Delamination Monitoring Research Articles

Large Section of Soft Rock Gob-Side Entry Retaining Surrounding Rock Control

When cutting roof and pressure relief, the impact of blasting is especially obvious on the integrity of the roof of a large-section soft-rock roadway. The reasonable parameters of blasting roof cutting were studied through using Xiaohezui coal mine -12110 roadway as the engineering background. The LS-Dyna simulation results show that: Interval blasting is beneficial to the expansion of interhole cracks and the damage to the perimeter of the hole is smaller than that of adjacent blasting, the lower the charge uncoupling factor, the larger the perimeter of the hole fragmentation zone. The mechanical model of the large-section soft-rock roadway after retrieval was established, the support resistance equation of the roadway side support and the gangue in the extraction area was derived, and the minimum support force required for the roadway side support was solved. According to the site situation, the roadway support scheme for different areas was proposed, and after continuous delamination monitoring of the roof plate, it was found that the amount of roof-plate delamination was finally stabilized within 180 mm after the working face was advanced, and the effect of leaving the roadway was good.

Efficacy comparison of two methods for determining the position of the rebate edge (formed after MDF machining) during automatic monitoring of workpiece delamination

: Efficacy comparison of two methods for determining the position of the rebate edge (formed after machining) during automatic monitoring of workpiece delamination. Delamination is one of the most common defects in the processing of wood-based materials. It has a huge impact on the quality of the final product. In order to determine the delamination indicators in a simple and reliable way, the automatic image processing method can be used (Śmietańska et al. 2020). Bator and Śmietańska (2019) proposed the special algorithm to estimate the straight line representing a milling edge. However, this algorithm is quite complicated. The aim of this article is to check whether the aforementioned (complicated) algorithmic way can be replaced by a much simpler idea – the precise manual positioning of the scanned sample on the scanner (using very simple device installed on the scanner). The special experimental research was carried out to compare the effectiveness of the two different methods. The straight line which represents the rebate edge identified by Bator and Śmietańska (2019) algorithm was usually accurate to 1 pixel (0.02 mm). The analogue line based on the assumption that the scanned samples were perfectly positioned on the scanner only sometimes fit just as well. At worst, the distance between these lines is 0.2 mm. Usually the distance did not exceed 0.16 mm but was significant and quite random. There was no statistically significant correlation between this parameter (Dmax) and tool condition (VB). It means that sample were not perfect positioned. They were placed more or less in the same position because of imperfect stiffness of the frame installed on the scanner and human errors.

A Model-Assisted Probability of Detection Framework for Optical Fiber Sensors

Optical fiber sensors (OFSs) represent an efficient sensing solution in various structural health monitoring (SHM) applications. However, a well-defined methodology is still missing to quantify their damage detection performance, preventing their certification and full deployment in SHM. In a recent study, the authors proposed an experimental methodology to qualify distributed OFSs using the concept of probability of detection (POD). Nevertheless, POD curves require considerable testing, which is often not feasible. This study takes a step forward, presenting a model-assisted POD (MAPOD) approach for the first time applied to distributed OFSs (DOFSs). The new MAPOD framework applied to DOFSs is validated through previous experimental results, considering the mode I delamination monitoring of a double-cantilever beam (DCB) specimen under quasi-static loading conditions. The results show how strain transfer, loading conditions, human factors, interrogator resolution, and noise can alter the damage detection capabilities of DOFSs. This MAPOD approach represents a tool to study the effects of varying environmental and operational conditions on SHM systems based on DOFSs and for the design optimization of the monitoring system.

Efficacy comparison of two methods for determining the position of the rebate edge (formed after MDF machining) during automatic monitoring of workpiece delamination

Delamination is one of the most common defects in the processing of wood-based materials. It has a massive impact on the quality of the final product. In order to determine the delamination indicators simply and reliably, the automatic image processing method can be used (Śmietańska et al., 2020). Bator and Śmietańska (2019) proposed a special algorithm to estimate the straight line representing a milling edge. However, this algorithm is quite complicated. The aim of this article is to check whether the aforementioned (complicated) algorithmic way can be replaced by a much simpler idea – the precise manual positioning of the scanned sample on a scanner (using a very simple device installed on the scanner). Special experimental research was carried out to compare the effectiveness of the two different methods. The straight line representing the rebate edge identified by the Bator and Śmietańska (2019) algorithm was usually accurate to 1 pixel (0.02 mm). Based on the assumption that the scanned samples were perfectly positioned on the scanner, the analogue line only sometimes fit just as well. At worst, the distance between these lines is 0.2 mm. Usually, the distance did not exceed 0.16 mm but it was significant and quite random. There was no statistically significant correlation between this parameter (Dmax) and tool condition (VB). It means that the samples were not perfectly positioned. They were placed, more or less, in the same position because of the imperfect stiffness of the frame installed on the scanner and human errors.

