Individual Cracks Research Articles

A Finite Element Model for Compressive Ice Loads Based on a Mohr-Coulomb Material and the Node Splitting Technique

Abstract This paper presents a finite element model for the simulation of ice–structure interaction problems, which are dominated by crushing. The failure mode of ice depends significantly on the strain rate. At low strain rates, the ice behaves ductile, whereas at high strain rates it reacts in brittle mode. This paper focuses on the brittle mode, which is the dominating mode for ship–ice interactions. A multitude of numerical approaches for the simulation of ice can be found in the literature. Nevertheless, the literature approaches do not seem suitable for the simulation of continuous ice–structure interaction processes at low and high confinement ratios in brittle mode. Therefore, this paper seeks to simulate the ice–structure interaction with the finite element method (FEM). The objective of the here introduced Mohr-Coulomb Nodal Split (MCNS) model is to represent the essential material behavior of ice in an efficient formulation. To preserve mass and energy as much as possible, the node splitting technique is applied, instead of the frequently used element erosion technique. The intention of the presented model is not to reproduce individual cracks with high accuracy, because this is not possible with a reasonable element size, due to the large number of crack fronts forming during the ice–structure interaction process. To validate the findings of the model, the simulated maximum ice forces and contact pressures are compared with ice extrusion and double pendulum tests. During validation, the MCNS model shows a very good agreement with these experimental values.

Miraculous mussels heal in days

For many of us, breaking a bone is rare and hopefully no more than a once in a lifetime experience. It's excruciating and recovery can take weeks. But the shells of mussels (Mytilus californianus) clinging to the shoreline are continually at risk of harm, battered by waves and debris hurled by the surf. Even when the tide is out, mussel shells are vulnerable to hungry crustaceans taking a nip with their powerful claws. ‘The intertidal zone can be a particularly dangerous place. It is a harsh environment’, says Rachel Crane from Stanford University, USA. So how much damage do these resilient structures sustain after a substantial assault and how quickly can they recover? Crane, along with José Diaz Reyes and Mark Denny, both from the same university, headed down to the seashore below the Hopkins Marine Station, USA, to find out.Back in the lab with a bucket full of the molluscs, Crane and Diaz Reyes repeatedly compressed the mussels between two plates to stress them, adjusting the level of force depending on their size. Then, the duo checked the shells for damage by testing how much total force bearing down they could withstand. Sure enough, the shells of the squashed mussels were significantly weaker than shells that had not been compressed; they could only withstand forces that were 54 N less (equivalent to the weight of 5.4 kg) than unstressed mussels of the same size. And when Crane and Diaz Reyes opened up the mussels and looked at the surface of the shells within, they sometimes saw networks of cracks radiating across the dome of the shell or larger individual cracks. Repeatedly pounding the mussels had taken a toll on their shells, but how well and how quickly could the molluscs recover?Allowing the mussels 1, 2 and 4 weeks to recuperate, the team was astonished to see that the squashed shells were every bit as tough as the unharmed shells within a week. ‘We were amazed when we saw the data. We were expecting the mussels to take weeks or maybe even months to repair their shells; I never thought the response would be so fast’, says Crane. And, when she and Diaz Reyes rechecked the mussels 4 weeks later, they were impressed that the shells dealt the hardest blows were the most resilient, coming back even stronger. However, the effort of recovery had taken a toll on the molluscs, with the soft internal part of the mussels weighing 7% less after 4 weeks of recovery than the soft tissue of the mussels that had remained unassailed.In addition, when the team scrutinised the shells for signs of recovery, although some of the shells showed evidence of regrowth in the area near and surrounding cracks, many of the fissures remained unhealed, even though the shells were restored to full strength. ‘Mussels may have a self-healing or compensatory mechanism that does not involve shell deposition’ says Crane. And when the team compared the mollusc's healing rates with those of other armoured surf residents, the mussels were streaks ahead, recuperating in a matter of days, whereas snails take weeks and even months to repair damage. Crane also suggests that the mussels’ ability to recover rapidly could account for their undisputed success in one of the world's most turbulent environments. ‘Molluscs protect themselves with this amazing dynamic armour – these animals not only can resist repeated insults, but they can respond, repair and strengthen so quickly’, says Crane.

