Residual stress in turbine disk materials, effect of low cycle fatigue

Les disques de turbo-réacteur fonctionnent à haute température et chargements élevés. Ils sont soumis à des déformations thermiques et mécaniques. Les contraintes résiduelles de compression sont introduites en surface par grenaillage. Durant le service, les contraintes appliquées sont réduite jusqu'à zéro ou passent en tension, cela est causé par la fatigue oligocyclique. La base de données FMA des contraintes résiduelles dans les disques en fonction du nombre de cycles, mise en place par FMA-PROTO, a montré une tendance linéaire. La pente de la droite dépend de la sévérité des conditions de fatigue et de service cumulés. Les courbes de Wöhler obtenues en flexion rotative ont montré une augmentation de la durée de vie pour les échantillons grenaillés pour les chargements appliqués faibles et aucun bénéfice pour les chargements appliqués élevés,Aircraft turbine engine disks operate at high cyclic loads. Thermal strain and mechanical strain are applied. Compressive residual stresses are introduced to the surface by shot peening. Applied stresses, when they accumulate cycles above yield will gradually cause the surface compressive residual stress to be reduced until the surface becomes residually stressed to zero or in tension. The FMA database of disk residual stress measurements versus cycles accumulated by PROTO-FMA on turbine disks has shown a general linear trend. The slope of the linear fit depends on the severity of the cumulative service conditions. The S/N curves obtained from rotating beam testing showed extended lifetime on shot peened specimens at lower applied loads and no benefit at higher loads because of the surface condition

Residual Stress Measurements Inside a Small Inner Diameter Hole at Low Bragg Angle Using X-Ray Diffraction Technique

Abstract. A new X-Ray diffraction (XRD) goniometer has been specially developed to nondestructively measure residual stress (RS) on the inner diameter (ID) of small holes in metal and ceramic components. The major advantage of this novel goniometer is its ability to perform RS measurements on the ID of small holes without the need to section the component, thus maintaining the integrity of the residual stress field inherent to the component of interest. This new patented XRD goniometer has been used on a wide variety of aerospace components on features such as holes in airframe/structural components, as well as fastener/bolt holes, air holes, and confined areas on rotating and non-rotating turbine engine components. In many instances, measurements can be performed at 2θ angles much lower than the widely accepted lower limit of approximately 130°. The selection of the actual Bragg angle used depends upon the material itself, the hole ID, and the thickness of the component. Results obtained indicate that the new goniometer can be used to measure RS on the ID of small holes with good accuracy and precision even at relatively low 2θ angles in the vicinity of 100°

Capacitive parameters and voltage surges in the winding of an asynchronous motor with power supply from a PWM converter

A method is proposed for calculating the capacitive parameters and voltage surges in the winding of an asynchronous motor with power supply from a frequency converter. Wave processes in an asynchronous motor with a short-circuited rotor are simulated on this basis. © 2005 by Allerton Press, In

The relationship between case depth and bending fatigue strength of gas carburized SAE 8620 steel

The fatigue performance of gas carburized SAE 8620 steel was evaluated as a function of case depth. To vary the case depths, different carburizing times were applied. The typical times were: 45 min, 3 and 5 h at the temperature of 940 °C. To cause failure in the rotating bending fatigue specimens, the applied load was chosen as the equivalent load at 106 cycles for the material when is subjected to bending fatigue. The characterization of the specimens was carried out using X-ray diffraction technique for stress measurement and retained austenite and optical metallographic examination. The fractured surfaces were cleaned in an ultrasonic bath and examined using scanning electron microscope (SEM) equipped with EDX to evaluate the crack initiation and growth characteristics of the materials in the core and carburized case regions of specimens. The results showed that the fatigue limit was associated with the microstructure, the case depth, the distribution of retained austenite, the depth of the internal oxidation and the compressive residual stresses near the surface. The bending fatigue strength of gas carburized specimens was showed to decrease with the increasing case depths caused by the increasing of internal oxidation and nonmartensitic transformation present at the surface. © 2006 Elsevier B.V. All rights reserved

The effect of high temperature gas carburizing on bending fatigue strength of SAE 8620 steel

