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The kick-start technique in competitive swimming generates a force acting on the starting platform owing to gravity, muscle contraction and resulting joint torque. To understand optimal body movement on the starting platform for maximising take-off velocity, it is necessary to investigate the joint torque in relation to the joint's rotation effects. Joint torques were calculated by inverse dynamics using kinetic and kinematic data. A one-way ANOVA showed significantly greater extensional torque for shoulders than for elbows or wrists, and for hips than for knees or ankles. The results indicated that the force of the hands was mainly influenced by extension torque at the shoulder joint. Hip joint extension torque on the front side lower limb (FSLL) was mainly used for supporting the body weight until hands off. After hands off, the front-foot force originated mainly by increases in ankle joint plantar flexion and knee joint extension torque on the FSLL. Rear side lower limb torque increases in the hip, knee and ankle joints provided the rear-foot force. This investigation clarified the magnitudes and functions of each joint torque acting on the extremities during the kick-start, providing practical information for improving starting performance.

Introduction. Currently in Russia, innovations in urban subsoil facilities construction are among the key factors of economic development. To improve the efficiency of holding a pit wall in restraint urban conditions and prevent soil loosening around the pit, it is proposed to optimize the pre-tension forces of the bottom-up anchors. It has been determined that the pre-tension forces of the active anchors create extra retention forces in the sliding wedge and, in some specified sense, reinforce the walled soil. Research methodology. When modeling the complex calculation of a pit wall, 4 main stages of the pit excavation and 3 stages of preliminary level tensions of anchor ties were preset. The numerical solution of the beam bending problem is the basic method of calculating the walling strength; the beam laying on the elastoplastic base and retained by the anchors as bonds. The bottom-up anchor structure is modeled in the operating environment of GeoWall software. The values of bottom-up anchors pre-tension are set following the ordinates of forces in the anchors, obtained from the walling stability calculation by the deterministic approach. Experimental research was carried out of the impact made by pit opening stages on the walling stress strained state. Results. Analysis and discussion. The efficiency of bottom-up anchors optimal pre-tension, according to the research results, is obtained by constructing the diagrams reflecting the correlation dependence between the anchors loading and the walling displacement. An obvious advantage of the software is the opportunity to calculate walling and retaining structures stage by stage ignoring their construction technologies. Experimental calculation in GeoWall has shown a high bearing capacity of the bottom-up anchor support. Summary. The nature of the obtained dependence between the anchor longitudinal forces and the pit walling horizontal displacement reflects the actual situation. Thus, for a quiet expectable value of horizontal displacement, it is required to correct the optimal value of pre-tension using the empiricalformula dependences.

The main structure of a fiber-reinforced composite is determined by a preform. The manufacturing of preforms is associated with the generation of fiber hairiness or even breakage due to friction, w...

Bolting and anchoring products are mostly pre-tensioned after their putting into the construction. Pre-tensioning force is a force with clearly defined size and direction and helps the construction to transfer loads. After pre-tensioning a cable bolt some pre-tension losses occur immediately after releasing the jack and other losses progress during their working time. These losses may occur due to the mechanical properties of the cable bolt and its structure itself, but also due to the properties of the surrounding rock mass.The article deals with the enumeration and description of individual losses in accordance with applicable legislation and their measurements both in the laboratory and in actual mining conditions. The comparison of calculated and measured losses and a brief overview of pre-tensionable bolting technology within OKD coal deep mines is a part of the content as well. The result of the tests is quantification of these types of pre-tension losses including proposals for their reduction.

The selection of surgical site for the femoral tunnel during anterior cruciate ligament (ACL) reconstruction surgery remains controversial. However, it is not only surgical site that lacks scientific consensus but also the level of pre-tension force applied during implanted graft fixation. This study aims to propose the optimal femoral tunnel position considering appropriate pre-tension in ACL reconstruction surgery. To select the optimal position, the stress and strain on the implanted graft in 40 cases was calculated by testing combinations of 10 recommended tunnel positions on the femoral epicondyle and four pre-tension forces (0, 10, 20, and 30 N) using multi-flexible body dynamics. The lowest implanted graft stress and strain was found in a posterior proximal site at 15 mm from the lateral femoral epicondyle; the pre-tension force here showed no significance. In conclusion, changes in stress on the implanted graft were affected more by tunnel position than by pre-tension.

