Constant Shear Force Research Articles

Solvent Volatilization-Induced Cross-Linking of PDMS Coatings for Large-Scale Deicing Applications

Icing of surfaces has become a serious issue, and effective methods for preventing ice accretion have received much attention in recent years. Here, a solvent volatilization-induced cross-linking hydroxy-terminated dimethylsiloxane (Si–OH) coating with tetramethoxysilane (TMOS) as a cross-linker is proposed for large-scale deicing applications. Interfacial adhesion tests and shear force analysis were conducted to confirm the large-scale deicing properties of the polydimethylsiloxane (PDMS) coating. Through characterization of morphology, it was found that there were negative correlations between roughness and constant shear force and shear strength. The mean constant shear force per unit width could be lower than 14 N/cm when the roughness was in the highest range fabricated in this research. In addition to the morphology of the surface, the mass ratio of the cross-linker to the premonomer affected the state of the surface and the deicing properties. When the mass ratio was lowered, uncross-linked molecular chains of the premonomer existed on the surface, which resulted in an increase in interfacial toughness and a reduction in shear strength. Finally, durability tests showed that the coating had excellent durability and could endure at least 50 cycles without an apparent increase in the constant shear force.

Effect of Doping SiO2 Nanoparticles and Phenylmethyl Silicone Oil on the Large-Scale Deicing Property of PDMS Coatings.

Recently, low interfacial toughness (LIT) materials have been developed to solve large-scale deicing problems. According to the theory of interfacial fracture, ice detachment is dominated by strength-controlled or toughness-controlled regimes, which are characterized by adhesive strength or constant shear force. Here, a new strategy is introduced to regulate the interfacial toughness of poly(dimethylsiloxane) (PDMS) coatings using silicon dioxide nanoparticles (SiO2 NPs) and phenylmethyl silicone oil (PMSO). By systematically adjusting the doping proportion of SiO2 NPs and PMSO, it is found that a lower interfacial toughness can be achieved with a lower constant shear force. The synergistic effect of the two dopants on the adhesive strength and interfacial toughness is analyzed. Meanwhile, finite element method (FEM) analysis of ice detachment is conducted to show the cracking process intuitively and explicate the mechanism of lowering the interfacial toughness of PDMS by doping SiO2 NPs and PMSO. It can be concluded that the cohesive zone material (CZM) model is effective for simulating the deicing process of PDMS coatings and provides a comprehensive understanding of the modulation of interfacial toughness.

A promising self-assembly PTFE coating for effective large-scale deicing

Ice accretion is detrimental for the safety of transmission lines, aircraft, and buildings, which may also result in economic loss. In this study, a thin polytetrafluoroethylene (PTFE) coating on the aluminum substrate was fabricated by electrostatic attraction self-assembly technique and proposed for large-scale deicing application. The shear-force Fice analysis on deicing and related ice adhesion is conducted while interfacial toughness between solid-ice interfaces was also measured. Moreover, the surface morphology, wettability of the PTFE coated aluminum plate was also characterized. It was observed that the critical bonded length Lc between ice and PTFE coated surface is about 2.85 cm. When the bonded length L was higher than this value, the shear-force of dislodging ice could stay constant at about 50 N for the first deicing cycle. From the second deicing cycle, the constant shear-force is increased to 70 N and kept constant for at least ten cycles. Meanwhile, the surface roughness and water contact angle kept on increasing along with the loss of PTFE nanoparticles during icing-deicing cycles. Ultimately, An ice layer with the size of 98 cm × 96 cm×1 cm (L × w×h) was developed on the surface of PTFE coated aluminum substrate for the demonstration of its fracture and falling off under ice’s weight.

