Publications
188 results found
Wang W, Zhang R, Shirzadi AA, et al., 2024, Thermal cracking: Clarifying the effects of phases, voids and grains through characterisation and crystal plasticity modelling, Journal of the Mechanics and Physics of Solids, Vol: 186, ISSN: 0022-5096
Thermally-induced cracking typically occurs during the cooling stage of various manufacturing processes, and is commonly seen in multiphase or the joints of dissimilar materials due to mismatch in their thermo-mechanical properties, such as thermal expansion, elastic-plastic deformation and, in some cases, phase transformation. However, the underlying cracking mechanism associated with local microstructure is still elusive. To improve the mechanistic understanding of thermal cracking, this work uses the diffusion-bonded 9Cr-1Mo steel as an example to study the key microstructural variables, such as interfacial phases, voids, grain boundary migration and crystallographic orientations. Meanwhile, a temperature-dependent crystal plasticity model coupled with a cohesive zone model is developed to provide more insights into the thermal-induced stress distribution at the grain scale. It is found that the stress at the void-free boundary of martensite and ferrite is dominated by shear, and its magnitude is insufficient to nucleate cracks. Whereas voids at phase boundaries can induce significant tensile stress, resulting in cracking at the phase boundaries as well as diffusion-bonded interfaces. Also, the occurrence of interfacial grain boundary migration plays an important role in local stress distribution. These microstructure features and their evolution are experimentally observed and used to verify the developed crystal plasticity models. These findings enhance the understanding of the influence of microstructure features on thermal cracking and provide a guide to designing and fabricating the microstructure with improved thermal crack resistance in various manufacturing processes.
Piao Y, Balint DS, 2024, On the role of plastic relaxation in stress assisted grain boundary oxidation, Journal of the Mechanics and Physics of Solids, Vol: 185, ISSN: 0022-5096
The influence of plasticity on the high-temperature stress-assisted grain boundary oxidation of nickel-based superalloys used in applications such as turbine rotor discs is investigated using the method of discrete dislocation plasticity (DDP). The misfit stress fields of nib-shaped intrusions are captured by a continuous distribution of edge dislocations whose extra half planes represent the volumetric misfit of the oxide, which is implemented in a planar formulation of DDP by invoking the linear superposition principle. DDP simulations show that stresses generated by an intrusion several microns or more in size are large enough to generate dislocation pileups with associated stresses at the intrusion interface on the order of 1 GPa, which in turn lead to localized growth and morphology change of the intrusion by stress-assisted diffusion. This morphology change relaxes the compression stress inside the intrusion near the base, and therefore increases the fracture resistances of the intrusion. The effects of applied loading and background plasticity on the growth rate of the intrusion in defect-free and prestrained samples are predicted. It is found that applied tensile stress generally increases grain boundary oxidation, while in prestrained samples the enhancement of the intrusion growth rate by the applied load is insignificant due to dislocation pile-ups ahead of the oxidation process.
Langcaster JD, Balint DS, Wenman MR, 2024, Adapting U-Net for linear elastic stress estimation in polycrystal Zr microstructures, Mechanics of Materials, Vol: 191, ISSN: 0167-6636
A variant of the U-Net convolutional neural network architecture is proposed to estimate linear elastic compatibility stresses in α-Zr (hcp) polycrystalline grain structures. Training data was generated using VGrain software with a regularity α of 0.73 and uniform random orientation for the grain structures and ABAQUS to evaluate the stress fields using the finite element method. The initial dataset contains 200 samples with 20 held from training for validation. The network gives speedups of around 200x to 6000x using a CPU or GPU, with significant memory savings, compared to finite element analysis with a modest reduction in accuracy of up to 10%. Network performance is not correlated with grain structure regularity or texture, showing generalisation of the network beyond the training set to arbitrary Zr crystal structures. Performance when trained with 200 and 400 samples was measured, finding an improvement in accuracy of approximately 10% when the size of the dataset was doubled.
