Time-Lapse Helical X-ray Computed Tomography (CT) Study of Tensile Fatigue Damage Formation in Composites for Wind Turbine Blades

Abstract

Understanding the fatigue damage mechanisms in composite materials is of great importance in the wind turbine industry because of the very large number of loading cycles rotor blades undergo during their service life. In this paper, the fatigue damage mechanisms of a non-crimp unidirectional (UD) glass fibre reinforced polymer (GFRP) used in wind turbine blades are characterised by time-lapse ex-situ helical X-ray computed tomography (CT) at different stages through its fatigue life. Our observations validate the hypothesis that off-axis cracking in secondary oriented fibre bundles, the so-called backing bundles, are directly related to fibre fractures in the UD bundles. Using helical X-ray CT we are able to follow the fatigue damage evolution in the composite over a length of 20 mm in the UD fibre direction using a voxel size of (2.75 µm)3. A staining approach was used to enhance the detectability of the narrow off-axis matrix and interface cracks, partly closed fibre fractures and thin longitudinal splits. Instead of being evenly distributed, fibre fractures in the UD bundles nucleate and propagate locally where backing bundles cross-over, or where stitching threads cross-over. In addition, UD fibre fractures can also be initiated by the presence of extensive debonding and longitudinal splitting, which were found to develop from debonding of the stitching threads near surface. The splits lower the lateral constraint of the originally closely packed UD fibres, which could potentially make the composite susceptible to compressive loads as well as the environment in service. The results here indicate that further research into the better design of the positioning of stitching threads, and backing fibre cross-over regions is required, as well as new approaches to control the positions of UD fibres.

A New Non-Invasive Air-Based Actuator for Characterizing and Testing MEMS Devices

“…In previous studies [15][16][17][18][19][20][21][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], the focus was on developing a specific handler for a specific domain for ATE parallel testing. However, in a situation of existing different domains such as electrostatic, piezoelectric, and piezoresistive, a methodology capable of handling all the domains are required.…”

“…Laser-Doppler Vibrometer [33] Out of plan motion scanning laser microscope [34] abnormal vertical displacements scanning electron microscopy [35] Imaging defects computed tomography (CT) [36] Visualizing 3D structure transition electron microscopy [37] Thin-film deposited on MEMS energy-dispersive X-ray spectroscopy (EDS) [38] Chemical composition of surface wavelength X-ray spectroscopy (WDS) [39] Chemical composition of surface In retrospect, the 2000s witnessed a severe lack of universal MEMS standards for all MEMS vendors, while during this time offshoots from IC ATE providers began to emerge. In the middle of the 2000s, some regulations were established for MEMS standardization in design for standard testing.…”

“…Here, we have proved that AbFM is a good option for such analysis and to determine whether there is an internal non-ideality or not. Computed Tomography (CT) is another solution for taking internal photos, but simplicity and high throughput is the main drawback in front of this technology [36]. Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray Spectroscopy (EDS) [38], Wavelength-Dispersive X-ray Spectroscopy (WDS) [39], Infrared Microscopy [40], and Thermally Induced Voltage Alteration (TIVA) [41] are some of the methods for MEMS material testing and chemical composition evaluation that are non-destructive.…”

“…The last decade has witnessed an admirable surge for the introduction of diverse general characterizing and testing methods for MEMS devices, some of which are shown in Table 1 [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. These methods are categorized into two main groups: destructive and non-destructive testing approaches.…”

Analysis of Impregnation Mechanism of Weft-Knitted Commingled Yarn Composites by Staged Consolidation and Laboratory X-Ray Computed Tomography

“…Higher energy X-ray beams, such as those in synchrotron facilities are more adapted to the in-situ µCT imaging which is required for the in-situ characterization at high time resolution and at resolutions lower than one micrometer. In-situ µCT analyses are more suitable to monitor damage (Böhm et al, 2015;Rolland et al, 2017;Yang et al, 2017;Jespersen et al, 2018;Wang et al, 2018), to characterize time dependent phenomena taking place during the process, such as the impregnation of reinforcement (Vilà et al, 2015;Sisodia et al, 2016;Larson and Zok, 2018) and the fiber bed compression (Latil et al, 2011;Ferré Sentis et al, 2017). In case the readers need more information about application of µCT characterization of polymer matrix composites, some reviews are already available in the literature (Maire and Withers, 2014;Duchene et al, 2018;Garcea et al, 2018).…”