Imperial College London

ProfessorMariaCharalambides

Faculty of EngineeringDepartment of Mechanical Engineering

Professor of the Mechanics of Materials
 
 
 
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Contact

 

+44 (0)20 7594 7246m.charalambides Website

 
 
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Location

 

516City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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127 results found

Samaras G, Bikos D, Cann P, Masen M, Hardalupas Y, Vieira J, Hartmann C, Charalambides Met al., 2024, A multiscale finite element analysis model for predicting the effect of micro-aeration on the fragmentation of chocolate during the first bite, European Journal of Mechanics A: Solids, Vol: 104, ISSN: 0997-7538

The emerging need to reduce the calorific value of foods, while simultaneously improving the consumerperception drives the quest for developing new food structures that satisfy both criteria. Aiming to shedlight on the influence that micro-aeration has on the breakdown of chocolate during the early stages of theoral processing, this paper summarises the development of multi scale, in silico Finite Element (FE) modelsfor the first bite. A micro-mechanical analysis was first employed to predict the impact on the mechanicalproperties of chocolate at two microaeration levels, i.e. 𝑓 = 10vol% and 𝑓 = 15vol%. The estimated elastic,plastic and fracture properties from the micromechanical model were subsequently fed into a macroscopicsimulation of the first bite. Both micromechanical and the macromechanical models for the 10vol% and 15vol%porosity chocolate are compared to experimental data for validation purposes. The micromechanical modelsare compared to data from literature on mechanical testing of the same two chocolate materials whereas thefirst bite macromechanical model was compared to in vitro experimental data obtained in this study using a3D printed molar teeth test rig mounted to a mechanical tester. Finally, the particle size distribution of thefragmented chocolate during the first bite was estimated from the in silico model and compared to in vivoliterature data on the same chocolate materials and in vitro experimental data from this work. All comparisonsbetween the in silico models and the in vitro/in vivo data led to good agreement. Our modelling methodologyprovides a cost-efficient tool for the investigation of new food structures that reduce the calorific value whileenhancing the taste perception.

Journal article

Samaras G, Bikos D, Skamniotis C, Cann P, Masen M, Hardalupas Y, Vieira J, Hartmann C, Charalambides Met al., 2023, Experimental and computational models for simulating the oral breakdown of food due to the interaction with molar teeth during the first bite, Extreme Mechanics Letters, Vol: 62, Pages: 1-11, ISSN: 2352-4316

The first bite involves the structural breakdown of foods due to the interaction with teeth and is a crucial process in oral processing. Although in vitro experiments are useful in predicting the oral response of food, they do not facilitate a mechanistic understanding of the relationship between the intrinsic food mechanical properties and the food behaviour in the oral cavity. Computer simulations, on the other hand, allow for such links to be established, offering a promising design alternative that will reduce the need for time consuming and costly in vivo and in vitro trials. Developing virtual models of ductile fracture in soft materials, such as food, with random and non-predefined crack morphology imposes many challenges. One of the most important is to derive results that do not depend on numerical parameters, such as Finite Element (FE) mesh density, but only physical constants obtained through independent standard mechanical tests, such as fracture strain and/or critical energy release rate. We demonstrate here that this challenge can be overcome if a non-local damage approach is used within the FE framework. We develop a first bite FE modelling methodology that provides mesh independent results which are also in agreement with physical first bite experiments performed on chocolate. The model accounts for key features found in chocolate and a wide range of compliant media, such as rate dependent plasticity and pressure dependent fracture initiation strain. As a result, our computational methodology can prove valuable in studying food structure-function relationships that are essential in product development.

