Enhanced assessment of technological factors for Ti-6Al-4V and Al-Cu-Mg strength properties

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Mechanical properties of D16 – ultimate tensile strength σ u = 423 MPa ( △ ), – yield point σ 0.2 = 320 MPa ( ▲ ), – modulus of elasticity E = 73.400 MPa. The surface of the working part of the sample, intended for measuring the temperature with a thermal imager, was covered with a thin layer of amorphous carbon, which allows the emissivity to be brought closer to unity. Experimental studies carried out with simultaneous measurement of two components of the strain tensor and the radiation temperature of the surface make it possible to provide completeness of data in solving problems of identifying material properties and in studying the processes of accumulation of irreversible deformations and energy dissipation by a sample. Equipment To load samples of VT6 and D16 , an Instron 8801 universal test system (England) was used. During testing, soft loading was implemented. To measure the increment of the total strain tensor components in situ, standard extensometers were used: “Dynamic Extensometer” No. 2620-601, “Transverse / Diametral Extensometer” No. W-E-404-F. The temperature was measured using an ImageIR “ InfraTec ” 8355 thermal imager with a temperature resolution of 0.02 K (Germany). Method for determining the critical stress-strain state of a material under cyclic loading In this work, it was required to determine the critical stress amplitude during cyclic loading of a material sample by changing the deformed state and dissipative heating. For this purpose, a technique was used in which critical stresses can be determined using a diagram of the accumulation of irreversible deformations or by the temperature of dissipative heating of the material [26, 27, 32]. During the tests, the sample, which was in thermodynamic equilibrium, was subjected to soft loading with a certain constant average component of the stress cycle and a monotonically increasing stress amplitude, for example, increasing in proportion to time. Loading with a constant average component of the cycle made it possible to exclude the in fl uence of the average stress and obtain the amplitude dependences of the characteristics of the deformed state and temperature on the stress amplitude. A scheme of a typical loading program is shown in Fig. 3. It was a loading block consisting of 4 steps in which the following was performed: – quasi-static deformation (“Step 1”), – holding at this voltage for 180 sec (“Step 2”), – soft loading with a step-like increase in the voltage amplitude (“Step 3”), – unloading (“Step 4”). Fig. 3. A single loading block. “Step 1”: quasi-static loading; “Step 2”: holding under constant stress; “Step 3”: harmonic cyclic loading with linearly increasing stress amplitude; “Step 4”: unloading