Induction hardened shafts lend
themselves very well to most torsional
applications because induction hardening
increases the hardness near the
surface where it is most needed and it
leaves the surface in compression,
which improves fatigue life. When a
shaft is loaded torsionally, the shear
stress is highest at the surface and zero
at the center. In the absence of a stress
concentration factor, stress increases
linearly from the center to the surface.
Thus, only the surface needs to be
hardened to a depth to adequately exceed
the applied stress. When the surface
layer is hardened, martensitic
transformation causes it to expand
leaving the surface in compression, as
opposed to through hardening where
the core also expends leaving the surface
in tension.
Induction hardened shafts lendthemselves very well to most torsionalapplications because induction hardeningincreases the hardness near thesurface where it is most needed and itleaves the surface in compression,which improves fatigue life. When ashaft is loaded torsionally, the shearstress is highest at the surface and zeroat the center. In the absence of a stressconcentration factor, stress increaseslinearly from the center to the surface.Thus, only the surface needs to behardened to a depth to adequately exceedthe applied stress. When the surfacelayer is hardened, martensitictransformation causes it to expandleaving the surface in compression, asopposed to through hardening wherethe core also expends leaving the surfacein tension.
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