Tensile Pulling Research Articles

Myosin and upalpha-actinin regulation of stress fiber contractility under tensile stress

Stress fibers are actomyosin bundles that regulate cellular mechanosensation and force transduction. Interacting with the extracellular matrix through focal adhesion complexes, stress fibers are highly dynamic structures regulated by myosin motors and crosslinking proteins. Under external mechanical stimuli such as tensile forces, the stress fiber remodels its architecture to adapt to external cues, displaying properties of viscoelastic materials. How the structural remodeling of stress fibers is related to the generation of contractile force is not well understood. In this work, we simulate mechanochemical dynamics and force generation of stress fibers using the molecular simulation platform MEDYAN. We model stress fiber as two connecting bipolar bundles attached at the ends to focal adhesion complexes. The simulated stress fibers generate contractile force that is regulated by myosin motors and alpha-actinin crosslinkers. We find that stress fibers enhance contractility by reducing the distance between actin filaments to increase crosslinker binding, and this structural remodeling ability depends on the crosslinker turnover rate. Under tensile pulling force, the stress fiber shows an instantaneous increase of the contractile forces followed by a slow relaxation into a new steady state. While the new steady state contractility after pulling depends only on the overlap between actin bundles, the short-term contractility enhancement is sensitive to the tensile pulling distance. We further show that this mechanical response is also sensitive to the crosslinker turnover rate. Our results provide new insights into the stress fiber mechanics that have significant implications for understanding cellular adaptation to mechanical signaling.

Biochemical mechanism involved in the enhancement of the Young's modulus of silk by the SpiCE protein

Silk fibers are known for their superior mechanical properties, with the strongest possessing over seven times the toughness of kevlar. Recently, low molecular weight non-spidroin protein, spider-silk constituting element (SpiCE), has been reported to enhance the mechanical properties of silk; however, its specific action mechanism has not yet been elucidated. Here, we explored the mechanism by which SpiCE strengthened the mechanical properties of major ampullate spidroin 2 (MaSp2) silk through hydrogen bonds and salt bridges of the silk structure via all-atom molecular dynamics simulations. Tensile pulling simulation on silk fiber with SpiCE protein revealed that the SpiCE protein enhanced the Young's modulus by up to 40% more than that of the wild type. Bond characteristic analysis revealed that SpiCE and MaSp2 formed more hydrogen bonds and salt bridges than the MaSp2 wild-type model. Sequence analysis of MaSp2 silk fiber and SpiCE protein revealed that SpiCE protein contained more amino acids that could act as hydrogen bond acceptors/donors and salt bridge partners. Our results provide insights into the mechanism by which non-spidroin proteins strengthen the properties of silk fibers and lay the groundwork for the development of material selection criteria for the design of de novo artificial silk fibers.

Residual stress impact on corrosion behaviour of hot and cold worked 2205 duplex stainless steel: A study by X-ray diffraction analysis

The use of 2205 duplex stainless steel (2205 DSS) in the petrochemical and nuclear industries is fast replacing carbon steel and other convectional alloys due to its excellent corrosion resistance and improved mechanical properties it offers. The effect of residual stress on corrosion behaviour of hot and cold rolled 2205 DSS in a chloride environment is investigated. As received hot and cold rolled duplex stainless-steel samples were characterized using a scanning electron microscope (SEM) for microstructural phase analysis. Residual stresses of varying percentages (20, 40, and 60%) were applied to duplex stainless steel samples machined to micro tensile dimensions. The residual stress analysis of the necked region was analyzed using Bruker D8 Advance X-ray diffractometer, while potentiodynamic polarization was carried out in 3.5 wt% NaCl to access the corrosion integrity of the necked region. The center and average principal stress analysis (S11 and S22) of hot and cold-rolled stainless steel in the necked region showed the deformation of austenite and ferrite phases due to tensile pulling with more tensile stress in the austenite phase. SEM micrographs of corrosion substrates revealed the dominance of corrosion in the austenite phase within the necked region in hot rolled samples.