Wang W, Chan CK, Wang Y, et al., 2024, Fabricating carbon steel/Ti composites through forge-welding via in-situ interfacial reaction of Ni coating, Materials Science and Engineering: A, Vol: 893, ISSN: 0921-5093
Solid-state bonding is paramount in joining dissimilar materials, often combined with metal forming, such as forging, rolling and extrusion, to fabricate composites with a designed structure. Owing to its superior mechanical properties and low density, the carbon steel/Ti composite structure is attractive in automotive and aerospace industries but is difficult to fabricate due to the decarburization of carbon steel's faying surface. In this work, a carbon steel/Ti6Al4V composite structure was first fabricated via a forge-bonding method with the assistance of a Ni coating layer. Results show that the Ni layer on the faying surfaces precludes the decarburization of the steel and the growth of the TiC phase so as to improve the bonding quality. Meanwhile, the in-situ eutectic reaction between the Ni layer and β-Ti was observed. As a result, a seamless bonded interface with the total elimination of the Ni layer can be obtained. The bonding strength was examined to establish the relationship between bonding windows, microstructure and the resulting mechanical properties. An experimentally validated thermal-mechanical finite element model was also developed to understand the process-dependent interface evolution. This work opens a new avenue for fabricating carbon steel/Ti6Al4V composite, extending the flexibility of achieving complex structures by combining solid-state bonding with other metal-forming technologies.
Hortelano-Roig D, Kumar R, Balint DS, et al., 2023, Discrete dislocation dynamics simulations of 〈a〉-type prismatic loops in zirconium, International Journal of Plasticity, Vol: 171, ISSN: 0749-6419
Neutron irradiation of zirconium alloys in light water nuclear reactors generates nano-scale defects in the form of vacancy and interstitial 〈a〉-type prismatic loops which lie in prismatic planes of the sample. The dynamics of idealised conservative square 〈a〉-type prismatic loops have been investigated for a range of loop lengths in the framework of linear isotropic elasticity. Three-dimensional dislocation dynamics (DD) simulations of a dislocation-loop interaction have been performed to investigate the dislocation-loop interaction mechanism. For this purpose, a mobility law developed for hexagonally close-packed materials has been implemented and described in detail. Analytical and numerical calculations have been performed to obtain expressions for the restoring force and angular stability of prismatic loops. These analyses have been used to inform a 2.5D discrete dislocation plasticity (DDP) model in order to emulate realistic prismatic loop physics and improve irradiation hardening simulations. From the 2.5D DDP prismatic loop analyses, it has been observed that the stable angle of smaller sized loops is less sensitive to external stresses compared to that of larger loops, which may have implications for the mechanisms of irradiation hardening. Furthermore, initial 2.5D single-slip simulations predict that prismatic loops cause significantly elevated flow stress that increases with increasing loop density in accord with experimental observations, and that the restraining effect of the out-of-plane loop segments (the restoring force) plays an important role in the strengthening caused by loops.
Ebrahimi MT, Balint DS, Dini D, 2023, An analytical solution for multiple inclusions subject to a general applied thermal field, JOURNAL OF THERMAL STRESSES, Vol: 46, Pages: 1180-1198, ISSN: 0149-5739
Wang W, Balint DS, Shirzadi AA, et al., 2023, Imparted benefits on mechanical properties by achieving grain boundary migration across voids, Acta Materialia, Vol: 256, Pages: 1-12, ISSN: 1359-6454
Understanding the interaction of micro-voids and grain boundaries is critical to achieving superior mechanical properties for safety-critical parts. Micro-voids and grain boundaries may interact during advanced manufacturing processes such as sintering, additive manufacturing and diffusion bonding. Here, we show imparted benefits on mechanical properties by achieving grain boundary migration across voids. The micro-mechanisms and quantitative analysis of grain boundary migration on local deformation were studied by integrated in-situ EBSD/FSE and crystal plasticity finite element modelling. It is revealed that a migrated grain boundary does not alter the activated slip systems but precludes grain boundary-multislip interaction around interfacial voids to alleviate stress concentrations. The stress mitigation caused by grain boundary migration is almost the same as that caused by void closure under the example diffusion bonding thermal-mechanical process used in this study. This new understanding sheds light on the mechanistic link between GND hardening, grain boundary migration and the corresponding material tensile behaviour. It opens a new avenue for achieving superior mechanical properties for metallic parts with micro-defects such as those generated in diffusion-bonded, sintered and additive manufactured components.
