We can actually do what Andy says: assuming the threads are perfectly lubricated (i.e. the bolts can rotate with no friction in the threads), the work done in one full rotation of a bolt is 2*pi* torque. For a metric 8 x 0.75 chainring bolt the compression force is
(work done in one rotation)/(thread pitch) = 2*pi*torque_in_Nm / (0.75 * 10^-3 m) = 850 kgf * torque_in_Nm.
For a 1 Nm torque this is 850 kg force. Are we getting the number right?
Of course there is also friction between the bolt head and the washer/bash guard.