Thermoelastic damping (TED) is one of the main energy dissipation mechanisms in micro/nano resonators and one of the major concerns in respect to performance of micro-electromechanical systems and ...

In this paper, the energy dissipation in a bolted lap joint is studied using a continuum microslip model. Five contact pressure distributions compliant with the power law are considered, and all of them have equal pretension forces. The effects of different pressure distributions on the interface stick-slip transitions and hysteretic characteristics are presented. The calculation formulation of the energy dissipation is introduced. The energy dissipation results are plotted on linear and log-log coordinates to investigate the effect of the pressure distribution on the energy distribution. It is shown that the energy dissipations of the lap joints are related to the minimum pressure in the overlapped area, the size of the contact area and the value of the power exponent. The work provides a theoretical basis for further effective use of the joint energy dissipation.

Since numerical structural calculations of sailing yachts' rigs strictly depend on the dock tuning load (DTL), it is necessary to evaluate it during vessels' normal operations even when it cannot be estimated by load cells installed onboard. In this paper, a novel approach for the determination of the pre-tension load of stays and shrouds for large sailing vessels is presented and it based on the coupling of an analytical approach to the cables’ dynamics and the evaluation of natural modes by using Experimental Modal Analysis (EMA). The validation of the method herein proposed as been validated by numerical non linear Finite Element calculations.

This article describes the strengthening of normal sections of reinforced concrete beams by pre-stressed reinforcement under load. Experimental samples had the length of 2100 mm, the width of 100 mm and the height of 200 mm. Strengthening of experimental beams is designed from flat frames and isolated rods, which were combined into a spatial frame by transverse rods. In all the be the longitudinal working reinforcement were steel bars of 2 2 O 12 A500C, constructive and transverse reinforcement was represented by– O 8 A240C bars with spacing of 50…100 mm. The load was applied by means of a hydraulic jack in thirds of the span. The beams were tested for bending. The beams were reinforced with the use of two unstressed or pre-stressed reinforcement rods of O12 A500C mm.

Mooring lines are the most commonly used station-keeping systems for floating platforms, and the pre-tension of the mooring lines has significant effect on the dynamics of floater/mooring system. However, during the model test, which is the most important method for the research on the floater/mooring system, the pre-tension of the designed mooring lines in the basin are always significantly different with the target values of the ideal model due to the error of the manufacture of the mooring lines and positon locating of the anchor point and so on. As a result, the adjustment of the pretension of the mooring lines based on the ideal model is an important task during the model test. The pre-tension is always adjusted by increasing or decreasing mooring line length. While all the mooring lines are connected with the floater and coupled with each other, pre-tension adjustment is an unwarranted and cyclic process which often wastes a lot of time. This paper presents a novel methodology for regulating the mooring line pre-tension based on matrix calculation. The increment matrix of the mooring line tension can be obtained by increasing or decreasing the length of each mooring line in the numerical model. Assuming that the increment the mooring line tension is linear to the change of the mooring line length, the adjustment amount of each mooring line length can be calculated from the difference of the real pre-tension and the target pre-tension. However, the mooring line tension is always nonlinear to the mooring line length. Calculating the increment matrix of the mooring line tension and adjustment of the mooring line length is also a cyclic process until the error of real pre-tension of the model in the basin and target value can meet the accuracy requirement. This method is used in a model of a mooring system with 12 mooring lines which are connected with a semi-submersible platform. The test results show that the pre-tension of mooring lines can be adjusted to the target value quickly based on the method proposed in this paper.

