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Development of Strain Measurement Based On-line Impact Monitoring System for Composite Structures

M. J. AUGUSTIN, DATTA AMITABHA, SATHYA P. SAKTHI, GUPTA NITESH, S. R. VISWAMURTHY, GADDIKERI KOTRESH, RAMESH SUNDARAM

Abstract


The high specific strength and tailorable properties have made advanced composites structures to find increased use in the aircraft industry. Impact damages due to events such as tool drops, runway debris etc. can reduce the load carrying capacity of composite structures and impair safe operation of the aircraft. Often they result in barely visible external damage and as such they may get missed during visual inspection of large aircraft structures. Impact events are random in nature, in both time domain (uncertain when it will occur) and spatial domain (where it will occur), hence, the challenge is to develop a smart impact monitoring system, which will remain active to report the impact event on the structure. This paper describes the experimental studies carried out towards the development of an online impact monitoring system, which can estimate the impact location and severity of impact in terms of impact energy/force. Such a system can assist in carrying out inspection only in the identified locations instead of inspecting the whole structure. An impact test setup developed in-house is used to carry out impact tests on composite structures. The portable impact tower comprises of a drop weight and a tup instrumented with a force sensor to measure the force response during impact. Sensor sensitivity studies are carried out to determine the optimum sensor locations on the structure. Fiber Bragg Grating (FBG) and Resistance Strain Gauges (RSG) sensors are used in this study to measure strains in the structure during impact. A comprehensive method based on a building block approach is followed. Several laminates of different thicknesses are tested first before moving on to more complex configurations such as skin-stringer panels and wing-box like structures. These studies allow us to understand the complexities in the structural response towards impact and help in design of sensor networks as well as algorithms for estimation of impact location and severity. In order to determine the impact location using strain data acquired during the impact event, various algorithms are developed, validated and implemented in LabVIEW platform. Support vector regression and system identification techniques based algorithms are used to determine the impact severity. Comparative results of the algorithms will also be discussed through Probability of Detection/Confidence.


DOI
10.12783/shm2017/14008

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