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Item type:Publication, Access status: with files , A two-scale FEM-BAM approach for fingerpad friction under electroadhesionThe complex physics behind electroadhesion-based tactile displays poses an enormous modeling challenge since not only the fingerpad structure with multiple nonlinear layers, but also the roughness at the microscopic scale play a decisive role. To investigate tactile perception, a potential model should also offer the possibility to extract mechanical stimuli at the sites of the relevant mechanoreceptors. In this paper, we present a two-scale approach that involves a finite element model (FEM) at the macroscopic scale and a simple bearing area model (BAM) that accounts for the measured roughness on the papillary ridges. Both separate scales couple in an iterative way using the concept of an equivalent air gap. We show that the electroadhesion-induced changes in friction and contact area predicted by the proposed model are in qualitative agreement with recent experimental studies. In a simple example, we demonstrate that the model can readily be extended by a neural dynamics model to investigate the tactile perception of electroadhesion.Publicationtype: Journal ArticleScopus© Citations 4 48 123 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Thermal conductivity of Ti-6Al-4V in laser powder bed fusion(Frontiers Media S.A., 2022-07-01); ; ; ; With increasing maturity of the laser powder bed fusion (PBF-LB/M) process, the related products are becoming more complex. The more conventional parts are integrated into one design, the more requirements regarding local material properties arise. This concerns for instance products with high demands regarding temperature management. Here, different thermal conductivities within the part enable the control of the temperature distribution as well as the direction of heat flows. The realization of those local properties poses a challenge, though, as the use of multiple materials in PBF-LB/M is not broadly available. However, the different states of material in PBF-LB/M, i.e. bulk and powder material, provide the opportunity to create thermal metamaterials with locally varied thermal conductivities. To enable part design utilizing the bulk material as well as enclosed powder, this study investigates the respective thermal conductivities of Ti-6Al-4V. Powder and printed samples were measured at RT by the Modified Transient Plane Source method, resulting in an effective thermal conductivity of 0.13 W/mK for powder and 5.4 W/mK for bulk material (compared to 6.5 W/mK in prior experiments). For complete assessment of the powder material, because of the many uncertainties due to the particle size distribution and powder application, a computational model following the network modeling approach is created. The model is used to create a data set of 60 different powder bed configurations, which is then statistically evaluated to provide a description independent from powder packing. Finally, the application of the investigations to achieve thermal metamaterials capable of local temperature management with a single material is presented in a numerical study. Here, the use cases of thermal shielding as well as the concentration of heat flow is demonstrated.Publicationtype: Journal ArticleScopus© Citations 2 149 551 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A simplified theory of electroadhesion for rough interfacesElectroadhesion is a very hot topic in tribology due to its implications for the science of surface haptics. Building on theories of Persson, we develop a simpler theory for electroadhesion between rough surfaces using the bearing area model of Ciavarella. The theory is derived for the cases of conducting and insulating bodies and shows that pull-off forces depend mostly on the applied voltage, the surface root mean square (RMS) height, and the longest wavelength in the surface representation. However, the real contact area and friction additionally depend on rms slopes and hence on truncation of the roughness spectrum. Two stickiness criteria are derived based on the present theory and on the energy balance proposed by Persson and Tosatti. The coefficient of friction decays with the normal pressure, tending to a plateau in a manner consistent with existing experiments.Publicationtype: Journal ArticleScopus© Citations 5 61 228