Abstract: A test system for testing specimens to determine crack propagation utilizing a factor relating to stress intensity at the end of the crack as a control parameter for the loading means.

Abstract: A vibrating wire gage for use with a mine rockbolt. The wire is anchored within the hollow portion of a cylindrical gage body that has an adjustable lower member. Rotation of the adjustable member changes the tension in the wire and as a result its frequency of vibration. Forces acting on the bolt imbedded in the rock cause the gage body to deform as well as its wire since the upper end of the gage body is held to a rockbolt anchored firmly within the earth. By noting variations in the frequency of the wire from an initial setting, the change in the amount of force the rockbolt is under can be determined. A rotatable pick can be inserted through a hole in the lower adjustable member to mechanically pluck the wire. The readout of the vibrations from the plucked wire may be accomplished by a mechanics stethoscope held against the gage or by an electrically operated pickup head which engages the vibrating wire.