Setup for Testing Materials with Plotting Complete Stress–Strain Diagrams

A setup for testing materials and processing the results obtained with construction of complete stress–strain diagrams is described. The setup has been created with allowance for the authors' previous experience and new ideas in testing materials of various classes under conditions of equilibrium deformation, as well as computer-based state-of-the-art technologies. The efficiency of the use of the setup developed is illustrated by the example of testing a maraging steel under equilibrium deformation involving construction of complete diagrams.     

Fracture Mechanism in Plastic Sheet Materials

The method of complete stress–strain diagrams has been proved efficient for the assessment of a sheet material's resistance to macrocrack propagation in thin-wall structural elements and for the prediction of stresses that correspond to the growth onset of macrocracks of various lengths in wide plates by the results of testing small specimens.     

Deformation-Strength Relationships in Short-Term Tension of Heat-Resistant Materials

The analysis of 124 curves obtained in short-term tensile tests demonstrate that they can be described by varying strain hardening and softening characteristics. Different stress–strain curves can be produced at invariable yield strength and ultimate strength and interrelated proportional variations of the above characteristics. To determine some specific stress–strain curve, it is necessary to take account of yield strength and ultimate strength as well as strain corresponding to the latter. The relations between yield strength, ultimate strength and hardening and their practically complete absence between these parameters and softening were statistically established.     

Procedure and Setup for the Investigation of Composite Materials in Torsion at Temperatures up to 3300 K

A procedure and a setup are proposed for the investigation of strength properties of composite materials under torsion at temperatures of up to 3300 K in vacuum and in an oxidizing or inert medium. The setup is fitted with a system for the program heating of specimens to realize conditions that are close to the working conditions of the material. This makes it possible to carry out tests at a heating rate of about 500 deg/s with a uniform temperature field maintained along the specimen length.     

Specific Features of the Behavior of Ceramics Based on ZrO2 with an Admixture of 9 Mole% CeO2 in the Process of Deformation

For zirconia ceramics stabilized with 9 mol.% CeO ₂, we study specific features of the processes of deformation and formation of the zones of transformation of the tetragonal phase into the monoclinic phase under the action of mechanical stresses. It is shown that, at room temperature, this transition occurs explosively (autocatalytically) and is accompanied by the formation of large zones of the -phase in the form of strips on the surface of tension of the specimen and the appearance of a nonlinear sawtooth section in the stress–strain diagram. As the testing temperature increases, the degree of autocatalyticity decreases together with the degree of nonlinearity and the diagrams lose their sawtooth character. At the same time, the strength of the material becomes almost four times higher at ~ 200°C and then decreases to the initial level at 400°C. It is assumed that this Type of mechanical behavior can be explained by changes in the mechanisms of hardening of ceramics.     

Analysis of the Results of Mechanical Testing of Metals by Constructing the Diagrams of Structural States

For polycrystalline metals and alloys with bcc (Mo, Fe, and Fe–Si) and fcc (Ni and Cu) crystal lattices, it is shown that the application of the method of reconstruction of parabolic stress–strain diagrams on S –eⁿcoordinates, where S and e are the actual stress and strain, respectively, and n is the strain-hardening index, makes it possible to represent the results of mechanical testing in the form of a diagram of structural states plotted in the form of the dependences of actual stresses and strains on temperature. This diagram practically completely describes the changes in the strength and plastic characteristics of the materials and their structural states in the process of plastic deformation. We study specific features of the construction of these diagrams depending on the composition of the alloy, its structural state, the energy of stacking faults, etc. On the basis of the analysis of the character of correlations between the critical values of strains and stresses and the mechanisms of plastic deformation within broad ranges of temperature and structural states, we discuss the possibilities of scientific and practical application of the diagrams of actual stresses and strains vs temperature.