Publications
179 results found
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.
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.
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.
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.
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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- Citations: 5
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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- Citations: 4
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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- Citations: 6
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.
Bhowmik A, Lee J, Adande S, et al., 2020, Investigating spatio-temporal deformation in single crystal Ni-based superalloys using in-situ diffraction experiments and modelling, Materialia, Vol: 9, Pages: 1-14, ISSN: 2589-1529
In this study, we perform a detailed analysis of room temperature deformation of a [100]–orientated singlecrystal Ni-based superalloy, CMSX-4 micropillar, using a combinatorial and complimentary characterisation approach of micro-Laue diffraction coupled with post-deformation microscopy and crystal plasticity modelling.Time-resolved micro-Laue data indicated that deformation was initiated by activation of multiple slip (after 5%engineering strain) which led to the generation of a plastic strain accumulation accompanied by a two-foldincrease in the dislocation density within the micropillar. Subsequent to that, slip occurred primarily on two systems (11̄1)[101] and (111)[1̄01] with the highest Schmid factor in the single crystal micropillar thereby resultingin little accumulation of unpaired GNDs during a major part of the loading cycle, upto 20% strain in this case.Finite element crystal plasticity modelling also showed good agreement with the experimental analyses, wherebysignificant strains were found to develop in the above slip systems with a localisation near the centre of themicropillar. Post-deformation transmission electron microscopy study confirmed that deformation was mediatedthrough a/2<110> dislocations on {111} planes in the 𝛾-phase, while high stress levels led to shearing of the 𝛾′precipitates by a/2<110> partials bounding an anti-phase boundary free to glide on the {111} planes. Duringthe deformation of the single crystal micropillar, independent rotations of the 𝛾 and 𝛾′ phases were quantified byspatially resolved post-deformation micro-Laue patterns. The degree of lattice rotation in the 𝛾-phase was higherthan that in the 𝛾′-phase.
Prastiti NG, Xu Y, Balint DS, et al., 2020, Discrete dislocation, crystal plasticity and experimental studies of fatigue crack nucleation in single-crystal nickel, International Journal of Plasticity, Vol: 126, Pages: 1-14, ISSN: 0749-6419
Dislocation configurational energy and stored energy densities are determined in discrete dislocation and crystal plasticity modelling respectively and assessed with respect to experiments on single crystal nickel fatigue crack nucleation. Direct comparisons between the three techniques are provided for two crystal orientation fatigue tests. These provide confirmation that both quantities correctly identify the sites of fatigue crack nucleation and that stored energy density is a reasonable approximation to the more rigorous dislocation configurational energy. GND density is shown to be important in locating crack nucleation sites because of its role in the local configurational energy density.
Bordas SPA, Balint DS, 2020, Advances in Applied Mechanics Preface, ADVANCES IN APPLIED MECHANICS, VOL 53, Editors: Bordas, Balint, Publisher: ELSEVIER ACADEMIC PRESS INC, Pages: IX-IX
Reali L, El Chamaa S, Balint DS, et 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
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- Citations: 1
Xu Y, Balint D, Dini D, 2019, A new hardness formula incorporating the effect of source density on indentation response: a discrete dislocation plasticity analysis, Surface and Coatings Technology, Vol: 374, Pages: 763-773, ISSN: 0257-8972
Planar discrete dislocation plasticity (DDP) calculations that simulate thin single crystal films bonded to a rigid substrate indented by a rigid wedge are performed for different values of film thickness and dislocation source density. As in prior studies, an indentation size effect (ISE) is observed when indentation depth is sufficiently small relative to the film thickness. Thedependence of the ISE on dislocation source density is quantified in this study, and a modified form of the scaling law for the dependence of hardness on indentation depth, first derived by Nix and Gao, is proposed, which is valid over the entire range of indentation depths and correlates the length scale parameter with the average dislocation source spacing. Nanoindentation experimental data from the literature are fitted using this formula, which further verifies the proposed scaling of indentation pressure on dislocation source density.
