where N (=48) is the total number of available radial cracks around the indentation and ΔN is the number of radial cracks propagating after ther- mal shock loading. In the present work, the initial crack length for lami- nated and monolithic ceramics is about 80 μm and 100 μm, respectively.
The percentage crack length increase with respect to the as-indent- ed crack length has been calculated from the growth of the individual cracks along the surface, and Fig. 4 show crack-growth behavior after single quench into a bath of water at room temperature as a function of the temperature difference, ΔT, for the laminated and monolithic 70 vol.% TiB2 + 20 vol.% SiC + 10 vol.% graphite flake ceramic. It is shown that the fraction of cracks propagated and crack extension are dependent on ΔT. In all cases, the monolithic 70 vol.% TiB2 + 20 vol.% SiC + 10 vol.% graphite flake ceramic shows poor crack-growth resis- tance after a single thermal shock than for the laminated TSG ceramics. For the laminated and monolithic TiB2-based ceramics cracks grow in a stepwise manner at the micro-scale, which suggests that each crack will not start to grow at the same ΔT. This is illustrated by Fig. 4, which shows the percentage of cracks that have started to grow at each ΔT. One reason for the stepwise crack growth is due to the variation in the microstructure at the tip of each crack, which leaded to the scatter be- tween the individual crack sizes [38]. And the other reason for the step- wise crack growth may be considered is the stress release near the cracks extended that makes the possibilities to grow of the near cracks
where N (=48) is the total number of available radial cracks around the indentation and ΔN is the number of radial cracks propagating after ther- mal shock loading. In the present work, the initial crack length for lami- nated and monolithic ceramics is about 80 μm and 100 μm, respectively.The percentage crack length increase with respect to the as-indent- ed crack length has been calculated from the growth of the individual cracks along the surface, and Fig. 4 show crack-growth behavior after single quench into a bath of water at room temperature as a function of the temperature difference, ΔT, for the laminated and monolithic 70 vol.% TiB2 + 20 vol.% SiC + 10 vol.% graphite flake ceramic. It is shown that the fraction of cracks propagated and crack extension are dependent on ΔT. In all cases, the monolithic 70 vol.% TiB2 + 20 vol.% SiC + 10 vol.% graphite flake ceramic shows poor crack-growth resis- tance after a single thermal shock than for the laminated TSG ceramics. For the laminated and monolithic TiB2-based ceramics cracks grow in a stepwise manner at the micro-scale, which suggests that each crack will not start to grow at the same ΔT. This is illustrated by Fig. 4, which shows the percentage of cracks that have started to grow at each ΔT. One reason for the stepwise crack growth is due to the variation in the microstructure at the tip of each crack, which leaded to the scatter be- tween the individual crack sizes [38]. And the other reason for the step- wise crack growth may be considered is the stress release near the cracks extended that makes the possibilities to grow of the near cracks
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