Tearing Process Research Articles

Constructing graphene nanostructures with zigzag edge terminations by controllable STM tearing and folding

Graphene nanostructures with specified edge terminations has attracted considerable attention owing to their unique electronic properties induced by the edges. However, an efficient way to controllably fabricate such nanostructures is still highly desired. Here, we show that graphene nanostructures with zigzag edge terminations can be easily and efficiently constructed at room-temperature by tip manipulation of a scanning tunneling microscope (STM). Though intentionally increasing the tip-graphene interaction, we controllably tear and fold graphene sheets against step edges and successfully fabricate nanoscale graphene islands such as quantum dots and nanoribbon-like structures on graphite. Interestingly, the tearing directions are found to mainly along the zigzag orientations of graphene hexagonal lattice, leading to the generated graphene nanostructures possessing the same specified edges with well zigzag terminations. Theoretical modelling demonstrates that the enhanced tip-graphene repulsive force can account for the tearing and folding processes, whereas the preferential zigzag-tearing is attributed to the predicted lowest bond-breaking energy of the zigzag orientation in graphene. Our experiment provides a simple and controllable method for fabrication of graphene nanostructures with precise zigzag edge terminations. The obtained zigzag-edge-terminated graphene nanostructures also provide a platform for engineering novel quantum properties.

Evolution of slab tearing-related high potassium volcanism: Petrogenetic findings from the Emirdağ and İscehisar volcanic units

Volcanism that has been active since the early Miocene along a N-S trending line from Eskisehir to Isparta displays calc-alkaline and alkaline character and is closely associated with slab tearing processes. However, the geodynamic setting of these volcanic units between Afyon and Emirdag is still poorly known. In this study, petrological characteristics of the Emirdag and Iscehisar volcanic units have been investigated using petrography, whole-rock geochemistry and Sr-Nd isotopes. The Emirdag and Iscehisar volcanic units overlap the SeydileIgnimbrites. The Emirdag volcanic unit is trachyandesite and the Iscehisar volcanic unit is trachyte, basaltic trachyandesite and trachydacite in composition. The Emirdag volcanic unit displays calc-alkaline character, while the Iscehisar volcanic unit is alkaline but the rocks from both the units have shoshonite character defined by their high K 2 O contents. The Emirdag volcanic unit has 87 Sr/ 86 Sr ratios of 0.706790-0.706284 and 143 Nd/ 144 Nd ratios of 0.512472-0.512463, while these ratios in the Iscehisar volcanic unit are of 0.707650-0.706527 and 0.512464-0.512424, respectively. Data revealed by this study indicate that these volcanic units were affected by crustal contamination, fractional crystallization and magma mixing. Rising of asthenosphere in the region due to the extensional regime in the Early Miocene appears to have caused formation of volcanism that pass from calc-alkaline to alkaline in character. The Emirdag and Iscehisar volcanic units are the products of the volcanism that developed in the late stages of southward slab roll-back and in the extensional regime prior to the slab tearing event.

ПОРІВНЯЛЬНЕ ДОСЛІДЖЕННЯ РІЗНИХ СТРАТЕГІЙ ТЕХНІЧНОГО ОБСЛУГОВУВАННЯ

A characteristic feature of complex technical objects for special purposes is the presence in their composition of a large number (tens, hundreds of thousands) of various types component parts, which have different levels of reliability, different patterns of their wear and tear processes. This feature requires a more subtle approach to the organization and planning of maintenance in course of their operation. The problem is that in the development of such facilities, all issues related to maintainability and maintenance should be addressed already at the early stages of facility design. If you do not provide in advance the necessary hardware and software for the built-in monitoring of technical condition (TC) of the object, do not develop and "build" the maintenance technology into the object, then it will not be possible to realize in the future a possible gain in the reliability of the object due to maintenance. Since all these issues must be resolved at the stage of object creation (when the object does not yet exist), mathematical models of the maintenance process are needed, with the help of which it would be possible to calculate the possible gain in the level of reliability the facility due to maintenance, to estimate the cost costs required for this. Then, on the basis of such calculations, make a decision on the need for maintenance for this type of objects and, if such a decision is made, develop the structure of the maintenance system, choose the most acceptable maintenance strategy, and determine its optimal parameters. The article shows that the optimal parameters of various maintenance strategies significantly depend on both the reliability and cost structure of the facility and specified requirements for the facility's reliability . The higher the specified value , the more serviced items should be included in the optimal maintenance strategy. It has also been proven that the effectiveness of various maintenance strategies depends significantly on the reliability and cost structure of object. If the distribution of cost restored (including serviced) elements is closely correlated with the distribution of their reliability indicators, difference in effectiveness of different maintenance strategies is reduced. This is clearly seen in the example of Test-2 object, for which the least reliable elements are also the most expensive.

