[en] This paper describes part of an extensive program at Battelle-Colombus concerned with measuring propagating crack toughness, Ksub(D), and defining the conditions under which a rapidly moving crack will arrest. Earlier publications have discussed the Ksub(D) data that have been generated and the testing procedures, including specimen size requirements. Here the authors concentrate on describing a method for determining the relation between Ksub(D) and crack velocity which bypasses the need for direct velocity measurements. As a result the test procedures are considerably simplified. The test method involves wedge-loading of duplex double cantilever beam specimens containing a blunt starter notch. Particular care is taken to approach fixed-grip conditions as closely as possible. As a result it is possible to initiate a rapidly moving crack and to arrest it. The results are analyzed with the aid of a finite difference procedure. (Auth.)