On the simultaneous growth of multiple hydraulic fractures emanating from an inclined well

The primary focus of this paper is to investigate the interaction between simultaneously propagating multiple fractures, initiated from an inclined well. In particular, the aim is to better understand the influence of the well inclination angle on the stress shadow between the fractures and on the overall resulting geometry of individual cracks. To simplify the analysis, the paper assumes the limit of large perforation friction, which leads to a uniform flux distribution between the fractures. The mathematical model for multiple hydraulic fractures is constructed by coupling together the respective models for individual fractures, each representing a single planar fracture model. In this approach, the fracture induced stress or stress shadow from a previous time step is used as an input for a given single hydraulic fracture to propagate independently. Further, to reduce computational burden, the effects associated with tangential stresses and displacements are neglected, whereby the stress interaction between the fractures is solely described by the normal opening and the normal stress component. Numerical results are presented for the storage viscosity dominated regime, whereby the effects of toughness and leak-off are negligible. An interesting behaviour is observed, demonstrating that the well inclination angle plays a significant role on the overall fracture symmetry. For zero inclination, all the fractures are nearly symmetrical and identical. However, once well inclination is introduced, this breaks the symmetry, making a profound effect on the final result.

Characterizing environment‐dependent fracture mechanisms of ceramic matrix composites via digital image correlation

AbstractHere, we unveil a methodology for a novel assessment of the fracture mechanics of SiC/SiC ceramic matrix composites enabled by in situ stereoscopic digital image correlation to quantify in‐process flexural strain and crack opening displacement measurements. This technique isolates individual cracks on the composite surface as discontinuities in the spatial displacement field and correlates key fracture characteristics with the flexural strain of composite specimens during coupled four‐point bend / hermeticity testing. Fracture was observed along the specimen length, originating at the tensile underside and propagating around the circumference of the tubular specimens with generally uniform spacing. Multiple specimens were also tested after heat treatments to 1200°C in open air, in vacuum, and in helium for 48 h to evaluate the environmental effects on the fracture mechanisms of SiC/SiC composites, which revealed degradation of flexural properties after treatment in open air resulting in brittle failure. Indentation‐based fracture toughness measurements were performed, which confirmed a 25% reduction in toughness after open air heat treatment relative to the other heat treatments. This assessment indicated that significant oxidation may occur within the composites from these heat treatments and suggested that further protection of the composites may be necessary for high‐temperature applications.

Anaerobic Degradability of Commercially Available Bio-Based and Oxo-Degradable Packaging Materials in the Context of their End of Life in the Waste Management Strategy

There are discrepancies concerning the time frame for biodegradation of different commercially available foils labeled as biodegradable; thus, it is essential to provide information about their biodegradability in the context of their end of life in waste management. Therefore, one-year mesophilic (37 °C) anaerobic degradation tests of two bio-based foils (based on starch (FS), polylactic acid (FPLA)) and oxo-degradable material (FOXO) were conducted in an OxiTop system. Biodegradation was investigated by measuring biogas production (BP) and analyzing structural changes with differential scanning calorimetry, polarizing and digital microscopic analyses, and Fourier transform infrared spectroscopy. After 1 year, FOXO had not degraded; thus, there were no visible changes on its surface and no BP. The bio-based materials produced small amounts of biogas (25.2, FPLA, and 30.4 L/kg VS, FS), constituting 2.1–2.5% of theoretical methane potential. The foil pieces were still visible and only starting to show damage; some pores had appeared in their structure. The structure of FPLA became more heterogeneous due to water diffusing into the structure. In contrast, the structure of FS became more homogenous although individual cracks and fissures appeared. The color of FS had changed, indicating that it was beginning to biodegrade. The fact that FS and FPLA showed only minor structural damage after a one-year mesophilic degradation indicates that, in these conditions, these materials would persist for an unknown but long amount of time.

