Observations: By A) Adjusting the gear ratio such that twist could be introduced in the steel axle; and B) Reversing (and re-reversing) that twist enough ti

Observations: By A) Adjusting the gear ratio such that twist could be introduced in the steel axle; and B) Reversing (and re-reversing) that twist enough times, eventually a stress crack was formed; C) That stress crack, coupled with enough additional reversing and re-reversing of the twist, resulted in the steel eventually becoming completely cracked. So yes, under certain circumstances, plastic Lego can indeed break a steel axle...