Breakaway Force Research Articles

Full-scale experimental study on tribological performance of FPBs for highway bridges with various solid lubricants under fast loading

Friction pendulum bearings (FPBs) have proven to be effective for the seismic isolation of highway bridges. Previous studies often employed scaled model shaking table tests to investigate dynamic responses of the structures or quasi-static tests to assess the hysteretic performance of FPBs. However, it is noteworthy that the stress on the friction surface is reduced due to the size effect in scaled model in shaking table tests, while quasi-static tests of prototype bearings cannot simulate the sliding velocity experienced during seismic events, which is a sensitive parameter for the performance of FPBs with solid lubricant plates. Research on the performance of full-scale FPBs under fast frictional loading is very limited. This paper addresses this knowledge gap by studying the velocity demand for a highway bridge with FPBs and conducting fast sliding performance tests using full-scale FPBs. The results indicate that under a 0.2 g PGA earthquake, the velocity demand for FPBs can reach 0.5 m/s. Through testing full-scale FPBs at various loading speeds, it was found that solid lubricant plates by UHMWPE material exhibit poor thermal stability during wear tests, solid lubricant plates by PTFE material lack sufficient tangential tear strength under fast loading, and solid lubricant plates by PET material show good wear resistance but have a high breakaway force and levered maximum force during the running-in stage. Subsequently, this study developed ultra-high performance friction plate (UHPF) as the solid lubricant for FPBs, achieving ideal hysteretic performance under fast loading. The full-scale FPB specimens in this paper are the ones manufactured for the continuous beam bridges in the Shenzhen-Zhongshan Sea-crossing Link project in China. The dimensions of the bearing, axial load, and loading speed is much more stringent than those in previous FPB tests, providing results that are highly important for engineering applications.

Experımental determination of the breakaway force of working rolls when processing semi-finished products

The effect of varying the number of layers of a semi-finished product, that is, its thickness, and the pressing force between the working rolls on the breakaway force of a multi-layer package of semi-finished products is experimentally investigated in the article. The dependence of the required breakaway force of the working rolls on the change in the number of layers of semi-finished products supplied for mechanical processing between the working rolls at different pressure forces was experimentally determined. The values of the required breakaway force for the working rolls at the established values of the pressing force of the working rolls for packages consisting of five, ten, and sixteen layers of semi-finished products were obtained.

Possibility of estimation of mechanical stresses in nickel by the magnetic ponderomotive method

The paper considers a technique for assessing mechanical stresses in coatings by the magnetic ponderomotive method, based on the use of the magnitude of the magnet breakaway force and its relation to the magnetic characteristics of nickel (magnetic susceptibility), which change under the action of internal stresses. It is shown that the existing mechanical stress measuring equipment using X-ray, magnetic or ultrasonic methods have specimen size limitations or have low measurement locality. At the same time, a magnetic ponderomotive method for controlling mechanical stresses is presented, which does not have the indicated disadvantages. The change in the magnetic breakaway force on the thickness, applied and residual stresses caused by elastic and plastic deformations in the sample is theoretically substantiated. It is shown that the presence of residual stresses in the sample changes the nature of the dependence of the magnet breakaway force on the applied stresses. A calculation algorithm has been developed that allows measuring the magnet breakaway force to obtain the ratio between the applied and residual stresses. It is shown that the ratio between residual and applied stresses can be used to assess the degree of proximity to the critical stresses levels that lead to failure. Calibration surfaces are constructed for the dependence of applied stresses on magnetic separation force and thickness, corresponding to elastic-plastic deformation, as well as leveled calibration surfaces, corresponding to elastic deformation in the presence of residual stresses in the material. Experiments have been carried out on real samples and coatings, that determine the degree of approximation of internal stresses in the material to critical levels that may lead to destruction. It is shown that when comparing the readings of calibrated gauges with a certified tool, the largest deviation occurs at low stress values due to the inverse dependence of the breakaway force on the stress level.