Journal article

Charalambides M, Taylor A, Young C, Zhang R, Balint D, Blades N, Barbera Det 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

Journal article

Bikos D, Samaras G, Cann P, Masen M, Hardalupas I, Vieira J, Hartmann C, Huthwaite P, Lan B, Charalambides Met al., 2023, Destructive and non-destructive mechanical characterisation of chocolate with different levels of porosity under various modes of deformation, Journal of Materials Science, Vol: 58, Pages: 5104-5127, ISSN: 0022-2461

Chocolate exhibits a complex material response under the varying mechanical loads present during oral processing. Mechanical properties such as Young’s modulus and fracture stress are linked to sensorial attributes such as hardness. Apart from this link with hardness perception, these mechanical properties are important input parameters towards developing a computational model to simulate the first bite. This study aims to determine the mechanical properties of chocolate with different levels of micro-aeration, 0–15%, under varying modes of deformation. Therefore, destructive mechanical experiments under tension, compression, and flexure loading are conducted to calculate the Young’s modulus, yield, and fracture stress of chocolate. The values of Young’s modulus are also confirmed by independent ultrasonic mechanical experiments. The results showed that differences up to 35% were observed amongst the Young’s modulus of chocolate for different mechanical experiments. This maximum difference was found to drop with increasing porosity and a negligible difference in the Young’s modulus measurements amongst the different mechanical experiments is observed for the 15% micro-aerated chocolate. This phenomenon is caused by micro-pores obstructing the microscopic inelastic movement occurring from the early stages of the material’s deformation. This work provides a deeper understanding of the mechanical behaviour of chocolate under different loading scenarios, which are relevant to the multiaxial loading during mastication, and the role of micro-aeration on the mechanical response of chocolate. This will further assist the food industry’s understanding of the design of chocolate products with controlled and/or improved sensory perception.

Journal article

Tan Z, Berry A, Charalambides M, Mijic A, Pearse W, Porter A, Ryan M, Shorten R, Stettler M, Tetley T, Wright S, Masen Met al., 2023, Tyre wear particles are toxic for us and the environment

This briefing paper discusses the current knowledge on the effects of tyre wear particles on our health and environment, highlights the need for an ambitious research agenda to build further understanding of the impacts on people and nature and develop solutions, and includes recommendations for policymakers.

Report

Bikos D, Samaras G, Charalambides M, Cann P, Masen M, Hartmann C, Vieira J, Sergis A, Hardalupas Iet al., 2023, A micromechanical based finite element model approach to accurately predict the effective thermal properties of micro-aerated chocolate, Innovative Food Science and Emerging Technologies, Vol: 83, ISSN: 1466-8564

Micro-aeration is a method to modify the sensorial attributes of chocolate but also affects the material properties of chocolate, which in turn, determine its material response during manufacturing and oral processes. This study aims to define the effect of micro-aeration on the thermal properties of chocolate by considering the changes of chocolate microstructure due to micro-aeration. Micro-aeration was found to alter the chocolate microstructure creating a layer of a third phase at the porous interfaces, which is argued to consist of cocoa butter of higher melting properties. A multiscale Finite Element Model is developed, which was confirmed by macroscale heat transfer measurements, to parametrically simulate the structural changes of micro-porous chocolates at the microscale level and estimate their effective properties, such as thermal conductivity and specific heat capacity. The developed multiscale computational model simulates the porous chocolate as a two-phase (chocolate- pores) or three-phase material (chocolate-cocoa butter layer- pores). The investigation identified a new, complex transient thermal mechanism that controls the behaviour of micro-aerated chocolate during melting and solidification. The results showed a maximum 13% reduction of keff and 15% increase of Cpeff with 15% micro-aeration resulting to a slower transient heat transfer through the micro-aerated chocolate. The reason is that the micro-aerated chocolate can store a larger amount of thermal energy than its solid counterpart. This effect slows down the transient heat transfer rate in the chocolate and modifies melting/solidification rate and impacts sensorial attributes during oral processing and cooling during manufacturing.

Journal article

Iqbal M, Zhang R, Ryan P, Lewis D, Connors S, Charalambides Met al., 2022, Mechanical characterisation and cohesive law calibration for a nitrocellulose based - cyclotetramethylene tetranitramine (HMX) polymer bonded explosive, Experimental Mechanics, Vol: 63, Pages: 97-113, ISSN: 0014-4851

