Bearing failure causes:  

V-belt failure analysis:  

Bolt failure examples:  

Bolt failure causes (animated):  

Bolted Joints:

http://en.wikipedia.org/wiki/Bolted_joint

Hydraulic hose failures:

http://www.plantengineering.com/search/search-single-display/nine-reasons-why-hydraulic-hoses-fail/f497ef39ef.html

Hose vs. Tube?

http://www.machinerylubrication.com/Read/25963/hydraulic-equipment-hose-tube