Sheet Tension Research Articles

Enhancing Palpation Skills Through the Use of Stereognosis Drills

Context: Musculoskeletal palpation is taught in our athletic training programs as part of the injury evaluation process. However, as palpation skills are taught, the focus is oftentimes on accuracy of surface-anatomy landmarks instead of the ability to discriminate qualitative information such as tissue tone, spasm, or pain response from the soft tissue. Because palpation is foundational for evaluation and intervention, a need exists for further development of this skill. Objective: Provide educators with instructional techniques to enhance palpation skills. Background: Manual medicine techniques are increasingly common in athletic training and require superb palpation and soft tissue discrimination skills. The ability to detect large and small differences in tissue qualities during orthopaedic evaluation can lead to a more accurate assessment as well as enhance manual medicine intervention techniques. Description: We describe 4 activities to enhance palpation skills (coin discrimination, sheet tension, vacuum-immobilizer assembly, and spring-scale compression). Each activity is presented with progressions to improve the foundation of a student's palpation skills and provide advanced training to better refine palpation skills. Clinical Advantage(s): Integrating tasks to improve palpation skills throughout the athletic training curriculum may help improve student confidence, accuracy, and precision while performing patient evaluation and manual medicine interventions. Improved ability to detect and discriminate musculoskeletal pathology can lead to more accurate assessment and efficient intervention techniques. Conclusion(s): Palpation is an essential skill in musculoskeletal evaluation and intervention. With consistent and progressive instruction, this skill can be practiced and refined, improving student confidence and skill application.

Prediction of Forming Limit Curves from Hardness for Steels

This paper presents a method for predicting the strain-based forming limit curve (FLC) for steels using hardness. The stretching side (positive minor strain component) of the FLC was calculated by using a Marciniak-Kuczynski model with a non-quadratic yield function, while the drawing side (negative minor strain component) of the FLC was predicted based on the relationship between the major and minor critical strains, in accordance with the theory of maximum sheet tension for local necking. The requisite parameter that describes the plastic flow behavior (in this case, the strain hardening exponent) was calculated, based on correlations with the measured microhardness. Additionally, the strain rate sensitivity was considered in the model by using a newly developed empirical correlation between hardness and strain rate sensitivity. This hardness-based model was used to predict FLCs that demonstrate good agreement with experimental FLCs of a high-strength low-alloy steel and a dual-phase steel. Equations are provided that enable the calculation of the FLC from given hardness values for different severities of the material inhomogeneity.

Microstructure evolution of AZ31B magnesium alloy sheets deformed in different deformation directions

Based on the in-plane tension and compression tests of AZ31B magnesium sheets at temperature of 200–300°C and strain rate of 0.001–0.1s−1, the microstructure evolution was investigated. The results show that when the sheets are stretched above 200°C, the {101̅1} contraction twin (CT) is not activated, but many tiny {101̅2} extension twin (ET) particles are formed, inducing secondary recrystallization. When the sheets are compressed below 250°C, the grains may rotate several times by ET because of the diversity of grain orientation and the compatible deformation, causing the basal texture deviated about 30° from normal direction (ND). When the sheets are compressed at 300°C, the ET particles also induce large secondary recrystallization grains. Furthermore, the dynamic recrystallization (DRX) mode is continuous dynamic recrystallization (cDRX), whose texture is controlled by the initial texture, the dominant activated slip systems and the deformation, and the misorientation angle Chi-Square (χ2) distributes with the density peak in 25–35°.

Casimir effect on graphene resonator

We theoretically investigated the influence of the Casimir effect on mechanical properties of a graphene resonator, where a graphene sheet is located in parallel with a perfectly conducting plate. The Casimir force arising from this effect strongly attracts a graphene sheet to a perfectly conducting plate and increases the tension of a graphene sheet as the separation distance between them decreases. The maximum vertical displacement of a graphene sheet to the substrate increases obeying a power law of a separation distance with an exponent of 4/3 as the separation distance decreases. For small separation distances, the Casimir force is excessively strong for the graphene sheet to maintain a free-standing shape, consequently resulting in the adhesion of the sheet to the substrate below a critical separation distance. The resonant frequency increases over a wide range as the separation distance decreases for large separation distances. However, it then rapidly decreases for small separations and converges to zero at a critical separation. These various behaviors enable the control of a graphene resonator.

