Determination of the plasticity of metals by impact indentation of a spherical indenter

The problems of measuring the plastic characteristics of metals are considered. It is shown that the characteristics of materials used to compare their plasticity are not comparable and depend in the different degrees on the values of strain, strain rate, and modulus of elasticity. At the same time, the value of plasticity is more physically substantiated, which is determined by the ratio of plastic strain to total strain. It is shown that one of the optimal methods for measuring plasticity (plasticity index) is indentation. The possibility of using impact microindentation for this purpose is studied and expressions are proposed that allow calculating the plasticity based on the results of a single indentation of a spherical indenter. The specialties of the calculation of strain for this type of testing are shown. It was found that the values of plasticity obtained from the ratios of the depths of the plastic and elastic penetration of the indenter are equivalent to the values calculated from the energy ratios upon impact. Experimental studies have been carried out on metals with different hardness and type of crystal lattice. For the first time, the effect of strain rate, deformation, and impact energy (initial impact velocity) on the calculated value of plasticity when a sphere is impressed with strain rates of ~ 103 s–1 is shown. It is shown that when the strain corresponding to the onset of full plasticity during indentation is reached, the maximum sensitivity of the measured plasticity parameter for various metals is achieved.

Application of a computational and experimental method of analysis the complexly stressed state of rubber membranes for effective solutions for their production

The competitiveness of rubber membranes determined by their durability, quality, reliability, including the time required to create. During operation, the membranes undergo complex deformations, as a result of which a large number of potential destruction zones of a different nature arise, which can lead to the failure of the product. The standard test methods used in the development of formulations for membranes involve testing the material under uniaxial tension conditions in most cases and do not take into account the actual loading conditions of the product during operation, which significantly increases the development time of new formulations for membranes. The paper presents and applies in practice a computational and experimental method of analysis the complexly stressed state of rubber membranes, including carrying out simple laboratory tests in a heterogeneous complexly stressed state, which is realized during the operation of rubber membranes, and analyzing the stress-strain state by the finite element method. An inhomogeneous complexly stressed state was realized by forcing the rubber membrane with a spherical indenter. The application of a computational-experimental method for analyzing the complexly stressed state of rubber membranes is considered on the example of a rubber corrugated membrane of an automatic valve of a bag filter purge system. An assessment of the physical and mechanical properties of rubbers in a heterogeneous complexly stressed state was carried out, as well as an analysis of the stress-strain state of the membrane when it was loaded with a spherical indenter, which made it possible to identify the most dangerous zones of the section. The complex use of this method made it possible to improve the resource of this corrugated membrane by thirty five percent in comparison with the standard, while reducing the creation time.

Time-Resolved Force Measurements to Determine Positioning Tolerances for Impulse-Based Indentations

High-throughput experimentation methods determine characteristic values, which are correlated with material properties by means of mathematical models. Here, an indentation method based on laser-induced shock waves is presented, which predicts the material properties, such as hardness and tensile strength, by the induced plastic deformation in the substrate material. The shock wave pushes a spherical indenter inside a substrate material. For reproducible indentations, the applied load is of importance. To compare different processes and process parameters, the measured plastic deformation is normalized by the applied load. However, eccentric irradiation leads to altered beam profiles on the surface of spherical indenters and the angle of incidence is changed. Thus, the influence of eccentric irradiation is studied with an adapted time-resolved force measurement setup to determine the required positioning tolerances. The spherical indenter is placed inside a cylindrical pressure cell to increase the laser-induced shock pressure. From the validated time-resolved force measurement method we derive that deviations from the indentation forces are acceptable, when the lateral deviation of the beam center, which depends only on the alignment of the setup, does not exceed ± 0.4 mm. A vertical displacement from the focus position between -3.0 mm and + 2.0 mm still leads to acceptable deviations from the indentation force.

DIAGNOSTICS OF THE PHYSICAL AND MECHANICAL PROPERTIES OF THE METAL BY THE PARAMETERS OF THE ELASTIC-PLASTIC INDENTATION OF A SPHERICAL INDENTER

The paper describes non-destructive methods for determining the physical and mechanical properties of metals based on the regularities of elastic-plastic indentation of a spherical indenter into the test material. Using the proposed methods makes it possible to construct a diagram of true tensile stresses based on the results of a single indentation of a spherical indenter.

OPERATIONAL CONTROL OF THE LIMIT UNIFORM PLASTIC DEFORMATION

The paper presents a non-destructive method for determining the limit uniform narrowing of structural steels by the parameters of the elastic-plastic indentation of a spherical indenter. An acceptable accuracy of the method for engineering assessment of the plastic properties of the material of parts is shown.

NON-DESTRUCTIVE CONTROL METHOD OF RELATIVE NARROWING AFTER RUPTURE

The paper presents the method of non-destructive determination of relative narrowing after rupture, based on the laws of elastoplastic indentation of a spherical indenter proposed by the authors. An acceptable accuracy of the method for engineering assessment of the plastic properties of carbon and alloyed structural steels is shown.