Isotropic Compressive Stress Research Articles

Hydrostatic pressure drives sprouting angiogenesis via adherens junction remodelling and YAP signalling

Endothelial cell physiology is governed by its unique microenvironment at the interface between blood and tissue. A major contributor to the endothelial biophysical environment is blood hydrostatic pressure, which in mechanical terms applies isotropic compressive stress on the cells. While other mechanical factors, such as shear stress and circumferential stretch, have been extensively studied, little is known about the role of hydrostatic pressure in the regulation of endothelial cell behavior. Here we show that hydrostatic pressure triggers partial and transient endothelial-to-mesenchymal transition in endothelial monolayers of different vascular beds. Values mimicking microvascular pressure environments promote proliferative and migratory behavior and impair barrier properties that are characteristic of a mesenchymal transition, resulting in increased sprouting angiogenesis in 3D organotypic model systems ex vivo and in vitro. Mechanistically, this response is linked to differential cadherin expression at the adherens junctions, and to an increased YAP expression, nuclear localization, and transcriptional activity. Inhibition of YAP transcriptional activity prevents pressure-induced sprouting angiogenesis. Together, this work establishes hydrostatic pressure as a key modulator of endothelial homeostasis and as a crucial component of the endothelial mechanical niche.

Ultrafine-grained microstructure and controllable magnetic domains in Fe-based nanocrystalline alloys with excellent magnetic properties induced by hot isostatic pressing

The coarsening and inhomogeneous distribution of nano-grains caused by traditional heat treatment processes are the biggest obstacles for obtaining ultrahigh permeability and excellent comprehensive soft magnetic properties in Fe-based nanocrystalline alloys. Here, we propose a new strategy to control grain growth and magnetic anisotropy, by introducing isotropic compressive stress field in the annealing process to optimize the magnetic properties. Compared with conventional isothermal annealing, the coupling of stress-temperature field generated by hot isostatic pressing (HIP) induced the microstructure, magnetic domain evolution and magnetic properties in Si-rich Fe73.5Si15.5B7Nb3Cu1 amorphous ribbons have been systematically investigated. We demonstrate that HIP treatment promotes more Si atoms to dissolve in Fe unit cell to form Fe(Si) solid solution causing an increase in interplanar spacing. Also, the high-density Cu clusters precipitate in the amorphous matrix upon HIP serving as nucleation sites for α-Fe(Si) grains, which facilitate a high volume fraction, uniform and ultrafine-grained microstructure. Moreover, the existence of stress field introduces induced anisotropy effectively controls the magnetization mechanism and magnetic structure evolution. Furthermore, the Fe73.5Si15.5B7Nb3Cu1 nanocrystalline alloy treated by HIP exhibit excellent comprehensive magnetic properties, such as high Ms, high μe, low Pcv, low AC Hc and high Br/Bm.

A new gradient elasticity model for the elastic boreholes

A new gradient elasticity model is employed to discuss strain gradient effects and its ability in predicting size effects on an elastic rock mass with microstructure, around an axisymmetric borehole under internal pressure and remote isotropic compressive stress. The constitutive equation of the model involves the Laplacian of the strain tensor multiplied by the gradient coefficient. The formulated boundary value problem is solved analytically to derive stress, strain, and displacement distributions and discuss respective gradient effects on the mechanical behavior of the rock mass and the corresponding borehole stability. The paper concludes with the employment of the Rankine failure criterion to investigate size effects on the stress concentration factor at the perimeter of the borehole, and the comparison with another gradient elasticity model which involves the Laplacian of the hydrostatic part of the strain tensor.

INFLUENCE OF CRACK DENSITY ON THE HYDRO-MECHANICAL BEHAVIOR OF A HORIZONTAL BOREHOLE UNDER ISOTROPIC COMPRESSIVE STRESS

The excavation of boreholes induces a damage zone in the vicinity of the boreholes, and thereby affects the hydro-mechanical properties of the rock mass surrounding. This paper outlines analytical models of effective permeability and moduli of the porous rock containing a randomly crack distribution, which is an explicit function of the dimensionless crack density, crack conductivity, crack length and matrix permeability. These proposed models are then introduced into a finite element open source code, Code_Aster, to study hydro-mechanical responses of the medium around a horizontal borehole under isotropic far-field compressive stress for different cases of crack density. The results showed that the crack density changes the effective permeability and moduli and therefore under isotropic compressive stress it influences significantly the behavior of the borehole.

