Publications
114 results found
Pham M-S, Dovgyy B, Hooper P, et al., 2020, The role of side-branching in microstructure development in laser powder-bed fusion, Nature Communications, Vol: 11, ISSN: 2041-1723
In-depth understanding of microstructure development is required to fabricate high quality products by additive manufacturing (i.e. 3D printing). Here we report the governing role of side-branching in the microstructure development of alloys by laser powder bed fusion. We show that perturbations on the sides of cells (or dendrites) facilitate crystals to change growth direction by side-branching along orthogonal directions in response to changes in local heat flux. While the continuous epitaxial growth is responsible for slender columnar grains confined to the centreline of melt pools, side-branching frequently happening on the sides of melt pools enables crystals to follow drastic changes in thermal gradient across adjacent melt pools, resulting in substantial broadening of grains. The variation of scan pattern can interrupt the vertical columnar microstructure, but promotes both in-layer and out-of-layer side-branching, in particular resulting in the helical growth of microstructure in a chessboard strategy with 67 rotation between layers.
Rolfe E, Arora H, Hooper PA, et al., 2020, Comparative assessment of hybrid composite sandwich panels under blast loading
The use of composite sandwich structures across multiple disciplines, including the naval sector, is ever increasing. A combination of high specific strength, corrosion resistance and low radar signature make composite sandwich structures an attractive material choice. However, the brittle behaviour of the composite skins results in overdesign of composite sandwich components, counteracting their weight saving benefits. Since naval vessels must withstand a range of loads including blast loading, representative materials need to be tested under real blast conditions in order to avoid unnecessary safety factors and overdesign. The research detailed here is concerned with full-scale air blast testing of two composite sandwich panels with different glass-fibre/carbon-fibre hybrid face-sheets. The panels were subjected to a 100 kg nitromethane charge at 15 m stand-off distance. High speed 3D digital image correlation was used to record the displacement of the rear skins of the sandwich panels during the blast event. Strain gauges were adhered to the front skins of the panels to enable comparison between the front and rear skins at certain locations. Overall the two sandwich panels demonstrated similar deflection and strain. Under blast loading the presence of both types of fibres is the key factor not the position of each fibre fabric layer.
Rolfe E, Arora H, Hooper PA, et al., 2020, Comparative assessment of hybrid composite sandwich panels under blast loading
© CCM 2020 - 18th European Conference on Composite Materials. All rights reserved. The use of composite sandwich structures across multiple disciplines, including the naval sector, is ever increasing. A combination of high specific strength, corrosion resistance and low radar signature make composite sandwich structures an attractive material choice. However, the brittle behaviour of the composite skins results in overdesign of composite sandwich components, counteracting their weight saving benefits. Since naval vessels must withstand a range of loads including blast loading, representative materials need to be tested under real blast conditions in order to avoid unnecessary safety factors and overdesign. The research detailed here is concerned with full-scale air blast testing of two composite sandwich panels with different glass-fibre/carbon-fibre hybrid face-sheets. The panels were subjected to a 100 kg nitromethane charge at 15 m stand-off distance. High speed 3D digital image correlation was used to record the displacement of the rear skins of the sandwich panels during the blast event. Strain gauges were adhered to the front skins of the panels to enable comparison between the front and rear skins at certain locations. Overall the two sandwich panels demonstrated similar deflection and strain. Under blast loading the presence of both types of fibres is the key factor not the position of each fibre fabric layer.
Davies CM, Sandmann P, Ronneberg T, et al., 2020, RESIDUAL STRESS MEASUREMENTS IN A 316L UNIAXIAL SAMPLES MANUFACTURED BY LASER POWDER BED FUSION, ASME Pressure Vessels and Piping Conference (PVP), Publisher: AMER SOC MECHANICAL ENGINEERS
Yavari R, Williams R, Cole K, et al., 2020, THERMAL MODELING IN METAL ADDITIVE MANUFACTURING USING GRAPH THEORY: EXPERIMENTAL VALIDATION WITH IN-SITU INFRARED THERMOGRAPHY DATA FROM LASER POWDER BED FUSION, 15th ASME International Manufacturing Science and Engineering Conference (MSEC), Publisher: AMER SOC MECHANICAL ENGINEERS
Williams R, Ronneberg T, Piglione A, et 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.
Sancho A, Cox M, Cartwright T, et 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.