A measurement structure for in-situ electrical monitoring of cyclic delamination

Cyclic delamination is the root cause for many different failure modes in semiconductor devices that are related to a loss of mechanical, electrical, or thermal contact. Some of them, such as failure due to local melting, can be considered as catastrophic. An accurate root cause analysis or precise localization of the failure is very challenging or even not possible at all. For this reason, the development of experimental methods capable of assessing early-stage delamination is desired. This work introduces a novel delamination-sensing structure integrated onto an actively heated microelectronic test chip. Actuation of the chip causes thermo-mechanical stress that initiates and drives cyclic delamination of a metallization from a functional base layer. The delamination-sensing structure allows continuous monitoring of the delamination progress by in-situ electrical resistance measurements. Its distinct geometric layout features have the effect that, when passed by a gradually advancing delamination crack front, result in characteristic responses in the monitored signal. This allows a straightforward interpretation of the measurement data without having to rely on modeling or separate calibration. The proper function of the delamination sensor is validated by a comparison of independently determined delamination distances from electrical measurements and cross-sectional inspections, respectively. Its distinguishing property of allowing a simple and time-efficient quantification of delamination is demonstrated by a study comprising 80 delamination experiments. This study investigates the effect of different heating amplitudes ΔT on the delamination rate.

Low‐cost carbon black‐loaded functional films for interlaminar toughening and in‐situ delamination monitoring of carbon fiber/epoxy composites

AbstractFunctional polyethersulfone (PES)/carbon black (CB) films were fabricated and interleaved into carbon fiber/epoxy composite laminates to simultaneously improve the mode I interlaminar fracture toughness (GIC) and delamination monitoring sensitivity. It was found that when the CB content in the functional film was 7.5 wt%, the initial and propagation GIC of the laminate achieved the greatest improvements of 99.16% and 82.83%, respectively. The toughening mechanism was mainly attributed to the formation of phase separation structure, the plastic deformation of PES and the pull‐out of epoxy and CBs. Meanwhile, a delamination increment‐resistance change relationship equation was proposed to predict the delamination increment of the laminate during mode I delamination. Moreover, the effect of CB content in the film on the delamination monitoring sensitivity was investigated. The pure PES film showed the largest sensitivity coefficient k of 4.55, which was much higher than that of Control (0.14). When the CB content was in the range of 2.5–7.5 wt%, both GIC and k remained at relatively high levels, indicating that PES/CB films have promising applications in advanced multifunctional composites due to their low cost, simple manufacturing process, and large‐scale industrial manufacturability.

Effective interlaminar reinforcing and delamination monitoring of carbon fibrous composites using a novel nano-carbon woven grid

To date, it is still a challenge to simultaneously reinforce and well monitor the delamination of carbon fiber reinforced plastics (CFRPs) using nanocarbon-based interleaf due to the high electrical conductivity of CFRPs. Herein, this work prepares a novel woven grid composed of carbon nanotubes and graphenes (CG) with various grid densities and suitable resistivity. Results reveal that the CG woven grid-based interleaf could significantly reinforce the interlaminar shear properties of CFRPs, i.e. mode II interlaminar fracture toughness and interlaminar shear strength can be improved by 38–60% and 17–25%, respectively. Meanwhile, the relative resistance change (ΔR/R0%) of CFRPs at the delamination initiation stage can reach ~12% or more, which is greater than that reported by previous literatures. The results suggest that the prepared CG woven grid can not only greatly enhance the delamination resistance, but also can sensitively monitor the delamination of the highly conductive CFRPs.

Detection of delamination in carbon fibre reinforced composite using vibration analysis and artificial neural network

From recent years damage detection in composite structures is given a prior attention to avoid failure and breakdown of the structures. Delamination in composite structures is one of the main reasons for the failure and also affects the properties of the composite structures. Carbon fibre reinforced composite has a wide applications in industries which requires monitoring and detection of delamination for proper functioning. There are various methods such as non-destructive methods, mathematical models etc. to detect the delamination but are quiet costly, time taking and inefficient. In the present investigation, Artificial neural network (ANN) is used to determine delamination defect in carbon fiber reinforced polymer composite. ANN model can solve complex problems. Hence, the ANN model is developed to predict the delamination length and location from the fixed end by analyzing the first three carbon fiber composite structures three natural frequencies. The natural frequencies and mode shapes are obtained using finite element analysis (FEA). It has been found that the ANN can predict delamination length and location in carbon fiber reinforced polymer composite.

