Axles are rotating or non-rotating members which are
subjected to only bending moments due to members supported
by it. It does not transmit torque. In other words, an axle
is not twisted it only bends.
Shafts are rotating members which are subjected to bending
moments and twisting moments and sometimes to axial loads.
It twists and transmits power.
Shaft and Axle both performs revolutionary motion about its
axis. But main difference is being that SHAFT is always
DRIVEN for eg. crankshaft of the I.C. engine. While AXLE
causes other member to drive for e.g. the front and rear
axle of 4 wheeler always drives the wheels.