Comparative Analysis of Actuator Dimensioning Methods in Pneumatics

In the modern automation technology, there are often two ways to complete a drive task: pneumatically or electrically. In order to remain competitive with the electromechanics and to contribute to the achievement of climate protection goals, manufacturers and users of pneumatic systems are required to increase the energy efficiency of pneumatics. One of the primal and simplest methods to reduce the energy consumption of existing and to-be-developed pneumatic systems is the correct sizing of actuators. However, even in the most modern machines drives are often overdimensioned thus creating a higher energy consumption than necessary. To counteract this, different dimensioning methods have been developed in the last few years, which could contribute to a significant reduction of energy consumption. Design tools based on dynamic simulations are highly reliable, but their calculation methods can be complex and non-transparent. Therefore, more pragmatic and simple dimensioning methods have been developed, based on algebraic approaches like force equilibrium, exergy equilibrium and pneumatic frequency ratio. In this paper these methods are evaluated using mathematical analysis and practical drive examples. Their possible application fields and limitations are shown and compared.

The Symmpact: A Direct-Impact Hopkinson Bar Setup Suitable for Investigating Dynamic Equilibrium in Low-Impedance Materials

Background Measuring the dynamic behavior of low-impedance materials such as foams is challenging. Their low acoustic impedance means that sensitive force measurement is required. The porous structure of foams also gives rise to dynamic compaction waves, which can result in unusual behavior, in particular if the foam material is so thick, that dynamic force equilibrium is not reached. Objective This work investigates comparatively large polyurethane foam specimens with densities in the range of 80 – 240 kg/m3 to deliberately achieve a state away from force equilibrium during high-rate compaction. The aim is to understand how an increase in strain rate leads to a reduction in strength for such materials. Methods A specialized direct-impact Hopkinson bar is employed. It uses polycarbonate bars to achieve the required long pulse duration of 2.6 ms to compress the large specimens into the densification regime. In contrast to existing setups, both striker and output bar are instrumented with strain gauges to monitor force equilibrium. The absence of an input bar allows monitoring force equilibrium more accurately. Special attention is paid to the calibration of strain gauges, taking non-linear effects, wave dispersion and attenuation into account. Digital Image Correlation is employed to analyze elastic and plastic compaction waves by means of Lagrange diagrams. Results Depending on density, the specimens show saturation of dynamic strength increase at high rates of strain $$\approx$$ ≈ 500 /s, or even negative strain rate sensitivity in case of the lowest density. The occurrence of apparent negative strain rate sensitivity is accompanied by a localized structural collapse front, moving at a low velocity of $$\approx$$ ≈ 10 m/s through the material. This apparent strain rate sensitivity is a structural effect which is related to the thickness of the specimen. Conclusions The primary aim of material characterization using Hopkinson bars is to achieve a state of force equilibrium. For this reason, very thin specimens are usually employed. However, data gathered in this way is not representative for thick foam layers. Here, an increase of strain rate can lead to a decrease of strength if homogeneous deformation is replaced by a dynamic compaction wave. This behavior can occur at strain rates encountered under conditions such as automotive crash.

Displacement Analyses for a Natural Slope Considering Post-Peak Strength of Soils

A natural slope undergoing recurrent movements caused by rainfall-induced groundwater table rises is studied using a novel method. The strength and displacement parameters are back-calculated using a force-equilibrium-based finite displacement method (FFDM) based on the first event of slope movement recorded in the monitoring period. Slope displacements in response to subsequent rainfall-induced groundwater table rises are predicted using FFDM based on the back-calculated material parameters. Important factors that may influence the accuracy of slope displacement predictions, namely, the curvature of the Mohr-Coulomb (M-C) failure envelope and post-peak strength softening, are investigated. It is found that the accuracy of slope displacement predictions can be improved by taking into account post-peak stress-displacement relationship in the analysis. The accuracy of slope displacement predictions is not influenced by the curvature of the M-C failure envelope in the displacement analysis.

