Imperial College London

Dr Catrin Mair Davies

Faculty of EngineeringDepartment of Mechanical Engineering

Reader in Structural Integrity of Alloys
 
 
 
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Contact

 

+44 (0)20 7594 7035catrin.davies

 
 
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Location

 

517UnknownSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

165 results found

Liu Y, El Chamaa S, Wenman MR, Davies CM, Dunne FPEet al., 2021, Hydrogen concentration and hydrides in Zircaloy-4 during cyclic thermomechanical loading, Acta Materialia, Vol: 221, Pages: 1-16, ISSN: 1359-6454

Hydride formation in Zircaloy-4 under cyclic thermomechanical loading has been investigated using characterized notched beam samples in four-point beam testing, and microstructurally-representative crystal plasticity modelling of the beam tests which incorporates an atomistically-informed equilibrium-state model for hydrogen concentration. The model provided the locations within the microstructure of high hydrogen content, above that required for saturation, hence predicting the anticipated locations of hydride observations in the experiments. The strain rate sensitivity of this alloy over the temperature range considered led to considerable intragranular slip and corresponding stress redistribution, and cyclic strain ratcheting leading to high hydrostatic stresses and in turn hydrogen concentrations, which explains the locations of experimentally observed hydride formation. The interstitial hydrogen interaction energy as well as the intragranular geometrically necessary dislocation density were shown to be important in controlling the spatial distributions of observed hydrides.

Journal article

Williams RJ, Davies CM, Hooper PA, 2021, In situ monitoring of the layer height in laser powder bed fusion, Material Design and Processing Communications, Vol: 3

In situ process monitoring has frequently been cited as an critical requirement in certifying the performance of laser powder bed fusion (LPBF) components for use in high integrity applications. Despite much development in addressing this need, little attention has been been paid to monitoring the layer thickness during the process. In this paper, a laser displacement sensor has been integrated into the build chamber of an LPBF machine, and the height of the top surface layer of a component has been monitored during a build. This has permitted the deposited layer thickness to be measured throughout the build, and the effect on this of a change in processing conditions is characterised. The thermal contraction of the top layer in between successive laser scans has also been evaluated. This demonstrates the potential of utilising laser displacement sensory as a process monitoring tool in LPBF and provides insightful data for implementation in detailed process models.

Journal article

Calvet T, Wang Y, Pham MS, Davies CMet al., 2021, Prediction of j-integrals at defects in W-9CR steel sandwich-type cooling pipes, ISSN: 0277-027X

Sandwich-type cooling pipes of the first wall of future fusion nuclear reactors (i.e. DEMO) will likely consist of tungsten brazed to a Reduced Activation Ferritic Martensitic (RAFM) steel. Under a high heat flux (HHF) (1-5 MW/m2) the mismatch in thermal expansion between tungsten and steel results in significant thermal stresses in the brazing region. These stresses can cause crack initiation and growth and thus compromise the structural integrity of such pipes. Finite element analyses have been performed on the brazed joints of a reference cooling assembly under HHF. Thermal stresses and resulting plastic strains were estimated for both the braze interlayer and parent materials. As images of brazed joints revealed, brazing processes are very likely to induce defects near the edges of the joints. A crack is therefore introduced in the brazed region where simulated stresses and strains are found to be the highest. Jintegrals were calculated for cracks growing from an edge to the center of the considered piping assembly. The results are discussed in relation to the current sandwich-type piping design of the DEMO reactor.