A Capillary Controlled Hydrogel Microchannel for Isotropic Compressive Stress Quantification

A Capillary Controlled Hydrogel Microchannel for Isotropic Compressive Stress Quantification

Surface mechanical properties of shot-peened CNT/Al–Mg–Si alloy composites

A carbon nanotube (CNT)-reinforced Al matrix composite was fabricated and treated by shot peening. After shot peening, isotropic compressive residual stress fields were induced in surface shot-peened layers. As the mechanical properties of the peened layers were improved and therefore varied from the base metal, a specific in-situ X-ray stress analyzer combined with the tensile test technique was used to measure the stress–strain relationship of the strengthened surface layer. On the basis of the measurement and the Von Mises stress criterion, the surface yield strength was calculated and improved by 25% relative to that of the matrix. Moreover, a relaxation behavior of compressive residual stress was observed under cyclic loading. The results showed that the rapid relaxation of surface residual stress chiefly occurred in the first few cycles and then stabilized gradually in subsequent cycles. The retained residual stress under all given applied cyclic loadings possibly occurred in the compressive state consistently.

Effect of water imbibition on hydration induced fracture and permeability of shale cores

During a hydraulic fracturing operation with water-based fracturing fluids, in-situ compressive stress was applied on shale. To study whether or not hydration induced fracture can be created to improve oil and gas recovery under isotropic compressive stress conditions, time-elapsed computerized tomography (CT) was used to obtain cross section images of shale cores with confining pressures loaded. Based on CT data, cut faces parallel to the core axial through the middle of core and 3D fracture images were reconstructed. To study the effects of hydration on shale pore fluid flowing under isotropic compressive stress conditions, shale permeability was measured with Nitrogen (N2), distilled water, 4% KCl solution, and 8% KCl solution. Hydration induced fractures came into being for Mancos shale with low confining pressure (15 psi) loaded. However, with high confining pressure (3000 psi) loaded, fractures tended to close eventually due to hydration. For the Eagleford shale, with either a low or a high confining pressure loaded, fractures eventually became nearly closed. In the Mancos shale which contained more swelling clay minerals, larger reduction of fracture apertures or permeability was observed than that in the Eagleford shale with confining pressure applied. Adding KCl into the water-based fracturing fluid during fracturing could decrease shale hydration and reduce shale permeability damage. Our study shows that 8% KCl solution could help reduce the permeability damage of Mancos shale, and 4% KCl solution was feasible to reduce the permeability damage of the Eagleford shale under isotropic compressive stress conditions.

IMPURITY INDUCED WRINKLING PATTERNS IN METAL FILMS DEPOSITED ON SOFT ELASTIC SUBSTRATES

Metal (iron and nickel) films have been deposited on soft elastic polydimethylsiloxane (PDMS) substrates by direct current sputtering technique and the impurity induced wrinkling patterns are investigated by using optical microscopy and atomic force microscopy. It is found that the metal films can spontaneously form disordered wrinkles due to the isotropic compressive stress. In the vicinity of film impurities such as extraneous particles, linear defects, cracks and thickness-gradient film edges, the stress field becomes anisotropic owing to symmetry breaking and thus complex wrinkling patterns including straight stripes, herringbones, crossings, labyrinths and their transitions can be observed. The morphological evolutions, structural characteristics and physical mechanisms of the impurity induced wrinkles have been discussed and analyzed based on the continuum elastic theory.

Stretching ferroelectrics from within

Ferroelectrics Squeezing or stretching ferroelectric materials can strongly affect their properties. Although it is relatively easy to apply isotropic compressive stress, tensile stress is trickier. Wang et al. have found a way to do that in nanowires made out of the ferroelectric PbTiO3. The wires initially had a tetragonal structure, but when they were exposed to air and high temperatures, they transformed into the so-called perovskite phase, which is much denser. The densification progressed from the surface of the wires inward, inflicting tensile stress and causing voids to form inside the wires. For a narrow range of wire diameters, this resulted in a deformation along the polarization axis and the enhancement of ferroelectric properties. Nat. Mat. 10.1038/nmat4365 (2015).

Effective Masses and Electronic and Optical Properties of Nontoxic MASnX3 (X = Cl, Br, and I) Perovskite Structures as Solar Cell Absorber: A Theoretical Study Using HSE06

We calculated the effective masses and electronic and optical properties of CH3NH3SnX3 (X = Cl, Br, I) perovskites as a solar cell absorber using the HSE06 hybrid functional. The computed band gaps are direct at the Γ point, ranging from 1.67 to 3.0 eV. The effective masses of carriers and the band gaps decrease from chlorine to iodine. Moreover, their hole masses are comparable to those of CH3NH3PbX3 (X = Br and I) phases. The optical dielectric constant does not decrease monotonically when going from X = Cl to Br to I for CH3NH3SnX3 perovskites. Under a small isotropic compressive stress, the photon absorption efficiency of CH3NH3SnX3 perovskites is slightly improved due to the reduction of the fundamental band gap.

