Invisible Damage Research Articles

Capability analysis of Puck damage model in predicting the damage behavior of unidirectional composite laminates under different scenarios

Composite materials have been broadly used in many engineering fields because of their distinctive properties. They have advantages over metals as their properties offer significant advantages such as very good strength to weight ratio. However, failure in composite structures due to interlaminar and intralaminar raises a maintenance concern because it can lead to invisible damage. Therefore, this paper presents the capability of three-dimensional Puck failure criteria with gradual degradation rule to predict the structural responses, as well as the onset and propagation of failure due to variation of the situation in a composite laminate. The proposed damage model is achieved via the implementation of user-subroutines both in statics and explicit analysis using Abaqus software. Three different scenarios are investigated which were open-hole tension, low-velocity impact, and multi-bolt double-lap joint. The force-displacement and force-time curves are recorded and compared with experimental data taken from literature to measure the performance of such damage model. It is found out that the model adopted here responses well with test curves and demonstrates the high capability of predicting the damage in the direction of in-plane and out-of-plane in a composite laminate.

Technological Sensor on Coupled Radial Spirals

We present the sensor with a sensitive element (SE) based on coupled radial spirals, which can be used for monitoring technological processes in the Electronic Industry, as well as for detecting damages on the pipelines under protective coatings. The main properties and characteristics of such SE are analyzed and measured. It is shown that the concentration of the electromagnetic field in a measuring space, caused by slowing down of the the wave, and splitting of the electric and magnetic fields leads to a significant increase in sensitivity, whereas the multiple increases in the slowdown makes it possible to use the advantages of SE with distributed parameters at relatively low operating frequencies. The practical realization of the described sensor is demonstrated in measuring the ion implantation processes and the thickness of the metallization, as well as in monitoring the invisible cracks and damages through the protective coats on the metal surfaces.

Online structural state assessment for aerospace composite structures using an acousto-ultrasonics-based multi-damage index identification approach

The development of aerospace manufacturing has promoted the application of lightweight composite materials into aerospace structures. Although the aerospace composite structures possess numerous advantages, invisible internal structural damage such as delaminations induced by various external factors can significantly reduce the mechanical affordability, safety, and life-cycle of the structure. Therefore, it is of great significance to monitor and assess the health state and predict accurately the lifetime of aerospace composite structures. An acousto-ultrasonics-based multi-damage index identification approach is thus proposed in this study to identify and quantify possible multiple damage in thin-walled aerospace composite structures. In this approach, two indices for damage quantification were proposed: the energy and phase divergence indices. The energy index defines the reflected energy resulting from damage, and the phase divergence index defines the instantaneous phase variation of propagating waves due to damage. The two damage indices are obtained through the developed mode decomposition and spectral element analysis using sensor response signals collected by a transducer array placed onto the examined structure. Through a series of relevant experimental tests on the fabricated laminated composite panels with/without damage, the proposed acousto-ultrasonics-based multi-damage index identification approach was validated. The developed damage indices are competent to evaluate a structural health state in terms of damage quantification, and all of the validation results fell well in the prospected ranges. Moreover, it shows a linear and consistent trend between the variation of two damage indices and damage extents. Based on the particular relation, the linear regressive prediction functions were established separately regarding the two damage indices. They can be used to assess a structural health state due to the damage growth in real time. The proposed multi-damage index identification approach demonstrates its potential to serve as an online assessment tool to be aware of the reliability condition of a composite structure.

X-ray micro computed tomography in cultural heritage.

X-ray micro computed tomography (μCT) can reveal the internal structure of several types of objects by exploiting differences in their X-ray absorption. It can: provide information about the objects' relative composition and density without taking any samples or causing any damage; reveal invisible defects, cracks or damage; show if there are any inclusions and if the object is a single piece or is made of different parts joined together; and, uncover methods of construction and even show if repairs and additions have been made. For this reason, it has increasingly been used in archaeology and cultural heritage.