Background: Mechanical characterisation of polymer bonded explosives (PBXs) is crucial for their safe handling during storage and transportation. At temperatures higher than the binder's glass transition temperature, fracture is caused predominantly by interface debonding between the binder and explosive crystals. Interfacial friction between debonded crystals can lead to accidental detonation of the PBX material, even under a very small external load. Cohesive zone laws can describe this interfacial debonding. Objective: This study aims to experimentally calibrate the interfacial cohesive zone parameters of a nitrocellulose based - cyclotetramethylene tetranitramine (HMX) PBX, a particulate composite with a 88% volume fraction of crystals. Methods: Compact tension fracture tests, coupled with Digital Image Correlation (DIC) were used to capture the strain fields around the crack tip. The experimental data were used in conjunction with an extended Mori-Tanaka method considering the effect of interfacial debonding. Results: The cohesive zone parameters were successfully calibrated and were found to be crosshead rate independent. The values of the critical traction σ_int^max and interfacial energy release rate, γ_if, dropped significantly with increasing temperature. The experimental method followed in this study is generic, and it can be employed to extract the cohesive zone parameters characterising the interface behaviour between the filler and matrix in other particulate filled, polymer composite materials. Conclusions: Cohesive zone properties can be experimentally determined to provide inputs in micromechanical simulations linking the microstructure of the PBX composite to its macroscopic response as well as enabling the estimation of hot spot formation at debonded crystal interfaces.

Journal article

Charalambides M, 2022, Modelling deformation and flow of food during oral and gastric processing, Science Talks, Vol: 3, Pages: 100069-100069, ISSN: 2772-5693

The breakdown of food structure in the oral cavity influences textural perception, flavour release and consumer preference. It also marks the beginning of a complex chain of events within the digestive tract which can drastically affect the metabolism and health of individuals. In this talk, I will summarise our findings related to the effect of micro-aeration on the oral process of chocolate, using a multidisciplinary approach considering mechanics, thermal analysis, rheology and tribology, mimicking the various stages that food is subjected to in the oral process. In addition I will also present the development of preliminary numerical models that can simulate food flow in the gastric process as well as future plans to extend the modelling capability towards more realistic conditions.

Journal article

Jebalia I, Kristiawan M, Charalambides MN, Humphry-Baker S, Valle GD, Guessasma Set al., 2022, Microstructure and local mechanical properties of pea starch / protein composites, Composites Part C: Open Access, Vol: 8, Pages: 100272-100272, ISSN: 2666-6820

Biopolymer composites based on pea starch-protein blends and pea flour are processed using extrusion at various levels of specific mechanical energy (SME). Their morphology was a continuous matrix phase of starch with embedded protein particles, as revealed by Confocal Laser Scanning Microscopy (CLSM). The motivation is to correlate the local Young's modulus (E) in starch and protein phases, as well as their interphase, through nanoindentation tests to macroscopic three-point bending testing results of starch-protein composites. The differences between E of starch and protein phases and interphase were significant and their values were found to vary in the ranges of 4.2–7, 3–6.9 and 4–6.9 GPa, respectively. The local E can be tuned by the protein content and composite morphology, the latter depending on the level of transformation of the biopolymers during extrusion (SME). Pea flour composites have larger modulus values, which can be attributed to the presence of fibres.

Journal article

Bikos D, Samaras G, Charalambides M, Cann P, Masen M, Hartmann C, Vieira J, Sergis A, Hardalupas Yet al., 2022, Experimental and numerical evaluation of the effect of micro-aeration on the thermal properties of chocolate, Food and Function, Vol: 13, Pages: 4993-5010, ISSN: 2042-6496

Thermal properties, such as thermal conductivity, specific heat capacity and latent heat, influence the melting and solidification of chocolate. The accurate prediction of these properties for micro-aerated chocolate products with varying levels of porosity ranging from 0% to 15% is beneficial for understanding and control of heat transfer mechanisms during chocolate manufacturing and food oral processing. The former process is important for the final quality of chocolate and the latter is associated with sensorial attributes, such as grittiness, melting time and flavour. This study proposes a novel multiscale Finite Element Model to accurately predict the temporal and spatial evolution of temperature across chocolate samples. The model is evaluated via heat transfer experiments at temperatures varying from 16 °C to 45 °C. Both experimental and numerical results suggest that the rate of heat transfer within the micro-aerated chocolate is reduced by 7% when the 15% micro-aerated chocolate is compared to its solid counterpart. More specifically, on average, the thermal conductivity decreased by 20% and specific heat capacity increased by 10% for 15% micro-aeration, suggesting that micro-pores act as thermal barriers to heat flow. The latter trend is unexpected for porous materials and thus the presence of a third phase at the pore’s interface is proposed which might store thermal energy leading to a delayed release to the chocolate system. The developed multiscale numerical model provides a design tool to create pore structures in chocolate with optimum melting or solidifying response.

