Average Shear Strain Research Articles

Effects of carbonation modification on shear performance of recycled aggregate concrete beams: Test and mechanism analysis

The effective use of recycled aggregates (RAs) in construction significantly contributes to environmental preservation and the conservation of non-renewable natural resources. However, RAs typically exhibit inferior performance relative to natural aggregates (NAs). To improve the quality of RAs, carbonation modification has been introduced as an eco-friendly and practical method. This study explores the shear performance of concrete beams that incorporate various replacement ratios (30 %, 50 %, 70 %, and 100 %) of carbonated recycled aggregates (CRAs). The experiment employed Digital image correlation (DIC) system to evaluate the stress distribution on the concrete surface within the shear span section. The evaluation of shear performance was conducted through comprehensive analysis includes load-deflection curve, steel strain, the width of the primary diagonal crack, average principal tensile strain, orientation of principal directions, average shear strain, and shear deflection. A practical approach was adopted to separate the shear strength contributions of transverse steel (Vs) and concrete (Vc), based on transverse steel strains along the primary diagonal crack. Results indicate that carbonated recycled aggregate concrete (CRAC) beams demonstrate enhanced shear performance in comparison to recycled aggregate concrete beams. Shear strength significantly decreases with replacement rates exceeding 70 %. Furthermore, the experimental results were compared against shear strength with the design codes, and shear deflection with existing models.

Linear static, geometric nonlinear static and buckling analyses of sandwich composite beams based on higher-order refined zigzag theory

This study aims at developing finite element formulations based on higher-order refined zigzag theory (HRZT) to analyze sandwich composite beams under linear static bending, geometric nonlinearity and buckling. In HRZT, the higher-order terms associated with average shear strain and rotation due to zigzag are added based on refined zigzag theory (RZT). In linear static bending analysis, both C0 and C1 elements are developed. For the C0 element, an extra node is used in order to eliminate shear locking. For geometric nonlinear static analysis, the two-node C0 element is developed to solve the bending response with lateral loading and buckling response. The numerical results are compared with those calculated by 2D exact solutions, analytical solutions of HRZT and 2D models using commercial software. Various beam theories such as first-order shear deformation theory (FSDT), higher-order shear deformation theory (HSDT), RZT, and other types of higher-order zigzag theory are also introduced for comparisons. Through comprehensive comparisons with existing works on FEM or zigzag theories, the HRZT beam elements developed in this study exhibit superior accuracy and are free from shear locking in linear static analysis. Furthermore, the study also demonstrates that these elements achieve high accuracy in geometric nonlinear analysis and buckling analysis.

Direction-dependent failure envelopes of sand-structure interfaces with snakeskin-inspired surfaces

Snakeskin-inspired surfaces generate direction-dependent interface strengths, with shearing in the cranial direction (i.e.; against the scales) generating greater strength than in the caudal one (i.e.; along the scales). This directionality is enabled by the transfer of load in friction and passive resistances. It is unclear if failure of these interfaces can be captured by models used for purely frictional interfaces. Interface shear tests complemented with particle image velocimetry (PIV) analyses were performed on snakeskin-inspired surfaces with different asperity geometries and on reference rough and smooth surfaces. The results of experiments performed at different initial effective stresses under constant normal stiffness boundary conditions show significant dilation-induced increases in effective stress. These increases were greater during cranial than caudal shearing, producing greater cranial strengths. These surfaces yielded nonlinear failure envelopes, with greater shear to effective stress ratios at smaller effective stresses, while the rough and smooth surfaces mobilized linear failure envelopes. The PIV analyses indicate that the snakeskin-inspired surfaces induce localized strains in the vicinity of the asperities, leading to wavy failure planes. The average shear strains are correlated with the mobilized shear strengths, with increases in effective stress leading to decreases in both strains and stress ratio.

