High spatial resoln. synchrotron x-ray strain measurements and radiog./tomog. were combined to study the progressive fragmentation process during a single fiber full-fragmentation test. It was possible to observe the fragmentation sequence and to det. the interfacial shear stress as a function of position along the fiber. The SCS-6 fiber failed after it was elastically strained locally to 1.5%. The interfacial frictional shear strength inferred from the longitudinal strain profile of the broken fiber was calcd. to be around 200 MPa, whereas a conventional post mortem full fragmentation anal. based on the mean fragment length would have incorrectly given a value of .apprx.700 MPa. This is due to the degrdn. of the fiber strength after the initial fiber fracture event. After failure, interface sliding was obsd. along considerable lengths of the fiber matrix interface. Upon unloading some reverse frictional sliding was found to take place. The morphol. of the fiber cracks as well as the occurrence of matrix cracks as the sample approaches satn. fragmentation were also detd. from radiog. and tomog. images. [on SciFinder (R)]