Invisibility and indistinguishability in structural damage tomography

Structural damage tomography (SDT) uses full-field or distributed measurements collected from sensors or self-sensing materials to reconstruct quantitative images of potential damage in structures, such as civil structures, automobiles, aircraft, etc. In approximately the past 10 years, SDT has increased in popularity due to significant gains in computing power, improvements in sensor quality, and increases in measurement device sensitivity. Nonetheless, from a mathematical standpoint, SDT remains challenging because the reconstruction problems are usually nonlinear and ill-posed. As such, the ability to reliably reconstruct or detect damage using SDT is seldom guaranteed due to factors such as noise, modeling errors, low sensor quality, and more. Further, damage processes may be rendered invisible due to data indistinguishability. In this paper we identify and address key physical, mathematical, and practical factors that may result in invisible structural damage. Demonstrations of damage invisibility and data indistinguishability in SDT are provided using experimental data generated from a damaged reinforced concrete beam.

Local damage detection of a fan blade under ambient excitation by three-dimensional digital image correlation

Damage detection based on dynamic characteristics of a structure is one of important roles in structural damage identification. It is difficult to detect local structural damage using traditional dynamic experimental methods due to a limited number of sensors used in an experiment. In this work, a non-contact test stand of fan blades is established, and a full-field noncontact test method, combined with three-dimensional digital image correlation, Bayesian operational modal analysis, and damage indices, is used to detect local damage of a fan blade under ambient excitation without use of baseline information before structural damage. The methodology is applied to detect invisible local damage on the fan blade. Such a method has a seemingly high potential as an alternative to detect local damage of blades with complex high-precision surfaces under extreme working conditions because it is a noncontact test method and can be used under ambient excitation without human participation.

Feasibility of freeze-thaw damage analysis for asphalt mixtures through dynamic nondestructive testing

Invisible freeze-thaw damage is commonly associated with many durability problems in asphalt pavement. Therefore, the freeze-thaw damage of asphalt pavement should be detected in situ to evaluate the pavement condition. This study aimed to explore the feasibility of freeze-thaw damage analysis for asphalt mixtures through dynamic nondestructive testing. Free–free resonance testing method and Rayleigh wave testing technology were selected for this analysis. Natural frequency, damping ratio, and Rayleigh wave velocity were used to describe the freeze-thaw damage. Optimal experimental parameters were proposed by analyzing the effect of test parameters on the stability and accuracy of results. Variations in the dynamic parameters of asphalt mixtures under freeze-thaw action were analyzed. Results showed that natural frequency, damping ratio, and Rayleigh wave velocity changed regularly during the freeze-thaw process and could be used to analyze the damage after freeze-thaw cycles. The effects of different types of asphalt mixture on the dynamic test parameters during the freeze-thaw process were also examined. Nondestructive testing revealed that the type of asphalt and the gradation of asphalt mixture affected the damage degree of freeze-thaw cycles. The sensitivities of the different test parameters of the freeze-thaw damage were compared via principal component analysis, and the second-order damping ratio was proposed as a reasonable parameter to identify the in situ freeze-thaw damage in asphalt pavement.

Rich and Poor Chinese Vocabulary in the Context of Convergent Media

With the development of society and science and technology, traditional media and new media interweave with each other, forming a network three-dimensional structure, namely, convergent media. Media platforms such as radio, television and the Internet have become the mainstream way of information dissemination. Under this background, Chinese vocabulary has also developed unprecedentedly. New words change with each passing day and spread rapidly on the convergent media platform, making traditional Chinese vocabulary face unprecedented challenges. On the face of it, the vocabulary ranks are expanding continuously, showing various and flexible features. In essence, under the constant pursuit and imitation of vocabulary users, the current Chinese vocabulary has the coexistence of increasingly rich and increasingly poor. This will not only affect the purity of Chinese, from a certain point of view, it will also cause invisible and huge damage to people's spiritual world. Therefore, the development trend of Chinese vocabulary in the future is worth our deep thinking.

