Delamination Behaviour of Embedded Polymeric Sensor and Actuator Carrier Layers in Epoxy Based CFRP Laminates—A Study of Energy Release Rates

Abstract

Fiber reinforced composites combine low density with high specific mechanical properties and thus became indispensable for today’s lightweight applications. In particular, carbon fibre reinforced plastic (CFRP) is broadly used for aerospace components. However, damage and failure behaviour, especially for complex fibre reinforcement set-ups and under impact loading conditions, are still not fully understood yet. Therefore, relatively large margins of safety are currently used for designing high-performance materials and structures. Technologies to functionalise the materials enabling the monitoring of the structures and thus avoiding critical conditions are considered to be key to overcoming these drawbacks. For this, sensors and actuators are bonded to the surface of the composite structures or are integrated into the composite lay-up. In case of integration, the impact on the mechanical properties of the composite materials needs to be understood in detail. Additional elements may disturb the composite structure, impeding the direct connection of the composite layers and implying the risk of reducing the interlaminar integrity by means of a lower delamination resistance. In the presented study, the possibility of adjusting the interface between the integrated actuator and sensor layers to the composite layers is investigated. Different polymer layer combinations integrated into carbon fibre reinforced composite layups are compared with respect to their interlaminar critical energy release rates GIc and GIIc. A standard aerospace unidirectionally reinforced (UD) CFRP prepreg material was used as reference material configuration. The investigations show that it is possible to enhance the mechanical properties, especially the interlaminar energy release rate by using multilayered sensor–actuator layers with Polyimide (PI) outer layers and layers with low shear stiffness in between.

High velocity impact on generic CFRP blade specimen: baseline free method for impact localisation and damage assessment on complex structures

“…This test confirms the discussion about the manufacturing and application of the sensing layer, and how to improve it, to achieve a robust sensing system. An approach for robust manufacturing process is given in [38], [39]. Results confirm the validity of the proposed localisation technique.…”

Embedded sensing and actuating in CFRP composite structures—concept and technology demonstration for tailored embeddable sensor-actuator layers (TEmSAL)

“…This is performed in an 'off-the-shelf' manner for a seamless integration into the standard industrial series production process. It will be shown that the proposed concept is capable of withstanding the manufacturing conditions in terms of handling, positioning accuracy and processing temperature and results in full sensing/actuation functionality with a negligible impact on the structural performance in terms of interlaminar properties at the same time [11].…”

“…However, approaches on the integration of large insulation layers and their impact on the composite properties of CFRPs are only marginally described in literature [5,[7][8][9][10]. Recently, the influence of embedded polymeric layers on the interlaminar behaviour of CFRP composites has been investigated in detail in [11]. It has been shown that a combined PI-PO configuration could be particularly effective as a carrier material for electric components, due to its negligible impact on the interlaminar properties and electric insulation capabilities.…”

“…It is a technology suitable for the serial production of smart composite CFRP structures and designed to resist up to 180 • C during manufacturing. Based on findings from [11], the production and design of the layers themselves is described and discussed. The concept is applied to a thick walled generic CFRP demonstrator structure and experimentally verified by impact sensing and pitch-catch tests.…”

Carboxylated Carbon Nanotube/Polyimide Films with Low Thermal Expansion Coefficient and Excellent Mechanical Properties

“…Among these polymer materials, polyimide (PI) film materials have outstanding properties [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ]: low density, high mechanical properties, great thermal stability, radiation resistance, corrosion resistance, excellent dielectric properties, and so on. Therefore, PI films can be used in microelectronics, aerospace, and other fields [ 9 , 10 , 11 , 12 ]. However, the coefficient of thermal expansion (CTE) of polyimide is much higher than that of inorganic materials such as metals and ceramics.…”