Effect of Combined Hydrophilic Activation on Interface Characteristics of Si/Si Wafer Direct Bonding

Wafer direct bonding is an attractive approach to manufacture future micro-electro-mechanical system (MEMS) and microelectronic and optoelectronic devices. In this paper, a combined hydrophilic activated Si/Si wafer direct bonding process based on wet chemical activation and O2 plasma activation is explored. Additionally, the effect on bonding interface characteristics is comprehensively investigated. The mechanism is proposed to better understand the nature of hydrophilic bonding. The water molecule management is controlled by O2 plasma activation process. According to the contact angle measurement and FTIR spectrum analysis, it can be concluded that water molecules play an important role in the type and density of chemical bonds at the bonding interface, which influence both bonding strength and voids’ characteristics. When annealed at 350 °C, a high bonding strength of more than 18.58 MPa is obtained by tensile pulling test. Cross sectional SEM and TEM images show a defect-free and tightly bonded interface with an amorphous SiOx layer of 3.58 nm. This amorphous SiOx layer will induce an additional energy state, resulting in a lager resistance. These results can facilitate a better understanding of low-temperature hydrophilicity wafer direct bonding and provide possible guidance for achieving good performance of homogenous and heterogenous wafer direct bonding.

Molecular mechanics of the swelling clay tactoid under compression, tension and shear

Montmorillonite is the principal constituent of many expansive soils. The swelling of expansive clays upon hydration can cause significant distress to infrastructure. On the other hand, the swelling characteristics lead to many beneficial applications of these clays, such as barrier materials and in nanocomposites. The montmorillonite hierarchical structure plays a vital role in the swelling of expansive clays. The hierarchical structure of montmorillonite consists of four levels, clay mineral layers, tactoids, aggregates, and assembly of aggregates. The clay tactoid is considered as the fundamental clay particle, which consists of several clay mineral layers stacked in the Z direction. We report here for the first time a molecular mechanics study of the clay tactoid. The molecular model of sodium-montmorillonite (Na-Mt) tactoid was built, and its mechanical properties were evaluated using Molecular Dynamics (MD) and Steered Molecular Dynamics (SMD) simulations. The mechanical response of Na-Mt tactoid was evaluated under compression, tension, and shear. Compression tests revealed a short linear characteristic with a compression modulus of 125 GPa followed by a nonlinear portion with increasing modulus approaching 640 GPa, which is the modulus of a single clay mineral layer. The tensile pulling of the tactoid also indicated an influence of the tactoid nanostructure with the influence of multiple neighboring layers of tactoid. The shearing simulations indicated first a mechanical response with a modulus of 10 GPa ending with locking of interlayer cations into tetrahedral cavities followed by small displacements exhibiting a modulus of 70 GPa. All of the mechanical behaviors were related to the evaluated interaction energies between clays and cations during loading. These studies elucidated key mechanisms of swelling clay tactoid response to loading.

Spider silk with weaker bonding resulting in higher strength and toughness through progressive unfolding and load transfer

The superior mechanical properties of silk is known to come partly from its hydrogen bonds, which is determined by its amino acid sequences. Hydrogen bonds are one of the main sources of strength of silk fiber, yet the toughest silk fibers have amino acids sequences that results in lesser number of hydrogen bonds than other silk fibers. In this work, we show how such silk fiber with lower number of hydrogen bonds may result in fiber with higher toughness by investigating the process of how hydrogen bond characteristics of silk are translated into its mechanical properties. From the tensile pulling tests via molecular dynamics simulations on silk fiber with varying number of hydrogen bonds, the mechanism of how weaker bonded silk results in higher strength and toughness by synergic effect with the characteristic progressive unfolding and load transfer of silk fiber is explained. The results provide new perspectives on how silk and other fibers should be designed to achieve higher toughness.