Effects of hydrothermal alteration on shear localization and weakening in the mantle lithosphere

Hydrothermal alteration occurs in upper-mantle fault zones and significantly modifies the rheological properties of ultramafic rocks. To understand how hydrothermal alteration affects shear localization and the strength of the fault zones, we conducted simple-shear deformation experiments on water-saturated harzburgite (70 wt% olivine +30 wt% orthopyroxene) gouges sandwiched between three types of shear pistons (tungsten, yttria-stabilized zirconia, and corundum) using two deformation-DIA apparatuses at confining pressures of 1–4 GPa, temperatures of 500–580 °C, average shear strain rates of 6.1 × 10−6 s−1 to 1.0 × 10−4 s−1, and water contents of 4–30 wt%. The harzburgitic gouges with water contents of 10 and 30 wt% exhibited steady-state sliding or strain-hardening behavior, and the shear strength of the latter sample was less than one-third of that of the former sample, possibly reflecting the difference in pore fluid pressure. Olivine/orthopyroxene grains exhibit distributed microfracturing and grain rotation towards P foliation, indicating the operation of cataclastic flow. Shear displacement is also accommodated by the development of serpentine- or talc-bearing multiple shear zones including B, R1, and/or Y shears, where intense cataclasis-related grain size reduction and dissolution/precipitation occur. For experimental runs using tungsten and zirconia shear pistons, the serpentine or talc blades that wrap finer-grained and dissolved olivine/orthopyroxene grains form an interconnected network, indicative of frictional sliding or dislocation glide on their basal planes as a dominant deformation mechanism. Raman spectra of the serpentine minerals indicate that they represent antigorite with low crystallinity. These findings suggest that when deep lithospheric fault zones undergo hydrothermal alteration, deformation is controlled by competition between cataclastic flow in olivine/orthopyroxene matrix and slip or glide of antigorite or talc in semi-brittle fault zones, the predominance of which depends on the amount of the hydrous phyllosilicates and the magnitude of pore fluid pressure.

Nanoindentation behaviour simulation of a polycrystalline NiTi shape memory alloy using the crystal plastic finite element method

Polycrystalline NiTi shape memory alloys (SMAs) are inevitably involved in plastic deformation under the action of an external force, thus significantly affecting the mechanical behaviour of materials. To deeply understand the plastic deformation mechanism of the NiTi SMA at 400 ℃, the representative volume element (RVE) model combined with the crystal plastic finite element method and the improved Voronoi algorithm were used to construct a three-dimensional polycrystalline spherical nanoindentation model for studying the contribution of different slip systems to the plastic deformation. The calculation results show that the constructed polycrystalline model can well match the experimental curve of the macroscopic stressstrain response curve of the polycrystalline NiTi SMA; the nanoindentation curve also confirms this result. Based on the constructed 3D polycrystalline nanoindentation model, three slip systems ({110}<100>, {010}<100>and {110}<111>) were introduced at the same time. According to the average cumulative shear strain calculated during the indentation process, the results show that the {110}<111> slip system provides the largest contribution to plastic deformation, and the {010}<100>slip mode provides the smallest contribution. The elastic modulus of the model was calculated using the Oliver-Pharr method, and the calculated results are consistent with the experimental results, which proves the validity of the model.

Investigation on the crystal plasticity of α phase Ti-6Al-4V based on nano-indentation simulation and experiment

