Damage In Plates Research Articles

Damage localization with fiber Bragg grating Lamb wave sensing through adaptive phased array imaging

Fiber Bragg gratings are known being immune to electromagnetic interference and emerging as Lamb wave sensors for structural health monitoring of plate-like structures. However, their application for damage localization in large areas has been limited by their direction-dependent sensor factor. This article addresses such a challenge and presents a robust damage localization method for fiber Bragg grating Lamb wave sensing through the implementation of adaptive phased array algorithms. A compact linear fiber Bragg grating phased array is configured by uniformly distributing the fiber Bragg grating sensors along a straight line and axially in parallel to each other. The Lamb wave imaging is then performed by phased array algorithms without weighting factors (conventional delay-and-sum) and with adaptive weighting factors (minimum variance). The properties of both imaging algorithms, as well as the effects of fiber Bragg grating’s direction-dependent sensor factor, are characterized, analyzed, and compared in details. The results show that this compact fiber Bragg grating array can precisely locate damage in plates, while the comparisons show that the minimum variance method has a better imaging resolution than that of the delay-and-sum method and is barely affected by fiber Bragg grating’s direction-dependent sensor factor. Laboratory tests are also performed with a four–fiber Bragg grating array to detect simulated defects at different directions. Both delay-and-sum and minimum variance methods can successfully locate defects at different positions, and their results are consistent with analytical predictions.

An improved time reversal method for diagnostics of composite plates using Lamb waves

The time reversal method has been widely used to detect damage in composite plates. Based on the time reversibility of Lamb waves, the waveform of the original input signal will be reconstructed after the time reversal process. However, the time reversal operator of Lamb waves in composite plates is a function of frequency. Thus the shape of the reconstructed signal will not be identical to that of the original input signal. To alleviate the effects of the time reversal operator, an improved time reversal method (ITRM) is proposed. In this method, the response signal in the forward path and the reconstructed signal in the time reversed path are both modulated by a weight vector which is obtained as the product of a window function and the reciprocal of amplitude dispersion. The window function varies with the excitation signal adaptively, and its shape is also determined by a threshold. An experimental example is then introduced to illustrate the effectiveness of the ITRM. The results show that the time reversibility can be greatly enhanced and the impact damage in the composite plate can be exactly located by the ITRM.

Low cost technique for detecting adhesive debonding damage of glass epoxy composite plate using an impedance based non-destructive testing method

In general, components in composite structures are usually achieved with adhesive bonding, a preferred choice over a conventional mechanical fastening approach. For this reason, debonding of an adhesive layer can be a serious problem as the reliability of the overall structure is influenced by its adhesion characteristics. In addition due to the fact that composites can be formed into various shapes and sizes with ease, this creates a challenging problem for the non-destructive testing (NDT) methods when detecting damage. In this study, a relatively new contact NDT method known as the electromechanical impedance method is used to detect adhesive debonding of glass epoxy composite plates. Furthermore, a metal wire concept is utilized to monitor up to three composite plates using a single impedance measuring device. To achieve this, various piezoelectric transducers are cut into different sizes and connected in series. The results from the experiments introduced in this study shows promising outcome which opens up new possibilities in the field of NDT.

The Influence of Sensor Size on Acoustic Emission Waveforms—A Numerical Study

The performance of Acoustic Emission technique is governed by the measuring efficiency of the piezoelectric sensors usually mounted on the structure surface. In the case of damage of bulk materials or plates, the sensors receive the acoustic waveforms of which the frequency and shape are correlated to the damage mode. This numerical study measures the waveforms received by point, medium and large size sensors and evaluates the effect of sensor size on the acoustic emission signals. Simulations are the only way to quantify the effect of sensor size ensuring that the frequency response of the different sensors is uniform. The cases of horizontal (on the same surface), vertical and diagonal excitation are numerically simulated, and the corresponding elastic wave displacement is measured for different sizes of sensors. It is shown that large size sensors significantly affect the wave magnitude and content in both time and frequency domains and especially in the case of surface wave excitation. The coherence between the original and received waveform is quantified and the numerical findings are experimentally supported. It is concluded that sensors with a size larger than half the size of the excitation wavelength start to seriously influence the accuracy of the AE waveform.

