# Failure Detection within Composite Materials in System Engineering Applications
## 6 Failure Detection
The success rate was approximately 50% for simple designs. This detection rate is expected to rise significantly with utilising the same principles but with conductive material with a similar Young's modulus, obviously for CF structures this would be CF itself. However, issues over such a large surface area would be that small fracture points could go undetected as the electrical current would simply take the path of least electrical resistance. To register such small differences, the electronics would need to be significantly enhanced leading to larger more expensive failure system such as tomography. The requirements and processing power for such a system is deemed infeasible for the applications other than high cost or static applications. By utilising an approach where an extra redundant layer is added on the inner surface of a structure, such as non-conductive/conductive reinforcement material, i.e., fibre glass/CF, it may be possible to detect non visible damage before a serious failing occurs with low level electronics and very low power consumption for its operation. Multiple methods can be taken for this approach and research is currently ongoing. Figure 7 below shows simple layout utilising carbon fibres inherent electrical conductivity with glass fibre isolation mat. The inherent electrically conductive properties of CF and recent advancements in graphene production on high lignin woods offer the opportunity to potentially monitor resistance changes directly on the structure of the material. Figure 7 (left image) shows a square of CF with a layer of thin fibre glass as an electrical isolation, stacked on top of this is a simple CF pattern in which the open ends allow for simple connection to monitoring circuitry. Should the CF layer fail or become damaged the electrical properties will alter and can be flagged up by the circuitry. As the layers will be placed during the build process,  
Figure 7: Inherent concept system for failure detection. they will all undergo the same curing stages and should maintain as close as possible the structural properties of the component. Similarly, Figure 7 (right image) shows the layout with a Wheatstone bridge configuration. Typically used with resistors to measure strain. The central conductive space would be supplied with an electrical potential and the outer voltage would be used to measure the potential. When the bridge is in balance there will be no potential difference at the output, however, changes in one of the bridges arms will result in a potential difference at the output which can be monitored by the accompanying electronics. It would be highly unlikely that all four arms of the bridge suffer similar damage in the event of damage and hence would register the change. Although this may be of little relevance in its current form, when such a setup is within the inner circumference of a tube then valuable changes in structure can be reported back. The addition due to its construction will also add extra strength to sections of interest. Research is still underway into methods for a simple low-cost solution to apply and monitor changes within composites for consumer use, in order for a simple and effective solution for end users to gauge possible approaching failures and fatigue.