BS 7910:2019 Annex N — low-constraint toughness elevation $K_{mat}^c$ and constraint-modified FAD
Deeply-cracked bend specimens give a high-constraint lower-bound K_{mat}. Shallow flaws or tension loading have lower constraint and a higher effective toughness. Annex N quantifies that elevation.
\beta L_r = \beta\cdot L_r,\qquad K_{mat}^c = K_{mat}\left[1+\alpha(-\beta L_r)^k\right]\ (\beta L_r<0)
Procedure I modifies the FAD: f_c(L_r)=f(L_r)\cdot K_{mat}^c/K_{mat}; \rho becomes \rho_c=\rho\cdot K_{mat}^c/K_{mat}.
Constraint relief raises reserve factors — confirm with sensitivity studies (N.2.4.6). High constraint (\beta L_r\ge0) reduces to conventional Clause 7. Not to be used with Annex I.
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