On impact damage detection and quantification for CFRP laminates using structural response data only

Abstract

The overall purpose of the research is to detect and attempt to quantify impact damage in structures made from composite materials. A study that uses simplified coupon specimens made from a Carbon Fibre-Reinforced Polymer (CFRP) prepreg with 11, 12 and 13 plies is presented. PZT sensors were placed at three separate locations in each test specimen to record the responses from impact events. To perform damaging impact tests, an instrumented droptest machine was used and the impact energy was set to cover a range of 0.37-41.72 J. The response signals captured from each sensor were recorded by a data acquisition system for subsequent evaluation. The impacted specimens were examined with an X-ray technique to determine the extent of the damaged areas and it was found that the apparent damaged area grew monotonically with impact energy. A number of simple univariate and multivariate features were extracted from the sensor signals recorded during impact by computing their spectra and calculating frequency centroids. The concept of discordancy from the statistical discipline of outlier analysis is employed in order to separate the responses from nondamaging and damaging impacts. The results show that the potential damage indices introduced here provide a means of identifying damaging impacts from the response data alone.

Condition Structural Index using Principal Component Analysis for undamaged, damage and repair conditions of carbon fiber–reinforced plastic laminate

“…The fast Fourier transform (FFT) is used to convert the time domain signals to a frequency spectrum of the conditions studied. During the post processing steps, the calculation of the frequency centroid or known as the Damage Index (DI; Sultan et al, 2011) is shown below…”

Damage assessment of smart composite structures via machine learning: a review

“…They also identified the location and size of delamination via virtual grids. Sultan et al [109] employed the concept of discordancy from the statistical discipline of outlier analysis, to identify and quantify the damaging and non-damaging impact in smart composite laminates. Frequency centroids were obtained from the transient response clustering and wavelet packet transform (WPT).…”

“…Damage indices for non-damaged and damaged cases; (solid line) threshold value: a sensor 1, b sensor 2, and c sensor 3[109] Mahalanobis squared distances for non-damaged and damaged cases; (solid line) threshold value[109] …”

Capacitive imaging of impact damage in composite material

“…Upon low or intermediate velocity impacts the damage inside the target panel could be large and the laminated composite panel can suffer a significant loss of its designed strength sometimes without a visible indication of damage on the impacted surface [4], thus this is considered to be the most detrimental damage; the impact damage being difficult to detect and often leading to a serious reduction of the structural integrity and mechanical properties [5]. Inter-laminar stresses or mismatching of bending stiffness between two adjacent laminate have been suggested as causes of delamination in the composite laminates subjected to low velocity impact [6] and it has been reported that the apparent damaged area increases monotonically with impact energy [7]. Tolerance to damage is an important requirement in the design and fabrication of composite structural components.…”