Global　bifurcations　and　multipulse-type　chaotic　dynamics　in　the　interactions　of　two　flexural　modes　of　a　cantilever　beam　are　studied　using　the　extended　Melnikov　method.　The　cantilever　beam　studied　is　subjected　to　a　harmonic　axial　excitation　and　transverse　excitations　at　the　free　end.　After　the　governing　nonlinear　equations　of　nonplanar　motion　with　parametric　and　external　excitations　are　given,　the　Galerkin＇s　procedure　based　on　the　first　flexural　mode　in　each　direction　is　applied　to　the　partial　differential　governing　equation　to　obtain　a　two-degree-of-freedom　non-autonomous　nonlinear　system.　The　resonant　case　considered　here　is　one-to-one　internal　resonance,　principal　parametric　resonance-1/2　subharmonic　resonance.　The　method　of　multiple　scales　is　used　to　derive　four　first-order　nonlinear　ordinary　differential　equations　governing　the　modulation　of　the　amplitudes　and　phases　of　two　interacting　modes.　After　transforming　the　modulations　equations　into　a　suitable　form,　the　extended　Melnikov　method　is　employed　to　show　the　existence　of　chaotic　dynamics　by　identifying　Silnikov-type　multipulse　jumping　orbits　in　the　perturbed　phase　space.　We　are　able　to　obtain　the　explicit　restrictions　on　the　damping,　forcing,　and　the　detuning　parameters,　under　which　multipulse-type　chaotic　dynamics　is　to　be　expected,　Physically,　such　jumping　means　sudden,　large-amplitude　departures　of　the　beam　from　its　planar　oscillations.　Numerical　simulations　indicate　that　there　chaotic　responses　and　jumping　phenomenon　in　the　nonlinear　nonplanar　oscillations　of　the　cantilever　beam.　Copyright　©　2010　by　ASME.