In this study, to obtain the basic data on impact fatigue behaviour of steel plates following the previous study, low-cycle impact fatigue tests are carried out on five kinds of plate specimens of mild steel SS 41, i.e., smooth specimens, circular notched specimens (stress concentration factor K_t=l.6) and V notched specimens (K_t=2.4, 3.5 and 4.8), under repeated impact tensile loads. The obtained results in this study are summarized as follows: (l) The process of fracture of the smooth and circular notched specimens having small K_t-values is creep type as well as that of circular bar specimens having small K_t-values. The process of fracture of V notched specimens having large K_t-values is local creep type in case of high stress level and is crack type in case of low stress level. (2) Pursuing permanent strain ε which evaluated by using change of plate thickness at the minimum cross section, it is found that there exist three types of cyclic behavlour of ε depending on above mentioncd types (A), (B) and (C) of the process of fracture and in each type the stable stage where permanent strain rate Δε_c is constant occupies most of fatigue life. (3) The relations between impact tensile stress σ and Δε_c, impact fatigue life N_f and Δε_c and σ and N_f for the case of the two creep types (A) and (B) are clarified (see Table 3). At the same time, it is found that these relations for the case of the crack type (C) are different from above relations because the value of Δε_c is fairly smaller than one for the creep types. (4) Comparing above results for plate specimens with those for circular bar specimens, it is found that there exjst considerable difference in effccts of shape of specimen on impact fatigue behaviour between the two.
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