This paper describes an in-situ tensile test in synchrotron tomography achieved for the first time with a frequency of 20 tomograms per second (20 Hz acquisition frequency). This allows us to capture rapid material fracture processes, such as that of a metal matrix composite composed of 45 % of alumina particles embedded into 55 % of pure aluminium, which fractures by the sudden coalescence of internal damage. Qualitatively, the images show the nucleation and propagation of a crack during 9 s leading to total fracture of the sample. The images are then post-processed quantitatively to analyze the evolving shape of the crack and to derive the instantaneous speed of its tip. It is shown that the crack clearly propagates from one particle to the next, pausing briefly before propagating to the next particle, lending experimental support to a local load sharing analysis of the fracture of this class of composite.