Due to its meshless nature, the smoothed particle hydrodynamics method (SPH) provides high potential for the simulation of free-surface flows and mixing in complex geometries. We used SPH to analyze the flow inside five typical screw elements of corotating twin-screw extruders, two conveying elements, two kneading elements and a mixing element. Our results show conveying capabilities, pressure generation and power input for various operation states, completely and partially filled. We conducted a detailed mixing analysis based on tracer particles, which yielded the time evolution of the intensity of segregation for different tracers. From that, we determined exponential mixing rates, which describe the relative decrease of the intensity of segregation per screw revolution and characterize the mixing performance in different operation states. This provides valuable input information for simplified models of extruders, which are relevant to industrial applications and can significantly contribute to the efficient design, optimization and scale-up of extruders. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2451-2463, 2017