In-situ monitoring and detection of spatter agglomeration and delamination during laser-based powder bed fusion of Invar 36

Invar 36 (FeNi36) is a weldable nickel alloy, known for its low thermal expansion properties, that contains 36% of nickel and 64% iron. The laser-based powder bed fusion process is often associated with defects and flaws that should be controlled for production quality. Spatter formation and delamination are two phenomena that could be observed in thermal images taken during the laser melting process. This paper presents an in-situ monitoring setup for detecting spatters and delamination of Invar 36. The size, shape, count, and cooling rate of spatter particles are evaluated using a combination of infrared pyrometer and high-speed infrared thermography. Thermograms of Invar 36 are processed to determine the spatter characteristics. The influence of processing conditions on the spatter count, spatter size, and size of melt track is discussed. The effect of spatters on the surface morphology of Invar 36 parts is also investigated. The processing conditions that cause melt pool instabilities, excessive spattering, and delamination are presented. This paper concludes recommendations for avoiding delamination and excessive spatter formation during the laser-based powder bed fusion of Invar 36.

Steels for Bridge Structures

We consider domestic and foreign standards for rolled metals used in bridge building. Domestic standards contain elevated requirements to the reliability of rolled metals in terms of their fracture resistance by delamination. Foreign standards admit the application of rolled metals in broader strength ranges but do not contain obligatory requirements imposed on Z-properties and the necessity of monitoring of possible delaminations. Due to the obligatory control of reliability, bridge steels of domestic production are also extensively used in the construction of special building structures.

Measurement of delamination and tool wear with sensors in end-milling using solid and carbide-tipped K10 end mills

An investigation on the machinability of glass-fibre reinforced plastic (GFRP) fabricated using hand moulding was conducted on a vertical-milling centre (VMC) with solid K10 carbide and carbide-tipped K10 end mills having four flutes. This revealed that the machinability of GFRP depends on tool wear and delamination. Sensor-fusion techniques were used to measure tool wear and delamination and the tests were conducted utilising a Taguchi L8 orthogonal array that included the data from the sensors' output. These tests illustrated the suitability of the sensor technique for online monitoring of delamination and tool wear and for improving the machinability of composites for a wide variety of applications. The results showed that using solid carbide end mills leads to less delamination of materials during milling of GFRP and carbide-tipped end mills resulted in little tool wear or change in the depth of cut when used at high speeds along with an appropriate feed rate.

Fracture mechanics test standards for fiber-reinforced polymer composites: Suggestions for adapting them to Industry 4.0 and the digital age

Fracture mechanics is expected to play an increasingly important role in design and development of components or structural elements made of fiber-reinforced polymer-matrix (FRP) composites, e.g., from carbon fiber epoxy. Test standard development in this sector has been slow. However, there are additional issues that impede implementation of the existing standards in Industry 4.0 and the digital age test facilities. Selected examples focus on recent developments in digital technologies, specifically imaging and image analysis and use of nondestructive test methods as well as handling of big data. Using these tools will reduce scatter (e.g., in determination of delamination lengths) and dependence on operator experience or qualification (i.e., the "human factor"). Further aspects discussed are automated data analysis and data fitting for evaluating materials properties, or for providing data for modelling and simulation of fracture behavior. It is argued that test set-ups with non-destructive delamination monitoring combined with automated analysis will efficiently provide reliable data for fracture mechanics based FRP structural design. Such data can also be compiled in data bases, e.g., for suppliers’ data sheets or for comparing different FRP composites for use in structural applications. This is expected to have effects on the quality of data and on the test requirements as well as the related cost.

