Damage In Plates Research Articles

Micro-finite element damage modeling in steel plate shear walls

Collapse assessment of Steel Plate Shear Walls (SPSWs) requires thorough simulation of damage-induced softening by using deteriorating behavioral models. However, developing predictive equations that allow degradation modeling requires either costly experiments or detailed experimentally-verified micro finite element (FE) studies. The latter method is utilized in this study to simulate damage of infill plates using ductile damage theory. This starts by collecting all experimental results appropriate to the purpose. Next, an FE model is established and verified by comparing the model results against those of the experiments. The verification specifically concentrates on the damage model parameters whose dependency to specimens geometry is evaluated at the next stage. To this end, a Bayesian regression analysis is performed and a predictive equation is developed for future studies on modeling degradation of SPSW systems. An evaluation of the regression results is also used for obtaining an insight into the effect of SPSW geometry on damage initiation strain. This evaluation indicates that tensile damage starts at an equivalent plastic strain (EPS) of about 0.4 irrespective of SPSW properties. In compressive loading, however, the EPS at which damage starts ranges from 1000 to 4000. According to regression results, this strain reduces by increasing plate's aspect ratio while it increases by elevating plate's thickness or slenderness.

Research on damage of typical water-containing composite structure under different types of charge

The damage of the water-containing composite structure subjected to underwater explosion is caused by multiple damage elements, such as charge structures, water-containing composite structure, experimental mode and so on. The underwater explosion experiments and the numerical calculations have been performed to study the damage of water-containing composite structure under the different kinds of charge underwater explosion and under different experimental mode, The result shows that the damage of structure under the action of shaped charge is more serious than that of blasting charge in the case of the same charge equivalent. The combined action of shaped penetrator and shock wave can cause perforation and plastic deformation of the rear plate and target of the water-containing composite structure e. The tearing hole on the front board is 2∼3 times of the shaped charge diameter. The damage of the rear plate is the penetration of the penetrator which is about 1/3 times of the shaped charge diameter. When shaped charge explodes in air or underwater, the plastic deformation of the rear plate is very different.

Do cartilage laminar compositional changes as assessed by T2 relaxometry predict incident and worsening of structural morphologic damage in the same plate 3 years later?

Purpose: T2 mapping is capable of showing intrachondral matrix alterations prior to the appearance of visually detectable surface damage. Identification of specific regions of cartilage with a high risk of subsequently developing focal surface damage will potentially help in identifying individuals who are likely to benefit from preventive interventions before the onset of such macroscopic lesions. A recent small study showed that mean local T2-values are persistently elevated prior to lesion onset in the same location, suggesting focal T2 elevation is able to predict focal cartilage damage development at the same location.

Location of micro-cracks in plates using time reversed nonlinear Lamb waves**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFF0203000), the State Key Program of the National Natural Science Foundation of China (Grant No. 11834008), the National Natural Science Foundation of China (Grant No. 11774167), the Fund from the State Key Laboratory of Acoustics, Chinese

A promising tool to detect micro-cracks in plate-like structures is used for generating higher harmonic Lamb waves. In this paper, a method combining nonlinear S0 mode Lamb waves with time reversal to locate micro-cracks is presented and verified by numerical simulations. Two different models, the contact acoustic nonlinearity (CAN) model and the Preisach–Mayergoyz (PM) model, are used to simulate a localized damage in a thin plate. Pulse inversion method is employed to extract the second and fourth harmonics from the received signal. Time reversal is performed to compensate the dispersion of S0 mode Lamb waves. Consequently, the higher harmonics generated from the damaged area can be refocused on their source. By investigating the spatial distribution of harmonic wave packets, the location of micro-cracks will be revealed. The numerical simulations indicate that this method gives accurate locations of the damaged area in a plate. Furthermore, the PM model is proved to be a suitable model to simulate the micro-cracks in plates for generation of higher harmonics.