3D projection of the LuGre friction model adapted to varying normal forces

In this paper, we develop an adaptation of the LuGre friction model so as to allow the development of the friction force and its application in any directions on systems subjected to varying normal forces. This is achieved by projecting a modified LuGre model adapted to varying normal forces in 3D along an arbitrary orthogonal system. Consequently, the direction of the friction force is automatically oriented in the correct direction, thus stick, stick-slip, and slip behavior can be represented in all directions. The projected friction model has the following friction features: stick-slip, presliding displacement, frictional lag, varying break-away force, viscous friction, Stribeck effect, and is adapted to varying normal forces. The equivalence of this projected LuGre model with the modified one is proven analytically. The friction model is then applied to simulate the friction on two mechanical systems. The first system consists of a cube sliding on a plane with a transition from stick to slip due to varying normal forces and with a pulling force oriented in multiples directions of the contact plane. The second one is a more complex system consisting of three turbine blades that uses friction to damp their resonance. The results obtained for both systems are consistent with literature.

Evaluation of the Magnet Breakaway Force Measurement Accuracy of the NT-800 Sensors for Early Detection of Defects of Their Manufacturing

Сontrol of mechanical stresses formed with the deposition of nickel coatings plays an important role in the diagnosis of coatings’ technical condition. Large internal stresses can lead to cracking or flaking of coatings which is completely unacceptable for critical parts and assembly units used, for example, in space technology for which reliability is of paramount importance. An important aspect of internal stresses monitoring is the measurement error of the instruments used. The purpose of this work was to determine the characteristics of the device sensors, which make the assessment of their manufacturing possible at the preliminary stage of the measuring equipment assembling in order to maintain the required accuracy of subsequent measurements.In most cases the measurement error assessment is possible only after the equipment manufacture and calibration. In this paper it is proposed to evaluate the accuracy characteristics of device sensors based on the precision (repeatability and reproducibility) of the primary informative parameter recording. In the case of the NT-800 device that was developed at the Institute of Applied Physics of the National Academy of Sciences of Belarus the effect of precision characteristics deterioration on the eventual measurement error is demonstrated. Determining the precision parameters before establishing correlation dependences between the primary informative parameter and the measured characteristic is proposed in order to reject poorly manufactured sensors and reduce labor costs.In particular, measurements of the magnitude proportional to the magnetic breakaway force were carried out using the NT-800 device with nickel specimens simulating coatings with a thickness of 200 to 700 μm and a rolling value from 0 to 40 %. It was established that in the case of well-made sensors the variation coefficient calculated from the dispersion of repeatability is in the range 0.2–0.6 %, and the variation coefficient calculated from the dispersion of reproducibility does not exceed 0.9 %. In the case of a sensor with the sensitive element parameters worsened, the variation coefficient of repeatability and reproducibility were up by one and a half times. Deterioration of the precision characteristics resulted in significant changes in the readings of the calibrated instrument. Thus the absolute measurement error for a sensor with a poorly made sensitive element turned out to be approximately 3 times higher in the range of 200– 300 MPa than that for a sensor with good precision parameters.

Identification of the Effect of Ultrasonic Friction Reduction in Metal-Elastomer Contacts Using a Two-Control-Loop Tribometer

Pneumatic cylinders are widely used in highly dynamic processes, such as handling and conveying tasks. They must work both reliably and accurately. The positioning accuracy suffers from the stick-slip effect due to strong adhesive forces during the seal contact and the associated high breakaway forces. To achieve smooth motion of the piston rod and increased position accuracy despite highly variable position dynamics, sliding friction and breakaway force must be reduced. This contribution presents a specially designed linear tribometer that has two types of control. Velocity control allows the investigation of sliding friction mechanisms. Friction force control allows investigation of the breakaway force. Due to its bearing type, the nearly disturbance-free detection of stick-slip transients and the dynamic contact behavior of the sliding friction force was possible. The reduction of the friction force was achieved by a superposition of the piston rod’s movement by longitudinal ultrasonic vibrations. This led to significant reductions in friction forces at the rubber/metal interface. In addition, the effects of ultrasonic frequency and vibration amplitude on the friction reduction were investigated. With regard to the breakaway force, significant success was achieved by the excitation. The force control made it possible to identify the characteristic movement of the sealing ring during a breakaway process.

