Experimental Determination of Mechanical Properties of Waste Steel Sheets

The paper is primarily focused on the determination of the ultimate strength of pressed materials in the form of steel sheets. The breaking strength of homogeneous materials such as e.g. steel sheet is not a relevant indication for pressed steel sheet waste material. The ultimate strength serves as a main parameter in the design of sheet metal cutting machines. For the design and technological design of machines and equipment for shearing steel waste in the form of pressed sheets, it is necessary to know the limit strength of the material. The paper describes in detail the experimental procedure and the principle of determining the ultimate strength of the steel waste sheet. Several dozen experimental samples of pressed metal waste were used. The very principle of the experiment consisted of sheared samples, while monitoring the shear force and the thickness of the pressed material. The ultimate strength of the shear material was calculated from the measured data. The measured and calculated data were statistically processed to increase the objectivity of the determination of the already mentioned ultimate strength parameter of the pressed waste sheets.

Comparison of different titanium alloys welded by Yb:YAG fibre laser for thin sheet applications used for T-ducts in bleed air systems

Research in aerospace applications includes the replacement of well-known materials by newly developed alloys or by new manufacturing methods for the existing materials. In the frame of TiB-Air project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) the development of a process chain consisting of deep drawing at elevated temperatures, chemical milling, contour machining by laser cutting and laser beam welding to produce pneumatic T-ducts used in bleed air systems is in focus. This production process of sheet metal parts could lower costs in terms of the process itself and the used materials: low alloyed Ti-alloys. Commercially pure titanium alloy (cp-Ti) is commonly used for these structures because of its balanced mechanical properties regarding tensile strength, yield strength, plastic strain and fatigue strength as well as good resistance against corrosion and oxidation. The possibility to substitute cp-Ti by low-alloyed Ti-alloys is examined in this work, by the comparison of two different low alloyed Ti-alloys, namely KS1.2ASN and Ti XT, with a cp-Ti alloy (Grade 4). Mechanical properties of the base materials, their weldability and the mechanical assessment of the laser beam welded butt joints in terms of static, cyclic and fracture mechanical behaviour is compared for sheet materials, with a thickness of 0.9 mm. Defect-free welding according to EN13919 acceptance criteria B was possible for all three alloys, no porosity problems occurred. The low strength alloy KS1.2ASN exhibited mechanical anisotropy between longitudinal direction and transverse direction in the tensile test, welded specimens of this alloy broke in the base material. Due to the tensile properties, both weld and base material of KS1.2ASN showed the least values for the fatigue strength and endurance limit strength. Ti XT and Grade 4 showed similar mechanical anisotropy and fractured in the base material, too. Fatigue strength of Ti XT is below Grade 4, but for the 50%-percentile the endurance limit strength is equal. Fracture mechanical testing showed that KS1.2ASN is a very promising alloy in the welded condition.

Effect of Stress Ratio(R) and Stress Concentration Factor (Kt) on Fatigue Properties of WSTi6211 Titanium Alloy

In this paper, the author studied the effects of different stress ratios（R） and stress concentration factors(Kt) on the fatigue properties of WSTi6211 titanium alloy.Through S-N curve, the author obtained the fatigue ultimate strength of the material under different conditions and analyzed characteristics of fatigue fractures, including the crack source sourse, the crack growth region and the final rupture region. The results show that when Kt=1, R=0.5, the fatigue ultimate strength σD is 626MPa; when Kt = 1, R=0.06, the fatigue ultimate strength σD is 527.5MPa; when Kt=3, R=0.06, the ultimate fatigue strength σD is 267MPa. Fatigue performance is very sensitive to R and Kt. The larger R is, the larger the fatigue ultimate strength is. The larger Kt is, the smaller the fatigue limit strength is. The fracture morphology shows typical fatigue fracture morphology. Most of the cracks originate on the surface of specimens and have typical fatigue bands. With the decrease of stress, the area of crack growth zone increases.

INVESTIGATION OF PHYSICAL-MECHANICAL PROPERTIES AND IMPACT ON SOIL OF GRANULATED MANURE COM-POST FERTILIZERS

In recent years, the European countries recycle only 5−7% of bio-waste. One activity of the biological waste disposal is granulation. The production of fertilizer from animal manure with supplement represents an important area of environmentally friendly bio-fertilizer production. This paper presents an investigation of estimation manure compost physical-mechanical properties for reuse of organic waste − cattle and cow manure, sugar production waste − molasses through new technology pellets production and of granulated fertilizer impact on soil. The experimental manure samples produced by industrial methods and samples produced in the laboratory from the time period of 2014 to 2017 were investigated. The following physical – mechanical characteristics were estimated: biometric indicators (dimensions, mass), volume and density of raw material and pellets, material and pellet’s humidity and pellets strength. Experiments results have shown that the difference in limit strength between experimental and industrial organic compost pellets was about 5%. Experiments of fertilizers on the impact on soil shown that the amount of nutrients added to the soil depends on the rate of the granulated compost fertilizer. As the norm increases, organic carbon, humus, mobile phosphorus and potassium increase in soil. Increases in soil fertility, improved agrochemical properties, soil organic matter accumulation and humus increase. Granulated compost fertilizers have no effect on soil acidity. The presented results could be helpful to the development of the fertilizing process by the granulated compost fertilizer for improvement of soil quality in small farms.

Particular Fatigue Resistance of Stabilized Stainless Steel: Endurance Limit, Strength and Ductility of Fatigued Steel

Comprehensive experimental research on fatigue performance of niobium stabilized (type 347) X6CrNiNb1810mod steel has revealed particular features of cyclic performance. This paper reports and discusses on the endurance limit behavior studied by strain controlled HCF tests at room and elevated temperatures. In contrast to carbon steels, stainless steels can tolerate notable amounts of plastic strain and display broad hysteresis loops at and below endurance limit. Together with pronounced secondary hardening, this results to abrupt endurance limit behavior. The modified Miner rule with S-N–curves extrapolated to low amplitudes is generally applicable for carbon steels, but not for stainless. Effectiveness of the endurance limit even with variable amplitude straining was shown for 347 type steel. Extrapolation of ε-N curves beyond a few million cycles is conservative. An increase of temperature decreases, but does not vanish the endurance limit. Another peculiar feature of the studied stainless steel is its superior ductility, which is not affected by partial fatigue ‘damage’. Five LCF tests at 325°C and 0.22 ≤ εa ≤ 0.5% were interrupted beyond the half-life condition (N/N25 ≥ 0.5) at 0.5 ≤ CUF ≤ 0.9. Cyclic straining was directly followed by monotonic pulling to fracture. Surprisingly low correlation between tensile properties and fatigue usage was observed. The ultimate tensile strength was preserved within 10 MPa (2.5%) in all cases. Yield strength and elongation remained practically unchanged by pre-fatigue. This paper provides new experimental results. They are discussed together with earlier observations on the same steel extracted from a pipe, which has been manufactured for use in primary loop of a German NPP.

Compression strength perpendicular to grain of Serbian spruce (Picea omorika (Pancic) purkyně) wood from plantations and natural stands

This paper presents the results of testing the compression of Serbian spruce wood from plantations and natural stands. Compression perpendicular to grain in radial and tangential direction was tested. A dilatation of 1% was taken for a conditional boundary dilatation, and the appropriate strength for the conditional limit strength was taken. Six trees from plantations and nine trees from natural stands were analyzed. In total, 309 samples were tested. The regression analysis examined the dependence of these mechanical properties on the width of the annual rings, the percentage of late wood and wood density.