The bending fatigue performance of high temperature gas carburized SAE 8620 steel was evaluated and compared to conventional temperature gas carburization. To vary the case depth, different carburizing times were applied. The typical times were: 3 and 5 h at a temperature of 940 °C and 1 and 2 h at a temperature of 980 °C. To cause failure in the rotating bending fatigue specimens, the applied load was chosen as the equivalent load at 106 cycles when the material is subjected to bending fatigue. The characterization of residual stress and percent retained austenite in the specimens was performed using X-ray diffraction techniques; optical metallographic examination was also carried out. The fracture surfaces were cleaned in an ultrasonic bath and examined using a scanning electron microscope (SEM) equipped with EDX to evaluate the crack initiation and growth characteristics of the materials in the core and carburized case regions of the specimens. The results indicate that the fatigue performance of the high temperature gas carburized specimens was relatively poor compared to the conventionally gas carburized specimens. © 2008 Elsevier Ltd. All rights reserved

Comparison of Residual Stress Measurement Techniques and Implementation Using X-Ray Diffraction

Abstract. Regardless of the particular residual stress (RS) measurement technique being used, all are based on the same basic principles when using x-ray diffraction (XRD). Every technique has both its advantages and disadvantages, many of which are well known to engineers and scientists however, some of the important "finer points" are unfortunately not widely discussed or known by those not well versed in the subject. This paper will try to bring to light many of these commonly misunderstood issues by comparing the different techniques and attempt to illuminate the associated problems a user may encounter when measurements become challenging i.e. when RS measurements are to be performed in tight grooves or on textured materials for example. In this study, different techniques including the: Cosα technique, MET (used in Psi, Omega, or Modified Psi mode) have been evaluated and tested on a variety of materials and geometries. Introduction RS measurements using XRD techniques were first performed as early as 1925 In this study, different techniques including the: Cosα technique, MET (used in Psi, Omega, or Modified Psi mode) will be evaluated and tested on a variety of materials and geometries. This paper will emphasize the different findings and the limitations associated with each of the techniques evaluated

The relationship between case depth and bending fatigue strength of gas carburized SAE 8620 steel

The fatigue performance of gas carburized SAE 8620 steel was evaluated as a function of case depth. To vary the case depths, different carburizing times were applied. The typical times were: 45 min, 3 and 5 h at the temperature of 940 °C. To cause failure in the rotating bending fatigue specimens, the applied load was chosen as the equivalent load at 106 cycles for the material when is subjected to bending fatigue. The characterization of the specimens was carried out using X-ray diffraction technique for stress measurement and retained austenite and optical metallographic examination. The fractured surfaces were cleaned in an ultrasonic bath and examined using scanning electron microscope (SEM) equipped with EDX to evaluate the crack initiation and growth characteristics of the materials in the core and carburized case regions of specimens. The results showed that the fatigue limit was associated with the microstructure, the case depth, the distribution of retained austenite, the depth of the internal oxidation and the compressive residual stresses near the surface. The bending fatigue strength of gas carburized specimens was showed to decrease with the increasing case depths caused by the increasing of internal oxidation and nonmartensitic transformation present at the surface. © 2006 Elsevier B.V. All rights reserved

strength of SAE 8620 steel

The bending fatigue performance of high temperature gas carburized SAE 8620 steel was evaluated and compared to conventional temperature gas carburization. To vary the case depth, different carburizing times were applied. The typical times were: 3 and 5 h at a temperature of 940 degrees C and 1 and 2 h at a temperature of 980 degrees C. To cause failure in the rotating bending fatigue specimens, the applied load was chosen as the equivalent load at 106 cycles when the material is subjected to bending fatigue. The characterization of residual stress and percent retained austenite in the specimens was performed using X-ray diffraction techniques; optical metallographic examination was also carried out. The fracture surfaces were cleaned in an ultrasonic bath and examined using a scanning electron microscope (SEM) equipped with EDX to evaluate the crack initiation and growth characteristics of the materials in the core and carburized case regions of the specimens. The results indicate that the fatigue performance of the high temperature gas carburized specimens was relatively poor compared to the conventionally gas carburized specimens. (C) 2008 Elsevier Ltd. All rights reserved

Interests of synchrotron radiation for internal stress analysis

The interest of the method of X-ray diffraction for residual stress measurement is in continuous progress due to the advances in theoretical research and the development of new equipment. Usually, the shift and broadening of a diffraction peak reveal respectively the macrostrain (or stress) and microstrain. The limits of the X-ray provided by classical tubes in laboratory are its low intensity, fixed wavelength and relatively poor optic and spectrum resolution. This paper is a review of the use and interest of the synchrotron radiation in internal stress or strain analysis