Journal article

Barbera D, Young C, Charalambides M, Taylor AC, Zhang Ret al., 2022, A methodology for the use of alkyd paint in thermally aged easel painting reconstructions for mechanical testing, Journal of Cultural Heritage, Vol: 55, Pages: 237-244, ISSN: 1296-2074

For the preservation of painted cultural heritage on wooden substrates, it is important to understand the fracture mechanisms in the multilayer system of which they are constructed and how the environment plays a role in the composites’ physical properties. Past research has investigated the material response of each constituent layer but much more needs to be done to represent the heterogeneous composite structure of easel paintings. In recent years fracture mechanics concepts have been applied to glue and glue/chalk multilayers. However, few experiments have been conducted on multilayers that include oil paint, due to its very long, and impractical drying time, which can be a few years up to decades depending on the type of study. The paper presents a methodology for the use of thermally aged alkyd paint in easel painting reconstructions for mechanical testing, specifically as a substitute for naturally aged traditional linseed oil paint. Elastic and failure properties of the paint have been obtained from environmentally-controlled tensile tests on thin free-film samples. To obtain the characteristic properties of increased elastic modulus and reduced ductility, a thermal ageing protocol has been experimentally developed. The results are compared with data from the published literature, theoretical models and with 30-year-old samples of cold-pressed linseed oil lead white paint tested within this research work. The final methodology provides the research community with a viable way to produce samples that can be used to understand the behaviour of a (simplified) but complete multilayer system.

Journal article

Zhang R, Mohammed IK, Taylor AC, Charalambides MNet al., 2022, A microstructure image-based numerical model for predicting the fracture toughness of alumina trihydrate (ATH) filled poly(methyl methacrylate) (PMMA) composites, Composites Part B: Engineering, Vol: 232, Pages: 109632-109632, ISSN: 1359-8368

A novel finite element model is proposed here for predicting the fracture toughness using real microstructuralimages and accounting for several parameters that can affect the crack propagation such as filler content, particleshape, particle agglomeration and particle debonding. The damage energy prior to the catastrophic failure of thewhole microstructure is taken as the energy required for crack initiation, and the fracture toughness is calculatedusing the concept of a critical crack size. The predictions agree well with the measured values of the criticalenergy release rate at 20 ◦C as a function of both volume fraction and mean particle size. In addition, a para-metric study showed that an increase in interfacial cohesive energy leads to higher fracture energies at 60 ◦C. Theproposed methodology shows great potential and can be widely applied to other particulate composites, enablingindustry to cost-effectively develop tougher, hence safer and more durable, particulate composites

Journal article

Kansou K, Laurier W, Charalambides MN, Della-Valle G, Djekic I, Feyissa AH, Marra F, Thomopoulos R, Bredeweg Bet al., 2022, Food modelling strategies and approaches for knowledge transfer, Trends in Food Science and Technology, Vol: 120, Pages: 363-373, ISSN: 0924-2244

BackgroundScientific software incorporates models that capture fundamental domain knowledge. This software is becoming increasingly more relevant as an instrument for food research. However, scientific software is currently hardly shared among and (re-)used by stakeholders in the food domain, which hampers effective dissemination of knowledge, i.e. knowledge transfer.Scope and approachThis paper reviews selected approaches, best practices, hurdles and limitations regarding knowledge transfer via software and the mathematical models embedded in it to provide points of reference for the food community.Key findings and conclusionsThe paper focusses on three aspects. Firstly, the publication of digital objects on the web, which offers valorisation software as a scientific asset. Secondly, building transferrable software as way to share knowledge through collaboration with experts and stakeholders. Thirdly, developing food engineers' modelling skills through the use of food models and software in education and training.

