Constant Tensile Force Research Articles

Large-scale control of morphology and tensile strength enhancement of PEEK fibers after post-treatment

In this study, a post-treatment method was carried out to increase the tensile strength of poly ether ketone (PEEK) fibers, with a maximum increase of 69%. The effects of the post-treatment process parameters on the diameter shrinkage ratio, mechanical properties of PEEK fibers, and the aggregated state structure were also quantitatively investigated by optical measurements, uniaxial tensile tests, differential scanning calorimetry, and two-dimensional-wide angle X-ray diffraction. These studies revealed that the enhanced orientation of PEEK fibers with increasing post-treatment temperature and constant tensile force is the major reason for the significant increase in uniaxial tensile strength. The diameter shrinkage ratio can be used as an indicator of the degree of fiber orientation. More critically, this study also presented mathematical models that described the high linearity of the increase in diameter shrinkage ratio and uniaxial tensile strength of fibers with post-treatment temperature and constant tensile force, respectively. That also revealed the equivalence of temperature and constant tensile force in the post-treatment process and obtained the conversion factor. These in-depth understandings provided positive guidance for improving the strength of PEEK fibers and achieving controllable morphology and mechanical properties in PEEK fiber production.

MD Simulation Reveals Regulation of Mechanical Force and Extracellular Domain 2 on Binding of DNAM-1 to CD155

Two extracellular domains of the adhesive receptor DNAM-1 are involved in various cellular biological processes through binding to ligand CD155, usually under a mechano-microenvironment. The first extracellular domain (D1) plays a key role in recognition, but the function of the second extracellular domain (D2) and effects of force on the interaction of DNAM-1 with CD155 remain unclear. We herein studied the interaction of DNAM-1 with CD155 by performing steered molecular dynamics (MD) simulations, and observed the roles of tensile force and D2 on the affinity of DNAM-1 to CD155. The results showed that D2 improved DNAM-1 affinity to CD155; the DNAM-1/CD155 complex had a high mechanical strength and a better mechanical stability for its conformational conservation either at pulling with constant velocity or under constant tensile force (≤100 pN); the catch-slip bond transition governed CD155 dissociation from DNAM-1; and, together with the newly assigned key residues in the binding site, force-induced conformation changes should be responsible for the mechanical regulation of DNAM-1's affinity to CD155. This work provided a novel insight in understanding the mechanical regulation mechanism and D2 function in the interaction of DNAM-1 with CD155, as well as their molecular basis, relevant transmembrane signaling, and cellular immune responses under a mechano-microenvironment.

Elephant trunks use an adaptable prehensile grip

Elephants have long been observed to grip objects with their trunk, but little is known about how they adjust their strategy for different weights. In this study, we challenge a female African elephant at Zoo Atlanta to lift 20–60 kg barbell weights with only its trunk. We measure the trunk’s shape and wrinkle geometry from a frozen elephant trunk at the Smithsonian. We observe several strategies employed to accommodate heavier weights, including accelerating less, orienting the trunk vertically, and wrapping the barbell with a greater trunk length. Mathematical models show that increasing barbell weights are associated with constant trunk tensile force and an increasing barbell-wrapping surface area due to the trunk’s wrinkles. Our findings may inspire the design of more adaptable soft robotic grippers that can improve grip using surface morphology such as wrinkles.

Numerical simulation of deformations of a specimen of a composite helicopter blade as part of a resonant vibration set-up

To determine the fatigue life of the tail rotor blade of a helicopter made of polymer composite materials (CM), a method of fatigue testing of the specimens of the blade with accompanied numerical modeling of the deformed state has been developed. The tests are carried out on a resonant vibration set-up, with simultaneous reproduction of a forcing harmonic transverse force and a constant longitudinal tensile force. The tests are carried out by a vibration loading mode equivalent in fatigue damage, which includes one level of variable load in the thrust plane and in the plane of rotation. The equivalent mode is formed based on the variable loading spectrum of the blade, which is obtained from the results of flight measurements of the loads on the tail rotor, as well as the repeatability of the expected operating conditions of the helicopter. The tests are accompanied by computational and experimental studies, which include finite element calculation of the stress state and modal analysis of the standard blade and the test specimen, as well as the strain measuring of the structure. According to the results of the research, the vibration loading modes are corrected.