Prediction of hydrogeomechanical processes in undermining of water bodies

Rivers, arable land, engineering structures, urban buildings, and communications often fall into the zone of influence of mining operations. Insufficiently justified mining development often leads to negative environmental and social consequences of the violation or destruction of these objects. On the other hand, surface and underground waters often complicate the development of minerals, negatively affecting the safety of production. The paper deals with the interaction of hydrogeological and geomechanical processes near water bodies in complex mining and hydrogeological conditions. One field of research is based on the development of an engineering approach to the analysis of the interaction of hydrogeological and deformation processes. In this case, the results of instrumental field observations and experience of mining operations near water bodies are used. In this approach, it is assumed that six zones can be distinguished in the under-worked rock mass: collapsed rock; through cracks; partially through cracks; individual cracks that do not form a single system; the zone without discontinuities of continuity; the zone of high stresses and compression deformations. As an example of the application of this approach, the development of a mineral deposit under a river is considered and recommendations are made for the preservation of the earth’s surface from waterlogging. The second field of research is related to mathematical modeling and the use of crack theory. The results of the simulation showed that a spontaneous hydraulic fracturing crack may develop in the underworked rock mass, which can serve as a main channel for the penetration of underground or surface water into the mine workings. The nature of spontaneous hydraulic fracturing of rocks is determined by the fact that when a man-made impact on the rock mass, one of the main stresses of the rock mass can become less than the hydrostatic pressure of water. In this case, a hydraulic fracturing crack develops in the area where this condition is met. As an example, the breakthrough of water from a surface reservoir into an underground mine is considered. It is shown that at a low crack resistance of rocks, it is possible for a crack to grow into the mine, which may result in a sudden water breakthrough. The acquired knowledge expands the scientific basis for the development of appropriate supplements to the instructions for mining operations under water bodies.

Ductile failure of flat plates containing two through-wall cracks: Experimental investigation and numerical modeling

Multiple cracks are frequently detected in structural components and should be assessed aimed to judge whether they can be treated as individual cracks or be combined to a larger crack. To study the ductile failure and crack interaction behavior, tensile tests using flat plates with two through-wall cracks were conducted, and 3D digital image correlation method (3D-DIC) was applied to acquire the displacement and full-field strain measurement. A damage evolution model integrated with a non-monotonic fracture strain locus was implemented to model the ductile fracture and crack interaction. Simulation results including load-displacement curves and predicted crack coalescence results fit well to the experiment data. Effects of mesh size and cut-off value of stress on the simulation results were investigated to ensure the accuracy of finite element analysis. The findings show that FE predictions using non-monotonic fracture strain locus are not only superior to those using monotonic ones, but also more accurate than alignment and combination rules in fitness-for-service codes.

Evaluation of liquid metal embrittlement crack in resistance spot welds under intensive welding condition using industrial X-ray computed tomography and machine learning

In this work, the industrial X-ray computed tomography was exploited for measuring maximum crack depths across the weld interfaces within resistance spot welding (RSW) specimens welded under intensive welding condition. Individual crack profiles were measured for each sample and presented in terms of the total crack length, the maximum crack depth and the median crack width. A linear trend between maximum crack depth and median crack width was observed, where the associated coefficient of determination was sufficiently high (R2 = 0.79). Hence, the crack width is proposed to predict the crack depth. Based on the experimental findings, the effectiveness of the proposed method is demonstrated through machine learning studies, and a simple relation to predict the internal crack depth from the surface crack width was further developed. Semantic segmentation results proposed an algorithm succeeded in separating enough crack areas to calculate the crack width. Since Zn-assisted liquid metal embrittlement (LME) is now accepted as an inevitable consequence with respect to RSW process, the methodology demonstrated in this work can potentially offer the insights into an effective and automatic method of quantifying LME cracks.