Novel two-level strategy to exactly solve multilayer composite cantilever tubes of cylindrically orthotropic materials

A novel two-level strategy is employed to solve the multilayer composite cantilever tubes in elasticity theory. On the first level of our strategy, a complete stress field is developed for the inclined winding cantilever tubes. Thus the tube can be considered as a bending-like tube including the proportional moments together with a shear-like tube including the constant shear forces. The pure bending formula is used to obtain the solution for the bending-like tube. However, the shear-like tube includes some additional terms from the bending-like tube. Therefore, on the second level of our strategy, the shear-like tube is broken into two independent systems according to whether the additional terms are included. Thus their different circumferential functions can be satisfactorily separated from the radial functions. In addition, an approach of undetermined coefficients is employed to find the particular solution for the second independent system. In the examples the method in this paper is used to exactly solve the composite cantilever tubes [90°], [45°] and [75°] as well as [45°/75°], [75°/−75°] and [(75°/−75°)40]. The good agreement of our exact results with the numerical simulation with fine finite elements shows the accuracy and effectiveness of the method in this paper.

Stress Redistribution of Headed Stud Connectors Subjected to Constant Shear Force

In order to evaluate the stress concentration of stud shear connectors considering creep effect of concrete, finite element analysis of the push-out specimen is carried out. The rate of creep method is used in the solid model to reflect the creep property of concrete. Local bearing stress and splitting stress of concrete are analyzed. The stress concentration of steel beam and stud near the weld toe are obtained. Results show that owing to the creep effect of concrete, the local stresses of the stud are redistributed, even under constant shear force. The stress concentration factor (SCF) of concrete bearing stress in front of the weld collar decreases by about 52%, while the bending deformation of the stud increases due to the stress redistribution given 10 years of creep time. SCF at the weld toe of steel beam increases about 1.5 times of short-term, and SCF of stud shank increases about 3 times. The stress concentration at the root of studs become more obvious under constant shear force due to concrete creep, which is adverse for the long-term behavior of studs in the normal service stage.

Experimental test of coupling effect on CLT hold-down connections

This paper investigated the coupling effect of tension and shear loading on Cross Laminated Timber (CLT) hold-down connections through experimental tests. Monotonic and cyclic tests of the connections were carried out in tension with 3 different levels of co-existent constant shear forces, and in shear with 5 different levels of co-existent tension forces. Failure mode, hysteresis loops, strength and stiffness, equivalent viscous damping and strength degradation, energy dissipation, and coupling effect were described and discussed in details. The results show co-existent shear load weakened both the axial loading capacity and energy dissipation capacity at large vertical displacement; small co-existent tension load (0–20 kN) strengthened the shear behaviour while higher levels of co-existent tension load (30–60 kN) decreased the shear capacity and energy dissipation capacity rapidly at large lateral displacement. The research finds that, nails travelling in the gap within the wood embedment received resistance due to the co-existent force in the perpendicular direction under bi-axial loading, which caused the coupling effect. The study gives a better understanding of hysteretic behaviour of hold-down connections for CLT where rocking motions occur, and provides reliable data for future numerical analysis of CLT structures.

A liquid spring–magnetorheological damper system under combined axial and shear loading for three-dimensional seismic isolation of structures

This study focuses on experimental investigation of a fail-safe, bi-linear, liquid spring magnetorheological damper system for a three-dimensional earthquake isolation system. The device combines the controllable magnetorheological damping, fail-safe viscous damping, and liquid spring features in a single unit serving as the vertical component of a building isolation system. The bi-linear liquid spring feature provides two different stiffnesses in compression and rebound modes. The higher stiffness in the rebound mode prevents a possible overturning of the structure during rocking mode. For practical application, the device is to be stacked together along with the traditional elastomeric bearings that are currently used to absorb the horizontal ground excitations. An experimental setup is designed to reflect the real-life loading conditions. The 1/4th-scale device is exposed to combined dynamic axial loading (reflecting vertical seismic excitation) and constant shear force that are up to 245 and 28 kN, respectively. The results demonstrate that the device performs successfully under the combined axial and shear loadings and compare well with the theoretical calculations.

