Detection Of Transverse Cracks Research Articles

Transverse cracking signal characterization in CFRP laminates using modal acoustic emission and digital image correlation techniques

The process of formation and subsequent propagation of transverse cracks in 90° plies of carbon-fiber laminated composites was studied using modal acoustic emission approach and digital image correlation techniques. The results from modal acoustic emission approach, which included a newly developed processing tool for acoustic emission waveforms, provided information for identification and subsequent characterization or localization of signals originating from transverse cracking by analysis of the separated flexural and extensional Lamb wave modes in terms of their modal parameters. The digital image correlation method served as a verification tool of the acoustic emission data outputs in the terms of activity of significant localized events originating from the formation of the transverse crack in the 90oply. This made it possible to specify more locally the accompanying activity belonging to the formation or propagation of the magistral transverse crack. The manuscript also presents results related to the evolution of flexural/extensional wave modal parameters as the function of loading force for both [0/0/0/90]S and [90/0/0/0]S panels. It can be concluded that the detection of transverse cracks requires the need for applying a more complex acoustic emission data analysis methodology, while the standard parametric analysis, including the waveform peak frequency, is not sufficient. The presented methodology may serve as a basis for development of robust analysis tool capable of detecting the investigated phenomena.

Detection of transverse cracks in steel beams using damage location coefficients and artificial neural networks

Structural health monitoring plays a crucial role in ensuring the integrity and safety of engineering structures such as steel beams. This research paper presents a comprehensive methodology for detecting transverse cracks in beams with a constant section and any boundary conditions. The proposed approach utilizes the normalized squared modal curvature of the beam, the damage severity, and the natural frequency of the undamaged beam. By analyzing the natural frequencies of both the undamaged and damaged states, Relative Frequency Shift (RFS) values are obtained. Subsequently, the Damage Location Coefficients (DLC) are calculated by normalizing the RFS values. These DLC values are then employed to establish a comprehensive database of known damage signatures, enabling the training of an artificial neural network (ANN) in MATLAB. The trained ANN can predict the locations of damages for new scenarios by utilizing DLC values obtained from measurements. To validate the effectiveness of the ANN, extensive simulations using Finite Element Method (FEM) and experimental measurements are conducted on a steel cantilever beam. The results demonstrate the ANN’s capability to accurately predict the locations of transverse cracks, showcasing its potential as a reliable tool for structural health monitoring of steel beams.

Detection of a single transverse crack in a CFRP cross-ply laminate by visualizing mode conversion of Lamb waves

Detection of transverse crack (TC) is important in establishing reliable structural health monitoring (SHM) and nondestructive inspection (NDI) for warning the potential occurrence of large-scale damage in carbon fiber reinforced plastic (CFRP) structures at an earlier stage. In this research, a diagnostic method that is sensitive to a single TC was established by visualizing laser-induced guided ultrasonic waves in a cross-ply CFRP laminate. First, the phenomenon of TC-induced mode conversion in the laminate was clarified using finite element analysis (FEA) of harmonic oscillations. This FEA method is explicit and precise for investigating the conversion behavior of individual modes in a cracked plate. Then, the conversion phenomenon was also validated by another FEA-based pulse laser ultrasonic simulation. Finally, to observe the mode conversion phenomenon in practice, we conducted an experiment with a laser ultrasonic visualizing inspector (LUVI). The LUVI system could visualize the wave propagation in a two-dimensional (2D) wavefield that was formed on the surface of the CFRP cross-ply laminate with a single TC. By observing the image results of wave propagation, we verified that the wave component of the A0 mode was converted from the S0 mode at a TC even though the converted A0 mode had a much smaller amplitude than the incident S0 mode in the cross-ply CFRP laminate. Thus, those visualization results could be used to detect a single TC in the CFRP cross-ply laminate reliably.

