Abstract:Shear tests under static and cyclic loadings were performed with direct shear equipment in order to explore the shear behaviors of brittle materials such as concrete,rock,etc. under different loadings. The direct shear equipment that allows static and dynamic shear tests,was designed based on MTS in the Vibration Laboratory of Hohai University;and brittle materials were modeled by mortar. Test results under static and cyclic loadings including 1,2,3 and 5 Hz show: (1) shear stress-displacement curves under static loading are similar to the strength envelope curves under cyclic loading that can be divided into four parts;(2) the peak strength and residual strength under cyclic loading are larger than those under static loading when other conditions were same,but they change inconspicuously with the frequency changes;(3) peak strength and residual strength increase with normal stress increase under both loading conditions;(4) failure strains under static loading are larger than those under dynamic loading and both increase with the normal loading increasing;and (5) shear dilatancy is obvious during the shearing process. The failure mechanism was described simply at last.