ОБГРУНТУВАННЯ ОПТИМАЛЬНИХ ПАРАМЕТРІВ СТРАТЕГІЇ ТЕХНІЧНОГО ОБСЛУГОВУВАННЯ, ЩО РЕГЛАМЕНТУЄТЬСЯ

A characteristic feature of complex technical objects for special purposes is the presence in their composition of a large number (tens, hundreds of thousands) of different types component parts that have different levels of reliability, different patterns of their wear and tear processes. This feature requires a more subtle approach to the organization and planning maintenance in the course of their operation. The problem is that in the development of such facilities, all issues related to maintainability and maintenance should be addressed already at the early stages of facility design. If you do not provide in advance the necessary hardware and software for the built-in monitoring of the technical condition (TC) of the facility, do not develop and “build” the maintenance technology into facility, then it will not be possible to realize in the future a possible gain in the reliability of the facility due to maintenance. Since all these issues must be resolved at the stage of object creation (when object does not yet exist), mathematical models of the maintenance process are needed, with the help of which it would be possible to calculate the possible gain in the level of reliability facility due to maintenance, estimate the cost costs required for this. Then, based on such calculations, make a decision on the need for maintenance given type of objects and, if such a decision is made, develop the structure of the maintenance system, choose the most acceptable maintenance strategy, and determine its optimal parameters. The paper shows that the model for the regulated maintenance strategy is an improved version of the already known models and is introduced into the complex model for the purpose of comparative assessment of various maintenance strategies. In addition, it should be borne in mind that in practice, some cases, a regulated maintenance strategy may be preferable to MCC strategies.

Measurement of the steady state tearing in thin sheets using the contactless system

The purpose of the present paper is the diagnostic method of the steady state tearing tests in thin steel sheets. The camera-based contactless system was used in the experimental research. The MATLAB software was used for the processing of real-time images. The data collected in the experiments were used to establish the R-curves in terms of the CTOD (crack tip opening displacement) based resistance curves. The innovative techniques allow extracting a large amount of geometrical information about the entire tearing process and the crack tip development. The steady state tearing was evaluated using automotive steel sheets and the tearing resistance was determined for three grades of thin sheets. The paper describes a comprehensive method of obtaining the material properties necessary for modelling and simulation. The proposed methodology for the testing and evaluation of the steady state tearing is applicable to thin sheets. The measurement method within the test for the determination of the tearing resistance was based on the image analysis.

Development of car wishbone using sheet metal tearing process via the theory of inventive problem-solving (TRIZ) method

In the automotive industry, sheet metal forming process design is of great importance. The cold forming process in particular is the most widely preferred of these methods. In the production of car parts in complex forms, forming problems such as tearing, wrinkling, back spring and unwanted thinning can appear. Recently, numerical analysis technology and software tools have been widely used in process design and metal forming. Elimination of these problems without the use of analysis programs means the use of the trial and error method, which results in much wasted time and huge costs. In addition to the use of analysis programs, resolving problems without mold process and design knowledge is also problematic. In this study, the theory of inventive problem-solving (TRIZ) approach was utilized to reach an analytical solution. In this methodology, the improving and worsening features were determined and a TRIZ 39 × 39 contradiction matrix was created which led to the solutions. Virtual experiments were carried out on a wishbone mold model designed via the Siemens NX 12 CAD program using the Autoform R7 analysis program. Real environment experiments were then performed, and the problem of tearing during the forming process was eliminated. The measured thickness value of this area, which was formed without tearing, was measured as 2.7 mm in the virtual environment experiments and 2.9 mm in the real environment experiments. In addition, the wishbone was subjected to two-axis (x and z) dynamic testing, with acceptable values reached at 500,000 cycles.