Inductive Thermography as Non-Destructive Testing for Railway Rails

Inductive thermography is a non-destructive testing method, whereby the specimen is slightly heated with a short heating pulse (0.1–1 s) and the temperature change on the surface is recorded with an infrared (IR) camera. Eddy current is induced by means of high frequency (HF) magnetic field in the surface ‘skin’ of the specimen. Since surface cracks disturb the eddy current distribution and the heat diffusion, they become visible in the IR images. Head checks and squats are specific types of damage in railway rails related to rolling contact fatigue (RCF). Inductive thermography can be excellently used to detect head checks and squats on rails, and the method is also applicable for characterizing individual cracks as well as crack networks. Several rail pieces with head checks, with artificial electrical discharge-machining (EDM)-cuts and with a squat defect were inspected using inductive thermography. Aiming towards rail inspection of the track, 1 m long rail pieces were inspected in two different ways: first via a ‘stop-and-go’ technique, through which their subsequent images are merged together into a panorama image, and secondly via scanning during a continuous movement of the rail. The advantages and disadvantages of both methods are compared and analyzed. Special image processing tools were developed to automatically fully characterize the rail defects (average crack angle, distance between cracks and average crack length) in the recorded IR images. Additionally, finite element simulations were used to investigate the effect of the measurement setup and of the crack parameters, in order to optimize the experiments.

Assessment and visualization of performance indicators of reinforced concrete beams by distributed optical fibre sensing

The implementation of structural health monitoring systems in civil engineering structures already in the construction phase could contribute to safer and more resilient infrastructure. Due to their lightweight, small size and high resistance to the environment, distributed optical fibre sensors stand out as a very promising technology for damage detection and quantification in reinforced concrete structures. In this article, the suitability of embedding robust distributed optical fibre sensors featuring a protective sheath to accurately assess the performance indicators, in terms of vertical deflection and crack width, of three reinforced concrete beams subjected to four-point bending is investigated. The results revealed that a certain strain attenuation occurs in embedded robust distributed optical fibre sensors compared to commonly used thin polyimide-coated distributed optical fibre sensors bonded to steel reinforcement bars. However, the presence of the protective sheath prevented the appearance of strain reading anomalies which has been a frequently reported issue. Performance wise, the robust distributed optical fibre sensors were able to provide a good estimate of the beam deflections with errors of between 12.3% and 6.5%. Similarly, crack widths computed based on distributed optical fibre sensor strain measurements differed by as little as ±20 µm with results from digital image correlation, provided individual cracks could be successfully detected in the strain profiles. Finally, a post-processing procedure is presented to generate intuitive contour plots that can help delivering critical information about the element’s structural condition in a clear and straightforward manner.

Identification, segregation, and characterization of individual cracks in three dimensions

Cracks and fractures commonly exist in rocks and other brittle media and can significantly impact material deformation and fluid migration. Adequate characterization of cracks is essential to address relevant mechanical and fluid dynamic problems. A key challenge in characterizing cracks in three-dimensional space lies in the effective identification and separation of individual cracks from their intersected networks. We present a method for identifying, segregating and characterizing cracks in 3D space directly from a volumetric image acquired from microtomography as follows: 1) pre-processing digital images and segmentation; 2) analysing basic information of the binary images statistically; 3) filtering and/or removing non-crack related structures in the images; 4) smoothing and mending images; 5) thinning the void structures to reduce thickness in preparation for the separating step; 6) separating intersections in a crack network; 7) labelling cracks across intersections by the same identifier and restoring cracks to their original thickness. The characterization of cracks in three dimensions can be achieved after the above-described processing steps. Once the detailed characteristics of individual cracks in a 3D system are documented, statistical variables such as fractal dimensions can be extracted and thus the scaling law of the cracks can be defined. Potential application of our method and procedure includes predicting the characteristics of fractures at large scale and the relationships among the geometry of cracks, permeability, and stress states.

