Volume 56, Issue 4

The prediction of the plastic collapse load of cylindrical pressure vessels is very often made by using expensive Finite Element computations. The calculation of the collapse load requires an elastic-plastic material model and the consideration of non-linear geometry effects. The plastic collapse load causes overall structural instability and cannot be determined directly from a Finite Element analysis. In the present paper the plastic collapse load for a cylindrical pressure vessel is determined by an analytical method based on a linear elastic perfectly plastic material model. When plasticity occurs the material is considered to be incompressible and the tensor of plastic strains to be parallel to the stress deviator tensor. In this case the finite stress-strain relationships of Henkel can be used for calculating the pressure for which plastic flow occurs. The analytical results are completely confirmed by Finite Element predictions.

The effect of the weld joint configuration on components has been studied, which are under service loads, under repair or construction and the residual stresses as well as the mechanical properties of the joint have been determined. For this purpose, a horizontal positioned tensile testing device and a semi-automatic MIG welding machine have been used and then the weld joints of the plates were subjected to different elastic stresses. When the temperature of the joined elements decreased to room temperature, applied elastic stresses were released. By this means, the effects of the existing tensile stresses in the joined parts and the tensile stresses created by the welding processes were investigated. The tensile stresses occurring in the joined elements were determined by using the photo-elasticity analysis method and the hole-drilling method. Also, tensile-shear tests were applied in order to determine the effect of permanent tensile loads on the mechanical properties of the joint. Experimental results showed that the application of corner welded lap joints for components under tensile loading significantly decrease the shear strength and yielding capacities of the joint.

Ductile cast irons have several engineering and manufacturing advantages compared to other cast materials such as steels. These include high damping capacity, wear resistance, to and lower manufacturing cost. The combination of good mechanical properties and casting abilities of ductile cast iron makes its usage successful in structural applications especially in the energy and automotive industries. In this study, the influence of the section thickness on the microstructure and hardness of spheroidal graphite cast iron was investigated with a cascaded model using the full mold casting method. By the high linear correlation coefficient, R 2 > 0.90, it was observed that the section thickness directly affected the microstructure and hardness. An increase in the cross-sectional thickness decreases hardness and number of graphite nodules per square millimeters, however, percentage of ferrite was increased.

In this study, the effect of austempering heat treatment on the cutting forces and surface roughness was investigated during the processing of vermicular graphite cast irons (VGCI) which are widely used in the automotive industry due to their high strength properties. The samples were austenitized at 900 °C for 90 minutes and then austempered at different temperatures (320 °C and 370 °C) for 60 min, 90 min, and 120 min. Machinability tests were carried out under dry conditions at the CNC machining center with the cutting parameters selected in accordance with ISO 3685. As a result of processing of austempered vermicular graphite cast irons with different characteristics the formed cutting forces, surface roughness, cylindricity, and circularity were measured and compared. At the end of the tests, it turned out that the ausferrite morphology (fine or coarse structure) can to be controlled with the austempering heat treatment as well as cutting forces and surface roughness were optimized, respectively. The best surface roughness value was obtained for the austempering parameters of 370 °C and 120 minutes.

AISI316Ti (EN1.4571) austenitic stainless steel plates with a thickness of 7 mm were welded by plasma arc welding (PAW) process. Joints were obtained using 316L type of filler metal as well as without filler metal called as Weld 1 and Weld 2, respectively. Tensile and bend testing of the joints were carried out. Impact toughness tests carried out at temperatures from 20 °C down to −60 °C have shown encouraging results. Chemical analysis of the weld deposits were made by glow discharge optical emission spectrometry (GDOES). Photomacrographs and photomicrographs of the cross-sections were used to determine ferrite content and hardness. Intergranular corrosion tests in accordance with TSEN 3157/ENISO 3651-2 were carried out. No corrosion sign was reported. The effect of the consumable has the most influence on the toughness properties. Promising mechanical, toughness and corrosion results are useful, considering the implementation of an innovative process, thus PAW of 316Ti stainless steel.

