DESIGNING A SHAPED SEAT-PAN CUSHION TO IMPROVE POSTURAL (DIS)COMFORT REDUCING PRESSURE DISTRIBUTION AND INCREASING CONTACT AREA AT THE INTERFACE

Remaining seated for extended periods increases the risk health issues and discomfort perception. Consequently, the seat-pan design is crucial and could be mainly influenced by two factors: pressure distribution and seat contour. For seat pan discomfort, the lower average pressure is accompanied by less discomfort. Moreover, a seat contour with a large contact area is correlated with more comfort. Thus, a shaped cushion had been accurately designed (Virtual Prototype) and realized (Physical Prototype) aiming to translate the pressure distribution due to interaction between seat and buttock in a geometric shape, suitable for the international population (including P5 females and P95 males). With this shape, the pressure should be more uniform and lower, the contact area at interface bigger, and the perceived comfort higher. Both Virtual and Physical Prototype design had been described in this paper through a repeatable and straightforward approach. Also, experiments had been performed to validate the hypothesis through a comparison with a standard flat cushion. Results showed the goal of the design had been reached: the shaped cushion scored less pressure distribution and higher contact area than the flat cushion.

Design and Control Method of a Planar Omnidirectional Crawler Mechanism

Omnidirectional mobility is a popular method of moving in narrow spaces. In particular, the planar omnidirectional crawler previously developed by the authors can traverse unstable and uneven terrain with a large contact area. A novel point is that the proposed system is unique in its ability to carry heavy loads in all directions without getting stuck because of the large pressure-receiving area between the crawler and ground. This work will facilitate omnidirectional motion, which has important implications for the use of robots in spaces such as not only factories, distribution centers, and warehouses but also soft soil in disaster sites. The objective of the present study was to establish a design and control method for an omnidirectional crawler mechanism that can conduct holonomic and two-axis cross driving. Only two motors are set on the crawler base for translation in the X- and Y-directions, and two large crawler units are arranged for turning. We design a small crawler that has higher traversing ability with a derailment prevention mechanism and tapered track. Further, the relationship between the motor rotational speed as input and crawler velocity as output was verified for control. In addition, it was demonstrated experimentally that the proposed crawler could travel across various types of rough terrain in a target direction.

Method for Calculating Plastic Deformation of High Resolution and Large Contact Area

In a rolling contact, the tribological properties in terms of friction, wear, and fatigue are significantly influenced by the surface roughness. Due to solid contact of the surfaces in the contact area, the roughness and thus also the tribological properties change during the service life of the contact. The initial load leads to major changes of the tribological properties figured out by Brecher et al. (2019, “Influence of the Metalworking Fluid on the Micropitting Wear of Gears,” Wear, 61(434–435), p. 202996). Prediction of the initial changes in topography in the contact area is necessary for specific optimization of rolling contacts. Especially for dry rolling–sliding contact, the roughness of the surfaces is crucial for the lifetime, which is part of the investigations within the DFG priority program 2074 (357505886). In this work, an elastic-plastic contact algorithm for calculating plastic deformation for dry contact of rough surfaces with large contact area and high resolution is presented. Due to the nonlinearity behavior associated with plastic deformation, the plastic contact algorithm is based on an iterative approach. An optimized meshing strategy is implemented to calculate the elastic pressure distribution on the surface. Corresponding to the two-dimensional pressure distribution, the three-dimensional stress distribution allows the consideration of residual stresses and interactions of the microscopic peaks of the rough surface. Furthermore, the three-dimensional plastic strain distribution allows the application of an analytical approach to represent the plastic deformation of the surface. Finally, the solution of a plastic contact calculation with an exemplary topography measured on a real rough surface is presented.