Engineering of hyaline cartilage with a calcified zone using bone marrow stromal cells

In healthy joints, a zone of calcified cartilage (ZCC) provides the mechanical integration between articular cartilage and subchondral bone. Recapitulation of this architectural feature should serve to resist the constant shear force from the movement of the joint and prevent the delamination of tissue-engineered cartilage. Previous approaches to create the ZCC at the cartilage-substrate interface have relied on strategic use of exogenous scaffolds and adhesives, which are susceptible to failure by degradation and wear. In contrast, we report a successful scaffold-free engineering of ZCC to integrate tissue-engineered cartilage and a porous biodegradable bone substitute, using sheep bone marrow stromal cells (BMSCs) as the cell source for both cartilaginous zones. BMSCs were predifferentiated to chondrocytes, harvested and then grown on a porous calcium polyphosphate substrate in the presence of triiodothyronine (T3). T3 was withdrawn, and additional predifferentiated chondrocytes were placed on top of the construct and grown for 21 days. This protocol yielded two distinct zones: hyaline cartilage that accumulated proteoglycans and collagen type II, and calcified cartilage adjacent to the substrate that additionally accumulated mineral and collagen type X. Constructs with the calcified interface had comparable compressive strength to native sheep osteochondral tissue and higher interfacial shear strength compared to control without a calcified zone. This protocol improves on the existing scaffold-free approaches to cartilage tissue engineering by incorporating a calcified zone. Since this protocol employs no xenogeneic material, it will be appropriate for use in preclinical large-animal studies.

Cyclic Pull-Out Push-In Shear-Lag Model for Post-installed Anchor-Infill Assembly

A cyclic piecewise linear shear-lag material model representing the local bond behavior of the post-installed anchor-infill assembly used for simulating its cyclic pull-out push-in response is presented. The anchor-infill assembly is such that used in various strengthening techniques to strengthen reinforced concrete structures. The properties of the infill material used for installing post-installed anchor-infill assembly are characterized by a nonlinear interface between the surrounding concrete and the anchor. A new type of anchor-infill assembly is introduced in which the infill material is divided into two layers for the purpose of providing a larger failure path length resulting in increase of the energy absorption capacity. The cyclic response is divided into two categories, namely the one with indentation and the one without indentation, where indentation represents concrete crushing at the base of drilled hole used for installing anchor bar. Each cycle is further subdivided into six paths of elastic loading followed by de-bonding in pull-out direction, unloading, reloading, de-bonding in push-in direction and unloading again. The stiffness degradation upon de-bonding and stiffness recovery upon reloading due to the lateral pressure effect and Poisson’s effect is incorporated in the form of stiffness and constant shear force update at the beginning of each loading path. Rules are formulated to plot the cyclic response, by a trial and error approach, to suit the presented material model. The sequential conceptual diagram showing the development of global cyclic load–displacement response of the anchor-infill assembly is also presented. Finally, the response of the anchor-infill assembly is plotted using thefinite element method under three different support conditions and comparisons are made with the results of numerical rules and good agreement is found. The effectiveness of the proposed two-layer model is also confirmed by comparing its cyclic pull-out push-in response with that of single-interface model, and it is found that the energy absorption capacity increases by 24 % and the failure path length increases by 80 %.

Creep tests on GFRP pultruded specimens subjected to traction or shear

In this paper, experimental long-term tests on pultruded GFRP specimens are presented. Specimens have been subjected to constant traction and shear forces for about 760days. The tests have been performed under controlled temperature (20°C) and humidity (60% RH) inside a climatic room. The specimens under traction have been cut from plates and from the flanges of a wide flange GFRP pultruded beam; the specimens under shear loadings have been extracted from the web of the same beam. Moreover, some specimens have been stiffened by bonding CFRP sheets to both sides, in order to study how their introduction may reduce the specimen deformability under long term loading. Results from the unstiffened specimens have been interpreted by means of the Findley law, the reference model for creep in polymers and FRP, in terms of strains and creep coefficient. A simple model has been finally proposed to predict strains in stiffened specimens and by taking stress redistribution into account.

Molecular dynamics simulation of the grain boundary sliding behaviour for Al Σ5 (2 1 0)

In this study the grain boundary sliding (GBS) behaviour driven by a constant shear rate or shear force was investigated for the Al Σ5 (210) grain boundary at 500–750K. It is found that regardless of the type of driving force, the bi-crystal system tended to resist the force applied by GB rotation which resulted from the surface strain, GB migration, or GB coupled motion. The GB generally rotated to the (100) plane of the left grain by 26.57° and in particular cases to the (010) plane of the right grain by 63.43°. Under a constant shear force the GBS only experienced a certain GB rotation and slid away when a threshold stress was reached. This threshold stress decreased with the increase of temperature, but under a constant shear rate, the GBS was strongly related to the temperatures. At 500K, the GBS experienced a relatively complicated process involving GB migration, coupled motion, grain rotation, released defects and the beginning of cracks, while at 750K, GB rotation dominated GBS behaviour.