FORMABILITY OF INVAR 36 ALLOY AT HIGH TEMPERATURES

By using of hot tensile tests, which were performed on simulator HDS-20, the formability of Invar 36 alloy was investigated. By a special type of a tensile test, involving a continuous control heating of the tested specimens and their simultaneous load by a constant tensile force of 80 N, a nil-strength temperature of investigated alloy 1419 °C was determined. By continuous uniaxial tensile tests to rupture the strength and plastic properties of the Invar 36 alloy were determined in the wide range of deformation temperatures (from 800 °C to 1390 °C) and mean strain rates (from 0.09 s-1 to 75 s-1). On the basis of obtained results the 3D maps were constructed, expressing the dependence of the contractual hot ultimate tensile strength, hot ductility and hot reduction of area of the Invar 36 alloy on the deformation temperature and on the mean strain rate. Based on the determined plastic properties, the nil-ductility temperature of the investigated alloy of 1390 °C was also determined.

The evolution of creep curves of high impact polystyrene and polyurethane specimens after aging

Specimens of high impact polystyrene and polyurethane were studied for creep at room temperature and constant tensile force without aging and after aging according to various programs. For polyurethane specimens after aging, an increase in creep time for a given deformation by 3 times compared to specimens without aging is observed. For high impact polystyrene in the creep experiments after aging, a decrease of deformation by 6.5 times and the time to fracture by more than 24 times, compared with specimens without aging is shown. To describe the obtained experimental creep curves for polyurethane and polystyrene specimens without aging and after aging, modified versions of linear elastic–viscous models of Maxwell and Voigt written in the effective time scale are used. A good agreement between the theoretical and experimental creep curves is observed.

Research on the Influence of the Shape of an Object on Its Fluid Resistance

In the chapter on Fluids in Edexcel Physics, it is mentioned that different shapes have different effects on fluid resistance. In this study, the effect of the shape of the object on the fluid resistance is studied. Experimental methods are mainly used. In the experiment, by studying the movement speeds of different shapes of iron blocks in water, the different fluid resistances of different shapes of iron blocks were inferred, and the influence of different shapes on fluid resistance was further speculated. In the course of the experiment, different shapes of iron blocks were used, and weights and measuring cylinders were also used. The amount of resistance received is determined by measuring the length of time it takes for different iron blocks to move at a constant distance in water under constant tensile force. The final conclusion is that the more square the object moves in the fluid, the greater the fluid resistance is. The more sleek streamlined an object is, the less fluid resistance it is subjected to as it moves through the fluid.

Роль плантарного апоневроза в формировании кавусного компонента при рецидивах врожденной эквино-поло-варусной косолапости