STUDI PERBANDINGAN MENGENAI PERHITUNGAN BESARAN REGANGAN DI LAPISAN SUBGRADE AKIBAT BEBAN RODA KENDARAAN UNTUK JALAN RAYA KELAS I

ABSTRACTMulti-layer systems theory is one of the concepts used in finding out the amount of strain and stress that occurs in the road pavement system due to vehicle loads. The purpose and goal of this study is to analyze the amount of strain that occurs on the pavement systems in Indonesia, especially in the subgrade position. The type of multi-layer system theory used to calculate the amount of strain includes the theory of one layer systems, two-layer systems and three-layer systems with data analyzed in the form of pavement thickness and type of pavement material.Based on this study, the value of strain obtained by the theory of one-layer system in some of the road data reviewed are 533.8658 microstrains, 361.3456 microstrains, 1577.987601 microstrains, 618,012 microstrains and 140.3075 microstrains. For research with two-layers systems, the results obtained are 1116.2920 microstrains, 544.322 microstrains, 1448.0839 microstrains, 734.1844 microstrains and 738.7226 microstrains. For research with three-layers system, results obtained are 72.20275278; 70.80346908; 192.9638366; 123.1150377dan 391.8845636 microstrains. The results with the calculation of one-layer system are very large because the modulus values of the subgrade layers are not reviewed and only pavement thickness is reviewed. As for calculations with the theory of two-layer systems, the results obtained are far greater than one-layer systems, due to the limitations of the graph to find the value of the ratio between thickness and large contact area. Calculation with the theory of three-layers system is a strain calculation which has a much smaller value compared to the theory of one-layer system and two- layer system. This is because this theory divides the calculated pavement layers into three layers, which is in accordance with the flexible pavement system which divides the pavement layers into three layers, so this calculation is the most ideal calculation because it approaches its original condition.ABSTRAKTeori sistem lapis banyak merupakan salah satu konsep yang digunakan dalam mencari tahu besaran regangan dan tegangan yang terjadi pada sistem perkerasan jalan raya akibat beban kendaraan. Maksud dan tujuan dari penelitian ini adalah untuk menganalisis mengenai besaran regangan yang terjadi pada jalan raya di Indonesia pada lapisan tanah dasar khususnya di posisi permukaan tanah dasar. Adapun jenis teori sistem lapis banyak yang digunakan untuk menghitung besaran regangan tersebut antara lain teori one-layer systems, two-layers systems dan three-layers systems dengan data yang dianalisis berupa tebal perkerasan dan jenis material perkerasan jalan.Berdasarkan penelitian ini, adapun nilai dari regangan yang diperoleh dengan teori one-layer system di beberapa data jalan yang ditinjau, antara lain 533.8658 mikrostrain, 361.3456 mikrostrain, 1577.987601 mikrostrain, 618.012 mikrostrain dan 140.3075 mikrostrain. Untuk penelitian dengan two-layers system diperoleh hasil yaitu 1116.2920 mikrostrain, 544.322 mikrostrain, 1448.0839 mikrostrain, 734.1844 mikrostrain dan 738.7226 mikrostrain. Untuk penelitian dengan three-layers system diperoleh hasil antara lain 72.20275278; 70.80346908; 192.9638366; 123.1150377 dan 391.8845636 mikrostrain. Hasil dengan perhitungan one-layer system sangat besar dikarenakan nilai modulus lapisan dari subgrade tidak ditinjau dan hanya meninjau tebal perkerasan. Adapun untuk perhitungan dengan teori two-layers system, hasil yang diperoleh jauh lebih besar daripada one-layer system, yang disebabkan keterbatasan dari grafik untuk mencari nilai perbandingan antara ketebalan dan luas kontak yang besar. Perhitungan dengan teori three-layers system merupakan perhitungan regangan yang memiliki nilai jauh lebih kecil dibandingkan dengan teori one-layer system dan two-layer systems. Hal ini dikarenakan teori ini membagi lapisan perkerasan yang dihitung menjadi tiga buah lapisan, yang sesuai dengan sistem perkerasan lentur yang membagi lapisan perkerasan menjadi tiga buah lapisan, sehingga perhitungan ini merupakan perhitungan yang paling ideal karena mendekati kondisi aslinya.

