Shear Force Component Research Articles

Effects of bench press technique variations on musculoskeletal shoulder loads and potential injury risk.

While shoulder injuries resulting from the bench press exercise are commonly reported, no biomechanical evidence for lowering injury risk is currently available. Therefore, the aim of the present study was to compare musculoskeletal shoulder loads and potential injury risk during several bench press variations. Ten experienced strength athletes performed 21 technical variations of the barbell bench press, including variations in grip width of 1,1.5 and 2 bi-acromial widths (BAW), shoulder abduction angles of 45°, 70° and 90°, and scapula poses including neutral, retracted, and released conditions. Motions and forces were recorded by an opto-electronic measurement system and an instrumented barbell. An OpenSim musculoskeletal shoulder model was employed to estimate joint reaction forces in the glenohumeral and acromioclavicular joints. Time-series of joint reaction forces were compared between techniques by statistical non-parametric mapping. Results showed that narrower grip widths of BAW decreased acromioclavicular compression (p < 0.05), which may decrease the risk for distal clavicular osteolysis. Moreover, scapula retraction, as well as a grip width of BAW (p < 0.05), decreased glenohumeral posterior shear force components and rotator cuff activity and may decrease the risk for glenohumeral instability and rotator cuff injuries. Furthermore, results showed that mediolaterally exerted barbell force components varied considerably between athletes and largely affected shoulder reaction forces. It can be concluded that the grip width, scapula pose and mediolateral exerted barbell forces during the bench press influence musculoskeletal shoulder loads and the potential injury risk. Results of this study can contribute to safer bench press training guidelines.

Investigating the shear behaviour of high-performance fabrics

Shear modulus is a critical factor that significantly influences the mechanical properties and overall performance of these textiles. Understanding the mechanics behind fabric performance during forming operations is of paramount importance, especially given the diverse use of various fabric types as key components in composite products. Fabric's ability to undergo shear deformation is a pivotal attribute in forming and facilitating the transformation of 2-dimensional preforms into intricate 3-dimensional structures. In numerous industrial applications, the manufacturing of composite materials heavily relies on carbon and Kevlar fibers. This research investigates the relationship between shear stress and wrinkling in single-layer structures. The investigation involved woven fabrics composed of carbon, Kevlar, and hybrid carbon-Kevlar configurations. The study encompassed an assessment of shear characteristics, wrinkling force, and fabric stiffness for each fabric variant. To comprehensively analyze the intricate interplay among in-plane shear characteristics, fabric parameters, and tow properties in the scope of shear behavior, the study's findings underwent meticulous scrutiny. Selected tow and fabric parameters exhibit a substantial paired association with the fabric shear modulus, a deduction derived from analysis of experimental results. The formulated fabric shear index serves as a valuable tool for categorizing the fabric's response to shear forces. The shear force component that triggers the onset of buckling demonstrates a proportional relationship with the cube root of the fabric shear modulus. This observation sheds light on the intricate connection between shear properties and mechanical behavior, offering valuable insights into the fabric's performance under various conditions.

Predicting vertical and shear ground reaction forces during walking and jogging using wearable plantar pressure insoles

BackgroundThe development of plantar pressure insoles has made them a potential replacement for force plates. These wearable devices can measure multiple steps and might be used outside of the lab environment for rehabilitation and evaluation of sport performance. However, they can only measure the vertical force which does not completely represent the vertical ground reaction force. In addition, they are not able to measure shear forces which play an import role in the dynamic performance of individuals. Indirect approaches might be implemented to improve the accuracy of the force estimated by plantar pressure systems. Research questionThe aim of this study was to predict the vertical and shear components of ground reaction force from plantar pressure data using recurrent neural networks. MethodsGround reaction force and plantar pressure data were collected from 16 healthy individuals during 10 trials of walking and five trials of jogging using Bertec force plates at 1000 Hz and FScan plantar pressure insoles at 100 Hz. A long short-term memory neural network was built to consider the time dependency of pressure and force data in predictions. The data were split into three subsets of train, to train the model, evaluate, to optimize the model hyperparameters, and test sets, to assess the accuracy of the model predictions. ResultsThe results of this study showed that our long short-term memory model could accurately predict the shear and vertical force components during walking and jogging. The predictions were more accurate during walking compared to jogging. In addition, the predictions of mediolateral force had higher error and lower correlation compared to vertical and anteroposterior components. SignificanceThe long short-term memory model developed in this study may be an acceptable option for accurate estimation of ground reaction force during outdoor activities which can have significant impacts in rehabilitation, sport performance, and gaming.