Samieian M, Cormie D, Smith D, et al., 2019, On the bonding between glass and PVB in laminated glass, Engineering Fracture Mechanics, Vol: 214, Pages: 504-519, ISSN: 0013-7944
In blast protective design, laminated glass is used to facilitate the safety of building occupants. Laminated glass provides its safety through the maintenance of the bond between the glass and the interlayer, and also through the deformation of the interlayer. The amount of deformation is related to the stretching of the interlayer, which is related to the amount of adhesion between the glass and the interlayer. An experimental and modelling study has taken place on the bond between the glass and the interlayer at different testing rates and temperatures. Tensile tests on cracked laminated glass and pure PVB were carried out. These tests were coupled with fracture mechanics methods to calculate a bond fracture toughness. This bond fracture toughness was used to develop a finite element model to predict the separation between the glass and the interlayer. From the experimental studies it was found that the adhesion between the glass and the interlayer is temperature independent in the range of 20oC-60oC at a constant testing rate. In contrast, at a constant temperature the adhesion was found to be loading rate dependent. The finite element model developed showed good consistency with experimental data for a range of testing rates and temperatures.
Samieian M, Cormie D, Smith D, et al., 2019, Prediction of blast response in laminated glass, Engineering Structures, Vol: 188, Pages: 650-664, ISSN: 0141-0296
Laminated glass is often used in structures for protection against blast loads. The single-degree-of-freedom model has conventionally been used to design such structures and it continues to be widely in use today. The single-degree-of-freedom model includes mass and load transformation factors, which depend on the deflected shape of the structure. In this study, finite element models are used to derive the deflected shapes and transformation factors. The time-varying deflected shape history is taken into account in this analysis, as this is currently not included in other single-degree-of-freedom models. The analysis was conducted on a range of boundary conditions and aspect ratios along with different loading rates. For low-rate loading, the transformation factors were found not to vary during the deflected shape–time history. For high rate loading, however, the transformation factors were found to vary during the deflected shape–time history therefore requiring their inclusion in the single-degree-of-freedom design methods. These transformation factors were found to be insensitive to aspect ratios.
Whiteman G, Case S, Millett JCF, et al., 2019, Uniaxial compression of single crystal and polycrystalline tantalum, Materials Science and Engineering: A, Vol: 759, Pages: 70-77, ISSN: 0921-5093
A series of compression experiments characterising the elastic-plastic response of single crystal and polycrystalline tantalum from quasi-static to intermediate strain-rates (10−3 – 103 s−1) over a range of temperatures (233–438 K) are reported in this paper. The single crystal experiments show significant differences in the response of the three principle crystal orientations of tantalum in terms of yield, work hardening and ultimate deformed shapes. Modelling is undertaken using a dislocation mechanics based crystal plasticity finite element model giving insight into the underlying microscopic processes that govern the macroscopic response. The simulations show the importance of the dislocation mobility relations and laws governing the evolution of the mobile dislocation density for capturing the correct behaviours. The inclusion of the twinning/anti-twinning asymmetry is found to influence [100] orientation most strongly, and is shown to be critical for matching the relative yield strengths. In general the simulations are able to adequately match experimental trends although some specific details such as exact strain hardening evolution are not reproduced suggesting a more complex hardening model is required. 3D finite element simulations approximating the tests are also undertaken and are able to predict the final deformed sample shapes well once the twinning/anti-twinning asymmetry is included (particularly for the [100] orientation). The polycrystalline data in both as-received and cold rolled conditions shows the initial yield strength is highest and work hardening rate is lowest for the cold-rolled material due to the increase in mobile dislocation density caused by the prior work. The general behavioural trends with temperature and strain-rate of the polycrystalline materials are reproduced in the single crystal data however the specific form of stress versus strain curves are significantly different. This is discussed in terms of th
Sancho A, Cox MJ, Cartwright T, et 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
Davies CM, Zhou R, Withnell O, et 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
Ibrahim Y, Li Z, Davies C, et 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.