The paper reviews the theory of technical evaluation of the containment and the experience of using the mobile geodetic diagnostic system at the nuclear power plant unit No. 4 of Rostov NPS. The paper considers the results of a regular built-in system designed to determine and evaluate the strain-stress state of containments during the acceptance in service, commissioning stage and operating period. A comparison with the results of the geodetic system obtained at the same stages of containment existence.

A hot rolled and annealed Mg-5Sn-2Zn sheet was subjected to pre-tension and ageing treatment, and the microstructural evolution and mechanical property were carefully examined in this study. The as-annealed sheet exhibited an intense basal texture with bimodal grains, moderate yield strength and excellent elongation to failure. Samples directly aged at 150 °C for 48 h exhibited a small increment (∼10 MPa) in yield strength. In contrast, the yield strength was obviously improved by 48 MPa in RD and 49 MPa in TD through 3% pre-tension and ageing treatment. Moreover, the strength can be further increased by increasing pre-strain. Detailed microstructural characterization revealed that pre-tension refined the Mg2Sn precipitates and increased the number density, in addition, dense dislocation and a few twins were retained after ageing treatment. The pronounced improvement of yield strength was mainly ascribed for combination of the increased precipitation hardening of Mg2Sn and dislocation strengthening and the weakness of texture strengthening.

A relatively new experimental-analytical method for determining the location separating the cracking and decompression moments of a prestressed concrete (PC) flexural member is proposed. This metho...

Understanding the friction mechanism at microscale of fibrous material is important as it is one of the key roles in governing the behaviour of fibre assemblies at meso and macroscale. However, mechanical stress such as tension may also influence the frictional behaviour. In this study the frictional behaviour between fibres under pre-tension is explored. A new experimental setup was successfully developed to measure the friction force between two single aramid fibres at perpendicular contact. Although pre-tension influences the bending stiffness of the fibre, the results show that the effect of pre-tension on the contact length is relatively small. The elastic deformation of the contact dominates over the ‘wrapping effect’, generating the contact area over which the interfacial shear takes place.

Bolt pre-tension is regularly used in the practical case of bearing-type connection. Due to confinement of lap plates, complicate triaxial stress field can be observed near bolt hole, which may affect bearing behavior of the whole connection. Currently, investigations on the related issues are limited. To fill this research gap, this paper presents a combined experimental and numerical study on high strength steel single-bolt connections with bolt pre-tension. Results reveal several meaningful recognitions on the bearing behavior of connection with bolt pre-tension. Firstly, the effect of bolt pre-tension on the final tearout failure mode is negligible. Secondly, distribution of triaxial stress field initiates with a circular pattern and gradually shrinks to a localized pattern between shear fracture lines at ultimate resistance of the connection. Thirdly, out-plane confinement will limit the piling-up of plate material in front of bolt, which will reduce the related bearing resistance. However, increasing bolt grade is still beneficial to the whole connection due to a trade-off between ultimate resistance of the connection and related bearing resistance. Comparison with current code is further conducted. It is found that current Eurocode3 has adequate design safety for connection with bolt pre-tension while extra safety is needed for current AISC 360-16.

The non-uniform stress distribution of woven fabric has a significant influence not only on its mechanical performance in service, but also on its weaving efficiency in the fabrication process. For investigating the stress distribution in woven fabric, a numerical model at the yarn scale was established to simulate the interlacing process between the weft and warp yarns using an explicit finite element solver. The yarns were assumed to be a homogeneous continuum and the transversal isotropic constitutive equation was used. A modified lenticular initial shape was used as the cross-section of the yarn and trajectories of warp and weft yarns were set to be straight. The classical Amonton–Coulomb law was used for the tangential behavior between the weft and warp yarns. The simulation results reveal that the interaction between weft and warp yarns consists of three phases in terms of contact, adhesion and sliding. The sectional stress distribution in the weft yarn determined by multi-points contact between a single weft yarn and a group of warp yarns was also analyzed. The tension stress of the weft yarn was larger in the middle part than that in both sides. Based on the numerical model, the effects of two key parameters, namely the frictional coefficient and weft pre-tension, on the stress distribution were discussed in detail. The weft crimp angle and warp tension distribution uniformity decreased as the frictional coefficient decreased, whereas the warp tension fluctuation range did not obviously decrease. However, an improved method by exerting pre-tension in two ends of weft yarn was proposed and the warp tension fluctuation range was significantly decreased. The distribution trend of warp tension obtained from the numerical simulation showed an acceptable tendency with experiment measurements.

