Extent Of Deformation Research Articles

BENEFITS OF USE OF ACOUSTIC EMISSION IN SCRATCH TESTING

Scratch test is regularly used for assessment of cohesive and adhesive strength of thin films and coatings. By default, its evaluation is based on analysis of depth-load-time record and microscopic observation of residual scratch groove. The visual analysis of the residual groove provides the most detailed description of the final damage of the surface (crack patterns, extent of plastic deformation, delamination, etc.), but it may be a time demanding approach. Although the continuous recording of indenter penetration depth and applied load offers instantaneous information about the performance of the tested material, it may not provide sufficient description of the sample’s deformation behaviour. Therefore, other complementary techniques for description of the deformation response to scratch loading are desirable. Continuous recording of acoustic emissions (AE) generated during the test could be a possible solution. It is especially the ability of AE method to detect the very first and even subsurface failures of the material that is of the most importance and otherwise inaccessible by standardly used techniques. What is more, it is a non-destructive and real-time method. In principle, AE method can be beneficially employed for a wide range of materials explored via scratch test. The strength of the AE analysis of the nano/micro scratch test will be demonstrated on various types of materials including optical thin films, durable metal and hard ceramic films as well as bulk laser cladding. Selected phenomena and features of the use of AE during scratch testing will be presented, including effect of scratch load on character of AE records (burst vs. continuous) for TiO2 on glass, subsurface damage of SiC films on silicon and selective failure of hard carbide phase embedded in a metal matrix in case of laser re-melted layers.

Micromachining Imposed Subsurface Plastic Deformation in Single-Crystal Aluminum

In this work, we analyzed the nature and extent of deformation beneath the machined surface during orthogonal micromachining of single-crystal aluminum. We micromachined six different crystallographic orientations of a sample with [111] zone-axis and analyzed the sub-surface texture and resulting misorientations. The results indicate that the changes in crystallographic orientation induces variations in the depth of deformation, the degree of grain refinement and the lattice rotations. We observed up to 50% lattice rotations, shear bands varying from 55o to 60o from the direction of machining, and highly entangled dislocations, which confirmed the presence of strain hardening.

Improving strength of cold-drawn wire by martensitic transformation in a 0.65 wt% C low-alloy steel

Ultrahigh strength can be obtained by cold drawing of high-carbon steel wire, but the strength heavily relies on the extent of cold-drawn deformation and it is difficult to produce ultrahigh strength steel wire with large diameter. In this study, a new method by combination of cold-drawing and martensitic transformation was reported to significantly improve the strength of cold-drawn steel wire. By using the new method, the strength of the steel wire can be increased to over 2.4 GPa, which is much higher than its corresponding original cold-drawn wire (less than 2.0 GPa), while sacrificing only a small ductility. By using electrochemical etching, transmission electron microscopy and X-ray diffraction, the prior austenite grain size and the microstructure of the martensitic steel wires was analysed. After the heat treatment, the large cold deformed steel wire with 8 pass drawing displays grains of 4.9 μm and dislocation-substructured martensite; while the small cold deformed wire with 6 pass drawing results in coarser grains and a mixture substructure of dislocation and twin in martensite. The results demonstrate that the extent of cold-drawn deformation has a great influence on grain refinement in the later heat treatment; grain refinement to less than 5 μm will lead to martensite substructure transition from twin to dislocation, and thus endows the martensitic steel wire moderate ductility. In addition, calculation indicates that precipitate hardening and dislocation strengthening contribute about 76.9% to the yield strength, and martensite lath boundary strengthening contributes about 18% to the yield strength.

Electronic structure and carrier mobilities of twisted graphene helix

We have investigated the effect of twisting on electronic band structure, effective mass and carrier mobilities of three prototypes of AGNRs (N=6, 7 & 8) using Density functional theory combined with Deformation potential theory and Effective mass approximation. It is shown that the influence of twisted modes electron-phonon interaction is smaller than stretching modes, nonetheless, twisting has a profound effect on effective mass and mobilities. Similar to earlier reported conclusion in which the ideal N=3n wide HAGNR potentially exhibit an electron mobility comparable to intrinsic graphene, we also found that the ideal N=3n+2 HAGNRs hole mobility reside more closely to intrinsic graphene which could be increased further through Fluorine passivation. Thus, the control of the ribbon width along with passivation and extent of deformation are of paramount importance for determining the n-type or p-type of ribbons. Also, because of strong response to torsional strain, the N=8 F passivated AGNRs are the most appropriate for mechanical and high frequency switching. Our results suggest that twisting a ribbon can be considered as a good alternative way for controlled manipulation of the band structure and carrier mobilities for applications in mechanical switching devices.

