Damage monitoring

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Validation of mechanical damage monitoring on aluminium freestanding thin films using electrical measurements

Validation of mechanical damage monitoring on aluminium freestanding thin films using electrical measurements

To cite this version: Fourcade, Thibaut and Broue, Adrien and Dehnnin, Jeremie and Desmarres, Jean-Michel and Seguineau, Cédric and Dalverny, Olivier and Alexis, Joël and Masri, Talal Validation of mechanical damage monitoring on aluminium freestanding thin films using electrical measurements. (2013) Key

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Damage monitoring in sandwich beams by modal parameter shifts: a comparative study of burst random and sine dwell vibration testing

Damage monitoring in sandwich beams by modal parameter shifts: a comparative study of burst random and sine dwell vibration testing

interface region can be debonded and the core can be damaged through crushing and shear failure mechanisms. Safe and functional effectiveness of stressed sandwich structures can often depend on the retention of integrity of each of the different materials used in its manufacture. Therefore lightweight sandwich materials used in next generation of more advanced aircraft, marine craft, road and rail vehicles must possess the capability to absorb higher impact energy and retain a high degree of structural integrity. For aeronautical structures, a field where this problem has been quite studied, the components have to undergo low energy impacts caused by dropped tools, mishandling during assembly and maintenance, and in-service impacts by foreign objects such as stones or birds. In these low energy impacts normally, a small indentation is seen on the impact surface. This level of damage is often referred to as barely visible impact damage (BVID). There has been considerable research on the impact performance and damage development in carbon fiber composite materials and sandwich composite materials; see for example references [1-5].
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Distributed fiber optics sensing and coda wave interferometry techniques for damage monitoring in concrete structures

Distributed fiber optics sensing and coda wave interferometry techniques for damage monitoring in concrete structures

Keywords: distributed fiber optic sensors; coda wave interferometry; reinforced concrete; cracks; damage detection; structural health monitoring 1. Introduction The continuous growth in worldwide population and the climate changes (affecting the probability of natural hazards) are increasing the need for housing and better infrastructures. Nowadays, reinforced concrete is the most employed material in the construction industry, but the global trend is to reduce its consumption rate and thus to change the focus from “design of new structures” to “maintenance of the current constructions” [ 1 ]. For this reason, Structural Health monitoring (SHM) systems will play an increasingly important role. The main idea of SHM is to compare the “as-is” structural condition, which includes the damage, fatigue, load distribution, etc., to the “as-built” structural condition, which comes from the structural design. Then, the models can be updated so that the structural integrity can be evaluated based on the “as-is” model [ 2 ]. Civil infrastructure monitoring is required in cases where structures are subject to long-term degradation of materials like fatigue and where a feedback loop is needed to improve future design based on experience (like in the case of bridges and wind turbine foundations). Currently, the majority of research activities in the SHM area are focused on developing sensing technologies and damage detection algorithms [ 3 ]. Sensors developed within other engineering disciplines, such as Distributed Fiber Optics Sensing (DFOS) and Coda Wave
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Damage monitoring in sandwich beams by modal parameter shifts: a comparative study of burst random and sine dwell vibration testing

Damage monitoring in sandwich beams by modal parameter shifts: a comparative study of burst random and sine dwell vibration testing

interface region can be debonded and the core can be damaged through crushing and shear failure mechanisms. Safe and functional effectiveness of stressed sandwich structures can often depend on the retention of integrity of each of the different materials used in its manufacture. Therefore lightweight sandwich materials used in next generation of more advanced aircraft, marine craft, road and rail vehicles must possess the capability to absorb higher impact energy and retain a high degree of structural integrity. For aeronautical structures, a field where this problem has been quite studied, the components have to undergo low energy impacts caused by dropped tools, mishandling during assembly and maintenance, and in-service impacts by foreign objects such as stones or birds. In these low energy impacts normally, a small indentation is seen on the impact surface. This level of damage is often referred to as barely visible impact damage (BVID). There has been considerable research on the impact performance and damage development in carbon fiber composite materials and sandwich composite materials; see for example references [1-5].
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Bearing fatigue of composite laminates: Damage monitoring and fatigue life prediction

Bearing fatigue of composite laminates: Damage monitoring and fatigue life prediction