Evaluation of the efficiency of silicone polyether additives as antifoams in crude oil

AbstractIt is common for crude oil from wells to be accompanied by gas and water because of the presence of natural surfactants in the oil that stabilize the associated water. This causes foaming during processing in gas/oil separators because of the constant agitation and shear forces, which reduce the efficiency of the process and require chemical control by the addition of defoaming additives, or antifoams. In this work, we evaluated the chemical and physicochemical properties of commercial antifoam products based on silicone polyethers along with their efficiency in inhibiting foaming and water/oil (W/O) phase separation. The commercial surfactants were characterized by NMR spectroscopy, size exclusion chromatography, determination of solubility in different solvents, and measurement of the surface and interfacial tensions. A method to test the formation of foam in oil was used to mimic the operating conditions in gas/oil separators. Finally, tests were performed with the addition of aliquots of the additive solutions (30% p/v) in oil to evaluate their efficiency in breaking up the foam under different conditions. The results show that the most polar additive (SL2) was the most efficient in breaking up the foam. Additive SP1, which formed a heterogeneous phase in the oil, was also an efficient foam inhibitor and helped to separate these phases. The antifoam tests showed that these additives did not stabilize W/O emulsions, so they could be used in gravitational separation tanks in the field. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

On perforation of ductile metallic plates by blunt rigid projectile

Abstract In order to enhance the theoretical modeling of Chen and Li [Chen X.W., Li Q.M., 2003a. Shear plugging and perforation of ductile circular plates struck by a blunt projectile. Int. J. Impact Engng. 28 (5), 513–536], an intensive numerical study was performed on the perforation of ductile metallic plates by blunt rigid projectiles. The results of this numerical study agree with the modeling by Chen and Li [Chen X.W., Li Q.M., 2003a. Shear plugging and perforation of ductile circular plates struck by a blunt projectile. Int. J. Impact Engng. 28 (5), 513–536] and with the experimental observations of Borvik et al. [Borvik T., Langseth M., Hopperstad O.S., Malo K.A., 1999. Ballistic penetration of steel plates. Int. J. Impact Engng. 22, 855–886; Borvik T., Leinum J.R., Solberg J.K., Hopperstad O.S., Langseth M., 2001b. Observations on shear plug formation in Weldox 460E steel plates impacted by blunt-nosed projectiles. Int. J. Impact Engng. 25, 553–572; Borvik T., Hopperstad O.S., Langseth M., Malo K.A., 2003. Effect of target thickness in blunt projectile penetration of Weldox 460 E steel plates. Int. J. Impact Engng. 28 (4), 413–464]. The effect of target thickness on its ballistic performance is discussed by accounting for their structural response. Our study confirms the validity of the assumption of constant shear force during plugging perforation. In addition we show that the dynamic cavity expansion model is suitable for description of flat projectile impacting a thick plate, with lateral material flow.

Development of plastic zones in a body with rectangular slot under the conditions of antiplane deformation

We study the quasistatic development of plastic zones in a perfectly elastoplastic body with rectangular slot caused by the action constant shear forces applied at infinity. The exact analytic solution of the problem is obtained, and it is shown that the plastic zones can be studied in the initial stage of development on the basis of the elastic solution of the problem. The shapes of the plastic zones are analyzed depending on the loads for the cases of cracklike, wide, and square slots.

Shear strength of plate girder web panel at elevated temperature

This paper presents a theoretical model to predict the failure loads of plate girders with transverse stiffeners subjected to a specified constant temperature or isothermal condition. The work is based on classical plate girder theory at normal ambient conditions subjected to increasing load. The equations incorporating the temperature-dependent material properties and thermally-induced axial stress arising from surrounding structural restraint are derived. They can be used for the case when the plate girder is subjected to pure shear or to a combination of shear and axial stresses. To simplify the analysis, uniform temperature distribution is assumed within the full depth of web panel. Solution procedures are presented for the fire resistance analysis of web plate girder, either in terms of the shear strength corresponding to isothermal condition, or the limiting temperature for a prescribed set of constant shear force and axial thermal restraint. For both procedures, the predictions agree well with the finite element analyses.