Shear resistance of self-stressed elements without web reinforcement and with longitudinal bars made of polymer composites. Experimental studies. Verification of the proposed design model

Introduction. The critical shear crack theory (CSCT) was applied to devise a modified model on the basis of theoretical research into shear resistance models of concrete elements reinforced with polymer composite bars. Experimental studies were conducted for various loading patterns and cases to verify provisions of the proposed model, to find the shear resistance of elements made of expansive concrete and concrete containing Portland cement, reinforced with steel bars and FRP.&#x0D; &#x0D; Materials and methods. The proposed modified shear resistance model was verified using the experimental data obtained both by the authors and other researchers (the database had 301 elements).&#x0D; &#x0D; Results. Given the results of a parametric study, a phenomenological shear resistance criterion was proposed for flexible elements, reinforced with polymer composite bars. Its mission was to simplify the model design to determine the shear resistance of concrete elements reinforced by FRP bars. Hence, no analysis of the shear force components was needed.&#x0D; &#x0D; Conclusions. The proposed simplified shear resistance model of flexible self-stressed elements, reinforced with polymer composite bars, adequately evaluates the shear resistance of elements exposed to the load distributed in a span; it shows good convergence with experimental data.

Influence of adjacent segments on the torsional load-bearing behaviour of assembled half-shell towers

This article deals with the influence of adjacent segments on the torsional load bearing behaviour of assembled half-shell towers for wind energy turbines. The main objective is to detect and understand the load transfer in the modular tower structure considering the effects of adjacent segments. The engineering approach already developed for two assembled half-shells – based on the warping theory of thin-walled bars – is investigated for its applicability to the entire tower structure. Numerical comparative studies show that an adjacent half-shell pair level at the top and bottom is sufficient to take the influence of the entire tower structure into account. The adjacent segments affect the quantitative determination of the load-bearing components from shear force and torsion. Furthermore, the coupling conditions in the horizontal joint depend on the stress consideration and include only one (normal stresses via linear superposition) or both half-shells (shear stresses via Bredt shear flow). Therefore, an analytically and numerically based approach is presented that can be applied to the use case of segmental towers for wind turbines and the constant component heights of the precast segments. In this case, the methods take the decrease of the bending shear force component and the simultaneous increase of the torsion component in the system axis into account. The boundary conditions of the frame structure remain unaffected. Based on the further developed engineering model, the complex torsional load-bearing behaviour and the stress state in the horizontal joint of modular tower structures can now be analytically determined in the compressed and static friction condition based on the warping theory of thin-walled bars.

High-sensitivity flexible tri-axial capacitive tactile sensor for object grab sensing

In this paper, a high sensitivity, flexible capacitive tri-axial tactile sensor is constructed by pyramid-shaped microarray dielectric layer. The tactile sensor consists of a staggered 2 × 2 capacitive sensor array. Through the measure and analysis of the three-dimensional force, which was applied on the sensor, it could decompose into normal and shear force components. The sensor exhibits high sensitivity due to the pyramidal-shaped microarray and low modulus of the dielectric layer. The sensitivity of the sensor in the x,y and z-axis are 56.47, 53.45 and 90.39 %/N in the ranges of 0 ∼ 0.8, 0 ∼ 0.8 and 0 ∼ 0.6 N, respectively. In addition, the sensor also exhibits fast response and recovery times (60 ms), and longtime cycling stability. The low average test error (about 10.4 %) of the tri-axial tactile sensor provides the technical basis for the application of robotics and wearable devices.