Charalambides M, Taylor A, Young C, et al., 2023, A numerical model for predicting the time for crack initiation in wood panel paintings under low-cycle environmentally induced fatigue, Journal of Cultural Heritage, Vol: 61, Pages: 23-31, ISSN: 1296-2074
Determining the storage and display conditions for historical panel (wood) paintings requires a balance between ensuring the painting's preservation whilst also considering the energy consumption associated with climate control. The latter has become very important due to the need to lower the carbon footprint of museums and historical houses. In order to address this need, we have developed numerical models based on finite element analysis to simulate the initiation of two types of potential damage in panel paintings, namely interfacial and channelling cracks in the oil paint layer, under cyclically varying relative humidity. These models are based on our case study at Knole House (National Trust), Kent. Using known data for the past environment in which the paintings within the Brown Gallery at Knole House have been exposed, the ambient RH variation was approximated by three cycles, i.e., annual, biannual, and monthly varying cycles. Four RH cases, one containing all three cycles and each of the other three cases containing just two of the three cycles, were applied as boundary conditions to simplified geometries of the panel paintings in an effort to investigate the effects of the frequency and the amplitude of the variation on the possibility of cracking in the painting. The models need several material parameters as input which are not all available. Therefore, the study also includes some parametric studies to determine possible variations in the crack initiation. According to the model predictions, the channelling crack initiates slightly earlier than the interfacial crack. The crack initiation time in an uncontrolled environment (containing all three RH cycles) predicted by the model is approximately 120 years which empirically is a realistic estimate. Furthermore, the annual RH cycle (high amplitude and low frequency) has the most significant effect on the crack initiation. By removing the annual variation from the RH cycle, the initiation of both channelli
Xu Y, Balint D, Greiner C, et al., 2023, On the origin of plasticity-induced microstructure change under sliding contacts, Friction, Vol: 11, Pages: 473-488, ISSN: 2223-7704
Discrete dislocation plasticity (DDP) calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure. The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface, which can be quantitatively correlated to recent tribological experimental observations. Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads.
Marrey M, Huang D, Morscher GN, et al., 2023, ICME SIMULATION OF APS PROCESS AND DAMAGE IN CERAMIC COATINGS
This work shows an enhanced Integrated Computational Material Engineering (ICME) method for modeling of multi-material coating of Air Plasma Spray (APS) Ceramic Coating Process. ICME simulation of the APS process includes defects and the effect of defects (bending, curvature, delamination, and cracks), in-service analysis under Burner-Rig and furnace thermal loading conditions, and the effect of high temperature on Thermal Barrier Coatings (TBC) over the metallic substrate of dog bone specimens to demonstrate durability and damage tolerance (D&DT). To achieve this end, a multi-physics-based ICME methodology and virtual design of experiment (DOE) tools are developed to virtually generate multi-layered materials including high-temperature coatings for use in engine/aircraft high-temperature exhaust regions. The ICME innovation centers around: 1) Thermo-Physics Modeling (plasma, vapor, liquid, solid) to predict the material’s thermal profile, voids, densities, and thermal conductivities; 2) Multiscale Material Modeling of the top coat, bond coat, and substrate to predict material performance: a) temperature-dependent strength, stiffness, residual stresses and strains considering the effect of defects, and b) rumpling, surface waviness, and Thermal Growth Oxidation (TGO); 3) Structural Analysis and D&DT to predict coating and substrate failure evolution (i.e., delamination, oxidation, etc.) during thermo-mechanical in-service loading; and 4) Simulation of residual stress/strains due APS process. The simulation also shows rumpling and TGO growth have little effect on the as-built APS TBC specimen. Verification was performed using test data on TBC/Haynes230 systems under thermal loading. Tests and predictions were in close agreement. Both test and prediction showed an as-built specimen exhibiting bending during APS process and delamination during Burner-Rig testing.