Determination of cracking causes in building structural elements

The article deals with the problems of buildings built many years ago, in which current and major repairs were not carried out in an appropriate manner. At the same time, buildings experience various deformations, such as yield, heel, subsidence, deflections, bends, twists, distortions, horizontal displacements. The survey of residential buildings built in the 80s is described and the analysis of the results of the survey of one of these buildings is carried out. The theoretical problem of the distribution of moisture in depth and various degrees of soil moisture has been solved. The reasons for the appearance of cracks in structures and cracks between individual building elements are also determined. The survey of a 9-storey brick residential building, built in the late 80s, which is in the period of normal operation, is considered. At the same time, the considered building is operated with significant deviations from regulatory requirements. The causes of cracks in individual structures and cracks between individual elements in the building are found. The problem of the distribution of moisture in depth with local soaking is solved on the basis of a numerical method, and the character of soil moistening at different depths with different degrees of moistening and characteristics of the base soil is obtained.

Detection and Measurement of Cracks in Rock Massifs by Means of Ground Laser Scanning

The analysis of the cracking of the rock massifs is an important stage in the process of their characterization, as this largely determines their mechanical behavior. This is the main reason the mining engineers, who are angaged with the analysis of rock massifs, to require a most detailed and reliable study of the cracks that have arisen in them. Metric characteristics, such as the direction and angle of collapse of the cracks, roughness and average distances between the individual cracks, are extremely important for the study of the structural disturbance of the massif. In the process of the metrics forming of these characteristics, a few of methods of measurement and graphical representation, different in nature and technological features, have become necessary. Through these traditional methods, it is very often not possible to obtain adequate quantitative data for the complete geomechanical characteristics of the rock mass and for the analysis of the mechanisms for its instability. Here, the effectiveness of the ground laser scanning in the study of the structural disturbance (direction and angle of decay of the cracks) and the area cracking coefficient of the rock mass has been experimentally proved. Through this technology the research of the structural disturbance of the rock massifs acquires new quantitative and qualitative dimensions. On the basis of an extremely detailed 3D model, even of hard-to-reach sections of the rock massif, a realistic clustering of cracks and prerequisites for adequate determination of the area cracking coefficient of the massif are created. Moreover, ground-based laser scanning data are an indisputable source of valuable information about rock surface roughness. For an object of the experiment, was selected part of a rock massif, which has well-developed, clearly visible cracks. The scan was performed, using a ground-based laser scanner “Scan Station 2” of the company “Leica”.

Vision and Deep Learning-Based Algorithms to Detect and Quantify Cracks on Concrete Surfaces from UAV Videos.

Immediate assessment of structural integrity of important civil infrastructures, like bridges, hospitals, or dams, is of utmost importance after natural disasters. Currently, inspection is performed manually by engineers who look for local damages and their extent on significant locations of the structure to understand its implication on its global stability. However, the whole process is time-consuming and prone to human errors. Due to their size and extent, some regions of civil structures are hard to gain access for manual inspection. In such situations, a vision-based system of Unmanned Aerial Vehicles (UAVs) programmed with Artificial Intelligence algorithms may be an effective alternative to carry out a health assessment of civil infrastructures in a timely manner. This paper proposes a framework of achieving the above-mentioned goal using computer vision and deep learning algorithms for detection of cracks on the concrete surface from its image by carrying out image segmentation of pixels, i.e., classification of pixels in an image of the concrete surface and whether it belongs to cracks or not. The image segmentation or dense pixel level classification is carried out using a deep neural network architecture named U-Net. Further, morphological operations on the segmented images result in dense measurements of crack geometry, like length, width, area, and crack orientation for individual cracks present in the image. The efficacy and robustness of the proposed method as a viable real-life application was validated by carrying out a laboratory experiment of a four-point bending test on an 8-foot-long concrete beam of which the video is recorded using a camera mounted on a UAV-based, as well as a still ground-based, video camera. Detection, quantification, and localization of damage on a civil infrastructure using the proposed framework can directly be used in the prognosis of the structure’s ability to withstand service loads.