Experimental investigation on large deformation of silicon rubber

In this paper, both the displacement field and the strain field of silicon rubbers during the tearing process are investigated by means of 3D digital speckle correlation method. First, the speckle pattern is artificially sprayed on the surface of the standard silicon rubber sample. Second, a series of deformation images of the rubber tearing specimen are recorded during the tearing process, which indicates the failure evolution and different failure patterns. Finally, full-field three dimensional displacements and strain information are obtained for providing the development of a strain concentration zone in rubber material.

Mantle Dynamics of Western Pacific and East Asia: New Insights from P Wave Anisotropic Tomography

AbstractSeismic anisotropy records past and present tectonic deformations and provides important constraints for understanding the structure and dynamics of the Earth's interior. In this work, we use tremendous amounts of high‐quality P wave arrival times from local and regional earthquakes to determine a high‐resolution tomographic model of 3‐D P wave azimuthal anisotropy down to 1,000‐km depth beneath East Asia. Our results show that trench‐parallel fast‐velocity directions (FVDs) are visible in the shallow portion of the subducting Pacific slab (<80 km), whereas the deeper portion of the Pacific slab mainly exhibits trench‐normal FVDs, except for the stagnant slab in the mantle transition zone (MTZ) where obvious NE‐SW FVDs are revealed. The FVDs in the subslab mantle change from a subduction‐parallel trend at depths of 80–400 km to a subduction‐normal trend in the MTZ. Large‐scale low‐velocity anomalies are revealed beneath the Philippine Sea plate where the FVD is NE‐SW. The FVDs along the Izu‐Bonin arc and in a slab gap exhibit a striking anticlockwise toroidal trend. All these features may reflect complex 3‐D flows in the mantle wedge due to tearing and dehydration processes of the subducting Pacific slab. The subducting Pacific slab is split at ~300‐km depth under the Bonin arc and then penetrates into the lower mantle, whereas under East Asia the Pacific slab becomes stagnant in the MTZ and reaches the North‐South Gravity Lineament in China. The intraplate volcanoes in East Asia are caused by hot and wet upwelling flows in the big mantle wedge above the stagnant Pacific slab.

Current Concepts about the Etiology of Dry Eye Syndrome

The revolution in understanding the etiology and clinical manifestations of the disruption of the tearing process and the development of dry eye syndrome (CVS) has occurred in last 20–30 years. It has been established that the loss of the tear film homeostasis can occur not only because of a violation of systemic and autoimmune disorders, but also as a result of a blinking disorder and distribution of the tear film over the ocular surface. Therefore, new pathogenetic disease development mechanisms have been identified. The prevalence of diseases of the ocular surface and CVD in recent years has increased significantly. It is mostly caused not only by scientific discoveries in the field of understanding, for example, the etiological and pathophysiological role of the neurosensory mechanism of development of CVS. An important aspect is the emergence of new risk factors that potentiate the development of ocular surface diseases and CVL. These factors include the use of various drugs — antidepressants, antihistamines, hormone therapy, and others; instillation of eye drops — antiglaucoma drugs, etc., as well as the appearance of little-studied factors such as cosmetology procedures (eyelids tattooing, eyelash extensions, botulinum toxin injections for aesthetic purposes, etc.). They are carried out in proximate close to the eye and eyelids, causing multiple pathological reaction. The experience of observing patients, literature data, and the conducted study have showed that various cosmetological effects in the periorbital zone, whose popularity has increased in recent years, may cause the appearance of iatrogenic dry eye syndrome. The following most vivid clinical examples will help, encountered in our practice, to illustrate the data presented. Collecting the anamnesis, it is necessary to identify the presence of risk factors for the development of diseases of the ocular surface and CVD, to eliminate them, if possible, and to carry out adequate pathogenically based therapy.

