Monitoring Damage Growth Research Articles

A Comparative Study of Geometric Phase Change- and Sideband Peak Count-Based Techniques for Monitoring Damage Growth and Material Nonlinearity.

This work presents numerical modeling-based investigations for detecting and monitoring damage growth and material nonlinearity in plate structures using topological acoustic (TA) and sideband peak count (SPC)-based sensing techniques. The nonlinear ultrasonic SPC-based technique (SPC-index or SPC-I) has shown its effectiveness in monitoring damage growth affecting various engineering materials. However, the new acoustic parameter, "geometric phase change (GPC)" and GPC-index (or GPC-I), derived from the TA sensing technique adopted for monitoring damage growth or material nonlinearity has not been reported yet. The damage growth modeling is carried out by the peri-ultrasound technique to simulate nonlinear interactions between elastic waves and damages (cracks). For damage growth with a purely linear response and for the nonlinearity arising from only the nonlinear stress-strain relationship of the material, the numerical analysis is conducted by the finite element method (FEM) in the Abaqus/CAE 2021 software. In both numerical modeling scenarios, the SPC- and GPC-based techniques are adopted to capture and compare those responses. The computed results show that, from a purely linear scattering response in FEM modeling, the GPC-I can effectively detect the existence of damage but cannot monitor damage growth since the linear scattering differences are small when crack thickness increases. The SPC-I does not show any change when a nonlinear response is not generated. However, the nonlinear response from the damage growth can be efficiently modeled by the nonlocal peri-ultrasound technique. Both the GPC-I and SPC-I techniques can clearly show the damage evolution process if the frequencies are properly chosen. This investigation also shows that the GPC-I indicator has the capability to distinguish nonlinear materials from linear materials while the SPC-I is found to be more effective in distinguishing between different types of nonlinear materials. This work can reveal the mechanism of GPC-I for capturing linear and nonlinear responses, and thus can provide guidance in structural health monitoring (SHM).

Monitoring damage growth and topographical changes in plate structures using sideband peak count-index and topological acoustic sensing techniques

Some topographies in plate structures can hide cracks and make it difficult to monitor damage growth. This is because topographical features convert homogeneous structures to heterogeneous one and complicate the wave propagation through such structures. At certain points destructive interference between incident, reflected and transmitted elastic waves can make those points insensitive to the damage growth when adopting acoustics based structural health monitoring (SHM) techniques. A newly developed nonlinear ultrasonic (NLU) technique called sideband peak count – index (or SPC-I) has shown its effectiveness and superiority compared to other techniques for nondestructive testing (NDT) and SHM applications and is adopted in this work for monitoring damage growth in plate structures with topographical features. The performance of SPC-I technique in heterogeneous specimens having different topographies is investigated using nonlocal peridynamics based peri-ultrasound modeling. Three types of topographies – “X” topography, “Y” topography and “XY” topography are investigated. It is observed that “X” and “XY” topographies can help to hide the crack growth, thus making cracks undetectable when the SPC-I based monitoring technique is adopted. In addition to the SPC-I technique, we also investigate the effectiveness of an emerging sensing technique based on topological acoustic sensing. This method monitors the changes in the geometric phase; a measure of the changes in the acoustic wave’s spatial behavior. The computed results show that changes in the geometric phase can be exploited to monitor the damage growth in plate structures for all three topographies considered here. The significant changes in geometric phase can be related to the crack growth even when these cracks remain hidden for some topographies during the SPC-I based single point inspection. Sensitivities of both the SPC-I and the topological acoustic sensing techniques are also investigated for sensing the topographical changes in the plate structures.

Real-time sinusoidal parameter estimation for damage growth monitoring during ultrasonic very high cycle fatigue tests

Ultrasonic fatigue tests (UFT) are used to study the fatigue life behavior of metallic components undergoing a very high number of cycles (typically ≥107−109 cycles) under relatively low mechanical loads. By soliciting fatigue specimens at 20 kHz, ultrasonic fatigue machines are indispensable for monitoring damage growth and fatigue failures in a reasonable amount of time. As fatigue damage accumulates in the specimen, the specimen’s free-end exhibits a nonlinear dynamic response. The resulting quasi-stationary, harmonic signals have sinusoidal parameters (frequency and amplitude) which are slowly time-varying with respect to the excitation frequency. The discrete Fourier transform (DFT) is typically used to extract these evolving sinusoidal parameters from a window of finite data of the vibration signal. Alternative spectral estimation methods, specifically line spectra estimators (LSEs), exploit a priori information of the signal via their modeling basis and overcome limitations seen by the DFT. Many LSEs are known to have state-of-the-art results when benchmarked on purely stationary signals with unit amplitudes. However, their performances are unknown in the context of slowly time-varying signals typical of UFT, leading to a widespread use of the DFT. Thus, this paper benchmarks classical and modern LSEs against specific synthetic signals which arise in UFTs. Adequate algorithms are then recommended and made publicly available to process experimental data coming from ultrasonic fatigue tests depending on performance metrics and experimental restraints.

