Fatigue strength estimation of thread connections of drill-bit casing string elements based on similarity criterion of fatigue failure
Fatigue strength of metal structures elements is mainly characterized by stress and a number of load cycles. Stresses arising in such elements during are mostly variable and random functions of time. In this regard, the most reliable information about the origin and development of patterns of fatigue cracks in the elements of metal structures and parts of machines can be got following the results of statistical processing of experimental data. However, large size and design specific features of many elements often complicate performing of corrosion-fatigue tests. That’s why fatigue processes regularities in such details are studied on their scaled-down models or laboratory samples. Different researchers offered a lot of criteria to move from field samples to their models. The paper discusses one of the most common similarity criteria of fatigue fracture proposed by S.V. Serensen and V.P. Kogaev; its application for concentrators of various shapes is modified Some comparative analysis of field testing of З-42 threaded connections and experimental researches of laboratory samples was held to check the adequacy of the developed method. “UDTP-1” - a unit for fatigue cracks distribution was used for studying regularities of fatigue damage of lab samples. The obtained results with rather sufficient accuracy confirm the effectiveness of the suggested method.