Investigation on the impact and compression behavior of wet \upgamma -\hbox {Al}_{2}\mathrm{O}_{3} granules

The material behavior of dominant elastic–plastic \(\upgamma \) - \(\hbox {Al}_{2}\mathrm{O}_{3}\) granules has been experimentally studied by means of quasi static compression tests and dynamic impact tests until fracture. The obtained distributions of breakage velocity and specific breakage energy are compared. Thus, velocity dependent influences at stressing like viscous behavior can be derived. Additionally, the influences of particle size and moisture content on the material behavior are investigated.     

Ac conductivity and dielectric permittivity of poly(ethylene glycol) during crystallization: Percolation picture

Dielectric conductivity and permittivity of poly(ethylene glycol) were measured in the frequency range between 10¹ and 10⁶ Hz during non-isothermal crystallization and melting with different cooling/heating rates (5, 10 and 20 K/h). The time development of the conductivity and permittivity spectra during crystallization and melting is discussed in terms of charge carrier diffusion in a percolation network formed by the amorphous phase of the semi-crystalline polymer.     

Experimental verification of various methods for biological hydrogen production

The aim of the work was to compare two different biological methods for hydrogen production: fermentative and photosynthetic based upon the modality of batch cultures. For testing of fermentative bio-hydrogen production four mixed cultures representing anaerobic microorganisms (dominant strain Clostridium) were selected. The kinetic parameters on the intensity of bio-hydrogen production were established. The efficiency coefficient of transformation ranged from 1.65 mol H₂/mol glucose in the pectin culture up to 2.45 in the mixed culture. The bio-hydrogen concentration never exceeded 30%. The carbon dioxide was produced in a ratio of CO₂ to H₂ (0.5–0.67)/1. The testing of green algae proved that the most effective was the algae species Scenedesmus. High bio-hydrogen purity was analytically verified. The fermentative method of H₂ production is more efficient; it does not need light, has a longer efficiency of one charge and enables effective use of different biological wastes.     

Functional Gradation of Low Alloy Steel by Differentially Controlled Phase Transformation

In the present study, the phase transformation behaviour of 51CrV4 steel was investigated both in an actual flange forming process and under idealized isothermal bainitic transformation conditions. The results demonstrated that superimposed external stresses have only a minor effect on the kinetics of the phase transformation, whereas strains resulting from transformation plasticity were significant. Transmission electron microscopy revealed a preferential alignment of the bainite with respect to the external loading direction. This selection of favourably oriented variants in turn causes macroscopic strains. Understanding and minimizing these strains are a key factor in designing functionally graded components with minimum distortion.     

Bi-directional evolutionary level set method for topology optimization

A bi-directional evolutionary level set method for solving topology optimization problems is presented in this article. The proposed method has three main advantages over the standard level set method. First, new holes can be automatically generated in the design domain during the optimization process. Second, the dependency of the obtained optimized configurations upon the initial configurations is eliminated. Optimized configurations can be obtained even being started from a minimum possible initial guess. Third, the method can be easily implemented and is computationally more efficient. The validity of the proposed method is tested on the mean compliance minimization problem and the compliant mechanisms topology optimization problem.     

Determination of layer thickness in direct metal deposition using dimensional analysis

Direct Metal Deposition (DMD) is a blown powder laser deposition process that can be used to quickly produce fully dense metallic parts and to repair or modify high-value components. This paper illustrates the use of dimensional analysis to develop a mathematical model for the control of layer deposition in DMD. A brief explanation of the material deposition process is presented and the factors affecting the metal deposition is identified so that they can be used in modeling the height of the metal deposited. The validity of the generalized model is verified from experimental data of H13 steel and Ti material and it is found in good agreement with experimental findings.     

Topology optimization of hinge-free compliant mechanisms using level set methods

A new level set-based multi-objective optimization method is proposed for topological design of hinge-free compliant mechanisms. Firstly, the flexibility requirement of compliant mechanisms is formulated by using the mutual energy. Two types of mean compliance are developed to meet the stiffness requirement. Secondly, several objective functions are developed for designing hinge-free compliant mechanisms based on the weighting method in which a new scheme for determining weighting factors is used. Thirdly, several numerical examples are performed to demonstrate the validity of the proposed method. It is shown that the resulting compliant mechanism configurations contain only strip-like members which are suitable for generating distributed compliance and decreasing stress concentration.     

On the performance of a melamine–urea–formaldehyde resin for decorative paper coatings

The decorative laminates industry is a highly competitive industrial sector. To be profitable, manufacturers of impregnated papers for surface laminated MDF and particleboards need to significantly reduce their production costs. Melamine formaldehyde resin (MF) formulations are commonly used for impregnation and coating of such papers, melamine being an important, but costly raw material used in high quantities. While MF is substituted by cheaper urea formaldehyde resins (UF) in the core impregnation, for paper surface films pure MF is used. Therefore, a further reduction in cost could be achieved if a portion of the melamine in the surface film was replaced by urea. In the present contribution, recent results of technological tests on paper laminates using a novel melamine–urea–formaldehyde resin (MUF) formulation are reported and their performance is compared to traditional surfaces made from MF.     

Mechanical behavior of a cellular composite under quasi-static, static, and cyclic compression loading

The quasi-static, static, and cyclic compressive behavior of a novel epoxy matrix cellular composite reinforced with glass foam granules is investigated. Three different grain-size fractions of the granules are used: 0.5–1, 1–2, and 2–4 mm. The density of the cellular composite varies between 0.65 and 0.82 g/cm3. The material exhibits high specific compressive strength and stiffness within the class of cellular materials; these properties can be varied using appropriate size of granules. The glass foam granules increase the stiffness of the cellular composite compared to neat epoxy foam with the same weight. The measured elastic properties are in good agreement with results obtained from analytical and numerical homogenization methods. The fatigue behavior is determined in static tests and in cyclic tests at 1 and 20 Hz on one type of cellular composite. The fatigue process for cyclic loading is a result of an interaction between static and cyclic damage. The sensitivity to static damage is found to be higher than to cyclic damage. The damage behavior is investigated by evaluation specimen’s stiffness and using scanning electron microscopy.     

A novel, single-mode piezoceramic plate actuator for ultrasonic linear motors

A new type of piezoelectric plate actuator for ultrasonic linear motors has been developed. These new piezoelectric actuators use the principle of asymmetric resonant excitation of the piezoceramic plate in a special resonant mode consisting of a standing two-dimensional extensional wave in a piezoceramic plate. The behavior of the actuator has been simulated with finite-element method (FEM) software and the simulation results checked with single-point contact measurements on the surface of the actuator. This paper describes this work and closes by describing the new ultrasonic translation stages based on this design.