Presence Of Mechanical Stress Research Articles

Stress corrosion cracking failure of X80 carbon steel U-bend caused by Desulfovibrio vulgaris biocorrosion

Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris, which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel.

Highly Accelerated Stress Testing of Proton Exchange Fuel Cell Membranes for Heavy Duty Transportation Applications

According to the US DOE’s multi-year Fuel Cell research, development, and demonstration plan, a 30,000 h lifetime, approximately four times that of the light-duty vehicles (LDV), is required for Heavy Duty Vehicle (HDV) applications [1]. Thus, highly accelerated stress tests are necessary in order to assess the viability to novel membrane concepts within a reasonable amount of time. Previously we have reported the development of a highly accelerated stress test (HAST) to generate local stressful conditions that are representative of those in automotive fuel cell stacks [2]. Using a 50-cm2 cell cycled between 0.05 and 1.2 A/cm2 with a low inlet RH in the co-flow configuration, the HAST creates a distribution of combined mechanical/chemical stressors in the membrane with the maximum chemical stress occurring near the gas inlets and the maximum mechanical stress near the outlets. Conducting HASTs using a current distribution measurement tool and a shorting/crossover diagnostic method to track the state of health of a state-of-the-art membrane containing both a mechanical support and a cerium-containing chemical stabilizing additive, the result shows that the membrane location with the most severe thinning coincides with that of the deepest membrane hydration cycling. Upon examination of the cerium redistribution patterns after the test, it was found that the severe humidity cycling generated by the HAST condition near the outlet region not only generated the highest membrane mechanical stress but also resulted in the strongest water flux, which may cause local depletion of the cerium added as chemical stabilizer.In this study, we have focused on determining the root cause of membrane failure in the region of hydration cycling. Two hypotheses were investigated. The first is that chemical degradation can be accelerated in the presence of mechanical stress. The chemical degradation leads to membrane thinning which, in turn, leads to fewer sulfonic acid sites in the membrane available for Ce cation exchange. Two synergistic pathways for membrane degradation by combined mechanical and chemical stressors have been summarized by Kusoglu and Weber [3]. Ex-situ hydrogen peroxide vapor cell tests conducted with a pressure bias across the membrane to create a tensile stress were conducted to see if mechanical stress has an impact on membrane chemical degradation rate [4].The second hypothesis is that local depletion of the mobile Ce stabilizer in regions of high humidity gradients can lead to chemical degradation in those regions. We have shown previously that humidity gradients can cause cations to move with convective forces from wetter to drier regions within a perfluoro-sulfonic acid (PFSA) membrane [5]. To study this hypothesis, we conducted two types of tests. First, we repeated the HAST tests of the state-of-the-art membranes and stopped the tests prior to the onset on membrane thinning to see whether Ce depletion occurs before or after the onset of thinning. We also ran HAST tests on membranes which contained no Ce stabilizer to see if membrane failure still occurred in the region of strongest humidity cycles. In the absence of stabilizer, we expect chemical degradation to occur faster towards the cell inlets where, on average, the MEA is driest.We will show that the HAST test significantly accelerates membrane failure by increasing temperature and frequency of local deep humidity cycles without changing the primary failure mode or location of a state-of-the-art membrane. This work suggests that these HAST tests can be used to accelerate the development of membranes for HD fuel cell applications. DOE H2 Heavy Duty Truck Targets; https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf Y.-H. Lai et. al, J. Electrochem. Soc., 165 (6) (2018) F3100-F3103Kusoglu and Weber, J. Phys. Chem. Lett., 6, 4547 (2015)Y.-H. Lai et. al, ECS s 2021; https://iopscience.iop.org/article/10.1149/MA2021-02381128mtgabs F.D. Coms et. al, ECS s 2021; https://iopscience.iop.org/article/10.1149/MA2021-02381130mtgabs

Evolutionarily diverse LIM domain-containing proteins bind stressed actin filaments through a conserved mechanism

The actin cytoskeleton assembles into diverse load-bearing networks, including stress fibers (SFs), muscle sarcomeres, and the cytokinetic ring to both generate and sense mechanical forces. The LIM (Lin11, Isl- 1, and Mec-3) domain family is functionally diverse, but most members can associate with the actin cytoskeleton with apparent force sensitivity. Zyxin rapidly localizes via its LIM domains to failing SFs in cells, known as strain sites, to initiate SF repair and maintain mechanical homeostasis. The mechanism by which these LIM domains associate with stress fiber strain sites (SFSS) is not known. Additionally, it is unknown how widespread strain sensing is within the LIM protein family. We identify that the LIM domain-containing region of 18 proteins from the Zyxin, Paxillin, Tes, and Enigma proteins accumulate to SFSS. Moreover, the LIM domain region from the fission yeast protein paxillin like 1 (Pxl1) also localizes to SFSS in mammalian cells, suggesting that the strain sensing mechanism is ancient and highly conserved. We then used sequence and domain analysis to demonstrate that tandem LIM domains contribute additively, for SFSS localization. Employing in vitro reconstitution, we show that the LIM domain-containing region from mammalian zyxin and fission yeast Pxl1 binds to mechanically stressed F-actin networks but does not associate with relaxed actin filaments. We propose that tandem LIM domains recognize an F-actin conformation that is rare in the relaxed state but is enriched in the presence of mechanical stress.

