impact of the inlay's different sizes, types and patterns (existence of cavities) on composite were investigated by performing inter-laminar shear strength tests. The results of the inter-laminar shear strength tests clarified that not only can the flexibility of embedded sensors reduce the foreign-object effect of that in the composite, but also altering the size and substrate's patterning can play an important role in improving the properties of composite with the embedded sensors.
An online monitoring scheme to determine viscosity and permeability for a composite main spar infusion is presented. During the manufacturing process, defects such as dry spots and pores can occur and lead to poor part quality. In this study, dielectric sensors are used to create the information needed to model the process. Several experiments have been carried out to investigate the correlation between the sensors signal and the viscosity and to derivate constitutive equations. The provided data and the derived permeabilities are integrated into a simulation model of a cross section of the composite main spar. As a result, the real permeability can be identified. The knowledge of these parameters is one of the key aspects for a prediction of the resin flow and therefore for an improved process control.
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