Tearing and reliability of photovoltaic module backsheets

AbstractThe backsheet in photovoltaic modules belongs to an important class of layered materials where the tearing behavior of the individual layers does not necessarily represent the tearing behavior of the entire backsheet. Such characteristic arises from the interaction between the individual layers during the tearing process, where one layer of the backsheet is mechanically constrained by its neighboring layers and the layers may debond from each other. The mechanical constraint and debonding change the amount of energy dissipated during tearing and affect the overall tearing energy. In this work, we exposed a wide selection of backsheets with polymers including ethylene‐vinyl acetate (EVA), polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), and ethylene tetrafluoroethylene (ETFE) to damp heat (85°C/85%RH) for up to 2000 hours. We report on the effect of damp heat on the tearing energy as a function of damp heat exposure. We developed a model that describes the tearing energy of a layered structure by accounting for the tearing of the individual layers in the backsheet, the effect of mechanical constraint, and the adhesive debonding between the layers. Additionally, we explore the relationship between the microstructural change in the polymers which resulted from the damp heat exposure and the mechanical properties using modulated differential scanning calorimetry (MDSC), small and wide angle X‐ray scattering (SAXS and WAXS), and tensile testing.

Tearing behavior of membrane coated fabrics based on the DIC method under the effect of initial crack length

Abstract In this work, the digital image correlation (DIC) procedure is applied to experiments involving the tearing behavior of membranes under the effect of initial crack length, to obtain the displacement and corresponding strain results image and data of the tensile process, which intuitively shows the changes in the tearing process of the membrane. The experimental results and the analytical solution of the displacement of the orthotropic material in the fracture mechanics are compared and analyzed to verify the reliability of the theoretical model. Based on the theoretical model and the displacement values measured, mixed-mode (I, II) stress intensity factors at different angles of the crack tip are analyzed. This will make it possible to analyze the crack propagation law of the membrane and also provide a more effective measurement method and calculation method for a tearing test of orthotropic material under tensile loading.

Wear Mechanism of Cemented Carbide Tool in High Speed Milling of Stainless Steel

Adhesion of cutting tool and chip often occurs when machining stainless steels with cemented carbide tools. Wear mechanism of cemented carbide tool in high speed milling of stainless steel 0Cr13Ni4Mo was studied in this work. Machining tests on high speed milling of 0Cr13Ni4Mo with a cemented carbide tool are conducted. The cutting force and cutting temperature are measured. The wear pattern is recorded and analyzed by high-speed camera, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). It is found that adhesive wear was the dominant wear pattern causing tool failure. The process and microcosmic mechanism of the tool’s adhesive wear are analyzed and discussed based on the experimental results. It is shown that adhesive wear of the tool occurs due to the wear of coating, the affinity of elements Fe and Co, and the grinding of workpiece materials to the tool material. The process of adhesive wear includes both microcosmic elements diffusion and macroscopic cyclic process of adhesion, tearing and fracture.

Micro-mechanics based cohesive zone modeling of full scale ductile plate tearing: From initiation to steady-state

Ductile plate tearing, where the crack propagates multiple plate thicknesses, is targeted by the micro-mechanics based Gurson-Tvergaard-Needleman (GTN) model. The focus is on extracting detailed information on the fracture process that governs ductile crack initiation from a blunt pre-crack until the crack reaches steady-state propagation in order to enhance accuracy of the traditionally used cohesive zone traction-separation relations. The aim is to facilitate an accurate representation of the tearing process within the cohesive zone modeling framework as such simplistic models are largely exploited by engineers worldwide. Unfortunately, accuracy in the representation of crack propagation is often sacrificed for computation speed, but the present work allows correlating the cohesive zone modeling to a much more accurate, though computational expensive, micro-mechanics based (full 3D) model response. In the modeling of large-scale plate tearing, shell elements are typically employed to represent the engineering scale of the structure while the cohesive zone represents the micro-scale in terms of crack initiation and growth process. Thus, the cohesive zone essentially has to take over at the onset of the first localization (thinning far ahead of the crack tip). Calibration of the cohesive zone parameters has earlier been made in accordance with experimental observations such that the overall response of the system is well reproduced. But, the present work takes the calibration of the cohesive zone one step further and exploits details from a large-scale GTN model calculation. The goal is to match the response from the GTN model with the much less computation demanding cohesive zone modeling approach by incorporating knowledge of the loading history for individual cross-sections, in front of the pre-crack, through which the tearing crack propagates. The full 3D micro-mechanics based model set-up allows tracking of key parameters, such as peak traction and tearing energy, which goes into the cohesive traction-separation relation. The dependency on distance from the crack initiation site of the cohesive zone parameters is determined - from crack initiation to steady-state propagation - and followed up by a discussion on how to construct a traction-separation relation for ductile plate tearing.