Compilation of Pavement Interface Bond Strength Devices for Bond Strength Quantification

Flexible pavement is a multilayered structure constructed in layers. In order to ensure proper bonding such that a pavement behaved monolithically, tack coat is often applied. The developed pavement interface bond strength is therefore paramount in governing the overall performance of pavement serviceability. The present work reviews the current state of pavement interface bond strength quantification mechanisms, and the devices developed based on the mechanism. Related accessible literatures are collected and analyzed to compile the characteristics of each bond testing devices and evaluated for the capabilities and test performance. The investigation reveals 3 testing mechanisms incorporating shearing (pushing), tensile (pulling) and torsioning (twisting). However, shearing test seems to be the most popular device adopted to investigate the bond strength between two interfaces in contact, utterly due to the simplicity of the test setup. For tensile mechanism, the developed devices are generally portable and are mostly used to examine the tack coat quality. Finally, the device with torsional mechanism is not so popular as compared to the aforementioned mechanism. Nonetheless, it is developing steadily with the continuous research.

Design and Characterization of an Endovascular Mechanical Thrombectomy Device1

Design and Characterization of an Endovascular Mechanical Thrombectomy Device1

Surface activated bonding of copper through silicon vias and gold stud bumps at room temperature

A comprehensive investigation of the surfaces of copper through silicon vias (Cu-TSVs) and gold stud bumps is presented. These vias and stud bumps were bonded at room temperature using a nanobonding and interconnection equipment. The influence of heating on the bonded interface was also studied. In order to achieve an intimate contact between the Au-stud bumps and Cu-TSVs, the stud bumps were flattened under an external force of 20 N before bonding. The surface roughness of the flattened area was improved due to deformation of the bumps. Specimens with high deformation provided better alignment accuracy than those with low deformation. The Cu-TSV surface showed inhomogeneous behavior due to the influence of electroplating and chemical mechanical polishing. Tensile pulling test of the bonded interfaces showed three fractures modes in the bulk of the Au bump and the Au pad. The electrical resistance of the bonded interface was dependent on the surface morphology of the bumps and TSVs, the distance between the bumps and TSVs, the locations of the bumps and TSV with respect to the argon fast atom beams, and the distribution of external force during bonding. Heating at 200 °C for 60 h in air increased the electrical resistance of the bonded interface. This investigation shows that the vertical integration of Au/Cu at room temperature and low bonding force can be applied to three-dimensional interconnections for low cost miniaturized systems.

Investigation of bonding strength and sealing behavior of aluminum/stainless steel bonded at room temperature

This article reports the direct bonding of aluminum (Al) [99.999% (5N), 99% (2N)] and stainless steel SUS (304, 316) without heating for sealing in the ultra high vacuum (UHV) components. For bonding, the smooth surfaces of the Al and SUS specimens were activated using argon fast atom beam (Ar-FAB) for 1–60 and 60 min, respectively, in a background pressure of 6.0 × 10 −5 Pa followed by close contact under an external pressure of 960 N. High bonding strength resulted in the bonded mates of Al and SUS304 activated for 30 and 60 min, respectively, due to the adhesion forces of the surface atoms. Tensile pulling tests showed bulk fractures in Al with impurity dependent bonding strength. The bonding strengths for the Al5N/SUS304 and Al2N/SUS304 specimens were higher than 60 and 100 MPa, respectively. For the sealing test, the smooth surface of the SUS316 flange containing a hole was bonded with Al after surface activation 60 and 30 min, respectively. Leak rates for Al5N/SUS316 and Al2N/SUS316 specimens were 1.5 × 10 −11 and 2.0 × 10 −11 Pa m 3/s, respectively. These results satisfy the permissible leakage of a large-sized UHV chamber. Time dependence of the leak test behavior for both specimens shows a stable leak rate. Therefore, the sealing of Al/SUS316 may be utilized for the fabrication of corrosion free joints for fluid flow in the cooling of electron guns of small size equipment such as portable scanning electron microscopes in UHV pressure.