The Shape and Function of Solid Fascias Depend on the Presence of Liquid Fascias.

Scientific research is not a showcase of his own talent or own resources, it is a chance to improve common knowledge on certain topics for the collective well-being. A researcher should use multidisciplinarity to observe a phenomenon in its entirety and not only its alignment of thought, federations, committees, and knowledge; to get to understand it is necessary to exploit more tools and more disciplines. The article discusses the importance of the fluids (or liquid fascia) in maintaining the shape and function of the human body, as, currently, many texts forget how much body fluids are fundamental for understanding structural dynamics (bones and muscles, fibrils, and cells). By revisiting the current literature, the text wishes to highlight how the liquid fascia determines body adaptation in the presence of mechanical stress. Without fluids, there would be no body shape that we know.

X-ray determination of the stress state of rolling-stock components

For the example of steel rolling-stock components, the X-ray determination of the surface stress is considered, with special preparation of the surface at the point of measurement. The effectiveness of this method when using a prototype portable X-ray diffraction system is demonstrated. The operating principle of that system is as follows. In the presence of mechanical stress, the diffraction angle changes, and the diffraction peak is shifted in the recorded diffraction spectrum. The diffracted X-rays recorded by the detector are converted to digital information regarding their intensity distribution, by means of an analog–digital converter, and sent to a PC. STRESSCONTROLL software is developed for computer analysis of the diffraction spectra. That software displays the diffraction spectra in graphical form, controls the operation of the diffraction system, and calculates the stress by means of a database on metals and phases. The computer analysis includes determination of the spectrum’s center of gravity. The software separates out the background, approximates the data set as a curve, and permits precise calculation of the center of gravity of the smoothed profile. The surface stress is determined for fragments of a 20GL steel solebar cut from the edge of a bearing aperture of radius R55, Before testing, the fragments are subjected to normalization or to bulk–surface quenching. The surface stress is found to be close to zero for the normalized fragment, while considerable compressive stress is observed for the quenched sample. Thus, the shape of the diffraction peak and the level of surface stress are directly related to the microstructure of the steel. In that case, the X-ray determination of the surface stress may provide information regarding the state of the surface.

Uniaxial cyclic stretch promotes osteogenic differentiation and synthesis of BMP2 in the C3H10T1/2 cells with BMP2 gene variant of rs2273073 (T/G).

Ossification of the posterior longitudinal ligament of the cervical spine (OPLL) is characterized by the replacement of ligament tissues with ectopic bone formation, and this result is strongly affected by genetic and local factors. Two single nucleotide polymorphisms (SNPs) of rs2273073 (T/G) and rs235768 (A/T) of bone morphogenetic protein 2 (BMP2) gene which are associated with OPLL have been reported in our previous report. In this study, we confirmed the connection in 18 case samples analysis of BMP2 gene in OPLL patients; additionally, it was also shown from the OPLL patients with ligament tissues that enchondral ossification and expression of BMP2 were significantly higher compared with the non-OPLL patients by histological examination, immunohistochemistry and Western blotting analysis. To investigate the underlying mechanism, we studied the effect of SNPs in cell model. The C3H10T1/2 cells with different BMP2 gene variants were constructed and then subjected to uniaxial cyclic stretch (0.5 Hz, 10% stretch). In the presence of mechanical stress, the expression of BMP2 protein in C3H10T1/2 cells transfected by BMP2 (rs2273073 (T/G)) and BMP2 (rs2273073 (T/G), rs235768 (A/T)) were significantly higher than the corresponding static groups (P<0.05). In conclusion, these results suggested that BMP2 gene variant of rs2273073 (T/G) could not only increase cell susceptibility to bone transformation similar to pre-OPLL change, but also increase the sensibility to mechanical stress which might play an important role during the progression of OPLL.