Experimental and numerical investigation of anisotropic and twinning behavior in Mg alloy under uniaxial tension

In plane tension of magnesium alloy sheets is accommodated by prismatic and basal slip, whereas {10−12} twinning is activated when grains are elongated along the <c> axis. The plastic behavior of Mg-3Al-1Zn in tension has been investigated using a thick rolled plate with a strong basal texture. Tensile tests were performed along five directions distributed between the normal direction and the transverse direction, allowing various amount of {10–12} twinning, basal, and prismatic slip to take place. The twinning behavior has been investigated using EBSD measurement and EVPSC modeling, and Schmid factor analysis was performed. The observed amount of variants with a Schmid factor of high rank is higher than predicted, emphasizing the necessity of strain accommodation between grains and twins. Compared with compression, even when twinning activity is low, more {10–12} twin variants are predicted in tension. This study confirms extension twinning as a major deformation mechanism in all tensile directions and an efficient way to harden Mg alloys by twin-twin boundaries.

Ab initio simulation of gap discrete breathers in strained graphene

The methods of the density functional theory were used for the first time for the simulation of discrete breathers in graphene. It is demonstrated that breathers can exist with frequencies lying in the gap of the phonon spectrum, induced by uniaxial tension of a monolayer graphene sheet in the “zigzag” direction (axis X), polarized in the “armchair” direction (axis Y). The found gap breathers are highly localized dynamic objects, the core of which is formed by two adjacent carbon atoms located on the Y axis. The atoms surrounding the core vibrate at much lower amplitudes along both the axes (X and Y). The dependence of the frequency of these breathers on amplitude is found, which shows a soft type of nonlinearity. No breathers of this type were detected in the gap induced by stretching along the Y axis. It is shown that the breather vibrations may be approximated by the Morse oscillators, the parameters of which are determined from ab initio calculations. The results are of fundamental importance, as molecular dynamics calculations based on empirical potentials cannot serve as a reliable proof of the existence of breathers in crystals.

Asymmetry in the hot deformation behavior of AZ31B magnesium sheets

The in-plane tension and compression tests of AZ31B magnesium sheets were carried out at the temperature range of 473–573K and the strain rate range of 0.001–0.1s−1. The experimental results show that the mechanical response transforms from asymmetry to symmetry when the temperature is above 573K. Furthermore, the mechanical response under tension is rate-dependent, but that under compression can be decomposed to two parts of rate-dependent and rate-independent. The flow stress models under tension and compression were proposed to quantitatively describe the deformation behavior of AZ31B magnesium, respectively. Moreover, the microstructure and texture evolution were investigated. The results show that although the asymmetry of mechanical response does not exist at 573K, the microstructure evolutions during tension or compression are still different, which implies that the mechanism and preferred orientation of dynamic recrystallization (DRX) grains in different deformation directions are different.