Journal article

Charalambides M, Bikos D, Samaras G, Cann P, Masen M, Hartmann C, German J, Vieira J, Hardalupas Iet al., 2022, Effect of structure on the mechanical and physical properties of chocolate considering time scale phenomena occuring during oral processing, Food Structure, Vol: 31, Pages: 1-14, ISSN: 2213-3291

Micro-aeration has been employed by the chocolate industry as a texture and flavour modifier. However, the impact of micro-aeration on oral processing is still not well understood. This study quantifies the mechanical, thermal and tribological behaviour of chocolate materials of different porosity levels. These material properties were then linked to sensory data considering the temporal phenomena of the oral process. In-vivo mastication tests were utilised to define the level of fragmentation of chocolate and coupled with heat transfer numerical models to simulate the melting during oral processing. Micro-aeration affects all material properties resulting in lower fracture stresses, rapid melting and a lower friction coefficient. The sensory results showed that micro-aeration creates a perception of a softer, less sticky chocolate which melts fast inside the mouth, without compromising the sweetness perception. This research adopts an innovative multidisciplinary approach to the physics of chocolates, bringing together the fields of solid mechanics, heat transfer, tribology, and sensory analysis and employing engineering experimental and numerical approaches to provide a link between chocolate structure, material properties and sensory perception. The outcome can contribute a powerful design tool for controlling the perception of sensory attributes for specific chocolate composition.

Journal article

Charalambides M, Bikos D, Masen M, Hardalupas I, Cann P, Samaras G, Hartmann C, Vieira Jet al., 2021, Effect of micro-aeration on the mechanical behaviour of chocolates and implications for oral processing, Food and Function, Vol: 12, Pages: 4864-4886, ISSN: 2042-6496

Aeration in foods has been widely utilised in the food industry to develop novel foods with enhanced sensorial characteristics. Specifically, aeration at the micron-sized scale has a significant impact on the microstructure where micro-bubbles interact with the other microstructural features in chocolates. This study aims to determine the effect of micro-aeration on the mechanical properties of chocolate products, which are directly correlated with textural attributes such as hardness and crumbliness. Uniaxial compression tests were performed to determine the mechanical properties such as Poisson's ratio, Young's modulus and macroscopic yield strength together with fracture tests to estimate the fracture toughness. In vivo mastication tests were also conducted to investigate the link between the fracture properties and fragmentation during the first two chewing cycles. The uniaxial stress–strain data were used to calibrate a viscoplastic constitutive law. The results showed that micro-aeration significantly affects mechanical properties such as Young's modulus, yield and fracture stresses, as well as fracture toughness. In addition, it enhances the brittle nature of the chocolate, as evidenced by lower fracture stress but also lower fracture toughness leading to higher fragmentation, in agreement with observations in the in vivo mastication tests. As evidenced by the XRT images and the stress–strain measurements micro-aeration hinders the re-arrangement of the microscopic features inside the chocolate during the material's deformation. The work provides a new insight of the role of bubbles on the bulk behaviour of complex multiphase materials, such as chocolates, and defines the mechanical properties which are important input parameters for the development of oral processing simulations.

Journal article

Charalambides M, Zhang R, Taylor A, Balint D, Wood J, Young Cet 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.

Journal article

Mulakkal M, Castillo Castillo A, Taylor A, Blackman B, Balint D, Pimenta S, Charalambides Met 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.

Journal article

Zhang R, Stannard A, Street G, Taylor AC, Charalambides MNet al., 2021, Towards optimisation of rolling process of potato dough: Effect of processing on the microstructure and the mechanical properties, Journal of Food Engineering, Vol: 291, ISSN: 0260-8774

