Criterion Of Residual Stresses Research Articles

AN INFLUENCE OF ROLLER STRENGTHENING ON MULTCYCLIC FATIGUE OF SPECIMENS WITH CUTS OF VARIOUS DEPTH AND A PRESSURIZED HUB

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.

AN EVALUATION OF PARTS’ FATIGUE RESISTANCE AFTER SURFACE THERMO CHEMICAL MACHINING

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.

Multi-objective particle swarm optimisation of multilayer functionally graded coating systems for improved interfacial delamination resistance

In this paper a multilayer coating system was considered for a 316 L stainless steel substrate with potential application for hydrogen storage. The coating system was comprised of a 316 L stainless steel/Al2O3 functionally graded (FG) layer and a SiC top coat. The composition gradation and thicknesses of the FG layer and SiC top coat were considered as parameters to be optimized for higher edge interfacial delamination resistance within the system. A novel method of delamination energy variation was first used for finite element analysis (FEA) of the system and the best set of parameters were defined as well as an interfacial delamination criterion (maximum stable edge delamination crack length in the system). Analytical solutions of thermal residual stress, strain and strain energy density were also studied for the system. Two new multi-objective functions were derived based on the analytical equations and further investigated to maximize interfacial delamination resistance of the system using multi-objective particle swarm optimisation (MOPSO). The optimized conditions achieved by different methods were finally compared and concluded to be in good agreement. Overall, the use of the new objective functions for MOPSO, combined with FEA, increased the maximum stable delamination crack length from 7 μm (obtained by a thermal residual stress criterion used by previous researchers) to 50 μm (using the new method). Therefore, FEA based on energy variation and MOPSO with the new objective functions were found to be applicable for optimisation with respect to interfacial delamination resistance.

THE INFLUENCE OF HYDRO BLASTING ON THE EN-DURANCE LIMIT OF SPECIMENS WITH A CUT UNDER BENDING AND STRETCHING-COMPRESSION

The hydro blasting influence on an endurance limit of cylindrical specimens with circular cuts of a semicircular profile of 0,3 mm radius under bending and stretching-compression in a case of symmetric cycle has been examined. Specimens of 10 mm diameter for fatigue tests were made of steels 30ХГСА, 12Х18Н10Т, ЭИ961,45 and aluminum alloys В93, Д16Т.The influence of surface hardening on an endurance limit of specimens with cuts was valuated by two criteria: residual stresses on the concentrator surface and the average integral residual stresses calculated through the parts dangerous section surface layer thickness equal the critical depth of a non-propagating fatigue crack. 
 On results of residual stresses and specimens with cuts endurance limits determination its been stated that coefficients of surface hardening influence on an endurance limit increase under bending and stretching-compression by two criteria are approximately equal. Besides, the coefficient of the influence by the average integral residual stresses criterion changes within essentially lesser limits than the coefficient of the influence by the residual stresses on the concentrator surface criterion. So the average integral residual stresses criterion should be used for the evaluation of a surface hardening influence on an endurance limit of parts with concentrators.
 On an example of specimens within and without peening in a dangerous section its been shown that peening doesnt influence the endurance limit of a surface hardened part. The compressive residual stresses only influence the endurance limit of these parts.

THE ESTIMATION OF ROLLER STRENGTHENING INFLUENCE ON THE ENDURANCE LIMIT OF SHAFTS WITH PRESSURIZED HUB

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 influence of initial radial deformations on the residual stresses distribution in the hardened layer

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.

Damage evolution and safety assessment of tunnel lining subjected to long-duration fire

Tunnel linings would suffer heavy structural damage or even collapse when exposed to a long-duration fire. The damage is greatly affected by heating time. In this paper, a theoretical method is suggested to investigate the thermo-mechanical behaviors of tunnel lining subjected to a long-duration fire loading. A 2D unsteady-state thermo-mechanical model is established to analyze the time-dependent temperature and stresses distributions of tunnel lining under fire. A modified RABT fire curve is employed to describe the tunnel fire development. By using Laplace Transform and series solving method for ordinary differential equations (ODE), the analytical solutions of time-dependent temperature and stresses are obtained and numerically verified. Based on the temperature criterion and the residual stress criterion, damage evolution of tunnel lining is graphically presented and discussed. According to the comparison results, the consistence of these two criteria is theoretically verified.