The possibility of improving the bending strength of timber beams through prestress is discussed. Different prestressing and anchoring procedures are investigated: (i) post-tension, with mechanical anchorage on the ends of the wood elements; (ii) pre-tension, with the anchorages being either mechanical, as in the previous system, or glued, with the force being gradually transferred through shear stresses along a certain length of the wire/wood interface. The main conclusion is that any of the procedures may be advantageously used with either small (mass-production) or long glued-laminated timber beams, as a possible alternative to CFRP reinforced beams.

In this study, in order to asses the structural performance of trapezoidal PSC girder using a socket joint system and it is possible to calculate the optimized cross-section of the web element tests were carried out for each specimens. we conducted a socket joint performance test, web bending and shear performance tests and all tests were performed at 4 point loading method. The initial crack load of socket joint specimen was significantly lower than the reference specimen but post peak behavior was no significant differences. And the length of the loop joint of the reinforcing bars had no significant effect on the maximum load. As a web shear tests, to obtain a maximum load of the specimen has a prestressing rod reinforced at tension side. As a web flexural tests, to obtain higher diagonal cracking load in specimen of reinforced using prestressing rod than reference specimen.

This paper studies the effects of pre-tension on flow-induced vibration of a flexible cylinder with two degrees of freedom in a towing tank. A 0.45 m section of Tygon tubing with an outer and inner diameter of 7.9 mm and 4.8 mm respectively, was employed as a flexible test model, the mass ratio and aspect ratio of which is 0.77 and 57, respectively. It was towed from rest up to 0.8 m/s before slowing down to rest again over a distance of 1.6 m in still water with three cases of pre-tension from 0 to 8 N. The Reynolds number based on the cylinder’s outer diameter spanned from approximately 780–6300 while the reduced velocity ranged from 2 to 16. Emphasis was on revealing the possible relationship between pre-tension and response amplitude as well as the frequency. The vibration amplitude and frequency obtained during the brief constant towing speed were quantified and expressed in terms of reduced velocity. Narrowed lock-in bandwidth and reduced response amplitude were observed. The findings from this set of experiments are compared to the existing knowledge in the literature.

For basal textured Mg alloy plates, {10-12} twins can be easily generated by pre-compression perpendicular to the c -axis of grains. Thus, it should be practical to strengthen Mg alloy plates by introducing twin boundaries. In this study, we show that control of the a -axis distribution is also important for enhancing the strengthening effect by pre-inducing {10-12} twins. Pre-tension along rolling direction (RD) is applied on a rolled AZ31 Mg alloy plate, and then the sample is compressed along transverse direction (TD) to generate {10-12} twins. The experimental results show that pre-tension causes 〈10-10〉 orientations concentrating toward RD, which promotes the activation of multiple twin variants in each grain for subsequent compression along TD. As a consequence, twin nucleation rather than twin growth is favored, and the number of twin lamellae per grain is increased, which enhances the refinement hardening effect during compression of the twinned sample along RD. The underline mechanism is analyzed, which can also provide some insights into understanding deformation mechanism of Mg alloys.