Monitoring thermal barrier coating delamination progression by upconversion luminescence imaging

Upconversion luminescence imaging provided contrast for monitoring thermal barrier coating (TBC) delamination progression during interrupted furnace cycling to 1163 °C, with sensitivity even for early stages of subcritical delamination crack propagation. Image contrast for delamination monitoring is obtained because delamination cracks introduce an interface between a higher (TBC) and lower (air) index of refraction medium so that total internal reflection beyond a critical incident angle occurs for both the excitation and emission wave-lengths. Therefore, considerably greater luminescence emission is observed from regions containing delamination cracks. Upconversion luminescence produces exceptional image contrast because background fluorescence is very low when the detected emission is at a substantially shorter wavelength than the excitation. The upconversion luminescence emission was excited within a 6 μm thick Er3+/Yb3+ co-doped yttria-stabilized zirconia YSZ (YSZ:Er,Yb) layer beneath a 130 μm thick undoped YSZ layer, sequentially deposited with no interruption by electron-beam physical vapor deposition (EB-PVD) onto a NiPtAl bond-coated superalloy substrate. Excitation at 980 nm produced upconversion luminescence emission from Er3+ at 562 nm after two sequential energy transfers from Yb3+ co-dopant ions. Upconversion luminescence imaging, supported by scanning electron microscope inspection of interfacial damage, revealed that delamination progression proceeded by the formation of isolated microdelaminations with large separations between the TBC and thermally grown oxide (TGO) along with small-separation microcracks that propagated in the regions between the microdelaminations. In addition, upconversion luminescence imaging of the extent of delamination produced by Rockwell indentation clearly showed that the TBC becomes increasingly susceptible to mechanically induced damage throughout its cyclic life.

Detection and monitoring of delamination in composite laminates using ultrasonic guided wave

In is work, the delamination of composite double cantilever beams (DCBs) was detected and monitored using ultrasonic guided wave. The composite DCBs were prepared, and the experimental platform for damage detection based on ultrasonic guided wave was built up. The damage response signal was obtained from the composite DCBs by piezoelectric sensor (PZT). The signal was processed by Hilbert transform (HT), Fourier transform (FFT) and wavelet transform (CWT). The effective linear guided wave parameters and nonlinear guided wave parameters are extracted to characterize the delamination length. The experimental results show that the occurrence time and duration of high-order harmonics are related to the length of delamination. High-order harmonics are found in the response signal, which is due to the non-linear contact between the guided wave and the closed microcracks in the delamination region. It verifies that the main source of harmonics in the laminated composite structure is the non-linear acoustic contact.

Quantification of delamination in a composite floor using a novel damage index

ABSTRACTThe delamination of concrete from steel decking will reduce the strength and decrease the stiffness of the composite slab. Visual monitoring of delamination is typically not possible in many cases. A possible alternative is ultrasonic-based health monitoring. In this study, a novel damage index (DI) based on the absolute energy change (AEC) of the ultrasonic waves is adopted to quantify delamination damage in the composite floor. AEC-DI was constructed based on the decomposed signals provided by the wavelet transform. The monitoring process of the composite floor was conducted ultrasonically under flexural loading. An ultrasonic surface (Rayleigh) wave is employed for damage detection using gel-coupled piezoceramic sensors. The results revealed that the reliability and accuracy of AEC-DI in detecting composite floor separation is better than that of RMSD-DI.

Online monitoring of delamination mechanisms in drilling of Mwcnts reinforced Gfrp nanocomposites by acoustic emission

Among various unconventional Non-Destructive testing (NDT) methods, Acoustic Emission (AE) referred as the most suitable NDT method for detection and characterization of material defects during machining on nanocomposites. AE technique can also be applied for dynamic machining operation called drilling for better understanding of different drilling events from start to the end of the process. The present paper mainly focuses on on-line monitoring of drilling-induced delamination of multi-walled carbon nanotubes (MWCNTs) reinforced glass fiber reinforced plastic (GFRP) nanocomposites laminates through AE technique. A 4 mm thickness of 0.3wt% MWCNTs reinforced GFRP laminates were fabricated by 16 layers of glass fabric cloth with modified epoxy resins for drilling experimentation and trails were conducted on these laminates with uncoated, TiCN and TiAlN coated 6mm diameter carbide twist drills. Design of experiments were planned based on Taguchi L9 orthogonal array and speed, feed were considered as input process parameters. The AE output response parameters such as Root Mean Square (RMS) voltage, AE rise, energy, peak amplitude, hits, AE count, duration and counts to peak were helped to analyse the delamination mechanisms as well as cutting force generation during drilling on nanocomposites. From the experimental results, it was concluded that low feed rate (0.02 mm/rev) and high spindle speed (1500 RPM) with TiCN coated carbide drill gives the reduced delamination factor and thrust force values. Additionally, AE parameters were also highly influenced by the cutting parameters as well as delamination mechanisms. Out of all AE parameters AE-RMS voltage designated as the important parameter to analyse the delamination factor and increased RMS voltage observed with higher feed rate and cutting forces. The other AE parameters were very closely associated to the RMS voltage. Finally, it was confirmed that AE is most suitable NDT technique for on-line monitoring of drilling induced delamination for production of defect free holes on GFRP-MWCNTs composites laminates.