Reali L, Balint DS, Wenman MR, 2022, Discrete dislocation modelling of ? hydrides in Zr: towards an understanding of the importance of interfacial stresses for crack initiation, JOURNAL OF NUCLEAR MATERIALS, Vol: 572, ISSN: 0022-3115
Mercer C, Speck T, Lee J, et al., 2022, Effects of geometry and boundary constraint on the stiffness and negative Poisson's ratio behaviour of auxetic metamaterials under quasi-static and impact loading, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, Vol: 169, ISSN: 0734-743X
Reali L, Balint DS, Wenman MR, 2022, Dislocation modelling of the plastic relaxation and thermal ratchetting induced by zirconium hydride precipitation, Journal of the Mechanics and Physics of Solids, Vol: 167, Pages: 104988-104988, ISSN: 0022-5096
The precipitation of hydrides in zirconium alloys is accompanied by a significant and anisotropic volumetric expansion. Previous literature quantified the misfit both theoretically and experimentally, but these values differ greatly; the experimental values are consistently lower. One possibility is that the experimental measurements include the effect of dislocations generated by the hydride, which relax the transformation stresses. To test this hypothesis, it is important to determine the stress field of a hydride and its associated dislocations, combined. A simple planar dislocation model was developed of the hydride—dislocation ensemble in -Zr. By capturing details of the dislocation structures given in the literature, it is shown in this study that including the interfacial dislocations largely reconciles the predicted and experimental values. Discrete dislocation plasticity is then used to model the diffuse plastic relaxation associated with hydride formation. The effects of plastic relaxation on the equilibrium hydrogen profile, hence the implications for subsequent hydride precipitation, are discussed. In particular, precipitation–dissolution cycles were simulated to calculate the magnitude of the residual hydrostatic tension, which is argued to be the primary cause of the “memory effect” for the re-precipitation of both and hydrides.
Wang W, Politis NJ, Wang Y, et al., 2022, Solid-state hot forge bonding of aluminium-steel bimetallic gears: Deformation mechanisms, microstructure and mechanical properties, International Journal of Machine Tools and Manufacture, Vol: 180, ISSN: 0890-6955
Solid-state dissimilar bi- or multi-metallic bonding is promising for achieving lightweight or multifunctional components in automotive, nuclear power and aerospace industries. To understand how to achieve a high-quality bonding interface between dissimilar materials, aluminium alloy (Al)–steel (Fe) bimetal gears manufactured under hot forge bonding were systematically investigated. In this work, comprehensive analyses of forge bonding mechanics, microstructure features, bonding interface behaviours and resulting mechanical properties were undertaken using ex/in-situ experiments and finite element modelling. The results revealed that the bonding behaviour and microstructure evolution were significantly affected by the mechanical property mismatch between the two dissimilar workpieces (AA6082 and E355). This mismatch could be effectively adjusted by setting different forging temperatures. The interfacial bonding strengths of AA6082 and E355, manufactured at low and high temperatures, were observed to be governed by interdiffusion and oxide particles, respectively. Balancing interdiffusion and oxide breaking appears to be key to achieving optimized interface strength for dissimilar bimetallic forge bonding technology.
Siu D, 2022, Characterising Plastic Deformation in Metallic Materials using Uniaxial Tensile Tests and Microstructural Investigations
Zheng Z, Li R, Zhan M, et al., 2022, The effect of strain rate asymmetry on the Bauschinger effect: A discrete dislocation plasticity analysis, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, Vol: 16, Pages: 1904-1918, ISSN: 2238-7854
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- Citations: 2
Abdi F, Achanta S, Baid H, et al., 2022, ICME COMPUTATIONAL FRAMEWORK FOR CERAMIC APS COATINGS
Integrated Computational Material Engineering (ICME) framework for Air Plasma Spray (APS) process for ceramic coatings is developed for optimizing multifunctional coatings and APS process for Thermal Barrier Coating (TBC) system. ICME simulations of APS process for TBC, the burner rig test and furnace test of TBC have been performed along with the test validation of ICME predictions for Yttria-stabilized-zirconia (YSZ) TBC with APS 8YSZ top coating with / NiCoCrAlY bond over Waspaloy substrate. ICME predictions for residual deflection of TBC due to thermal loads after APS process, burner rig test and furnace test are in close agreement with the test results. Both test and ICME predictions show the asmanufactured TBC specimens exhibit bending after APS process and bending after Burner Rig and Furnace testing. Finite element model for TBC specimens shows bending induced by APS process, its thermal gradients and residual thermal stress. Microscale thermal models for APS process, burner rig test and furnace test have been used to predict thermal processes, porosity and stresses. Rumpling analysis of TBC predicts rumpling amplitude due to thermal stresses and thermal oxidation growth (TGO) in TBC, thickness of TGO, bond stress during rumpling and stresses in TGO layer. Predictions for the thickness of TGO compares well with experimental data. Progressive damage analysis revealed that failure is due to tension and out of plane shear, delamination growth due to oxidation penetrating YSZ TBC from the bond.