Damage evaluation in plates using modal data and firefly optimisation algorithm

This paper presents a method to identify the location and severity of the damages in plates. The location of damage is detected using a new damage index (MDC), based on the mode shapes and their derivatives. The mode shapes are calculated via modal analysis and their derivatives are obtained through central finite difference approximation. The results are fed into the proposed damage index to find the location of damaged areas. Thereafter, the quantity of damage in the damaged area is assessed using firefly algorithm (FA). The capability of the proposed damage evaluation procedure is shown through some examples. According to the results, the newly proposed index is capable of finding the damage locations with acceptable accuracy. In addition, FA can assess the damage severities in the damaged zones with an error less than 2%. The proposed approach has the ability to identify the damages even for noisy polluted data.

Analysis of the Deformation and Damage of Clamped Square Plates under Near‐Field Explosion Loads

The deformation and damage mechanism of shell structures under near‐field explosion loads has been of great significance in the theoretical study of impact dynamics and may serve as a dependable theoretic basis for the antiexplosion design of shell structures. In this paper, the plastic zone and crevasse size of clamped square plates under near‐field explosion loads were discussed based on the plastic hinge law and energy theory. The crevasse size of a plate moving at motion modes Ι and ΙΙ under medium load was obtained according to the ultimate plastic strain criterion. Furthermore, the plastic zone under a high load was determined in terms of the movement law of a plastic hinge line. When the applied load ended, the crevasse sizes of the plates at motion modes III and IV were deduced on the basis of the principle of energy conservation. Finally, numerical simulation was used to analyse the deformation and damage mechanism of the shell structures under near‐field explosion loads. The theory and method proposed in this paper are verified using ANSYS software and compared with the experimental results. This study verifies the validity of the proposed approach for analysis of the deformation and damage of a clamped square plate under near‐field explosion loads.

Baseline-free damage detection in composite plates based on the reciprocity principle

Lamb wave based damage detection techniques have been widely used in composite structures. In particular, these techniques usually rely on reference signals, which are significantly influenced by the operational and environmental conditions. To solve this issue, this paper presents a baseline-free damage inspection method based on the reciprocity principle. If a localized nonlinear scatterer exists along the wave path, the reciprocity breaks down. Through estimating the loss of reciprocity, the delamination could be detected. A reciprocity index (RI), which compares the discrepancy between the signal received in transducer B when emitting from transducer A and the signal received in A when the same source is located in B, is established to quantitatively analyze the reciprocity. Experimental results show that the RI value of a damaged path is much higher than that of a healthy path. In addition, the effects of the parameters of excitation signal (i.e., central frequency and bandwidth) and the position of delamination on the RI value are discussed. Furthermore, a RI based probabilistic imaging algorithm is proposed for detecting delamination damage of composite plates without reference signals. Finally, the effectiveness of this baseline-free damage detection method is validated by an experimental example.

Modic type 1 change is an autoimmune response that requires a proinflammatory milieu provided by the ‘Modic disc’

Background ContextModic changes (MCs) are magnetic resonance imaging (MRI) evidence of inflammatory and fibrotic vertebral bone marrow lesions that associate with adjacent disc degeneration and end plate damage. Although MC etiology is uncertain, historical data suggest a linkage to an autoimmune response of bone marrow triggered by the nucleus pulposus (NP). PurposeThe aim of this study was to test whether bone marrow has an autoimmune response to NP cells that is amplified by an inflammatory milieu and ultimately leads to MC development in vivo. We hypothesized that an inflammatory co-stimulus is required for bone marrow/NP crosstalk to stimulate MC. Study DesignThis is an in-vitro cell co-culture study plus in-vivo experiments in rat caudal vertebrae. MethodsIn in-vitro study, bone marrow mononuclear cells (BMNCs) and NP cells (NPCs) from rats were co-cultured with and without interleukin (IL)-1α stimulation. Cell viability (n=3) of BMNCs and NPCs and gene expression (n=7) were analyzed. In in-vivo study, proinflammatory lipopolysaccharide (LPS) and control disc nucleus surrogates (NP micromass pellets) were generated in vitro from rat NPCs and implanted into rat tail vertebrae, and the response was compared with sham surgery (n=12 each). Tissue changes were investigated with T1w and T2w MRI (7T), histology, and immunohistochemistry (tumor necrosis factor, CD3) 1 (n=6) and 2 weeks (n=6) after implantation. ResultsBMNC/NPC co-culture significantly increased lymphocyte viability (42%–69%, p<.05) and reduced NPC viability (96%–88%, p<.001), indicating immunogenicity of NPC. However, IL-1α was required to cause significant transcriptional upregulation of IL-1, IL-6, IL-10, and tropomyosin receptor kinase A. Therefore, an inflammatory activation is required to amplify the immune response. Immunogenicity of the NP was corroborated in vivo by CD3 cell accumulation around LPS and control disc surrogates at Day 7. However, only the LPS disc surrogate group demonstrated infiltration of CD3 cells at Day 14. Furthermore, end plate defects (p<.05, LPS: n=4/6, Ctrl: n=0/6, sham: n=0/6) and MC1-like MRI changes (T2w hyperintensity, p<.05) were only seen with LPS disc surrogates. ConclusionsNPCs are immunogenic but cannot trigger MC without an additional proinflammatory stimulus. Our data suggest that MC requires end plate defects that allow marrow/NPC co-mingling plus an adjacent inflammatory “MC disc” that can amplify the immune response.