Analysis and characterization of the friction of vehicle body vibration dampers

The friction at the contact surfaces of a vehicle body vibration damper, which are moved relatively to each other, influences its transmission behavior at the start of movement (breakaway force) as well as with excitation signals of higher velocity and thus has an impact on the comfort properties of the damper. According to Vibracoustic (Die wichtigsten Kriterien für deutsche Autofahrer beim Autokauf, Springer Fachmedien Wiesbaden GmbH, Wiesbaden, 2019), for most German drivers (63%) comfort (in addition to brand and appearance) before driving dynamics (53%) and environmental compatibility (48%) is the most important criteria when evaluating a new car, which explains the importance of this vehicle characteristics. Furthermore, the friction is present with any relative movement of the damper and is, therefore, relevant for the design of the damper and the associated vertical dynamics. The friction is generally determined in the fully assembled state of the damper, including oil filling and gas pressure at a very low movement velocity to eliminate the influence of the damping force. This measurement method allows no or only inadequate statements about the friction behavior at, e.g. more dynamic excitation scenarios. As a result, the aim should be to characterize the friction properties without the influence of hydraulic damping at the start of movement or reversal of movement, as well as at higher movement velocities. Another goal is to evaluate the influence of the internal pressure of the damper on its friction behavior. The test damper used here is a commercially available monotube damper that has been modified in accordance with the requirements for these tests. The results shown below can be used as starting variables for further investigations for the targeted optimization of the friction properties and thus for the improvement of driving comfort. The reduction in damper friction promises an increase in comfort due to the improved decoupling of the vehicle body from the road excitation. Furthermore, the data obtained enable the level of detail of simulation models to be increased and serve as a basis for comparing different friction pairings and contact surfaces in the damper. For the substitution of coatings (chrome-free piston rods → environmental protection) or tube materials (aluminum matrix composites → lightweight construction) as well as for changes in the surface structure and roughness, the results enable an evaluation of the friction properties compared to conventional dampers and the adjustment of the friction pairings in the sense of the best possible functionality.

Impact of Patient Interface Diameter and Vacuum Level on Suction Stability Using a Flat Applanating Interface for Femtosecond Laser-Assisted LASIK

ABSTRACT Purpose To investigate the impact of different patient interface (PI) diameters and different vacuum levels on the suction stability during vacuum application for femtosecond laser-assisted LASIK. Methods Break-away forces as a marker for suction stability were measured by an automated test bench set-up. The test bench was based on a customized stamp connected to a digital load cell. Three flat applanating PI with different diameters (8.5, 9.5 and 10.0 mm) and four different vacuum levels (500, 600, 700 and 800 mbar) were investigated using the FEMTO LDV Z8 (Ziemer Ophthalmic Systems AG, Switzerland). Results Mean break-away force was 5.23N (±0.99N) using the 8.5 mm PI and 500 mbar vacuum, 8.18N (±1.39N) using the 8.5 mm PI and 800 mbar, 3.37N (±0.56N) using the 10.0 mm PI and 500 mbar, and 6.14N (±0.68N) using the 10.0 mm PI and 800 mbar vacuum (p < .001; CI95%). Increasing the PI diameter from 8.5 to 10.0 mm resulted in a 28.89% (+1.97 ± 1.02N) lower break-away force (p < .001) when using default vacuum settings (700 mbar) compared to increasing vacuum from 500 to 800 mbar, which resulted in a 60.37% (+1.95 ± 1.40N) higher mean break away force (p < .001). Conclusion The vacuum level and the diameter of the PI showed significant impact on suction stability measured as break-away force during flat applanating docking for corneal and refractive surgery. Break-away forces were inversely related to the PI diameter and directly to the vacuum level. Increasing the PI diameter by one step or reducing vacuum by 100 mbar resulted in a comparable decrease of break-away forces. Therefore, the surgeon could potentially maintain stabile suction by increasing vacuum when choosing a larger PI diameter to obtain a larger treatment zone. Furthermore, reduction of the PI diameter and/or increasing vacuum could help improving suction stability in situations of poor suction and in situations with increased risk of suction loss during LASIK.

