D.G. Hattingh

The Use of Combs for Evaluation of Strain-free References for Residual Strain Measurements by Neutron and Synchrotron X-ray Diffraction

The measurement of residual strain using diffraction techniques relies on the determination of a change in lattice parameter relative to a reference or “strain-free” lattice parameter. Therefore, o...

Intelligent machine agent architecture for adaptive control optimization of manufacturing processes

Intelligent agents have been earmarked as the key enabling technology to provide the flexibility required by modern, competitive, customer-orientated manufacturing environments. Rational agent behavior is of paramount importance when interacting with these environments to ensure significant losses are not incurred. To achieve rationality, intelligent agents must constantly balance technical (process) and economic (enterprise wide) trade-offs through co-operation, learning and autonomy. The research presented in this manuscript integrates methodological commonalities in intelligent manufacturing research and prognostics to design and evaluate a generic architecture for the core services of self-learning, rational, machining process regulation agents. The proposed architecture incorporates learning, flexibility and rational decision making through the integration of heterogeneous intelligent algorithms (i.e. neural networks and genetic algorithms) from fields such as machine learning, data mining and statistics. The architectures ability to perceive, learn and optimize is evaluated on a high-volume industrial gun drilling process.

Residual stresses, microstructure and tensile properties in Ti-6Al-4V friction stir welds

Abstract This paper reports the results of a systematic investigation of residual stresses as a function of welding speed in a set of Ti–6Al–4V friction stir welds. The investigation focuses on residual stress but links these data with microstructural information derived from micrographs and hardness measurements as well as mechanical testing results. Residual stresses were determined using energy dispersive synchrotron X-ray diffraction, which allows phase specific stresses to be distinguished. The data presented in this paper demonstrate that welds with high tensile properties can be obtained, which also have relatively low peak tensile residual stress values of ∼30% of the tensile strength. The data also show a clear correlation between heat input and the width of the residual stress profile.

Optimizing Friction Stir Welding via Statistical Design of Tool Geometry and Process Parameters

This article considers optimization procedures for friction stir welding (FSW) in 5083-H321 aluminum alloy, via control of weld process parameters and tool design modifications. It demonstrates the potential utility of the “force footprint” (FF) diagram in providing a real-time graphical user interface (GUI) for process optimization of FSW. Multiple force, torque, and temperature responses were recorded during FS welding using 24 different tool pin geometries, and these data were statistically analyzed to determine the relative influence of a number of combinations of important process and tool geometry parameters on tensile strength. Desirability profile charts are presented, which show the influence of seven key combinations of weld process variables on tensile strength. The model developed in this study allows the weld tensile strength to be predicted for other combinations of tool geometry and process parameters to fall within an average error of 13%. General guidelines for tool profile selection and the likelihood of influencing weld tensile strength are also provided.

Residual Stresses in Overlapping Friction Taper Stud Welds

This paper presents microstructural, hardness and residual strain information for solid-state welds in creep-resistant Cr-Mo steel, made using the new local damage repair technique offered by friction taper stud welding (FTSW). The technique is suitable for making single welds to repair, for example, localised creep damage but can also be extended to deal with planar defects through the use of overlapping welds. Neutron diffraction was used to measure residual strains at a number of positions along a series of 5 overlapping FTS welds.

Computer-aided process planning-an object oriented structure

Machining process planning is a complex process requiring a variety of knowledge of design and manufacturing. This paper proposes an object oriented structure for process planning in the environment of a flexible manufacturing cell.

Multiaxial fatigue of aluminium friction stir welded joints: preliminary results

The aim of the present research is to check the accuracy of the Modified Wohler Curve Method (MWCM) in estimating the fatigue strength of friction stir (FS) welded tubular joints of Al 6082-T6 subjected to in-phase and out-of-phase multiaxial fatigue loading. The welded samples being investigated were manufactured by equipping an MTS I-STIR process development system with a retracting tool that was specifically designed and optimised for this purpose. These specimens were tested under proportional and non-proportional tension and torsion, the effect of non-zero mean stresses being also investigated. The validation exercise carried out by using the generated experimental results allowed us to prove that the MWCM (applied in terms of nominal stresses) is highly accurate in predicting the fatigue strength of the tested FS welded joints, its usage resulting in estimates falling with the uniaxial and torsional calibration scatter bands.

An Experimental Procedure to Determine the Interaction between Applied Loads and Residual Stresses

This paper presents a novel experiment to quantify both the initial residual stress state in a specimen and its redistribution due to plasticity induced by in-situ loading. The rate of relaxation of the residual stress with respect to permanent deformation is a measure of the elastic follow-up associated with the residual stress field. Residual stress measurements were made using high energy dispersive X-ray diffraction. Digital image correlation, verified by strain gauges, was used to measure full-field deformation on the specimen. The specimen was loaded and unloaded in-situ incrementally to promote plasticity, allowing the relaxation rate of the residual stress to be quantified. An elastic follow-up factor was calculated for the residual stress field, that indicated loading conditions of the residual stress field between fixed-displacement and fixed-load.

Optimising Weld Process Conditions for Enhanced Fatigue Performance

This paper presents some ideas on incorporating output from advanced synchrotron and neutron scanning strain methods in improved assessment of the influence of weld process parameters on residual strains at welds and on their fatigue performance. It very briefly outlines two different cases involving synchrotron diffraction strain scanning of friction stir welds in a strain hardened aluminium alloy and neutron diffraction strain scanning of MIG welds in high strength steel.

Crack initiation and propagation paths in small diameter FSW 6082-T6 aluminium tubes under fatigue loading

This paper reports results of fatigue tests of friction stir welded (FSW) aluminium tubes. Relatively small 38 mm diameter tubes were used and hence an automated FSW process using a retracting tool was designed for this project, as the wall thickness of the aluminium tube was similar to the diameter of the FSW tool. This is a more complex joint geometry to weld than the more usual larger diameter tube reported in the literature. S-N fatigue testing was performed using load ratios of R = 0.1 and R = -1. Crack path analysis was performed using both low magnification stereo microscopy and scanning electron microscopy, in order to identify crack initiation sites and to determine the direction of crack propagation. Work is still in progress to follow the crack path through the various microstructural zones associated with the weld. A simple statistical analysis was used to characterize the most typical crack initiation site. This work forms part of a wider project directed at determining multiaxial fatigue design rules for small diameter 6082-T6 aluminium tubes that could be of use in the ground vehicle industry.