Conference paper

Williams RJ, Al-Lami J, Hooper PA, Pham M-S, Davies CMet al., 2021, Creep deformation and failure properties of 316 L stainless steel manufactured by laser powder bed fusion under multiaxial loading conditions, Additive Manufacturing, Vol: 37, Pages: 1-11, ISSN: 2214-8604

316 L stainless steel has long been used in high temperature applications. As a well-established laser powder bed fusion (LPBF) alloy, there are opportunities to utilise additive manufacturing in such applications. However, the creep behaviour of LPBF 316 L under multiaxial stress conditions must first be quantified before such opportunities are realised. Uniaxial and double notched bar creep tests have been performed and characterised using power-law relations to evaluate the creep strain and rupture properties of LPBF 316 L. The creep response was found to be anisotropic with specimen build orientation, with samples loaded perpendicular to the build direction (Horizontal) exhibiting 8 times faster minimum creep rates than samples built parallel to the build direction (Vertical) and significantly shorter rupture lives. This was mainly attributed to the columnar grain structure, which was aligned with the build direction of the LPBF samples. The multiaxial creep rupture controlling stress was determined and found to be a combination of the equivalent and max. principal stress. X-Ray CT measurements in selected samples illustrated that the samples were approximately 99.6% dense post-build and the quantity of damage post testing was determined. Optical and EBSD microstructural characterisation revealed intergranular creep damage present in the specimens, however rupture was ultimately trans-granular in nature and influenced by the presence and orientation of pre-existing processing defects relative to the sample build and loading direction.

Journal article

Williams RJ, Vecchiato F, Kelleher J, Wenman MR, Hooper PA, Davies CMet al., 2020, Effects of heat treatment on residual stresses in the laser powder bed fusion of 316L stainless steel: Finite element predictions and neutron diffraction measurements, Journal of Manufacturing Processes, Vol: 57, Pages: 641-653, ISSN: 1526-6125

Heat treatments are used in laser powder bed fusion (LPBF) to reduce residual stress and improve service life. In order to qualify components for service, the degree of stress relaxation under heat treatment must be known. In this work, the effect of heat treatment on residual stress (RS) in LPBF 316L stainless steel was studied. Finite element (FE) models were developed to predict the RS distribution in specimens in the as-built state and subjected to heat treatment. The models simulated the thermo-mechanical LPBF build process, sample removal from the build plate and creep stress relaxation effects from a 2 h heat treatment at 700 C. The predictions were validated by neutron diffraction measurements in as-built and heat treated samples, in both build orientations. Large tensile RS of around 450 MPa were predicted at the vertical sample's outer gauge surfaces, balanced by high compressive stresses of similar magnitude at the centre. The residual stresses in the horizontal sample were significantly lower, by around 40%. The influence of sample removal from the base plate on the RS distribution was found to be strongly dependent on the sample orientation and geometry. The heat treatment preserved the unique microstructure of the LPBF process and reduced the peak RS by around 10% in the vertical sample and 40% in the horizontal sample. The FE model predictions were found in good agreement with the experimental measurements, thus providing an effective tool for RS predictions in LPBF components and proving the effectiveness of the heat treatment on RS relaxation.

Journal article

Moghaddam BT, Hamedany AM, Taylor J, Mehmanparast A, Brennan F, Davies CM, Nikbin Ket al., 2020, Structural integrity assessment of floating offshore wind turbine support structures, OCEAN ENGINEERING, Vol: 208, ISSN: 0029-8018

Journal article

Ibrahim Y, Davies C, Maharaj C, Li Z, Dear J, Hooper Pet al., 2020, Post-yield performance of additive manufactured cellular lattice structures, Progress in Additive Manufacturing, Vol: 5, Pages: 211-220, ISSN: 2363-9512

In energy absorption applications, post-yield behaviour is important. Lattice structures, having low relative densities, are an attractive way to obtain effective material properties that differ greatly from that of the parent material. These properties can be controlled through the manipulation of the cellular geometry, a concept that has been made significantly more attainable through the use of additive manufacturing (AM). Lattice structures of various geometries were designed, additively manufactured and tested to assess their structural integrity as well as to investigate the effect of varying the cell geometry on the overall performance of the structures. Uniaxial tensile and compressive tests were carried out on bulk material AM samples made of 316L, followed by tests on the lattice structures. Finite element (FE) analysis was also carried out and the results compared to the experimental data. The FE simulations were able to accurately predict the elastic response of both structures; however, the post-yield behaviour did not closely match the experimental data due to inadequate beam contact resolution in the FE model. The FE model yield stress was also overestimated in the regular lattice due to the presence of manufacturing defects found only in the manufactured test samples. The stochastic structure, both experimentally and in the FE model, displayed a transition in the elastic stiffness from a lower to a higher stiffness in the elastic region. This is due to changing load paths within the lattice from the beams in contact with the compression platens to the rest of the structure. This phenomenon did not occur within the regular structure.