Актуальность. Врожденная эквино-поло-варусная косолапость (ВЭПВК) является второй по частоте среди всех врожденных аномалий костно-мышечной системы у детей и одной из самых распространенных причин детской инвалидности в Украине. Частота ВЭПВК достигает 1–3 случая на 1000 новорожденных (35–40 % от всех деформаций стоп). По данным ряда авторов, выполнение плантарной фасциотомии позволяет улучшить форму и функцию опоры и ходьбы у пациентов. Цель: определить роль плантарного апоневроза в формировании кавусного компонента в случаях рецидива ВЭПВК у детей. Материалы и методы. Проведены математические исследования с использованием графоаналитического метода. Результаты. Для снижения высоты свода стопы при коррекции ее полой деформации необходимо увеличить длину апоневроза на значительную величину (до 25 % его начальной длины). Для выполнения такой задачи к апоневрозу необходимо приложить значительную растягивающую силу, величина которой зависит от величины снижения высоты свода стопы. Так, для снижения высоты свода на 10 мм нужно удлинить апоневроз на 12 мм, для чего к нему нужно применить постоянно действующую силу величиной 932 Н. Для снижения высоты свода стопы на 20 мм величину растягивающей силы, приложенной к апоневрозу, необходимо увеличить до 1438 Н, что осуществить практически невозможно. Поэтому наличие сокращенного апоневроза является значительным препятствием для эффективного устранения полой деформации стопы. Выводы. Коррекция полой деформации стопы требует значительного уменьшения высоты ее продольного свода, что приводит к значительному удлинению апоневроза — до 25 % от его первоначальной длины. Для обеспечения увеличения длины апоневроза необходимо наличие постоянно действующей растягивающей силы значительной величины, превышающей значение 1000 Н. Плантарный апоневроз играет непосредственную роль в поддержке продольного свода стопы и является одной из причин устойчивости кавусной деформации у пациентов с рецидивом ВЭПВК, что не поддается консервативному лечению. Для устранения кавусной деформации стопы при отсутствии эффекта от консервативного лечения необходимо удлинение апоневроза путем хирургического вмешательства (пересечения). Величину угла продольного свода стопы в 110° можно выбрать в качестве критерия принятия решения в пользу сохранения или отсечения апоневроза.

Experimental investigation and analytical modeling of the crack width effect on the fire performance of carbon textile-reinforced concrete composite

In comparison with fiber-reinforced polymer (FRP) composite, the textile-reinforced concrete (TRC) presents stability in mechanical performance at elevated temperatures thanks to a thermal protection layer by the cementitious matrix. This paper presents the experimental characterization and analytical modeling for fire performance of carbon TRC under the thermomechanical regime at constant tensile force. The carbon TRC is manufactured from the cementitious matrix with good thermal properties (refractory matrix) and the reinforcement of carbon textiles. In the experiment, the ultimate strength of the carbon TRC specimen was firstly identified from the direct tensile tests at ambient temperature. Afterwards, in the thermomechanical regime, the fire performance of carbon TRC specimens according to 5 loading levels ranging from 10% to 75% related to its ultimate strength was determined. As a result, the effect of crack appearance on this thermomechanical performance was highlighted and analyzed. For the analytical modeling, a model was calibrated with the experimental results to predict the fire performance of carbon TRC by taking into account the effect of crack width.

Prediction of Catch-Slip Bond Transition of Kindlin2/β3 Integrin via Steered Molecular Dynamics Simulation.

Kindlin2 is believed to be crucial in integrin activation, which mediates the cell-extracellular matrix adhesion and signaling, but the mechanoregulation of the interaction between Kindlin2 and integrin remains unclear. Here, we performed the so-called "ramp-clamp" steered molecular dynamics simulation on the crystal structure of Kindlin2 bound with β3 integrin. The results showed that the complex had a better mechanical strength for its rupture force of about 200 pN under pulling with the velocity of 1 Å/ns, and was mechanostable for its conformational conservation under constant tensile force (≤60 pN). The catch-slip bond transition with a force threshold of 20 pN was demonstrated by the dissociation probability, the interaction energy, the interface H-bond number, and the force-induced allostery of the complex. This study might provide a novel insight into force-dependent Kindlin2/integrin-related signaling and its structural basis in cellular processes as well as a rational SMD-based computer strategy for predicting the structure-function relationship of the stretched complex.

