Granular systems have been shown to be able to behave like solids under shear for a finite density range Φs < Φ < ΦJ, where ΦJ is the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the questions we address here is: how does shear jamming occur and how does inter-particle friction affect shear jamming? We propose a set of three particles in contact, denoted as a trimer, as the basic unit to microscopically characterize the deformation of the system. Trimers, stabilized by inter-grain friction, are then expected to bend in response to shear to make extra contacts to regain stability, which is later demonstrated by systematically studying their geometry. To study the effect of friction, we use photoelastic disks either wrapped with Teflon to reduce friction or with fine teeth on the edge to increase friction. Shear jamming is observed for all the cases, while the lowest packing fraction that can reach a shear jammed state increases with friction.