Technical note on Uniportal full endoscopic posterolateral approach transforaminal lumbar interbody fusion with reduction for grade 2 spondylolisthesis

BackgroundUniportal Endoscopic transforaminal posterolateral approach interbody fusion (Endo-TLIF) is becoming a popular method of fusion, it harnesses the advantage of both Trans Kambin approach endoscopic tranforaminal interbody fusion and biportal transforaminal interbody fusion into one single technique. There is no description of Endo-TLIF with reduction in Grade 2 isthmic spondylolisthesis in the spine literature. ObjectiveTechnical discussion on the management of grade 2 isthmic spondylolisthesis in an elderly population by Endo-TLIF. MethodsTechnique was applied in grade 2 isthmic spondylolisthesis with the focus on uniportal endoscopic transforaminal lumbar interbody fusion; particular attention was paid in endoscopic visualization to traversing and exiting nerve root to avoid neurological complications in reducing isthmic spondylolisthesis. Direct endoscopic visualization end plate preparation helped to avoid damage of end plates and ensure adequate disc preparations. Percutaneous rod fixation with complete reduction of isthmic spondylolisthesis of L4/5 was performed. ResultsSuccessful reduction of grade 2 isthmic spondylolisthesis with good post-operative clinical outcome was observed. ConclusionFull Uniportal Endoscopic Transforaminal Interbody Fusion is a new and evolving technique with potential advantages in end plate preparation, direct visualized neural decompression and safe placement of interbody fusion device. We showed a case of a patient with a grade 2 isthmic spondylolisthesis who had successful reduction of deformity and placement of a large size interbody cage with good post-operative clinical outcome.

Damage localization in cross-ply laminated composite plates under varying temperature conditions using Lamb waves

Lamb wave-methods are reported to be very effective in detecting and localizing defects in thin plate structures. However, the accuracy of damage detection using Lamb waves is affected significantly by variations of environmental and operating conditions. In the present study, an improved methodology is presented to calculate the damage residue measure from current state responses that compensates the effect of operational and environmental changes. The proposed damage residue is obtained by comparing the current state responses of identical paths with the same propagation distance and direction. For damage localization in the structure, a modified delay-sum damage localization algorithm is introduced. The proposed damage residue measure is used along with the modified delay-sum algorithm to locate damage in a composite plate. The methodology is first presented through numerical simulations based on a finite element model and validated through experiments on a carbon fiber cross-ply configured composite plate. The insensitiveness of the proposed residue measure to temperature changes is demonstrated experimentally.

Damage identification in a plate structure based on a cross-direction strain measurement method

Structural strain responses are extensively applied in the field of structural health monitoring (SHM); however, previous studies have focused on the damage identification methods based on strain responses. This paper focuses on measurement technology and proposes a new strain measurement method. Four strain gauges are set in a cross direction on the surface of the structure. Then, the Wheatstone full-bridge connection is used to measure the combined strain of the four strain gauges. The peak picking method is applied to estimate the strain modal shape and frequency of the structure under ambient excitation. The strain mode difference is used as a damage identification index. Finally, clamped plate experiments, including single-damage, multi-damage and damage distance experiments, are successfully implemented. Compared with traditional half-bridge strain measurements, the results show that the cross-direction strain measurement method is more sensitive to minor damage and has higher identification accuracy.

Dynamic failure of carbon fiber-reinforced plastics sandwich structures with polyvinyl chloride foam cores subjected to impact loading

The dynamic failure of carbon/epoxy sandwich plates with polyvinyl chloride foam core subjected to foam projectile impact is experimentally analyzed in this research. The effects of intensity of impact impulse, cores density, core thickness on the impact resistance of the composite sandwich plates in terms of deflection of rear sheets are also assessed. The 3D- digital image correlation technique is applied to measure the dynamic deformation of the sandwich plates. The results show that the carbon/epoxy sandwich plates exhibit more excellent impact resistance than aluminum sandwich plates with polyvinyl chloride cores at the similar area mass. The carbon/epoxy sandwich plates experience an obvious spring back, and only a slight plastic deflection can be observed after test. The failure modes of the sandwich plates include plastic deformation, fiber breakage, delamination, matrix crack, debonding, and compression of cores. The damage of plates become more serious with core density and core thickness decreasing, and impact impulse increasing, respectively.