Evaluation of a 3D Printed Soft Sensor for Measuring Fingertip Interaction Forces

Current force sensors used to capture fingertip interaction forces lack compliance to the fingertip tissue resulting in the loss of touch sensation of the user. 3D printing offers the possibility to create personalized soft sensing structures. This work evaluates a 3D printed soft sensor that measures normal and shear interactions forces based on the deformations of the thumb and index fingertips of 7 subjects using an instrumented object. Due to the use of (carbon doped) thermoplastic materials, the signals provided by these sensing structures suffer from nonlinearities. Therefore, two compensation models, based on a neural network and recurrent neural network analogous to an electrical model are used to compensate for the nonlinear effects. The performance of the sensors was analysed using the normalized cross-correlation and the root-mean-square error. The output of the force sensors are highly correlated with the applied shear and normal force components. When paired with compensation models the correlation and error of the sensor output can be further improved. These results indicate that the proposed flexible fingertip interaction force sensors have a high potential for future applications.

Application of MOORA &amp; COPRAS integrated with entropy method for multi-criteria decision making in dry turning process of Nimonic C263

This article presents an integrated multi-criteria decision making using Entropy, MOORA and COPRAS methods for turning Nimonic C263. Experiments were performed under L27 Taguchi orthogonal array. Dry turning was performed and cubic boron nitride (CBN) was used to turn the alloy. The variables speed, feed and depth of cut were chosen as factors. For each experiment, the shear force component was measured during on line. The insert flank wear was measured after every experiment. The main objective of this paper is to identify the suitable trial to ensure minimum force and flank wear simultaneously. Because of the cost reduction and quality improvement, the controlling factors level should be selected appropriately. Hence, the integrated MCDM technique using MOORA, COPRAS and Entropy was chosen to determine the best experiment out of 27 experiments. Alternatives were ranked and the results were evaluated. The best experiment for minimization of force and flank wear is found to be 125 m/min, 0.055 mm/rev and 0.25 mm. The experimental test were observed with lesser deviation and confirmed that proposal found is more suitable to obtain minimum force and flank wear.

Torque Around Axial Direction on Rotating Detonation Engines

A rotating detonation engine (RDE) generates a continuous thrust with one or more rotating detonation waves. Because of the velocity on the order of kilometers/second, the reaction zone is relatively small. Therefore, the RDE realizes a short combustion chamber length. However, the detonation waves induce an azimuthal motion of propellant, resulting in torque around the thrust axis. Because the motion does not contribute to the thrust, the torque is important in terms of performance loss. Herein, we conducted combustion tests with a six-axis force sensor to simultaneously measure torque and thrust. A comparison of detonation waves captured by high-speed camera revealed that the torque followed the direction and was offset when the waves existed in both of two directions simultaneously, which indicates the possibility of controlling the torque. Under a mass flow rate at and an equivalence ratio at , when the azimuthal component of shear force was of the thrust, of the total kinetic energy of the exit flow was distributed to the azimuthal component of velocity and did not contribute to the thrust. We therefore concluded that the effect of the azimuthal motion on the RDE’s performance was small.

A 3D-Printed Soft Fingertip Sensor for Providing Information about Normal and Shear Components of Interaction Forces

Sensing of the interaction forces at fingertips is of great value in assessment and rehabilitation therapy. Current force sensors are not compliant to the fingertip tissue and result in loss of touch sensation of the user. This work shows the development and characterization of a flexible fully-3D-printed piezoresistive shear and normal force sensor that uses the mechanical deformation of the finger tissue. Two prototypes of the sensing structure are evaluated using a finite element model and a measurement setup that applies normal and shear forces up to 10 N on a fingertip phantom placed inside the sensing structure, which is fixed to prevent slippage. Furthermore, the relation between strain (rate) and resistance of the conductive TPU, used for the strain gauges, is characterized. The applied normal and shear force components of the 3D-printed sensing structure can be partly separated. FEM analysis showed that the output of the sensor is largely related to the sensor geometry and location of the strain gauges. Furthermore, the conductive TPU that was used has a negative gauge factor for the strain range used in this study and might cause non-linear behaviors in the sensor output.