The quality of potato chips is highly dependent on the mechanical properties of the dough sheet produced prior to frying. It has been well established that poor mechanical properties result in fragile dough sheets and associated high product wastage. However, the effect of the rolling process on the mechanical properties of the dough is unknown so the optimum rolling process can only be obtained via a trial and error approach. This work reports for the first time the effects of dry flake size and rolling parameters on the mechanical performance of potato dough sheets. The laboratory scale rolling setup used a 10 cm roller diameter with a 0.2 mm gap height. Furthermore, an experimental method was developed enabling rigorous tensile testing of fragile potato dough sheets. The mechanical performance of the potato dough sheets was anisotropic, as the Young's modulus and strength were 35% and 57% higher across the rolling direction than those along the rolling direction, respectively. The formability, i.e. the ability to form a coherent sheet of the potato dough is improved by using smaller dry flakes (<500 μm). However, further decrease in the flakes size had no effect on the mechanical behaviour of potato dough sheets, i.e. flakes with diameter smaller than 212 μm showed similar tensile response to flakes smaller than 500 μm. Rolling the dough increases the coherence and the strength of the potato dough sheets, but also introduces defects orientated across the rolling direction which decrease the strength if the dough is rolled too many times. For example, sheets rolled for seven passes showed over 100% improvement in failure stress comparing to sheets rolled for five passes, but when the sheets were rolled for the eighth pass, the failure stress dropped by 17%. Due to the viscoelasticity of the dough, both the tensile modulus and strength of the sheets are higher when tested at higher strain rate. In addition, at higher strain rate, the defects in the shee

Journal article

Carvalho O, Charalambides MN, Djekic I, Athanassiou C, Bakalis S, Benedito J, Briffaz A, Castane C, Della Valle G, de Sousa IMN, Erdogdu F, Feyissa AH, Kavallieratos NG, Koulouris A, Pojic M, Raymundo A, Riudavets J, Sarghini F, Trematerra P, Tonda Aet al., 2021, Modelling Processes and Products in the Cereal Chain, Foods, Vol: 10, ISSN: 2304-8158

Journal article

Skamniotis CG, Edwards CH, Bakalis S, Frost G, Charalambides MNet al., 2020, Eulerian-Lagrangian finite element modelling of food flow-fracture in the stomach to engineer digestion, Innovative Food Science & Emerging Technologies, Vol: 66, ISSN: 1466-8564

Highly processed foods tend to form weak structures which breakdown rapidly in the gastrointestinal (GI) tract, often causing negative effects on human metabolism and health. Developing healthier foods has been limited by the lack of understanding of how foods are digested. Through computational modelling we reveal mechanical gastric food breakdown phenomena and relate food mechanical properties with performance during critical initial digestion stages. Our model relies strictly on a viscoplastic-damage constitutive law, calibrated via rheological experiments on an artificial biscuit bolus and validated by simulating cutting tests. Simulations suggest that bolus separation during bolus backward extrusion and/or indentation by peristaltic waves, and, bolus agglomeration due to hydrostatic compression near the pylorus, are two competing phenomena that can influence the bolus free surface to volume ratio. This showcases the importance of including mechanical aspects of breakdown when designing foods for controlled chemo-mechanical breakdown and associated nutrient release rates.

Journal article

Samaras G, Bikos D, Vieira J, Hartmann C, Charalambides M, Hardalupas Y, Masen M, Cann Pet al., 2020, Measurement of molten chocolate friction under simulated tongue-palate kinematics: effect of cocoa solids content and aeration, Current Research in Food Science, Vol: 3, Pages: 304-313, ISSN: 2665-9271

The perception of some food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact during mastication. This paper reports a new bench test to measure friction in the simulated tongue-palate contact. The test consists of a flat PDMS disk, representing the tongue loaded and reciprocating against a stationary lower glass surface representing the palate. The test was applied to molten chocolate samples with and without artificial saliva. Friction was measured over the first few rubbing cycles, simulating mechanical degradation of chocolate in the tongue-palate region. The effects of chocolate composition (cocoa solids content ranging between 28 ​wt% and 85 ​wt%) and structure (micro-aeration/non-aeration 0–15 ​vol%) were studied. The bench test clearly differentiates between the various chocolate samples. The coefficient of friction increases with cocoa solids percentage and decreases with increasing micro-aeration level. The presence of artificial saliva in the contact reduced the friction for all chocolate samples, however the relative ranking remained the same.