Journal article

Corcoran J, Davies CM, Cawley P, Nagy PBet al., 2020, A quasi-DC potential drop measurement system for materials testing, IEEE Transactions on Instrumentation and Measurement, Vol: 69, Pages: 1313-1326, ISSN: 0018-9456

Potential drop measurements are well established for use in materials testing and are commonly used for crack growth and strain monitoring. Traditionally, the experimenter has a choice between employing direct current (DC) or alternating current (AC), both of which have strengths and limitations. DC measurements are afflicted by competing spurious DC signals and therefore require large measurement currents (10’s or 100’s of amps) to improve the signal to noise ratio, which in turn leads to significant resistive Joule heating. AC measurements have superior noise performance due to utilisation of phase-sensitive detection and a lower spectral noise density, but are subject to the skin-effect and are therefore not well suited to high-accuracy scientific studies of ferromagnetic materials. In this work a quasi-DC monitoring system is presented which uses very low frequency (0.3-30 Hz) current which combines the positive attributes of both DC and AC while mitigating the negatives. Bespoke equipment has been developed that is capable of low-noise measurements in the demanding quasi-DC regime. A creep crack growth test and fatigue test are used to compare noise performance and measurement power against alternative DCPD equipment. The combination of the quasi-DC methodology and the specially designed electronics yields exceptionally low-noise measurements using typically 100-400 mA; at 400mA the quasi-DC system achieves a 13-fold improvement in signal to noise ratio compared to a 25A DC system. The reduction in measurement current from 25A to 400mA represents a ~3900 fold reduction in measurement power, effectively eliminating resistive heating and enabling much simpler experimental arrangements.

Journal article

Ronneberg T, Davies C, Hooper P, 2020, Revealing relationships between porosity, microstructure and mechanical properties of laser powder bed fusion 316L stainless steel through heat treatment, Materials and Design, Vol: 189, ISSN: 0264-1275

The understanding of relationships between processing, microstructure and mechanical properties in laser powder bed fusion is currently incomplete. Microstructure-property relations in 316L stainless steel are revealed in this study using isothermal heat treatments as an investigative tool. As-built material was heat treated to selectively remove microstructural features such as melt pool boundaries, microsegregations and the as-built grain structure to evaluate their influence on yield and failure behaviour. Anisotropic yield behaviour was found to be caused by microstructural features alone and not influenced by porosity. However, ductility and failure were dominated by lack of fusion porosity. The alignment of pores between tracks along layer boundaries was found to cause anisotropic ductility. Three strengthening mechanisms in as-built material were identified as grain boundaries, chemical segregation and dislocation density. Heat treatments were categorised into three regimes: recovery, homogenisation and annealing. The findings of this study show that the shape, size, orientation and distribution of pores are crucial parameters for evaluating the structural integrity of parts produced by laser powder bed fusion.

Journal article

Reali L, El Chamaa S, Balint DS, Davies CM, Wenman MRet al., 2020, Deformation and fracture of zirconium hydrides during the plastic straining of Zr-4, MRS ADVANCES, Vol: 5, Pages: 559-567, ISSN: 2059-8521

Journal article

Jones MD, Dean DW, Hughes D, Davies CMet al., 2020, A novel method for load line displacement rate partitioning in creep crack growth tests on Type 316H stainless steel, Engineering Fracture Mechanics, Vol: 223, Pages: 1-19, ISSN: 0013-7944