Investigations on amplitude adaptive sequential friction‐spring dampers

AbstractThis paper presents two sequential friction‐spring damper configurations and develops numerical and analytical models, which describe the systems' behavior. The dampers rely on the non‐smooth characteristics of dry friction to quench unwanted oscillations and only dissipate energy once a preset breakaway force of the friction element is exceeded. Since no additional control is required and the dissipation is only present within a given frequency range, this passive amplitude adaptive dissipation contributes to a higher energy efficiency. The dampers' equations of motion are derived and implemented in a numerical model to gain the first insights into the dampers' behavior. These equations of motion are analyzed via averaging methods in combination with a modal decoupling for nonlinear systems, which lead to the dampers' analytical models. The results from both models are compared and show reasonable agreement within the validity range of asymptotic methods. This work proposes two friction based amplitude adaptive dampers and offers a starting point for future experimental validation.

Comparative study between dry friction and electrorheological fluid switches for Tuned Vibration Absorbers

Tuned Vibration Absorbers are a widely used tool for suppressing the amplitude of a systems vibrations, one of the advantages being offered is that the absorber can be an add-on solution which is able to be adjusted offline. Many improvements have been made to the base system including the use of dry friction elements, and magneto- or electrorheological fluid (M-/ERF) elements. In this work the ability of both a dry friction based system and an electrorheological fluid (ERF) damper based system to reduce the amplitude response of a system over a wide range of frequencies through the use of the stick-slip effect is investigated through simulation. The unique advantage of using an ERF damper over a dry friction element are then investigated. Those are the ability of an ERF damper based system to adjust the breakaway force online and the ability of the damper to switch between the slip- and stick-states to further reduce the amplitudes over certain frequencies given that the excitation force is kept to a single frequency at a time. These investigations were first carried out through simulations and then through an experimental setup for both systems to prove the concepts in practice. The results of the experiment conclusively proved the ability of both systems to behave as predicted, especially the ability of the ERF damper to switch between stick- and slip-states to reduce vibration amplitudes in some frequencies.

Angular positioning of the objects by the system of two oblique friction force fields

The paper presents a model of the angular positioning process of cuboidal objects with the use the system of two oblique friction forces fields created by conveyor belts. In this model, the contact surface of the object with conveyors was divided into discrete elements. To describe the reaction of the frictional forces of discrete elements in the plane motion, the models of LuGre, MSC Adams with or without the Stribeck effect were used. Numerical tests show that due to the implementation of the positioning process at high sliding velocities, the object transition between the friction fields does not cause appearing the Stribeck effect. The disappearance of this effect is caused by disclosure of nonlinear phenomena, break-away force and stick-slip, which cause a drop in the friction limit force value, when the external force breaking the static friction builds up at high velocity.In addition, based on the analyses of numerical test results, determined recommended parameters of the conveyor belts motion, allowing to minimize the value of the final rotation angle of the object after passing through a system of two oblique friction force fields.

Will the Establishment of Circuit Tribunals Break Up the Circular Reforms in the Chinese Judiciary?

AbstractThis article examines the objectives for the establishment of circuit tribunals of the Supreme People’s Court of China and the politico-legal functions of such tribunals in the context of judicial reforms that were first launched in 1999. It starts with an analysis of the fundamental problems and difficulties that impeded judicial reforms in the last two decades. It then provides a careful analysis of the establishment of circuit tribunals and examines the political barriers to fundamental reforms towards genuine, though limited, independent adjudication in China. Although we do not believe that the circuit tribunals will be a breakaway force in the Chinese polity, the present reforms do have the potential to break up certain circular reforms and break through some fundamental barriers to deep reform. Further, while judicial independence, in the sense of the judiciary being an independent force in the political and constitutional scheme of checks and balances, is not attainable in the political environment in China today or indeed in the near future, it is hoped that the present reforms might grant the Chinese judiciary some limited, but much needed, autonomy within the Chinese political system.