Ti-6Al-4V parts are usually hypothesized as isotropic mechanical properties during micro-machining operation. However, the crystal anisotropic mechanical property is an influential factor in the machining of crystals with different sizes and orientations. The hypothesis causes distinct variation in predicting machining force, and consequently the surface integrity cannot be exactly predicted in the micro-machining. Actually, Ti-6Al-4V parts are pseudo isotropy composed of grains with different orientations, elastic modulus, and hardness. Simultaneously, the initiation mode of plastic slip system varies with the grain orientation when the crystal is subjected to an applied load. It is challengeable to evaluate the effect of crystal orientation on its macroscopic properties, either by traditional experimental methods or macroscopic finite element analysis. Nano-indentation provides one novel method to investigate the plastic deformation of selected grains with specific orientations to characterize their mechanical response properties. This research aims to investigate the plastic behavior of α phase Ti-6Al-4V with different orientation grains by means of nano-indentation experiment and crystal plastic finite element method. In the study, single crystals of α phase are classified into “hard grains” (θ < 30°), “soft grains” (θ > 60°) and “normal grains” (30° < θ < 60°) by defining the crystal inclination angle (θ). The elastic modulus and hardness of hard grains are 9% and 28% larger than those of soft grains, respectively. This difference in mechanical properties depends on the slip system that dominates the plastic deformation behavior. The plastic deformation of soft grains is dominated by prismatic slip (48%), while hard grains are accommodated to plastic deformation by basal slip (51%). The average total cumulative shear strain of the soft grains is double that of the hard grains at a maximum load of 10 mN. Meanwhile, the sensitivity analysis is performed to evaluate the effects of the three sets of < a > slip systems and the two sets of < c + a > slip systems on plastic deformation with different grain orientations. The research contributes to the understanding of the plastic deformation mechanism in micro-machining and the exactly predicting the surface integrity generated from micro-machining.

CONTROL OF THE SHEAR STRAIN IN THE HOMOGENIZATION ZONE OF THE DISK EXTRUDER

A simple method for determining the quality of a polymer melt is very important in production. A method that provides simplicity and quick use, making it valuable for optimizing extrusion processes.&#x0D; This work describes how the mixing effect can be improved by changing the velocity fields and thereby changing the shear strain values. The shear strain has been calculated for all four channels of the homogenization zone of a disk extruder. It was found that changing the disk rotation frequency allows changing mean value of the channel shear strain rate from 3324 to 4966 with constant performance for the entire homogenization zone. The impact of the different channels on the mixing effect was evaluated, with the first, second, third, and fourth channels contributing 21%, 57%, 15%, and 7% respectively to the overall homogenization zone's effectiveness of mixing. Additionally, it was found that the second channel experiences the highest shear strain values. In the case of the third channel, although the shear rate values are relatively high, the short residence time of the melt element results in comparatively smaller shear strain values. The average shear strain values remain constant for a given disk speed. It is indicated that it is possible to assess the quality of mixing by the amount of energy supplied, which simplifies the process of determining the quality of the melt, as well as its regulation.

Atomic-scale investigation of Pt composition on deformation mechanism of AuPt alloy during nano-scratching process

In this research, we performed molecular dynamics (MD) simulation to investigate the material removal mechanism and subsurface damage formation during nano-scratching of the gold-platinum (AuPt) alloy. In order to comprehend the deformation mechanism of AuPt alloy during nano-scratching, the influences of Pt composition in workpiece on the machining performance were analyzed. The results indicate that the Pt composition has a significant influence on the surface morphology including piling-up of workpiece atoms and elastic recovery on the machined surface. During the deformation process, the average shear strain of workpiece atoms decreases when the Pt composition increases. Besides, the average scratching force increases apparently with obvious fluctuation as the Pt composition increases. For the subsurface damage formation, typical crystal defects including atomic clusters, V-shape stacking fault couples, and stacking faults tetrahedra were observed in the workpiece subsurface. The lengths of perfect dislocations and Shockley partial dislocations gradually increase as Pt composition increases, while the overall length of sessile dislocations decreases obviously. Meanwhile, thinner stacking faults were formed in the workpiece subsurface as the balanced width of stacking fault gradually decreases when the Pt composition increases. This work contributes to a better understanding of the nanoscale deformation mechanism of bimetallic materials during micro or nano machining process.