A novel baseline-free approach for acousto-ultrasonic crack monitoring of rotating axles

Axles are widely used mechanical components in rotating machines. In many applications, axles are exposed to varying environmental and operational conditions, including for example, temperature, load and rotational speed. To apply acousto-ultrasonics–based structural health monitoring for axles, it is in some cases not economically feasible to collect data and to construct a baseline model for each combination of all possible environmental and operational conditions. In consideration of such a practical limit, a novel baseline-free method, called Dynamic Reference Method, is proposed in this article for the detection of transverse cracks in axles. Piezoelectric wafer active sensors are applied for exciting and sensing ultrasonic waves. In case a transverse crack is present in an axle, it is noticed that the crack will sequentially open and close within one revolution of the axle when it is mechanically loaded in the radial direction. Such an opening and closing phenomenon of the transverse crack will influence the propagation of the ultrasonic waves. During the short time of data acquisition, the environmental and operational conditions remain nearly constant and the changes in the propagation of the ultrasonic waves may indicate the appearance of a transverse crack on the axle, and a baseline model for the environmental and operational conditions is not needed. To validate the proposed baseline-free method, an axle is put on a rotating bending test rig to first initiate a fatigue crack on the surface of the axle and second to observe its growth. During the test, the ultrasonic waves are measured by piezoelectric wafer active sensor in situ and are analysed online using the proposed baseline-free method. According to the test results, not only can the crack be effectively detected, but also the progressive changes of the crack size can be differentiated. Such results demonstrate the potential of the proposed baseline-free method in condition-based maintenance and predictive maintenance for critical axle components.

Size and location detection of transverse cracks using a passive magnetic method

Reinforced concrete is widely used in urban and industrial structures. Exposure of such structures to cyclic loads may cause crack initiation in the reinforcement steel (rebar). In extreme cases, incremental crack propagation under the effects of accelerants such as corrosion and external loads can lead to catastrophic failures. To minimize the various risks resulting from unexpected loss-of-function, rebar condition can be assessed using a novel passive magnetic-based method. In this study, the magnetic properties of defective rebars with transverse cracks are recorded and assessed through experiments. Additionally, the self-magnetic behaviors of similar defective rebars are subsequently simulated using a finite-element based software. Analysis approaches are used on the magnetic data, and thresholds are defined for detecting and categorizing the cracks. For instance, it is demonstrated that the cracks causing rebars’ cross-sectional loss of about 30% are detected using the threshold of 0.95 percentile rank on the magnetic values’ absolute gradients.

Detection of transverse crack in weld by dual probe cross-weld scanning imaging

In order to solve the problem of transverse crack detection, the method of dual probe cross-weld scanning is proposed. Based on the designed artificial specimen containing two groups of pre-located defects, through the comparison study of CIVA simulation and experimental testing of the specimen, the variation of the gain of different sizes of cracks was obtained with the optimal eccentricity angle of 40∼50 degree. It was proved that this method has high detection sensitivity and high engineering application value.

Dynamic characteristics of cracked uncertain hollow-shaft

Abstract Considering the parametric uncertainties, the model of a rotor system with transverse crack is investigated. Polynomial Chaos Expansion is used to describe the uncertainties. The Harmonic Balance method is employed to solve the dynamic equations of cracked uncertain hollow-shaft system. The application of the PCE in hollow shaft structures will be tested and the results can provide practical reference for engineering context. Validation of present method is verified by comparing with Monte Carlo simulations. From the simulation results, the multi-vibration peaks near the first critical speed and the sub-critical speeds are sensitive to the uncertain parameters. When considering the uncertain parameters, the non-linear responses in harmonic components of the rotor system are key indicators for the detection of transverse crack.

Fault detection of composite beam by using the modal parameters and RBFNN technique

The detection of transverse cracks in terms of their location and intensity by using the radial basis function neural network (RBFNN) technique is analyzed in the current research and validated with experimental investigation. The glass fiber-reinforced epoxy composite is used in this research because of its valuable features, such as high stiffness and strength-to-weight ratios, good fatigue and wear resistance, and damage tolerance capability compared with isotropic material. The theoretical and numerical investigations are performed to obtain a relationship between the change in natural frequencies and mode shapes for the cracked and noncracked composite beam. Numerical analysis is performed by using the finite element software ANSYS on cracked and noncracked composite beams to measure the modal parameters, such as natural frequencies and mode shapes. These parameters are used to design an artificial intelligent controller based on the RBFNN-type neural network for predicting crack severity and its intensity. The relative natural frequencies and mode shapes (First, second, and third modes) of vibration are used as input data to the RBFNN controller, and the relative crack locations and crack depths are the output of RBFNN. Results from theoretical and numerical analysis are compared with the experimental results, and a good agreement is observed between them.

