Magnitude Of Strain Research Articles

Modelling the strain build-up in nitrogen implanted tungsten films on silicon substrates

A model of the strain accumulation in nitrogen implanted polycrystalline tungsten films deposited on 110 single-crystalline silicon substrates is presented. The films, with the nominal thickness of 500 nm, were implanted at room temperature, in a direction perpendicular to the sample surface with an energy of 60 keV N2+ ions and concentrations between 0.5 × 1017/cm2 and 5 × 1017/cm2. The proposed model is based on the simulations of the X-ray diffraction 2θ-ω scans in the vicinities of the 110 W most intense Bragg peak. Up to a fluence of 2 × 1017/cm2, the increase of asymmetry towards lower angles of the 110 W peak is interpreted as a linear increase in strain affecting the entire implanted region. Then, the solubility of N in W saturates and phase transition to fcc β-W2N is observed. The phase transition occurs at the surface strain regions of the implanted crystal volume while the lowest strained regions are masked by the β-W2N barrier and even evidence some relaxation. After 3 × 1017/cm2, the strain deduced for the 111 and 200 planes of the fcc β-W2N formed pseudo-layer increases at different rates. While the former comprises a maximum tensile deformation of 3.8 %, the latter is more resilient to nitrogen irradiation developing less than half of the strain magnitude (1.5 %). After 4 × 1017/cm2, Rutherford backscattering spectrometry measurements suggest partial sputtered N while X-ray diffraction indicates no strain-relief at the remaining surface fcc β-W2N. The N concentration derived by the ion beam technique and the combined 110 W/ (111, 200) β-W2N strain profiles as functions of depth agree with the Simulations of Ions and Radiation in Matter theoretical predictions.

Blocking toll-like receptor 4 mitigates static loading induced pro-inflammatory expression in intervertebral disc motion segments

While the anabolic effects of mechanical loading on the intervertebral disc (IVD) have been extensively studied, inflammatory responses to loading have not been as well characterized. Recent studies have highlighted a significant role of innate immune activation, particularly that of toll-like receptors (TLRs), in IVD degeneration. Biological responses of intervertebral disc cells to loading depend on many factors that include magnitude and frequency. The goals of this study were to characterize the inflammatory signaling changes in response to static and dynamic loading of IVD and investigate the contributions of TLR4 signaling in response to mechanical loading. Rat bone-disc-bone motion segments were loaded for 3 hr under a static load (20 % strain, 0 Hz) with or without an additional low-dynamic (4 % dynamic strain, 0.5 Hz) or high-dynamic (8 % dynamic strain, 3 Hz) strain, and results were compared to unloaded controls. Some samples were also loaded with or without TAK-242, an inhibitor of TLR4 signaling. The magnitude of NO release into the loading media (LM) was correlated with the applied frequency and strain magnitudes across different loading groups. Injurious loading profiles, such as static and high-dynamic, significantly increased Tlr4 and Hmgb1 expression while this result was not observed in the more physiologically relevant low-dynamic loading group. TAK-242 co-treatment decreased pro-inflammatory expression in static but not dynamic loaded groups, suggesting that TLR4 plays a direct role in mediating inflammatory responses of IVD to static compression. Overall, the microenvironment induced by dynamic loading diminished the protective effects of the TAK-242, suggesting that TLR4 plays a direct role in mediating inflammatory responses of IVD to static loading injury.

The effect of Mn containing dispersoids on the distribution of slip and fracture mode in Al-Mg-Si-Mn alloys

Improvements in the fracture performance of Al-Mg-Si extrusions are required to meet the demands of the automotive market. The fracture mode and the associated ductility results from competition between transgranular and intergranular fracture paths where intersection of slip bands and grain boundaries plays a significant role. In this study, the distribution of plastic strain within grains for microstructures with different spacings of Mn dispersoids was quantified using high resolution digital image correlation. It was observed that plastic strain was organized into slip bands where the magnitude of local shear strain decreased with reduced inter particle spacing of the dispersoids. It is proposed that this leads to a lower stress concentration on the grain boundary, decreasing the propensity for intergranular fracture. This was consistent with the findings that intergranular fracture was dominant in the dispersoid free material whereas low and high densities of dispersoids gave rise to a transgranular fracture mode.