Two-phase tension of a carbon nanotube

Heterostructures consisting of new two-dimensional nanomaterials may possess non-trivial physical and mechanical properties, promising for many applications. It is interesting that in some cases it is possible to create heterostructures simultaneously consisting of weakly and strongly stretched domains having the same chemical composition, as have been witnessed earlier for some polymer chains, DNA, and intermetallic nanofibres that demonstrate the effect of two-phase stretching. These materials with relatively large tensile forces tend to split into domains with less and greater tensile deformation. Within the two-phase region of deformation, the average deformation of the sample increases with a constant tensile force, with the growth of a domain with a higher strain due to a domain with a lower strain. In this paper, the two-phase stretching of carbon nanotubes has been studied by means of molecular dynamics simulation. It has been established that the load-deflection curves during axial tension exhibit hysteresis-like behavior due to energy dissipation during nucleation and motion of domain walls. It is shown that in the two-phase tension regime, a carbon nanotube is a special case of a heterostructure, the properties of which can be controlled by changing the size of the domains of each phase by applying elastic deformation.

Experimental and theoretical studies of the effect of long-term natural aging on the mechanical properties of high impact polystyrene

Effect of prolonged natural aging in the laboratory conditions at room temperature during 40 years on the mechanical properties of six different marks of high impact polystyrene (HIPS) was investigated. The deformation curves in tensile experiments were obtained. These curves indicated that the hardening effect is observed for all marks of HIPS after aging. The HIPS were also tested for creep at room temperature and constant tensile force. Specimens of most marks of HIPS does not fractured during 30 days. After natural aging during 40 years, the specimens were fractured in a time-to-fracture range from 10 minutes to 30 hours depending on the mark of HIPS. A modified version of the Maxwell equation written in the effective time scale is used to describe the obtained experimental creep curves. A good agreement between theoretical and experimental creep curves is observed.

The effective tensile and bending stiffness of nanotube fibers

We analyze the pure bending state, preliminarily considering the pure traction problem, for a fiber with circular cross-section composed by monodispersed Nano Tube (NT) segments, whose length is much lower than the length of the fiber, arranged in a cross-sectional square lattice, possibly inclined with respect to the bending plane. The proposed model accounts for the compliant shear coupling of the constituent NTs along their lateral contact surfaces, and considers that the position of each NT is offset with respect to the neighboring ones by a fixed distance. The shearing of the NTs permits their mobility in longitudinal direction, inducing an internal rearrangement, calculated through energy minimization, that affects the macroscopic response. With a micro-macro approach, the internal actions in the whole fiber are calculated. We find that uniform axial macroscopic strain is associated with constant tensile normal force in the fiber and null moment; correspondingly, constant macroscopic curvature provides a constant bending moment in the plane of bending and null axial force. It is then possible to consider the NT fiber as an equivalent homogeneous beam, whose effective tensile and bending stiffness can be calculated, finding a dependence upon the aspect ratio of the fiber, the aspect ratio of the individual NTs and, more important, the offset of the NTs. The model permits to interpret recent experimental results.

Thermomechanically transforming Notched NiTi Thin ribbon: Effect of Martensitic Transformation on Stress Gradients

In this work, we used numerical simulations to investigate the effect of thermally induced forward martensitic transformation (MT) under constant load on the stress redistribution around stress risers. Finite element simulations of stress redistribution around two-sided notches in a thin NiTi ribbon subjected to constant tensile force and homogeneous cooling from austenite to martensite were performed. Changes in stress gradients around the notches were analyzed with regard to heterogeneity of thermomechanically driven MT. A parametric study was performed in order to understand the effect of transformation strains, Young’s modulus of martensite and notch radius on the magnitude of notch-tip stresses after the completion of MT. We found that forward MT critically amplifies the initial elastic stress gradients around the notch. The increase in magnitude of notch-tip stress is closely related to elastic deformation in martensite needed to accommodate the transformation strain in the surrounding notch unaffected zone. This approximation holds for notch radii being small compared to the ribbon width. For large radii MT is more homogeneous, the notch-tip is more shielded from transforming surroundings and, hence, the notch-tip stress approach the nominal stress.

Graphene nanoribbon as an elastic damper

Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.

Method for Designing Springs Using Materials with Shape Memory as the Actuators of Power Units

The physical and mechanical behavior of titanium nickelide coil springs of different stiffness is experimentally investigated during thermal cycling through martensitic transformation ranges under a constant tensile force. The springs exhibit a reversible length change by reciprocating movements. In terms of classical mechanics, a method for the design calculation of springs with shape memory as actuators is proposed for a given stiffness range.