Journal article

Petropoulou K, Salt LJ, Edwards CH, Warren FJ, Garcia-Perez I, Chambers ES, Alshaalan R, Khatib M, Perez-Moral N, Cross KL, Kellingray L, Stanley R, Koev T, Khimyak YZ, Narbad A, Penney N, Serrano-Contreras JI, Charalambides MN, Miguens Blanco J, Castro Seoane R, McDonald JAK, Marchesi JR, Holmes E, Godsland IF, Morrison DJ, Preston T, Domoney C, Wilde PJ, Frost GSet al., 2020, A natural mutation in Pisum sativum L. (pea) alters starch assembly and improves glucose homeostasis in humans, Nature Food

Journal article

Skamniotis CG, Charalambides MN, 2020, Development of computational design tools for characterising and modelling cutting in ultra soft solids, Extreme Mechanics Letters, Vol: 40, Pages: 1-17, ISSN: 2352-4316

Computational modelling of the in vivo mechanical response of various biological materials within the human organism, such as brain tissue, bone, arteries, ingested food, is an increasingly cost-effective design tool for bio-medical, bio-engineering and surgical applications. This study addresses the knowledge gap in simulating deformation-fracture during cutting in continua that lie in the transition between a soft solid and a complex fluid state. Hydrated food is one such system produced naturally after swallowing. We show that a viscoplastic-damage constitutive law calibrated through compression tests on hydrated biscuit particles, can be utilised in Eulerian Finite Element (FE) analysis to predict complex localised deformation-fracture material behaviour during cutting at two length scales with high fidelity. We demonstrate that in such materials a fracture term is not always necessary to predict ultimate separation and that the Eulerian FE analysis is a versatile approach based on which largely different material cutting behaviours can be modelled. Our study provides a platform for understanding and optimising processes involving ultra-soft materials which flow excessively and exhibit weak or strong cutting resistance.

Journal article

Li-Mayer JYS, Lewis D, Connors S, Glauser A, Williamson DM, Arora H, Charalambides MNet al., 2020, Hierarchical multi-scale models for mechanical response prediction of highly filled elastic–plastic and viscoplastic particulate composites, Computational Materials Science, Vol: 181, Pages: 1-15, ISSN: 0927-0256

Though a vast amount of literature can be found on modelling particulate reinforced composites and suspensions, the treatment of such materials at very high volume fractions (>90%), typical of high performance energetic materials, remains a challenge. The latter is due to the very wide particle size distribution needed to reach such a high value of In order to meet this challenge, multiscale models that can treat the presence of particles at various scales are needed. This study presents a novel hierarchical multiscale method for predicting the effective properties of elasto-viscoplastic polymeric composites at high . Firstly, simulated microstructures with randomly packed spherical inclusions in a polymeric matrix were generated. Homogenised properties predicted using the finite element (FE) method were then iteratively passed in a hierarchical multi-scale manner as modified matrix properties until the desired filler was achieved. The validated hierarchical model was then applied to a real composite with microstructures reconstructed from image scan data, incorporating cohesive elements to predict debonding of the filler particles and subsequent catastrophic failure. The predicted behaviour was compared to data from uniaxial tensile tests. Our method is applicable to the prediction of mechanical behaviour of any highly filled composite with a non-linear matrix, arbitrary particle filler shape and a large particle size distribution, surpassing limitations of traditional analytical models and other published computational models.

Journal article

Chen KJ, Wood JD, Mohammed IK, Echendu S, Jones D, Northam K, Charalambides MNet al., 2020, Mechanical Characterisation and modelling of the rolling process of potato-based dough, Journal of Food Engineering, Vol: 278, Pages: 1-12, ISSN: 0260-8774

Motivated by social, economic and health factors, food product manufacturers are increasingly attracted towards the incorporation of potato into snack foods. However, the lack of gluten degrades the mechanical properties of potato dough, posing a challenge in ensuring optimal manufacturing processes. An important process of industrial dough production is the sheeting or rolling process. This study developed a computational design tool to ensure smooth sheeting processes for potato doughs. A visco-hyperelastic constitutive model was calibrated using uniaxial compression data, providing the required material parameters for the rolling simulation. The model output was validated through tests on a laboratory small-scale instrumented rolling rig, where the roller speed and roll gap were varied to determine the effect on the rolling force and sheet exit thickness. A good agreement between the experimental and numerical results for the roll force and sheet exit thickness was found for smaller reduction ratios. At larger reductions, the numerical rolling force and exit thickness values were higher than the experimental values, and this was attributed to the dough being damaged while being fed through small roll gaps. A critical tensile strain-based failure criterion was proven to be accurate in predicting conditions for sheet tearing. The combination of the newly developed numerical model and tensile strain failure criterion can serve as a simple and powerful design tool for predicting the roll forces, the rolled sheet height as well as the process conditions which may lead to damage in the potato dough. As a result, interruptions in the continuous sheeting process associated with sheet damage or tearing may be avoided. Since the present study focuses on rolling parameters in a laboratory scale setup, future work will provide greater insight in scaling up the results to industrial rolling processes.