Resolving the Molecular Determinants of Cadherin Catch Bond Formation

Classical cadherin Ca2+-dependent cell-cell adhesion proteins play key roles in embryogenesis and in maintaining tissue integrity. Cadherins mediate robust adhesion by binding in multiple conformations. We recently showed that one of these conformations, called an X-dimer, forms catch bonds that strengthen and become longer lived in the presence of mechanical stress. Here we use single molecule force clamp spectroscopy with an Atomic Force Microscope along with Molecular Dynamics and Steered Molecular Dynamics simulations to identify key interactions that mediate X-dimer catch bond formation and to resolve the role of Ca2+ ions in this process. We show that tensile force bends the cadherin extracellular region such that they form force-induced hydrogen bonds that lock X-dimers into tighter contact. When Ca2+ concentration is decreased, these hydrogen bonds are eliminated and catch bond formation is abolished. Based on these results, we formulate a simple ‘flex and lock’ kinetic scheme that quantitatively describes X-dimer catch bonds.

Placement Optimization of Flexible TFT Digital Circuits

Mechanical strain significantly affects thin-film transistor (TFT) device mobility; thus, strain awareness is indispensable to flexible TFT circuit design. This article presents a strain-aware placement technique to enhance TFT logic circuit performance in the presence of mechanical stress.

TGFβ Affects Collagen Cross-Linking Independent of Chondrocyte Phenotype but Strongly Depending on Physical Environment

Transforming growth factor beta (TGFβ) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFβ, such as extensive cross-linking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGFβ on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and α-smooth muscle actin (αSMA) were analyzed during 4 weeks with or without 2.5 ng/mL TGFβ2. TGFβ2 did not affect collagen deposition by primary cells. In expanded cells, TGFβ2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGFβ2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGFβ2. αSMA was not present in alginate cultures and barely upregulated by TGFβ2. Organized αSMA fibers were present in all monolayer cultures and became more pronounced with TGFβ2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGFβ. The presence of mechanical stress, determined with αSMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGFβ.

TGFβ Affects Collagen Cross-Linking Independent of Chondrocyte Phenotype but Strongly Depending on Physical Environment

Transforming growth factor beta (TGFbeta) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFbeta, such as extensive crosslinking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGFbeta on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and alpha-smooth muscle actin (alphaSMA) were analyzed during 4 weeks with or without 2.5 ng/ mL TGFbeta2. TGFbeta2 did not affect collagen deposition by primary cells. In expanded cells, TGFbeta2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGFbeta2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGFbeta2. alphaSMA was not present in alginate cultures and barely upregulated by TGFbeta2. Organized alphaSMA fibers were present in all monolayer cultures and became more pronounced with TGFbeta2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGFbeta. The presence of mechanical stress, determined with alphaSMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGFbeta.

Low-temperature polysilicon thin film transistors on polyimide substrates for electronics on plastic

In this work we show a new low-temperature polycrystalline silicon (LTPS) thin film transistor (TFT) fabrication process on polyimide (PI) layers. The PI is spun on Si-wafer used as rigid carrier, thus overcoming difficulties in handling flexible freestanding plastic substrates, eliminating the problem of plastic shrinkage with high temperature processing and allowing the use of standard semiconductor equipment. LTPS TFTs are fabricated according to a conventional non self-aligned process, with source/drain contacts formed by deposition of a highly doped Si-layer and patterned by a selective wet-etching. Laser annealing is performed providing simultaneous dopant activation and crystallization of the active layer. The maximum process temperature is kept below 350 °C. After LTPS TFTs fabrication, the PI layer is mechanically released from the rigid carrier, which can be re-used for a new fabrication process. The devices exhibit good electrical characteristics with field effect mobility up to 50 cm 2/V s. Analysis of electrical stability and characteristics in presence of mechanical stress is also shown.

Dynamics and statics of interphase and domain boundaries at diffusionless phase transitions

We consider the interface dynamics of diffusionless first-order phase transitions in the case of an arbitrary dimension. We examine the generalized dynamics of interphase boundaries in the presence of mechanical stress. The displacement patterns due to interphase and domain boundaries are calculated in the case of martensitic phase transitions.

Involvement of CTGF in TGF-beta1-stimulation of myofibroblast differentiation and collagen matrix contraction in the presence of mechanical stress.