Ligatures are used with many types of interspinous process devices to prevent instability in flexion movement by wrapping around upper and lower spinous processes. In this study, the effects of the pre-tension by tightening the ligature on the spinous process fracture were investigated using a finite element method. Five different interspinous process devices, Coflex-F®, Wallis™, Diam™, Viking, and Spear®, were chosen, and implanted after creating a defect consisting of bilateral facetectomy with a resection of the ligamentum flavum. Flexion and extension motions were simulated with various pre-tension values of the ligatures in the range of 0 to 400 N at 100 N increments. While stability at the surgical level in the flexion increased with increasing pre-tension of the ligatures, the spinous process fracture risk also increased with increasing ligature pre-tension. Furthermore, the fatigue life of the spinous process also decreased. Thus, the amount of pre-tension of the ligatures should be carefully selected depending on the materials and design of implants.

This paper reports on the effect of pre-tensions on needle and bobbin threads, sewing speed, thickness of fabric plies and the linear density of the threads on the tension peaks occurring on needle thread during sewing on a single needle lock stitch machine. The needle thread tensions are measured at two locations: above the needle bar (bottom segment) and above the needle thread tensioner (top segment). A factorial design approach is used to study the four parameters. The role of bobbin tension is studied in a separate experiment, while keeping the pre-tension on the needle thread constant. The highest tension observed on the needle thread is the stitch tightening tension which is directly affected by the pre-tension set on the needle thread disc tensioner. Heavier threads develop lower tightening tension which may affect the seam balance. The thickness of fabric plies does not affect the needle thread tension. Sewing speed has marginal influence on the stitch tightening tension near the needle thread tensioner. The pre-tension on the bobbin thread affects only the needle thread tension when the take up lever pulls up the needle thread loop to release it from the rotary shuttle hook gib.

The use of link chains became the decisive success factor in the mechanisation of coal mining in longwall face working. The development of chain technology in recent decades has been characterised by the rapid development of larger chains with more and more compactness and complex geometries. This article discusses potential further steps in development and the limitations of conventional chain technology. The objective of development is to increase conveyor capacity while at the same time improving operational safety. The conveyor capacity is limited by the actual loading cross section achievable and the chain's speed; both these parameters cannot be increased at will. Research relating to the fatigue strength of chains and the management of the required pre-tension force/slack of return chain indicates that, from the perspective of chain technology, longer longwall mining faces are possible than are mined today. Der Einsatz von Gliederketten wurde bei der Mechanisierung der Gewinnung von Kohle im Strebbau zum entscheidenden Erfolgsfaktor. Die Entwicklung der Kettentechnik in den letzten Jahrzehnten ist gekennzeichnet durch eine rasante Entwicklung groserer Ketten mit immer kompakteren und komplexeren Geometrien. Der vorliegende Beitrag diskutiert mogliche weitere Entwicklungsschritte und die Grenzen der konventionellen Kettentechnik. Ein Ziel der Entwicklungsbemuhungen ist die Erhohung der Forderkapazitaten bei gleichzeitiger Steigerung der Betriebssicherheit. Die Forderkapazitat ist durch den tatsachlich realisierbaren Beladungsquerschnitt und die Kettengeschwindigkeit begrenzt; beide sind nicht beliebig zu erhohen. Untersuchungen zu der Auslegung uber die Zeitfestigkeit von Ketten und uber die Beherrschung der erforderlichen Vorspannkrafte bzw. Hangkette zeigen, dass aus der Perspektive der Kettentechnik grosere Streblangen als bisher moglich sind.

In this paper, the planar membrane structure of an engineering example is analysed theoretically from the variation of pre-tension and membrane surface deformation with temperature. Then ANSYS software is used to analyse the pre-tension changes of the membrane structure and the membrane surface deformation with the uniform load under different temperatures (-50∼70 °C) for the membrane structure. The trend image of pre-tension and membrane surface deformation with temperature was obtained, and the minimum value of pre-tension of the membrane structure was obtained according to the relevant regulations. According to the variation law of pre-tension, the pre-tension selection scheme for the installation of planar membrane structure is summarized, which provides some references for the determination of pre-tension in the installation of planar membrane structure.