P.009 MDK gene expression is correlated with human brain activity during acceptance of monetary rewards

Computationally efficient methods for bridging length scales, from highly resolved micro/meso-scale models that can explicitly model crack growth, to macro-scale continuum models that are more suitable for modeling large parts, have been of interest to researchers for decades. In this work, an improved brittle damage model is presented for the simulation of dynamic fracture in continuum scale quasi-brittle metal components. Crack evolution statistics, including the number, length, and orientation of individual cracks, are extracted from high-fidelity, finite discrete element method (FDEM) simulations and used to generate effective material moduli that reflect the material’s damaged state over time. This strategy allows for the retention of small-scale physical behaviors such as crack growth and coalescence in continuum scale hydrodynamic simulations. However, the high-fidelity simulations required to generate the crack statistics are computationally expensive. Thus, steps were taken to produce a flexible constitutive model to reduce the number of costly high-fidelity simulations needed to produce accurate results. A new stress based degradation criterion is introduced for the degradation of individual material zones. This allows for the development of a heterogeneous damage distribution within the bulk material. Then a flow stress model is added to the hydrodynamic simulation to account for plasticity in quasi-brittle materials. As a result, the effective moduli model can be applied to a larger range of materials. The effective moduli constitutive model is used to simulate beryllium flyer plate experiments. The results from the continuum scale simulations using statistics from a single high-fidelity simulation are found to be in excellent agreement with numerical and experimental velocity interferometer data. The same set of crack statistics are used to extrapolate the results of a higher rate flyer plate case using the effective moduli model. The extension of this model to higher rate cases shows promise for further reducing the number of costly high-fidelity simulations needed to generate crack statistics.

Critical crack lengths of concrete gravity dam by using fracture mechanics

Concrete gravity dams are generally designed based on the principle that the tension does not occur in any portion of the dam, as concrete is weak in tension. Cracks will occur if concrete is subjected to undesirable tensile stresses. The modeling of crack propagation is of high importance in simulation of dam failure. Koyna concrete gravity dam was chosen for the present study. A seismic study of the dam – reservoir – foundation structure is conducted first by using ANSYS. On the basis of the results obtained, critical zones are identified within which the tensile strength of the concrete exceeds the allowable limits. In these zones cracks have been initiated and are modeled using the Extended Finite Element Method (XFEM). The stress intensity factor (SIF) has been chosen to estimate critical crack length. Further critical crack lengths of each initiated individual cracks are determined to know the structural stability. From the present analysis it was observed that SIF rises with an increase in the length of the crack and it was also observed that the structural failure occurs at the critical crack length of the crack after the fracture toughness of the dam material has been achieved.

Relationship between Aspect Ratio and Crack Density in Porous-Cracked Rocks Using Experimental and Optimization Methods

Aspect ratio and crack density are essential parameters to understand the physical properties of porous-cracked rocks, although it is difficult to independently determine each parameter, as both are closely linked. The objective of this study is to propose a relationship between aspect ratio and crack density that can be used to solve for each through experimental and optimization methods. Two different constitutive equations are solved to create expressions explicitly defining aspect ratio and crack density, with all remaining variables arranged as functions of elastic wave velocity. Ten core specimens extracted from construction sites, with diameters of 46 mm, are subjected to artificial weathering to identify how their crack density and aspect ratio evolved with time. The artificial weathering process consisted of chemical and physical weathering cycles using saline solution and slake durability tests, respectively. Compressional and shear wave velocities are measured at every weathering step, and both aspect ratio and crack density are calculated. The random forest as an optimization method is selected to define the important score among input variables. The calculated aspect ratios and crack densities are converted into a crack porosity, the reliability of which is verified through percentage of crack porosity (~6%) in total porosity. This study demonstrates that the relationship between aspect ratio and crack density is robust and has wide-ranging applications in determining individual aspect ratio and crack density parameters in porous-cracked rock.