Specifics of Damageability of the Silicon Single Crystal under Exposure of Powerful Plasma Streams and Fast Helium Ions

The results of experiments on the impact of fast helium ions (Ei ~ 100 keV) and helium plasma (v ~ 2 × 107 cm/s) on a silicon single crystal plate in the Vikhr plasma focus (PF) installation with radiation power density in the range of q ≈ 106–107 W/cm2 are presented. It is shown that, at low values of q = 106–1011 W/cm2, the damageability of silicon is due to its surface sputtering mainly in the zone of mechanical defects, while with more intense irradiation (108< q ≤ 1011 W/cm2) the processes of melting and evaporation of the surface layer occur with the formation of structural defects in the form of waves, flows, bubbles, craters and microcracks. The specific nature of damage of the Si plate at high power density and a large number of pulsed beam-plasma impacts (q ≥ 109 W/cm2, N = 50) is described. It is associated with the formation of a brittle fine-crystalline surface layer, which is easily separated from the base material and disintegrates in the form of a powder of particles of micron and nanoscale size. This result is a consequence of the action of thermal stresses in combination with the implantation of helium ions into the material as well as the possible influence of shock waves generated in the Si target during hard irradiation regimes. The presence of copper, carbon, and nitrogen on the silicon surface after its beam-plasma treatment, as well as an increase in the electrical resistivity on the irradiated side and backside of the plate, is noted. The results obtained are discussed taking into account the features of the experiments in the PF setup.

Pure S0 and SH0 detections of various damage types in aerospace composites

This paper proposes a new single-mode guided wave-based method to detect various types of damage in aerospace composites. In this method, single-mode guided wave excitation was achieved using adjustable angle beam transducers (ABT). The ABT tuning angles of various pure-mode guided waves were calculated based on Snell's law applied to the composite dispersion curves. A finite element (FE) simulation of pure S0 mode excitation in a crossply composite plate was conducted and the simulation results were validated by the experiment. For the first time, angle beam transducers were applied to generate pure shear horizontal (SH0) wave in a thick quasi-isotropic composite plate. The pure SH0 wave excitation was successfully verified by a three-dimensional (3D) FE simulation. SH0-mode wave propagation and interaction with delaminations were further conducted and strong trapped waves within the delamination regions were observed. Experiments using S0 or SH0 pure-mode guided waves were conducted to detect various types of composite damage, such as wrinkle damage in the crossply composite plate, multilayer delaminations by Teflon inserts, and actual impact damage in the thick quasi-isotropic composite plate. A significant amplitude drop was observed due to the presence of different composite damage types. In addition, a linear scanning method using pure SH0 wave was also developed to estimate the sizes of delaminations and impact damage. Both numerical and experimental results demonstrated the validity and usefulness of the proposed method for the detection of various damage types in composites.

Comparison between segmentation performances of a tool based on wavelet decomposition and multithreshold and of a U-net convolutional neural network applied to shearography images of carbon fiber reinforced plastic plates with low-velocity impact damages

Carbon fiber reinforced plastics (CFRPs) have been used to replace metallic alloys in many industries because of their high strength-to-weight ratio. Due to their anisotropic behavior, low-velocity impacts can produce defects whose effects on material performance are hard to foresee. Nondestructive testing (NDT) methods are a convenient alternative to evaluate their integrity. Shearography, an image-based optical interferometric technique for measuring deformation, is one of these NDT possibilities. The segmentation of defects in the resulting images provided by such a method is essential to correctly locate and indicate the severity of impact damage. This task is especially intricate for shearography images with barely visible impact damage because of their usual low signal-to-noise ratio. We compare a combination of wavelet decomposition with multithresholds introduced in a previous publication with a U-net convolutional neural network for analyzing impact damage in CFRP plates. Both tools are detailed and then evaluated using the Matthews correlation coefficient and the equivalent diameter criterion. The results showed that U-net provided a better impact damage characterization in both evaluation metrics, allowing a safer defect detection that is less dependent on the inspector’s ability to interpret them.

Research advances in repair of growth plate injury

Growth plate, the developmental center of endochondral osteogenesis, can be divided morphologically and functionally into a resting zone, a proliferative zone, a prehypertrophic zone and a hypertrophic zone. Injuries to growth plate often lead to bone growth defects including limb length discrepancy and angulation deformity in children. Currently, their orthopedic corrective surgeries are invasive and limitedly effective and no effective biotherapy has been available. Previous studies on animal models of growth plate damage have investigated the related cellular and molecular events in the repair of damaged growth plates in the 4 distinct inflammatory, fibrogenic, osteogenic and remodeling phases. Related molecules involved in the regulation of the above processes, such as inflammatory cytokines tumor necrosis factor alpha, mitogenic platelet-derived growth factor and bone morphogenetic protein, are found to participate in the regulation of growth plate injury. Exploration of the mechanisms may provide new targets for biotherapy. In addition, development of cartilage tissue engineering, especially application of mesenchymal stem cells, also provides potential interventions for growth plate injury. Key words: Tissue engineering; Wounds and injuries; Bone marrow cells; Growth plate; Chondrogenesis

