Fatigue life determination of plasma nitrided medical grade CoCrMo alloy

In this paper, the fatigue behaviour of plasma nitrided medical grade forged CoCrMo alloy was studied. Since metallic biomaterials are used for implant applications where high and/or cyclic stresses along with corrosive effects of human body are of concern, enhancing mechanical and surface properties of implant alloys is crucial. Plasma nitriding was implemented at three different temperatures as 600, 700 and 800 °C for time intervals of 1 and 4 h. S–N curves of untreated and nitrided specimens were obtained via axial tension compression fatigue tests. It was found that plasma nitriding treatment reduces the fatigue resistance of forged CoCrMo alloy by the ratios of 7–23% depending on the surface roughness, phase structure and hardness of the modified layer which are determined by the treatment parameters.     

Monotonic and low cycle fatigue behaviour of 2024‐T3 aluminium alloy between room temperature and 300 °C for designing VAWT components

In the present study, the results of the monotonic tension tests and low cycle fatigue tests performed on aluminium alloy EN AW‐2024‐T3 under various operating temperatures are presented in order to assess the fatigue behaviour of the aluminium alloy under evaluated temperatures. Monotonic tests were performed to determine the influence of temperature on mechanical properties of the material. The aim of cyclic tests was to acquire the parameters required for Manson–Coffin equation in order to plot strain–fatigue life curves. Moreover, stress–strain behaviour of the alloy and the cyclic hardening behaviour were evaluated using Ramberg–Osgood equation. Finally, P_SWT‐damage parameters for each temperature have been calculated for further investigation of the effects of the temperature on fatigue life using acquired data while taking the account of mean stress effect into calculations. Variations in the experimental data due to various test temperatures are presented for both monotonic and cyclic tests.     

Effect of FeB additions on sintering characteristics of injection moulded 17-4PH stainless steel powder

High density sintering of precipitation hardening stainless steel such as 17-4 PH involves a combination of relatively high temperature (>1350°C) and extended sintering time. In this study, the effect of addition of FeB on sintering characteristics of 17-4 PH stainless steel was investigated. Addition of boron is promoted to get highly dense sintered steels. The amount of boron plays a role in determining the sintered microstructure and properties. With the increased amount of FeB sintered density and tensile strength increase while sintering time and temperature decrease.     

Large-angle in-plane light scattering from rough surfaces

An in-plane light scattering setup that is capable of measuring large azimuthal scattering angles is presented. This type of measurement makes it easier to probe large k(parallel) at a fixed k(perpendicular) value (k(parallel) and k(perpendicular) are momentum transfer vectors parallel and perpendicular to the surface, respectively). Therefore the system allows us to explore small lateral scale and large vertical roughness (approximately lambda, the wavelength of the probe beam) of a rough surface. In-plane intensity measurements from a rough backside Si wafer and a Cu thin-film surface are reported. The structure factor that is related to surface roughness parameters is obtained from the measured in-plane intensity profiles. Both scalar (Beckmann-Kirchhoff) and vector (Rayleigh-Rice) theories have been applied to interpret the experimental data. The roughness parameters obtained from the scattering measurements are compared with those measured by atomic-force microscopy.     

The kinetics of diffusion of hydrogen in niobium

The kinetics of hydrogen diffusion in niobium were studied in the temperature ranges of 200° to 300°C and 600° to 700°C by gas-metal absorption experiments. The hardness profile was correlated with the concentration of hydrogen on specimens of various grain sizes. It was found that the diffusion kinetics of both temperature ranges could be represented by a single Arrhenius-type rate equation. The activation energy and the preexponential factor were found to be 10.000±320 cal per mole, and 1.8±1.0×10⁻² cq cm per sec., respectively. No observable effect of grain size was found on the diffusivity.     

An analysis of the Brazilian disk fracture test using the Weibull probabilistic treatment of brittle strength

It is pointed out that the Weibull multiaxial treatment of brittle strength contains limitations which are not present in the more familiar uniaxial formulation. Provided these limitations are satisfied, it is possible to use tension or bending data to predict multiaxial behavior when at least one principal stress is tensile. This is illustrated for the Brazilian disk test (diametral compression of a disk). Predictions based on bending tests agree well with observed strength values in disk tests on two types of rocks.     

A general finite element model for shells of arbitrary geometry

A finite element formulation is developed for the large displacement analysis of arbitrary shells. Formulation is based on a convected coordinate system and a tensorial approach is followed. The strain-displacement relationships used do not reflect the Kirchhoff hypothesis and Love's approximations. Isoparametric interpolation is used for the discretization of the problem, and the number of nodal points is variable. The numerical examples include the buckling analysis of cylindrical shells as well as two problems to test the convergence and accuracy of the algorithm.     

Hydrogen storage properties of magnesium nanotrees investigated by a quartz crystal microbalance system

We report enhanced low temperature hydrogen storage properties of magnesium “nanotrees” fabricated by glancing angle deposition (GLAD) method. The arrays of nanotrees and conventional thin films of elemental Mg have been deposited directly onto gold coated unpolished quartz crystal substrates. Mg nanotrees were about 15 μm in height, 10 μm by 1 μm in lateral size, and were composed of “nanoleaves” of about 20 nm in thickness, 2 μm length, and 1 μm width. Hydrogen absorption and desorption properties of Mg nanotrees and thin films were investigated using a quartz crystal microbalance (QCM) testing system that is capable of measuring weight changes with a nanogram sensitivity. QCM absorption tests were performed at temperatures 100, 200, and 300 °C under 30 bars of H₂ pressure. Measurements revealed that Mg nanotrees can absorb hydrogen at significantly higher weight percentage (wt%) and faster rates compared to conventional Mg films under similar conditions. Hydrogen storage of Mg thin film was observed to be at 0.02, 0.30 and 3.91 wt% (weight percentage), while it reached to 1.26, 3.75, and 5.86 wt% for nanotrees at temperatures 100, 200, and 300 °C, respectively, after 150 min. In addition, the results of desorption experiments show that Mg nanotrees can start to release hydrogen at temperatures as low as 100 °C at a rate of 0.11 wt% (vs. 0.01 wt% for thin film at the same temperature) with desorption rates reaching to 1.05 wt% at 200 °C (0.26 wt% for thin film) and 2.57 wt% at 300 °C (1.45 wt% for thin film), which are considerably lower desorption temperatures compared to previously reported values for bulk Mg (>300 °C). The enhancement in hydrogen absorption and desorption properties of Mg nanotrees is believed to originate from their thin and isolated nanoleaves that also have an improved oxidation resistance property.     

Domestic Arrangements: The Maid's Room in the Ataköy Apartment Blocks,Istanbul, Turkey

The first phase of Istanbul's Ataköy Housing Development, an icon of architectural modernism in Turkey, inflects modernist architectural forms with local domestic traditions. This study examines the maid's room, a sphere of the Turkish modern interior where post-war ideas and ideals both reconciled and contradicted the customary and the modern. The case study extends recent attempts to re-think postwar architectural culture and its global effects.     

Stress-Strain State of Soils Under Thin Shell Structures with Infill

Soil Mechanics and Foundation Engineering - The article presents the investigations of the stress-strain conditions at the foundation of structures made of thin shells with infill. A finite element...