Residual stresses and fatigue resistance of toothed wheels

Residual stresses in the dangerous section of toothed wheels made of materials and according to practices accepted in aviation engine construction have been determined using a mechanical method. The influence of the technology of manufacturing of toothed wheels, thermo-chemical treatment, hardening and coating on the residual stresses has been examined. Current technologies of manufacturing toothed wheels lead to significant dispersion of residual stresses, especially after thermo-chemical treatment. Therefore, the results have been statistically processed for each batch of parts and the average values are shown on the residual stress diagrams. We demonstrate the possibility of determining residual stress distribution in the dangerous section of a wheel tooth by the initial deformations of the reference specimen, which makes it possible to keep the part under examination unimpaired. A plate made of the same material as the toothed wheel and hardened simultaneously with the part under examination was used as a reference specimen. The influence of residual stresses on the fatigue resistance of toothed wheels by the average integral residual stresses criterion that takes into account both the value of residual stresses and the nature of their distribution in the dangerous section of toothed wheels was examined.

Investigation of preliminary surface rolling influence on the fatigue resistance of threaded specimens

The influence of preliminary surface plastic deformation on the endurance limit of parts made of steels 40X and 30ХГСА with the thread М16х2 has been examined. The investigation has been carried out by the computational-experimental method using the results of determining residual stresses mechanically on the specimens cut out of smooth workpieces and by modeling threaded specimens using finite-elements models. The method of thermal elasticity has been used for the calculation of the strain-stress state in the PATRAN/NASTRAN environment, whereby the distribution of initial deformations in the hardened layer is replaced by the appropriate temperature field. The graphs of distribution of axial residual stresses across the thread roots are plotted on the basis of the calculation. The increment of the endurance limit for threaded parts has been predicted by the average integral residual stress criterion. The calculation results are compared with the experimental data of testing the specimens. The specimens made of 30ХГСА steel without a nut were tested under the symmetrical cycle according to the pure bending pattern, the specimens made of 40X steel with a nut were tested under the zero-to-tension positive cycle in the case of stretching. Non-propagating fatigue cracks have been found in the specimens that withstood the tests and were destroyed.

Estimation of residual stress influence on the low-cycle fatigue of threaded parts

The possibility of using the criterion of average integral residual stresses to estimate the cyclic life of threaded parts in the area of low-cycle fatigue is examined in the article. The peculiarities of fracture under high-cycle and low-cycle stresses are pointed out. The problems of using equations and criteria of linear mechanics in the low-cycle fatigue area are specified. These problems are mostly related to the origination of plastic deformation regions; the sizes of the latter may be significantly greater than those of the cracks. Technological factors affecting the origination and distribution of residual stresses are considered. It is noted that the diameter of the workpiece for thread rolling, heat treatment, the force and time of rolling are of the greatest importance. The connection between the number of cycles prior to fracture and the residual stress value, expressed in terms of the average integral residual stress criterion under the influence of different technological factors is illustrated. According to the results of low-cycle fatigue tests of threaded parts it has been shown that the dependence of the number of cycles prior to fracture on the value of the average integral residual stress criterion is approximated closely by equations of the quadratic form. The appropriate magnitudes of approximation reliability are not lower than 0.9163.

Assessing the influence of surface hardening on the endurance limit of specimens made of steel 40X using residual stresses of reference specimen

The possibility of the employment of reference specimens hardened simultaneously with the parts has been examined for the hydroblasting influence estimation on the parts with concentrators endurance limit on the example of hollow cylindrical parts made of steel 40 with circular cuts of semicircular profile with the radius 0,3 mm. The investigation has shown that the difference between residual stresses values found by calculating and experimental methods doesnt exceed 8% in smooth specimens, in specimens with cuts 6%. Under the hydroblasting influence on the endurance limit estimation in conditions of bending in the case of symmetric cycle for hollow cylindrical specimens made of steel 40Х with cut of radius 0,3 mm its been established that the employment of residual stresses distribution calculated by the initial deformations of reference specimen let predict the specimens endurance limit increase under stress concentration conditions to an approximation of 8%. It has been shown that its reasonable to use the average integral residual stresses criterion calculated through the dangerous section surface layer thickness equal the non-propagating fatigue crack critical depth for the prediction of the endurance limit increase of hardened by hydroblasting specimens made of steel 40 with stress concentrators.

