Crawler robot kinematics modeling by using a two-wheeled approach

The aim of this paper is to analyze the kinematics of a small crawler robot. A mathematical model of kinematics based on a two-wheeled approach is proposed. This model is experimentally verified using vision-based motion measurements of a crawler vehicle equipped with encoders and a remote control system. It is assumed that the vehicle moves along a few curves with different angular speeds of its wheels. Based on the model of motion and the values of these speeds, numerical simulations are investigated. The results obtained from numerical and experimental validation are presented and discussed. The comparison delivered some important conclusions.

     

Numerical assessment of springback for the deep drawing process by level set interpolation using shape manifolds

In this paper, we introduce an original shape representation approach for post-springback characterization based on the automatic generation of parameterized level set functions. The central idea is the concept of the shape manifold representing the design domain in the reduced-order shape-space. Performing Proper Orthogonal Decomposition on the shapes followed by using the Diffuse Approximation allows us to efficiently reduce the problem dimensionality and to interpolate uniquely between admissible input shapes, while also determining the smallest number of parameters needed to characterize the final formed shape. We apply this methodology to the problem of springback assessment for the deep drawing operation of metal sheets.     

Flow patterns and gas fractions of air–oil and air–water flow in pipe bends

An experimental study of two-phase flow in a 180° pipe bends with 0.016, 0.022 and 0.03 m and the curvature radii of 0.11, 0.154, 0.21 m, respectively have been carried out. The experiments were conducted under the input superficial phase velocity: air from 0.038 to 5.4 m s⁻¹, water from 0.018 to 0.92 m s⁻¹ and oil from 0.014 to 0.92 m s⁻¹. The conducted research involved the observation of the forming flow patterns and determination of average volumetric in situ gas fraction. On the basis of the results of experimental flow map was created for gas–liquid flow and a method of calculating gas fractions was established.     

Fluidity and Temperature Profile of Ductile Iron in Thin Sections

 It has been shown that it is possible to produce thin wall ductile iron (TWDI) castings of considerable length using an Archimedes spirals with a wall of 1, 2 or 3 mm in thickness. The fluidities for different moulding materials ［(classical mould, chemically bonded silica sand and chemically bonded low-density alumina-silicate ceramic sand (LDASC)］, chemical composition, and pouring temperature were estimated. There is a significant temperature drop in thin sections (contrary to typical sections) during the mould filling. A profile of real temperature drop is presented along with theoretical predictions. The high temperature drop of liquid iron results in an increased cooling rate (before the eutectic equilibrium solidification temperature), which in turn affects the solidification and microstructure of TWDI castings. Microstructures were characterized quantitatively using an image analyser. Structure parameters for different wall thicknesses and moulding materials (graphite nodule count, ferrite and cementite fraction) are plotted, which is versus distance from the entrance to the mould cavity. It has been shown that the thin wall castings have a gradient structure. Moreover, a strong influence of LDASC sand (material with low ability to absorb the heat) on the structure parameters of TWDI castings is presented.     

Performance optimization of polymer electrolyte membrane fuel cells using the Nelder-Mead algorithm

The direct-search simplex method for function optimization has been adapted to performance optimization of polymer electrolyte membrane fuel cells (PEMFCs). The established method is strongly application oriented and uses only experimentally determined data for optimization. It is not restricted to discrete parameters optimums and does not require the use of third-party software or computational resources. Hence, it is easy to implement in fuel cell testing stations. The optimization consists of finding, for a given fuel cell load, an optimum set of values of the 7 fuel cell operating parameters: the fuel cell temperature, the reactants' stoichiometric ratios, the reactants' inlet relative humidity, and the reactants' outlet pressures, resulting in the highest fuel cell performance. The performance is measured using a scalar function of the operating parameters and the load and can be defined according to needs.Two PEMFC performance functions: the fuel cell voltage and the system-related fuel cell efficiency were optimized using the procedure for practically sized PEMFC stacks of two designs. With respect to the nominal operating conditions defined as optimal for each stack design by its manufacturer, the gains from the optimization procedure were up to over 12% and up to over 7% for the stack voltage and efficiency, respectively. The validation of the procedure involved 5 stack specimens and four laboratories and consistent results were obtained.     

Thermal and electrical conductivity of melt mixed polycarbonate hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets

In this work, we present thermoplastic nanocomposites of polycarbonate (PC) matrix with hybrid nanofillers system formed by a melt‐mixing approach. Various concentrations of multi‐walled carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were mixed in to PC and the melt was homogenized. The nanocomposites were compression molded and characterized by different techniques. Torque dependence on the nanofiller composition increased with the presence of carbon nanotubes. The synergy of carbon nanotubes and GnP showed exponential increase of thermal conductivity, which was compared to logarithmic increase for nanocomposite with no MWCNT. Decrease of Shore A hardness at elevated loads present for all investigated nanocomposites was correlated with the expected low homogeneity caused by a low shear during melt‐mixing. Mathematical model was used to calculate elastic modulus from Shore A tests results. Vicat softening temperature (VST) showed opposite pattern for hybrid nanocomposites and for PC‐MWCNT increasing in the latter case. Electrical conductivity boost was explained by the collective effect of high nanofiller loads and synergy of MWCNT and GnP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42536.     

Effect of plasma treatment on the surface properties of polydimethylsiloxane

In this work, the analysis of the plasma modification of polydimethylsiloxane (PDMS) substrates was conducted. The influence of the modification onto the changes occurred within the geometrical structure and chemical composition of the surface was analyzed. Due to the study of the atomic force microscopy, it was possible to determine the relationships between the surface development and applied process parameters, defining the conditions facilitating to obtain isotropic or anisotropic orientations of wrinkles. A precise analysis of the chemical composition of the surface, executed before and after the modification processes, enabled to define the changes in their elementary composition. Moreover, the modification influence onto the changes of the contact angle and the surface free energy were also analyzed. So, based on the research it was stated that the increase of value of the surface free energy is proportional to the sp³ phase contents in the DLC coatings. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41635.     

The improvement of ecological characteristics of coatings from cured epoxy resins by hot water extraction

Amine curing agents pose serious health hazards and controlling their release is crucially important. Extraction of unbounded amine from cured epoxy polymers can improve the ecological characteristics of such products. Even 1 min exposure of cured epoxy resins to hot water reduces three- to ten-fold the residual amount of amine present in the epoxy polymer. Different temperatures and extraction times were tested, enabling the selection of the most optimal extraction conditions, which correspond to 5 min of heating in 100°C. This additional cost-effective extraction step is very easy to perform and leads to a significant reduction of unbounded curing agent, making cured epoxy resins much more eco-friendly products. The documented positive and linear trends of logarithms of viscosity and the amount of released amine suggest the selection from such curing agents and such epoxy resins that are characterized by lowest possible viscosities, which guarantees that there is only a low amount of unbounded amine that needs to be released from the polymer.