On the detectability of transverse cracks in laminated composites using electrical potential change measurements

Real-time health monitoring of structures made of laminated composites is necessary as significant damage may occur without any visible signs on the surface. Inspection by electrical tomography (ET) seems a viable approach that relies on voltage measurements from a network of electrodes across the inspected domain to infer conductivity change within the bulk material. If conductivity decreases significantly with increasing damage, the obtained conductivity map can be correlated to the degradation state of the material. We focus here on detection of transverse cracks. As transverse cracks modify the in-plane transverse conductivity of a single ply, we expect them to be detectable by electrical measurements. Yet, the quality of detection is directly related to the sensitivity of the measurements to the presence of cracks. We use numerical experiments to demonstrate that the sensitivity depends on several material and geometrical parameters. Based on the results, the applicability of ET to detect transverse cracks is discussed. One conclusion from the study is that detecting transverse cracks using ET is more reliable in some laminate configurations than in others. Recommendations about the properties of either the pristine material or the inspected structures are provided to establish if ET is reliable in detecting transverse cracks.

Synthetic Aperture Focusing Technique for Detecting Transverse Cracks in Austenitic and Dissimilar Welds

The inspection of austenitic and dissimilar welds using ultrasound demands for sophisticated testing techniques. The application of reconstruction methods like the Synthetic Aperture Focusing Technique (SAFT) on the measurement results provides an appropriate approach for defect characterization and sizing. Nevertheless, the reconstruction algorithm has to consider the aniso-tropic wave propagation inside the inhomogeneous weld material. In recent years the detection of transverse cracks has become increasingly important for ensuring the structural integrity of pipes in the primary circuit of nuclear power plants or longitudinally welded, cladded pipes. However, relia-ble inspection techniques are hardly available. In this particular case, it is expected that the compar-atively long propagation path of the ultrasonic wave field inside the inhomogeneous weld material enhances the effect of anisotropy and influences the accuracy and the signal-to-noise-ratio of the reconstruction result. In this contribution we suggest an advanced ultrasonic testing technique for detecting and sizing of transversal cracks in austenitic and dissimilar welds. The method applies a SAFT reconstruction algorithm considering the anisotropy and the inhomogeneity. A V-arrangement of the transducers in pitch-catch technique is chosen to avoid a direct coupling on the weld face. The reconstruction algo-rithm is based on an extended 3-dimensional weld model and uses a ray-tracing approach for de-termining the wave propagation paths. Along with the reconstruction algorithm the transducer set-up and experimental results of different specimens with artificial transverse flaws are presented. The availability of the proposed method for crack sizing is assessed in comparison to conventional testing techniques.

Detection of Transverse Cracks in a Composite Beam Using Combined Features of Lamb Wave and Vibration Techniques in Ann Environment

Abstract The detection, location and sizing of transverse cracks in a composite beam, by combining damage features of Lamb wave and vibration based techniques in artificial neural network (ANN) environment, using numerical finite element model, is discussed. Four damage features, time of flight (TOF) and amplitude ratio, which are Lamb wave based features and first and second natural frequencies, which are vibration based features were used as input to ANN. The output of ANN was crack location and depth. It was demonstrated that through the simultaneous employment of features from the two modalities in an ANN environment, the sizing could be done more effectively.