Large Biaxial Recovered Strains in Self‐Shrinking 3D Shape‐Memory Polymer Parts Programmed via Printing with Application to Improve Cell Seeding

AbstractTrapping of strain in layers deposited during extrusion‐based (fused filament fabrication) 3D printing has previously been documented. If fiber‐level strain trapping can be understood sufficiently and controlled, 3D shape‐memory polymer parts could be simultaneously fabricated and programmed via printing (programming via printing; PvP), thereby achieving precisely controlled 3D‐to‐3D transformations of complex part geometries. Yet, because previous studies have only examined strain trapping in solid printed parts—such as layers or 3D objects with 100% infill—fundamental aspects of the PvP process and the potential for PvP to be applied to printing of porous 3D parts remain poorly understood. This work examines the extent to which strain can be trapped in individual fibers and in fibers that span negative space and the extent to which infill geometry affects the magnitude and recovery of strain trapped in porous PvP‐fabricated 3D parts. Additionally, multiaxial shape change of porous PvP‐fabricated 3D parts are for the first time studied, modeled, and applied in a proof‐of‐concept application. This work demonstrates the feasibility of strain trapping in individual fibers in 1D, 2D, and 3D PvP‐fabricated parts and illustrates the potential for PvP to provide new strategies to address unmet needs in biomedical and other fields.

Spatial Variation in Young Ovine Cortical Bone Properties.

Significant effort continues to be made to understand whether differences exist in the structural, compositional, and mechanical properties of cortical bone subjected to different strain modes or magnitudes. We evaluated juvenile sheep femora (age = 4 months) from the anterior and posterior quadrants at three points along the diaphysis as a model system for variability in loading. Micro-CT scans (50 micron) were used to measure cortical thickness and mineral density. Three point bending tests were performed to measure the flexural modulus, strength, and post-yield displacement. There was no difference in cortical thickness or density between anterior or posterior quadrants; however, density was consistently higher in the middle diaphysis. Interestingly, bending modulus and strength were higher in anterior quadrants compared to posterior quadrants. Together, our results suggest that there is a differential spatial response of bone in terms of elastic bending modulus and mechanical strength. The origins of this difference may lie within the variation in ongoing mineralization, in combination with the collagen-rich plexiform structure, and whether this is related to strain mode remains to be explored. These data suggest that in young ovine cortical bone, modulation of strength occurs via potentially complex interactions of both mineral and collagen-components that may be different in regions of bone exposed to variable amounts of strain. Further work is needed to confirm the physiological load state of bone during growth to better elucidate the degree to which these variations are a function of the local mechanical environment.

Mechanochemical induction of nuclear condensates during cell confined migration.

Cell movement through small constrictions is important in many physiological and disease contexts, such as in cancer metastasis. Such migration is rate-limited by squeezing the cell nucleus through the constriction, with associated deformation of the nuclear lamina and chromatin. However, other subnuclear structures are similarly deformed, including membraneless nuclear bodies or condensates, where the impact of cell mechanics on their formation by liquid-liquid phase separation is largely unknown. Here we investigate the response of chromatin-embedded nuclear condensates under mechanical stress using a microfluidic device. We find that the DNA damage response protein 53BP1 undergoes a switch in phase behavior at the rear of migrating breast cancer cell nucleus, independent of DNA damage response. Interestingly, confined migration does not induce nuclear condensation of phase-separated prone FET family proteins. We hypothesize that 53BP1 and potentially other nuclear condensates can sense mechanical stimuli by changing their phase behavior, which is thereby closely coupled to the heterogeneity of the chromatin network they are embedded in. By quantitatively mapping the displacement field of chromatin, we found that chromatin forms spatially distinct domains of correlated motions as well as different strain magnitudes. Our finding highlights the mechanical interplay between nuclear condensates and chromatin under physiological deformations, and suggests the potential role of LLPS in mechanochemical transduction.

