Jamming by shear in a dilating granular system*

Jamming can occur in frictional granular materials undergoing shear at a fixed packing fraction, φ, for φ within a range of packing fractions below the isotropic jamming point, and the amount of strain required to induce jamming, γ, increases with decreasing φ. We are interested in how the shear jamming process is affected if the system is dilating as it is sheared. We conduct experiments to shear a 2D granular system while continuously increasing the system volume. Below a certain dilation rate, the system is still able to jam at packing fraction, φ_c, smaller than the initial φ. We measure γ for different dilation rates and initial packing fractions by monitoring the coordination number of non-rattlers and the system pressure. We find that γ is the same as the γ required to jam a system with fixed packing fraction φ_c via pure shear.