Polyurea-coated glass-fibre-reinforced laminate under high-speed impact: experimental study

One of the promising methods to increase the resistance of polymer-matrix composite materials to impact damage is the use of protective coatings.In this work, the effect of polyurea coating on impact-performance parameters of a woven glass-fibre-reinforced laminate is studied. The study was performed on a specially developed ballistic experimental test rig employing a pneumatic gun. Eleven polymer composite targets with dimensions 200 mm x 300 mm x 8 mm were impacted orthogonally with a steel projectile with 23.8 mm diameter and weight 54.7 g in the range of the impact speed up to 150 m/s. A comparative assessment of the ballistic limit for targets with a 1.2 mm protective coating on the front and rear faces of the target, as well as for samples without any protective coating, was performed. The impact process was captured using two high-speed cameras for filming the front and top views at 25,000 frames per second.Experimental data on the ballistic limit for uncoated and polyurea coated fiberglass plates on the front and back surfaces were obtained. It was shown that 1.2 mm thick coating on the face surface increases the ballistic limit by 20%. The nature of the damage of the GRP base plate and coating has been analyzed.The obtained data can be used for validation of numerical models of ballistic impacts of polyurea-coated laminates.

One-way Lamb mixing method in thin plates with randomly distributed micro-cracks

It is crucial to detect and evaluate early material degradation caused by micro-cracks in key engineering structures. This paper investigates the resonant behavior of one-way Lamb mixing waves in thin plates with randomly distributed micro-cracks by numerical simulations. It is found that when the resonance condition ωS0/ωA0=2κ/(κ+1) is satisfied, a resonant A0 mode wave can be generated by a pair of A0 and S0 mode waves mixed in the micro-crack damage region. Meanwhile, it is manifested that the acoustic nonlinearity parameter increases with the crack density and the length of the micro-crack region, which is also related to the resonant frequency. Furthermore, it is proven that the location of the micro-crack region can be determined by the time-domain signals of the resonant wave. This study numerically reveals that the one-way Lamb mixing method is feasible to quantitatively identify micro-crack damage in thin plates.

On the performance of vibro‐acoustic‐modulation‐based diagnosis of breathing cracks in thick, elastic slabs

Vibro-acoustic modulation (VAM) is a nonlinear dynamics-based method for detecting damage in mechanical and structural components. Past studies have shown that VAM can be used for detecting contact acoustic nonlinearities and for mapping the extent of delamination or impact damage in thin composite plates. However, the suitability of VAM for mapping the extent of damage in thick, elastic slabs has not been studied. In this work, we investigate the performance of VAM in the context of localizing hidden, breathing cracks in thick elastic slabs using numerical simulations of the test procedure. We simulate the underlying nonlinear wave physics for two- or three-dimensional solids containing hidden cracks using the finite element method. We use our numerical model to perform computational VAM tests on elastic slabs containing cracks with known location and size. We propose a binary damage index for damage mapping, and we report on the sensitivity, specificity, and accuracy of the damage index-based damage localization procedure. We demonstrate the robustness of the damage localization procedure in the presence of measurement noise. We also perform parametric studies aimed at evaluating the effect of different test variables on damage detection and localization.

Elliptical Method for Damage Identification in Carbon Fibre Reinforced Polymer Laminates

Oftentimes, researchers in the area of vibration-based structural health monitoring (SHM) and damage detection focused their attention on the global properties of structures, which are modal frequencies and modal damping factors. However, the effect on the local properties for SHM, that is, modal constants, has not been extremely explored. In this paper, the elliptical plane modal identification method is proposed to be used as a damage identification method itself. It is observed that when the receptance is plotted in the elliptical plane, the area of the ellipse formed close to the resonant frequencies (which depends on the modal constants) can be used to detect damage, namely, composite carbon fibre reinforced polymer (CFRP) rectangular plates. Although a mathematical correlation has not been established yet, results show that the method is sensitive to the presence of damage in the test plates, as the area of the ellipse changes with damage.