Medial Meniscal Posterior Horn Tears Are Associated With Increased Posterior Tibial Slope: A Case-Control Study

Background: While the medial meniscal posterior horn (MMPH) is reported to bear a considerable portion of overall load on the knee joint, including compressive and shear forces, no study has yet investigated the relationship between the MMPH and posterior tibial slope (PTS), which is a geometric factor associated with the shear force component in the presence of a compressive load in the knee joint. Hypothesis/Purpose: The purpose was to investigate the relationship between the PTS and MMPH tears in patients without ligamentous injury. It was hypothesized that the PTS is greater in patients with MMPH tears as compared with those without. Study Design: Cohort study; Level of evidence, 3. Methods: From March 2015 to December 2018, 159 patients with isolated MMPH tears and 60 patients without any pathologic findings on magnetic resonance imaging (control group) were included in this study. The PTS in the affected and contralateral knees was compared between the groups, which were statistically matched according to baseline characteristics (ie, age, sex, body mass index, radiographic osteoarthritis grade according to the Kellgren-Lawrence scale, and hip-knee-ankle angle) via the inverse probability of treatment weighting method. Furthermore, the MMPH tear group was subdivided according to meniscal tear patterns; these subgroups were then compared with the control group. Results: The mean PTS was significantly greater in the MMPH tear group than in the control group (affected knee: MMPH tear group, 7.0°± 3.4° [mean ± SD]; control group, 5.2°± 2.1°, P < .001; contralateral knee: MMPH tear group, 6.7°± 3.3°; control group, 4.7°± 2.2°, P < .001). The mean PTS in each subgroup also tended to be greater than that in the control group. In the receiver operating characteristic curve analysis, the cutoff point of the PTS discriminating between the MMPH tear and control groups was 6.6° for the affected knee (sensitivity, 55.3%; specificity, 75.0%) and 5.5° for the contralateral knee (sensitivity, 61.0%; specificity, 76.7%). Conclusion: An increased PTS is strongly associated with an increased incidence of MMPH tears and less affected by the meniscal tear patterns.

Flexural vibration and power flow analyses of axially loaded beams with general boundary and non-uniform elastic foundations

In this article, flexural vibration and its power flow of an axially loaded beam with arbitrary boundary and non-uniform elastic foundation are analyzed via energy principle in conjunction with Rayleigh–Ritz procedure. A general solution is assumed as a modified version of Fourier series supplemented with boundary-smoothing auxiliary terms. Effects of axial load and elastic foundation of the beam are taken into account in terms of potential energy in system Lagrangian. Critical load of this axially loaded beam is obtained under elastic boundary condition and non-uniform foundation. Numerical examples are then presented to demonstrate the reliability and effectiveness of the established model by comparing results with those available in literature or calculated using finite element method. Results show that the current model can make an accurate dynamic analysis for the elastically restrained beam with axial load and non-uniform elastic foundation. Influence of some important factors, including boundary restraint, axial load, and non-uniform foundation, on the vibration characteristics and power flow transmission are studied and addressed. It is found that the supporting condition has a significant influence on power flow distribution across the whole beam, in which the shear force component plays a dominant role for the power flow transmission.