Experimental seismic study on shear walls with fully-connected and beam-only-connected web plates

Typically, in conventional steel plate shear walls (SPSWs), web plates are connected to both beams and columns; however, steel shear walls connected to beams only (SSW-BOs) with the idea of reducing surrounding columns demands and alleviating web plate damage was proposed since the mid-2000s. This paper presents an experimental investigation on seismic behavior of steel plate shear walls comprising SPSWs and SSW-BOs. Cyclic loading tests were performed on four 1:6 scaled one-story specimens with two plate thickness and two different web plate boundary conditions. The observed predominant failure modes include i: plate tearing at the corners, ii: slippage along connection zone of web plates, and iii: plate-to-frame connection bearing. Using frame connection for plates increases the energy dissipation, shear strength and elastic stiffness by up to 150%, 200% and 110% on average, respectively compared to those of beams-only connected walls. Experimental results indicate that the SSW-BO systems reached a ductility ratio of 7.3 on average, almost 1.5 times the value for SPSWs. It is demonstrated further that with an increase in the slenderness ratio (height to thickness), the strength, stiffness and energy absorbed by the SPSW and SSW-BO systems show a decreasing trend being less stiff for SSW-BO panels.

A New Method to Investigate the Progressive Damage of Imperfect Composite Plates Under In-Plane Compressive Load

Numerous studies have been conducted for failure criteria of fiber reinforced composites.The aim of this study is to present a new computational and mathematical method to analyze theprogressive damage and failure behavior of composite plates containing initial geometric imperfectionsunder uniaxial in-plane compression load. A new methodology is presented based on collocation methodin which the interested domain is discretized with Legendre-Gauss-Lobatto nodes. In order to avoid anexcessive number of nodes, an appropriate weight coefficient is considered for each node. The method isbased on the first order shear deformation theory and small displacement theory. Several failure criteria,including Maximum stress, Hashin and Tsai-Hill, are used to predict the failure mechanisms. The stiffnessdegradation is carried out by instantaneous and complete ply degradation model. Two different types ofboundary conditions are considered in this study. The effects of thickness, initial imperfections, andboundary conditions are studied, as well. The results are compared with the previously published data.It is found that the boundary conditions have significant effects on the ultimate strength of imperfectcomposite plates.

A High-Sensitivity Fusion Index for Delamination Identification of Composite Laminate Structures

A significant obstacle that hinders the extensive application of large composite structures in the aerospace industry is the lack of valid identification methods for composite damage, where the delamination damage is the most common one. In this paper, a high-sensitivity fusion index (HSFI) is proposed for detecting, locating, and quantifying damages in aerospace polymer composite structures. The proposed fusion index is developed based on modern information fusion of three vibration-based indexes: modal strain, modal flexibility and static strain indexes. And its advantage is high sensitivity and strong noise immunity. By detecting the delamination damage in a composite laminate plate, it is verified that this fusion index is highly sensitive for delamination position and size in both cases of little and large damage in the presence of 2% level noise.

Association of Retroplacental Blood With Basal Plate Myofibers.