Characterising the creep crack growth behaviour of Type 316H stainless steel is vital in obatining accurate predictions for the lifetime of high temperature components, for example in UK advanced gas cooled reactors. The correlation between creep crack growth rates and the fracture mechanics parameter C*, considered to govern the crack growth process, is obtained from creep crack growth tests. The C* parameter is experimentally determined using an expression which requires knowledge of the load line displacement rate due to creep. Historically this has been calculated by subtracting values for the elastic and plastic contributions to the load line displacement, obtained from available solutions, from the total experimentally measured load line displacement. However, the solutions available to determine the plastic contribution rely on generating a power-law fit to uniaxial tensile data, which is difficult to accomplish accurately over a large stress range. In addition, these expressions cannot account for strain history effects during crack growth. Consequently the elastic and plastic contributions are often erroneously large and can even be in excess of the experimental total load line displacement. A novel technique has been proposed to provide improved estimates of the creep contribution to the load line displacement rates during creep crack growth tests. This technique employs finite element analysis that incorporates material specific uniaxial tensile test data to simulate crack growth in an experimental test. A single elastic-plastic-creep simulation is used to determine the separate elastic-plastic and creep contributions to the load line displacement, meaning that, unlike historic analyses, creep stress relaxation and strain history effects can now be accounted for. The results have demonstrated that advanced predictions of the creep contributions to the load line displacement can be obtained using this technique.

Journal article

Williams R, Ronneberg T, Piglione A, Jones C, Pham M-S, Davies C, Hooper Pet al., 2019, In-situ thermography for laser powder bed fusion: effects of layer temperature on porosity, microstructure and mechanical properties, Additive Manufacturing, Vol: 30, ISSN: 2214-8604

In laser powder bed fusion(LPBF)the surface layer temperature is continually changing throughout the build process. Variations in part geometry, scanned cross-section and number of parts all inffluence the thermal field within a build. Process parameters do not take these variations into account and this can result in increased porosity and differences in local microstructure and mechanical properties, undermining confidence in the structural integrity of a part. In this paper a wide-field in-situ infra-redimaging system is developed and calibrated to enable measurement of both solid and powder surface temperatures across the full powder bed. The influence of inter-layer cooling time is in-vestigated using a build scenario with cylindrical comp onents of differing heights. In-situ surface temperature data are acquired through out the build process and are compared to results from porosity, microstructure and mechanical property investigations. Changes in surface temperature of u to 200°C are attributed to variation in inter-layer cooling time and this is found to correlate with density and grain structure changes in the part. This work shows that these changes are significant and must be accounted for to improve the consistency and structural integrity of LPBF components.

Journal article

Sancho A, Cox M, Cartwright T, Davies C, Hooper P, Dear Jet al., 2019, An experimental methodology to characterise post-necking behaviour and quantify ductile damage accumulation in isotropic materials, International Journal of Solids and Structures, Vol: 167-177, Pages: 191-206, ISSN: 0020-7683

The development of ductile damage, that occurs beyond the point of necking in a tensile test, can be difficult to quantify. An experimental methodology has been developed to accurately characterise the post-necking deformation response of a material through continuous monitoring of the specimens shape up until rupture. By studying the evolution of the neck geometry, the correct values of the local stress and strain have been determined in samples of grade 304L stainless steel and C110 copper. Notched bar specimens of various notch acuities were examined enabling the effects of stress triaxiality on ductile fracture to be determined. The methodology developed has provided a robust framework for macroscopic measurements of ductile damage during the necking process. To characterise the material degradation process, the elastic modulus reduction method was employed on hourglass-shaped specimens of the same materials. Stiffness degradation was measured using a small gauge extensometer during uninterrupted tensile tests with partial elastic unloadings. A metallographic study was conducted on progressively damaged specimens in order to validate the macroscopic damage measurements. A new non-linear ductile damage accumulation law has been developed and calibrated, which provides an advanced representation of the experimental results, and a significant improvement compared to linear accumulation models frequently employed. This realistic modelling approach considers the degradation of the material when it has undergone severe plastic deformation, and provides a more accurate representation of the near failure behaviour by considering the effects of stress triaxiality. The methodology provides accurate data for damage model development and calibration, to improve the predictions of remnant life from ductile damage in engineering components.