Residual strain orientation in rolled titanium determined with synchrotron X-ray Laue microdiffraction

Previously, synchrotron X-ray Laue microdiffraction has been used to measure the magnitudes of residual strain in materials. Recently the method was advanced to determine the orientation of the strain ellipsoid and applied to naturally deformed quartzites; however, the deformation history of these quartzites is ambiguous due to their natural origin. In this study, synchrotron X-ray Laue microdiffraction (µXRD) is used to measure the residual strain for the first time in a sample with known stress history, rolled titanium. A deviatoric strain tensor is calculated from each Laue diffraction image collected with two µXRD scans of a rolled titanium sheet in different sample orientations. The principal strain axes are calculated using an eigen decomposition of the deviatoric strain tensors. The results show that the principal axis of compression is aligned with the normal direction of the titanium sheet, and the principal axis of extension is aligned with the rolling direction. Pole figures are used to represent the 3D distribution of residual strain axes.

A Novel Multiresonant Chipless RFID Tag for Directional Strain Measurement on Metal Surface

In this article, a radio frequency identification (RFID) sensor tag for real-time health monitoring of the magnitude and direction of metal surface strain is presented. The chipless RFID sensor tag is composed of metal foil and F4B substrate, which is low-cost and works stably in harsh environments for a long time. Through highly sensitive strain monitoring, the risk can be predicted in the early stage of defect generation. The proposed tag includes a C-type resonator array, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> -type transmission line, and tag antennas. The C-type resonator has different sensitivities in the electrical length direction and width direction. Then, based on this characteristic, the resonator array creates a plurality of characteristic signatures containing strain information by optimizing the geometric parameters of the resonators. The strain information is transmitted to the tag antenna through the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> -type transmission line to complete the wireless communication between the tag and the reader. Finally, the performance of the strain monitoring system is verified by an experimental study. The experiment shows that the average sensitivity of the resonators is −4.94 and 1.14 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> in the electric length and width directions, respectively. When the strain is more than 150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> , the relative error of magnitude is less than 12.7% and the absolute error of direction is less than 13.3°. Therefore, the proposed chipless RFID tag can monitor the amplitude and direction of strain with higher sensitivity and a simpler structure, for the key structures, such as the high-speed running gear.

Localized strain characterization of cardiomyopathy in Duchenne muscular dystrophy using novel 4D kinematic analysis of cine cardiovascular magnetic resonance

BackgroundCardiomyopathy (CMP) is the most common cause of mortality in Duchenne muscular dystrophy (DMD), though the age of onset and clinical progression vary. We applied a novel 4D (3D + time) strain analysis method using cine cardiovascular magnetic resonance (CMR) imaging data to determine if localized strain metrics derived from 4D image analysis would be sensitive and specific for characterizing DMD CMP. MethodsWe analyzed short-axis cine CMR image stacks from 43 DMD patients (median age: 12.23 yrs [10.6–16.5]; [interquartile range]) and 25 male healthy controls (median age: 16.2 yrs [13.3–20.7]). A subset of 25 male DMD patients age-matched to the controls (median age: 15.7 yrs [14.0-17.8]) was used for comparative metrics. CMR images were compiled into 4D sequences for feature-tracking strain analysis using custom-built software. Unpaired t-test and receiver operator characteristic area under the curve (AUC) analysis were used to determine statistical significance. Spearman's rho was used to determine correlation. ResultsDMD patients had a range of CMP severity: 15 (35% of total) had left ventricular ejection fraction (LVEF) > 55% with no findings of myocardial late gadolinium enhancement (LGE), 15 (35%) had findings of LGE with LVEF > 55% and 13 (30%) had LGE with LVEF < 55%. The magnitude of the peak basal circumferential strain, basal radial strain, and basal surface area strain were all significantly decreased in DMD patients relative to healthy controls (p < 0.001) with AUC values of 0.80, 0.89, and 0.84 respectively for peak strain and 0.96, 0.91, and 0.98 respectively for systolic strain rate. Peak basal radial strain, basal radial systolic strain rate, and basal circumferential systolic strain rate magnitude values were also significantly decreased in mild CMP (No LGE, LVEF > 55%) compared to a healthy control group (p< 0.001 for all). Surface area strain significantly correlated with LVEF and extracellular volume (ECV) respectively in the basal (rho = − 0.45, 0.40), mid (rho = − 0.46, 0.46), and apical (rho = − 0.42, 0.47) regions. ConclusionStrain analysis of 3D cine CMR images in DMD CMP patients generates localized kinematic parameters that strongly differentiate disease from control and correlate with LVEF and ECV.