The interrelation between microfibril angle (MFA) and hygrothermal recovery (HTR) in compression wood and normal wood of Sugi and Agathis

Abstract Tree growth stress (GS) consists of an elastic component and a viscoelastic locked-in component. The elastic component is released instantaneously by cutting wood, whereas the locked-in component remains. The latter can be released by hot water treatment, which is known as hygrothermal recovery (HTR). In this paper the mechanism behind HTR is described and interpreted in terms of the microfibril angle (MFA) in the cell wall as follows: during cell-wall maturation, axial tensile stress is generated in the cellulose microfibrils (CMF), whereas isotropic compressive stress is generated in the matrix of lignin-hemicellulose (MT). Some amount of microscopic stresses remains following the removal of the wood from the living stem. Hygrothermal (HT) treatment induces recovery of remaining compressive stress in the MT, which causes its expansion. Axial tensile stress in the CMF are released by HT softening of the MT. This causes the CMF to contract along its length and to expand laterally. The combined effect of the expansions of the MT and contraction of the CMF causes the wood to deform anisotropically. This is the HTR of wood. The degree of anisotropy is determined by the MFA on the basis of reinforced-matrix theory.

Direct observation of an anisotropic in-plane residual stress induced by B addition as an origin of high magnetic anisotropy field of Ru/FeCoB film

Although boron-free FeCo films prepared on a Ru underlayer exhibits isotropic in-plane magnetic property, boron added FeCoB films prepared on Ru underlayer revealed large in-plane magnetic anisotropy with a high anisotropy field of 500 Oe. The effect of boron addition on the in-plane anisotropic residual stress in FeCoB film was investigated using sin2 ψ method of x-ray diffraction analysis. Large isotropic compressive stress was observed in Ru/FeCo film. In contrast, anisotropic in-plane residual stress was observed in Ru/FeCoB film. The compressive stress along the easy axis of Ru/FeCoB film is released more than that along the hard axis. Such anisotropic residual stress is regarded as an origin of the in-plane magnetic anisotropy through inverse magnetostriction effect. Owing to the configuration of the facing targets sputtering system, boron atoms are sputtered and deposited anisotropically, and so they penetrate FeCo crystals and release the compressive stress along the incidence direction.

Stress localization and strength optimization of frame material with periodic microstructure

Stress localization for an elastic material with periodic microstructure is applied to the optimal design of rigid-jointed cellular material. The discretized form of localization was published some 20 years ago but was primarily used for strain localization (and stiffness homogenization). The stress localization aspect did not receive much attention in the past and even more so for materials modeled as rigid- or pin-jointed lattices. With the present minimization of the maximum local stress under a macroscopic stress state efficient stress localization was a major concern and it has therefore received due consideration in this paper. A ground-structure approach was used for the optimal design where in addition to topological variables for the unit cell geometric variables determine the coordinates of two internal nodes and the overall shape of the representative volume element. In a first instance the material was subjected to a uniaxial and a pure shear macroscopic state of stress of arbitrary orientation. Three regular shapes emerged from the optimization: a square crossed by diagonals, an equilateral triangle and the Kagomé. The three figures, which exhibit predominant axial modes with no significant bending, have very similar strengths. In a second example the ground-structure was subjected to a transversely isotropic macroscopic tensile stress and to a transversely isotropic macroscopic compressive stress. The design space had a plethora of optimal configurations of same maximum strength. It is shown that these optimal designs, although anisotropic, expand isotropically under isotropic stresses and reach the Hashin–Shtrikman upper bounds for the bulk modulus of isotropic materials in the low density range. In the compressive case, slender elements were eliminated by the Euler buckling constraint and bulkier optimal patterns were obtained.

Force distributions in a triangular lattice of rigid bars

We study the uniformly weighted ensemble of force balanced configurations on a triangular network of nontensile contact forces. For periodic boundary conditions corresponding to isotropic compressive stress, we find that the probability distribution for single-contact forces decays faster than exponentially. This superexponential decay persists in lattices diluted to the rigidity percolation threshold. On the other hand, for anisotropic imposed stresses, a broader tail emerges in the force distribution, becoming a pure exponential in the limit of infinite lattice size and infinitely strong anisotropy.

