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The influence of roller strengthening on a residual stresses distribution and multicyclic fatigue of solid cylindrical specimens of 50 mm diameter made of steel 20 with cuts of various depths and a pressurized hub has been examined. As a result, an endurance limit of roller strengthened specimens diminishes. In order to preserve the effect of hardening with a cuts depth increase, its necessary to increase the thickness of a layer with compressive residual stresses. Surface hardening influence on an endurance limit of specimens has been estimated by two criteria: axial residual stresses on a concentrators surface and average integral residual stresses, calculated through the dangerous sections surface layer thickness that equal a critical depth of a non-propagating fatigue crack. Its been stated that its more reasonable to use the average integral residual stresses criterion for an evaluation of roller strengthening influence on an endurance limit of specimens with cuts of various depth and a pressurized hub.

In order to raise a fatigue resistance the calculation-experimental method of parts surface thermo chemical machining efficiency has been carried out. The employment of two types of reference specimens in experiments has been substantiated. The employment of smooth reference specimens for a determination of residual stresses in a surface layer and of corset reference specimens for fatigue tests has been recommended. The results of experimental study of two types of thermo chemical machining (cementation and nitriding) influence on a fatigue resistance of corset specimens made of high-strength allows ВКС-5 и ВНС-17 have been used in the work. . The calculations of the study have been carried out by the Finite Elements Modeling method using the calculation complexes ANSYS and PATRAN/NASTRAN. The residual strained state modeling is carried out by thermo elasticity method. On grounds of conducted calculation its been stated that an axial residual stresses distribution in a dangerous (smallest) section of a corset specimen doesnt practically differ from a similar distribution in smooth specimens. An endurance limit increment due to corset specimens hardening was determined with use of the average integral residual stresses criterion. Carried out results let also maintain that the optimal regimes of thermo chemical machining are the regimes under which average integral residual stresses are maximum.

The influence of cuts depth on residual stresses distribution and an endurance limit under bending of hollow cylindrical specimens made of steel 20 with external diameter 50 mm and interior diameter 40 mm after outstripping superficial plastic deforming by roller strengthening of two regimes has been examined. Its been stated that the value of compressive residual stresses in a dangerous section of specimens decreases on cuts depth increase. As a result, an endurance limit increment of hardened specimens with cuts diminishes. In order to preserve the effect of hardening by increasing the endurance limit under outstripping superficial plastic deforming with an increase in a cuts depth, it is necessary to increase the thickness of a smooth part with compressive residual stresses layer. Its been shown that in order to estimate the increase in the endurance limit of hardened specimens, one should use not residual stresses at the bottom of a cut, but average integral residual stresses through the parts dangerous section surface layer thickness that equal a critical depth of a non-propagating fatigue crack.

В работе исследовано влияние гидродробеструйной обработки на предел выносливости при изгибе и растяжении-сжатии в случае симметричного цикла цилиндрических образцов с круговым надрезом полукруглого профиля радиуса 0,3 мм. Образцы диаметром 10 мм для испытаний на усталость изготавливались из сталей 30ХГСА, 12Х18Н10Т, ЭИ961, 45 и алюминиевых сплавов В93, Д16Т. Влияние поверхностного упрочнения на предел выносливости образцов с надрезом оценивалось по двум критериям: остаточным напряжениям на поверхности надреза и среднеинтегральным остаточным напряжениям, вычисленным по толщине поверхностного слоя опасного сечения образцов, равной критической глубине нераспространяющейся трещины усталости. По результатам определения остаточных напряжений и предела выносливости образцов с надрезом установлено, что коэффициенты влияния поверхностного упрочнения на приращение предела выносливости при изгибе и растяжении-сжатии по обоим критериям примерно одинаковы. Однако коэффициент влияния по критерию среднеинтегральных остаточных напряжений изменяется в значительно меньших пределах, чем коэффициент влияния по критерию остаточных напряжений на поверхности концентратора. Поэтому для оценки влияния поверхностного упрочнения на предел выносливости деталей с концентраторами напряжений следует использовать критерий среднеинтегральных остаточных напряжений. На примере образцов при наличии и отсутствии наклёпа в опасном сечении показано, что в условиях концентрации напряжений наклёп не оказывает влияния на предел выносливости поверхностно упрочнённой детали. На предел выносливости таких деталей оказывают влияние только сжимающие остаточные напряжения.

The influence of roller strengthening on endurance limit under bending of the 25 mm and 50 mm diameter shafts made of steel 20 and 25 mm diameter shafts made of steel 40X with a pressurized hub has been examined. Its been stated that the endurance limit of roller strengthened shafts with a pressurized hub depends not only on a value of compressive residual stresses in their dangerous section but on the character of its distribution. The valuation of a surface hardening influence on the endurance limit of shafts by the surface residual stresses criterion and the average integral residual stresses criterion has been shown that the average integral residual stresses criterion calculated through the parts dangerous section surface layer thickness equal the critical depth of the non-propagating fatigue crack can be recommended for the hardened shafts with a pressurized hub endurance limit increase prediction. Its been shown that on a diameter of a shaft with a pressurized hub raising it is necessary to increase a thickness of a hardened surface layer with compressive residual stresses.

The study of the initial radial deformations influence on the residual strained state components distribution through the hardened layer thickness under various types of surface hardening has been conducted. Chemical thermal machining (CTM) and shot blasting (SB) have been examined on the example of smooth solid steel cylindrical specimens with diameters D=10 mm and D=25 mm under a linear distribution of initial deformations through the hardened layer thickness (the maximum value is on the surface and zero on the maximum depth of hardening). The calculation has been conducted with use of the program complex PATRAN/NASTRAN. The solution has been carried out in axial symmetric positing by thermo elasticity method. On study results its been stated that the radial stresses through the hardened layer thickness under CTM and SB are positive. Incidentally the radial component of initial deformations under chemical thermal machining and shot blasting doesnt exercise essential influence on the radial and axial residual stresses distribution through the hardened layer thickness. Hence the initial radial deformations havent much significance at the evaluation of the residual strained stress state influence on the hardened parts endurance limit increment calculated by the average integral residual stresses criterion.

Through the example of specimens of various diameters of steel 20, the use of the criterion of mean integral residual stresses has been experimentally found to be the most justified tool for predicting the influence of surface hardening on fatigue limit under stress concentration conditions.

It is established that the difference between the calculated values of endurance limit increments under bending and the experimental ones for hollow specimens made of steel 45 of various diameter (15–50 mm) with notches hardened by shot blasting does not exceed 7%.

As a result of the study performed, it has been found that for assessing the influence of surface hardening on the fatigue limit for the parts of different diameters made of steel 20, it is advisable to use a criterion for mean integral residual stresses.