Remote inspection system for impact damage in large composite structure

Abstract

A significant opportunity for reducing the weight of composite aircraft is through the development of an economically efficient method to detect barely visible or invisible impact damage sustained in service. In this paper, a structurally integrated, inert, wireless system for rapid, large-area impact damage detection in composite is demonstrated. Large-area inspection from single sensors using ultrasonic-guided waves is achieved with a baseline-subtraction technique. The wireless interface uses electromagnetic coupling between coils in the embedded sensor and inspection wand. Compact encapsulated sensor units are built and successfully embedded into composite panels at manufacture. Chirp-based excitation is used to enable single-shot measurements with high signal-torandom-noise ratio to be obtained. Signal processing to compensate for variability in inspection wand alignment is developed and shown to be necessary to obtain adequate baseline subtraction performance for damage detection. Results from sensors embedded in both glass fibre and carbon fibre-reinforced composite panels are presented. Successful detection of a 10 J impact damage in the former is demonstrated at a range of 125 mm. Quantitative extrapolation of this result suggests that the same level of impact damage would be detectable at a range of up to 1000 mm with an inspection wand alignment tolerance of 4 mm.

Monitoring cure and detecting damage in composites with inductively coupled embedded sensors

“…The advantage of using baseline techniques, is that the influence of a structures geometry is minimised. The signal processing techniques used by the ICTS to perform baseline subtraction are covered in more detail in the work of Zhong et al [38]. Figure 9.…”

“…The removal of data processing, or long range wireless data transmission requirements, allows the size and weight of the sensors to be reduced, which is beneficial in reducing the on structure weight, as well as allowing the sensors to be embedded without significantly reducing the mechanical properties of the composite part. [6] The implementation of baseline subtraction techniques to detect damage, and signal processing techniques used to account for misalignment between the embedded sensor and wand are covered in detail in the work of Zhong et al [38] …”

“…In this section the guided wave sensor (previously used to monitor cure) embedded in the plate shown in Figure 2b, was used to detect BVID created by a low energy impact. In a previous study carried out by Zhong et al [38], the influence of coil misalignment was studied, and techniques developed to help minimise its influence. In this work the effects of coil misalignment were not studied and the inductance wand was fixed to the panel shown in Figure 2b.…”

“…The electromagnetic coupling was optimised, by identifying the suitable geometrical properties for each of the coils using a model published by Zhong et al [37]. The system allows for rapid contactless measurements to be made, with a separation distance between sensor and inspection wand in the order of tens of millimetres [38]. The advantages that this system holds over conventional NDT measurements made using external transducers, are the speed and ease at which measurements can be made, and the possibility of employing baseline subtraction techniques, due to measurements being taken from fixed locations within a structure.…”

Damage Sensing in Blades

“…In addition to metallic structure inspection, composite inspection using guided waves has been investigated in the recent years (Cawley 1994;Monkhouse et al 1997;Su et al 2002;Han et al 2006;Lissenden and Rose 2008;Giurgiutiu and Santoni-Bottai 2011;Castaings et al 2012;Rose 2012;Torkamani et al 2014;Baid et al 2015;Rekatsinas et al 2015;Zhong et al 2015). Much interest has arisen in this topic due to the increasing implementation of composite materials in the aerospace and wind energy industries and the necessity to inspect and monitor large composite structures, such as wings or wind turbine blades, in a cost-effective and rapid way.…”