Automated shot counter system for through-life support of target rifles

Proceedings of the 4th International Conference on Through-life Engineering ServicesCompetitive target shooting requires rifles with high levels of performance and small margins of error. Optimal performance of rifles in terms shot velocity can be expected over a period of use until an indeterminate but critical number of rounds has been fired when it will start to deteriorate. The rifle barrel must then be renewed. Accurate and reliable record-keeping of number of shots fired is therefore critical to minimise the through-life cost of owning a target rifle and also maintaining maximum performance. This can be most effectively done using an automated means for monitoring the number of rounds fired. In this paper the acoustic emission technique is used to monitor and identify shot rounds fired based solely on the features of Acoustic Emission (AE) signals for the first time. The results obtained from experiments showed unambiguous identification of shots fired and the capability to monitor degradation of the barrel as a function of number of shots fired

Comparison of alternatives to amplitude thresholding for onset detection of acoustic emission signals

Acoustic Emission (AE) monitoring can be used to detect the presence of damage as well as determine its location in Structural Health Monitoring (SHM) applications. Information on the time difference of the signal generated by the damage event arriving at different sensors in an array is essential in performing localisation. Currently, this is determined using a fixed threshold which is particularly prone to errors when not set to optimal values. This paper presents three new methods for determining the onset of AE signals without the need for a predetermined threshold. The performance of the techniques is evaluated using AE signals generated during fatigue crack growth and compared to the established Akaike Information Criterion (AIC) and fixed threshold methods. It was found that the 1D location accuracy of the new methods was within the range of <1–7.1%<1–7.1% of the monitored region compared to 2.7% for the AIC method and a range of 1.8–9.4% for the conventional Fixed Threshold method at different threshold levels

Development of probability of detection data for structural health monitoring damage detection techniques based on acoustic emission

Structural Health Monitoring (SHM) techniques have been developed as a cost effective alternative to currently adopted Non-Destructive Testing (NDT) methods which have well understood levels of performance. Quantitative performance assessment, as used in NDT, needs to be applied to SHM techniques to establish their performance levels as a basis for technique comparison and also as a requirement for practical aerospace application according to set regulations. One such measurand is Probability of Detection (POD). This paper reports experiments conducted to investigate the location accuracy of the Acoustic Emission (AE) system in monitoring events from HsuNielson and fatigue crack AE sources as a route to establish the POD of AE in SHM. It was found that fatigue crack tips could be located at 90% POD within 10 mm accuracy

New methods for onset detection of acoustic emission signals

Acoustic Emission (AE) monitoring can be used to detect the presence of damage as well as determine its location in Structural Health Monitoring (SHM) applications. The onset time of AE signals detected at different sensors in an array is used to determine their relative time difference of arrival which is essential in performing localisation of the signals’ originating source.Typically, this is done using a fixed threshold which is particularly prone to errors when not set to optimal values. This paper presents three new methods for determining the onset of AE signals without the need for a predetermined threshold. The performance of the techniques in terms of location accuracy is evaluated using AE signals generated during fatigue crack growth and compared to the established fixed threshold method. It was found that the mean absolute error in performing 1D location using the new methods was between 11.6 to 14.3 mm compared to a range of 19.3 to 37.2 mm for the conventional Fixed Threshold method at different threshold levels

Validation and Veri cation of the Acoustic Emission Technique for Structural Health Monitoring

The performance of the Acoustic Emission (AE) technique was investigated to establish its reliability in detecting and locating fatigue crack damage as well as distinguishing between di erent AE sources in potential SHM applications. Experiments were conducted to monitor the AE signals generated during fa- tigue crack growth in coupon 2014 T6 aluminium. The in uence of stress ratio, stress range, sample geometry and whether or not the load spectrum was of constant or variable amplitude were all investigated. Timing lters were incor- porated to eliminate extraneous AE signals produced from sources other than the fatigue crack. AE signals detected were correlated with values of applied cyclic load throughout the tests. Measurements of Time di erence of arrival were taken for assessment of errors in location estimates obtained using time of ight algorithms with a 1D location setup. It was found that there was signi cant variability in AE Hit rates in otherwise identical samples and test conditions. However common trends characteristic of all samples could be observed. At the onset of crack growth high AE Hit rates were observed for the rst few millimetres after which they rapidly declined to minimal values for an extended period of crack growth. Another peak and then decline in AE Hit rates was observed for subsequent crack growth before yet another increase as the sample approached nal failure. The changes in AE signals with applied cyclic load provided great insights into the di erent AE processes occurring during crack growth. AE signals were seen to occur in the lower two-thirds of the maximum load in the rst few millimetres of crack growth before occurring at progressively smaller values as the crack length increased. These emissions could be associated with crack closure. A separate set of AE signals were observed close to the maximum cyclic stress throughout the entire crack growth process. At the failure crack length AE signals were generated across the entire loading range. Novel metrics were developed to statistically characterise variability of AE generation with crack growth and at particular crack lengths across di erent samples. A novel approach for fatigue crack length estimation was developed based on monitoring applied loads to the sample corresponding with generated AE signals which extends the functionality of the AE technique in an area which was previously de cient. It is however limited by its sensitivity to changes in sample geometry. Experiments were also performed to validate the performance of the AE tech- nique in detecting and locating fatigue crack in a representative wing-box struc- ture. An acousto-ultrasonic method was used to calibrate the AE wave veloc- ity in the structure which was used to successfully locate the `hidden' fatigue crack. A novel observation was made in the series of tests conducted where the complex propagation paths in the structure could be exploited to perform wide area sensing coverage in certain regions using sensors mounted on di er- ent components of the structure. This also extends current knowledge on the capability of the AE technique