PSI - Issue 37

Andrzej Katunin et al. / Procedia Structural Integrity 37 (2022) 195–202 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

196

2

1. Introduction Polymeric matrix composite (PMC) structures are successfully applied for load-bearing applications and effectively substitute conventional materials by an increased strength, and simultaneously, much lower mass, which were used primarily in the aircraft and aerospace engineering and similar industrial branches. Despite the superiority of these materials, they suffer from a high susceptibility to low-velocity impact damage. As a result of impact loading, a dense and complex net of cracks and delaminated interfaces occurs inside the structure, which forms a characteristic conic shaped damaged area (see e.g. Sławski et al., 2021) , while the surface often does not show any signs of damage or these signs are insignificant compared to the internal damage extent (Sohn et al., 2000; Bieniaś et al., 2015; Santos et al., 2021). Therefore, this type of damage, usually called the barely visible impact damage (BVID), remains one of the most challenging in the maintenance practice of PMC structures. Despite the invisibility or bare visibility of such a type of damage, it may significantly affect the structural residual life within both static (Sławski et al., 2020) and fatigue strength (Melin and Schön, 2001; Ogasawara et al., 2013). The identification of BVID usually requires the application of non-destructive testing (NDT) techniques which are able to visualize internal damage. Such techniques include primarily ultrasonic testing (UT), shearography, infrared thermography, and X-ray computed tomography (XCT), but due to a portability and high accuracy the routine inspections are usually limited to the application of UT. The results of UT inspections can be used for the evaluation of the structural residual life and prediction of its propagation. However, as it was observed in the previous studies (Wronkowicz-Katunin et al., 2019a; Wronkowicz-Katunin et al., 2019b), the damage extent detected in the results of UT is often under- or overestimated, depending on the applied scanning mode and testing parameters. This was confirmed in numerous other studies (Salvetti et al., 2016; Shoukroun et al., 2020). According to this, the evaluation of BVID extent needs to be performed using various data sources to obtain a valid model. This implies the development of the reverse engineering (RE) approach useful for the prognosis of a structural life. The aim of the performed studies was to develop a methodology of a reconstruction of BVID from UT scans with appropriate correction based on reference NDT results and numerical simulations, which can be then used for a simulation of BVID and a prediction of the residual life of PMC structures. To reach this goal, the reconstruction, unification, and fusion of NDT and numerical results are necessary. The reconstruction and fusion of NDT results used for the evaluation of damage extent were a subject of studies by numerous research teams. A similar idea was implemented by Bingol et al. (2017; 2019), where the authors used the results of UT for building computer aided design (CAD) and then finite element (FE) models. Another approach was proposed by Stefaniuk and Dragan (2014; 2016), where the authors performed the fusion and advanced image processing operations on UT and XCT results for structures with BVID to retrieve the geometry of damage and implement it into FE models. Despite the great effectiveness of such an approach with respect to numerically modelled BVID confirmed in the above-cited studies, the simulation of structural residual life based on real NDT results remain case-specific, and cannot be generalized. The following study is a first step to such a generalization – according to the main strategy, various types of NDT results as well as results of FE modelling of BVID were taken into consideration, which allowed minimizing discrepancies between various types of the used results as well as determining the generic shapes of BVID, being a composition of various NDT and FE results. Based on the obtained results the parametric CAD models were constructed, which provides a possibility of simulating the BVID in a certain range of impact energies and considering the shape of impactors. 2. Methodology of a residual life evaluation 2.1. Experimental studies The methodology is divided into several steps. Initially, BVID was introduced into PMC, which were carbon fiber reinforced polymeric (CFRP) structures with the dimensions of 100×100×2.5 mm manufactured and supplied by the Dexcraft s.c. (Helenów, Poland). The BVID was introduced with various impact energy values (the upper limit value was 20 J) and three types of hemispherical impactors with the radii of impactors’ tips of 11 mm, 8 mm, and 5 mm, respectively. The detailed description of the specimens and the predamaging procedure can be found in (Katunin et al., 2021).