Molecular dynamics investigations on polishing of a silicon wafer with a diamond abrasive

During the final stages of polishing silicon wafers, much of the interactions between silicon and diamond abrasive takes place at the silicon asperities. These interactions, leading to material removal, were investigated in a MD simulation of polishing of a silicon wafer with a diamond abrasive under dry conditions. Simulations were conducted with silicon asperities of different geometries, different abrasive configurations, and polishing speeds. Under the conditions of polishing, the silicon atoms from the asperities were found to bond chemically to the surface of the diamond abrasive. Continued transverse motion of the diamond abrasive (relative to the silicon asperity) leads to tensile pulling, necking, and ultimate separation of the silicon asperity material instead of conventional material removal in polishing (chip formation) involving cutting/ploughing, which takes place in the absence of chemical bonding between the abrasive and the asperity material. This phenomenon has not been reported previously in the literature. The thrust and cutting forces initially increase due to the increase in the number of asperity atoms affected finally reaching a maximum. This is followed by a decrease of these forces due to tensile pulling and formation of individual strings followed by ultimate separation or breakage of the final string. The ratio of thrust force (F z ) to the cutting force (F x ), i.e. |(F z /F x )| was found to increase continuously to a maximum of ∼0.8 followed by continuous decrease to ∼0.25. This is in contrast to a more or less constant value of ∼2 in the case of tools with rounded radii or tools with large negative rake angles, where material is removed in the form of chips ahead of the tool. Three regions of the asperity have been identified that are useful in the development of a phenomenological model for polishing that enables computation of material removal rates: (1) the region directly in front of the abrasive for which the probability of the removal of an asperity atom is close to unity, (2) the distant region where this probability is nearly zero, and (3) an intermediate region from which the probability of removal is close to half.

Tensile tests of micro anchors anodically bonded between Pyrex glass and aluminum thin film coated on silicon wafer

Micro anchor is a kind of typical structures in micro/nano electromechanical systems (MEMS/NEMS), and it can be made by anodic bonding process, with thin films of metal or alloy as an intermediate layer. At the relative low temperature and voltage, specimens with actually sized micro anchor structures were anodically bonded using Pyrex 7740 glass and patterned crystalline silicon chips coated with aluminum thin film with a thickness comprised between 50 nm and 230 nm. To evaluate the bonding quality, tensile pulling tests have been finished with newly designed flexible fixtures for these specimens. The experimental results exhibit that the bonding tensile strength increases with the bonding temperature and voltage, but it decreases with the increase of the thickness of Al intermediate layer. This kind of thickness effect of the intermediate layer was not mentioned in the literature on anodic bonding.

Measurement of Soil Tensile Strength and Factors Affecting its Measurements

ABSTRACT This paper describes the tensile strength measured for three kinds of statically compacted unsaturated soils; mixtures of clay ~ silt ~ sand, Narita-sand and Kanto loam. Specimens were directly prepared either under controlled compaction stress or under controlled dry density by statically compacting them within the tensile mold of the apparatus. Image analysis was done to show the normality of tensile force to the tensile failure plane. Tensile strengths (qt) were compared with the unconfined compressive strengths (qu) for silt ~ sand mixture, clay ~ sand mixture, clay ~ silt mixture and Narita sand, respectively. Increment in tensile strength (also qu/qt ratio) with the increase in the percentage and decrease in the size of finer soils could be seen. Effects of number of compaction layers and tensile pulling rates on the qt were also examined. Increase in the tensile strength with the increase in the number of compaction layers was observed; and it was suggested to prepare the unsaturated compacted specimen by 3 to 4 layers compaction. Increase in tensile strength of 0.3 kPa and 0.003 kPa per one cycle of logarithm of tensile pulling rate was observed for clay ~ sand-4 (1:3) and clay ~ sand-5 (3:1) for the pulling rate of 0.01 to 1.0 mm/min.