Del Linz P, Liang X, Hooper P, et al., 2018, A numerical method for predicting the deformation of crazed laminated windows under blast loading, Engineering Structures, Vol: 172, Pages: 29-40, ISSN: 0141-0296
The design of laminated glazing for blast resistance is significantly complicated by the post-crack behaviour of glass layers. In this research, a novel numerical method based on a semi-analytical energy model is proposed for the post-crack behaviour of crazed panes. To achieve this, the non-homogenous glass cracks patterns observed in literature experimental and analytical work was taken into consideration. It was assumed that, after the glass crazing, further deformations would occur in the cracked edge areas, whilst the central window surface would remain largely undeformed. Therefore, different internal work expressions were formulated for each zone and were then combined in the overall model. The resulting differential equation was then solved numerically. The results obtained were compared with data from four experimental full-scale blast tests for validation. Three of these blast tests (Tests 1 to 3) were presented previously (Hooper et al., 2012) on 1.5 x 1.2 m laminated glazing samples made up with two 3 mm glass layers and a central 1.52 mm PVB membrane, using a 15 and 30 kg charge masses (TNT equivalent) at 13-16 m stand-off. The fourth blast test (Test 4) was conducted on a larger 3.6 x 2.0 m pane of 13.52 mm thickness, using a 100 kg charge mass (TNT equivalent) at a 17 m stand-off. All blast tests employed the Digital Image Correlation (DIC) technique to obtain 3D out-of-plane deflections and strains. The proposed analytical method reproduced the experimental deflection profiles, with the best estimates obtained for the more severe loading cases. Reaction forces were also compared with experimental estimates. The predictive ability of the proposed method could permit more accurate designs to be produced rapidly, improving structures resistance to such loadings.
Sancho A, Cox MJ, Aldrich-Smith G, et 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.
Rolfe E, Kaboglu C, Quinn R, et al., 2018, High velocity impact and blast loading of composite sandwich panels with novel carbon and glass construction, Journal of Dynamic Behavior of Materials, Vol: 4, Pages: 359-372, ISSN: 2199-7446
This research investigates whether the layup order of the carbon-fibre/glass-fibre skins in hybrid composite sandwich panels has an effect on impact response. Composite sandwich panels with carbon-fibre/glass-fibre hybrid skins were subjected to impact at velocities of 75 ± 3 and 90 ± 3 m s−1. Measurements of the sandwich panels were made using high-speed 3D digital image correlation (DIC), and post-impact damage was assessed by sectioning the sandwich panels. It was concluded that the introduction of glass-fibre layers into carbon-fibre laminate skins reduces brittle failure compared to a sandwich panel with carbon-fibre reinforced polymer skins alone. Furthermore, if the impact surface is known, it would be beneficial to select an asymmetrical panel such as Hybrid-(GCFGC) utilising glass-fibre layers in compression and carbon-fibre layers in tension. This hybrid sandwich panel achieves a specific deflection of 0.322 mm kg−1 m2 and specific strain of 0.077% kg−1 m2 under an impact velocity of 75 ± 3 m s−1. However, if the impact surface is not known, selection of a panel with a symmetric yet more dispersed hybridisation would be effective. By distributing the different fibre layers more evenly within the skin, less surface and core damage is achieved. The distributed hybrid investigated in this research, Hybrid-(GCGFGCG), achieved a specific deflection of 0.394 mm kg−1 m2 and specific strain of 0.085% kg−1 m2 under an impact velocity of 75 ± 3 m s−1. Blast loading was performed on a large scale version of Hybrid-(GCFGC) and it exhibited a maximum deflection of 75 mm following a similar deflection profile to those observed for the impact experiments.
Rolfe E, Quinn R, Sancho A, et al., 2018, Blast resilience of composite sandwich panels with hybrid glass-fibre and carbon-fibre skins, Multiscale and Multidisciplinary Modeling, Experiments and Design, Vol: 1, Pages: 197-210, ISSN: 2520-8160
The development of composite materials through hybridisation is receiving a lot of interest; due to the multiple benefits, this may bring to many industries. These benefits include decreased brittle behaviour, which is an inherent weakness for composite materials, and the enhancement of mechanical properties due to the hybrid effect, such as tensile and flexural strength. The effect of implementing hybrid composites as skins on composite sandwich panels is not well understood under high strain rate loading, including blast loading. This paper investigates the blast resilience of two types of hybrid composite sandwich panel against a full-scale explosive charge. Two hybrid composite sandwich panels were mounted at a 15 m stand-off distance from a 100 kg nitromethane charge. The samples were designed to reveal whether the fabric layup order of the skins influences blast response. Deflection of the sandwich panels was recorded using high-speed 3D digital image correlation (DIC) during the blast. It was concluded that the combination of glass-fibre reinforced polymer (GFRP) and carbon-fibre reinforced polymer (CFRP) layers in hybrid laminate skins of sandwich panels decreases the normalised deflection compared to both GFRP and CFRP panels by up to 41 and 23%, respectively. The position of the glass-fibre and carbon-fibre layers does not appear to affect the sandwich panel deflection and strain. A finite element model has successfully been developed to predict the elastic response of a hybrid panel under air blast loading. The difference between the maximum central displacement of the experimental data and numerical simulation was ca. 5% for the hybrid panel evaluated.
