Mikromechanische Eigenschaften von Weizenkörnern

The investigation of deformation and breakage behavior of wheat grains by compression test was carried out. The force‐displacement curve was obtained at stressing rate 0.02 mm s^–1. The elliptical wheat grains show quasi‐elastic and elastic‐plastic deformation behavior depending on applied force. The simple transformation procedure was applied to adapt the contact model for spherical particles to elliptic wheat grains. The breakage force, energy, strength and displacement distributions were fitted with normal distribution function.     

Improvement of mechanical properties of AA1070 aluminium by the addition of borax under different holding conditions

In this study, mechanical properties of Al‐B alloys, prepared by the addition of different amounts of borax to 99.70% pure commercial aluminum, were improved. The main objective is to study the influence of borax addition and holding conditions on the mechanical properties of cast Al‐B alloys. In this process, amount of borax, holding temperature and holding time were realized as affecting parameters. By considering these parameters three specimens were prepared for each condition and they were subjected to mechanical tests such as tensile, impact and hardness tests. As a result of tests, tensile strength of the alloy with the incorporation of borax was found 33% increase in comparison to pure aluminum while 21% increase in impact energy and 54% in hardness value. A substantial quantity of aluminum‐boride flakes were observed in the microstructural investigation of the samples. Microscopic observations of alloyed samples reveal homogeneous distribution of aluminum boride particles and fewer porosity levels.     

Mühlen als Mechanoreaktoren

Mills as Mechano‐Reactors In addition to size reduction, other phenomena observed in mills and which have been exhaustively examined by scientific methods are attracting increasing technological attention. These include changes of materials and reactions going beyond dispersion and which are known by their terms mechanical activation, mechanochemistry, mechanical alloying, mechanofusion, etc. The present article assesses the suitability of certain types of mills for use as mechanoreactors. The significance of the nature, speed, and energy of the forces acting and of the derived quantities power and energy input is discussed. A methodological basis is given for upscaling from laboratory and pilot studies to industrial production and commercialisation. Recent results concerning mechanical activation, mechanical alloying, and mechanochemistry of various material systems are presented.     

The modified temperature term on Johnson Cook model for AZ31 magnesium alloy

The quasi‐state and dynamic mechanism of AZ31 magnesium alloy at a strain rates range of 0.001 s^‐1–2500 s^‐1 under a temperature range of 20 °C–250 °C were researched by compression tests using the electronic universal testing machine and split Hopkinson pressure bar system. The true stress‐strain curves at different strain rates and evaluated temperatures were obtained. The result shows that the thermal soften effect of AZ31 magnesium alloy is significant. By modifying the temperature term of the original Johnson Cook model of AZ31 magnesium alloy, a modified Johnson Cook model of AZ31 magnesium alloy has been proposed to reveal thermal soften effect on the deformation behavior of AZ31 magnesium alloy more precisely. With the modified Johnson Cook model and fracture model, the finite element method simulation of AZ31 magnesium alloy hat shaped specimen under impacting was conducted. The numerical simulation result is consistent with the experimental result, which indicates that the modified Johnson Cook model and fracture model are greatly valid to predict the deformation and fracture behavior of the AZ31 magnesium alloy hat shaped specimen under impacting.     

Impact experiments and finite element simulation of surface roughness reduction by machine hammer peening

Machine hammer peening (MHP) is a mechanical surface treatment that employs a tungsten carbide tool to hammer the surface of a work piece. It was the goal of this study to find relations between the process parameters and the surface smoothing effect of MHP by finite element simulations. Impact experiments have been conducted in order to find suitable load‐deformation‐relations for a selection of work piece materials and to validate the model. A finite element model has been established with good agreement to the experimental results. Simulations have been conducted to investigate the influence of main process parameters on the surface roughness reduction. Additional simulations were performed and a way of creating uniform smooth surfaces with respect to small duration of surface treatment is presented.     

Improvement of Mechanical Properties of Self Setting Calcium Phosphate Bone Cements Mixed With Different Metal Oxides

Calcium phosphate cements (CPC), based on multicomponent powder mixtures of calcium orthophosphates with medium particle sizes in the region of 1 ‐ 20 μm, set isothermally in an aqueous environment to form hydroxyapatite (HA). HA cement reactants include tetracalcium phosphate (TTCP), tricalcium phosphate (TCP), dicalcium phosphate anhydrate (DCPA), dicalcium phosphate dihydrate (DCPD), monocalcium phosphate (MCPA) or octacalcium phosphate (OCP). The aim of this study was to improve the mechanical performance of TTCP / DCPA cement by adding several metal oxides to tetracalcium phosphate during the fabrication process. Cements based on tetracalcium phosphate mixed with silica or titanium oxide showed significant increases in compressive strength, approximately 80 ‐ 100 MPa, whilst no change in the mechanical behavior of CPC was observed if zirconia was added. X‐ray diffraction measurement confirmed the setting reaction of doped cements was similar to that of pure CPC. Low crystalline HA was found to be the main constituant of set cement; additional phases, such as calcium titanate or calcium zirconate, were not involved in the reaction. A mechanical reinforcement effect was thought to result from changes in the thermodynamic or kinetic solubilities of doped tetracalcium phosphates, this would lead to slower HA crystal formation and a more cross‐linked cement structure.     

Mikrostrukturelle Pressschweißnahtcharakterisierung im strangpressten Zustand für Al‐Mg‐Si‐Legierungen

Weld seams form when profiles are extruded using porthole or bridge dies. These are inevitable when producing industrial relevant hollow profiles but imply the weak spot if the profiles are used for applications with high mechanical requirements. The characterization of formed weld seams together with their mechanical properties is problematic or sometimes even impossible due to the complex profile geometries. Expansion, bending or tensile tests of profiles or parts of the same were hitherto often used for their analysis lacking the possibility of basic assumptions about their properties. The investigations described herein circumvent the problem by using a flat profile exhibiting the weld seam in the middle. Flat profiles offer the possibility of standardised specimens for tensile testing. The extrusion experiments focused on the aluminium alloys EN‐AW 6060 and EN‐AW 6082. During the experiments billet temperature and extrusion speed have been varied. The microstructure was analysed subsequent to explain the obtained results and to offer a possibility of characterisation.