The elastic structure of the anchor-fixed monolayer cable net generates elastic displacement under pre-tension, so the designed tension of the cable can be consistent after repeated test and it is difficult to control in later construction. For this case, we get causes for elastic displacement based on comprehensive analysis, simulate and analyze it by using displacement compensation tension method to compute all initial tensions once time and guarantee consistent designed tensions after elastic distortion of a cable. We make the construction sequence and record the force and tension of each cable after it is strained in place based on computed initial pre-tension in order to monitor if the distortion is reasonable in tension and guarantee in-place tension in construction once time without repetition.

This paper presents and discusses the possibility of improving the bending strength of timber beams through the use of prestress. The emphasis is put on various methods of imposing the prestress force and transferring it into the wood part: i) through post-tension, with the force being mechanically anchored on the ends of the wood elements; ii) through pre-tension, with the anchorages being either mechanical, as in the previous system, or glued, with the force being gradually transferred through shear stresses along a certain length of the wire/wood interface. Although the risk of failure due to tension perpendicular to the grain in the anchorage regions exists, it is not specifically studied in here, due to the limited scope of the study. The main conclusion is that any of the procedures may be advantageously used with either small (mass-production) or large-span glued-laminated timber beams and, though they are mostly suited to the production of new elements, they may also be adapted to the strengthening of existing beams.

The structure design of the tension cable in monolayer cable net curtain wall is very important. Generally the diameter and initial pre-tension of the tension cable is identified via iterative computing in the past works. This paper proposes a simple computing method for this case, which not only quickly computes the maximal internal force of the tension cable by the known deflection limit and identify the diameter of the tension cable, but also deduces the initial pre-tension of the tension cable and assist engineers to analyze and calibrate the tension cable and guide field tension construction.

The yarn pull-out behavior of greige and scoured plain woven Kevlar fabrics was studied under various combinations of yarn pull-out speed and fabric pre-tension. Warp yarns showed higher pullout forces than the fill yarns. The pullout forces increased with increasing fabric pre-tension levels and decreased with increasing pull-out speeds. The variability in pull-out forces were generally higher for the dynamic pull-out forces compared to the static forces, generally higher at lower pull-out speeds, and generally higher for the greige fabrics compared to the scoured fabrics. These results indicate that the inter-yarn friction characteristics of woven Kevlar fabrics are sensitive to the yarn sizing, pull-out rates, as well as fabric pre-tension which have implications on the ballistic impact response of these Kevlar fabrics.

As a multifunction floating platform, Floating Drilling, Production, Storage and Offloading (FDPSO) combining the well-known Floating Production, Storage and Offloading (FPSO) with a drilling unit. For the environment condition of deep-water oilfield is very severe, the motion response and mooring line tension of FDPSO is a worthy topic of studying. In this study, the numerical time-domain coupled prediction method for the mooring line tension and motion response of FDPSO system is constructed by ANSYS AQWA software. Furthermore, the results of a model test conducted in Harbin Engimeering University are used to investigate the feasibility and validity of the commercial simulation. The effect of mooring line pre-tension on the response of FDPSO is studied by varying the pre-tension of mooring line during the calculation. The time series curve of the mooring line tension and motion response, and the comparison of motion spectrum and mooring line tension spectrum are provided in this article.Copyright © 2016 by ASME

Textile materials, which are different in fibre content, weave type, density and thickness, as well as multi-layered synthetic leathers, are used in soft furniture upholstery production. Deformation - relaxation behaviour, which depends on mechanical properties of such materials differs significantly, also. From this standpoint substantial problem exists in soft furniture production, because the dimensions of its upholstery patterns, i.e. initial pretention must be adjusted taking into account the differences of applied materials mechanical properties. Otherwise external view and quality of upholstery may be unacceptable due to obvious visual material excess on soft furniture surfaces, which is called pull-on ease. The aim of this investigation was to determine the dependencies between three different levels of soft furniture upholstery pre-tension and corresponding values of pull-on ease. New testing method presented in this study allows defining soft furniture upholstery deformational behaviour and its regularities in respect to the initial dimensions of upholstery patterns.DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3099