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
Davies CM, Withnell O, Ronnerberg T, et 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
Hooper PA, 2018, Melt pool temperature and cooling rates in laser powder bed fusion, Additive Manufacturing, Vol: 22, Pages: 548-559, ISSN: 2214-8604
In laser powder bed fusion, melt pool dynamics and stability are driven by the temperature field in the melt pool. If the temperature field is unfavourable defects are likely to form. The localised and rapid heating and cooling in the process presents a challenge for the experimental methods used to measure temperature. As a result, understanding of these process fundamentals is limited. In this paper a method is developed that uses coaxial imaging with high-speed cameras to give both the spatial and temporal resolution necessary to resolve the surface temperature of the melt pool. A two wavelength imaging setup is used to account for changes in emissivity. Temperature fields are captured at 100 kHz with a resolution of 20 μm during the processing of a simple Ti6Al4V component. Thermal gradients in the range 5–20 K/μm and cooling rates in range 1–40 K/μs are measured. The results presented give new insight into the effect of parameters, geometry and scan path on the melt pool temperature and cooling rates. The method developed here provides a new tool to assist in optimising scan strategies and parameters, identifying the causes of defect prone locations and controlling cooling rates for local microstructure development.
Ghouse S, Babu S, Nai K, et al., 2018, The influence of laser parameters, scanning strategies and material on the fatigue strength of a stochastic porous structure, Additive Manufacturing, Vol: 22, Pages: 290-301, ISSN: 2214-8604
Additive manufactured (AM) porous materials behave quantitatively and qualitatively differently in fatigue than bulk materials, and the relationships normally used for the fatigue design of continuous bulk materials are not applicable to AM porous materials particularly for low stiffness applications.This study investigated how the manufacturing methods and the material used during powder bed fusion affects the compressive strength and high cycle fatigue strength of a stochastic porous material for a given stiffness. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing) and 4 materials. The materials investigated were two titanium alloys: commercially pure grade 2 (CP-Ti) and Ti6Al4V ELI, commercially pure tantalum (Ta) and a titanium-tantalum alloy (Ti-30Ta).The trends observed during fatigue testing for monolithic metals and statically for solid and porous AM materials were not always indicative of the high cycle fatigue behaviour of porous AM materials. Unlike their solid counterparts, porous tantalum and the titanium-tantalum alloy had the greatest fatigue strength for a given stiffness, 8% greater than CP-Ti and 19% greater than Ti6Al4V ELI. Optimisation of the laser parameters and scan strategies was found to also increase the fatigue strength for a given stiffness of porous AM materials by 7–8%.
Piglione A, Dovgyy B, Liu C, et al., 2018, Printability and microstructure of the CoCrFeMnNi high-entropy alloy fabricated by laser powder bed fusion, Materials Letters, Vol: 224, Pages: 22-25, ISSN: 0167-577X
The CoCrFeMnNi high-entropy alloy is a promising candidate for metal additive manufacturing. In this study, single-layer and multi-layer builds were produced by laser powder bed fusion to study microstructure formation in rapid cooling and its evolution during repeated metal deposition. CoCrFeMnNi showed good printability with high consolidation and uniform high hardness. It is shown that microstructure in the printed alloy is governed by epitaxial growth and competitive grain growth. As a consequence, a bi-directional scanning pattern without rotation in subsequent layers generates a dominant alternating sequence of two crystal orientations.
Williams RJ, Davies CM, Hooper PA, 2018, A pragmatic part scale model for residual stress and distortion prediction in powder bed fusion, Additive Manufacturing, Vol: 22, Pages: 416-425
Parts manufactured by laser powder bed fusion contain significant residual stress. This stress causes failures during the build process, distorts parts and limits in-service performance. A pragmatic finite element model of the build process is introduced here to predict residual stress in a computationally efficient manner. The part is divided into coarse sections which activate at the melting temperature in an order that imitates the build process. Temperature and stress in the part are calculated using a sequentially coupled thermomechanical analysis with temperature dependent material properties. The model is validated against two sets of experimental measurements: the first from a bridge component made from 316L stainless steel and the second from a cuboidal component made from Inconel 718. For the bridge component the simulated distortion is within 5% of the experimental measurement when modelled with a section height of 0.8 mm. This is 16 times larger than the 50 μm layer height in the experimental part. For the cuboid component the simulated distortion is within 10% of experimental measurement with a section height 10 times larger than the experiment layer height. These results show that simulation of every layer in the build process is not required to obtain accurate results, reducing computational effort and enabling the prediction of residual stress in larger components.
