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Karlheinz Schaub Jurij Wakula Knut Berg Bastian Kaiser Ralph Bruder Ulrich Glitsch Rolf‐Peter Ellegast 《人机工程学与制造业中的人性因素》2015,25(3):329-339
Even in hi‐tech industries, physical workload is partly considerable and cannot be avoided because of product and process requirements. Especially in automotive, aviation, and marine industries, the assembly of the product geometry requires force exertions in ergonomically unfavorable conditions. Unfortunately, internationally accepted methods for the evaluation of those types of force exertions are rare. Besides some traditional German methods and EN 1005‐3 hardly any evaluation methods exist. Even those methods refer to force exertions in primarily upright symmetric working postures. To overcome these problems the Assembly Specific Fore Atlas was created during the recent years. From a sample of automotive workers (n = 273), a set of 54 whole‐body forces (6 main force directions while standing, sitting, kneeling; in an upward, bent, and overhead posture) and a set of 38 types of finger‐hand forces (all at maximum voluntary contractions [MVC] levels) were measured in the field. The inputs for the types of force exertions required in practice were sampled from a consortium of major European car and truck companies. In addition, evaluation methods were developed that allow “calculating” maximum recommended force limits from the measured maximum static forces (i.e., MVC) and task and user group relevant parameters. This contribution gives a short overview on the data collected and focuses on the evaluation methods that had been realized. First, qualitative results are presented from the first field tests. 相似文献
34.
Mihail Slabki Jiang Wu Michael Weber Patrick Breckner Daniel Isaia Kentaro Nakamura Jurij Koruza 《Journal of the American Ceramic Society》2019,102(10):6008-6017
Piezoceramics are widely-used in high-power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three-stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high-power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely-used in high-power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three-stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high-power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. 相似文献
35.
Mao-Hua Zhang Leif Carstensen Changhao Zhao Lovro Fulanović Wolfgang Donner Jurij Koruza 《Journal of the American Ceramic Society》2022,105(1):451-460
AgNbO3 is one of the prominent lead-free antiferroelectric (AFE) oxides, which readily exhibits a field-induced AFE to ferroelectric phase transition and thus a high energy storage density. The solid-state synthesis of AgNbO3 is considered difficult and an oxidizing atmosphere is typically employed during AgNbO3 processing, on the premise that oxygen can prevent possible decomposition of the silver oxide at high temperatures. However, details about the influence of processing parameters on the functional properties of AFE AgNbO3 are insufficiently understood. In this work, the solid-state reaction of a stoichiometric AgO and Nb2O5 mixture was investigated. We found that ball milling can convert AgO into metallic Ag, which is beneficial for lowering the reaction temperature for the formation of the perovskite phase to 500‒600℃. Moreover, the influence of the processing atmosphere (air, O2, and N2) was investigated by thermal analysis and in situ X-ray diffraction. Since the reaction between Ag and Nb2O5 to form AgNbO3 requires oxygen uptake, AgNbO3 was only found to form in air and O2, whereby the kinetics were faster in the latter case. All the sintered AgNbO3 samples exhibited a similar crystallographic structure, although the samples processed in O2 had a lower oxygen vacancy concentration. Despite this, well-defined AFE double polarization loops were obtained in all cases. Our results indicate that decomposition of sliver oxide during ball milling is beneficial for the solid-state reaction, while a pure O2 atmosphere is not essential for the synthesis of high-quality AgNbO3. These findings may simplify the processing and facilitate further research of AgNbO3-based antiferroelectrics. 相似文献
36.
Jurij J. Sidor Roumen H. Petrov Leo A. I. Kestens 《Journal of Materials Science》2014,49(9):3529-3540
The evolution of deformation and recrystallization (RX) textures in 6016 Al alloy is analyzed in the current study by means of experimental measurements and numerical simulations. The deformation texture is modeled with various Taylor-type homogenization models whereas the development of RX texture is analyzed by evaluation of energy stored during the plastic deformation in grains of various orientations employing crystal plasticity (CP) calculations. It is shown that the main features of texture which evolve during discontinuous RX could be reproduced by taking into consideration both a microgrowth selection criterion and orientation selection based on crystallographically resolved stored energy of deformation. The influence of the strain heterogeneities on the development of RX texture is analyzed on the basis of CP and results derived from finite element calculations. 相似文献
37.
Sebastijan Ri
ko Jurij Svete Bogdan tefane Andrej Perdih Amalija Golobi
Ane Meden Uro Groelj 《Advanced Synthesis \u0026amp; Catalysis》2016,358(23):3786-3796
Chiral 1,2‐diamines are privileged structural motifs in organocatalysis, whereas efficient 1,3‐diamine‐derived organocatalysts are very rare. Herein we report a highly efficient camphor‐1,3‐diamine‐derived squaramide organocatalyst. Its catalytic activity in Michael additions of 1,3‐dicarbonyl nucleophiles to trans‐β‐nitrostyrene derivatives provides excellent enantioselectivities (up to >99% ee).
38.
Koen Decroos Jurij Sidor Marc Seefeldt 《Metallurgical and Materials Transactions A》2014,45(2):948-961
A new analytical model is presented that expresses kinematically admissible velocity fields in rolling processes. Opposed to conventional streamline approaches, the current model does not force the material to flow along the prescribed lines, but introduces a new coordinate that is constant over these lines, to prescribe a fixed component of the velocity in the rolling direction as a function of that coordinate and the coordinate along the rolling direction. The interaction between the rolls and the surface is incorporated in the model via two scalar parameters which depend on the friction conditions between the roll and the sheet, and the properties of rolled material. The scalar parameters can be tuned with experimental observations of deformation flow across the thickness. The modelled material flow does not reveal significant deviation from the one calculated by streamlines. The obtained analytical expressions for the velocity gradient tensor components combined with polycrystal plasticity models enables the prediction of the through-thickness texture evolution for various friction conditions. 相似文献
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The differential evolution (DE) algorithm was deployed to calibrate microparameters of the DEM cohesive granular material. 4 macroparameters, namely, uniaxial compressive strength, direct tensile strength, Young’s modulus and Poisson’s ratio, can be calibrated to high accuracy. The best calibration accuracy could reach the sum of relative errors REsum < 0.1%. Most calibrations can be achieved with REsum < 5% within hours or REsum < 1% within 2 days. Based on the calibrated results, microparameters uniqueness analysis was carried out to reveal the correlation between microparameters and the macroscopic mechanical behaviour of material: (1) microparameters effective modulus, tensile strength and normal-to-shear stiffness ratio control the elastic behaviour and stable crack growth, (2) microparameters cohesion and friction angles present a negative linear correlation that controls the axial strain and lateral strain prior to the peak stress, and (3) microparameters friction coefficient controls shear crack friction and slip mainly refers to the unstable crack behaviour. Consideration of more macroparameters to regulate the material mechanical behaviour that is dominated by shear crack and slip motion is highlighted for future study. The DE calibration method is expected to serve as an alternative method to calibrate the DEM cohesive granular material to its peak strength. 相似文献