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.

Low velocity impact response and energy absorption behavior on glass fibre reinforced epoxy composites

A study was undertaken to determine the effects of several key geometry influencing factors on the impact response and energy absorption behavior of the glass fibre reinforced epoxy composites at low and intermediate energies. The energy-balance model was employed for characterising the energy absorption behavior and it depends strongly on the plate diameter and thickness. In addition, the damage vs. energy and force maps is effective in monitoring damage growth within the composite panel. The response of the composite laminate configurations characterized by different stacking sequences subjected to low velocity impacts with different impact energies have also been studied to estimate the damage initiation of composites.

Composite Aerospace Structure Monitoring with use of Integrated Sensors

Abstract One major challenge confronting the aerospace industry today is to develop a reliable and universal Structural Health Monitoring (SHM) system allowing for direct aircraft inspections and maintenance costs reduction. SHM based on guided Lamb waves is an approach capable of addressing this issue and satisfying all the associated requirements. This paper presents an approach to monitoring damage growth in composite aerospace structures and early damage detection. The main component of the system is a piezoelectric transducers (PZT) network integrated with composites. This work describes sensors’ integration with the structure. In particular, some issues concerning the mathematical algorithms giving information about damage from the impact damage presence and its growth are discussed.

A multi-helical ultrasonic imaging approach for the structural health monitoring of cylindrical structures

In the past few years, several efforts have been made to combine guided ultrasonic waves and imaging algorithms such as tomography for detecting and locating damage in complex structures. In this article, we introduce a multi-helical ultrasonic imaging approach for the structural health monitoring of cylindrical structures. An array of permanently installed piezoelectric transducers is used to generate and receive high-order helical guided waves around the cylindrical structure to artificially increase the ray density/resolution without increasing the number of sensors. A probabilistic-based imaging algorithm is used to identify metal loss defects. Experimental tests are carried out on a steel pipe instrumented with six piezoelectric transducers to validate the proposed approach. Three thickness recesses simulating corrosion are considered. Results demonstrate the efficacy of the proposed approach by identifying the simulated damage at the correct locations and qualitatively monitoring damage growth. No attempt is made in this study to quantify the extent of thinning.

Electrical resistance measurement for in situ monitoring of fatigue of carbon fabric composites

This study investigates whether fatigue damage can be monitored using the electrical resistance of the carbon fabric-reinforced thermoplastic. A four-probe method, using rivets for the current injection and conductive tape for the voltage measurement is presented. Quasi-static and hysteresis tests are presented to assess the method, with promising results. Then, fatigue tests at both 2 and 5 Hz are discussed. For the material under study, neither stiffness reduction nor permanent elongation occurred and therefore, fibre fracture is not the dominant mode of damage. As a result, the electrical resistance measurement was not capable of monitoring damage growth inside the specimen, since it is sensitive to fibre failure.

Debonding of Stitched Composite Joints under Static and Fatigue Loading

An experimental study was conducted to examine the effects of stitches on the static and fatigue failure of two different single lap joint configurations. To monitor damage growth, X-rays were taken periodically during the fatigue tests. The study showed that a 21/2 fold increase in static strength due to stitching. A similar increase was found in fatigue strength for a given fatigue life. Additionally, stitching significantly changed the pattern of damage growth.

Smart structure application in bonded repairs

In the aerospace industries bonded composite patches are being increasingly used to extend the operational life of aging aircraft. The application of bonded composite patches to repair or reinforce defective metallic structures is widely acknowledged as an effective and versatile procedure. Such patches have been successfully applied to the repair of cracked structures, to the reinforcement of components subject to material loss due to corrosion damage and as a general means of stress reduction through the provision of a supplementary load path. However, certification requirements mandate the need for a methodology for monitoring the damage state of both the defective underlying structure and of the repair. In this case, the concept of smart structures can be used to detect damage in the repair itself as well as monitor damage growth in the parent structure. This paper will report on the development of a ‘perceptive repair’ or ‘smart’ system which will provide information on the in-service performance of the repair and the associated structure. In this respect, this paper will focus on the detection of disbond in the adhesive layer between adherend and the metallic parent structure. Since this is a relatively new area, a series of numerical studies were initially performed to reveal the salient features of the signals expected. These numerical findings were subsequently confirmed experimentally.