Zhou W, Lin J, Balint D, et al., 2021, Clarification of the effect of temperature and strain rate on workpiece deformation behaviour in metal forming processes, International Journal of Machine Tools and Manufacture, Vol: 171, Pages: 1-6, ISSN: 0890-6955
In analysing metal forming processes the deformation mechanism map (elastic-plastic, elastic-viscoplastic, or creep type behaviour) for a particular process is commonly built solely in relation to temperature; which can be acceptable for a defined modest strain rate range. However, for a given temperature, if strain rate variation is large, the deformation mechanism could vary significantly. In this paper, a deformation mechanism map is proposed to clarify the interacting effect of deformation conditions (temperature and strain rate) on workpiece behaviour in metal forming processes. Rate type deformation equations which can be used to comprehensively model the effect of temperature and strain rate on deformation mechanism characteristics are elucidated and as examples, determined for Ti–6Al–4V and Al–Mg alloy.
Reali L, Balint DS, Sutton A, et al., 2021, Plastic relaxation and solute segregation to β-Nb second phase particles in Zr-Nb alloys: a discrete dislocation plasticity study, Journal of the Mechanics and Physics of Solids, Vol: 156, ISSN: 0022-5096
There is clear evidence in the literature that iron segregates to the interface of second phase particles (SPPs) in unirradiated Zr-Nb alloys, and that it does not do so in the presence of radiation damage. In this work, a discrete dislocation plasticity model is developed that takes into account the long-range stress field of the SPP interface. A simple analytical model is also outlined, providing an upper bound for estimating the amount of interstitial segregation. The model provides a possible mechanism to explain both the iron segregation to coherent SPPs and its subsequent loss after irradiation. Qualitatively, the model proved to be insensitive to variations of all geometrical and computational parameters, allowing for general conclusions to be drawn. The model suggests that the segregation originates from a tensile field of order 1 GPa induced by the dislocations generated during the plastic relaxation around the SPP. This leads to the six-fold increase in the iron concentration observed in experiments. In the model, the loss of SPP/matrix coherency after irradiation causes the dislocations to drift away from the interface, and the iron concentration is homogenised accordingly. The hydrogen concentration was also predicted and found to be about 50% higher than in the bulk zirconium matrix at room temperature. The computational framework is built to be fast, making possible a statistical analysis on over five hundred simulations for improved reliability of the predictions.Keywords: Discrete dislocation plasticity; Zr-Nb alloys; second phase particles; interfacial segregation.
Luan Q, Wang J, Huang Y, et al., 2021, How would the deformation bands affect recrystallization in pure aluminium?, Materials and Design, Vol: 209, ISSN: 0264-1275
Deformation bands (DBs), formed after plastic deformation, are known to have an impact on the recrystallization (RX) process. The exact mechanisms of how DBs influence grain nucleation and grain growth remain unclear. In this paper, deformed single and multicrystal pure aluminium samples are annealed to explore the likely effects of DBs on the grain nucleation and the subsequent grain growth. Regarding the prediction of the recrystallized (RXed) texture, it is noticeable that the orientations of nucleated grains nearby DB are originated from the orientation in DB. Regarding the nucleated positions, it is demonstrated that potential nucleation sites are more likely located in DBs in comparison with the initial grain boundary. Regarding the rate of RX, the number of nucleated grains is also predicted to have a strong positive correlation with the area fraction of DBs, which would consequently affect the kinetics of the grain growth in the deformed microstructure. All the above observations imply that the RX process is strongly controlled by the ensemble characteristics of DBs rather than the initial grain boundaries.