The influence of the configurations of multiple-impeller on canrenone bioconversion using resting cells of Aspergillus ochraceus

Abstract 11 α-Hydroxycanrenone is a key intermediate in the synthesis of eplernone which is a drug that protects the cardiovascular system. It can be obtained by microbial transformation of canrenone using Aspergillus ochraceus. The impeller configuration has a great impact on the microbial transformation efficiency. In this study, three kinds of multiple-impeller including six-blade Rushton turbine (lower) and six-blade Rushton turbine (upper) (RT + RT), six-blade Rushton turbine (lower) and six-arrow blade turbine (upper) (RT + ABT), six-blade Rushton turbine impeller (lower) and six-blade Chemineer CD6 impeller (upper) (RT + CD6) were employed to carry out the microbial conversion process, which was investigated by experiments and computational fluid dynamic (CFD) simulations. The CFD simulation was performed only for the hydrodynamic part of the bioreactor in this article. The results showed that RT + CD6 gave better conversion ratio compared to the other two multiple impellers. It had higher axial flow and better air volume fraction distribution which was benefit for the biotransformation process. A certain amount of cell content should be guaranteed in order to obtain a good substrate conversion (45 % approximately). The final conversion ratio of canrenone was proportional to the content of mycelium at the late stage of conversion, while the content of mycelium at the early stage had a subtle effect. Besides, A. ochraceus resting cells could tolerate the maximum and average shear strain rate in the order of 2598 s−1 and 52 s−1, respectively. The research results provided a guide for the selection of impeller for the biotransformation of canrenone in biopharmaceutical industry.

CFD simulation of hydrodynamics and mixing performance in dual shaft eccentric mixers

This work aims to systematically study hydrodynamics and mixing characteristics of non-Newtonian fluid (carboxyl methyl cellulose, CMC) in dual shaft eccentric mixer. Fluid rheology was described by the power law rheological model. Computational fluid dynamics was employed to simulate the velocity field and shear rate inside the stirred tank. The influence mechanism of the rotational modes, height difference between impellers, impeller eccentricities, and impeller types on the flow field have been well investigated. We studied the performance of different dual-shaft eccentric mixers at the constant power input with its fluid velocity profiles, average shear strain rate, mixing time and mixing energy. The counter-rotation mode shows better mixing performance than co-rotation mode, and greater eccentricity can shorten mixing time on the basis of same stirred condition. To intensify the hydrodynamic interaction between impellers and enhance the overall mixing performance of the dual shaft eccentric mixers, it is critical to have a reasonable combination of impellers and an appropriate spatial position of impellers.

Tensile responses of polycrystalline Mo via molecular dynamics simulation: Grain size and temperature effects

Polycrystalline Mo has excellent application prospects in micro-nano devices, and its mechanical properties play an essential role in the application. A series of molecular dynamic (MD) simulations has been executed to investigate the mechanical features of monocrystalline and polycrystalline Mo under tensile loading. The influences of mean grain size from 5.00 to 27.10 nm and temperature in the range of 10–1500 K on mechanical parameters are studied. The findings demonstrate that Young's modulus and yield strength increase with mean grain size. For ultimate tensile strength (UTS), the average grain size of 20.43 nm is an inversion point of the relation between UTS and the reciprocal of the square root of mean grain size d−1/2 at 300K. The average shear strain of polycrystalline Mo is higher than that of monocrystalline due to the existence of grain boundaries (GBs). We also found that the mechanical properties, including Young's modulus, UTS, and yield strength, decrease with the increase of temperature. Monocrystalline Mo is more sensitive to temperature than polycrystalline. At high temperatures above 900 K, the mechanical properties of monocrystalline Mo are lower than these of polycrystalline Mo. The results in the present work will accelerate the industrial application of polycrystalline Mo. Subject areasmaterial science, computational material.

