PSI - Issue 41

S.V. Uvarov et al. / Procedia Structural Integrity 41 (2022) 610–617 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The measurements were carried out using an automated microhardness tester EMCO-TEST DuraScan 70 with a load of 50 g on the indenter. The step between the microhardness measurement points outside the impact zone was 0.3 mm, in the impact area - 0.05 mm. 3. Experimental results The signals received from the VISAR and Oscilloscope systems were processed in a computer program (Bannikova et al. (2014)) and free surface velocity profiles were constructed. In Fig. 2 obtained on VT6 (a) and on VnP-1 (b) with foil and without foil. We observe an increase in the amplitude of the velocity (or the amplitude of the compression pulse) when reaching the metal surface in the absence of foil under laser loading. Due to the specific loading conditions and due to the preparation of the sample surface, the type of velocity profiles varied from experiment to experiment. But the appearance of the velocity profiles for both metals (VT6, VnP-1) is similar to the profiles obtained by other authors (Kanel et al. (2008), Saveleva et al. (2015), under different loading conditions, for example, by the explosive generator (EG) method and different sample thickness. In our experiments on the velocity profiles of the free surface, there is no spall fracture.

V sf , m/s

V sf , m/s

Fig. 2. Velocities of the free surface of metals: a – Titanium VT6, b – Vanadium VnP-1. The samples 1, 2 with Al foil and 3, 4 without Al foil).

The amplitude pressure σ* and the strain rate ε˙* on the plastic front of the compression wave were determined from the velocity profiles of the free surface [Kanel et al. (2008)]. The data for σ* and ε˙* are presented in Table 2. Analysis of unetched metallographic sections of vanadium and titanium samples (Fig. 3 and Fig. 4) after laser loading did not reveal pores, cracks, or other signs of damage in their structure. After etching with an aqueous solution of a mixture of HF and HNO 3 , a structure typical of two-phase titanium alloys was revealed (Fig. 3), significant differences in the structure inside and outside the impact zone, as well as differences between the samples tested with and without aluminum foil by optical metallography methods were not revealed. It should be noted that none of the used chemical compositions made it possible to reveal the grain boundaries in the vanadium samples, but only revealed the texture of the deformation of the original hot-rolled bar (Fig. 4). Analysis of metallographic sections of vanadium did not reveal any differences in the impact zone as the shock wave moved from the front surface to the back. Differences in the structure in the impact zone and outside it was also not revealed by optical metallography methods. Despite the presence of separate bursts of microhardness (Fig. 5 and Fig. 6), no regularities were found in the change in the microhardness of titanium samples after laser exposure. According to the result of microhardness data processing based on Pearson's goodness-of-fit test, it was found that they do not have statistically significant