Analytical determination of application point and normal reaction arm when rolling a wheel on a drum

Evaluation of the rolling resistance of car tires is now often performed on drum stands like car tests. This necessitates the study of the mechanics of interaction between the wheel and the drum in order to determine its force and kinematic characteristics, including the values and points of application of tangential and normal forces in contact with the drum. These problems can be solved taking into account that the mechanics of elastic wheel rolling on a drum is the same as when rolling on a flat rigid support surface. In this paper, from consideration of the mechanics of interaction between an elastic wheel and a drum, using the equations of power balance and force equilibrium of the wheel, the equations for determining the point of normal reaction in contact and its arm relative to the wheel axis during its rolling along one and two drums have been derived.. These dependencies have a simple form and can be applied when considering the rolling of both a single wheel and the car as a whole on a drum stand.

Investigating slow shock in low-impedance materials using a direct impact Hopkinson bar setup

This work implements a direct impact Hopkinson bar, suitable for investigating the evolution of dynamic force equilibrium in low-impedance materials. Polycarbonate as the bar material favours for a long pulse duration of 2.6 ms for an overall length of only 5 m, allowing to compress large specimens to high strains. This setup is applied to polyurethane foams with different densities ranging from 80 - 240 kg/m3. Dynamic compression tests are performed at strain rates of 0.0017, 0.5 and 500 /s on the foams at room temperature. Depending on density, they show a saturation in increase of yield strength at strain rates of 500 /s, or even show a negative strain rate sensitivity for the lowest density. This behaviour is explained by comparing the dynamic force equilibrium to a phenomenon similar to shock in solid materials: For low densities and high rates of strain, homogeneous compression is replaced by a localized collapse front with a jump in stress across the front. Digital image correlation is performed to analyse elastic and plastic compaction waves by means of Lagrange diagrams.

A Simplified Method for the Analysis of Hybrid Steel and FRP RC Beams

This paper suggests and validates a simplified analytical method for the analysis of hybrid steel and FRP reinforced concrete beams. The proposed method determines the flexural strength of the concrete beams based on strain compatibility and force equilibrium of the beam section under pure bending moment. The suggested method was validated against different experimental test results with very reasonable agreement. Afterward, the validated method was used to conduct parametric study to investigate the effect of two important parameters on the response and failure modes of hybrid steel and FRP RC beams. The proposed method can be implemented in the analysis and design of hybrid reinforced concrete beams with different reinforcement materials.

Numerical Modelization of the Oil Film Pressure for a Hydrodynamic Tilting-Pad Thrust Bearing

This study analyses the hydrodynamic characteristic of the tilting pad thrust bearing. Research content is simultaneously solving the Reynolds equation, force equilibrium equation, and momentum equilibrium equations. Reynolds equation is solved by utilizing the finite element method with Galerkin weighted residual, thereby determines the pressure at each discrete node of the film. Force and momentums are integrated from pressure nodes by Gaussian integral. Finally, force and momentum equilibrium equations are solved using Newton-Raphson iterative to achieve film thickness and inclination angles of the pad at the equilibrium position. The results yielded the film thickness, the pressure distribution on the whole pad and different sections of the bearing respected to the radial direction. The high-pressure zone is located at the low film thickness zone and near the pivot location.

Theoretical study of the effects of the shape of the spinning triangle

The spinning triangle is an important area in the spinning process, and the shape of the spinning triangle influences the yarn qualities. This paper aims to theoretically study the effects of the spinning parameters on the shape of the spinning triangle. In this paper, a model of the spinning triangle considering force equilibrium and torque equilibrium was built. The initial strain of fibers in the spinning triangle was determined by the profile of the spinning triangle. The initial height of the spinning triangle was obtained by the width of the spinning triangle and the twist angle. Based on the initial condition and boundary condition in the model, the displacements of the twisting point were obtained. With the displacements of the twisting point, the height of the spinning triangle and the deviation angle of the center fiber in the final spinning triangle, which represent the shape of the spinning triangle, were calculated. In the analysis, the spinning tension, yarn twist, and yarn radius were chosen as the independent parameters to analyze the geometric change of the spinning triangle.