Formation of Metallic Phase on Reducing-Gas Injection in Multicomponent Oxide Melt. Part 3. Separation of Ferronickel and Oxide Melt

Using the equations of physicochemical hydrodynamics and experimental results regarding the surface and interphase properties of metallic and oxide melts, the conditions in which metallic phase is formed in the bubbling of carbon monoxide through molten oxidized nickel ore are described. The critical dimensions of the gas bubble (Rb.cr) and the metal droplet (rd.cr) moving in oxide melt without change in size are determined in the range 1550–1750°C. It is found that Rb.cr increases slightly from 6.35 × 10–2 m at 1550°C to 6.58 × 10–2 m at 1750°C. With change in the droplet composition and the temperature, rd.cr varies from 2.1 × 10–3 to 2.9 × 10–3 m. The dimensions of the metal droplet formed at a single bubble during the reduction of nickel and iron from oxide melt are determined. As the content of nickel and iron oxides in the melt decreases with increase in the overall CO consumption, the nickel content in the ferronickel droplets falls from 89 to 18%, while the droplet diameter decreases from 1.4 × 10–3 to 8.0 × 10–4 m. The droplet mass falls correspondingly from 9.4 × 10–5 to 1.6 × 10–5 kg. The conditions in which the bubble–droplet system rises through the melt are determined. Over the whole range of temperature and Ni content, the bubble–droplet system begins to rise through the oxide melt when rd/Rb is less than 0.68–0.78. To assess the stability of the bubble–droplet system, with the given bubble and droplet dimensions, the parameters determining their joint motion are calculated. It is found that breakaway of the metal droplet from the bubble is not possible in pyrometallurgical systems. The formation of metal phase as a result of the bubbling of carbon monoxide through the oxide melt is described. In this process, the interaction of the oxide melt with the gas is accompanied by the formation of metal droplets, which become attached to the surface of gas bubbles and move to the surface of the oxide melt. Metal with 80–90% Ni is formed at first. With decrease in the nickel content in the oxide melt, its content in the metal declines to 20%. At the surface of the oxide melt, the metal droplets coalesce. When their diameter is greater than 5 × 10–3 m, they break away from the surface and fall to the bottom. If the falling drop collides with ascending bubble–droplet systems, they may coalesce with it or flow around it. On coalescence, the small droplets will be assimilated and rise to the surface. The breakaway force of the droplet from the bubble significantly exceeds the gravitational force on the droplet. Therefore, the bubble–droplet system is stable for all the size ratios considered.

Effects of Gloves and Pulling Task on Achievable Downward Pull Forces on a Rung.

Objective We examined the impacts of pulling task (breakaway and pull-down tasks at different postures), glove use, and their interaction on achievable downward pull forces from a ladder rung. Background Posture, glove use, and the type of pulling task are known to affect the achievable forces. However, a gap in the literature exists regarding how these factors affect achievable downward pulling forces, which are relevant to recovery from a perturbation during ladder climbing. Methods Forty subjects completed four downward pulling tasks (breakaway force; pull force at maximum height, shoulder height, and a middle height), using three glove conditions with varying coefficient of friction (COF) levels (cotton glove, low COF; bare hand, moderate COF; and latex-coated glove, high COF) with their dominant and nondominant hand. The outcome variable was the maximum force normalized to body weight. Results The highest forces were observed for the highest hand postures (breakaway and maximum height). Increased COF led to higher forces and had a larger effect on breakaway force than the other tasks. The dominant hand was associated with higher forces than the nondominant hand. Male subjects generated greater forces than female subjects, particularly for higher hand positions. Conclusion This study suggests that a higher hand position on the ladder, while avoiding low-friction gloves, may be effective for improving recovery from ladder perturbations. Application This study may guide preferred climbing strategies (particularly those that lead to a higher hand position) for improving recovery from a perturbation during ladder climbing.

