Brian Shaw

A numerical study of the residual stress pattern from single shot impacting on a metallic component

Shot peening is a process in which a stream of shot is blasted against an engineering component to generate a high compressive residual stress regime at the surface of the component. This paper describes a 3D finite element dynamic analysis of single shot impacting on a metallic component. The model is first validated against a published numerical study. A parametric study is conducted to investigate the effect of shot diameter, impact velocity, incident angle and component material properties on the resulting residual stress profile. Several meaningful conclusions can be drawn regarding the effect of shot diameter, impact velocity, incident angle and initial yield stress. The effect of strain-hardening parameter is more complex as it depends on the relative magnitude of the strain-hardening yield stress to the initial yield stress and the impact energy.

Magneto-Acoustic Emission and Magnetic Barkhausen Emission for Case Depth Measurement in En36 Gear Steel

There is a need in industry to supply safe, economical, and reliable techniques to characterize surface treatments such as case hardening and peening of steel components and structures, both at the manufacturing stage and in service. Magnetic Barkhausen emission (MBE) has proved successful for these tasks, but has severe limitations in terms of measurement depth of the technique and deeper treatments such as laser peening and case hardening often fall outside the scope of MBE inspection. The domain wall motion that generates MBE also causes a release of elastic energy known as magneto-acoustic emission (MAE), which has a much greater measurement depth, and so offers a complementary technique to extend the measurement depth for the characterization of surface treatments in steel. In this paper, comparative MBE and MAE results from case hardened En36 gear steels are presented in the form of signal profiles and correlations are drawn between MBE and MAE profile features and domain activity within the soft core and the case hardened layer. The results show that the overall amplitudes for both MBE and MAE exhibit a good correlation with case depth, but profile analysis for MAE is ambiguous, so possible interpretations of the MAE profile are discussed.

Martensite decay in micropitted gears

Abstract Metallographic examination performed on a number of micropitted gears has revealed microstructural features similar to those reported in the literature in fatigued bearings, namely, dark etching regions and white etching bands. In addition, a new type of fatigue-induced microstructural constituent was observed close to the surface below asperities referred to as the plastic deformation region. Finally, it is shown that the initiation and propagation of cracks leading to the formation of micropits are related to the phase transformations mentioned previously.

Analysis of Micro-Elastohydrodynamic Lubrication and Prediction of Surface Fatigue Damage in Micropitting Tests on Helical Gears

The paper describes results obtained from the micro-elastohydrodynamic lubrication (micro-EHL) modeling of the gear tooth contacts used in micropitting tests together with a contact fatigue and damage accumulation analysis of the surfaces involved. Tooth surface profiles were acquired from pairs of helical test gears and micro-EHL simulations were performed corresponding to surfaces that actually came into contact during the meshing cycle. Plane strain fatigue and damage accumulation analysis shows that the predicted damage is concentrated close to the tooth surfaces and this supports the view that micropitting arises from fatigue at the asperity contact level. A comparison of the micropitting performance of gears finish-ground by two alternative processes (generation-grinding and form-grinding) suggests that 3D “waviness” may be an important factor in explaining their different micropitting behavior.

High temperature failure envelopes for thermosetting composite pipes in water

Abstract This paper presents the results of an investigation of the biaxial stress–strain behaviour of filament wound glass fibre reinforced composite pipes exposed to high temperature water. Two matrix systems were investigated: cycloaliphatic amine cured epoxy resin; and siloxane modified phenolic alloy. Water absorption tests on pipe using the two systems at 95°C showed equilibrium moisture contents of 0.5 and 4.5%, respectively, saturation being achieved within seven days at this temperature in both cases. The axial moduli of the pipes were determined at temperatures up to 160°C, using a bending test. Reductions were observed in the T g of both systems in the water saturated condition. Biaxial loading tests were carried out on the two pipe systems at temperatures from 20 to 160°. The results are presented in the form of failure envelopes and stress–strain relationships under load. At the highest temperatures (above its T g ), significant weakening of the epoxy system was observed, especially in matrix dominated loading conditions. In contrast, the failure envelopes for the phenolic system showed remarkably little temperature influence.

The effect of the white layer on micro-pitting and surface contact fatigue failure of nitrided gears:

Abstract The effect of the ‘white layer’ in nitrided steel on micro-pitting of gears has been investigated by comparing the performance of case carburized and nitrided gears fabricated from modern, low-oxygen steels. It is shown that the white layer, produced during nitriding, imparts a high resistance to micro-pitting. Because surface contact fatigue is nucleated at micro-pits in low-oxygen steels, the resistance to micro-pitting also manifests itself in a higher fatigue resistance for the nitrided material.

Eddy current pulsed thermography for fatigue evaluation of gear

The pulsed eddy current (PEC) technique generates responses over a wide range of frequencies, containing more spectral coverage than traditional eddy current inspection. Eddy current pulsed thermography (ECPT), a newly developed non-destructive testing (NDT) technique, has advantages such as rapid inspection of a large area within a short time, high spatial resolution, high sensitivity and stand-off measurement distance. This paper investigates ECPT for the evaluation of gear fatigue tests. The paper proposes a statistical method based on single channel blind source separation to extract details of gear fatigue. The discussion of transient thermal distribution and patterns of fatigue contact surfaces as well as the non-contact surfaces have been reported. In addition, the measurement for gears with different cycles of fatigue tests by ECPTand the comparison results between ECPT with magnetic Barkhausen noise (MBN) have been evaluated. The comparison shows the competitive capability of ECPT in fatigue evaluation.

Magnetic Barkhausen emission measurements for evaluation of material properties in gears

The magnetic Barkhausen emission (MBE) technique is considered as a potential non-destructive evaluation (NDE) method for assessing material properties in case-hardened gears. For gear manufacturing industries, the evaluation of material properties such as tempering induced changes in hardness level and the associated microstuctural changes, variations in case-depth of hardened layer, grinding process induced alteration in microstructure, hardness and residual stress distributions are of primary importance in order to ensure the quality of gears during service. This paper presents an overview of different research and developmental studies carried out at Design Unit, Newcastle University on the MBE technique suitable for different applications in the evaluation of quality of gears.

The Effect of Superfinishing on the Contact Fatigue of Case Carburised Gears

The contact fatigue performance of two pairs of case carburised gears with either an as-ground or superfinished surface finish was studied. This comparison test was carried out using a back-to-back gear test rig. Test results showed that superfinished gears provided an enhanced contact fatigue resistance with only the development of minor scratches and light micropitting after running, while as-ground gears failed through a sequence of initial micropitting, progressive micropitting, macropitting and scuffing.

Monitoring the Progression of Micro-Pitting in Spur Geared Transmission Systems Using Online Health Monitoring Techniques

Micro-pitting is a fatigue effect that occurs in geared transmission systems due to high contact stress, and monitoring its progression is vital to prevent the eventual failure of the tooth flank. Parameter signature analysis has been successfully used to monitor bending fatigue failure and advanced phases of gear surface fatigue failure such as macro-pitting and scuffing. However, due to modern improvements in steel production the main cause of gear contact fatigue failure can be attributed to surface micro-pitting rather than sub-surface phenomena. Responding to the consequent demand to detect and monitor the progression of micro-pitting, this study experimentally evaluated the development of micro-pitting in spur gears using vibration and oil debris analysis. The paper presents the development of an online health monitoring system for use with back-to-back gear test rigs. The results validate the system capabilities in detecting early gear defects and reliably identifying the type of failure so that it can be used in predictive health monitoring (PHM) systems.