5. Conclusions The fatigue life of quasi isotropie laminates subjected to bearing loads can be predieted using damage parameters such as the per manent hole elongation accumulation rate or the cumulative hys teresis energy. Using such damage metries, clear trends can be obtained. The permanent hole elongation is difficult to measure and, as is the case with cumulative hysteresis losses, fatigue data need to be post processed However, it relates directly to the amount of damage, whereas hysteresis energy encompasses not only damage but also other dissipative phenomena such as visco elastiàty. Both damage metries can be used to prediet the fatigue life based on a limited amount of fatigue data, typieally accounting for Jess than 30% of the total fatigue life. To achieve an in service predietion of the residual fatigue life, a monitoring system should be implemented. The measurement of a given damage metric, either directly or indirectly, would then be possible. But such a system is still utopie, espeàally for rotating structures or compo nents. A more down to earth application of these damage metries would be to evaluate the capabilities of a damage mode!. lndeed, those would be useful to assess the consistency of the predieted damage rates or hysteresis losses, whieh would be key if the mode! in question were to be used to predict the fatigue life under spectral loadings. Finally, even though the existence of a fatigue limit has not been proven, the ditferent analyses strongly suggest that a practical fatigue limit does seem to exist. No fatigue failure would occur for alternating loads lower than about 20% of the statie failure Joad, since, at this Joad level, the expected fatigue lives are clearly located in cycle ranges that are not susceptible of being reached in any known industrial application. lt has been shown that this practieal fatigue limit is dosely related to the statie initiation Joad of kink bands, in full consistency with the fact that the latter drive the fatigue failure process.
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Bearing fatigue of composite laminates: Damage monitoring and fatigue life prediction

Bearing fatigue of composite laminates: Damage monitoring and fatigue life prediction

This investigation showed that hysteresis never completely vanished. However, two different trends emerged, so the experi mental data points could be fitted by a function that was a sum of two power laws ( Fig. 16 ). This probably means there was a shift in the way energy was dissipated. Dissipation might have occurred essentially through viscous mechanisms at low load levels, and damage would then play a more and more important rote as the alternating load increased. Referring to an S N curve (see Fig . 17 for example), the change in trend can clearly be associated with the frontier between the HCF and the VHCF(Nf� 1ü8) fatigue regimes. The existence of a fatigue limit still remains to be debated. 4. Does a bearing fatigue limit exist?
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Spatial integration of baseline-free damage detection algorithms based on dual-PZT for the structural health monitoring of anisotropic composite aeronautic structures

Spatial integration of baseline-free damage detection algorithms based on dual-PZT for the structural health monitoring of anisotropic composite aeronautic structures

1 CEA, LIST, Sensorial and Ambient Interfaces Laboratory, 91191 - Gif-sur-Yvette CEDEX, France. 2 Processes and Engineering in Mechanics and Materials Laboratory (PIMM, CNRS-CNAM-ENSAM-HESAM Paris, France) ABSTRACT The focus is put here on the Structural Health Monitoring (SHM) of composite aeronautic structure using Lamb waves emitted and recorded with piezoelectric transducers (PZT). Conventional algorithms perform Lamb waves acquisition in the healthy state of the structure (referred to as the “baseline”) and then compare incoming data from an unknown state with this one to detect, locate, classify and quantify any potential damage. The acquisition, storage, and update of the initially recorded baseline database constitute a severe drawback of such algorithms. Indeed, the structure under study as well as the environment may vary during its operational life without the appearance of any damage and thus the initial baseline may not be relevant at any instant where damage monitoring is needed. In order to circumvent this drawback, “baseline- free” method (such as the instantaneous baseline [BI] and rupture of reciprocity [RR]) have been developed. Moreover, the use of dual-PZT, i.e. concentric PZT made of a ring and a disk lying on the same ceramic, has been shown as attractive for baseline- free purposes. However, now that several algorithms based on dual-PZT are available, no study dealing with the spatial integration of the results provided by these algorithms have been reported in the literature. It is thus proposed in this paper to investigate strategies for the spatial integration of common baseline-free methods (namely BI and RR) on an experimental case of damage on a highly anisotropic composite plate. Results illustrate the decomposition of Lamb wave modes in signals measured via dual PZTs as well as the proposed spatial integration strategies for these methods.
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Spatial integration of baseline-free damage detection algorithms based on dual-PZT for the structural health monitoring of anisotropic composite aeronautic structures

Spatial integration of baseline-free damage detection algorithms based on dual-PZT for the structural health monitoring of anisotropic composite aeronautic structures