Journal article

Zheng J-H, Pan R, Wimpory RC, Lin J, Li C, Davies CMet al., 2019, A novel manufacturing process and validated predictive model for high-strength and low-residual stresses in extra-large 7xxx panels, Materials and Design, Vol: 173, ISSN: 0264-1275

A novel manufacturing process, enabling the production of high quality (i.e. with low and controllable residual stress distributions and good mechanical properties) T-section 7xxx panels, has been established. This process provides a solution to residual stress induced distortion problems, which greatly concerns a range of industries and especially the aircraft industry. This process consists of three sequential steps — water quenching (WQ), cold rolling (CR) and constrained ageing (CA). The effectiveness of this process was experimentally verified, through applying this process to laboratory sized 7050 T-section panels. The RS was measured by neutron diffraction and X-ray techniques, in addition to deflections and hardness at each processing stage. An integrated Finite Element (FE) model, including all three steps, was developed to simulate this manufacturing process and predict both the RS and the final strength distributions. It has been concluded that this novel process can effectively reduce the residual stresses from ±300 MPa to within ±100 MPa and produce T-section panels with required mechanical properties (i.e. hardness: ~159 HV10). A cold rolling level of 1.5% was found most appropriate. The residual stress and yield strength distributions were accurately predicted by FE, providing a valuable prediction tool to process optimization for industrial applications.

Journal article

Pan R, Pirling T, Zheng J, Lin J, Davies CMet al., 2019, Quantification of thermal residual stresses relaxation in AA7xxx aluminium alloy through cold rolling, Journal of Materials Processing Technology, Vol: 264, Pages: 454-468, ISSN: 0924-0136

Residual stresses (RS) are often induced through quenching of aluminum alloys and present a potential risk of developing crack or distortion in subsequent manufacturing processes. Study of methods to minimise the RS in quenched components is of practical importance. In this paper, cold rolling (CR) has been carried out to remove the RS in quenched AA7050 blocks. The CR effect on relaxing RS in quenched AA7050 blocks has been evaluated via the neutron diffraction (ND), X-ray diffraction (XRD) and contour techniques. The results reveal that although CR transforms near-surface residual stresses from large compression to large tension along the rolling direction, it results in remarkable RS relief in the core part of the material. An integrated finite element model for RS evolution through the CR process was put forward and has been validated by the experimental results.

Journal article

El Chamaat S, Patel M, Wenman MR, Davies CMet al., 2019, MULTISCALE STRESS-DIFFUSION ANALYSIS OF NOTCH-TIP HYDROGEN PROFILES IN ZIRCALOY-4, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Ejaz M, Davies CM, 2019, TDFAD ANALYSIS OF CREEP CRACK INITIATION IN 0.5CMV/2.25CRMOV STEEL WELDMENTS, ASME Pressure Vessels and Piping Conference, Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Ejaz M, Ab Razak N, Morris A, Lockyer S, Davies CMet al., 2019, LONG TERM CREEP LIFE PREDICTION OF NEW AND SERVICE EXPOSED P91 STEEL, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Moghaddam BT, Hamedany AM, Mehmanparast A, Brennan F, Nikbin K, Davies CMet al., 2019, Numerical analysis of pitting corrosion fatigue in floating offshore wind turbine foundations, 3rd International Conference on Structural Integrity (ICSI), Publisher: ELSEVIER SCIENCE BV, Pages: 64-71, ISSN: 2452-3216

Conference paper

Sancho A, Cox MJ, Cartwright T, Hooper PA, Dear JP, Davies CMet al., 2019, Effects of strain rate and temperature on ductile damage of metals, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: Amer Soc Mechanical Engineers