Elastohydrodynamics of a deformable porous packing in a channel competing under shear and pressure gradient

Elastohydrodynamics of a deformable porous medium sandwiched between two parallel plates is investigated under the influence of an externally applied pressure gradient as well as an induced shear due to the movement of the upper plate. Biphasic mixture theory is used to describe the macroscopic governing equations for the fluid velocity and the solid displacement, assuming the deformable porous medium as a continuum space. The corresponding reduced mathematical model is a coupled system of elliptic partial differential equations. It is assumed that the fluid at the lower plate experiences slip due to the surface roughness of the plate. The exact solution for unidirectional fluid velocity and solid deformation resembling plain Poiseuille–Couette flow are presented for steady and unsteady states. Asymptotic analysis of the biphasic mixture in the case of low and high Darcy numbers is performed to validate the obtained solution using Prandtl’s matching technique. It is observed that the Womersley number dictates whether the fluid is trapped inside the channel or escapes the channel. The competition between the shear and the pressure gradient is analyzed, and a critical criterion is established that dictates the dominant factor. A mathematical analysis of the current problem is invaluable in understanding the mechanical behavior of biomass under pressure-driven flow in applications such as tissue engineering or shear driven flow inside endothelial glycocalyx layers, which are discussed in brief. In this context, our analysis on the extent of tissue deformation in response to frequency variations is expected to give useful insights to identify the right diagnosis.

Extent of Atrial Deformation in Catheter Ablation of Atrial Fibrillation.

Anatomical atrial distortion during catheter mapping and ablation has not been elucidated in atrial fibrillation (AF) ablation. This study aimed to characterize the regional anatomical distortion in common ablation areas according to different contact forces (CFs) with radiofrequency and cryoballoon catheters.Ten patients underwent distortion mapping with low (5-10 g) and high CFs (10-30 g) at the pulmonary vein (PV) antra, left atrial (LA) roof line, mitral isthmus line, cavotricuspid isthmus line, and superior vena cava (SVC)-right atrial (RA) junction. Fifteen patients underwent distortion mapping with a 28-mm second-generation cryoballoon surrounded by a decapolar catheter at each PV antrum following creating the LA geometry. High CFs distorted the PV antra as compared to low CFs and the extent was greater at the anterior PV aspect, and the catheter was located more inside the PVs. The inflated cryballoon stretched the PV surface in the postero-superior direction in the upper PVs and posterior direction in the lower PVs. High CFs as compared to low CFs distorted the LA roof and cavotricuspid isthmus in the postero-inferior and inferior directions, respectively, but not the mitral isthmus line even with deflectable sheaths. High CFs distended the SVC-RA junction as compared to low CFs, and the extent was greatest at the lateral side and smallest at the antero-septal side.Human atria significantly distend during radiofrequency and cryoballoon ablation, and there are regional heterogeneities of the extent of the distortion. This information might aid operators in performing safe and effective AF ablation procedures.

Toughness evaluation of poly(butylene terephthalate) nanocomposites

This research investigates the toughness of poly(butylene terephthalate) (PBT) nanocomposites, based on mechanical characterizations and subsequent microstructural observations. Montmorillonite (MMT) and nano-precipitated calcium carbonate (NPCC) were selected as nano-reinforcing phases. Notched Izod impact test, tensile test as a quasi-static loading, and mode-I fracture toughness test, were conducted to evaluate the toughness. The corresponding fracture surfaces were analyzed using scanning electron microscopy (SEM). Tensile test results were linked with the morphologies of corresponding tensile-fractured surfaces. The results indicated that massive fibrillation in PBT/MMT nanocomposites dissipated lower energy relative to the large plastic deformation that was induced in the fracture surface of pure PBT. For PBT/NPCC samples, however, surface roughening mechanism was observed to increase the toughness in the tensile test, as compared to plain PBT. The fracture morphology of compact tension (CT) specimens exhibited a low extent of plastic deformation for pure PBT. However, the crack initiation zone of both nanocomposites showed a fibrillated morphology, leading to the increase of stress intensity factor up to 57% and 45% with the application of MMT and NPCC, respectively, as compared to pure PBT. The crack propagation region was, however, associated with shallow fibrils for MMT and local polymer yielding for NPCC.

