Materialwissenschaft und Werkstofftechnik最新文献

This work is carried out to investigate the anisotropic hardening behavior of MS1180 steel through experiment and analytical modeling. Dogbone and hydraulic bulging specimens were machined to test the mechanical behavior of MS1180 steel plate under different loading directions and stress states. The loading process was recorded by the three-dimensional digital image correction system. The result uncovers that the strength under equi-biaxial tension is larger than that under uniaxial tension. Mechanical behavior under different loading directions presents the obvious difference related to the plastic strain. Hardening behavior under uniaxial tension and equi-biaxial tension is characterized by the Swift-Voce and polynomial equations, respectively. Three yield functions are adopted to describe the anisotropic behavior, including Yld2000-2d, S-Y2009, and CQN-Chen. A convexity analysis method based on geometric definition is used to determine the convex region of the CQN-Chen yield surface under large strain. By comparing the yield surfaces of the three yield functions under different plastic strain, the CQN-Chen yield function possesses a more flexible and reasonable characterization ability than the Yld2000-2d and S-Y2009 yield functions. The anisotropic hardening behavior of MS1180 steel plate is modeled with an error of less than 0.03 by the CQN-Chen yield function, showing high prediction accuracy.

The biomass composites were prepared by hot molding with a pressure of 10 MPa, a temperature of 125 °C, a time of 15 minutes using soybean straw powder, poplar wood fibers, and soy protein as raw materials. The effects of different straw species, the ratio of soybean straw powder to poplar wood fibers, the particle size of soybean straw powder, and the theoretical density on the performance of biomass composites were investigated. The experimental results show that under the condition that the ratio of soybean straw powder and poplar wood fibers is 1 : 1, 20 mesh to 40 mesh soybean straw powder and 20 mesh to 60 mesh wood fibers are selected to copolymerize and strengthen the soy protein biomass composites when the theoretical density is 0.80 g/cm³, the actual density of the biomass composites is 0.90 g/cm³, the tensile strength was up to 22.04 MPa, and the bending strength was up to 44.92 MPa. Biomass composites have good water resistance while obtaining excellent mechanical properties. The above figures not only meet the relevant technical requirements of automotive interior parts but also enable the lightweight design of automobiles and the sustainable development concept of green, low carbon, and environmental protection.

Due to its high energy intensity and the associated high welding depth, electron beam welding is particularly suitable for welding steel plates with high wall thicknesses. These are used, for example, in offshore wind power systems. However, due to the cooling conditions, the required cold toughness for offshore applications is often not achieved. The aim is to develop S355 ML steels – within the EN10025 4 standard – for welding monopiles for wind turbines. For this purpose, three parameters with different energy input are developed on three steels. The tests are carried out on plates with a wall thickness of 80 mm, whereby a full penetration weld must be achieved. The resulting top and bottom bead of the welds meet the standard DIN EN ISO 13919-1. The parameters have an energy per unit length of 9.5 kJ mm⁻¹ to 15.5 kJ mm⁻¹. The resulting weld seams have an average width of 5.5 mm to 7.5 mm, and burn-off of the manganese alloy element is observed, particularly on the top side of the seam. In addition, T8/5 times close to the weld seam of 11 s to 27 s are estimated using a simulation.

In the current experimental work, using secondary phase hard nano titanium carbide (TiC) particles as reinforcement, two different magnesium metal matrices i. e., AZ31B/TiC and AZ61 A/TiC composite materials were synthesized by friction stir processing. Using the traditional testing approach for the developed materials, the simultaneous gain in metallurgical, mechanical, electrical, and tribological characteristics compared to the base substrate was examined. The microstructure study results for AZ31B/TiC and AZ61 A/TiC composites showed a uniform distribution of reinforced particles as well as an evolution in grain size, from 82 μm to 4.2 μm and from 74 μm to 3.7 μm, respectively, which consequently contribute in a significant gain in the microhardness of both composites i. e., around 2.2 times and 2.67 times respectively, greater than the base metal. When compared to monolithic alloys, the synthesized AZ31B/TiC and AZ61 A/TiC composites showed improvements in the areas of tensile strength, compressive strength, and coefficient of friction up to 1.81 times, and 1.64 times, 1.74 times and 1.58 times, and 57.92 % and 58.47 %, respectively. Furthermore, these improvements in characteristics also increase the final strengthening of the nanocomposite and reduce electrical conductivity.

In the present study, electrostatic powder coating waste was recycled and employed to reinforce high-density polyethylene. The hydrolysis method was preferred to modify the powder coating waste of various systems, and they were mixed with high-density polyethylene at various weight ratios. The mixtures were prepared in a mechanical mixer and then in an extruder to obtain a homogeneous mixture. This homogeneous structure was pressed into molds with a plastic injection device to obtain standard tensile samples. Mechanical and thermal tests were conducted on the samples. It was determined that the tensile stress of the sample decreased with the increase in filler content. The changes in sample tensile strength were investigated after the samples were aged. Three-point bending strength of the samples was also investigated and it was observed that they became more resistant to vertical loads as the filler content increased. The Izod impact strength of the samples differed based on the filler type and weight ratio. Furthermore, mass loss in the produced mixtures was determined with thermogravimetric analysis. The matrix and filler bonding mechanisms were observed under an electron microscope.

In the present work, the hydrogen diffusion during cyclic stress testing in the ferritic chromium steel 1.4521 (X2CrMoTi18-2) is investigated. Therefore, electrochemical hydrogen permeation measurements are carried out on a hollow cylinder geometry. Simultaneously an alternating stress is applied using a stress ratio of R=-1. At low stress amplitudes, no influence on the diffusion behaviour of hydrogen is found. At a higher stress amplitude, close to the macroscopic yield strength, a delayed hydrogen permeation by a factor of two is observed. It is postulated that this observation is a result of the nucleation of new hydrogen traps during the measurement. Hydrogen content measurements using carrier gas hot extraction support this hypothesis.

Wheelset shafts are usually coated to protect them from mechanical and corrosive influences. However, damage during operation requires close inspection intervals to check permissible damage depths. The focus of this research is to investigate a possible increase in corrosion fatigue strength through inductive surface layer treatment for the wheelset shaft material EA4T (25CrMo4+quenched and tempered). For this purpose, process parameters for inductive surface hardening were identified and optimized in order to achieve a sufficiently high hardening depth and hardness of the surface layer on lightly notched test specimens. Subsequently, fatigue strength tests were carried out in air and in 5 % NaCl solution for the initial state and the hardened state. By comparing the fatigue strength results determined, the expected potential for increasing fatigue strength and corrosion fatigue strength was confirmed. In order to demonstrate stone chipping and corrosion stress, further tests were repeated with damage specifically introduced into the surface layer. The findings indicate the potential of surface layer hardening for significantly lower-maintenance wheelset shafts in freight transport in the future.