Experimental study on strain field evolution around a simulated thrust fault

Earthquakes result from continuous geodynamic processes. A topic of significant interest for the scientific community is to elaborate on the phenomena governing the faulting and fracturing of crustal rocks. Therefore, in this study, uniaxial compressive shear failure experiments were conducted on Fangshan marble rock samples with a prefabricated slot to simulate thrust faulting. The center of each marble plate (105 mm × 80 mm × 5 mm) was engraved with a 30-mm long double-sided nonpenetrating slot (depth: 2 mm, width: 0.5 mm). The deformation and destruction processes of the rock surface were recorded using a high-speed camera. The digital image correlation method was used to calculate the displacement and strain distribution and variation at different loading stages. The accumulative and incremental displacement fields u and v, strain field ex and ey, and shear strain exy were analyzed. When the loading level reached its ultimate value, the strain field was concentrated around the prefabricated slot. The concentration reached a maximum at the ends of the prefabricated slot. The magnitude of shear strain reached 0.1. This experiment contributes to our understanding of the dynamic process of active faulting.

Assessment of the mechanical role of cranial sutures in the mammalian skull: Computational biomechanical modelling of the rat skull.

Cranial sutures are fibrocellular joints between the skull bones that are progressively replaced with bone throughout ontogeny, facilitating growth and cranial shape change. This transition from soft tissue to bone is reflected in the biomechanical properties of the craniofacial complex. However, the mechanical significance of cranial sutures has only been explored at a few localised areas within the mammalian skull, and as such our understanding of suture function in overall skull biomechanics is still limited. Here, we sought to determine how the overall strain environment is affected by the complex network of cranial sutures in the mammal skull. We combined two computational biomechanical methods, multibody dynamics analysis and finite element analysis, to simulate biting in a rat skull and compared models with and without cranial sutures. Our results show that including complex sutures in the rat model does not substantially change overall strain gradients across the cranium, particularly strain magnitudes in the bones overlying the brain. However, local variations in strain magnitudes and patterns can be observed in areas close to the sutures. These results show that, during feeding, sutures may be more important in some regions than others. Sutures should therefore be included in models that require accurate local strain magnitudes and patterns of cranial strain, particularly if models are developed for analysis of specific regions, such as the temporomandibular joint or zygomatic arch. Our results suggest that, for mammalian skulls, cranial sutures might be more important for allowing brain expansion during growth than redistributing biting loads across the cranium in adults.

An elastic-plastic kinking layer model for parallel-to-grain wood embedment behavior considering wood drilling damage

This paper presents the results of the experimental and numerical studies on the influence of drilling damage of wood on the wood embedment behavior. Wood drilling tests were conducted to quantify the distribution of wood residual strain by use of digital image correlation technique. Parallel to wood grain repetitive compression tests were also conducted to determine the mechanical properties of wood within the kinking zone. Wood half-hole bolt embedment tests were conducted, and a wood kinking layer model was proposed and incorporated into a FEM model for the wood embedment behavior simulation. The model predictions were compared with the embedment test results and results from FEM models with different consideration of the weakened wood around the bolt holes. It was found that drilling can develop significant parallel and perpendicular to grain and shear residual strain in the surrounding wood. The distribution and magnitude of the residual strains were correlated with the hole diameter and drilling speed, and the thickness of a kinking layer can be taken as 1/13 and 1/7 of the hole diameter under the low and high drilling speeds considered in this study, respectively. It was observed from the repetitive tests of wood that during the steady-state kinking process, wood exhibited nearly constant peak stress and reloading modulus of elasticity. The FEM model with the proposed kinking layer model achieved a better agreement with the test results than FEM models based on wood foundation theory or a nonlinear contact model regarding the embedment elastic modulus, the maximum load, and the distribution of the strain in the embedment zone.