Thermal damage assessment of metallic plates using a nonlinear electromagnetic acoustic resonance technique

Low efficiency of energy transition is generally considered to be the only weakness of electromagnetic ultrasonic transducers (EMATs). Electromagnetic acoustic resonance (EMAR) technique has been successfully used to overcome this disadvantage with a combination of the EMATs with the ultrasonic resonant method. In this paper, a nonlinear EMAR technique has been proposed to evaluate the thermal damage of metallic materials, which combines the feature of EMAR with the merit of higher harmonic generation that provides an effective indicator to material damage. The use of contactless EMATs can isolate the material nonlinearity and maintain the coupling condition consistently on measurements of higher harmonics generated. EMAR provides high enough signal magnitude for higher harmonic generated. An experimental scheme is proposed and applied to assess the thermal damage in aluminum and nickel plates. In addition, conventional EMAR techniques based on the measure of shear wave velocity and attenuation within a certain frequency range, are also carried out for the specimens. The experimental results show a monotonic relationship between the normalized amplitude of higher harmonic generated and the artificial thermal loading time, while no stable trends are observed by conventional linear EMAR approaches. The results in this paper indicate that nonlinear EMAR technique proposed can be used to assess the thermal damage in both nonferromagnetic and ferromagnetic materials, with improved reliability and sensitivity over linear one.

Analysis of damage and interlaminar stresses in laminate plates with interacting holes

In a laminate plate with an open hole, the damage initiation and progression and the interlaminar stresses that appear close to hole edge are modified when a second hole is made close to the first. The purpose of this study is to analyse the interaction between two holes when the plate is subjected to compressive loads. The Serial/Parallel Mixing Theory is used as the constitutive law of the composite, and a Continuum Damage Model is applied to predict failure initiation and propagation due to fibre microbuckling and matrix cracking. The model is validated using data from the literature. The developed model is able to predict the differences in the initiation and propagation of damage due to fibre microbuckling and matrix cracking in the area around the two holes. The variation of the distance between holes significantly modifies the damage due to both mechanisms. Also, the interlaminar stresses along the laminate thickness are changed. The results of this study can be applied to predict the critical distance between holes to avoid damage initiation by matrix cracking and microbuckling.

Analysis on the influence of Poisson’s ratio on brittle fracture by applying uni-bond dual-parameter peridynamic model

Poisson’s ratio is a crucial mechanical parameter of materials, but its significance is normally underrated in practical application. Aiming at investigating how Poisson’s ratio influences the fracture of brittle materials by using peridynamic (PD) method, a uni-bond dual-parameter peridynamic (UDPD) model is proposed. The expressions of normal stiffness and tangential stiffness by elastic modulus and Poisson’s ratio are derived. The two-parameter characteristic makes UDPD break the limitation of the specific Poisson's ratio of bond-based peridynamics, thus the modeling of the mechanical behavior of materials with various Poisson's ratio can be achieved. With single-bond property, UDPD inherits the simplicity and stability of the traditional bond-based peridynamics. In addition, the critical value of micro strain energy density for UDPD model is given to judge the damage. The validity and accuracy of UDPD model are illustrated by three numerical examples: the plate deformation subject to static load, the Kalthoff-Winkler experiment and the brittle plate fracture subject to biaxial loads. Ultimately, by simulating and comparing the damage of brittle plates under tension of different Poisson’s ratio, it is concluded that Poisson’s ratio has substantial effect on fracture initiation time and crack propagation path. The larger Poisson’s ratio has the plate, the earlier the fracture initiates. The cut-through locations and crack propagation paths in plates of different Poisson’s ratio are significantly different.

Some new algorithms for locating a damage in thin plates using lamb waves

The aeroplane structures are aerodynamic complex shapes with multiple stiffeners attached to them. The presence of stiffeners poses complexity in the nondestructive evaluation of the aeroplane structures using guided (Lamb) waves. Thus, in the present study, this issue is addressed and resolved by carrying out experiments on a thin Aluminium plate with a stiffener using Lamb waves. In the present work, there are four piezoelectric wafer transducers, which are bonded onto the plate. These transducers have functions of generating and sensing Lamb waves in the plate. Authors have developed, two different algorithms for finding location of a damage in the plate by processing the data obtained from the experiments. The algorithms are named as Curve-Intersection and Sub-Quadrant methods based on their working principles. Thus, presented algorithms are capable of finding location of a damage in thin plate structures in the presence of stiffener using a minimal number of transducers.