A carbon nanofibre scanning probe assembled using an electrothermal microgripper

Functional devices can be directly assembled using microgrippers with an in situ electronmicroscope. Two simple and compact silicon microgripper designs are investigated here.These are operated by electrothermal actuation, and are used to transfer a catalyticallygrown multi-walled carbon nanofibre from a fixed position on a substrate to the tip of anatomic force microscope cantilever, inside a scanning electron microscope. Scanningof high aspect ratio trenches using the nanofibre supertip shows a significantlybetter performance than that with standard pyramidal silicon tips. Based onmanipulation experiments as well as a simple analysis, we show that shear pulling (lateralmovement of the gripper) is far more effective than tensile pulling (vertical movementof gripper) for the mechanical removal of carbon nanotubes from a substrate.

Molecular dynamics (MD) simulations of the dependence of C–C bond lengths and bond angles on the tensile strain in single-wall carbon nanotubes (SWCNT)

Molecular dynamics (MD) simulations of tensile pulling of carbon nanotubes (SWCNTs) (both armchair and zigzag configurations) were conducted using the Brenner potential to investigate the variation of the six carbon–carbon bond lengths and bond angles of the hexagons in single-walled carbon nanotubes (SWCNT) as a function of tensile strain. The correlations between stress–strain, bond lengths and bond angles with strain, and the variation of a parameter in the interaction potential, namely, D min have been studied. Simulations at higher values of strain were also performed to obtain the values of breaking strain. A sharp change in the stress–strain behavior, C–C bond lengths, and bond angles with strain was observed for strains equals to 0.30 for the armchair and 0.18 for the zigzag SWCNTs. The dependence of bond stretching and breaking strain on the chirality of the nanotubes and the functional form of the empirical potential has been investigated. The results of our investigations suggest that the presence of attenuation functions in empirical potentials may cause problems, if bond distances or strains become larger than the onset point of these functions. The effect of the duration of relaxing/thermostating of the nanotube after every stretch on the value of the breaking strain has also been discussed.

アルミニウムとステンレスの表面活性化接合とそのシール特性

In order to consider the application of the vacuum parts to the vacuum procedures in a joining process called surface-activated bonding (SAB), we conducted a SAB experiment at room temperature for the combinations of Al5N/SUS304, Al2N/SUS304, Al5N/SUS316 flange, and Al2N/SUS316 flange. We examined the influence of the cleaning state and the surface roughness on Al/SUS joining performance, as well as the bonding strength and the sealing characteristics of such joined samples. We have found the following. (1) Before joining, smooth surfaces of the Al5N and SUS304 samples were sputter cleaned using an argon fast atom beam (FAB) for 10 and 60 min, respectively, to completely remove surface oxide and organic materials. However, these samples can be joined even if the removal is imperfect. (2) When the FAB irradiation time was longer than 20min for Al5N and 30min for Al2N, the tensile pulling tests indicated bulk fractures in Al without an interface and that the bonding strength of the interface of the joined samples was higher than the Al strength. (3) Leak rates for Al5N/SUS316 and Al2N/SUS316 samples were 1.5 × 10-11 Pa · m3/s and 2.0 × 10-11 Pa · m3/s, respectively. These are within the permissible equivalent leakage of a large ultrahigh-vacuum (UHV) chamber. The leak test behavior with time for both samples indicated stable leak rates and sustainable sealing.