A living plant cell-based biosensor for real-time monitoring invisible damage of plant cells under heavy metal stress

Heavy metals inevitably cause invisible or visible damage to plants, leading to significant economic losses. Therefore, it is necessary to develop a method for timely monitoring the damage of plants under the stress of heavy metals. Here, vitronectin-like proteins (VN) on the surface of plant cells is as an important biomarker for monitoring damage of plants under the stress of heavy metals. A living plant cell-based biosensor is constructed to monitor invisible damage of plant cells induced by cadmium [Cd(II)] or lead [Pb(II)]. To fabricate this sensor, l-cysteine was first modified on the glassy carbon electrode followed by the modification of anti-IgG-Au antibody. Then, the living plant cells, incubated with the anti-VN, were modified onto the electrode. The sensor worked by determining the change in electrochemical impedance. Cd(II) and Pb(II) was detected in the linear dynamic range of 45–210 and 120–360 μmol·L−1, respectively. And the detection limit of Cd(II) and Pb(II) of this biosensor was 18.5 nmol·L−1 [with confidence interval (95%) 18.4–18.6 nmol·L−1] and 25.6 nmol·L−1 [with confidence interval (95%) 25.4–25.8 nmol·L−1], respectively. In both Arabidopsis and soybean, when the content of VN increased by about 20 times under the stress of Cd(II) or Pb(II), which means when the electron-transfer resistance increased by 35%, chlorophyll content showed significant decrease about 17%. Therefore, by establishing a quantitative relationship among the content of biomarker, the electron-transfer resistance and chlorophyll content in plant cells, the invisible damage of plants under the stress of heavy metals was detected. These results can provide a reference method for early-onset warning systems for heavy metal pollution in the environment.

Single-sided access remote imaging via resonant airborne activation of damage

The feasibility of remote imaging of damage by using resonant airborne acoustic activation combined with laser vibrometry is studied experimentally. Two-step optimization to stimulate the damage vibration comprised resonant oblique incidence followed by frequency selective local resonance in the damaged area (LDR). The methodology is applied to a wide variety of flaws from artificial planar defects to real damages in composite parts. Various types of damage are shown to manifest LDR in two different ways depending on the structure of the damage. The resonance is activated either as in-phase vibration over a total damaged area at a single frequency (normal LDR) or includes weakly coupled resonant vibrations of its parts at different frequencies. In the latter case, LDR is a combination of multiple so-called fractional resonances. Both kinds of the resonances enhance the sensitivity of remote defect-selective imaging and are applicable to a wide range of flaws from clearly visible to barely visible and even virtually invisible damage in composites.

Damage imaging for composite using Lamb wave based on minimum variance distortion-less response method

It is highly probable for the structures of carbon fiber reinforced plastics (CFRP) to suffer from invisible impact damage, for which the identification of such damage is of great significance. For the purpose of damage localization, this paper proposes a minimum variance distortion-less response (MVDR) algorithm that employs linear array sensor. In addition, a near field signal model based on active Lamb wave is established and the propagation of Lamb wave is investigated in composite laminates through the method of simulation. Moreover, a damage imaging system is also set up for composites to verify the effectiveness of the MVDR algorithm. Besides, in the study, wavelet transform is used as well to extract narrowband signals and promote signal-to-noise. It is shown by the results that the proposed algorithm can accurately identify the location of damage through the method of imaging. It is concluded that the maximum error of damage identification is 1.2 cm and MVDR algorithm has great potential in the field, damage imaging of composite materials. As a result, it provides a novel idea for damage imaging of composite materials.

Impact Localization of CFRP Structure Based on FBG Sensor Network

Low energy impact can induce invisible damage of carbon fiber reinforced polymer (CFRP). The damage can seriously affect the safety of the CFRP structure. Therefore, damage detection is crucial to the CFRP structure. Impact location information is the premise of damage detection. Hence, impact localization is the primary issue. In this paper, an impact localization system, based on the fiber Bragg grating (FBG) sensor network, is proposed for impact detection and localization. For the completed impact signal, the FBG sensor and narrow-band laser demodulation technology are applied. Wavelet packet decomposition is introduced to extract available frequency band signals and attenuate noise. According to the energy of the available frequency band signal, an impact localization model, based on the extreme learning machine (ELM), is established with the faster training speed and less parameters. The above system is verified on the 500 mm × 500 mm × 2 mm CFRP plate. The maximum localization error and the minimum localization error are 30.4 mm and 6.7 mm, respectively. The average localization error is 14.7 mm, and training time is 0.7 s. Compared with the other machine learning methods, the localization system, proposed in this paper, has higher accuracy and faster training speed. This paper provides a practical system for impact localization of the CFRP structure.