Plane cracks with frictionally constrained surfaces

This paper examines the class of problems dealing with the mechanics of planar cracks that are subjected to incremental loading and where the surfaces of the crack exhibit a non-linear constraint over a finite region. Since the effects of the non-linearity are restricted to pre-defined surfaces, the boundary element technique can be applied quite successfully to determine the influence of such non-linearity on the development of stress intensity factors at the crack tip. In particular, attention is focussed on the evaluation of the stress intensity factors for plane crack with a non-linear surface constraint, which is subjected in turn to an isotropic compressive stress field followed by an incremental uniaxial loading in either tension or compression.

Water and synthetic urine sorption capacity of cellulose‐based hydrogels under a compressive stress field

AbstractA new apparatus was developed and used to investigate the swelling behavior of crosslinked hydrophilic polymers under an applied load as a function of the absorbed weight in both water and water solutions. A model able to predict the material water uptake as a function of the isotropic compressive stress was also studied. Centrifugation tests were performed to measure the material retention capacity under load, in both water and synthetic urine. The polymers studied in the tests were from a particular class of superabsorbent hydrogels based on cellulose derivatives chemically crosslinked with divinyl sulfone. The hydrogels showed high sorption and retention capacity in both water and water solutions, both in the free state and under load, and significant variations were observed during the modulation of the dry sample porosity.© 2004 Wiley Periodicals, Inc.J Appl Polym Sci 91: 3791–3796, 2004

Structural investigation ofPby(Zr0.57Ti0.43)2−yO3films deposited on Pt(001)/MgO(001) substrates by rf sputtering

We performed structural studies on PZT thin films, ${\mathrm{Pb}}_{y}({\mathrm{Zr}}_{0.57}{\mathrm{Ti}}_{0.43}{)}_{2\ensuremath{-}y}{\mathrm{O}}_{3};$ $y=0.97,$ 1.07, 1.15. The thin films were deposited on Pt (001)/MgO (001) substrates by rf-magnetron sputtering. Every film grew epitaxially in a tetragonal phase with the ``cube on cube'' relationship to the substrate, and contained no other crystalline phases, such as PbO or pyrochlore. It is known that PZT bulk ceramic with Zr/Ti of about 57/43, the composition of which is on the Zr-rich side of the morphotropic phase boundary (MPB), has a rhombohedral structure at room temperature. These PZT films, however, had tetragonal perovskite structures (space group: $P4mm).$ The Pb atoms mainly occupy the A $(1a)$ site, and the Zr and Ti atoms occupy the B $(1b)$ site at random. When y is less than unity in ${\mathrm{Pb}}_{y}({\mathrm{Zr}}_{0.57}{\mathrm{Ti}}_{0.43}{)}_{2\ensuremath{-}y}{\mathrm{O}}_{3},$ the excess Zr/Ti tends to enter the Pb (A) sites and randomly occupy the sites together with Pb; and when y is more than unity, the excess Pb tends to mix with the Zr and Ti at Zr/Ti (B) sites. In all these films, the atomic positions of Zr/Ti, O(1), and O(2) shift mutually along the c axis in the tetragonal structure. With increasing y, $c/a$ approaches unity and the crystal structure shifts toward the rhombohedral phase, especially in the O(2) atomic position, where a large shift was observed. The PZT thin films were grown under the restraint of a Pt (001) square lattice, and under isotropic compressive plane stress. These are the major reasons that the film crystallizes into tetragonal perovskite and polarizes spontaneously in the c-axis direction perpendicular to the substrate surface.

Residual stress in deuterium implanted nominal copper coatings

The effects of deuterium (D) implantation on the residual stresses in Cu and CuAl2 phases present in nominal Cu coatings (containing Al) deposited on Al-alloy (Al-6061) substrates were measured using an x-ray diffraction technique. The coatings were deposited by radio frequency magnetron sputtering of a pure Cu target under identical conditions and Al was incorporated in the coatings during growth by diffusion from the substrate. Deuterium was implanted in the coatings at energies of 40 or 40+120 keV with fluences of 1×1021, 2×1021, or 3×1021 D+/m2. Pole figures of the Cu phase in the coatings prior to and after implantation indicated no effect of implantation on the fibrous texture. Triaxial stress analysis indicated the surface normal stress component to be negligible in Cu and slightly tensile in CuAl2 under all conditions. Furthermore, under all conditions, the in-plane residual stresses in both phases were found to be compressive and nearly isotropic. The magnitude of the isotropic compressive stress was always higher in CuAl2 as compared to Cu. The compressive residual stresses in the Cu phase changed only mildly with increasing coating weight, ion energy, and fluence. However, in the CuAl2 phase the compressive residual stresses changed markedly with increasing ion energy (initial decrease followed by leveling off) and increasing ion fluence (initial decrease followed by an increase), but remained unaffected by increasing coating weight.