Atomic insights into the size effect of glassy domain on the propagation of plastic deformation carriers in crystal-glass nanocomposite

Crystal-glass nanocomposites with the synergy of high strength and exceptional ductility are promising for future applications in micro-electromechanical systems. Deformation behaviors of crystal-glass nanocomposites are governed by the formation and propagation of their plastic deformation carriers, namely, dislocations in the crystalline phase and strain-activated atomic clusters (e.g., shear transformation zones and shear bands) in the glassy phase. Yet, it is challenging to unveil the size effect of a glassy domain on the propagation of plastic deformation carriers in crystal-glass nanocomposites. To clarify the above issue, in this work, we perform molecular dynamics simulation on simple configurations fabricated by embedding a series of cylinder glass domains with different radii into the single-crystal matrix. Their stress–strain response and microstructures, especially the deformation carriers in the two phases evolving with the applied compressive strain, are quantitively analyzed. The average shear strain of glassy atoms is found to significantly decrease with the increased glassy domain volume, accordingly alleviating the strain localization in the glassy phase. The formation and propagation of strain-activated atomic clusters are also suppressed by enlarging the glassy domain volume due to the lowered shear strains sustained by glassy atoms. Moreover, dislocation densities in the crystalline matrix also decrease in the configuration with a larger-volume glassy domain, which can be ascribed to the enhanced dislocation absorption effect from the amorphous-crystal interfaces. This work indicates that the mechanical properties of multi-phase nanocomposites can be improved by rationally optimizing the phase contents and provides new knowledge on designing high-performance nanocomposites.

Tensile and Compressive Mechanical Properties of Polycrystalline Tungsten–Molybdenum Alloy

To clarify the mechanical performance of word line metal film, molecular dynamics simulations to explore the tensile and compressive responses of W–Mo alloys are utilized. The results reveal that all the mechanical parameters, including Young's modulus, yield strength, flow stress, and platform stress, decrease linearly by about 13–20% with the increase in Mo concentration. The development of the amorphous region and grain boundaries (GBs) dominates the deformation process of W–Mo alloys under tensile and compressive loadings. A large number of body‐centered cubic atoms transforms into amorphous atoms during the loading process. The average shear strain is independent of Mo concentration, and the value of the W50Mo50 sample under tension and compression rises to 1.11 and 1.98, respectively, as the strain increases from 0 to 0.6. In addition, the temperature sensitivity of mechanical features is independent of the concentration of Mo. The results may provide guidance and reference for the industrial application of W–Mo metal films in semiconductor manufacturing.

Atomic study on deformation behaviors of crystal-glass nanocomposite with a typical hierarchical structure

The deformation behaviors of crystal-glass nanocomposites with structural heterogeneities that contain different grain sizes in their crystal phase are studied by using molecular dynamics simulation. Their stress–strain response and microstructures evolved with the applied tensile strain are quantitively analyzed. It is found that the mechanical response of the nanocomposite is sensitive to the average grain size of its crystal phase, and the specimen with the smallest grain size exhibits the highest strength among all. Strain partitioning inevitably occurs between the crystal phase and the glassy domains during the tensile loading, while the average atomic shear strain of the glassy phase is increased with the grain size of the crystal phase. As well, the increased grain size also aggravates the strain localization inside the glassy domains, which promotes the formation of shear transformation zones (STZs) and facilitates the strain heterogeneities there. A mass of lath-like stain paths with severe strain localization are also observed to form in the nanocomposite specimen with a larger grain size, which can function as the transmission medium for delivering the shear strains between different domains and accommodating the plastic flows during the deformation. The present work is aimed to underline that the configuration of structural heterogeneities in the glass-crystal nanocomposite can alter the strain partitioning between different phase domains, which can be used to tune the mechanical performance of the nanocomposite. The unveiled atomistic deformation mechanism of the crystal-glass nanocomposite also provide new sights on designing and optimizing the structural heterogeneities of nanocomposites for achieving better mechanical properties in future.