In this study, a dense bulk material was produced from pure aluminum powders by the equal channel angular densification (ECAD) and the equal channel angular pressing (ECAP) method. The combination of densification and ECAD/ECAP tests were carried out at temperatures of 50 °C, 100 °C, and 200 °C, a pressing speed of 1 mms −1 , and a pressure in the range of 10–30 metric tons. By using these parameters, for the first time pure aluminum powders were successfully densified into fully bulk materials without additional sintering process. After the ECAD/ECAP tests, the specimens were characterized regarding microstructure, grain size, hardness, and density. The mean grain size was remarkably decreased with an increasing ECAP pass number. With the application of the ECAD/ECAP process, the severe plastic deformation entails that the particles are consolidated into fully dense materials at much lower temperatures and shorter times, as compared to the conventional sintering process. Finally, determining the effective ECAP temperature was very important to control the nano-scaled microstructure, hardness, and density, repectively.

Within this study, AISI 304 austenitic stainless steel material was processed with tangential cylindrical grinding method as a new method. The purpose of this study is to investigate effects of machining parameters on surface roughness by using Taguchi experimental design method. Results were analyzed by analysis of variance (ANOVA) and effects of parameters on surface roughness were determined as percentage rate. Furthermore, the statistical error ratio was revealed. Consequently, it was observed that this new machining method has brought a different approach to grinding methods and surface quality values exhibited a similar quality as the results of the fine grinding.

The effect of inclusion size and residual stresses of spring steel grade 51CrV4 on fatigue lifetime in high cycle was investigated by experimental results obtained by fatigue testing. Since spring with obvious surface defects or inclusions at the surface are failed during pre-stress, the residual stress profile under surface becomes relevant for fatigue crack initiation and failure. Investigation shows that fatigue threshold for high cycle fatigue depends, besides residual stresses, on inclusion size and material hardness. In order to determine allowed size of inclusions in spring steel and the influence of residual stresses, the Murakami's and Chapetti's models and concepts have been used. The stress loading limit regarding inclusion size and applied stress has been determined for loading ratio R = −1 and 0.1 on specimens with and without residual stresses.

In this study, high alloyed steel bars with a diameter of 12.30 mm made up of 1.4871 (X53CrMnNiN219) and 1.4718 (X45CrSi93) steels were used as experimental material for friction welding. Metallographic and X-ray diffraction investigations as well as microprobe sampling were performed on the samples. Mechanical orientation of particles caused by plastic deformation and carbide scattering has been observed. The diffusion behaviour has been investigated for the elements Cr, Ni, Mn, and Si, respectively. The existence of (Cr,Fe) 7 C 3 carbides in the welding region was also observed.

This study investigates the determination of the mechanical performance of polyamid 66 and the influence of moisture and short glass fiber content (15 wt.-% and 30 wt.-%) at six different conditioning times (1, 2, 4, 8, 16, 32 minutes) in 105 °C water vapor. It was determined that as the glass fiber content increases, moisture absorption decreases. While the moisture absorption increases, tensile strength decreases and the percental elongation and toughness increases. It can also be derived that continuation of moisture absorption after 16 minutes is not effective and beneficial. The moisture absorption values observed in this study are equivalent to the amount of moisture that can be absorbed at 50 % relative humidity and 23 °C room temperature in the air for four months.

A novel copolymer was synthesized by modifying starch-g-polylactic acid (MSt-g-PLA). The results indicated that the starch was efficiently esterified by maleic anhydride (MAH) (2 wt.-%) with polyethylene glycol-400 (PEG-400, 1 wt.-%) as dispersant. Then MSt-g-PLA was synthesized by the reaction of modified starch with D,L-lactic acid. The copolymer was amphiphilic and its molecular weight was 4.789 × 10 4 (M n ), molecular weight distribution was 6.921 × 10 4 (M w ), and polydispersity index was 1.445 (PDI), respectively. Subsequently, CTX/MSt-g-PLA microspheres containing the model drug and cefotaxime sodium (CTX) were prepared. The appearance of the microspheres was smooth and regular. 90 % of particle size was under 150.3 μm and mean diameter was 99.3 μm. The degradation rates of microspheres increased with the increase of pH-value of the buffer. With the amphiphilic copolymer MSt-g-PLA as drug carrier, the microspheres had no burst during drug release, and had the similar sustainable release as the PLA carriers.

A transmission line ice thickness real-time simulation and online monitoring system were designed by using the coplanar multi-point capacitance sensor technology. The capacitance sensing type ice thickness sensor is used in the system to detect the metal electrode capacitance change on various positions surrounding the analog transmission line, and verify the ice thickness on analog line. By theoretical analysis and simulation of a plurality of coplanar metal line electrode fields and capacitors, as well as the freezing test of the system in low temperature, the system is validated to have the feasibility of monitoring the ice thickness of transmission lines.