1 CEA, LIST, Sensorial and Ambient Interfaces Laboratory, 91191 - Gif-sur-Yvette CEDEX, France. 2 Processes and Engineering in Mechanics and Materials Laboratory (PIMM, CNRS-CNAM-ENSAM-HESAM Paris, France) ABSTRACT The focus is put here on the Structural Health Monitoring (SHM) of composite aeronautic structure using Lamb waves emitted and recorded with piezoelectric transducers (PZT). Conventional algorithms perform Lamb waves acquisition in the healthy state of the structure (referred to as the “baseline”) and then compare incoming data from an unknown state with this one to detect, locate, classify and quantify any potential damage. The acquisition, storage, and update of the initially recorded baseline database constitute a severe drawback of such algorithms. Indeed, the structure under study as well as the environment may vary during its operational life without the appearance of any damage and thus the initial baseline may not be relevant at any instant where damage monitoring is needed. In order to circumvent this drawback, “baseline- free” method (such as the instantaneous baseline [BI] and rupture of reciprocity [RR]) have been developed. Moreover, the use of dual-PZT, i.e. concentric PZT made of a ring and a disk lying on the same ceramic, has been shown as attractive for baseline- free purposes. However, now that several algorithms based on dual-PZT are available, no study dealing with the spatial integration of the results provided by these algorithms have been reported in the literature. It is thus proposed in this paper to investigate strategies for the spatial integration of common baseline-free methods (namely BI and RR) on an experimental case of damage on a highly anisotropic composite plate. Results illustrate the decomposition of Lamb wave modes in signals measured via dual PZTs as well as the proposed spatial integration strategies for these methods.
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Chromatin Dynamics upon DNA Damage

Chromatin Dynamics upon DNA Damage

Most of the studies on chromatin mobility are based on the analysis of MSD curves calculated from the trajectories of fluorescently labeled chromatin loci. Using this approach, the diffusion coefficients reported in the literature varies from 5 × 10 −5 to 10 −3 μm 2 /s depending on the organ- isms, the loci studied, and the type of damage [66, 67]. In several studies, chromatin undergoes confined diffusion [22, 59, 68–71], while others have reported anomalous diffusion [69, 70, 72–75]. So far, no consensus has been reached to describe the nature of DNA motion prob- ably because these studies have been performed using different microscopy techniques and illumination settings. Indeed, multi time-scales observation of chromatin motion revealed that chromatin is driven by different types of diffusion at each time scale [76–78]. As a consequence, the type of diffusion depends on the time scale of observation. While comparing studies on chromatin dynamics, it is thus important to compare studies performed at similar time scales. Several studies have investigated DNA motion in the context of DNA damage. Since DSB is the most deleterious type of damage in the cell, chromatin dynamics in the context of DNA repair has been mainly investigated in response to DSBs. The changes in chromatin architecture and dynamics following DSB have been studied mostly in yeast, Drosophila and mammalian nuclei. In budding yeast, chromatin mobility has been investigated during the process of HR, when a Rad52 focus is already formed at the damaged locus [23, 25]. In diploid, where a homologous template is available, chromatin mobility is dramatically increased at the damaged site, allow- ing the damaged locus to explore a nuclear volume 10 times larger [23]. Increased mobility may facilitate homology search; however, haploid yeast cells, where no homologous template is present, also exhibit increased mobility in response to DSBs [25]. Since the two broken ends stay in contact during the process of HR repair [79], the current view is that the two broken ends explore the nuclear space together.
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Damage Measurements via DIC

Damage Measurements via DIC

Dierent aspects related to damage measurements via DIC and DVC will be ex- emplied in the sequel. First, the distinction between physical and mechanical damage will be explained since it has some important consequences in terms of experimental and numerical procedures. Second, the use of new imaging means (e.g., computed to- mography) and their subsequent analysis with correlation techniques are introduced. Physical and mechanical damage will then be studied essentially for a given material, namely, plasterboard. This material, which is not classical, was selected because it is representative of the class of quasi brittle materials for which CDM is one tool of choice to describe their degradation. It should however not be concluded that the results re- ported herein are restricted to this class of materials. Other materials and mechanisms have been and still are analyzed with some of the tools introduced hereafter [90,62, 57].
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Progressive damage and quasibrittle solids

Progressive damage and quasibrittle solids

In the TLS model one prescribes the shape of the damage function d within the moving layer of thickness l c where the transition between the sound material and the completely damaged one occurs. In particular, progressive damage that takes place in the transition zone is given as an explicit function of the distance φ to the boundary Γ o of the undamaged portion of the domain

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Blasting and building damage

