has been working as part of a consortium to create a graphene sensor capable of detecting defects in composite materials during the manufacturing process and the normal service life of a component.
The Innovate UK-funded Graphosite Project has seen TWI working alongside ADVISE-DETA, Haydale Composite Solutions Ltd, Cambridge Nanomaterials Technology Ltd, DZP Technologies, and Brunel University London (through the Brunel Composites Innovation Centre), with the project due to end in 2021.
The most common defect that occurs during the manufacturing process of composite materials is porosity, which is when small voids are present in the matrix. Porosity can affect mechanical performance and lead to issues such as inter-laminar shear stress.
In-service damage is usually caused by impact, which can result in barely visible internal delamination or puncture damage to the surface of a component. Sandwich structures can also suffer from skin delamination and matrix cracking as a result of impact. Core crushing is another problem caused by impact energy, leading to distortion and folding.
Although components will generally return to their original shape there is still a problem with reduced compressive strength as a result. As composites are increasingly being used in the aviation, automotive and marine industries, as well as in civil structures, the need for a solution is evident.
The graphene sensor aims to offer increased sensitivity and high flexibility for defect detection in composites and thereby provide a solution superior to the existing strain gauges. This improved defect detection capability will, for example, have a positive impact on the monitoring of wind turbine blades, which are prone to damage from impacts in service.
TWI has been performing mechanical testing of composite specimens in order to validate the graphene sensors. The composite specimens are being tested under different loading conditions to evaluate the performance of the sensors before being compared to metallic strain gauges as a method of monitoring the deformation process of the specimens.
The gauge factor (GF) of the graphene sensors will now be evaluated based on the strain measured by the strain gauges.