Stress state analysis and tensile-shear fracture criterion in combined puncture and cutting of soft materials

The mechanics of the combined puncture and cutting of protective materials by a pointed blade are studied theoretically and experimentally, by means of stress state analysis. Through analysis of the stresses occurring during the puncture cutting of a variety of neoprene and nitrile rubber membranes by pointed blades with different cutting-edge angles, a force state of pushing/shear-dependent loading is formulated and discussed. By considering this combined loading as an asymmetric fracture, two equations—for pushing force component and shear force component—are then derived from the stress intensity factors. From this stress analysis, a model based on fracture mechanics theory is developed to calculate the critical force involved in the puncture cutting of soft elastomeric membranes. Stress state analysis also shows that the puncture cutting of elastomeric membranes involves all three fracture Modes, I, II and III, which are highly dependent on the friction coefficient of the cutting edge, the cutting-edge angle and the material thickness. It is found that combining compressive and shear stresses leads to the failure of elastomer materials under tensile-shear fracture regimes. Based on this study, we propose a unified strength criterion to explain the stress state that occurs in the puncture cutting of elastomeric membranes by a pointed blade. This criterion can describe all puncture-cutting mechanisms for materials undergoing a combination of compressive stress and shear stress. It can therefore be applied to a variety of soft materials punctured by pointed blades with cutting edges of different angles.

Reference-Free Traction Force Microscopy Platform Fabricated via Two-Photon Laser Scanning Lithography Enables Facile Measurement of Cell-Generated Forces.

Cells sense and respond to the physical nature of their microenvironment by mechanically probing their surroundings via cytoskeletal contractions. The material response to these stresses can be measured via traction force microscopy (TFM). Traditional TFM platforms present several limitations including variable spatial resolution, difficulty in attaining the full three-dimensional (3D) deformation/stress profile, and the requirement to remove or relax the cells being measured to determine the zero-stress state. To overcome these limitations, we developed a two-photon, photochemical coupling approach to fabricate a new TFM platform that provides high-resolution control over the 3D placement of fluorescent fiducial markers for facile measurement of cell-generated shear and normal components of traction forces. The highly controlled placement of the 3D marker array provides a built-in, zero stress state eliminating the need to perturb the cells being measured while also providing increased throughput. Using this platform, we discovered that the magnitude of cell-generated shear and normal force components are linked both spatially and temporally. The facile nature and increased throughput of measuring cell-generated forces afforded by this new platform will be useful to the mechanotransduction community and others.

The evolution of cutting forces during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composites

Cutting forces generated during traditional machining of fiber reinforced polymer composites play an important role in determining machined surface quality. The cutting force signals also provide a live indicator of the dynamic behavior of the chip formation process. Cutting forces in machining FRPs are dependent primarily on the instantaneous fiber cutting angle, chip thickness, cutting edge geometry and the current state of cutting edge wear. In this study, effects of the cutting edge rake angle and tool wear on cutting force evolution during slot milling of unidirectional carbon fiber reinforced polymer (UD-CFRP) composite was investigated. The cutting forces were measured in the feed and normal directions and then transformed to the tangential and radial directions of the tool path. A simplified cutting force model consisting of a shearing region and a pressing was used to determine the shearing and friction force components. This allowed determination of the friction coefficient on the clearance face of the tool. It was found that the friction coefficient varied significantly with rake angle and fiber cutting angle. The effect of rake angle on cutting forces is more discernable in the shearing region with positive rake angle tool providing the most efficient cutting. Furthermore, correlations were found between machining damage and the magnitude and orientation of the resultant shearing force.

Analytical prediction of chatter stability in turning of low-stiffness pure iron parts by nosed tool

Regenerative chatter is a pivotal obstacle for achieving required machining quality and efficiency in turning operations, especially when turning of low-stiffness parts. Accurate prediction of chatter stability prior to actual machining is of great significance for the judgment on feasibility and the optimization selection of cutting parameters that are free of chatter. To this end, this paper presents a comprehensive study which allows accurately predicting the chatter stability in turning of low-stiffness parts made of pure iron. The dynamic model for a double-flexible turning system with the regenerative effect is established in orthogonal directions on the basis of a nonlinear turning force model with accurately calibrated nonlinear force coefficients. In the nonlinear turning force model, both shearing and edge effects are considered, in which shearing force components are formulated as the exponential functions of the instantaneous uncut chip thickness to reflect the size effect. In addition, the geometric feature of the tool nose radius is also taken into account by precisely discretizing the instantaneous uncut chip area. The chatter stability of the resulting system is further predicted by an extended second-order semi-discretization method (2nd SDM). To verify the proposed method, a series of cutting tests are conducted on a CNC lathe, and experimental results indicate that proposed method can achieve an accurate prediction of chatter stability in turning of low-stiffness pure iron parts.