Deformation dynamics of an active compound particle in an imposed shear flow—a theoretical study

Active particles encapsulated in a droplet are called active compound particles. In addition to the activity induced fluid flows, these multiphase structures may experience imposed flows in the process of generating and manipulating them in microfluidic devices or in their natural habitats. Therefore, we investigate the deformation dynamics and stability of a drop encapsulating a model microswimmer, a spherical squirmer (shaker) concentrically placed in a drop, when subjected to an imposed shear flow. Using Lamb’s general solution, Stokes equations are solved to determine the flow field and consequently the shape of the droplet interface. Shear flow always deforms the drop and the flow induced by the active particle may enhance or impede this deformation based on its orientation. The extent of deformation also depends on (i) the size of the active particle and the droplet, (ii) the viscosity of the droplet fluid and the fluid in which it is dispersed, (iii) the orientation of the active particle, and (iv) the relative strength of activity and imposed shear. Finally we find that the presence of an imposed vorticity field has a stabilizing effect on the active compound particle as it rotates the encapsulated swimmer and the drop undergoes a time periodic deformation.

Direct measurement of the intrinsic electric dipole moment in pear-shaped thorium-228

It is now well established that atomic nuclei composed of certain combinations of protons and neutrons can adopt reflection-asymmetric, or octupole-deformed, shapes at low excitation energy. These nuclei show promise in the search for a permanent atomic electric dipole moment, the existence of which has implications for physics beyond the Standard Model. Theoretical studies have suggested that certain isotopes of thorium may have the largest octupole deformation. However, due to experimental challenges, the extent of the octupole collectivity in the low-energy states in these thorium nuclei has not yet been demonstrated. This paper reports measurements of the lifetimes of low-energy states in 228Th (Z = 90) undertaken using the mirror symmetric centroid difference method, which is a direct electronic fast-timing technique. Lifetime measurements of the low-lying Jp = 1- and 3- states, which are the first for a thorium isotope, have allowed the B(E1) rates and the intrinsic dipole moment to be determined. The results are in agreement with those of previous theoretical calculations allowing the extent of the octupole deformation of 228Th to be estimated. This study indicates that the nuclei 229Th and 229Pa (Z = 91) may be good candidates for the search for a permanent atomic electric dipole moment.

The Effect of Lamellar and Globular α-Phase on Mechanical Behavior of Strongly Textured Ti–6Al–4V alloy

In this study, the effect of lamellar and globular α-phase on mechanical properties of strongly textured Ti–6Al–4V alloy was investigated. The strong transverse texture was developed in Ti–6Al–4V alloy via α + β rolling at 950 °C. In the following, lamellar and equiaxed microstructures have been separately promoted in the Ti–6Al–4V alloy during annealing at β- and α + β regions, respectively. According to EBSD analysis, it was revealed that deformation texture was not considerably changed during different annealing processes. Then, room temperature mechanical properties of the studied alloy including uniaxial tensile, compression and bending tests were evaluated. According to the tensile test, work hardening capacity was obtained as 1.10 and 0.64 for equiaxed and lamellar microstructures, respectively. Fracture limit curve revealed that equiaxed microstructure had more extent of homogeneous deformation in comparison with lamellar one. In addition, bending properties of the Ti–6Al–4V alloy were significantly improved as a result of equiaxed microstructure.

Effect of Spacer Configuration on the Characteristics of FO Membranes: Alteration of Permeation Characteristics by Membrane Deformation and Concentration Polarization.