Conference paper

Jones MD, Nikbin KM, Davies CM, 2019, LOAD LINE DISPLACEMENT PARTITIONING IN CREEP CRACK GROWTH ANALYSES OF 316H STAINLESS STEEL, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

O'Connor AN, Davies CM, Nikbin KM, 2019, FRACTURE TOUGHNESS OF DEFECTS ORIENTATED PARALLEL TO A DISSIMILAR METAL WELD BOUNDARY, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Khosla G, Balint D, Farrugia D, Davies CMet al., 2019, Toughness measurements of a Cr martensitic high alloy steel susceptible to clinking, Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, Vol: 233, Pages: 63-72, ISSN: 1464-4207

'Clinking’ is an audible fracture that occurs during the cool down and reheating of as-cast high alloy materials. When this process occurs, audible fracture can be heard and observed as large transverse cracks that propagate through large slabs. This causes high material losses and major disruption to processing operations. Given the fracture is known to be brittle, this research is aimed at developing a way to predict the onset of clinking through the application of fracture mechanics. Linear elastic and elastic–plastic fracture mechanics were both used to assess the fracture behaviour. The stress state during cool down and reheating was estimated through finite element analysis using a three-dimensional finite element model. Tensile tests were conducted to obtain the stress–strain characteristics to be used in the fracture analysis. Charpy tests were completed to assess the relative toughness dependent on temperature across the temperature range for which the high alloy steel is susceptible to clinking. Four C(T) specimens were tested at a room temperature. Despite showing little ductile crack propagation on the fracture surface, the fractured samples did not meet the Linear Elastic Fracture Mechanics (LEFM) validity criterion but did meet the Jcvalidity criterion. This allows a minimum Jcvalue of 118 N/mm to be attributed to the onset of unstable fracture. Conversion into a KJcgives 164MP√m, which gives a minimum critical crack length of 138 mm for the onset of brittle fracture. Charpy tests showed a pronounced increase in the energy for fracture between 20 ℃ and 300 ℃ which is in line with practical observations, where the onset of clinking is reduced with a higher reheat temperature.

Journal article

Davies CM, Zhou R, Withnell O, Williams R, Ronneberg T, Hooper PAet al., 2019, FRACTURE TOUGHNESS BEHAVIOUR OF 316L STAINLESS STEEL SAMPLES MANUFACTURED THROUGH SELECTIVE LASER MELTING, ASME Pressure Vessels and Piping Conference (PVP 2018), Publisher: AMER SOC MECHANICAL ENGINEERS

Conference paper

Ibrahim Y, Li Z, Davies C, Maharaj C, Dear J, Hooper Pet al., 2018, Acoustic resonance testing of additive manufactured lattice structure, Additive Manufacturing, Vol: 24, Pages: 566-576, ISSN: 2214-8604

Additive manufacturing (AM) allows engineers to design and manufacture complex weight saving lattice structures with relative ease. These structures, however, present a challenge for inspection. A non-destructive testing and evaluation method used to assess material properties and quality is the focus of this paper, namely acoustic resonance (AR) testing. For this research, AR testing was conducted on weight saving lattice structures (fine and coarse) manufactured by powder bed fusion. The suitability of AR testing was assessed through a combined approach of experimental testing and FE modelling. A sensitivity study was conducted on the FE model to quantify the influence of element coarseness on the resonant frequency prediction and this needs to be taken into account in the application and analysis of the technique. The analysis was extended to extract effective modulus values for the lattice structures and the solid materials from every detected overtone, allowing for multiple measurements from a single AR test without the need to carefully isolate the fundamental. The AR and FE modelling modulus of elasticity values were validated using specimens of known properties. There was fair agreement between the FE and compression test extracted values of effective modulus for the coarse lattice. For the fine lattice, there was agreement in the values of effective modulus extracted from AR, 3-point bend, and compression experimental tests carried out. It was found that loose powder fusing from AM resulted in the fine lattice structure having a higher density (at least 1.5 times greater) than calculated due to the effect of loose powder adhesion. This effect resulted in an increased stiffness of the fine lattice structure. AR can be used as a measure of determining loose powder adhesion and other unique structural characteristics resulting from AM.