Objectives Diagnosed clinical abruption showing blood clot should be signed out in the pathology report as retroplacental hemorrhage with or without parenchymal indentation, and submitted clot separate from the placenta should be weighed. In our experience, some cases sent as clinical abruptions have been cases of morbid adherence. This study was undertaken to evaluate the association of retroplacental blood with basal plate myofibers (BPMF). Methods One hundred fifty-six placentas reviewed by a board-certified pediatric pathologist at a community hospital were evaluated for significant retroplacental blood. Basal plates were reviewed for deviations from normal. Results Of the 156 placentas, 33 (21%) had significant retroplacental blood; 21/156 (13%) had a separate clot, of which 11/21 (52%) had BPMF. Eleven BPMF-associated separate clots ranged from 10.5 to 60 g (average 23), while the clots of 10 cases with no demonstrated BPMF ranged from 19 to 440 g (average 82), tending to be larger ( p < .03). Basal plate damage prior to delivery was noted in both sets of placentas. BPMF placentas could have myometrial damage prior to delivery. Conclusions Since BPMF may confer a risk for accreta in a subsequent pregnancy, submission of a separate clot with the placenta should lead the pathologist to evaluate for basal plate myofibers on H&E and consider if there is an evidence-based indication to do an actin stain, before presuming a diagnosis of abruption.

A numerical–experimental study for structural damage detection in CFRP plates using remote vibration measurements

The performance and behavior of composite structures can be significantly affected by degradation and damage. Degradation can be caused by exposure to environmental conditions and damage can be caused by handling conditions, such as impact and loading. Such damages are not always visible on the surface and could potentially lead to catastrophic structural failures. This paper addresses the specific challenge of using numerical simulations to assess damage detection techniques applied to composite laminated plates. This study aims to solve the direct and inverse problem of damage detection by combining numerical and experimental data. Finite element analysis was carried out to analyze the direct problem of mechanical response. Heuristic optimization techniques were used to solve the direct and inverse problem by combining data from a model with that of the experiment to identify structural damage. This study also sought to update the finite element model by minimizing the objective function. The structure studied was constituted of a composite plate. Two damage models were used: (i) circular hole and (ii) delamination (local stiffness reduction). The results of the optimization algorithms show good efficacy in the detection of structural damage, identifying the damaged location on the structure and also quantifying the size of the damage in real composite structures. A method has been proposed to identify the damage in CFRP plates using remote vibration measurements. Furthermore, the numerical simulation and experimental tests have been used to verify the method.

Cooperative Coevolution with Dynamic Species-Size Strategy for Vibration-Based Damage Detection in Plates

Vibration-based damage detection is based on the fact that vibration characteristics such as natural frequencies and mode shapes of structures are changed when the damage occurs. This paper proposes dynamic species-size strategy in cooperative coevolution concept. The resulting algorithm, cooperative coevolutionary genetic algorithm with dynamics species-size (CCGADSS), is used as the optimization algorithm in the vibration-based damage detection in plates. The objective function is numerically calculated from the difference between experimentally vibration characteristics and numerically evaluated vibration characteristics of the predicted damage. In finite element model for objective calculation, the plates are equally divided into 64 elements. There are 2 different cases with dissimilar occurred damage in plates are considered. In first case, the plate hase only one region consisting of 4 elements which are together connected and have same damage. In second case, there are 5 separated elements which are damaged differently. In order to demonstrate the performance of the dynamic species-size strategy, 3 optimization algorithms, which are genetic algorithm (GA), cooperative coevolutionary genetic algorithm (CCGA), and CCGADSS. The results indicate that CCGADSS is superior to GA and CCGA. Moreover solutions obtained using CCGADSS are quite close the actual damage. These results show that the dynamic species-size strategy can enhance performance of cooperative coevolution concept.

Radiofrequency Ablation in Chondroblastoma of the Femoral Head in Skeletally Immature Individuals: A Case Report

Surgical management of chondroblastoma of the femoral head in skeletal immaturityis challenging due to difficult access and a risk of epiphyseal plate injury. A 13-year oldboy presented with left hip pain and limping for over 1 year. Based on imaging andpathology report, chondroblastoma was diagnosed. The size of the tumor was 1.7 cmin diameter. To avoid epiphyseal plate and articular damage, percutaneous radiofrequencyablation was performed under fluoscopic guidance with a 70o Celsius monopolar probefor 3 minutes’ duration repeated 3 times. The 2nd ablation procedure was performedafter 3 months to minimize risk of recurrence. The pain had subsided at the 3 monthsfollow up. Over the 4 years follow up period, this case shows good functional outcomewithout deformity of the femoral head or tumor recurrence.