Quantitative evaluation of transverse cracks in carbon fiber reinforced plasticquasi-isotropic laminates with embedded small-diameter fiber Bragg grating sensors

The authors have applied newly developed small-diameter fiber Bragg grating (FBG) sensors, whose claddingis 40 µm in diameter, for the detection of transverse cracks in carbon fiber reinforced plastic (CFRP)laminates. In previous research, the small-diameter FBG sensors were embedded in CFRPcross-ply laminates. When transverse cracks occurred, reflection spectra from the FBGsensors broadened with an increase in the crack density. Thus, the authors showed thatsmall-diameter FBG sensors had the potential to detect the occurrence of cracks. In thepresent research, this technique is applied to the detection of the transverse crack evolutionin CFRP quasi-isotropic laminates, whose laminate configuration is more suitable forpractical use. Through the experiment and the theoretical calculation, it was found thatthe small-diameter FBG sensor could also detect transverse cracks in quasi-isotropiclaminates quantitatively.

Effect of fiber coating on crack detection in carbon fiber reinforced plasticcomposites using fiber Bragg grating sensors

Fiber Bragg grating (FBG) sensors have been applied to the detection oftransverse cracks in carbon fiber reinforced plastic (CFRP) cross-ply laminatesusing the sensitivity of the sensors to non-uniform strain distribution. However,there is the possibility that the resin coatings of the FBG sensors willrelax the non-uniform strain distribution and deteriorate the sensitivity ofthe sensors. Hence, in the present research, the strain transfer from thelaminate to the core of an embedded optical fiber was calculated by atheory developed from the shear-lag model. As a result, it was found thatthe variation of the axial strain in the core of a polyimide coated FBGsensor was smaller than that of an uncoated FBG sensor. Nevertheless, thereflection spectra of the coated FBG sensor and the uncoated one, which werecalculated from the strain distributions in their cores, were almost thesame. This result shows that the coating of the optical fiber does notdeteriorate the sensitivity of the FBG sensor for crack detection. Furthermore,the effectiveness of the coated sensor was also confirmed experimentally.

Detection of microscopic damages in composite laminates

Small-diameter fiber Bragg grating (FBG) sensors, of outside diameter 52 μm, have been developed by the authors and Hitachi Cable Ltd. for embedding inside a laminate without deterioration of the mechanical properties of the composite laminate. In this research, the small-diameter FBG sensor was embedded in the 0° ply of a CFRP cross-ply laminate for the detection of transverse cracks in the 90° ply. The reflection spectra from the FBG sensor were obtained at various tensile stresses. As a result of damage, the spectrum became broad and had some peaks with increase in the transverse crack density. Furthermore, theoretical calculation reproduced the change in the spectrum very well. These results show that small-diameter FBG sensors have the potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width.

Detection of transverse cracks in CFRP composites using embeddedfiber Bragg grating sensors

In the present research, fiber Bragg grating (FBG) sensors wereapplied for the detection of transverse cracks, which cause straindistribution within the gage length, in carbon fiber reinforced plastic(CFRP) cross-ply laminates. An uncoated FBG sensor was embedded in0° ply on the border of 90° ply in a CFRP cross-ply laminate.The reflection spectra from the FBG sensor were measured at various tensilestresses. As a result, the reflection spectrum became broad and had somepeaks with an increase of the transverse crack density in the 90°ply. After the crack density was saturated, the spectrum became narrow andhad one large peak again. In order to confirm that the change in thespectrum was caused by transverse cracks, the spectra were calculatedtheoretically. The calculated result reproduced the change in the measuredspectrum very well. These results show that the occurrence of transversecracks can be detected from the change in the form of the reflectionspectrum, and that the spectrum width at the half maximum is a goodindicator for the quantitative evaluation of the transverse crack densityin real time.

On-line eddy current testing of hot CC slabs : towards the inspection of the whole product surface

In order to achieve a non destructive testing of the whole surface of CC slabs, the option of two independent eddy current devices has been taken.The detection of transverse cracks on slab edges has been industrial since 1985, bringing drastic economical savings and making direct charging rate evolve towards 100 %.The newly developed inspection of large sides looking for longitudinal cracks has given very good results, thanks to eddy current imaging, during on-line qualification trials.