A symmetric over-nonlocal microplane model M4 for fracture in concrete

This paper analyzes the effectiveness of a nonlocal integral-type formulation of a constitutive law such as microplane model M4 in which the yield limits soften as a function of the total strain for prediction of fracture propagation. For a correct regularization of the mathematical problems caused by the softening behavior, an “over-nonlocal” generalization of the type proposed by Vermeer and Brinkgreve [Vermeer, P.A., Brinkgreve, R.B.J., 1994. A new effective non-local strain measure for softening plasticity. In: Chambon, R., Desrues, J., Vardoulakis, I. (Eds.), Localization and Bifurcation Theory for Soil and Rocks, Balkema, Rotterdam, pp. 89–100.] is adopted. Moreover, the symmetric weight function, proposed by Borino et al. [Borino, G. Failla, B., Parrinello, F., 2003. A symmetric nonlocal damage theory. International Journal of Solids and Structure 40, 3621–3645.] for damage mechanics, is introduced for the calculation of the nonlocal averaging of the total strain upon which the yield limits depend. The capability of the proposed model for reproducing the stress and strain fields in the vicinity of a notch is also investigated. Finally, the symmetric over-nonlocal generalization of microplane model M4 has been applied for the simulation of a mixed-mode fracture test such as the four-point-shear test and the test of axial tension at constant shear force [Nooru-Mohamend, M.B., 1992. Mixed-mode fracture of concrete: an experimental approach. Doctoral Thesis Delft University of Thechnology, Delft, The Netherlands.]

Targeting Angiogenesis in Cancer: Bevacizumab-Induced Platelet Activation as a Possible Cause for Unexpected Arterial Thromboembolic Events in Clinical Trials.

The humanized monoclonal VEGF antibody, bevacizumab (Avastin, Genentech), is approved in combination with standard chemotherapy for first-line treatment of patients with metastatic colorectal cancer (CRC) and also shows promising efficacy as anti-angiogenic immunotherapy in patients with non-small-cell lung cancer (NSCLC). A pooled analysis of five randomized, controlled trials (n=1745) showed that, compared to placebo, bevacizumab was associated with an increased risk of arterial thromboembolic events, especially in patients 65 years of age and older (8.5% vs. 2.9%, P<0.01). Because platelets play a crucial role in arterial thrombosis, we hypothesized that bevacizumab has direct platelet-stimulating activity. In a washed platelet system, bevacizumab alone had no effect on platelet aggregation. However, when combined with heparin (0.3 U/ml) and recombinant human VEGF (rhVEGF165 — a homodimeric protein with heparin binding sites) in a 1:2 molar ratio of antibody to antigen to allow optimal formation of immune complexes (ICs) in solution, bevacizumab potently induced platelet aggregation (up to 80–100%; n=5). Bevacizumab-induced platelet aggregation (BIPA) was functionally dependent on Fc domain binding to the platelet low-affinity IgG receptor, FcγRIIA, as demonstrated by an inhibitory monoclonal CD32 antibody (IV.3). BIPA was potentiated in platelets pre-sensitized with low concentrations of ADP or epinephrine. In contrast, BIPA was virtually absent at excess concentrations of heparin (100 U/ml), suggesting that translocation of ICs to the platelet surface via available heparin binding sites (on platelets) was crucial for this platelet response. Unfractionated heparin and the low-molecular-weight heparin, enoxaparin, were equally effective in promoting BIPA. In a manner similar to heparin-PF4 antibodies from patients with heparin-induced thrombocytopenia (HIT), bevacizumab-rhVEGF165-heparin ICs induced significant FcγRIIA-dependent dense granule release (>80%) in a 14C-serotonin release assay (SRA). While strong platelet responses were observed in both SRA and aggregometry, in which platelets were subjected to constant movement and low shear forces, respectively, bevacizumab-rhVEGF165-heparin ICs had only negligible effects on platelet CD62P expression under static conditions, indicating a critical role for platelet-platelet contacts in bevacizumab-mediated FcγRIIA signaling. In summary, our results suggest bevacizumab can induce strong FcγRIIA-dependent platelet activation in vitro when complexed with rhVEGF165 and heparin in an optimal stoichiometry. Due to their analogy to the pathomechanism of HIT, an acquired IgG-mediated disorder potentially associated with deleterious thrombosis, these findings may have direct clinical implications for older cancer patients with cardiovascular comorbidity, especially considering that many patients receive low doses of heparin for thromboprophylaxis and that elevated serum VEGF levels have been demonstrated in various types of malignancy, including CRC and NSCLC.

