Vibration-based damage growth monitoring in beam-like structures

Damage growth monitoring plays an important role in providing early warning of structural failure. The existing methods for damage growth monitoring are mainly local inspection methods, such as acoustic emission. These methods need a priori knowledge of accessible damage vicinity, which may not be realized in practice. Hence, vibration-based global approach is adopted to overcome these difficulties. Natural frequency, as a global modal parameter, can be measured easily and is used for vibration-based damage growth monitoring in this study. A concept of damage-induced relative natural frequency change (RNFC) curve is defined first and its relation with mode shape is then derived analytically, giving a good way to approximate RNFC curves. For monitoring damage growth, a damage growth indicator is proposed based on RNFCs between two damaged stages of a beam. The effectiveness of the indicator for damage growth monitoring is proved by both numerical and experimental cases in beam-like structures

Damage localization in beams based on the analysis of modal parameters

This paper presents a two-step method for damage localization in beams by combining natural frequencies and mode shapes. The general locations of the damage are first identified from an indicator developed using relative natural frequency change (RNFC) curves and the values of RNFCs. A curvature-mode-shape-based method is then utilized to determine the specific location of the damage in the second step. The proposed two-step method is verified by detecting damage in a simulated simply-supported beam. The identified damage location agrees well with the actual damage location. A strategy for fast and accurate damage localization based on general localization using natural frequencies and specific localization using mode shapes is the main novelty of the paper

Application of a Laser-Based Time Reversal Algorithm for Impact Localization in a Stiffened Aluminum Plate

Non-destructive testing and structural health monitoring (SHM) techniques using elastic guided waves are often limited by material inhomogeneity or geometrical irregularities of the tested parts. This is a severe restriction in many fields of engineering such as aerospace or aeronautics, where typically one needs to monitor composite structures with varying mechanical properties and complex geometries. This is particularly true in the case of multiscale composite materials, where anisotropy and material gradients may be present. Here, we provide an impact localization algorithm based on time reversal and laser vibrometry to cope with this type of complexity. The proposed approach is shown to be insensitive to local elastic wave velocity or geometrical features. The technique is based on the correlation of the measured impact response and a set of measured test data acquired at various grid points along the specimen surface, allowing high resolution in the determination of the impact point. We present both numerical finite element simulations and experimental measurements to support the proposed procedure, showing successful implementation on an eccentrically stiffened aluminum plate. The technique holds promise for advanced SHM, potentially in real time, of geometrically complex composite structures

Extended Non-destructive Testing for Surface Quality Assessment

AbstractThis chapter introduces various extended non-destructive testing (ENDT) techniques for surface quality assessment, which are first characterized, then enhanced, and finally applied to assess the level of pre-bond contaminations intentionally applied to carbon fiber reinforced plastic (CFRP) adherends following the procedures described in the previous chapter. Based on two user cases comprising different scenarios that are characteristic of either aeronautical production or repair, the detailed tests conducted on two types of sample geometry, namely flat coupons and scarfed pilot samples with a more complex shape, form the basis for applying the advanced ENDT procedures for the monitoring of realistic and real aircraft parts, as will be described in Chap. 10.1007/978-3-319-92810-4_5. Specifically, the reported investigations were performed to assess the surface quality of first ground and then intentionally contaminated CFRP surfaces using the following ENDT tools: the aerosol wetting test (AWT), optically stimulated electron emission (OSEE), two differently implemented approaches based on electronic noses, laser-induced breakdown spectroscopy (LIBS), Fourier-transform infrared (FTIR) spectroscopy, laser-induced fluorescence (LIF), and laser vibrometry

Barely visible impact damage identification in a 3D core sandwich structure

3D core sandwich structure (3DCSS) is a popular lightweight construction material in the automotive, aerospace and marine industries. However, barely visible low-speed impact-damage (BVLID) may occur in the 3DCSS due to foreign-object-impact that can significantly reduce the load-bearing capacity of the structure. This paper presents a guided wave (GW) propagation based BVLID identification technique for the 3DCSS. A global-matrix formulation based semi-analytical model is applied to generate the dispersion curve for the GW propagation in the 3DCSS. It is observed that the GW propagation in the 3DCSS is multi-modal in nature. Finite-element numerical simulation of GW propagation in the 3DCSS is carried out in Abaqus. A significant increment in the primary antisymmetric mode is noticed due to the presence of BVLID region in the structure. Experiments are then conducted on a 3DCSS sample to validate the simulation results. There is a good agreement between the simulation and experimental results in all the cases

Crack Identification in CFRP Laminated Beams Using Multi-Resolution Modal Teager–Kaiser Energy under Noisy Environments

Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of high-resolution measurement technologies, mode-shape-based crack identification in such laminated beam components has become an active research focus. Despite its sensitivity to cracks, however, this method is susceptible to noise. To address this deficiency, this study proposes a new concept of multi-resolution modal Teager–Kaiser energy, which is the Teager–Kaiser energy of a mode shape represented in multi-resolution, for identifying cracks in carbon fiber reinforced polymer laminated beams. The efficacy of this concept is analytically demonstrated by identifying cracks in Timoshenko beams with general boundary conditions; and its applicability is validated by diagnosing cracks in a carbon fiber reinforced polymer laminated beam, whose mode shapes are precisely acquired via non-contact measurement using a scanning laser vibrometer. The analytical and experimental results show that multi-resolution modal Teager–Kaiser energy is capable of designating the presence and location of cracks in these beams under noisy environments. This proposed method holds promise for developing crack identification systems for carbon fiber reinforced polymer laminates

Online detection of barely visible low-speed impact damage in 3D-core sandwich composite structure

3D-core sandwich composites are novel lightweight construction materials being used heavily in defense, aerospace, marine, and automobile industries. In spite of the many commendable advantages, the 3D-core sandwich composite structures are prone to barely visible low-speed impact damages that may significantly jeopardize the safety and integrity of the structural assembly. The aim of this paper is to develop an advanced structural health monitoring framework to efficiently identify such damages in the sandwich structure using ultrasonic guided wave propagation. Theoretical analysis, numerical simulations and laboratory experiments of guided wave propagation in 3DCSCS have been carried out to demonstrate the effectiveness of the identification of barely visible impact damages. It is found that the presence of such damage regions significantly magnifies the fundamental antisymmetric mode of the propagating signals. The 3D numerical simulation gives physical insight and a good agreement has been observed with experimental results which affirms our understanding of the effect of damage on the propagating waves. The impact damage regions in the sandwich structure are experimentally identified using a modified signal difference algorithm based health monitoring framework. The proposed structural monitoring framework is found to be significantly efficient for the detection of impact damages in a sandwich structure

Damage Identification in Various Types of Composite Plates Using Guided Waves Excited by a Piezoelectric Transducer and Measured by a Laser Vibrometer

Composite materials are widely used in the industry, and the interest of this material is growing rapidly, due to its light weight, strength and various other desired mechanical properties. However, composite materials are prone to production defects and other defects originated during exploitation, which may jeopardize the safety of such a structure. Thus, non-destructive evaluation methods that are material-independent and suitable for a wide range of defects identification are needed. In this paper, a technique for damage characterization in composite plates is proposed. In the presented non-destructive testing method, guided waves are excited by a piezoelectric transducer, attached to tested specimens, and measured by a scanning laser Doppler vibrometer in a dense grid of points. By means of signal processing, irregularities in wavefield images caused by any material defects are extracted and used for damage characterization. The effectiveness of the proposed technique is validated on four different composite panels: Carbon fiber-reinforced polymer, glass fiber-reinforced polymer, composite reinforced by randomly-oriented short glass fibers and aluminum-honeycomb core sandwich composite. Obtained results confirm its versatility and efficacy in damage characterization in various types of composite plates

Shear Strain Singularity-Inspired Identification of Initial Delamination in CFRP Laminates: Multiscale Modulation Filter for Extraction of Damage Features

Identification of initial delamination is crucial to ensure the safety of the fiber-reinforced laminated composite structures. Amongst the identification approaches based on mode shapes, the concept of multiscale shear-strain gradient (MSG) has an explicit physical sense of characterizing delamination-induced singularity of shear strains; moreover, it is robust against noise interference owing to the merits of multiscale analysis. However, the capacity of the MSG for identifying initial delamination is insufficient because the delamination-induced singularity peak can be largely obscured by the global component of the MSG. Addressing this problem, this study proposes an enhanced approach for identifying initial delamination in fiber-reinforced composite laminates. In particular, the multiscale modulation filter (MMF) is proposed to modulate the MSG with the aim of focusing on damage features, by which a new concept of enhanced MSG (EMSG) is formulated to extract damage features. By taking advantage of the MMF with the optimal frequency translation parameters, the EMSG is concentrated in a narrow wavenumber band, which is dominated by the damage-induced singularity peak. As a consequence, the delamination-induced singularity peak in the EMSG can be isolated from the global component. The capacity of the approach for identifying initial delamination is experimentally validated on a carbon fiber reinforced polymer (CFRP) laminate, whose mode shapes are acquired via non-contact laser measurement. The experimental results reveal that the EMSG-based approach is capable of graphically characterizing the presence, location, and size of initial delamination in CFRP laminates