tailieunhanh - Ferroelectrics Physical Effects Part 5

Tham khảo tài liệu 'ferroelectrics physical effects part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 150 Ferroelectrics - Physical Effects The crack length increased with increasing hydrogen concentration in the samples. Therefore the cracks can also grow with the prolongation of dwell time during indentation test in a precharged sample since the hydrogen concentration will increase at the indentation crack tips by stress-induced diffusion. The experimental results indicate that the longer the indentation load hold the larger the indentation crack length is and the smaller fracture toughness Kic H t measures as shown in Figure 14 Zhang et al. 2008 . Under a constant load the HIDC can occur by the stress-induced hydrogen diffusion and enrichment. Fig. 14. The normalized fracture toughness Kic H t Kịc versus the logarithm of the dwell time during the indentation test for the charged sample Zhang et al. 2008 Hydrogen-induced delayed cracking in ferroelectric ceramics During single-edge-notched-tensile sample of PZT ferroelectric ceramics hydrogen charging dynamically in l NaOH g 1 AS2O3 solution hydrogen-induced delayed cracking HIDC can occur Wang et al. 2003a and depends on the relative orientation between notch plane and the polarization vector . the HIDC also shows anisotropy in ferroelectric ceramics as shown in Figure 15 Wang et al. 2003b . Hydrogen concentration Ch under different charging current densities is given in Table 2. The curve of Kih Kịc vs i or Ch can plot based on Table 2 and one can find a linear relationship between Kih Kịc and the IiĩCh Wang et al. 2003b Kfc KỈH K c 5 where superscript a and b denote polarization vector parallel and perpendicular to the crack plane respectively. K c MPam1 2 and Kp. MPam1 2 for PZT ferroelectric Hydrogen in Ferroelectrics 151 i mA cm2 5 50 300 CH ppm Kjh MPami 2 Kjh MPami 2 - IH i IC -KỈH -KÌc - Table 2. The threshold stress intensity factors of HIDC