Membrane deformation is a significant problem in osmotically driven membrane processes, as it restricts practical operating conditions and reduces overall process performance due to unfavorable alteration of membrane permeation characteristics. In this respect, a spacer plays a crucial role, as it dictates the form and extent of membrane deformation in association with concentration polarization (CP), which is also influenced by spacer-induced hydrodynamic behavior near the membrane surface. These two roles of spacers on membrane permeation characteristics are inherently inseparable with the coexistence of hydraulic and osmotic pressures. Here, we suggest a novel analytical method to differentially quantify the proportions of effective osmotic pressure drop caused by membrane deformation and CP. Furthermore, we tested two different FO membranes with three different spacer configurations to define and discuss different forms of membrane deformation and their effects on membrane permeation characteristics. The differential analysis revealed the effect of spacer configuration on effective osmotic pressure drop in membrane deformation (up to ∼201% of variation) is much greater than that in CP (up to ∼20.1% of variation). In addition, a combined configuration of a feed spacer and tricot spacer demonstrated its ability of mitigating membrane deformation with lower selectivity loss and channel pressure drop under pressurization.

Dynamic response of fiber-composite-reinforced shell structure subjected to internal blast loading

In this study, we report the analysis of a dynamic response process of a fiber-composite-reinforced shell when subjected to internal blast loading of different TNT equivalent by using a three-dimensional digital image correlation method. And it was compared with the dynamic response of the metal shell with the same TNT equivalent and the same surface density. We received the relationship between dynamic deformations and the sizes of the two shells under different TNT equivalence. Through comparison of the results, it was shown that the response process of the fiber-composite-reinforced shell was much more complex than that of the metal shell. Our experimental results suggest that the shock wave intensity, the material mechanical properties and the structure symmetry had important influences at different stages of the structural dynamic response. Fiber composites with high strength restricted the structural deformation extent and deformation rate. In addition, the interaction between fiber composite and metal liner reduced the probability of structural damage caused by the energy concentration. This work provides important insights for the design of cylindrical explosion vessels.

Effect of Wire-Drawing Process Conditions on Secondary Recrystallization Behavior During Annealing in High-Purity Copper Wires

The relationship between the process condition of wire-drawing and the microstructural evolution during the subsequent annealing was investigated for the production of high-purity copper wires. Three wire-drawing process conditions were considered according to the reduction in the area per pass and the die angle, and their effects on the evolution of the grain structure and texture during annealing were investigated. Strain distributions, calculated using the finite element method, showed that the shear strain near the wire surface varies according to the process condition. The electron backscatter diffraction results indicate that the location on the cross-section of the wire, where secondary recrystallization initiates during annealing, is closely related to the shear strain during wire-drawing. Meanwhile, the effect of shear deformation on the grain structure and texture after primary recrystallization is insignificant. Drawing process conditions with a small reduction in the area per pass and die angle resulted in a relatively small shear strain and gave rise to the onset of secondary recrystallization at the central region of the wires. In contrast, the condition with a large reduction in the area per pass and die angle led to a high shear strain and the onset of secondary recrystallization at the peripheral region of the wire. The observed primary and secondary recrystallization behavior during annealing was explained from the viewpoint of dynamic material phenomena and inhomogeneity in the local recrystallization texture, regulated by the extent of shear deformation during wire-drawing.

Ice-Seabed interaction analysis in sand using a gene expression programming-based approach

Arctic subsea pipelines are usually buried for physical protection against the ice-induced scours. Determination of the maximum horizontal deformations for guaranteed operational integrity and cost-effective design is probably the most challenging aspect of subsea pipelines in ice-prone areas. The large uncertainties associated with the design of ice-protected subsea pipeline using the existing empirical equations, advanced experimental and sophisticated numerical studies with significant time and cost impacts are usually preferred to ensure the sufficiency and the cost-effectiveness of the pipeline design against the ice attack. This has caused the industry to keep looking for more effective and less-costly solutions for modeling the ice impact on buried pipelines. In this study, a Gene Expression Programming (GEP) model representing the Artificial Intelligence (AI) approaches was used for the first time to simulate the subgouge soil deformation in the sand. A database was constructed using some of the published experimental studies identifying the key input parameters including soil depth, bearing pressure, the maximum vertical extent of subgouge deformation, attack angle, and dilation index. Subsequently, six GEP models were developed and validated by using a K-fold cross-validation method. The performance of the GEP method was compared with an Artificial Neural Network (ANN) model, and uncertainty analysis (UA) along with a partial derivative sensitivity analysis (PDSA) was conducted to assess the influence domain of the key parameters. The study showed that the evolutionary numerical methods could be used as an accurate and cost-effective alternative for modeling of the ice-induced subgouge deformations.

