The development of the method for identifying the hardening curves of materials based on the results of torsion tests of notched specimens

The article is devoted to studying the rheological properties of metals and alloys in a cold state. The method is proposed to identify the hardening curve of a material based on torsion tests of round specimens with a notch. Determining the hardening curve is based on measuring the coordinates of points on the surface of the specimen after testing and determining the corresponding value of the torque. Based on these values the coefficients in an equation for the stress-strain dependence can be determined by minimizing the derived functional. The paper proposes the algorithm for the numerical implementation of the new identification method. The results of the computer simulation confirmed its effectiveness.

Enhancing the Geometrical Performance Using Initially Conical Cylinder Liner in Internal Combustion Engines—A Numerical Study

Reducing friction is an important aspect to increase the efficiency of internal combustion engines (ICE). The majority of frictional losses in engines are related to both the piston skirt and piston ring–cylinder liner (PRCL) arrangement. We studied the enhancement of the conformation of the PRCL arrangement based on the assumption that a suitable conical liner in its cold state may deform into a liner with nearly straight parallel walls in the fired state due to the impact of mechanical and thermal stresses. Combining the initially conical shape with a noncircular cross section will bring the liner even closer to the perfect cylindrical shape in the fired state. Hence, a significant friction reduction can be expected. For the investigation, the numerical method was first developed to simulate the liner deformation with advanced finite element methods. This was validated with given experimental data of the deformation for a gasoline engine in its fired state. In the next step, initially conically and/or elliptically shaped liners were investigated for their deformation between the cold and fired state. It was found that, for liners being both conical and elliptical in their cold state, a significant increase of straightness, parallelism, and roundness was reached in the fired state. The combined elliptical-conical liner led to a reduced straightness error by more than 50% compared to the cylindrical liner. The parallelism error was reduced by 60% to 70% and the roundness error was reduced between 70% and 80% at different liner positions. These numerical results show interesting potential for the friction reduction in the piston-liner arrangement within internal combustion engines.

Verification of a New Torsion Test Method to Study the Rheological Properties of Materials in a Cold State

The most important parameter, characterizing the rheological properties of steels and alloys, is the strain resistance. The new method of testing cylindrical specimens for torsion with variable grip’s accelerations is proposed (application No. 2018132149 of 07.09.2018 for the patent of the Russian Federation for the invention). This method is designed to study the rheological properties of steels and alloys mainly in a hot state. However, this method is universal and can be used to determine strain resistance of materials in a cold state. The article is devoted to the applicability evaluation of the proposed torsion testing method, to study the rheological properties of materials in a cold state. It’s done on the basis of comparison of the hardening curves, obtained during the testing of specimens for tensile and torsion. The CrWMn steel was used. The results show that the hardening curves obtained during the torsion and tensile tests are close, and the yield stress values differ by about 3%. It can be assumed that the developed method of torsion testing allows to obtain reliable values of the material’s strain resistance in a cold state.