Development of plastic strips and fracture in the vicinity of two unequal cracks in a plate

We studied the process of development of plastic strains and fracture in tension of a thin infinite plate with two collinear unequal cracks. An ideally elastoplastic material of the plate satisfies the Tresca condition. We investigated the propagation of narrow plastic strips on the continuation of the cracks by using the well-known method for the simulation of such strips by segments with jumps of displacements satisfying the plasticity condition. We also present a general algorithm for the solution of the problem under consideration. Within the framework of this algorithm, the results for two equal cracks are obtained as a special case. In the case of unequal cracks, we computed the value of loading whose application results in the joining of strips lying between the cracks and deduced equations for the determination of the length of these strips and crack tip opening displacements both at the time of joining of the strips and after this event. The numerical analysis of results demonstrates that the largest strips appear (prior to their joining and opening) between the cracks in the vicinities of the tips of the longer crack. According to the strain criterion, the processes of fracture and joining of the cracks are initiated just at the indicated sites. It is shown that, under a load of 0.6 _t, at the ends of cracks, one observes the initiation of secondary strips following the primary ones and making an angle of 59° with them (just as in the case of a single crack). We also indicate the principal shortcomings of the solution of the problem suggested by Theocaris [Eng. Fract. Mech,18, No. 3, 545–560 (1981)].Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 6, pp. 17–29, November – December, 1995.     

Low-Cycle Durability of Steels in High-Pressure Hydrogen

We deduce the dependences of low-cycle durability of 11 corrosion-resistant steels from basic structural classes on the pressure of gaseous hydrogen within the range 0.1–35 MPa at 293°K. It is discovered that the highest serviceability in hydrogen is exhibited by homogeneous austenitic steels and steels with intermetallic hardening. The durability of Ni–Al–Ti steels treated for maximum heat resistance in hydrogen is proportional to the content of Ti and Ti//Al ratio and depends on the conditions of treatment. Steels in the state of substitutional solution are not affected by the medium. The materials from the transient class and steels with unstable austenite are characterized by medium sensitivities to hydrogen. High-strength martensite-aging and ferritic steels exhibit catastrophic embrittlement in hydrogen.     

Methodological Aspects of Determination of Hydrogen Resistance of Steels

We consider main conditions of the adequate estimation of degradation of mechanical properties of chromium–nickel alloys in gaseous hydrogen. We establish that evacuation is a necessary procedure for preparing a working chamber for testing. The low-cycle fatigue and relative contraction are the most sensitive to hydrogen embrittlement. We determine the strain rate and hydrogen pressure that maximally impair mechanical properties.