= David Roylance
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<David Roylance> developed an engineering treatment of <fracture mechanics> connecting cracks, loading and a material's resistance to failure. His notes derive an energy-balance description and introduce the <stress intensity factor> as a measure of crack-tip loading.<Introduction to Fracture Mechanics by David Roylance>[Energy-balance approach and stress-intensity treatment]{ref}
In a simple linear-elastic mode-I geometry, $K_I=Y\sigma\sqrt{\pi a}$, with crack scale $a$ and dimensionless geometry coefficient $Y$. Comparing $K_I$ with the relevant <fracture toughness> shows why a nominally moderate bulk stress can be critical when a sufficiently large flaw is present. The geometry and elastic regime are essential assumptions.
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