Room temperature wafer level glass/glass bonding

The findings of this study report the bonding of glass/glass wafers by using the surface activated bonding (SAB) method at room temperature (RT) without heating. In order to bond, the glass wafers were activated by a sequential plasma activation process, in which the wafers were cleaned with reactive ion etching (RIE) oxygen radio frequency (rf) plasma and nitrogen radical microwave (MW) plasma one after another and then contacted under hand-applied pressure followed by cold rolling under 20kg load in atmospheric air. High bonding strength for glass/glass was achieved. Paramount influence of N2 radical MW plasma on the adhesion enhancement of silicon/silicon bonding motivated the investigation of the N2 radical MW plasma relationship with the bonding strength of glass/glass. A considerable influence of N2 pressure on the bonding strength was not observed except in N2 gas pressure of 30Pa, which might be due to the debonding between glue and fixture used for tensile pulling test. No significant effect of OH density of glass wafers on the bonding strength was found below 400°C. The result was evident from 400°C and it was about twofold higher at 600°C than that of RT to 400°C. This result indicated that the sequential process bonding mechanism was consisting of long bridges of hydrogen bonding by water molecules. Significant environmental influence on the bonding strength was found and which could be correlated with OH molecules of glass wafers.

Temperature and pressure dependence in thermocompression gold stud bonding

Low temperature metal bonding plays a very important role in the interconnection for 3D packaging technologies in VLSI integrated circuits. The effects of temperature ranging from 100–300 °C and pressure ranging from 200–600 g/bump on the direct gold–gold bond quality were measured using shear and tensile pulling techniques, respectively. A critical bonding temperature was observed below which no bonding will occur. Above this temperature, the shear strength improves with bonding temperature because of the increase in the true bonded area. This critical temperature can be interpreted to be the onset of the break-up of organic barrier films. Beyond this critical temperature, the tensile strength of the Au–Au bond exhibits a maximum with bonding pressure. This can be associated with the pressure dependence of the interfacial stress distribution and its effect on unbonded radius, r.

Why interface testing by single-fibre methods can be misleading

The reasons for our interest in the interface are reviewed, and bond-strength sensitive properties are discussed. It is shown that the four direct methods currently used for interface measurement have problems that make their results inconsistent between methods and inaccurate. The failure process has been monitored in glass/epoxy pull-out specimens with very short fibre free lengths, so that crack propagation is stable. This showed that, close to ultimate failure, a very small length of the interface was carrying nearly all the (very high) load. This apparently high interfacial shear strength can be explained on the basis of the recently documented lack of a shear failure mode for most polymers. All four interface tests are centro-symmetric, or nearly so. In this situation, a matrix that cannot fail in shear, must fail in tension. Yet tensile failure is strongly inhibited by the centro-symmetry. Hence shear failure is forced at the interface itself by a tensile-type process. This involves tensile pulling of the polymer over the high points on the fibre. (No surface is perfectly smooth.) The result is thus unduly influenced by the surface roughness of the fibre and the shrinkage pressure, neither of which are directly related to adhesion. Although great progress has been made with fracture analysis of interface failure, this cannot resolve the problem of the unrealistic centro-symmetry of the tests. It is, therefore, recommended instead that direct tests on composites be examined for relevance and usefulness. The most useful method may well be to measure the off-axis tensile strength of unidirectional composites. This has been shown to be more sensitive to interface properties than both the fragmentation test and the pull-out test. Single-fibre tests and fracture analyses of these tests should be used only for basic research into centro-symmetric failure modes.

Methods of measuring adhesion for thermally grown oxide scales

High temperature alloys and coatings rely on the formation of adherent scales to protect against further oxidation, but scale spallation is often problematic. Despite the technical importance of the problem, ‘practical adhesion’, which refers to the separation of the oxide from the metal, has mainly been treated qualitatively in the past. Various techniques now exist such that the subject can be assessed in quantitative or semiquantitative terms. Some of the techniques are described in this paper, and their weaknesses and strengths are discussed. The experimental methods addressed here include tensile pulling, microindentation, scratch tests, residual stress induced delamination, laser-induced or shock wave induced spallation, double-cantilever beam bending and several four-point beam bending approaches. To date, there is not a universal, easy test for oxide adhesion measurement that can provide reproducible information on interfacial fracture energy for a variety of oxide/metal systems. Much experimentat...