The helium flow steadily increases

The helium flow steadily increases until the failure point due to coalescence of microfractures from rupture of mineral grains and fluid inclusions and the subsequent increase in diffusive surface area and specimen permeability as a result of fracturing (Figure 4). After specimen macrofracture, axial displacement was halted and held,and the helium release rate decreased backdown to values near or slightly above the predeformation value.