On break-away forces in actuated motion systems with nonlinear friction

The phenomenon of so-called break-away forces, as maximal actuation forces at which a sticking system begins to slide and thus passes over to a steady (macro) motion, is well known from the engineering practice but still less understood in its cause-effect relationship. This note analyzes the break-away behavior of systems with nonlinear friction, which is well-describable analytically by combining the Coulomb friction law with the rate-independent presliding transitions and, when necessary, Stribeck effect of the velocity-weakening steady-state curve. The break-away conditions are brought into an analytic form of the system description and shown to be in accord with a relationship between the varying break-away force and actuation force rate – that is observable in experiments reported in various independently published works.

Comparison of Four Friction Models: Feature Prediction

In this paper, we provide not only key knowledge for friction model selection among candidate models but also experimental friction features compared with numerical predictions reproduced by the candidate models. A motor-driven one-dimensional sliding block has been designed and fabricated in our lab to carry out a wide range of control tasks for the friction feature demonstrations and the parameter identifications of the candidate models. Besides the well-known static features such as break-away force and viscous friction, our setup experimentally demonstrates subtle dynamic features that characterize the physical behavior. The candidate models coupled with correct parameters experimentally obtained from our setup are taken to simulate the features of interest. The first part of this work briefly introduces the candidate friction models, the friction features of interest, and our experimental approach. The second part of this work is dedicated to the comparisons between the experimental features and the numerical model predictions. The discrepancies between the experimental features and the numerical model predictions help researchers to judge the accuracy of the models. The relation between the candidate model structures and their numerical friction feature predictions is investigated and discussed. A table that summarizes how to select the most optimal friction model among a variety of engineering applications is presented at the end of this paper. Such comprehensive comparisons have not been reported in previous literature.

Cytotoxic and genotoxic effects on gingival fibroblasts from static magnetic fields produced by dental magnetic attachments.

To investigate cytotoxic and genotoxic effects of static magnetic field (SMF) produced by dental magnetic attachments on human gingival fibroblasts in vitro. Magnetic attachments have numerous roles in dental prosthesis fixation, but few reports evaluate possible biological effects of static magnetic field (SMF) on human gingival tissues, particular genotoxic effects. The Dyna (500-gr breakaway force) and Steco (173-gr breakaway force) dental magnetic attachments were embedded into autopolymerising acrylic resin in four different configurations each, including single and double magnets. Gingival biopsy was performed on 28 individuals during third molar extraction, and each sample was divided into two pieces for culture under SMF exposure or as a control. In total, seven test and seven control gingival fibroblast cultures were performed for each group resulting in 56 gingival fibroblast cultures. The test culture flasks were placed atop the magnet-embedded resin blocks. After cultures were terminated, mitotic index (MI) and micronucleus (MN) rates were analysed at a p=0.05 significance level by Wilcoxon's test; intergroup differences were analysed with a Kruskal-Wallis test. There was no significant difference in intragroup or intergroup MI rates. The double Dyna (p=0.023) and double Steco (p=0.016) groups had statistically significant intragroup differences in the MN rates. There were no statistically significant differences in MN rates in intergroup analyses. In particular, higher magnetic fields from dental magnetic attachments might be toxic genetically to human gingival fibroblasts. However, there is need for further investigations from different aspects to detect any genotoxicity.