A Distributional Model of Bound Ligand Conformational Strain: From Small Molecules up to Large Peptidic Macrocycles.

The internal conformational strain incurred by ligands upon binding a target site has a critical impact on binding affinity, and expectations about the magnitude of ligand strain guide conformational search protocols. Estimates for bound ligand strain begin with modeled ligand atomic coordinates from X-ray co-crystal structures. By deriving low-energy conformational ensembles to fit X-ray diffraction data, calculated strain energies are substantially reduced compared with prior approaches. We show that the distribution of expected global strain energy values is dependent on molecular size in a superlinear manner. The distribution of strain energy follows a rectified normal distribution whose mean and variance are related to conformational complexity. The modeled strain distribution closely matches calculated strain values from experimental data comprising over 3000 protein-ligand complexes. The distributional model has direct implications for conformational search protocols as well as for directions in molecular design.

Damage amplification during repetitive seismic waves in mechanically loaded rocks

Cycles of stress build-up and release are inherent to tectonically active planets. Such stress oscillations impart strain and damage, prompting mechanically loaded rocks and materials to fail. Here, we investigate, under uniaxial conditions, damage accumulation and weakening caused by time-dependent creep (at 60, 65, and 70% of the rocks’ expected failure stress) and repeating stress oscillations (of ± 2.5, 5.0 or 7.5% of the creep load), simulating earthquakes at a shaking frequency of ~ 1.3 Hz in volcanic rocks. The results show that stress oscillations impart more damage than constant loads, occasionally prompting sample failure. The magnitudes of the creep stresses and stress oscillations correlate with the mechanical responses of our porphyritic andesites, implicating progressive microcracking as the cause of permanent inelastic strain. Microstructural investigation reveals longer fractures and higher fracture density in the post-experimental rock. We deconvolve the inelastic strain signal caused by creep deformation to quantify the amount of damage imparted by each individual oscillation event, showing that the magnitude of strain is generally largest with the first few oscillations; in instances where pre-existing damage and/or the oscillations’ amplitude favour the coalescence of micro-cracks towards system scale failure, the strain signal recorded shows a sharp increase as the number of oscillations increases, regardless of the creep condition. We conclude that repetitive stress oscillations during earthquakes can amplify the amount of damage in otherwise mechanically loaded materials, thus accentuating their weakening, a process that may affect natural or engineered structures. We specifically discuss volcanic scenarios without wholesale failure, where stress oscillations may generate damage, which could, for example, alter pore fluid pathways, modify stress distribution and affect future vulnerability to rupture and associated hazards.

Fluid flow migration, rock stress and deformation due to a crustal fault slip in a geothermal system: A poro-elasto-plastic perspective