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Smith LC, Chapman DJ, Hooper PA, et al., 2018, On the Dynamic Response of Additively Manufactured 316L, 20th Biennial Conference of the Topical-Group of the American-Physical-Society (APS) on Shock Compression of Condensed Matter (SCCM), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Samieian MA, Cormie D, Smith D, et al., 2018, Temperature effects on laminated glass at high rate, International Journal of Impact Engineering, Vol: 111, Pages: 177-186, ISSN: 0734-743X
The load bearing capacity of a laminated glass pane changes with temperature. In blast protection, laminated glass panes with a Polyvinyl Butyral (PVB) interlayer are usually employed. The post-crack response of the laminated pane is determined by the interlayer material response and its bond to the glass plies. An experimental study has been performed to determine the effects of temperature on the post cracked response of laminated glass at a test rate of 1 m/s for PVB thicknesses of 0.76 mm, 1.52 mm and 2.28 mm. Tensile tests were carried out on single cracked and randomly cracked samples in a temperature range of 0 °C–60 °C. Photoelasticity observation and high speed video recording were used to capture the delamination in the single cracked tests. Competing mechanisms of PVB compliance and the adhesion between the glass and PVB, were revealed. The adhesion showed an increase at lower temperatures, but the compliance of the PVB interlayer was reduced. Based on the interlayer thickness range tested, the post-crack response of laminated glass is shown to be thickness dependent.
Rolfe E, Arora H, Hooper PA, et al., 2018, Hybrid composite sandwich panels under blast and impact loading, 12th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading (DYMAT), Publisher: E D P SCIENCES, ISSN: 2100-014X
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Rolfe E, Kelly M, Arora H, et al., 2018, Blast Performance and Damage Assessment of Composite Sandwich Structures, BLAST MITIGATION STRATEGIES IN MARINE COMPOSITE AND SANDWICH STRUCTURES, Editors: Gopalakrishnan, Rajapakse, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 209-225, ISBN: 978-981-10-7169-0
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Jiang J, Hooper P, Li N, et al., 2017, An integrated method for net-shape manufacturing components combining 3D additive manufacturing and compressive forming processes, International Conference on the Technology of Plasticity (ICTP 2017), Publisher: Elsevier, Pages: 1182-1187, ISSN: 1877-7058
Additive manufactured (AM) or 3D printed metallic components suffer poor and inconsistent mechanical properties due to the presence of a large number of micro-voids, residual stress and microstructure inhomogeneity. To overcome these problems, a new forming process has been proposed, which effectively combines AM and compressive forming. The aim of this study is to prove the feasibility of this newly proposed method by providing preliminary results. Thus, we compared the tensile performance of hot-forged additive manufactured stainless steel 316L samples to none-hot-forged additive manufactured ones. Significant improvement in mechanical properties has been found in the tensile tests as well hardness test. In addition, our EBSD characterized grain orientation maps at each stage of the process revealed the corresponding microstructure revolution which provides insights into underlying mechanistic.
Minh-Son P, Hooper P, 2017, Roles of Microstructures on Deformation Response of 316 Stainless Steel Made by 3D printing, 20th International ESAFORM Conference on Material Forming, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Ghouse S, Babu S, van Arkel R, et al., 2017, The influence of laser parameters and scanning strategies on the mechanical properties of a stochastic porous material, Materials & Design, Vol: 131, Pages: 498-508, ISSN: 0261-3069
Additive manufacturing enables architectured porous material design, but 3D-CAD modelling of these materials is prohibitively computationally expensive. This bottleneck can be removed using a line-based representation of porous materials instead, with strut thickness controlled by the supplied laser energy.This study investigated how laser energy and scan strategy affects strut thickness and mechanical strength of porous materials. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing), 2 porous architectures and 2 materials (Titanium, Stainless Steel), with strut thickness, density, modulus, mechanical strength and build time measured.Struts could be built successfully as low as 15° with a minimum diameter of 0.13 mm. Strut thickness was linearly related to the specific enthalpy delivered by the laser to the melt-pool. For a given stiffness, Titanium specimens built at low power/slow speed had a 10% higher strength than those built at high power/fast speed. The opposite was found in Stainless Steel. As specimen stiffness increased, the Contour Strategy produced samples with the highest strength:stiffness and strength:weight ratio. The Points strategy offered the fastest build time, 20% and 100% faster than the Contour and Pulsing strategies, respectively. This work highlights the importance of optimising build parameters to maximize mechanical performance.
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