Blasting and building damage

Apart from the uncertainties mentioned, two others may be noted. There appears to be little variation pound for pound, among the common blasting materials in vibration levels produced at a distance. There is an interesting relation, however, between elastic vibration and rock breakage: if a charge does a good job of shattering and displacing the surrounding material, it produces slightly lower vibration levels than one that fails to break through to the free surface of the material. Within the building structure there is, of course, a correlation between damage and strength. Thus, a monolithic concrete wall in good condition will endure somewhat more than a unit masonry wall. These variables also affect the vibrations produced in the structure, and it is for this reason that particle velocity is a more precise index of the damage threshold than merely charge and distance. Consequently it is suggested that Figure 3 be used for guidance as long as charge and distance can be confined to the no-damage zone. Operations in the intermediate zone should be guided by vibration measurements.
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Hyperelasticity with volumetric damage

Hyperelasticity with volumetric damage

can be called a volumetric damage. In the general framework of large strain, the material is sup- posed homogeneous, isotropic and hyperelastic. Moreover, we assume that it initially contains small flaws that can be considered as holes. To simplify the derivation, the RVE is assumed to deform as sketched in Figure 1; the deformation gradient F is separated into two parts:

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Flooring damage by heels

Flooring damage by heels

The Division decided the problem warranted the attention of a wider audience and in- itiated an investigation into (1) the nature and magnitude of the heel pres- sur[r]

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Hygrothermal damage of building materials and components: state-of-the-art report on studies of hygrothermal damage and pApproach for damage assessments

Hygrothermal damage of building materials and components: state-of-the-art report on studies of hygrothermal damage and pApproach for damage assessments

https://doi.org/10.4224/20386602 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Hygrothermal damage of building materials and components: state-of- the-art report on studies of hygrothermal damage and pApproach for damage assessments

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Continuum damage modelling in geomechanics

Continuum damage modelling in geomechanics

After having recalled how the local integration of the constitutive relation can be performed in the same spirit as for plasticity-based models, we will deal with more speci[r]

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Condition monitoring of bearing damage : test implementation and data acquisition

Condition monitoring of bearing damage : test implementation and data acquisition

The field of preventive maintenance has seen continued interest in the condition monitoring of roller element bearings. The push towards creating "smart bearings"[r]

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BlobSeer Monitoring Service

BlobSeer Monitoring Service

The embedded database is located at REPOSITORY_HOME/pgsql_store. To start it, first go to the bin directory and type: pg_ctl start -D ../data. The -D switch specifies where the data folder of the database is located. We may also use a different location for the storage, say on a more stable partition of the hard disk. Use the command psql -d mon_data to get into console of the default database. Using the \dt command helps to show all the tables available in the current database. The monitor_ids table contains all of the regular monitoring parameter for every monitored node. Typically, every monitoring metric will have 2 or more resolutions which are indicated by the name of the table, such as 1y_1min and 1y_1sec (one value per min/sec during one year).
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Soil vibrations and damage criteria

Soil vibrations and damage criteria

The authors extend their thanks to Goran Lande, Nitro Consult AB, for valuable opinions and a critical scrutiny of the manuscript, as well as to Burnis Lidmark for transcribing the manus[r]

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Monitoring Electronic Exams

Monitoring Electronic Exams

Quantified Event Automata (QEAs). We express properties as QEAs [4,5]. We present QEAs at an abstract level using intuitive terminology and refer to [4] for a formal presentation. A QEA consists of a list of quantified variables together with an event automaton. An event automaton is a finite-state machine with transitions labeled by parametric events, where parameters are instantiated with data-values at runtime. Tran- sitions may also include guards and assignments to variables. Note, not all variables need to be quantified. Unquantified variables are left free, and they can be manipulated through assignments and updated during the processing of the trace. Moreover, new free variables can be introduced while processing the trace. We extend the initial definition of QEAs in [4] by i) allowing variable declaration and initialization before reading the trace, and ii) introducing the notion of global variable shared among all event automaton instances. Note, we use global variables in our case study presented in Sec. 4.2 and in the extended version of this paper. Global variables are mainly needed in QEAs to keep track and report data at the end of monitoring. Such QEAs may also require some ma- nipulation of the quantified variables which is not currently supported by MarQ. Thus, we could not implement them and hence omitted them from the paper. The shaded states are final (accepting) states, while white states are failure states. Square states are closed to failure, i.e., if no transition can be taken, then there is a transition to an implicit fail- ure state. Circular states are closed to self (skip) states, i.e., if no transition can be taken, then there is an implicit self-looping transition. We use the notation assignment [guard ] to write guards and assignments on transitions: : ˆ = for variable declaration then assignment, := for assignment, and = for equality test. A QEA formally defines a language (i.e., a set of traces) over instantiated parametric events.
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