This study was undertaken to investigate the role of connective tissue growth factor (CTGF) in fibroblast-to-myofibroblast differentiation and fibroblast-mediated collagen matrix contraction in the presence of mechanical stress. An in vitro three-dimensional contraction model of human corneal-fibroblast-seeded collagen lattices (FSCLs) in the presence of mechanical stress generated by attaching the lattices to the culture well was used to measure FSCL contraction. FSCLs were treated with CTGF; TGF-beta1; serum-free (SF) control medium; or TGF-beta1 plus antisense oligodeoxynucleotides to CTGF; TGF-beta1 plus scrambled-sequence oligodeoxynucleotide to CTGF; or TGF-beta antibody. Expression of alpha-smooth muscle actin (alpha-SMA) by fibroblasts in FSCLs was detected by immunostaining and confocal microscopy, whereas ELISA was used for the fibroblasts cultured on plastic. The conditioned media were analyzed by ELISA for CTGF production. Exogenous CTGF stimulated significantly less collagen matrix contraction and myofibroblast differentiation than TGF-beta1, but similar to that stimulated by SF. TGF-beta1 stimulated fibroblasts to express CTGF. CTGF antisense oligodeoxynucleotide inhibited TGF-beta1-stimulated myofibroblast differentiation and FSCL contraction. Exogenous CTGF circumvented the inhibitory effects of CTGF antisense on FSCL contraction. TGF-beta antibody significantly inhibited FSCL contraction and myofibroblast differentiation under mechanical stress and SF control conditions. In the presence of mechanical stress, CTGF is necessary for TGF-beta1-stimulation of myofibroblast differentiation and subsequent collagen matrix contraction, but CTGF alone is not sufficient to induce myofibroblast differentiation and collagen matrix contraction. Thus, TGF-beta1 appears to regulate multiple genes that are essential for fibroblast-mediated contraction of stressed matrix, one of which is CTGF.

Redox Potential Distribution in the Presence of Mechanical Stress. The Case of Electroactive Polymers

The current/potential response during the redox switching of electroactive polymers derived from substituted arylamines is analyzed in terms of a sigmoidal distribution of apparent formal potentials. This kind of polymers shows expansion and contraction during the redox switching. A thermodynamic analysis of these systems, including mechanical stresses developed during the oxidation and reduction cycles, leads to a distribution of apparent formal potentials. It is shown that the concept of electron binding can be applied to describe the redox switching of an electroactive polymer. On the basis of this concept, simple statistical thermodynamic models can be applied to describe the distribution of apparent formal potentials during the redox switching of this kind of polymers. In particular, a simple model based on the mean field approximation, including interaction between near neighbors, leads to a linear distribution of the apparent formal potential. On the other hand, a statistical thermodynamical model, including the development of strains during the redox switching, successfully describes the experimental sigmoidal distribution of apparent formal potentials.

Complementary application of electron microscopy and micro-Raman spectroscopy for microstructure, stress, and bonding defect investigation of heteroepitaxial chemical vapor deposited diamond films

The evolution and interdependence of microstructure, stress, and bonding defects of heteroepitaxial diamond films deposited on silicon substrates has been investigated by applying scanning electron microscopy, transmission electron microscopy (TEM), and micro-Raman spectroscopy to the same places in the films. For this purpose, TEM plane-view specimens were prepared and the same grains in the electron transparent areas were characterized by all three methods that allowed crystalline defects and their relation to spectral features of the Raman spectrum to be identified. To the authors’ knowledge, this is the first successful complementary application of these methods to diamond films. Concerning microstructure evolution, dislocations in the silicon substrate and a residual plastic deformation of the silicon wafer prove that plastic deformation of the silicon substrate had occurred with the presence of mechanical stress during deposition. Evolutionary selection of randomly oriented, highly defective diamond grains observed at a film thickness of 300 nm leads to a textured film at 4 μm (an intermediate state) consisting of truncated pyramids with defect-free {001} growth sectors, bounded by four {111} growth sectors which exhibit a high density of twins and stacking faults. During further growth, merging of {001} growth sectors begins and apart from the formation of low-angle grain boundaries, the formation of partial wedge disclinations takes place, partly accommodating the misorientation between grains by elastic deformation. The latter process is shown to be more favorable than the formation of low-angle grain boundaries below a certain misorientation. Merging of grains introduces a high number of dislocations and mechanical stress into the {001} growth sectors. The comparison of the Raman spectra with electron micrograph images shows that the G band of the Raman spectrum originates exclusively from grain boundaries having an associated {111} growth sector. Very localized luminescence sources have been detected, not correlating to microstructure elements. Stress inhomogeneities measured within single grains and an earlier observed transition of the biaxial stress state in the film plane to a more complicated stress state after grain merging is shown to originate from disclinations.

Mapping stress with ultrasound

THE speed of sound in a solid is altered in the presence of mechanical stress. This effect can be exploited to form the basis of 'acoustic microscopy', whereby images of stress patterns in a material are obtained by monitoring the times of flight of sound pulses1. The sensitivity of this approach is limited because wave speeds typically change by less than 1%, even when materials are stressed until they yield. Here we demonstrate a more sensitive form of acoustic microscopy. In an isotropic elastic medium, stress-induced anisotropies affect wave polarizations and phases, giving rise to interference between waves that would, in the absence of stress, remain in phase; the resulting patterns of interference between these waves reveal the underlying patterns of stress. This technique, by using acoustic waves of different wavelengths, permits the imaging of stress in objects ranging in size from microelectric devices to welds in pressure vessels.