OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 Indentation elastic modulus Macro-indentation Measurement of the elastic modulus during macro-indentation of a Ti alloy plate fabricated by 3D printing was carried out by the instrumental indentation system AIS3000 HD (FRONTICS, Korea) [32, 33, 36] presented in fig. 3, а, b. The procedure is schematically illustrated in fig. 3, c, d. b а c d 2 1 5 mm R = 0.25 m m Fig. 3. General view of the AIS3000 HD (a); indentation assembly (b): 1 – Vickers indenter (Dia. 0.5/1.0 mm), 2 – specimen; schematic indentation (c): 1 – rounded tip, 2 – specimen; points of indentation (d) The AIS3000 HD operating principle is based on the penetration of an indenter into the inspected object under a gradual loading and subsequent periodic partial unloading followed by complete unloading after reaching the maximum penetration depth. Firmware controls the system operation and displays control parameters such as load, depth, loading rate. External software is installed on a PC to control the system operation and display, store, communicate, and statistically process results of measurement. External software detects such properties as elastic modulus, hardness, residual stress, tensile strength, and crack resistance (fracture toughness) based on the load-penetration curve. The indentation load is measured by a strain gauge, and the indentation depth is determined by a displacement sensor. The system operation is based on instrumented indentation, i.e., indentation of the tip (indenter) into the inspected material according to both GOST R 8.748-2011 [17] and ASTM E2546-15 [15]. The instrumental indentation technique helps to determine the dependence between the penetration force and depth at its gradual variation. The AIS3000 HD provides fast and easy inspection not only of parts, but also various products. A WC spherical indenter with a radius of 250 mm was used for indentation at a load of 600 N. Each test included 15 “loading →partial loading → intermittent unloading” cycles at a loading rate of 0.3 mm/ min. Load-penetration curves were continuously obtained during indentation and then converted into “true stress-true strain” curves. All indentation tests were performed at room temperature. The elastic modulus is determined by the contact stiffness S (the slope of the tangent to the unloading curve when the force F is removed, shown in fig. 4). The straight section of the unloading curve describes the elastic recovery of the material. The unloading curve can be expressed as: ( )m f F k h h = − , (3) where m and k are correlation constants.
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