Using digital image correlation for in situ strain and damage monitoring in hybrid fiber laminates under in‐plane shear loading

AbstractUtilizing resistive strain gauges for V‐notch shear tests in fiber reinforced laminates is usually limited to low strain values due to technical uncertainties imposed by the measurement technique and also the progressive damage development in the notched region of the composite. Therefore, this study investigates an alternative approach by using digital image correlation system and further comparison with resistive strain gauge to identify the effect of heterogenous nature of damage development on measurement results. Moreover, glass/carbon fiber hybrid and non‐hybrid laminates are tested in two major directions through the same approach to determine the effect of stacking sequence in spatial microdamage accumulation. It is shown that tailoring appropriate region of interest for full field strain measurement at various stages of loading enables proper monitoring of microdamage accumulation and thereby delivers a precise stress–strain behavior for hybrid and non‐hybrid laminates. Comparison of the strain maps for hybrid laminates tested in 0° direction, shows that the presence of carbon plies at the surface results in uniform strain distribution between the notches of the test sample. In contrast, a non‐homogeneous strain map with separate regions of high strain gradient are observed for hybrid specimens with glass plies at surface, which can cause underestimation of average shear strain by resistive strain gauges. On the other hand, it is shown that strain maps for hybrid samples tested at 90° configuration is analogous regardless of the stacking sequence, and damage accumulation in these samples is most likely related to relative volume fraction of various fibers in hybrid laminate.

Dynamic response of timber pile ground improvement: 3D numerical simulations

Driven timber displacement piles are being increasingly used to densify and reinforce soils against earthquake-induced ground deformations. However, the role of timber piles to reinforce the soils and redistribute cyclic stresses to timber piles has not been established, despite their excellent flexural properties. This study presents a series of dynamic 3D, linear-elastic, numerical simulations set with the unit cell framework to evaluate the role of the tapered timber pile and design variables such as pile length, spacing and relative density on the amplification and stress redistribution possible with this ground improvement technique. The simulations indicate that the depth-dependent shear strain and shear stress redistribution variously depend on the pile length, spacing, relative density, and input motion frequency. Further, the previously-accepted shear strain compatibility assumption developed for stone columns served to greatly overestimate the magnitude in cyclic shear stress reduction. Due to the tapered pile geometry and the depth-varying soil properties implemented, the accuracy of a recently proposed approach to estimate shear stress redistribution to account for column flexure was found to depend on the flexibility of the composite soil-pile system: longer, more flexible piles and lower relative density were predicted more accurately than shorter, stiffer timber piles with higher relative density. In general, the average shear strain ratio between the improved and unimproved soil is most sensitive to pile length, moderately sensitive to relative density, and least sensitive to pile spacing, and the average ratio of shear stress reduction coefficients is most sensitive to pile spacing, moderately sensitive to pile length, and is least sensitive to relative density.

Evaluating the mechanical performance of asphalt mixtures in cyclic torsional shear test

In this paper, the mechanical performance of asphalt mixtures was examined in cyclic torsional shear test, in which the relationship between the averaged shear strain, γav, and the number of cyclic loading, N, was obtained by using a short, about 25mm height, specimen. In these tests, the effects of some influencing factors such as the type of asphalt mixture, the thickness of specimen and the temperature were examined. In each test, four indices; i.e., the slope of plastic flow line, the slope of stripping line, the number of load applications at the inflection point for stripping and the averaged shear strain at the inflection point for stripping, were defined for the relationship between γav and N. As a result of this study, we clarified that various performances such as rutting resistance, fatigue failure resistance and the stripping resistance of asphalt mixture can be appropriately evaluated by using the cyclic torsional shear test.

The evolution of texture and microstructure uniformity in tantalum sheets during asymmetric cross rolling

The evolution of texture and microstructure uniformity in tantalum (Ta) sheets for sputtering target applications is analyzed in detail across the thickness during asymmetric cross rolling (ACR). Three samples with different strains, i.e. 60%, 70% and 80% are obtained via ACR processing. X-ray diffraction suggests that the increase of strain during ACR results in the randomization of deformation texture across the sample thickness due to the penetration of shear strain into the center. Electron backscatter diffraction results indicate that the increasing strain in ACR can alleviate region-dependent microstructure inhomogeneity. This is also confirmed by the distributions of Vickers hardness and geometrically necessary dislocations. Taylor model analysis along with strain contouring maps suggest that relatively low and centralized number of active slip systems in the 80% sample effectively reduces strain concentrations and thus homogenizes the average shear strain of most active slip system in different grain orientations. Upon annealing, nuclei with random orientations can grow evenly from the deformed matrix in the 80% sample because of relatively homogeneous grain fragmentation and random deformation texture. These contribute to uniform and fine grain size combined with random crystallographic orientations after the completion of recrystallization.