Laboratory study on the effects of fault waviness on granodiorite stick-slip instabilities

SUMMARY The effects of fault waviness on the fault slip modes are unclear. Laboratory study on the effects of the centimetre-scale fault contact distribution, which is mainly controlled by the fault waviness, on granodiorite stick-slip instabilities may help to unveil some aspects of the problem. The fast and slow stick-slip motions were separately generated in two granodiorite samples of the same roughness but different fault contact distributions in the centimetre scale in the laboratory. The experimental results show the following: (1) the fault with the small contact area and heterogeneous contact distribution generates fast stick-slip instabilities, while the fault with the large contact area and homogeneous contact distribution produces slow stick-slip events; (2) the nucleation processes of the fast stick-slip events are characterized by abrupt changes once the nucleation zones expand to the critical nucleation length that is observed to be shorter than the fault length, while the slow stick-slip events appear as a gradual evolution of the nucleation zones leading to total fault sliding. These indicate that, unlike the micron-scale fault contact distribution controlled by roughness, which depends mainly on the grain size of the abrasives used for lapping the fault surface, the centimetre-scale fault contact distribution, which depends mainly on the waviness of the fault surface profile, also plays an important role in the fault slip modes. In addition, the effects of the fault waviness on the fault friction properties are preliminarily analysed based on the rate- and state-dependent friction law.

Multistaged discharge constructing heterostructure with enhanced solid-solution behavior for long-life lithium-oxygen batteries

Inferior charge transport in insulating and bulk discharge products is one of the main factors resulting in poor cycling stability of lithium–oxygen batteries with high overpotential and large capacity decay. Here we report a two-step oxygen reduction approach by pre-depositing a potassium carbonate layer on the cathode surface in a potassium–oxygen battery to direct the growth of defective film-like discharge products in the successive cycling of lithium–oxygen batteries. The formation of defective film with improved charge transport and large contact area with a catalyst plays a critical role in the facile decomposition of discharge products and the sustained stability of the battery. Multistaged discharge constructing lithium peroxide-based heterostructure with band discontinuities and a relatively low lithium diffusion barrier may be responsible for the growth of defective film-like discharge products. This strategy offers a promising route for future development of cathode catalysts that can be used to extend the cycling life of lithium–oxygen batteries.

Contact splitting in dry adhesion and friction: reducing the influence of roughness

Splitting a large contact area into finer, sub-contact areas is thought to result in higher adaptability to rough surfaces, stronger adhesion, and a more uniform stress distribution with higher tolerance to defects. However, while it is widely believed that contact splitting helps to mitigate the negative effects of roughness on adhesion- and friction-based attachment, no decisive experimental validation of this hypothesis has been performed so far for thin-film-based adhesives. To this end, we report on the behavior of original and split, wall-shaped adhesive microstructures on different surfaces ranging across four orders of magnitude in roughness. Our results clearly demonstrate that the adhesion- and friction-driven attachment of the wall-shaped microstructure degrades, regardless of the surface waviness, when the surface roughness increases. Second, splitting the wall-shaped microstructure indeed helps to mitigate the negative effect of the increasing surface unevenness by allowing the split microstructure to adapt more easily to the surface waviness and by reducing the effective average peeling angle. These findings can be used to guide the development of biomimetic shear-actuated adhesives suitable for operation not only on smooth but also on rough surfaces.

Understanding receptor-mediated endocytosis of elastic nanoparticles through coarse grained molecular dynamic simulation

The membrane wrapping of the soft nanoparticle (NP) is faster than that of the stiff one at the early stage, due to the NP deformation induced large contact area between the NP and membrane. However, because of the large energy penalties induced by the NP deformation, the membrane wrapping speed of soft NPs slows down during the late stage.