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A. F. Bower is the author of Applied Mechanics of Solids by A. F. Bower, an online text whose title page gives his name as Allan F. Bower. The text connects elasticity, plasticity in continuum mechanics and fracture mechanics to explicit models of how solids deform. Its treatment of single-crystal plastic deformation follows slip systems and the rotation of the tensile axis, showing why a single crystal's response depends on its orientation.^[ref]

Single-crystal plastic deformation is irreversible shape change of a single crystal, often through dislocation motion on particular slip systems. A slip system specifies a crystallographic plane and a direction within it. Applied loading resolves into a shear stress that drives slip, making the response depend on crystal orientation.^[ref]

Under uniaxial stress $\sigma$, the resolved stress on a slip system is $\tau =\sigma \cos \varphi \cos \lambda$, where $\varphi$ is the angle between the loading axis and plane normal and $\lambda$ the angle to the slip direction. For compatible $45$-degree angles, $\tau =\sigma /2$. Slip begins when the relevant resistance is reached; subsequent deformation can rotate the lattice and change which systems carry further strain.^[ref]