A model of low-velocity impact damage of composite plates subjected to Compression-After-Impact (CAI) testing

The paper presents a simplified model of damage of composite plates (SDM) subjected to low-velocity impact testing. The damage model assumes reduced thickness of laminate plies versus impact energy. The decrease in strength of the lay-up was measured by Compression-After-Impact (CAI) tests. The numerical analysis was performed on composite plates made of CFRP laminate subjected to uniform compression, with represented regions of damage caused by different impact energies. The numerical results show the behaviour of the laminate during compression, taking into account the damage process evaluated by a progressive damage criterion. The numerical analysis was performed using the ABAQUS® programme. The results were verified based on experimental findings reported in the literature and the numerical results of the tested composite plates subjected to CAI testing.

Anisotropic damage of titanium plates under uniaxial tension after reverse bending

Influence of low-cycle reverse bending and the crystallographic texture on damage anisotropy of commercial titanium sheets during the subsequent uniaxial tensile tests was studied. The fourth-rank order damage tensor D was used at the analysis of damage anisotropy of titanium sheets. Only the sole component D=1−E/E0 of this tensor is not equal to zero for uniaxial tension (E0 and E is the elastic modulus of intact material and current modulus determined from the uniaxial tensile tests, respectively). Damage caused by stresses of proof strength and ultimate strength is estimated. The damage increases with increasing of number of reverse bending cycles. The correlations of damage and mechanical properties anisotropy with the crystallographic texture are found.

An experimental study of scaling effects in the perforation resistance of woven CFRP laminates

Scaling effects in the perforation resistance of a carbon fibre-reinforced polymer (CFRP) composite have been investigated under quasi-static and low velocity impact loading conditions. The perforation data have been supplemented with results from additional flexural tests on scaled composite beams, which highlighted a decrease in both strength and failure strain as scale size increases. Strain-rate effects in this composite have been also identified, with the plates absorbing less energy as the loading-rate is increased. Tests on scaled plates have shown that the normalised perforation energy increases rapidly with scale size. An examination of the load-displacement response indicates that the elastic response obeys a simple scaling law, whereas that the damage does not. It was found that fibre damage was more severe in larger composite panels. It is argued that the energy absorbed in fibre fracture does not scale in the expected manner, leading to greater levels of fibre damage in the larger plates.

Study of modal acoustic emission to monitor the impact damage in a composite plate

Based on the theory of modal acoustic emission, this paper describes a new method to determine whether a plate made of a composite material has been damaged following external impact. Using modal acoustic emission theory, the relationship between the Lamb-wave mode of acoustic emission and the force direction in the plate was analyzed. This relationship was then verified using a lead-break experiment. The Lamb-wave mode of the acoustic emission signals produced by the damage in the plate was investigated, and the criterion for assessing the impact damage was proposed. During the impact experiments, the proposed criterion was employed to monitor the impact damage of the plate. The results indicate that it is feasible to use acoustic emission signals to directly determine whether an impact had caused damage to the plate.

Active detection of block mass and notch-type damages in metallic plates using a refined time-reversed Lamb wave technique

A recently proposed refined time-reversed Lamb wave method for baseline-free damage detection is tested experimentally for detecting block mass and notch-type damages in isotropic plates. The experimental results were compared with finite element simulations. The frequency of best reconstruction has been determined experimentally for the actuator–plate–sensor system by performing the time reversal process for a range of frequency, which is found to be very different from the sweet spot frequency exciting a single mode, hitherto recommended for improving the performance of the time reversal process-based techniques. It is shown that the damage indices (DIs) computed by using the conventional main wave packet of the reconstructed signal are less sensitive to the presence of damage, which is consistent with some recently reported experimental results by other groups. The present method with extended wave packet shows excellent sensitivity to damage for both block mass and notch-type damages and also ensures a low threshold for the undamaged case when used at the best reconstruction frequency. The refined DIs reflect the true severity of damage. It was observed that a putty on the plate has no significant change in the DIs in the present method, whereas a baseline method would identify it as a damage due to very significant scattering by the putty.