The influence of foot position on scrum kinetics during machine scrummaging

ABSTRACTThe purpose of this study was to investigate the effect of variations in the alignment of the feet on scrum kinetics during machine scrummaging. Twenty nine rugby forwards from amateur-level teams completed maximal scrum efforts against an instrumented scrum machine, with the feet in parallel and non-parallel positions. Three-dimensional forces, the moment about the vertical axis and sagittal plane joint angles were measured during the sustained pushing phase. There was a decrease in the magnitude of the resultant force and compression force in both of the non-parallel conditions compared to parallel and larger compression forces were associated with more extended hip and knee angles. Scrummaging with the left foot forward resulted in the lateral force being directed more towards the left and the turning moment becoming more clockwise. These directional changes were reversed when scrummaging with the right foot forward. Scrummaging with the right foot positioned ahead of the left may serve to counteract the natural clockwise wheel of the live scrum and could be used to achieve an anti-clockwise rotation of the scrum for tactical reasons. However, this would be associated with lower resultant forces and a greater lateral shear force component directed towards the right.

Analysis of shoulder compressive and shear forces during functional activities of daily life

BackgroundKnowledge of forces acting through the glenohumeral joint during activities of daily living is a prerequisite for improving implant design and aiding rehabilitation planning. Existing data are limited by the number of activities performed and, in some cases, the lack of representation of the glenohumeral loading direction, although high shear force components may cause joint dislocation or implant loosening. This study aims to analyse shoulder compression and shear force components during essential functional activities of daily living. MethodsThis is a combined modelling and experimental study. Motion data and external forces measured from 25 participants for 26 activities of daily living serve as input into an upper limb musculoskeletal model that quantifies glenohumeral loading. FindingsThe shoulder contact force exceeds 50% of the body weight in 10/26 activities of daily living with a maximum contact force of 164% of the body weight (SD 69%) for a sit to stand task. The ratio of glenohumeral shear force component to compression force component exceeds 0.5 in 8/26 functional activities, with maximum ratios for reaching across the body (1.09; SD 0.41) and pick and place an everyday object (0.88; SD 0.36). InterpretationThis study demonstrates substantial loads through the glenohumeral joint during activities of daily living. The ratios of glenohumeral shear force component to compression force component are considerable when high loads act at long lever arms and at high angles of arm elevation. These glenohumeral ratios represent a key component of loading that should be considered when designing implants, surgical procedures, or rehabilitation protocols.

Effects of helium gas flow rate on arc shape, molten pool behavior and penetration in aluminum alloy DCEN TIG welding

Helium arc bead-on-plate welding has been observed using a high-speed video filming technique. Both the arc diameter and area were compressed with increasing gas flow. The arc compressed in the radial direction and stretched in length, causing a voltage increase. There was no negative-pole atomization in the direct current electrode negative (DCEN) mode, and the helium arc could tear the oxidation film on Al alloys. The broken oxidation film flowed on the molten pool under various forces. The arc shear force and arc pressure component are the dominant driving forces to tear the oxidation film. The ability of the helium arc to tear the oxidation film decreased with gas flow rate varying from 5 to 20 L/min. Penetration increased with gas flow because of the compression effect.

Probabilistic Prediction of Cutting and Ploughing Forces using Extended Kienzle Force Model in Orthogonal Turning Process

Probabilistic prediction of cutting and ploughing forces is performed by applying Bayesian inference to an extended Kienzle force model. Prior probabilities are established and posterior force predictions are completed. The results of the probabilistic force predictions are then verified using forces measured under other cutting conditions, as well as a simplified slip-line force model. Additionally, probabilistic simulation results are compared with the results of a non-linear least squares fitting technique to isolate the shearing and ploughing force components of the cutting force.