Xu Y, Balint D, Dini D, 2021, On the origin of plastic deformation and surface evolution in nano-fretting: a discrete dislocation plasticity analysis, Materials, Vol: 14, Pages: 1-14, ISSN: 1996-1944
Discrete dislocation plasticity (DDP) calculations were carried out to investigate a single-crystal response when subjected to nano-fretting loading conditions in its interaction with a rigid sinusoidal asperity. The effects of the contact size and preceding indentation on the surface stress and profile evolution due to nano-fretting were extensively investigated, with the aim to unravel the deformation mechanisms governing the response of materials subjected to nano-motion. The mechanistic drivers for the material’s permanent deformations and surface modifications were shown to be the dislocations’ collective motion and piling up underneath the contact. The analysis of surface and subsurface stresses and the profile evolution during sliding provides useful insight into damage and failure mechanisms of crystalline materials subject to nano-fretting; this can lead to improved strategies for the optimisation of material properties for better surface resistance under micro- and nano-scale contacts.
Charalambides M, Zhang R, Taylor A, et al., 2021, A numerical investigation of interfacial and channelling crack growth rates under low-cycle fatigue in bi-layer materials relevant to cultural heritage, Journal of Cultural Heritage, Vol: 49, Pages: 70-78, ISSN: 1296-2074
In traditional and modern paintings on canvas or wood, two crack types have been identified, these are: (i) delamination between two of the many layers and (ii) channelling through the paint layer, terminating at the paint-substrate interface. One cause of this damage can be attributed to environment-induced low-cycle fatigue, specifically through relative humidity and temperature fluctuations. We present novel 2D as well as 3D finite element models that, for the first time, identify the time for each type of crack to initiate under a variety of realistic relative humidity (RH) cycles, as well as the corresponding crack growth rates. The focus is on modern paintings that have some layers executed in alkyd paint, found to be a vulnerable layer in a relatively short period of time. The paintings are idealised as a two-layer construction with a visco-hyperelastic alkyd paint layer on a linear elastic (acrylic) primed canvas substrate. Cracks, both interfacial and channelling, are represented using cohesive elements. To simulate the damage caused by a relative humidity cycle, a fatigue damage parameter was incorporated in the traction-separation law using a user-defined field. It was found that channelling cracks initiate slightly earlier than interfacial cracks for all the environmental conditions studied. Specifically, for an RH cycle of 35%–90%, channelling cracks initiate at 2.2 years and grow at an accelerating rate, while the interfacial crack initiates at 2.6 years and grows at a stable rate of approximately 0.1 mm/year. Narrower RH cycles lead to longer crack initiation times, e.g. the channelling crack initiates at 13.9 years under 40%–65% RH, and when the RH cycle was further narrowed to 45%–55%, the initiation time increased to 86 years. Our models are applicable to other painted or coated cultural heritage objects and can be used to inform preservation and environmental control strategies.
Patel M, Reali L, Sutton AP, et al., 2021, A fast efficient multi-scale approach to modelling the development of hydride microstructures in zirconium alloys, COMPUTATIONAL MATERIALS SCIENCE, Vol: 190, ISSN: 0927-0256
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Xu Y, Ruebeling F, Balint DS, et al., 2021, On the origin of microstructural discontinuities in sliding contacts: a discrete dislocation plasticity analysis, International Journal of Plasticity, Vol: 138, Pages: 1-15, ISSN: 0749-6419
Two-dimensional discrete dislocation plasticity (DDP) calculations that simulate single crystal films bonded to a rigid substrate under sliding by a rigid sinusoid-shaped asperity are performed with various contact sizes. The contact between the thin film and the asperity is established by a preceding indentation and modelled using a cohesive zone method (CZM), whose behavior is governed by a traction-displacement relation. The emergence of microstructural changes observed in sliding tests has been interpreted as a localized lattice rotation band produced by the activity of dislocations underneath the contact. The depth of the lattice rotation band is predicted to be well commensurate with that observed in the corresponding tests. Furthermore, the dimension and magnitude of the lattice rotation band have been linked to the sliding distance and contact size. This research reveals the underpinning mechanisms for the microstructural changes observed in sliding tests by explicitly modelling the dislocation patterns and highly localized plastic deformation of materials under various indentation and sliding scenarios.