A bolted joint is a typical connection that is widely used in machine assemblies and structural components. These joints encounter several types of working load. This paper is concerned with the analysis of a bolted joint under shear and tensile loading using a three-dimensional finite element method. Modeling a bolted joint with three-dimensional finite element (FE) applications is not an established technique. We make a full three-dimensional FE model complete with contact surfaces, clearance between bolt and hole, and pre-tension. This model identifies the localized points of high stress concentration, which is not possible with the simplified two-dimensional or axi-symmetric models previously reported. A comprehensive investigation is made on the effect of clearance and pre-tension on the mechanical behavior of a single bolt joint under shear loading. Certain of the numerical results are verified by measuring the performance under load of a bolt shear joint. The study is then extended by analyzing the bolted joint in tension with varying levels of pre-tension.

Pre-tension of filament is critical to the characteristics of solo-sirofil composite yarn. In this paper, solo-sirofil yarns under filament pre-tension of 5-25cN were produced by modified EJM-128K ring spinning frame. The hairiness, breaking strength, breaking work and yarn evenness were tested under standard test conditions. It’s explored that when the pre-tension of filament is 15cN, perform of solo-sirofil achieve the best level with lower hairiness, higher breaking strength and breaking work, and better yarn evenness.

In this paper, the influence of pre-tension on elongation percentage at specified load for knits was studied .First of all, initial elongation and elongation percentage at specified load for different retractility knits were tested and analyzed at different pre-tension. And then significance of influence of pre-tension on initial elongation and elongation percentage at specified load for knits were analyzed by means of variance analysis. Results show that the pre-tension has significant influence on initial elongation for different retractility knits, and it has no significant influence on elongation percentage at specified load for little retractility knits, and it has significant influence on elongation percentage at specified load for well retractility knits. The greater the pre-tension is, the more significant the influence is, Therefore it is suggested that pre-tension is generally less than 0.1N in the test.The research results can provide a certain reference to stretch and recovery test for knits and test standard recension .

This paper adopts contacting finite element method to perform exact stress and strain analysis on bolt joint structure, and the curve of pre-tension stress-life σp-N was drawn. According to the curve, production practice can be well guided and the optimum pre-tension stress may be obtained .By the means of curve between load and deformation, the curve shape of σp-N was analyzed in detail, the results showed that the analysis by finite element was coincident with mechanics analysis.

Several mechanisms have been proposed in the literature to explain the robust attachment and rapid, controllable detachment of geckos' feet on vertical walls or ceilings, yet, it is still debatable, which one is ultimately responsible for geckos' extraordinary capabilities for robust and reversible adhesion. In this paper, we re-examine some of the key movements of geckos' spatula pads and seta hairs during attachment and detachment, and propose a sequence of simple mechanical steps that would lead to the extraordinary properties of geckos observed in experiments. The central subject under study here is a linear distribution of pre-tension along the spatula pad induced by its sliding motion with respect to a surface. The resulting pre-tension, together with a control of setae's pulling force and angle, not only allows for robust and strong attachment, but also enables rapid and controllable detachment. We perform computational modelling and simulations to validate the following key steps of geckos' adhesion: (i) creation of a linear distribution of pre-tension in spatula through sliding, (ii) operation of an instability envelope controlled by setae's pulling force and angle, (iii) triggering of an adhesion instability leading to partial decohesion along the interface, and (iv) complete detachment of spatula through post-instability peeling. The present work not only reveals novel insights into the adhesion mechanism of geckos, but also develops a powerful numerical simulation approach as well as additional guidelines for bioinspired materials and devices.

A warm pre-tension rotation bending process is presented to bend the AZ31 profile. A 3D elastic-plastic thermo-mechanical coupled finite element model is established to investigate the effect of forming temperature on the geometric accuracy of the profile. The results indicate that with increasing forming temperature, the springback angles decrease from 8.37° to 7.2°; the bending radii decrease from 90.69 mm to 89.67 mm; the cross-section distortion of the bent profile increases.