Monitoring damage growth in titanium matrix composites using acoustic emission : 55042 Bakuckas, J.G.; Prosser, W.H.; Johnson, W.S. Journal of Composite Materials, Vol. 28, No. 4, pp. 305–328 (1994)

Monitoring damage growth in titanium matrix composites using acoustic emission : 55042 Bakuckas, J.G.; Prosser, W.H.; Johnson, W.S. Journal of Composite Materials, Vol. 28, No. 4, pp. 305–328 (1994)

Monitoring damage growth in titanium matrix composites using acoustic emission : 53826 Bakuckas, J.G.; Prosser, W.H.; Johnson, W.S. National Aeronautics and Space Administration, Hampton, Virginia (United States), N93-25072/8/GAR, 46 pp. (Mar. 1993)

Monitoring damage growth in titanium matrix composites using acoustic emission : 53826 Bakuckas, J.G.; Prosser, W.H.; Johnson, W.S. National Aeronautics and Space Administration, Hampton, Virginia (United States), N93-25072/8/GAR, 46 pp. (Mar. 1993)

Prediction of impact damage thresholds of glass fibre reinforced laminates

Thick glass fibre reinforced laminates subject to low velocity impact have been investigated using an instrumented drop-weight test rig with a flat-ended impactor. Two sets (small and large) of circular specimens of four different thicknesses are used with incident kinetic energy (IKE) ranging from 15 J to 3000 J. Static tests of the small plates are also conducted. It is demonstrated that using impact response to predict the threshold values of damage initiation is significantly faster and cheaper because it does not need to examine impacted specimens. The ultimate thresholds are found to be dependent on the in-plane dimension of the laminates, two sets of specimens provide two bounds which become close as the thickness of the laminates increases. It is shown that the damage energy and force maps are effective in monitoring damage growth in addition to identifying the thresholds of damage initiation, which are close to the predicted values based on impact response. It is also shown that damage initiation when dominated by delamination can be predicted by a simple analytical model. It is found that strain rate effect is insignificant with moderate damage and becomes appreciable when the laminate load bearing capability is approached.

Monitoring Damage Growth in Titanium Matrix Composites Using Acoustic Emission

In this study, an initial application of the acoustic emission (AE) technique to locate and monitor damage growth in a relatively new and advanced titanium matrix composite (TMC) system was investigated. Damage growth was evaluated in SCS-6/Timetal-21S TMC using several optical techniques including a long focal length, high magnification microscope system with image acquisition capabilities. Fracture surface examinations were conducted using a scanning electron microscope (SEM). The AE technique was used to locate damage based on the arrival times of AE events between two sensors. Using model specimens exhibiting a dominant failure mechanism, correlations were established between the observed damage growth mechanisms and the AE results in terms of the events amplitude. The correlation between the damage mechanisms and the AE parameters must be established whenever a new class of material is being evaluated using the AE technique since the AE parameters are highly dependent on the specimen geometry as well as the type of material. These correlations were then used to monitor the damage growth process in laminates exhibiting multiple modes of damage.

Thermoelastic assessment of damage growth in composites

This paper examines, experimentally and numerically, the use of thermal emission measurements as a means of assessing severity of damage and monitoring damage growth in composite materials. In contrast to most traditional methods the thermal emission profile reflects the interaction of load, geometry, material and damage in a non-destructive fashion. It represents a possible method for the scaling of test data, obtained from coupon tests, to tests on full scale structures.

A Fiber Optic System for Damage Assessment of FRP Composite Structures

ABSTRACTThere are a limited number of nondestructive techniques available for field inspection of large composite structures and practically none for inservice inspection. An innovative damage assessment system is proposed which uses an optical fiber mesh implanted into the body of a fiber reinforced composite structure. This mesh would become an integral part of the structure on fabrication. The selection of the mesh fibers would be predicated on their strain to failure characteristics and strain compatibility with the base composite reinforcing fibers. This optical system will be capable of locating damage, assessing severity and monitoring damage growth. A successful implementation of the total damage assessment system would involve the interaction of the optical fiber mesh with an adequately designed interrogative electronic package. This paper focuses on the former aspect of the total system. It will address some recent experimental work showing the practicality of the concept for large, complex composite structure.