Issue 41

E. Tolmacheva (Lyapunova) et alii, Frattura ed Integrità Strutturale, 41 (2017) 552-561; DOI: 10.3221/IGF-ESIS.41.65 554 S TATIC INDENTATION EXPERIMENT or static indentation of ceramic samples a handmade holder was used to fix the indenter in the testing machine (Fig. 2, photo). In these experiments the indenter moved into the sample with the velocity of 50 and 100 µm/min. Static indentation force curves obtained for different loading velocities are presented at Fig. 2. It was obtained that in static experiments material does on exhibit rate sensitivity. Figure 2 : Static indentation of alumina samples and photo of the experiment configuration. D YNAMIC INDENTATION EXPERIMENT wo schemes of dynamic indentation setup were developed to achieve different amplitudes of impulse loading (Fig. 3). In both experimental schemes a sample tablet of 9 or 14 mm in diameter and 5 mm in thickness was stuck by a thin layer of glue (cyanoacrylate) onto the end surface of the hard aluminum alloy rod of 20 mm in diameter and 3 m in length. The rod with the glued sample strikes against the fixed indenter. The movement of the sample was caused by an elastic compression wave initiated in the loading rod by a collision with a stainless steel ball (7 mm in diameter, weighting 1.5 g) or a small rod of the same aluminum alloy (10 mm diameter, 70 mm length, 15.7 g mass). To produce striker acceleration in the pneumatic gas gun the stainless steel ball or aluminum alloy rod was put into the expanded polystyrene foam pallet, which has the same caliber as the pneumatic gun. Using strikers of different mass and geometry and varying the air pressure in the gas gun we could obtain loading impulses of different duration and amplitudes. For registration of the transverse compression-tension wave we used four strain gauges arranged in series along the rod surface (Fig. 3). The longitudinal displacement of the rod end surface was calculated from the gauge data by a well- established method [13]. Typical values of the sample displacement were ~100 µm and the time scale ~ 80-100 µs. Depending on the values of the applied load, two ways of registration of the load acting on the indenter were used. For loads up to 500 N we used a piezoelectric load sensor 9217А (Kistler) with the charge meter Kistler (Fig. 3,a). Due to a difference in the designs of the load sensor and the indenter, an original stainless steel adapter was made for their coupling (denoted by 2 in Fig. 3,a and by 5 in Fig. 4). From one side the adapter provides the tight insertion and fixture of the indenter and from the other side it has M3×1 thread for fitting the load sensor (Fig. 3,a). The indenter and load sensor coupled via the adapter were fixed in the frame-like stainless steel holder 4 equipped with a limiting hollow screw 3 (Fig. 4), which protects the indenter and restricts the maximum indentation depth achieved during the experiment. Since the load sensor used in the experiment is rated at maximum applied load of 500 N, we have used the second scheme of load registration in order to achieve higher loading amplitudes (Fig. 3,b). In this scheme, indenter 3 was screwed into additional long aluminum alloy rod 1 (Fig. 3,b) and the second line of strain gauges 2 was used to register the transmitted elastic deformation. This signal was used to calculate the value of load applied to the indenter by the sample. Such experimental scheme allowed us to obtain loading amplitudes up to 2000 N. F T