Notch insensitivity

LCF) resistance in combination with a high notch insensitivity underlines the applicability of C/SiC composites as structural ceramic materials. 

Fracture mechanics concepts have also been applied to predict the behaviour of natural fibre FRC. Fracture parameters were found to be dependent on the moisture content, with wet composites having higher toughness values [40,51], Wet composites were also found to be notch-insensitive, suggesting that LEFM cannot adequately model the behaviour of such composite [51 ]. This was probably the result of the cracking mode, in which the crack path was tortuous, with some fibres failing by pull-out. 

Tests of notched specimens (Figure 26) and determination of notch sensitivity coefficient (K) show that, despite thickness of rolled semiproducts, the Kt coefficient (for a dendritic structure) is less than K2 (for a nondendritic structure) by 20—25% for room and cryogenic temperatures. Thus, K2 > 1.5 for plates and K2 = 1 for thick sheets, which indicates their full insensitivity to a notch. 

The pitch of the helix for compound 42 was found to be approximately 0.2-0.3 xm, thus the material selectively reflects visible light over a wide temperature range. Moreover, the pitch is relatively temperature insensitive thus the material can be used in large area non-absorbing polarizers, or in optical notch filters or reflectors. In addition, in the glassy state the helical macrostructure of the chiral nematic phases is retained, thus similar applications are possible. 

In slightly corrosive services, it may pay to use a stainless steel distributor even when carbon steel is satisfactory as the packing material. Successful applications of this practice have been reported (84, 346). Alternatively, a distributor which is insensitive to corrosion, such as the notched-trough type, can be used. 

At room temperature, all of the alloys are relatively insensitive to notches, as indicated by relatively high ratios (notch-yield ratios above 1.06), and ratios that are nearly the same for all compositions in -T6-type tempers. For the —W temper, the notch yield ratio is appreciably higher, but this is accomplished at considerable sacrifice in yield strength. 

Alloys X7006-W, X7005-T6, X7006-T63, and X7106 in the -T6 and -T63 tempers are relatively insensitive to notches over the entire temperature range from room temperature to —423°F. Notch yield ratios of some of these materials with sharply notched specimens decrease somewhat, but are about equal to or greater than about 1.0 at —320°F and about 0,95 at —423°F,... 

Morgan JP, Dauskardt RH. Notch strength insensitivity of self-setting hydroxyapatite hone cements. J Mater Sci-Mater M. 2003 Jul 14(7) 647-53. 

A version of PA 66 insensitive to notching, scratches, does not concentrate stress and does not become brittle at -20° C... 

The notch-tensile strengtlis of the alloys, both plain and welded, are higher at the lower temperature than at room temperature, as indicated by ratios of notch strengths at -320 F to those at room temperature. None of these ratios is below 1.06 and most range upward from 1.10 for plain material and from 1.16 for welds, with little significant difference among the alloys. Indications that the welds are more insensitive to notches than the parent metal itself have been reported previously for tests at temperatures ranging down to -423 F [4]. 

The obvious effect of specimen geometry on strength indicates that data obtained from tests of notched specimens should be interpreted with caution. Considerably different ratios were obtained with the various notches and no one notch is wholly suitable for the evaluation of notch sensitivity under conditions other than those in this test. However, the data are sufficient to indicate that plain and welded aluminum-magnesium alloy plate is relatively insensitive to notches, at least to temperatures as low as -320 F. 

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