Numerical Analysis of Fretting-Wear With a Hybrid Elastoplastic Friction Model

Fretting-wear is a common problem in different industries, especially when it comes to interactions between metallic components. Flow-induced excitation forces in heat exchangers for instance cause tube-support interactions. The long-term interaction is an important phenomenon, which may cause fretting-wear of the tubes. Experimental tests of the interaction show the occurrence of stick–slip intermittent behavior in the tube response. To precisely simulate the intermittent stick–slip behavior, it is crucial to refine the conceptual model of the coefficient of friction for the entire motion from absolute zero velocity to gross slip phase. The incorporated friction model plays an important role in the determination of the level of fretting-wear in the system. The friction model should satisfy two important criteria. The first important aspect is the strategy of the friction model to detect the cessation of sticking, the beginning of partial-slipping, and establishment of the sliding region. The second important aspect is defining a friction coefficient function for the entire system response to precisely represent the transient stick–slip regions. In the present work, the velocity-limited friction model was compared with the LuGre model, which is a rate-dependent friction model. The effect of varying the break-away force and Stribeck effect on the stick–slip region were also investigated. Furthermore, the criteria to demarcate the stick–slip region in the LuGre model are discussed, and a different method to incorporate the Stribeck effect and presliding damping in the Dahl friction model is proposed. Using the tangential stress distribution in the contact area, a new hybrid spring-damper friction model is developed. The model is able to estimate the elastic, plastic, and partial-slipping distances during the relative motion. The ability of the model to reproduce experimental tests is investigated in the present work.

Feasibility and safety of a novel in vivo model to assess playground falls in children

Falls are the leading cause of nonfatal unintentional injuries among hospitalized children with playground equipment accounting for more than 50%. National standards for playground rung and rail design exist, but there a lack of in vivo models available to test these standards. We developed a novel in vivo model to test rung and rail design. We report the feasibility and safety of the model. A device was built to simulate children hanging onto a playground bar until their hand slips off. This was defined as breakaway strength. The handle unit was mounted on a vertical cable that was mechanically raised and lowered using a linear actuator controlled by the experimenter. The unit was padded and contained a video camera that recorded the posture of the hand during each trial. Breakaway force and torque were recorded as they held onto the handle by LabView software. In addition, standard anthropometrics and grip strength were recorded. Biomedical engineering approved the device. There were 425 eligible students aged 5 years to 11 years. Of these, 93% (397) participated (212 males and 185 females). Ninety-nine percent (396 of 397) completed all three experimental stations, one declined because of fear. There were no injuries and no falls. Average time to complete the study was 22 ± 0.5 minutes. Ninety-one percent of participants were right handed; the ethnicity was representative of the local area with 79% being white. Mean ± SD height, weight, and body mass index for the 397 participants were 1.28 ± 0.11 m, 28.0 ± 8.12 kg, and 16.31 ± 2.59 kg/m², respectively. Hand size, grip strength, and maximum breakaway force increased with age. This model is safe and feasible and maybe a viable method to assess rung and rail design for playgrounds.

The Effect of Handhold Orientation, Size, and Wearing Gloves on Hand-Handhold Breakaway Strength

The aim of this study was to quantify the effect of handhold orientation, size (diameter), and wearing a glove on the maximum breakaway strength between a hand and handhold. Manual breakaway strength is known to be greatly reduced for vertical compared with horizontal handholds, but oblique orientations have yet to be studied. For this study, 12 young adults (6 female) attempted to hold on to fixed overhead cylindrical handholds with one hand in low-speed simulated falls as forces on the handhold were recorded in two experimental designs. Breakaway strength was measured for (a) three different-sized cylinders in four orientations while the participants were using the dominant hand and (b) a single-sized cylinder in four orientations while the participants were bare-handed or wearing a glove on the nondominant hand. Handhold orientation (p < .001), handhold diameter (p < .001), and wearing gloves (p < .001) significantly affected breakaway strength. Breakaway strength increased 75% to 94% as the orientation of the handhold was moved from vertical to horizontal. Breakaway strength decreased 8% to 13% for large-diameter (51-mm) handholds as compared with smaller diameters (22 mm to 32 mm), depending on orientation. Gloves may increase or decrease the ability to hang on depending on interface friction; greater friction increased breakaway force. Handles oriented perpendicular to the pull direction and high-friction gloves provide the greatest breakaway strength. Smaller handhold diameters than predicted by grip strength afford greater capability in these orientations. These insights can be used to design handholds that increase the ability to support one's body weight and reduce the effort needed to pull or lift heavy items.