Short carbon fiber is an effective and essential reinforced material in composite domains. Generally, it is produced by chopping technology, among which pressing roller and grooved wheel are two popular chopping techniques. According to the working principle of these two techniques, the pressing roller can be simplified as a flexible-support cutting in off-axis transverse cutting, meanwhile the grooved wheel can be represented by a non-support cutting. To reveal the fracture difference of carbon fiber between the pressing roller and the grooved wheel technique, comparative investigation of failure behavior between a single carbon fiber (also simplified as a filament) with flexible support and with non-support was performed in off-axis transverse cutting using a custom-designed fixture. Both the cutting force and the fracture surface of the filament were comparatively analyzed in cutting process. It was found that the failure of single carbon fiber was caused by tensile effect in a non-support cutting, whereas that in a flexible-support cutting was caused by bending effect. The cutting-off force and cutting-off depth of filament cut by use flexible support are significantly lower than that by use non-support under low pre-tension. It is interesting to find out that the failure spot of carbon fiber filament in non-support cutting under low pre-tension tends to occur randomly. Meanwhile, in a flexible-support cutting, the break point of carbon fiber filament is determined by the tip of the blade. After a comprehensive comparison, the flexible-support cutting is a prior selection to produce short carbon fibers compared with the non-support cutting.

The results of fused multilayer systems pre-tension level upon biaxial loading are presented in this research work. The values of initial pre-tension of fused multilayer systems in longitudinal and transverse directions were: 0.0 %, 0.4 %, 0.8 %, 1.2 %, 1.7 % and 2.1 %. The results of the investigations have shown that deformational characteristics (F, N and Hmax, mm) in longitudinal and transverse directions differ with the increase of pre-tension level. Thus, seam allowances can be defined more accurately in more deformable direction at the stage of product development. Cotton fabric (100 %) of plain weave was used as base material for fused systems. Biaxial tension testing was performed with three types of interlinings: woven, nonwoven and knitted, which differed not only in surface density, but in the density of adhesive layer, which was 52 and 76 dots/cm2, as well. The samples of fused systems were punched from the side of the main cotton fabric in order to maintain the same friction force between the punch and the specimen. Obtained results have shown that different number of force peaks, i.e. breakings is characteristic for different fused systems. For initial pre-tension from 0.0 % to 2.1 % the first breaking always appears in longitudinal direction irrespectfully to longitudinal or transverse pre-tension direction. It means that at low levels of pre-tension, e.g. 2.1 % it is possible to control the height of punching deformation, but not to change the location of critical stresses.DOI: http://dx.doi.org/10.5755/j01.ms.21.2.5788

Cable supported structures offer an elegant and economical solution for bridging over long spans with resultant low material content and ease of construction. In this paper, a model of shallow cable supported footbridge with reverse profiled pre-tensioned cables is treated and its load deformation characteristics under different quasi-static loads are investigated. Effects of important parameters such as cable sag and pre-tension are also studied. Numerical results performed on a 3D model show that structural stiffness of this bridge (model) depends not only on the cable sag and cross sectional areas of the cables, but also on the pre-tension in the reverse profiled cables. The tension in the top supporting cables can be adjusted to a high level by the pre-tension in the reverse profiled bottom cables, with the total horizontal force in the bridge structure remaining reasonably constant. It is also evident that pre-tensioned horizontally profiled cables can greatly increase the lateral horizontal stiffness and suppress the lateral horizontal deflection induced by eccentric vertical loads.

The perfect interlacing of needle and bobbin thread in the stitch formation process and seam appearance depends first of all on correct pre‐tension of the tension regulator. Changes in the pre‐tension settings also have a direct influence on the tensile force during the sewing process. This contribution presents the influence of pre‐tension in a defined area on the tensile force in important phases of the stitch formation process. In addition the influence of the stitch velocity on tensile force was investigated. On the basis of statistic analysis it was ascertained in which pre‐tension area and stitch velocity the significant differences between tensile forces occurred.