Thermodynamics and Kinetics of Globular Polymers under an Applied Force

We examine the problem of a polymer chain, folded into a globule in poor solvent, subjected to a constant tensile force. This system represents a Gibbs thermodynamic ensemble, and is useful for analysing force-clamp AFM measurements - now common in molecular biophysics. Using a basic Flory mean-field theory, we account for surface interactions of monomers with solvent. Under an increasing tensile force a first-order phase transition occurs. The compact globule ruptures and fully extends, in an ‘all-or-nothing’ unfolding event. This contrasts with the regime of imposed extension, first studied by Halperin and Zhulina, where there is a regime of coexistence of a partial globule with an extended chain segment. We relate the transition forces in this problem to the solvent quality and degree of polymerisation, and find analytical expressions for the energy barriers present in the problem. From these, we analyse the kinetic problem of a force-ramp experiment, showing that the rupture force depends on the rate of loading. We then change the system by inserting a super-hydrophobic ‘core’ at a given point in the polymer chain. This acts as a crude model for a large class of folded biomolecules with hydrophobic or hydrogen-bonded cores. Again, we consider applying a constant tensile force. Introducing a ‘core’ leads to an intrinsic (quenched) stochastic variation in the unfolding rate, even when the positions of the added monomers are fixed along the sequence. This gives rise to non-exponential population dynamics, which is consistent with a variety of experimental data. It does not need any structural disorder of the type thought to be at the origin of non-exponential relaxation laws.

Dynamics of a beam-column element on an elastic foundation

An exact analytical solution of a harmonically vibrating beam-column element resting on an elastic Winkler foundation is derived. The solution covers four cases comprised of constant compressive or tensile axial force with the restrictions ks – mω2 < 0 and ks – mω2 > 0. The proposed solution is not restricted to a particular range of magnitudes of the foundation parameter. Closed form solutions of dynamic shape functions are explicitly derived for each sub-case to obtain frequency-dependent dynamic stiffness terms that constitute the exact dynamic stiffness matrices. Four numerical examples are provided to demonstrate the merits of the present study.

Calculation-experimental analysis of the thermocyclic deformation of titanium nickelide coil springs

The physicomechanical behavior of a cylindrical spring made of titanium nickelide is experimentally studied during thermal cycling through the martensitic transformation ranges at a constant tensile force. The spring exhibits a reversible change in the length and the diameter, the relative change in the length reaches 1476%, and the relative change in the diameter is 33%. The alternation of reciprocating rotary motion and translational motion of the spring is observed during deformation. A method is proposed to estimate the stresses and the strains that appear in the material at large spring elongations. Thermal cycling at a constant axial force is shown to be accompanied by a reversible hysteretic change in the tangential and normal stresses and the shear strains and by a reversible hysteretic reversible change in the axial strains.

Unfolding of globular polymers by external force.

We examine the problem of a polymer chain, folded into a globule in poor solvent, subjected to a constant tensile force. Such a situation represents a Gibbs thermodynamic ensemble and is useful for analysing force-clamp atomic force microscopy measurements, now very common in molecular biophysics. Using a basic Flory mean-field theory, we account for surface interactions of monomers with solvent. Under an increasing tensile force, a first-order phase transition occurs from a compact globule to a fully extended chain, in an "all-or-nothing" unfolding event. This contrasts with the regime of imposed extension, first studied by Halperin and Zhulina [Europhys. Lett. 15, 417 (1991)], where there is a regime of coexistence of a partial globule with an extended chain segment. We relate the transition forces in this problem to the solvent quality and degree of polymerisation, and also find analytical expressions for the energy barriers present in the problem. Using these expressions, we analyse the kinetic problem of a force-ramp experiment and show that the force at which a globule ruptures depends on the rate of loading.