Journal article

Sancho A, Cox MJ, Aldrich-Smith G, Cartwright T, Davies CM, Hooper PA, Dear JPet al., 2018, Experimental methodology for the measurement of plasticity on metals at high strain-rates, DYMAT 2018 - 12th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, Publisher: EDP Sciences, ISSN: 2101-6275

An experimental methodology has been developed for the tensile characterisation of ductile isotropic metals at high strain-rate. This study includes the region beyond plastic instability or necking, which is rarely analysed for conventional applications. The research explores an imaging technique used to track the geometry of the specimen during tensile tests and calculate true local values of stress and strain by applying Bridgman theory [1]. To improve the quality of the images taken at high strain-rate an in-situ high speed shadowgraph technique has been developed, and to obtain better results from the images a sub-pixel accuracy edge detection algorithm has been implemented. The technique has been applied to an austenitic stainless steel. Its tensile behaviour has been assessed by testing round samples at strain-rates ranging from quasi-static to ~103 s-1. The results obtained with the proposed methodology have been validated by comparison with more conventional techniques such as video-extensometer and digital image correlation in the pre-necking region and good performance even at the highest strain-rate tested has been proved.

Conference paper

Ahn J, He E, Chen L, Dear JP, Shao Z, Davies Cet al., 2018, In-situ micro-tensile testing of AA2024-T3 fibre laser welds with digital image correlation as a function of welding speed, International Journal of Lightweight Materials and Manufacture, Vol: 1, Pages: 179-188, ISSN: 2588-8404

In this paper, the influence of welding speed on tensile properties of AA2024-T3 fibre laser welds was investigated by monitoring the deformation behaviour during tensile loading. In-situ micro-tensile testing combined with a high-resolution optical microscope and DIC was used to measure strain distribution in narrow weld regions showing characteristics of fibre laser beam welding with limited metallurgical modifications. A chemical etching technique was used to generate a micro-scale random speckle pattern by revealing the weld microstructure. Such pattern enabled a sufficient spatial resolution of strain while keeping the weld seam visible during deformation. The results of microstructural and mechanical properties determined under numerous welding speeds indicated that increasing the welding speed led to the transition of weld pool shape from circular to elliptical to teardrop with a greater fraction of equiaxed dendrites. The weaker strength of the weld, as measured by local lower micro-hardness values, constrained significant plasticity development locally within the weld. Tensile tests revealed that increasing the welding speed resulted in greater yield strength and ultimate tensile strength, whereas, total elongation to failure dropped. The tensile properties improved with increasing welding speed as the fraction of equiaxed dendrites increased.

Journal article

Williams RJ, Hooper PA, Davies CM, 2018, Finite element prediction and validation of residual stress profiles in 316L samples manufactured by laser powder bed fusion, 22nd European Conference on Fracture (ECF) - Loading and Environmental Effects on Structural Integrity, Publisher: ELSEVIER SCIENCE BV, Pages: 1353-1358, ISSN: 2452-3216

Conference paper

Davies CM, Withnell O, Ronnerberg T, Williams R, Hooper PAet al., 2018, Fracture Analysis of 316L Steel Samples Manufactured by Selective Laser Melting, 22nd European Conference on Fracture (ECF) - Loading and Environmental Effects on Structural Integrity, Publisher: ELSEVIER SCIENCE BV, Pages: 1384-1389, ISSN: 2452-3216

Conference paper

Khosla G, Balint D, Farrugia D, Hole M, Davies CMet al., 2018, Analysis of an as-cast high Si slab to elucidate fundamental causes of the fracture mechanism: Clinking, 22nd European Conference on Fracture (ECF) - Loading and Environmental Effects on Structural Integrity, Publisher: ELSEVIER SCIENCE BV, Pages: 1447-1452, ISSN: 2452-3216

Conference paper

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