The inflation response of the human lamina cribrosa and sclera: Analysis of deformation and interaction

This study investigated the inflation response of the lamina cribrosa (LC) and adjacent peripapillary sclera (PPS) in post-mortem human eyes with no history of glaucoma. The posterior sclera of 13 human eyes from 7 donors was subjected to controlled pressurization between 5–45 mmHg. A laser-scanning microscope (LSM) was used to image the second harmonic generation (SHG) response of collagen and the two-photon fluorescent (TPF) response of elastin within the volume of the LC and PPS at each pressure. Image volumes were analyzed using digital volume correlation (DVC) to calculate the three-dimensional (3D) deformation field between pressures. The LC exhibited larger radial strain, Err, and maximum principal strain, Emax, (p < 0.0001) and greater posterior displacement (p=0.0007) compared to the PPS between 5–45 mmHg, but had similar average circumferential strain, Eθθ, and maximum shear strain, Γmax. The Emax and Γmax were highest near the LC-PPS interface and lowest in the nasal quadrant of both tissues. Larger LC area was associated with smaller Emax in the peripheral LC and larger Emax in the central LC (p ≤ 0.01). The Emax, Γmax, and Eθθ in the inner PPS increased with increasing strain in adjacent LC regions (p ≤ 0.001). Smaller strains in the PPS were associated with a larger difference in the posterior displacement between the PPS and central LC (p < 0.0001 for Emax and Err), indicating that a stiffer pressure-strain response of the PPS is associated with greater posterior bowing of the LC. Statement of SignificanceGlaucoma causes vision loss through progressive damage of the retinal ganglion axons at the lamina cribrosa (LC), a connective tissue structure that supports the axons as they pass through the eye wall. It is hypothesized that strains caused by intraocular pressure may initiate this damage and that these strains are modulated by the combined deformation of the LC and adjacent peripapillary sclera (PPS). In this study we present a method to measure the pressure-induced 3D displacement and strain field in the LC and PPS simultaneously. Regional strain variation in the LC and PPS was investigated and compared and strains were analyzed for associations with age, LC area, LC strain magnitude, and LC posterior motion relative to the PPS.

Through-thickness patterns of shear strain evolve in early osteoarthritis

Given the structural changes associated with the progression of Osteoarthritis (OA), we hypothesized that patterns of through-thickness, large-strain shear evolve with early-stage OA. We therefore aimed to determine whether and how patterns of shear strains change during early-stage OA to 1) gain insight into the progression of OA by quantifying changes in local deformations; 2) gauge the potential of patterns in shear strain to serve as image-based biomarkers of early-stage OA; and 3) provide high-resolution, through-thickness data for proposing, fitting, and validating constitutive models for cartilage. We completed displacement-driven, large-strain shear tests (5, 10, 15%) on 44 specimens of variably advanced osteoarthritic human articular cartilage as determined by both Osteoarthritis Research Society International (OARSI) grade and PLM-CO score. We recorded the through-thickness deformations with a stereo-camera system and processed these data using digital image correlation (DIC) to determine full-thickness patterns of strains and relative zonal recruitments, i.e., the average shear strain in a through-thickness zone weighted by its relative thickness and normalized by the applied strain. We observed three general shapes for the curves of averaged through-thickness, Green-Lagrange shear strains during progression of OA. We also observed that during the progression of OA only the deep zone is recruited differently under shear in a statistically significant way. We propose that changes in through-thickness patterns of shear strain could provide sensitive biomarkers for early clinical detection of OA. The relative zonal recruitment of the deep zone decreases with progressing OA (OARSI grade) and microstructural remodeling (PLM-CO score), which do not consistently affect recruitment of the superficial and middle zones.