Stability of a moving radial liquid sheet: experiments

A recent theory (Tirumkudulu &amp; Paramati, Phys. Fluids, vol. 25, 2013, 102107) for a radially expanding liquid sheet, that accounts for liquid inertia, interfacial tension and thinning of the liquid sheet while ignoring the inertia of the surrounding gas and viscous effects, shows that such a sheet is convectively unstable to small sinuous disturbances at all frequencies and Weber numbers $(We\equiv {\it\rho}_{l}U^{2}h/{\it\sigma})$. Here, ${\it\rho}_{l}$ and ${\it\sigma}$ are the density and surface tension of the liquid, respectively, $U$ is the speed of the liquid jet, and $h$ is the local sheet thickness. In this study we use a simple non-contact optical technique based on laser-induced fluorescence (LIF) to measure the instantaneous local sheet thickness and displacement of a circular sheet produced by head-on impingement of two laminar jets. When the impingement point is disturbed via acoustic forcing, sinuous waves produced close to the impingement point travel radially outwards. The phase speed of the sinuous wave decreases while the amplitude grows as they propagate radially outwards. Our experimental technique was unable to detect thickness modulations in the presence of forcing, suggesting that the modulations could be smaller than the resolution of our experimental technique. The measured phase speed of the sinuous wave envelope matches with theoretical predictions while there is a qualitative agreement in the case of spatial growth. We show that there is a range of frequencies over which the sheet is unstable due to both aerodynamic interaction and thinning effects, while outside this range, thinning effects dominate. These results imply that a full theory that describes the dynamics of a radially expanding liquid sheet should account for both effects.

Uniaxial tension of thin rubber liner sheets and hyperelastic model investigation

Uniaxial tension tests were performed on two different thin rubber liner sheets, the silica-filled and the Kevlar-filled EPDM rubber, for the purpose of establishing the constitutive relations via different hyperelasticity models. Due to the fact that the rubber liner sheet can sustain large amount of deformation, over 700 % engineering strain, we used the non-contact, optical technique of digital image correlation to measure local deformation over the sample surface. Three different hyperelastic models were considered for analyzing the experimental measurement, one is the neo-Hookean including the generalized neo-Hookean (GNH), the second is the Rivlin-type models including the special case of Mooney–Rivlin model, and the third is the Ogden model. Model parameters were determined by fitting the hyperelastic model to the experimental data. It was found that the Rivlin model up to the second order and the Ogden model capture the constitutive behavior of both the silica-filled and the Kevlar-filled rubber sheets quite well, while the GNH model can only describe the stress-stretch relation of the Kevlar-filled rubber sheet.

Research on New Type Quantitative Nondestructive Pre-Stress FRP Sheet Tension Fixture

Traditional pre-stress FRP sheet tension fixture must have the beam of the bridge slotted to reduce the cross-section of the beam. Besides, stress on the FRP sheet is irregular with local stress concentration. Its indirect load pre-stress, as well as quantitative criterion of pre-stress born by FRP sheet is not accurate. To solve the above problems, a newly-developed self-balanced type pre-stress FRP sheet tension fixture has been introduced. Such a tension fixture consists of welded steel frame, a mechanical jackscrew, a dynamometer and a strain gauge. It is able to give specified stress onto the FRP sheet accurately while not damaging the beam cross-section. At the same time, with the combination of ANASYS Workbench and UG8.0 Software, also states the simulation analysis of the new type tension fixture, including its stress under practical work and deformation state, which initially proves the scientific and economic usefulness of such tension fixtures.

Investigation of the rupture in tension and bending of DP980 steel sheet

This work is focused on the characterization and numerical prediction of the onset of rupture in bending for a dual phase steel . Indeed, numerical validation of forming processes involving bending over very small radii cannot rely on forming limit curves and demands taking the rupture into account. To reach this goal, the mechanical behavior up to fracture of dual phase DP980 steel sheets was studied by means of experiments and numerical simulations. In a first step, monotonic tensile tests on straight samples up to rupture were performed and a local strain measure was used to assess the fracture strain . Numerical simulation of the tensile test was performed in order to identify parameters specific to four macroscopic rupture criteria. Then, interrupted bending tests over a radius much lower than the sheet thickness were performed and local strains were measured by digital image correlation . Moreover, the bent area was observed by scanning electron microscopy at different stages to detect crack development. In this study, the limit in bending corresponds to the appearance of the first cracks and not to the final splitting in two halves of the specimen. Numerical simulation of the bending test was then performed in order to compare the macroscopic load and local strains with experiments. Finally, critical values of the four macroscopic rupture criteria identified in tension were used to predict onset of rupture in bending. • Investigation of the mechanical behavior in bending of DP980 steel sheet. • Experimental determination of the strain at rupture in tension and bending. • Characterization of crack onset in bending by scanning electron microscopy. • Numerical prediction of rupture in bending by using macroscopic rupture criteria.

Formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet

In this paper, the formability of magnetic pulse uniaxial tension of AZ31magnesium alloy sheet at room temperature were investigated by the numerical simulation and experimental method. The numerical simulation for the magnetic pulse uniaxial tension of AZ31 sheet is performed by means of the ANSYS FEA software. The changes in velocity and strain rate were analyzed by simulation. The approximate rectangular flat spiral coil was employed to carry out the magnetic pulse uniaxial tensile experiments. The forming process was recorded by the high-speed camera, and the simulation result was consistent with it. The experimental results indicate that the total elongation of AZ31 sheet improves about 37 % compared with the quasi-static case. The major and minor principal strains at most increase by approximately 112 and 96 % under 5.12 kJ energy, respectively.

Flow Behaviour of 2024 Aluminium Alloy Sheet during Hot Tensile and Compressive Processes

Sheet-bulk metal forming is a new class of sheet forming technology with intended three dimensional material flows as bulk forming process. This new technology usually comprises several traditional forming processes, such as drawing, upsetting, ironing, etc. which exhibits different strain states. The flow behaviours of 2024 aluminium alloy sheet in hot tension and compression were paid attention considering the effect of forming parameters including temperature and initial strain rate in this paper. By regression analysis, the values of deformation activation energy of different processes were calculated. To determined reasonable forming parameters for sheet-bulk metal forming, the power dissipation map and instability map were established based on dynamic materials model theory.

Research and Application of a New Constant Tension Control Device of the Carbon Fiber Warping Machine

This paper presents a new constant tension control device which is suitable for warping of the carbon fiber or the flake yarns which are zero twist, high tensile strength, low shear strength, high specific modulus and self-lubrication and can meet the requirements of the warp tension of the carbon fiber multi-layer weaving equipment which is in the process of development. The device can make yarn tension consistent in warping process. Especially with the decrease of the diameter of yarn tube, the tension of yarn sheet is consistent in warping process. In the process of warping the warp doesnt twist and wear is small. The experimental results show that the mechanism can realize accurate control on the tension of the single yarn and the yarn sheet, and is able to meet the requirements of the warp tension of the carbon fiber multi-layer weaving equipment which is in the process of development.

Modeling of deformation behavior and texture evolution in magnesium alloy using the intermediate ϕ-model

The viscoplastic intermediate ϕ-model was applied in this work to predict the deformation behavior and texture evolution in a magnesium alloy, an HCP material. We simulated the deformation behavior with different intergranular interaction strengths and compared the predicted results with available experimental results. In this approach, elasticity is neglected and the plastic deformation mechanisms are assumed as a combination of crystallographic slip and twinning systems. Tests are performed for rolling (plane strain compression) of random textured Mg polycrystal as well as for tensile and compressive tests on rolled Mg sheets. Simulated texture evolutions agree well with experimental data. Activities of twinning and slip, predicted by the intermediate ϕ-model, reveal the strong anisotropic behavior during tension and compression of rolled sheets.

A modified displacement adjustment method to compensate for surface deflections in the automobile exterior panels

Surface deflections are becoming more and more concerned by automotive manufacturers because these defects spoil the appearance of automobiles greatly. In this paper, a modified displacement adjustment (DA) method is proposed to compensate for surface deflections in the automobile exterior panels. The proposed modified DA method has two advantages. One is that it distinguishes the global deviation and the local deviation and is able to compensate for the local deviation (surface deflection) independently. The other feature is that the iterative scheme in the DA method is substituted with a compensation factor so that time-consuming iterations are reduced and the convergence problems caused by the small tolerance of surface deflection are avoided. In order to test the effectiveness of the proposed method, it is applied to compensate for surface deflections in a cylinder shallow shell part and a door handle part. The compensation results show that the proposed method is effective in reducing surface deflections in both parts. The work in this study provides a new method to reduce surface deflections by die design. For parts in which mechanical methods to increase the sheet tension during bending are not effective or suitable, the proposed modified displacement adjustment method is an effective alternative.