Tectono-magmatic events of the Qilian orogenic belt in northern Tibet: new insights from detrital zircon geochronology of river sands

ABSTRACT The Precambrian–Palaeozoic evolution of the Qilian orogen is widely debated due to the complexity of the orogen’s structure and the extent of Phanerozoic deformation. In order to identify the tectono-magmatic events of the Qilian orogenic belt, we conducted detrital zircon U-Pb geochronology on river sediments across the orogen. The results indicate that the detrital zircon ages mainly comprise five populations: 220–280 Ma, 400–520 Ma, 800–1000 Ma, 1200–2100 Ma, and 2200–2700 Ma. The sediments in the Central Qilian Block exhibit zircon age peaks at ~1.8 Ga and ~1.0 Ga, which support that the Central Qilian Block successively accreted to the Columbia and Rodinia supercontinents. The sediments in the Quanji Block exhibit zircon age peaks at ~1.8 Ga and ~2.5 Ga, revealing possible affinity of the Quanji Block to the North China Craton prior to the Neoproterozoic. The detrital zircon age population in 400–520 Ma of all the sediments recorded the continental aggregation process among the Quanji, Qaidam, and Central Qilian Blocks. The widespread 200–300 Ma zircon ages in Central Qilian, Quanji, and North Qaidam regions, reflect a tectono-magmatic event which was most likely associated with the low-angle Paleo-Tethys subduction at the southern margin of Qaidam Block. Our results underline that the overlooked Neoarchean to Paleoproterozoic and Permian to Triassic tectono-magmatic events of the Qilian orogenic belt deserves more attention in the future study. The detrital zircon age populations of different river sand samples indicate fairly high variability, highlighting that caution should be exercised while using modern river sand detrital zircon age signatures to track tectono-magmatic history of such complex orogens.

Industrial Gear Oils: Influence of Bulk Oil Temperature and Contact Pressure on Tribological Performance and Subsurface Changes

This study was designed to investigate the influence of oil temperature and contact pressure on the tribological performance of three industrial gear oils but also on the corresponding changes taking place beneath the metal surfaces in contact. The result shows that increase in the oil temperature and contact pressure increases surface–additive interaction, promoting the formation of low-friction tribofilms. Subsurface characterisation of the worn surfaces shows that higher oil temperature and contact pressure promotes surface hardening of spheroidised AISI 52100 steel, degradation of the near-surface (< 0.8 µm) microstructural integrity and corresponds to an increase in wear. This study clearly shows that the gear oil formulations and the tribofilms they form uniquely influence the extent of subsurface deformation and wear.

Characterisation and mapping of land subsidence based on geodetic observations in Lagos, Nigeria

The pervasive seasonal flooding, aquifer contamination, and saline water intrusion in parts of Lagos are some of the long-term effects of land subsidence caused by the excessive groundwater exploitation and land reclamation that has been taking place in the city. Efforts to monitor the extent and pattern of land deformation will help in many ways to mitigate the effects of flooding and other geohazards associated with land subsidence. In this study, we characterised and mapped the land subsidence in the Lagos city based on the analyses of geodetic data, which included Global Positioning Satellite (GPS), Envisat, Sentinel-1, and GRACE data. We applied the SBAS technique to the Envisat and Sentinel-1 datasets acquired from 2004–2011 and 2015–2019, respectively, and to perform multi-temporal analyses and produce corresponding subsidence maps over the Lagos city. The GRACE data were used to infer the extent and trend of groundwater changes at the GPS location. The results indicate that the subsidence is a widespread phenomenon in Lagos city, with subsidence rates varying between −2 mm/year and −87 mm/year. The highest subsidence rate was observed around the coastal zones and areas where heavy structures are built on landfills. With the highest rate at present, subsidence has gradually increased in the last 15 years. With the development of indiscriminate groundwater exploitation, urbanization, and rapid population growth, the subsidence rate in Lagos city is likely to rise significantly in the coming years, which, in turn, may further escalate the flood rate and other associated geohazards.