Periodicity as a Factor in the Generation of Isotropic Compressive Growth Stress Between Microfibrils in Cell Wall Formation during a Twenty-Four Hour Period

Summary Field emission scanning electron microscopy and energy-dispersive X-ray microanalysis were used to investigate the generation of growth stress in connection with the deposition of cell wall materials along the innermost surface of radial walls during secondary wall formation of differentiating tracheids of Cryptomeria japonica. Samples were collected when the turgor pressure of the tree was low (16:00 h), and when the pressure was high (6:00 h). In samples collected at 16:00 h, cellulose microfibrils deposited on the innermost surface of radial walls were clearly evident and amorphous material was rarely found. Conversely, in samples collected at 6:00 h, cellulose microfibrils were rarely observed and the amorphous material was prevalent. Cellulose microfibrils were evident, however, after removing the amorphous material with chlorite. The concentration of potassium on the inner surface of radial walls was greater at 6:00 h than at 16:00 h. After chlorite treatment, the concentration of potassium measured in the samples collected at 6:00 h decreased to a level equivalent to that in samples collected at 16:00 h and thus potassium was found to be associated with the amorphous material on the cellulose microfibrils. The amorphous material is probably a matrix of hemicellulose and monolignol, material that is abundant on the inner surface of developing cell walls, especially during expansion (as a result of high turgor pressure) of differentiating tracheids. A matrix of hemicellulose and lignin deposited in the expanded gaps between cellulose microfibrils and daily expansion of the gaps probably produces an isotropic compressive stress (growth stress). This paper demonstrates periodicity in cell wall formation as a result of the cycles of compressive growth in the differentiating cell wall.

Perpendicular anisotropy detected by transversely biased initial susceptibility via the magneto-optic Kerr effect inFexSi1−xthin films andFexSi1−x/Simultilayers: Theory and experiment

We studied experimentally and theoretically the perpendicular anisotropy and the stripe-domain structure in both ${\mathrm{Fe}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ thin films and ${\mathrm{Fe}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}/\mathrm{Si}$ multilayers, the latter being in the low-modulation-length regime $(0.4\mathrm{nm}<\mathrm{\ensuremath{\lambda}}<7\mathrm{}\mathrm{nm}).$ The experimental study was made by means of the transversely biased initial susceptibility ${\ensuremath{\chi}}_{t\ensuremath{\beta}}$ via the magneto-optic Kerr effect. The samples under study were prepared by dc triode sputtering at ${T}_{S}=300\mathrm{K}.$ It is found that the appearance of stripe domains is more pronounced for decreasing \ensuremath{\lambda} as $x$ remains constant and may be caused by both the increase in effective magnetic thickness and the reduction in effective magnetization as \ensuremath{\lambda} decreases. For multilayers with $\ensuremath{\lambda}=0.4\mathrm{nm},$ the observed field dependence of ${\ensuremath{\chi}}_{t\ensuremath{\beta}}^{\ensuremath{-}1}$ is similar to that found in homogeneous thin films when weak stripe-domain structures arise as a consequence of the existence of perpendicular anisotropy ${K}_{N}.$ We propose a quasistatic one-dimensional model to explain the behavior of ${\ensuremath{\chi}}_{t\ensuremath{\beta}}^{\ensuremath{-}1}$ when stripe domains are present, and we analyze the critical occurrence of stripe domains. We calculated the so-called pseudo-uniaxial anisotropy field ${H}_{\mathrm{Ks}},$ associated with the stripes, in two extreme cases: exchange-driven susceptibility or magnetic free poles (nonzero divergence in the bulk). The latter case agrees better with experiment. We found that perpendicular anisotropy is not exclusive of a well-defined multilayer structure; i.e., ${K}_{N}$ arises even when there are no interfaces in the volume. By setting the experimental saturation field ${H}_{s}$ (obtained by hysteresis loops) into our model, we obtain both the perpendicular anisotropy constant ${K}_{N}{=10}^{4}--{10}^{5}{\mathrm{J}/\mathrm{m}}^{3}$ and the critical thickness ${t}_{c}$ for the occurrence of a stripe-domain structure. Some possible sources of perpendicular anisotropy are discussed, for example, the associated isotropic compressive stress \ensuremath{\sigma}, whose contribution is found to be $|{K}_{N}{|}_{\mathrm{magnetoel}}\ensuremath{\approx}1.5--4.5\ifmmode\times\else\texttimes\fi{}{10}^{4}{\mathrm{J}/\mathrm{m}}^{3}.$