Pulsatile blood flow, shear force, energy dissipation and Murray's Law

BackgroundMurray's Law states that, when a parent blood vessel branches into daughter vessels, the cube of the radius of the parent vessel is equal to the sum of the cubes of the radii of daughter blood vessels. Murray derived this law by defining a cost function that is the sum of the energy cost of the blood in a vessel and the energy cost of pumping blood through the vessel. The cost is minimized when vessel radii are consistent with Murray's Law. This law has also been derived from the hypothesis that the shear force of moving blood on the inner walls of vessels is constant throughout the vascular system. However, this derivation, like Murray's earlier derivation, is based on the assumption of constant blood flow.MethodsTo determine the implications of the constant shear force hypothesis and to extend Murray's energy cost minimization to the pulsatile arterial system, a model of pulsatile flow in an elastic tube is analyzed. A new and exact solution for flow velocity, blood flow rate and shear force is derived.ResultsFor medium and small arteries with pulsatile flow, Murray's energy minimization leads to Murray's Law. Furthermore, the hypothesis that the maximum shear force during the cycle of pulsatile flow is constant throughout the arterial system implies that Murray's Law is approximately true. The approximation is good for all but the largest vessels (aorta and its major branches) of the arterial system.ConclusionA cellular mechanism that senses shear force at the inner wall of a blood vessel and triggers remodeling that increases the circumference of the wall when a shear force threshold is exceeded would result in the observed scaling of vessel radii described by Murray's Law.

Measurements of the yield stress in frictionless granular systems

We perform extensive molecular dynamics simulations of two-dimensional frictionless granular materials to determine whether these systems can be characterized by a single static yield shear stress. We consider boundary-driven planar shear at constant volume and either constant shear force or constant shear velocity. Under steady flow conditions, these two ensembles give similar results for the average shear stress versus shear velocity. However, near jamming it is possible that the shear stress required to initiate shear flow can differ substantially from the shear stress required to maintain flow. We perform several measurements of the shear stress near the initiation and cessation of flow. At fixed shear velocity, we measure the average shear stress Sigma(yv) in the limit of zero shear velocity. At fixed shear force, we measure the minimum shear stress Sigma(yf) required to maintain steady flow at long times. We find that in finite-size systems Sigma(yf) > Sigma(yv), which implies that there is a jump discontinuity in the shear velocity from zero to a finite value when these systems begin flowing at constant shear force. However, our simulations suggest that the difference Sigma(yf) - Sigma(yv), and thus the discontinuity in the shear velocity, tend to zero in the infinite-system-size limit. Thus, our results imply that in the large-system limit, frictionless granular systems can be characterized by a single static yield shear stress. We also monitor the short-time response of these systems to applied shear and show that the packing fraction of the system and shape of the velocity profile can strongly influence whether or not the shear stress at short times overshoots the long-time average value.

Shear Strength Analysis and Prediction for Reinforced Concrete Beams without Stirrups

The analysis of shear strength of longitudinally reinforced concrete beams, in which a constant shear force acts throughout the shear span, is performed. The shear mechanism is found to be governed by a second order differential equation linking the internal lever arm with the distance from the support. The solution of the shear governing equation is provided, and then the corresponding shear expression is parametrically defined by means of a mechanical analysis. The empirical parameters are determined from more than 900 test data and results found in the literature. The proposed shear strength formula predicts the experimental behavior in a more accurate and uniform way than most known expressions. It is also proposed a design formula, which is more consistent and reliable than the Eurocode one and even than the laborious procedures suggested by ACI Code and AASHTO Standards, since it exhibits a minor number of unsafe predictions.