Mulakkal M, Castillo Castillo A, Taylor A, et al., 2021, Advancing mechanical recycling of multilayer plastics through finite element modelling and environmental policy, Resources, Conservation and Recycling, Vol: 166, ISSN: 0921-3449
Plastics are attracting negative publicity due to the scale of current pollution levels, yet they are irreplaceable in several applications such as food packaging, where different types of plastics are combined in laminate form to produce multilayered packaging (MLP) materials which extend the life of food items packaged within them. Increased plastic recycling is urgently needed, however for MLP it is particularly difficult. For the first time, this study combines engineering tools with environmental policy towards developing solutions for current single use plastic packaging. This study investigates recycling challenges for MLP and emerging melt-blending based mechanical recycling solutions as this is the main current method for material recovery of conventional plastics. Melt-blending of MLP with compatibilisers is explored, and the current lack of models addressing the influence of compatibilisers is identified. This gap in knowledge is addressed using novel engineering models based on the finite element (FE) micromechanical modelling technique to estimate the mechanical properties of recycled blends. Our model output is compared with experimental data available in literature and the good agreement highlights its predictive ability, providing a fast and cost-effective novel method for optimising recycled plastics. The policy aspect proposes the introduction of twenty policies based on mission-oriented innovation strategy to enable deployment of the recycling technologies studied whilst improving the viability of recycling of material currently not recycled. Implementation of these measures by the stakeholders will enable adoption of new MLP recycling techniques, create demand for recycled materials from MLP and incentivise MLP collection to mitigate pollution.
Aldegaither N, Sernicola G, Mesgarnejad A, et al., 2021, Fracture toughness of bone at the microscale, Acta Biomaterialia, Vol: 121, Pages: 475-483, ISSN: 1742-7061
Bone's hierarchical arrangement of collagen and mineral generates a confluence of toughening mechanisms acting at every length scale from the molecular to the macroscopic level. Molecular defects, disease, and age alter bone structure at different levels and diminish its fracture resistance. However, the inability to isolate and quantify the influence of specific features hampers our understanding and the development of new therapies. Here, we combine in situ micromechanical testing, transmission electron microscopy and phase-field modelling to quantify intrinsic deformation and toughening at the fibrillar level and unveil the critical role of fibril orientation on crack deflection. At this level dry bone is highly anisotropic, with fracture energies ranging between 5 and 30 J/m2 depending on the direction of crack propagation. These values are lower than previously calculated for dehydrated samples from large-scale tests. However, they still suggest a significant amount of energy dissipation. This approach provides a new tool to uncouple and quantify, from the bottom up, the roles played by the structural features and constituents of bone on fracture and how can they be affected by different pathologies. The methodology can be extended to support the rational development of new structural composites.
Reali L, Wenman MR, Sutton AP, et al., 2021, Plasticity of zirconium hydrides: a coupled edge and screw discrete dislocation model, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 147, ISSN: 0022-5096
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Bordas SPA, Balint DS, 2021, Advances in Applied Mechanics Preface, ADVANCES IN APPLIED MECHANICS, VOL 54, Editors: Bordas, Balint, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: IX-IX
Croteau J-F, Kulyadi EP, Kale C, et al., 2020, Effect of strain rate on tensile mechanical properties of high-purity niobium single crystals for SRF applications, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 797, ISSN: 0921-5093
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Zhou X, Shao Z, Pruncu CI, et al., 2020, A study on central crack formation in cross wedge rolling, Journal of Materials Processing Technology, Vol: 279, ISSN: 0924-0136
Cross wedge rolling (CWR) is an innovative roll forming process, used widely in the transportation industry. It has high production efficiency, consistent quality and efficient material usage. However, the continual occurrence of crack formation in the centre of the workpiece is a critical problem excluding the CWR technique from more safety-critical applications, in particular, aerospace components. The mechanisms of central fracture formation are still unclear because of a combination of complicated stress and strain states at various stages of CWR. Thus, the aim of this study is to understand the stress/strain distribution and evolution during the CWR process and identify the key variables which determine central crack formation. A comprehensive investigation was then conducted to simulate 27 experimental cases. The stress and strain distributions in the workpiece were evaluated by finite element analysis. Various damage models from literature were applied and compared. A new fracture criterion was proposed, which was able to successfully determine the central crack formation in all 27 experimental cases. This criterion can be applied in CWR tool and process design, and the enhanced understanding may enable the adoption of CWR by the aerospace industry.
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