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The objective of this case study is to characterise and to numerically assess the volume of impact damages in composite laminates with multiple non-destructive testing techniques. Reliable and robust assessments of the damage volume will be used as input and validation data for the existing and developing numerical models of composite materials.
In everyday work, researchers in the area of composite materials mostly use 2D assessment of the damaged area acquired with conventional inspection methods as ultrasonic c-scan. This practice is supported by the relative simplicity of the data analysis carried in 2D. It is proposed to assess the damage volume in 3D which may serve as a more reliable criterion to improve coupling with the numerical modelling.
In this paper micro X-ray computed tomography (CT) was used as the reference technique for the damage volume assessment and comparison with an industrial ultrasonic c-scan. In addition, for this case study, ultrasonic phased array technique with the full matrix capture algorithms was used for the inspection together with shearography (speckle pattern shearing interferometry). A comparison of all techniques referenced to the CT data formed the guidance for their applicability. In addition, an attempt to fuse the multiple assessments was made to support the comparison of 2D and 3D inspection techniques.
For the experimental part, carbon fiber reinforced polymer (CFRP) specimens of three layups were manufactured and damaged with 4 different impact energies in the range of 18-45 J. The layups were orthotropic, quasi-isotropic and a novel one adapted for the impact events. In total 12 specimens were inspected with multiple non-destructive testing techniques to numerically assess the volume of the impact damages. 3 additional specimens were used to assess the repeatability of the damage in the specimens with the same layup and impact energy. 3D CT reconstructions were made by a rotation of specimens using a cone-beam system with the voxel side size of 50 μm. A developed automatic segmentation algorithm was used for the damage volume estimation in all specimens. The phased array inspection was made with a full-matrix capture technique with the frequencies of 2.25 and 5 MHz. An available 3D shape shearography setup was used to characterise the damages both with the in- and out-of-plane surface strains with a thermal loading of the specimen.
Future developments include the comparison of the inspection results together with the numerical modelling predictions and with residual strength after the impact.
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