Wood J, Gauvin C, Young C, et al., 2019, Reconstruction of historical temperature and relative humidity cycles within Knole House, Kent, Journal of Cultural Heritage, Vol: 39, Pages: 212-220, ISSN: 1296-2074
It is essential for the preservation of cultural heritage that the effects of climate change are investigated. With this in mind, the daily temperature and relative humidity (RH) cycles within the Brown Gallery at Knole House, Kent, have been reconstructed for the period 1605 – 2015 enabling the study of low-cycle environmental fatigue on a set of 17th century panel paintings. By establishing a relationship between the temperature in the Brown Gallery and the Hadley Centre Central England Temperature (HadCET) dataset over a sixteen year period (2000 – 2015), it is possible to use the full HadCET dataset to obtain the daily minimum and maximum temperatures in the Brown Gallery for the period 1878 – 2015. Using a Fourier series to fit the periodic data it is then possible to extrapolate back to 1605. Furthermore, correction factors derived using the HadCET average daily temperature in the period 1772 – 1877 and average monthly temperature in the period 1659 – 1771 are applied to the temperature data to increase the model accuracy. The daily minimum and maximum RH for the period 1605 – 2015 are obtained using the Brown Gallery maximum and minimum temperatures respectively, and assuming that the daily dew point temperature at Knole is calculated by subtracting a monthly-dependent constant from the daily minimum temperature at Knole, thus enabling the calculation of the daily actual water vapour pressure of air. Changes in RH are a result of the daily temperature cycle changing the saturation vapour pressure of air in the gallery. This data is valuable as it enables a study of the effects of low-cycle fatigue on the 17th century panel paintings housed in the Brown Gallery at Knole House, Kent due to these temperature and relative humidity cycles. Furthermore, the method presented offers a technique that can be utilised to replicate the internal environment for any unheated monument building so that the effects of past and future temper
Zheng Z, Prastiti NG, Balint DS, et al., 2019, The dislocation configurational energy density in discrete dislocation plasticity, Journal of the Mechanics and Physics of Solids, Vol: 129, Pages: 39-60, ISSN: 0022-5096
Dislocation configurational energy is the term assigned to describe the elastically-stored energy associated with the interaction of dislocations and their structures. It is the energy which is over and above that from the summation of the dislocation line energies when considered isolated and non-interacting. It is therefore different to the free energy and the stored energy. This paper presents a formulation for its determination utilising discrete dislocation plasticity. The total geometrically necessary (GND) and statistically stored dislocation density mean free distance allows the configurational energy density to be determined, thus providing a length scale over which the configurational energy is stored. This quantity is assessed in polycrystals undergoing fatigue loading showing that clear microstructural locations, often associated with high GND density, become established at which the progressive, cyclic, increasing configurational energy occurs. A higher length scale crystal plasticity stored energy density has recently been introduced which attempts to capture local dislocation configurational energy density as an indicator of fatigue crack nucleation and growth. The former is compared and assessed against the dislocation configurational energy density in this paper.
Ebrahimi M, Balint D, Sutton A, et al., 2019, A discrete crack dynamics model of toughening in brittle polycrystalline material by crack deflection, Engineering Fracture Mechanics, Vol: 214, Pages: 95-111, ISSN: 0013-7944
This paper focuses on the study of the effect of the interfacial strength of grain boundaries and elliptical inclusions on crack path deflection. The method is developed to channel a crack into a toughening configuration (arrays of elliptical holes and inclusions are considered) in order to obtain the optimised microstructure required to enhance fracture toughness through different mechanisms. The proposed technique is shown to reproduce experimental crack propagation paths in various configurations and is capable of capturing the effect of that variation of the GB and the inclusion interfacial strength; it provides a powerful tool to understand the interplay between microstructural features and improve materials performance.
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