Water Film Formation and Performance Effect on Compressor Stage in Water Injection Process

Abstract In this study, the thickness of water film, which is frequently formed on compressor blade surface, was investigated. Simultaneously, its movement and extra torque demand were provided by a simulation model of the code. Having taken into account the transformation in blade’s profile and the thickness feature of the films, the working medium characteristic transformation in compressor stage was analyzed. In addition, formation, development and movement of the water film on a compressor stage were simulated by using unsteady numerical methods in various water injected conditions. Movement characteristics of water droplets in cascade were investigated to understand the flow mechanisms responsible for water film formation process. The forming and the tearing process of water films, which formed on the blade surface, were analyzed at different injection conditions. In consideration of the “Scoop effect” in actual situation, the maximum quantity of injected water can reach 12 %. Results indicated that continuity and region of the film would be developed with the increment of droplet size and injection rate. It was also found that water film’s tearing process brought about flow losses near blade surface due to the increment of surface roughness.

Influence of Wave State and Sea Spray on the Roughness Length: Feedback on Medicanes

Occasionally, storms that share many features with tropical cyclones, including the presence of a quasi-circular “eye” a warm core and strong winds, are observed in the Mediterranean. Generally, they are known as Medicanes, or tropical-like cyclones (TLC). Due to the intense wind forcings and the consequent development of high wind waves, a large number of sea spray droplets—both from bubble bursting and spume tearing processes—are likely to be produced at the sea surface. In order to take into account this process, we implemented an additional Sea Spray Source Function (SSSF) in WRF-Chem, model version 3.6.1, using the GOCART (Goddard Chemistry Aerosol Radiation and Transport) aerosol sectional module. Traditionally, air-sea momentum fluxes are computed through the classical Charnock relation that does not consider the wave-state and sea spray effects on the sea surface roughness explicitly. In order to take into account these forcing, we implemented a more recent parameterization of the sea surface aerodynamic roughness within the WRF surface layer model, which may be applicable to both moderate and high wind conditions. The implemented SSSF and sea surface roughness parameterization have been tested using an operative model sequence based on COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) and WRF-Chem. The third-generation wave model SWAN (Simulating Waves Nearshore), two-way coupled with the WRF atmospheric model in the COAWST framework, provided wave field parameters. Numerical simulations have been integrated with the WRF-Chem chemistry package, with the aim of calculating the sea spray generated by the waves and to include its effect in the Charnock roughness parametrization together with the sea state effect. A single case study is performed, considering the Medicane that affected south-eastern Italy on 26 September 2006. Since this Medicane is one of the most deeply analysed in literature, its investigation can easily shed some light on the feedbacks between sea spray and drag coefficients.

ANALYSIS OF WEAR AND TEAR OF WORKING ELEMENTS WITH A REPLACEABLE CUTTING EDGE IN AN ABRASIVE SOIL MASS

This paper presents an analysis of the wear and tear process of different technological solutions of plough blades with a replaceable cutting edge. The experiment was conducted under natural operating conditions. Workpieces made of B27, Hardox 500, and Hardox 500 with padding weld, and two types of boron steel with non-hardfaced and hardfaced cutting edges were tested. The analyses of chemical composition and microstructure were performed using light microscopy and scanning electron microscopy methods. Operational research included the measurement of mass changes and geometry in the characteristic points of the plough blades. Based on the results obtained, it was found that the components made of Hardox 500 steel with padding welding were more durable than component without the padding layer. In contrast, the weight loss intensity was similar for all the examined materials.