Selective laser illumination method for enhanced damage monitoring of micro cracking and delamination in GFRP laminates

Transmitted light photography, microscopy and transmitted light scanning are well-established methods of optical damage characterization in glass fiber-reinforced composites. Subsequent damage evaluation such as determination of crack density and delaminated areas can either be done by hand or by means of image analysis software. Digital image analysis, however, is rather sensitive to damage illumination and contrast. Results tend to be inaccurate when damage states are complex, showing overlapping cracks and delamination. Therefore, a new laser-based illumination method capable of separately illuminating transverse cracks and interfacial delamination is presented. An exemplary [90/0]s cross-ply laminate tested in the very high cycle fatigue range was evaluated using transmitted light photography as well as the new method.

Delamination monitoring in CFRP laminated plates under noisy conditions using complex-wavelet 2D curvature mode shapes

Delamination monitoring in carbon fiber reinforced polymer (CFRP) laminated plates is crucial to ensure the integrity and safety of the structures that accommodate the plates. To identify delaminations in CFRP laminated plates, the two-dimensional (2D) curvature mode shape method is a prevailing method that features instant and simultaneous determination of the presence and location of the delamination. However, this method has two noticeable deficiencies in characterizing incipient small-sized delaminations, namely lack of damage sensitivity and inadequate noise robustness. To this end, this study proposes a new dynamics feature of the complex-wavelet 2D curvature mode shape to discriminate small-sized delaminations. This feature is delicately formulated based on the integration of the 2D curvature mode shape with the complex wavelet. The complex-wavelet 2D curvature mode shape is superior to the 2D curvature mode shape by virtue of its stronger damage sensitivity and noise robustness. These merits can be attributed to the adjustable localization and the multi-scale properties of the second-order Gabor wavelet, respectively. Proof of concept of the complex-wavelet 2D curvature mode shape is numerically undertaken in a finite-element laminated CFRP plate with a small-sized delamination, with emphasis on sensitivity to damage and robustness against noise. The applicability of the feature is experimentally validated on a CFRP laminated plate with a small-sized delamination, whose mode shapes are acquired via the non-contact measurement using a scanning laser vibrometer. The numerical and experimental results show that the complex-wavelet 2D curvature mode shape can effectively designate the presence and location of the delaminations in CFRP laminated plates under noisy conditions.

Online monitoring of surface cracks and delaminations in carbon fiber/epoxy composites using silver nanoparticle based ink

In this study, we present an online-monitoring approach using silver nanoparticle based ink on carbon fiber reinforced plastics (CFRP). After production of CFRP plates in a prepreg autoclave process and printing conductive paths on the material, we investigate the conductive paths of printed silver nanoparticle-based ink on CFRP by light microscopy. Mechanical tests with simultaneous electrical resistance measurements demonstrate the possibility to detect particular modes of failure with samples specifically designed to promote inter-fiber failures and delaminations under bending. Delaminations can be detected and localized inside the material by electrical through-thickness measurements and resistance measurements of the conductive paths allow for surface crack detection.

Buckling and postbuckling behaviour of Glare laminates containing splices and doublers. Part 1: Instrumented tests

The progressive damage and fracture behaviour of Glare® fibre-metal laminates (FMLs) was investigated experimentally for the buckling and postbuckling regimes of laminates containing internal ‘splice’ and ‘doubler’ joints. Specimens were either ‘pristine’ or contained artificial delaminations in the form of strips of release film to represent manufacturing defects. Each was tested under in-plane compression. Tests were monitored using Digital Image Correlation (DIC) for visualisation of three-dimensional full-field displacements whilst acoustic emission (AE) monitoring – combined with the novel Delta-T location algorithm – was used for the first time to detect and locate damage events in these FML structures. Results were validated using Scanning Electron Microscopy (SEM) to determine the damage mechanisms present. Large numbers of AE events were recorded at the splice and doubler locations during initial loading and throughout the postbuckling regime, suggesting that the novel AE location algorithm used is suitable for the monitoring of delaminations and matrix cracks in internal features in Glare® laminates. Moreover, AE events located away from internal features correlated well with buckling and postbuckling deformation as identified by the full-field DIC data. Finally, good correlation was observed between the onset of buckling and a rapid increase in cumulative AE energy, demonstrating that as well as locating damage, AE monitoring is able to indicate quite clearly when the buckling load has been reached.