FT-IR measurement on the damage of Japanese paper induced by PIXE analysis

Analysis of cultural heritage samples by PIXE involves the risk of damaging precious samples due to MeV-proton irradiation. To investigate appropriate methods to detect invisible damage due to PIXE analysis, we analyzed the change in chemical bonding of the sample surface subjected to PIXE and RBS measurement by Fourier Transform InfraRed spectroscopy (FT-IR). We used Japanese hemp paper as a simulated cultural property sample. The proton irradiation for the PIXE/RBS measurement was performed in a vacuum with an incident beam energy of 2.5 MeV, a beam current of 1 nA, and an irradiation time up to 10 min. The corresponding beam flux and fluence were 0.06 nA/mm2 and 4 [Formula: see text]Coulomb/cm2, respectively. When the irradiation time was 10 min, the absorbed dose was 480 kGy on the sample surface. We identified neither change of elemental composition nor visible change such as discoloration due to irradiation. However, we found changes in peak heights in the measured FT-IR spectra, which suggest the destruction of chemical bonds such as O–H and C–O due to proton-induced radiation damage.

Detection of Defects in Reinforced Concrete Structures Using Ultrasonic Nondestructive Evaluation with Piezoceramic Transducers and the Time Reversal Method.

Reinforced concrete is of vital importance in many civil and industrial structural applications. The effective bonding between steel and concrete is the core guarantee of the safe operation of the structures. Corrosion or other interface debonding in steel-concrete is a typical failure mode during the long service period of the structures, which can severely reduce the load-bearing capacity. The Non-destructive Evaluation technique has been applied to civil engineering structures in recent years. This paper investigates the evaluation of reinforced concrete structures that have interface defects, including the cross-sectional loss and cracks, by using the piezoceramic induced ultrasonic wave and time reversal method. Ultrasonic wave is used as actuating wave to obtain the signals with defect information. Time reversal method is applied to localize and characterize defect along the interface of the steel-concrete and to image the defect through the cross-sectional scanning. Experiments were conducted to perform Nondestructive Evaluation by using six reinforced concrete components with different levels of defects. The invisible damages were made by the cutting part of the steel and embedding a table tennis ball inside concrete structures. The results show that the time reversed method can locate and evaluate the defects along the steel reinforced concrete, and the obtained defect images at the cross-section of the concrete structure are accurate.

Application of Travelling Wave Method for dynamic analysis of plane frame structures

The dynamic behavior of a structure can be formulated in terms of the waves propagating through its members. This approach is commonly known as the Travelling Wave Method (TWM). The propagation of an external excitation within structural members, and the behavior of waves at a discontinuity are defined by the amplitude of displacement waves, and the wave reflection and transmission coefficients. The assemblage of these properties provides a concise method to formulate the dynamic response of structures. Although it has been used for the analysis of aerospace structures, the TWM has rarely been used for the analysis of civil engineering structures. This paper presents the theoretical basis and the formulation of the wave-propagation approach to analyze the dynamic response of civil-engineering-type structures, and discusses its advantages over the commonly used Finite Element Method (FEM). It is shown by examples that TWM requires less computational time than FEM, can incorporate the frequency-dependent soil–structure interaction effects in the analysis directly, and gives more accurate results at high frequencies. The last one is particularly important for detecting small and invisible damages in structures, since most of such damage is hidden in high frequencies.