Geothermal systems are commonly genetically and spatially associated with volcanic complexes, which in turn, are located nearby crustal fault systems. Faults can alter fluid flow in their surroundings, potentially acting as barriers or conduits for fluids, depending on their architecture and slip-rate. However, this fundamental control on fluid migration is still poorly constrained. Most previous modeling efforts on volcanic and hydrothermal processes consider either only fluid flow in their formulations, or only a mechanical approach, and seldom a full, monolithic coupling between both. In this work, we present a poro-elasto-plastic Finite Element Method (FEM) to address the first-order, time-dependent control that a strike-slip crustal fault exerts on a nearby geothermal reservoir. For the model setting, we selected the Planchón-Peteroa geothermal system in the Southern Andes Volcanic Zone (SAVZ), for which the geometry and kinematics of a potentially seismogenic fault and fluid reservoir is constrained from previous geological and geophysical studies. We assess the emergence and diffusion of fluid pressure domains due to fault slip, as well as the development of tensile/dilational and compressive/contractional domains in the fault' surroundings. Mean stress and volumetric strain magnitudes in these domains range between ±1 [MPa] and ±10−4 [-], respectively. Our results show the appearance of negative and positive fluid pressure domains in these dilational and contractional regions, respectively. We also investigate the spatial and temporal evolution of such domains resulting from changes in fault permeability and shear modulus, fluid viscosity, and rock rheology. These variations in fluid pressure alter the trajectory of the reservoir fluids, increasing migration to the eastern half of the fault, reaching a maximum fluid flux of 8 to 70 times the stationary flux. Pressure-driven fluid diffusion over time causes fluid flow to return to the stationary state between weeks to months after fault slip. These results suggest that the mechanism that exerts a first-order control is similar to a suction pump, whose duration heavily depends on fault permeability and fluid viscosity. We also show how a von Mises plasticity criterion locally enhances fluid flow. The transient process analyzed in this work highlights the importance of addressing the solid-fluid coupling in numerical models for volcano-tectonic studies.

Effect of Scanning Strategy on Thermal Stresses and Strains during Electron Beam Melting of Inconel 625: Experiment and Simulation.

This paper develops a hybrid experimental/simulation method for the first time to assess the thermal stresses generated during electron beam melting (EBM) at high temperatures. The bending and rupture of trusses supporting Inconel 625 alloy panels at ~1050 °C are experimentally measured for various scanning strategies. The generated thermal stresses and strains are thereafter simulated using the Finite-Element Method (FEM). It is shown that the thermal stresses on the trusses may reach the material UTS without causing failure. Failure is only reached after the part experiences a certain magnitude of plastic strain (~0.33 ± 0.01 here). As the most influential factor, the plastic strain increases with the scanning length. In addition, it is shown that continuous scanning is necessary since the interrupted chessboard strategy induces cracking at the overlapping regions. Therefore, the associated thermal deformation is to be minimized using a proper layer rotation according to the part length. Although this is similar to the literature reported for selective laser melting (SLM), the effect of scanning pattern is found to differ, as no significant difference in thermal stresses/strains is observed between bidirectional and unidirectional patterns from EBM.

Розклинювання підінтерфейсної тріщини пластичним наплавленням

The model problem of tension of a two-layer cylinder with an annular subcladding crack located at the base material of the cylinder is considered. It is assume that the base material of the cylinder is linear elastic. The cladding of the cylinder is considered as elastic-plastic with bilinear strengthening. The base material of the cylinder is considered to be linear-elastic, the cladding is considered to be elastic-plastic with bilinear strengthening. The dependence of the stress intensity factor on the internal crack front on the value of the tension stresses and the magnitude of the residual strains in the cladding is investigated. The problem was solved numerically using the finite element method. It was established that the plastic zone in cladding does not develop in the direction of crack extension, but at some angle to it. A preliminary analysis of the stress state in the absence of a crack made it possible to explain this phenomenon, as well as some other regularities obtained in the numerical results. The conclusions presented in the work can be useful in evaluating of the crack resistance of equipment and pipes with anti-corrosion cladding.

Comparative evaluation of variations in torque expression in maxillary incisor and canine using different bracket prescriptions placed at different crown levels by finite element (FE) method: An in-vitro analysis.