Effect of gap flow on the shallow wake of a sharp-edged bluff body—Coherent structures

This experimental study was carried out to investigate the turbulent wake generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. This paper is the third part of an extensive study to characterize the gap-flow effects and is primarily focused on the characteristics of vortices in the wake flow. Two different gap heights were studied which were compared to the no-gap flow case. The Reynolds number based on the water depth was 45 000. Extensive measurements of the flow field in the vertical and horizontal planes were made using a particle-image velocimetry (PIV) system. The large vortices were exposed by analyzing the PIV velocity fields using the proper orthogonal decomposition (POD) method. Only a few modes for the POD reconstruction were used to recover ∼50% of the energy content. A vortex identification algorithm was then employed to quantify the properties of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the vortices. The results revealed that the gap flow causes an increase in the number of vortices up to ∼81% higher than the no-gap flow case, but a decrease in the vortex size and strength. The occurrence of pairing and tearing processes is observed in the wake flow. In addition, a mathematical model was used to predict the relationship between the vortex circulation and vortex size, which is found to be a function in several parameters.

Self-folding mechanics of graphene tearing and peeling from a substrate

Understanding the underlying mechanism in the tearing and peeling processes of graphene is crucial for the further hierarchical design of origami-like folding and kirigami-like cutting of graphene. However, the complex effects among bending moduli, adhesion, interlayer interaction, and local crystal structure during origami-like folding and kirigami-like cutting remain unclear, resulting in challenges to the practical applications of existing theoretical and experimental findings as well as to potential manipulations of graphene in metamaterials and nanodevices. Toward this end, classical molecular dynamics (MD) simulations are performed with synergetic theoretical analysis to explore the tearing and peeling of self-folded graphene from a substrate driven by external force and by thermal activation. It is found that the elastic energy localized at the small folding ridge plays a significant role in the crack trajectory. Due to the extremely small bending modulus of monolayer graphene, its taper angle when pulled by an external force follows a scaling law distinct from that in case of bilayer graphene. With the increase in the initial width of the folding ridge, the self-folded graphene, motivated by thermal fluctuations, can be self-assembled by spontaneous self-tearing and peeling from a substrate. Simultaneously, the scaling law between the taper angle and adhesive energy is independent of the motivations for thermal activation-induced self-assembly and external force tearing, providing effective insights into the underlying physics for graphene-based origami-like folding and kirigami-like cutting.

Ultra-fast responsive colloidal\u2013polymer composite-based volatile organic compounds (VOC) sensor using nanoscale easy tear process

There is an immense need for developing a simple, rapid, and inexpensive detection assay for health-care applications or monitoring environments. To address this need, a photonic crystal (PC)-based sensor has been extensively studied due to its numerous advantages such as colorimetric measurement, high sensitivity, and low cost. However, the response time of a typical PC-based sensor is relatively slow due to the presence of the inevitable upper residual layer in colloidal structures. Hence, we propose an ultra-fast responsive PC-based volatile organic compound (VOC) sensor by using a “nanoscale easy tear (NET) process” inspired by commercially available “easy tear package”. A colloidal crystal-polydimethylsiloxane (PDMS) composite can be successfully realized through nanoscale tear propagation along the interface between the outer surface of crystallized nanoparticles and bulk PDMS. The response time for VOC detection exhibits a significant decrease by allowing the direct contact with VOCs, because of perfect removal of the residual on the colloidal crystals. Moreover, vapor-phase VOCs can be monitored, which had been previously impossible. High-throughput production of the patterned colloidal crystal–polymer composite through the NET process can be applied to other multiplexed selective sensing applications or may be used for nanomolding templates.

Mechanical exfoliation of two-dimensional materials

Two-dimensional materials such as graphene and transition metal dichalcogenides have been identified and drawn much attention over the last few years for their unique structural and electronic properties. However, their rise begins only after these materials are successfully isolated from their layered assemblies or adhesive substrates into individual monolayers. Mechanical exfoliation and transfer are the most successful techniques to obtain high-quality single- or few-layer nanocrystals from their native multi-layer structures or their substrate for growth, which involves interfacial peeling and intralayer tearing processes that are controlled by material properties, geometry and the kinetics of exfoliation. This procedure is rationalized in this work through theoretical analysis and atomistic simulations. We propose a criterion to assess the feasibility for the exfoliation of two-dimensional sheets from an adhesive substrate without fracturing itself, and explore the effects of material and interface properties, as well as the geometrical, kinetic factors on the peeling behaviors and the torn morphology. This multi-scale approach elucidates the microscopic mechanism of the mechanical processes, offering predictive models and tools for the design of experimental procedures to obtain single- or few-layer two-dimensional materials and structures.