FBGs Real-Time Impact Damage Monitoring System of GFRP Beam Based on CC-LSL Algorithm

Glass-fiber reinforced polymer (GFRP) composite materials have an undisputed dominance over conventional metallic materials. However, susceptibility to barely visible or invisible internal damage due to impact has increased the demand for these composite materials in robust real-time structural health monitoring (SHM) system since they are capable of localizing the source of impact. Thus, in this paper, an in situ FBG sensor was embedded in a GFRP beam, providing an online real-time monitoring system and with the knowledge of cross-correlation linear source location (CC-LSL) algorithm, the impact location was capable of being determined in a split second. The consistency of cross-correlation function in providing repeatable results for all trials estimated a consistent time difference for all the impact points. The CC-LSL algorithm also revealed that the highest percentage of error was only 4.21% away from the actual hit. In the meantime, FBGs also showed good results as a dynamic strain measuring device in capturing frequency response at certain orientations compared to the AE sensor.

Evaluation of saw damage using diamond-coated wire in crystalline silicon solar cells by photoluminescence imaging

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future.

FAMI Screws for Mandibulo-Maxillary fixation in mandibular fracture treatment – Clinico-radiological evaluation

Mandibulo-maxillary fixation (MMF) is indispensable for mandibular fracture treatment. Various means for MMF have been proposed, of which arch bars are widely considered to be the mainstay. However, disadvantages to this method have initiated a quest for an alternative, leading to the introduction of MMF screws. MMF screws have frequently been criticized for poor stability of fracture sites, root damage, hardware failure, and nerve damage. We retrospectively evaluate the FAMI (Fixation and Adaptation in Mandibular Injuries) screw in mandibular fracture treatment by scanning for clinically and radiologically visible complications. In total, 534 FAMI screws were used in the successful treatment of 96 males and 34 females. Condylar fractures were most commonly encountered, representing 120 of 241 fracture sites. 15 general fracture-related complications occurred, with the most common being nerve function impairment (3.8%) and postoperative malocclusion (4.6%). In nine cases (7%), clinically visible FAMI-screw-related complications occurred, with the most prevalent being screw loosening (2.3%) and mucosal signs of inflammation (3.1%). Duration of FAMI screws was associated with the occurrence of clinically visible complications (p = 0.042). Radiologically, clinically invisible dental hard tissue damage was noted in 21 individuals (16%). Therefore, FAMI screws seem to be a reliable and safe method for mandibulo-maxillary fixation.

Experimental Analysis for the Effect of Impactor Geometry on Carbon Reinforced Composite Materials

For the last three decades, composites have become very preferable materials to be used in the automotive industry, structural parts of aircraft and military systems and spacecraft, due to their high strength and modulus. Composite materials are sometimes exposed to invisible or visible damage due to impact loading during their service life. In this study, the effect of impactor geometry with four different contact surfaces on woven carbon fibre-reinforced composite plates having three different thicknesses are investigated. In the first stage, composite plates were manufactured with the ply orientations of [45/-45/0/90/45/-45]2s, [45/-45/0/90/45/-45]3s, [45/-45/0/90/45/-45]4s based on conventional usage. In the second stage, carbon fibre-reinforced composite test panels were exposed to low velocity impact tests to obtain force-time, energy-time and force-displacement curves. Finally, semi and full penetration of composite panels and damage magnitude were determined. It was found that the impactor geometries with lower contact surfaces such as conical and ogive types were much more penetrative on composite plates than the other geometries, but they caused larger damage area in the vicinity of the impact point.

Delamination Identification in Stiffened Composite Panels Using Surface Strain Data

The structural integrity of a composite structure can be greatly compromised by damage inside the component. Invisible damage, e.g. caused by low-speed impact, can significantly reduces composite components capability to efficiently carry loads. In the present study, an innovative approach of strain-based delamination identification and localization is investigated, based on the efficient processing of full-field surface strain measurements. Surface strain data, potentially derived by full-field optical methodologies are used in the assessment of the delamination pattern, through strain field perturbations caused due to damage evolution. Relations between delamination damage and surface strain field disturbances are established by exploiting data decomposition methods using Zernike polynomial moments. The methodology is successfully demonstrated in the case of a stiffened composite panel.