Journal article

Iqbal M, Li-Mayer JYS, Lewis D, Connors S, Charalambides MNet al., 2020, Mechanical characterization of the nitrocellulose-based visco-hyperelastic binder in polymer bonded explosives, Physics of Fluids, Vol: 32, Pages: 023103-023103, ISSN: 1070-6631

A rheological constitutive model is required to characterize the behavior of a nitrocellulose-based material used as a binder in polymer bonded explosives. The behavior of the binder is extremely important as it heavily influences the mechanical response of the polymer composite; this is due to the binder having stiffness five orders of magnitude lower than the stiffness of the explosive crystals. Determination of the material model parameters is not straightforward; a constitutive law that will capture the pronounced time-dependent, temperature-dependent, and highly non-linear, large deformation response of this material is required. In this study, the material properties of the binder are determined using constant shear strain rate, shear stress relaxation, and monotonic tensile test results obtained over a wide range of temperature and strain rates. A visco-hyperelastic model is parameterized using the derived test data. In addition, recommendations are made regarding accurate data derived from rheological testing on such materials falling in the soft solid rather than the complex fluid domain.

Journal article

Mohammed IK, Skamniotis CG, Charalambides MN, 2020, Developing Food Structure for Mechanical Performance, HANDBOOK OF FOOD STRUCTURE DEVELOPMENT, Editors: Spyropoulos, Lazidis, Norton, Publisher: ROYAL SOC CHEMISTRY, Pages: 199-224, ISBN: 978-1-78801-216-4

Book chapter

Djekic I, Mujčinović A, Nikolić A, Jambrak AR, Papademas P, Feyissa AH, Kansou K, Thomopoulos R, Briesen H, Kavallieratos NG, Athanassiou CG, Silva CLM, Sirbu A, Moisescu AM, Tomasevic I, Brodnjak UV, Charalambides M, Tonda Aet al., 2019, Cross-European initial survey on the use of mathematical models in food industry, Journal of Food Engineering, Vol: 261, Pages: 109-116, ISSN: 0260-8774

Mathematical modelling plays an important role in food engineering having various mathematical models tailored for different food topics. However, mathematical models are followed by limited information on their application in food companies. This paper aims to discuss the extent and the conditions surrounding the usage of mathematical models in the context of European food and drinks industry. It investigates the knowledge, nature and current use of modelling approaches in relation to the industry main characteristics. A total of 203 food companies from 12 European countries were included in this research.Results reveal that the country where the company operates, and size of the company, are more important predictors on the usage of mathematical models followed by the type of food sector. The more developed countries are positioned at the higher level of knowledge and use of available models. Similar pattern was observed at the micro level showing that small or medium sized companies exhibit lack of knowledge, resources and limiting usage of models.

Journal article

Wood J, Gauvin C, Young C, Taylor A, Balint D, Charalambides Met 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

Journal article

Charalambides M, Skamniotis C, Matthew E, 2019, Computer simulations of food oral processing to engineer teeth cleaning, Nature Communications, Vol: 10, Pages: 1-12, ISSN: 2041-1723

Oral biofilm accumulation in pets is a growing concern. It is desirable to address this problem via non-invasive teeth cleaning techniques, such as through friction between teeth and food during chewing. Therefore, pet food design tools are needed towards optimising cleaning efficacy. Developing such tools is challenging, as several parameters affecting teeth cleaning should be considered: the food’s complex mechanical response, the contacting surfaces topology as well as the wide range of masticatory and anatomical characteristics amongst breeds. We show that Finite Element (FE) models can efficiently account for all these parameters, through the simulation of food deformation and fracture during the first bite. This reduces the need for time consuming and costly in-vivo or in-vitro trials. Our in-silico model is validated through in-vitro tests, demonstrating that the initial oral processing stage can be engineered through computers with high fidelity.

Journal article

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