Issue 41

E. Tolmacheva (Lyapunova) et alii, Frattura ed Integrità Strutturale, 41 (2017) 552-561; DOI: 10.3221/IGF-ESIS.41.65 557 R ESULTS Dynamic indentation loading curves. ynamic indentation loading curves obtained with two experimental schemes for different values of maximum load are shown in Fig. 6. For comparison, the figure also presents the initial segment of one of the static indentation curves (Fig. 2) corresponding to the loading velocity of 100 µm/min. Since in this paper we restrict our discussion only to large values of loading impulses, we show here only one curve for the first experimental scheme corresponding to a low magnitude of load (numbered as 1). Figure 6 : Dynamic indentation curves (1-4) and initial interval of static indentation curve (5). X-ray computer tomography of deformed samples. Four ceramic samples subjected to dynamic indentation with different maximum values of applied load were studied by X-ray computer tomography (CT). For each sample a stack of raw CT images (about 720-760 pictures) was analyzed using the ImageJ free software package [11, 12]. The internal porosity of the material as well as its fracture pattern (pores and microcracks) in the vicinity of the indenter was visualized by the thresholding technique built in the software. Typical examples of such CT images with superimposed pores/microcracks objects shown in red are presented in Figs. 7 and 9. First, we measured the cavity radius r for different samples and plotted it versus the loading amplitude. As a result, we obtained a linear relationship (Fig. 7). Moreover, as expected, the crack pattern becomes more pronounced with increasing applied load (Fig. 7, upper images). Figure 7 : Radius of indentation cavity as a function of the maximum loading force. Pictures above the graph are the CT images of the corresponding cavities. Numbering of images corresponds to the numbers of dynamic indentation curves showed in Fig. 6. Scale bar size is 254 µm. D