Impact of sleeping position, gravitational force & effective tissue stiffness on obstructive sleep apnoea

Accurate prediction of deformation and collapse of the upper airway during breathing is required for effective and personalised treatment of obstructive sleep apnoea (OSA). While numerical modelling techniques such as fluid–structure interaction (FSI) are promising, an outstanding challenge is to accurately predict the deformation of the airway during breathing and thus the occurrence of OSA. These difficulties arise because the effective stiffness of the soft tissue in the human upper airway varies due to neuromuscular effects on the stiffness of the underlying muscles. In addition, both the elasticity and anisotropy of the soft tissues along the upper airway are poorly characterised. Finally, gravitational effects on anatomic features are yet to be considered. In this study, a validated FSI technique is introduced that allows prediction of the extent and position of the major deformation in the upper airway. This technique is used to analyse the behaviour of the upper airway in the two most common sleeping positions and for a range of effective tissue stiffnesses. The results demonstrate that sleeping position, gravity and soft tissue stiffness (used here as a proxy for neuromuscular effects) are the main factors that affect upper airway collapse. Therefore, this study provides new insights into the mechanisms of OSA and a new methodology that significantly advances the patient-specific treatment of OSA.

Suspension of flexible cylinders in laminar liquid flow

AbstractA methodology for particle‐resolved simulation of dense suspensions of flexible cylindrical particles in Newtonian liquid flow is described. It is based on the Lattice–Boltzmann method for solving the liquid flow and an immersed boundary method for imposing no‐slip at the particle surfaces and providing the distribution of liquid–solid interaction forces over the particle surfaces. These forces—along with contact forces—translate, rotate as well as bend the cylindrical particles. Verification tests have been performed for a single cylinder settling and deforming under gravity at a low Reynolds number. The method has been applied to a clamped flexible cylinder in microchannel flow for which experimental data are available. It then is used to investigate the behavior of hundreds of flexible cylinders with length over diameter aspect ratios of 4 and 6 in a container agitated by an impeller at a Reynolds number of 87 which implies laminar flow. The overall solids volume fraction is 15%. We study the effect of the bending stiffness of the particles on the solids suspension process, on the extent of particle deformation as well as on the torque required to spin the impeller.

Application of Geogrids in Stabilizing Rail Track Substructure

Large-scale direct shear tests were conducted to assess the performance of geogrid-reinforced ballast-subballast interface followed by triaxial tests to explore the deformation and degradation response of geogrid-reinforced ballast under cyclic loading. While the direct shear testing was performed at applied normal stresses (n) ranging from 20 to 100 kPa and rate of shearing (Sr) from 2.5 to 10.0 mm/min, the cyclic triaxial tests were performed to capture the role of loading frequency (f) ranging from 10 to 40 Hz. Fresh granite ballast and subballast with mean particle size (D50) of 42 and 3.5 mm, and five geogrids having different aperture shapes and sizes (A) were used in this study. The tests results indicated that the behavior of ballast-subballast interface is highly influenced by n and Sr. The friction (φ) and dilation angles (ψ) of unreinforced and geogrid-reinforced ballast-subballast interface is found to reduce from 67.96° to 47.82° and 14.56° to 3.34° with the increase in n and Sr. Marsal’s Breakage (Bg: an index to quantify the breakage of ballast) of unreinforced ballast was found to increase from 2.84 to 6.69 % with the increase in n and Sr. However, the inclusion of geogrids significantly enhanced the friction angle (φ), reduced the extent of dilation angle (ψ), and minimized Bg. The interface efficiency factor () and Bg were found to be a function of A/D50 ratio. Accordingly, a model is developed using multiple linear regression analysis to predict the values of φ, ψ and Bg in terms of the input parameters n, Sr and A/D50 ratio. The results from triaxial tests indicate the deformation and degradation behavior of ballast under cyclic loading conditions to be influenced by the loading frequency (f). The extent of ld and Sv of unreinforced ballast increases from 5.48 to 28.32 mm and 20.13 to 45.40 mm with the increase in f. The value of Bg increased from 4.3 to 11.69 % when the value of f was increased from 10 to 40 Hz. Similarly, the extent of lateral and vertical deformation of ballast was found to be a function of A/D50 ratio.