Effect of Process Variables on Transformation-Texture Development in Ti-6Al-4V Sheet Following Beta Heat Treatment

The effect of preheat time, prestrain, cooling rate, and concurrent deformation during cooling on the preferential selection of hcp alpha variants during the decomposition of the high-temperature, bcc beta phase in two-phase titanium alloys was established using Ti-6Al-4V sheet material. For this purpose, sheet tension samples were pre-soaked in the beta phase field for 0 or 10 minutes (to vary the beta grain size), subjected to a prestrain of 0 or 0.1, and cooled at a rate of 11 or 155 K/min (11 or 155 °C/min) under conditions comprising free ends, fixed ends, or concurrent deformation at a strain rate between ~10−5 and 3 × 10−4 s−1. Electron-backscatter diffraction was used to determine the orientations of the alpha variants so formed, from which the underlying high-temperature, beta-grain microstructure and orientations were reconstructed. These measurements revealed that the parent beta texture changed due to grain growth during preheating. A comparison of the alpha- and beta-phase textures indicated that preferential variant selection was most noticeable under conditions involving a slow cooling rate especially when prestrain or concurrent straining was imposed.

An embedded crack in a constant strain triangle utilizing extended finite element concepts

This paper revisits the formulation of the CST element with an embedded discrete crack taking advantage of the direct formulations developed within the framework of the extended finite element method, XFEM. The result is a simple element for modeling cohesive fracture processes in quasi-brittle materials. The element is easily fitted a standard FEM code, and as such it is an alternative to more cumbersome XFEM elements which require special d.o.f.’s and extra administration. The crack description is embedded, in the sense that extra d.o.f.’s controlling the crack opening are eliminated at the element level. The cracked element is stress-compatible in the sense that stresses are continuous across the crack. A special shape function is introduced to allow for the discontinuous displacements without eradicating the stress compatibility. The simplicity of the element comes at the cost of inter-element discontinuity of displacements. The formulation is based on a variational principle of virtual work involving only the interpolation of displacements. The good performance of the element is demonstrated through the comparison with three benchmark tests in which a single crack is propagated: The center cracked sheet in uni-axial tension, the three-point bending test and the four-point shear beam test.

Effects of skin pass rolling parameters on mechanical properties of steels

The influence of skin pass rolling on tensile and microstructural properties of three industrial grade steels was investigated. Skin pass rolling was performed on a laboratory mill equipped with a device designed to reproduce the effects of sheet tension and with load cells aimed at measuring the main working parameters. Analysis on tensile properties of skin pass rolled samples showed for an ultralow C grade and a low C grade a decreasing trend of the yield strength down to a minimum, followed by progressive rising values with increasing rolling elongation. This trend was related to changes of the tensile curve shape, leading to a transition from discontinuous to continuous yielding. A zinc-coated mild steel grade featured a tensile curve with a knee at transition from elastic to plastic regime. Accordingly, the change in yield strength with increasing skin pass elongation followed a linear trend. Microstructural and crystallographic information supplied by EBSD analyses suggested that the plastic strain induced by skin pass rolling originated a fairly homogeneous deformation field even on grains directly exposed on the strip surface. Micro-hardness profiles taken across strip thickness highlighted both increasing peak hardness values at strip surfaces and rising values at mid-thickness.

An Empirical Formula for Stress Intensity Factors of Double Edge Half-Circular-Hole Cracks in a Rectangular Sheet in Tension

This note deals with the stress intensity factors (SIFs) for double edge half-circular-hole cracks in a rectangular sheet in tension by means of the displacement discontinuity method with crack-tip elements (a boundary element method) proposed recently by the author. Moreover, an empirical formula of the SIFs of the crack problem is presented and examined. It is found that the empirical formula is simple, yet accurate for evaluating the SIFs of the crack problem.