Hydrogen interacts with many metals to reduce their ductility (2) and frequently their strength also. It enters metals in the atomic form, diffusing very rapidly even at normal temperatures. During melting and fabrication, as well as during use, there are various ways in which metals come in contact with hydrogen and absorb it. The absorbed hydrogen may react irreversibly with oxides or carbides in some metals to produce a permanently degraded structure. It may also recombine at internal surfaces of defects of various types to form gaseous molecular hydrogen under pressures sufficiently high to form metal blisters when the recombination occurs near the outer surface. In other metals, brittle hydrides that lower the mechanical properties of the metal are formed. Another type of embrittlement is reversible, depending on the presence of hydrogen in the metal lattice during deformation for its occurrence. Under some conditions the failure may be delayed for long periods. A number of different mechanisms have been postulated to explain reversible embrittlement. According to some theories hydrogen interferes with the processes of plastic deformation in metals, while according to others it enhances the tendency for cracking.
Brittle metals subjected to blast loads shatter into a large number of very small particles, the number and size of which are well characterized by the semiempirical cumulative distribution function of Mott. This function, however, contains no information regarding either the manner of breakup or the reason for a particular distribution. An earlier analytical study of the phenomenology of brittle fragmentation used statistical arguments to establish relationships between the energies associated with crack branching and the Mott parameters that characterize the particle distribution. That model predicts that the average mass of a particle from the shattered body is proportional to the fourth power of the crack-branching stress-intensity factor. In the present work on hypereutectoid steels, the ratio (KH/KIC)3.4 was experimentally determined to be linearly related to the average particle mass in reasonably good agreement with the model prediction, where KH is the dynamic stress intensity factor for incipient microbranching (hackle), and KIC is the plane-strain fracture toughness.
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