While using preadjusted brackets, the position of the bracket on the crown is one of the deciding factors that determine the tooth's final tip, torque, height, and rotation. The final tooth position is not optimal if the bracket is placed incorrectly or if the varying crown morphology does not correspond with the bracket design. The present study was conducted to evaluate and compare the variations in torque expression in maxillary incisor and canine using different bracket prescriptions placed at different crown levels by finite element method. For the present study, three-dimensional models of maxillary right central incisor and canine were made using CREO version 4.0 software. CREO is a powerful three-dimensional (3-D) computer-based, computer-aided design (CAD) software developed by Parametric Technology Corporation (PTC) to aid in design processes. Simulation was done to replicate the clinical situation of an active palatal root torque acting on the incisor and canine. The induced palatal movement of root tips and labial movement of crowns tips, overall stress, and von Mises stress generated in the brackets and the total equivalent strains developed in the periodontal ligament (PDL) were calculated, while the values obtained were tabulated and subjected to statistical analysis. Based on the findings of the present study, the average maximum stress produced in the bracket was calculated as 265.069 Mpa in incisor and 166.742 Mpa in the canine. Likewise, the average of the maximum displacement of root apex observed in the present study was calculated as 0.01401 mm in the incisor and 0.00421 mm in the canine, while the average strain developed in the PDL was calculated as 0.0587 for incisor and 0.0498 for the canine. Furthermore, it was, also, observed that the magnitude of strain developed in the PDL increased with increase in the stress produced by the bracket prescription for both incisor and canine. Within the limitations of the present study, it was concluded that the magnitude of displacement of root apex was significantly influenced by bracket prescription and bracket position. Also, the stress developed in the bracket was influenced by bracket prescription and position, while the variation in crown morphology in the incisor and canine played a significant role in the eventual strain developed in the PDL after torque application.

Micromechanical aspects of the effect of temperature and local plastic strain magnitude on the fracture toughness of ferrite steels

The paper shows that the influence of plastic strain and temperature on the rate of crack nuclei (CN) formation is a crucial factor controlling the shape of the temperature dependence of fracture toughness and its scatter limits. Within the framework of the microscopic model described, it is explained that the dependence of the incompatibility of microplastic deformation at grain boundaries or interfaces on the value of plastic strain and temperature is the reason for the effect of these factors on the rate of CN formation. The dependencies of the CN bulk density on temperature and plastic strain are given. In the latter case, a non-monotonic change in CN density is observed. The maximum intensity of CN formation is observed when the critical value of plastic strain is reached. For ferritic structural steels, this strain is about 2%. Using reactor pressure vessel steel and cast manganese steel as examples, it is shown that not taking these effects into account in the local fracture approach leads to considerable errors in the prediction of the temperature dependence of the fracture toughness and its scatter limits.

Age-, Sex-, and Race-Based Normal Values for Left Ventricular Circumferential Strain from the World Alliance Societies of Echocardiography Study

Left ventricular (LV) circumferential strain has received less attention than longitudinal deformation, which has recently become part of routine clinical practice. Among other reasons, this is because of the lack of established normal values. Accordingly, we aimed to establish normative values for LV circumferential strain and determine sex-, age- and race-related differences in a large cohort of healthy adults. Complete 2D transthoracic echocardiograms were obtained in 1572 healthy subjects (51% male), enrolled in the World Alliance of Societies of Echocardiography (WASE) Study. Subjects were divided into 3 age groups (<35, 35-55, >55 years) and stratified by sex and by race. Vendor-independent semi-automated speckle tracking software was used to determine LV regional and global circumferential strain (GCS) values. Limits of normal for each measurement were defined as 95% of the corresponding sex and age group falling between the 2.5th and 97.5th percentiles. Intergroup differences were analyzed using unpaired t-tests. Circumferential strain showed a gradient, with lower magnitude at the mitral valve level, increasing progressively towards the apex. Compared to men, women had statistically higher magnitude of regional and global strain. Older age was associated with a stepwise increase in GCS despite an unaffected EF, a decrease in LV volume and a relatively stable GLS in men with a small gradual decrease in women. Asian subjects demonstrated significantly higher GCS magnitudes than whites of both sexes and blacks in women only. In contrast, no significant differences in GCS were found between white and black subjects of either sex. Importantly, despite statistical significance of the above differences across sex-, age- and races, circumferential strain values were similar in all groups, with variations of the order of magnitude of 1-2%. Notably, no differences in GCS were found between brands of imaging equipment. This study established normal values of LV regional and global circumferential strain, and identified sex-, age- and race-related differences, where present.