Sound propagation in Arctic-like waveguides

Sound propagation in Arctic-like waveguides (regions with a strong interaction of the acoustic field propagating in the water layer with both ice cover and the bottom) is complex phenomenon. The authors have performed more than two dozen experiments in different seasons on the shelf of the White Sea and in Moscow region both in the active regime and in the noise interferometry regime. In the active regime, it was demonstrated that the presence of ice leads to a decrease in the critical frequencies of the modes. If the bottom gives off gas, its accumulation under the ice layer significantly affects the boundary conditions. Flexural waves propagate over the ice and can radiate energy into the water layer. Interference occurs and is significant, especially near and below the cutoff frequency of the waveguide. Ice movement causes crackling. Using the acoustic noise caused by the crackling as a signal (noise interferometry regime) on the Arctic shelf allowed to solve the inverse problem and to reconstruct the sea parameters, for example, tidal activity. Using several horizontally spaced hydrophones, it was possible to study the processes of the propagation of individual cracks in the ice.

Field measurements of soil cracks

AbstractShrink–swell soils, often classified as Vertisols or vertic intergrades, are found world‐wide and are a leading cause of damage to infrastructure such as buildings, roads, and pipelines. Crack networks act as dominant environmental controls on the movement of water, contaminants, and gases. Numerous methods have been proposed to quantify the size (e.g., width, depth, volume) and connectivity of individual cracks and of larger crack networks. To measure and quantify the size and variability of cracks, we focus on two nondestructive methods, called here the tape and rod and displacement approaches, and one destructive method, called here the cast and excavate protocol. The nondestructive methods are relatively inexpensive and can allow repeated measurements, which makes them conducive to use in larger environmental studies such as observing hydrological partitioning between infiltration and surface runoff. However, the nondestructive methods are often biased toward larger cracks (due to physical limitations on the crack sizes that can be measured), require assumptions of crack geometry to determine crack volumes, and typically do not provide information on subsurface connections between cracks. The destructive cast and excavate method is better suited to sample aoftentimes can only be used once (precluding repeated measurements) and is labor intensive. A combination of measurements may therefore be required to best understand crack dynamics in both time and space. Altogether, the methods surveyed here enable accurate measurement and quantification of soil crack characteristics.

Automatic edge detection of ply cracks in glass fiber composite laminates under quasi-static and fatigue loading using multi-scale Digital Image Correlation

Digital image correlation is utilized to detect automatically crack density in glass/epoxy laminates with different lay-ups under quasi-static and fatigue loading conditions. The DIC setups used in the present work are 2D-DIC and 3D-DIC which are considered to be at meso-scale and macro-scale, respectively. The main objective of this work is to study whether the DIC technique is reliable in automatic crack detection and functional in calculation of crack density. Therefore, an optimization analysis is implemented to evaluate the resolution and the standard uncertainty in strain and displacement measurements. An optimized compromise is attained between the resolution and the uncertainty of both measurements to decide about the final configuration of the DIC setup. The setup is executed by acquiring in-situ images under quasi-static and fatigue experiments so that the images are synchronized with the data acquired from the testing machine. The crack detection analysis is attained by DIC analysis using strain and displacement fields in order to obtain optimum results. Then a semi-automatic program is created to evaluate the crack density and weighted crack density from the edge and top of the specimen, respectively. Moreover, a comparison is established between both strain and displacement fields in crack characterization. Consequently, the displacement field has proved to deliver better and more accurate results than strain fields in crack density calculation and individual crack characterization. Accordingly, the results obtained from DIC analysis are compared and validated by microscopic images which are acquired after performing each test.