Forecasting an increment in the parts’ endurance limit due to surface hardening

Rolling with various forces influence on the endurance limit of specimens made of steel 20 of 50 mm diameter with cuts of various radiuses and pressurized bush has been examined. The estimation of the surface hardening influence on the specimens endurance limit has been carried out using two criterions, namely: residual stresses on the dangerous section surface and the average integral residual stresses through the dangerous section thickness, equal the fatigue non-propagating crack critical depth. On base of carried out experiments its been established that the employment of the average integral residual stresses criterion is more rightful for the endurance limit prediction of surface hardened cylindrical specimens made of steel 20 with diameter 50 mm with cuts and pressurized bush taking into account the concentration degree. The residual stresses on the concentrator surface is not acceptable as a criterion for the endurance limit prediction of surface hardened specimens made of steel 20 with cuts and pressurized bush because the corresponding coefficient of the criterion influence on the endurance limit has a essential dispersion. Besides, the dependence of the fatigue non-propagating crack critical depth on the specimen (part) dangerous cross-section sizes has been confirmed.

Dependence of the endurance limit on the character of residual stresses distribution in the surface layer of hardened parts

The influence of the character of compressive residual stress distribution on the endurance limit of surfacehardened specimens made of various steels and alloys under bending has been examined. Specimens madeof ВНС40 and 38Х2МЮА steels with V-shaped notches were hardened by nitriding, foundation specimensmade of ВКС-5 alloy by cementation and ionic cementation, flat specimens made of ЭИ698ВД alloy by airshot-blasting. The influence of surface hardening on the endurance limit was assessed using two criterions,namely: residual stresses on the dangerous section surface and the average integral residual stresses. It was establishedthat the endurance limit of surface-hardened specimens (parts) is determined not by the value of compressiveresidual stresses on the surface but by the completeness of the diagram of the residual stress over the partsurface layer thickness on condition that the surface layer thickness is equal to the critical depth of the nonpropagatingfatigue crack. The average integral residual stress criterion calculated over the thickness of a surfacelayer of the dangerous section equal to the critical depth of the non-propagating fatigue crack gives a rather accurateestimation of the influence the character of compressive residual stress distribution has on the endurancelimit of hardened specimens (parts). In practice the estimation of the increment of surface- hardened specimens(parts) endurance limit by the criterion of residual stresses on the dangerous section surface may lead to a significanterror.

Forecasting the endurance limit of surface-hardened cylindrical parts made of steel 20 by the initial deformations of reference specimen

The possibility of forecasting the increment of endurance limit for solid and hollow cylindrical parts made of steel 20 with semicircular notches after outstripping superficial plastic deforming has been analyzed using the residual stresses (initial deformations) of a reference specimen hardened simultaneously with the part . It is established that the compressive residual stresses calculated in smooth parts by the initial deformations of the reference specimen differ insignificantly (less than 6%) from those found experimentally. The increments of endurance limits of hardened notched parts have been calculated by a well-known method using the average integral residual stresses criterion. Its established that the design values of endurance limit increments differ from the experimentally found ones by no more than 15%.

Influence of Residual Stresses on Product Quality on Cold Forming of Sheet Workpieces

The authors present the experimental and estimated technique of non-destructive method of X-ray diffractometry as well as the results of investigation of residual stresses on cold forming of metals. The article describes the results of estimation of axisymmetric part quality by the criterion of residual stresses when manufacturing them by multistage rotary forming of sheet workieces.

Effects of residual stresses on fatigue resistance in torsion with bending in the presence of stress concentrations

Fatigue-test results are given for torsion with bending in cylindrical steel 45 specimens having small semicircular profile notches and with and without residual stresses. The effects of hardening on the fatigue resistance are evaluated from a residual-stress criterion. The test data for the unhardened and hardened specimens are closely described by the equation of an ellipse, which enables one to express the margin coefficient in torsion with bending with allowance for the residual stresses.

Influence of cross sectional dimensions of surface strengthened specimens of D16T alloy on fatigue resistance under stress concentration conditions

The influence of cross sectional dimensions of solid and hollow strengthened cylindrical specimens of D16T alloy with stress raisers of semicircular profile on fatigue limit in loading by pure bending with rotation and transverse bending in a single plane is considered. For evaluation of the influence of strengthening on the fatigue limit of specimens with stress raisers a criterion of residual stresses taking into consideration the character of their distribution across the thickness of the surface layer and the scale factor is proposed. It is established that with a change in the diameter of the shot peened specimen from 10 to 40 mm the ratio of the increase in fatigue limit as the result of strengthening to the criterion of residual stresses changes within narrow limits and is an average of 0.36.