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
to

110 results found

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, Pages: 1-9, 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

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, ISSN: 2042-6496

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

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

Zhou J, Liu J, Zhang X, Yan Y, Jiang L, Mohagheghian I, Dear J, Charalambides Met al., 2019, Experimental and numerical investigation of high velocity soft impact loading on aircraft materials, Aerospace Science and Technology, Vol: 90, Pages: 44-58, ISSN: 1270-9638

Bird strike on aircraft remains a serious threat to flight safety. Experimental investigations employing real birds are associated with high cost and low reproducibility. Therefore, physical substitute materials are often used instead of real birds. This study investigates the soft impact loading on aluminium and laminated glass targets from ballistic gelatine and rubber projectiles. The two targets simulate strike on the aircrafts' fuselage and windshield respectively. The full field out of plane displacements of the targets were recorded for velocities 110 to 170 m s−1 using digital image correlation during gas gun experiments. A simulation model based on Smoothed Particle Hydrodynamics was developed and validated against the experimental data from all four projectile-target material combinations. It was shown that for the same momentum, a rubber projectile exerts a higher pressure on a target as compared to gelatine, even though the out of plane displacements and in-plane strains are similar. This led to fractures in the impacted laminated glass when rubber was used. The study offers new experimental data as well as efficient design modelling tools to mitigate damage imposed during bird strike. The models provide a way towards enabling the optimisation of real, large scale aircraft structures and components.

Journal article

Skamniotis CG, Elliott M, Charalambides MN, 2019, On modelling the constitutive and damage behaviour of highly non-linear bio-composites - Mesh sensitivity of the viscoplastic-damage law computations, International Journal of Plasticity, Vol: 114, Pages: 40-62, ISSN: 0749-6419

The large strain fracture of non-linear complex solids concerns a wide range of applications, such as material forming, food oral processing, surgical instrumental penetration as well as more recently, the design of biodegradable composites for packaging and bio-medical use. Although simulations are a powerful tool towards understanding and designing such processes, modelling ductile fracture in materials such as soft natural composites imposes a new challenge, particularly when the fracture patterns cannot be pre-defined. Here we bring to light new information on these aspects of benefit to the multidisciplinary community, by characterising and modelling the deformation and fracture of short cellulose fibre starch extruded composites. Hyperviscoelastic-Mullins damage laws show merits in modelling such complex systems. Yet they are inferior to a viscoplastic-damage law able to capture exactly their highly non-linear, rate dependent and pressure dependent pseudo-plastic stress-strain response. The viscoplastic-damage law also predicts fracture based on experimental toughness values without pre-specifying the crack path in a Finite Element (FE) model, displaying superiority over the conventional cohesive zone approach. Yet, despite using a toughness parameter to drive crack propagation, spurious mesh dependency is still observed while other previously unreported sources of error imposed by the finite element aspect ratio are also highlighted. The latter is rectified by developing a novel numerical strategy for calculating the characteristic element length used in the damage computations. Inherent mesh dependency suggests that non-local damage models may be essential to model this newly investigated class of natural composites.

Journal article

Ilic J, Charalambides M, Tomasevic I, Bikos D, Wood JD, Djekic Iet al., 2019, Effect of the direction of m. psoas major fibres on the results of tensile test - can we model meat as a material?, 60th International Meat Industry Conference (MEATCON), Publisher: IOP PUBLISHING LTD, ISSN: 1755-1307

Conference paper

Wood JD, Gauvin C, Young CRT, Taylor AC, Balint DS, Charalambides MNet al., 2018, Cracking in paintings due to relative humidity cycles, 22nd European Conference on Fracture (ECF) - Loading and Environmental Effects on Structural Integrity, Publisher: Elsevier B.V., Pages: 379-384, ISSN: 2452-3216

A numerical study is performed using the finite element method to consider the effects of low-cycle fatigue, specifically induced through relative humidity cycles on paintings. It has been identified that there are two major crack types in paintings, these being (i) an interfacial crack (delamination) between paint and support and (ii) a through-thickness (channel) crack in the paint layer itself, arresting on the interface. Therefore a 2D plane strain model for each type of crack has been created, which both consist of an alkyd paint modelled using a visco-hyperelastic material model and a primed canvas which is assumed to behave in a linear elastic manner. To account for fatigue damage in both models, cohesive elements located along the interface or through the film thickness respectively, are used and the traction-separation law has been modified to incorporate a fatigue damage parameter. It is possible to expose the models to the same relative humidity cycles, which would typically be seen in museums, enabling the prediction of time to first crack and which crack type is more readily grown in the painting.

Conference paper

Butt S, Mohammed I, Raghavan V, Powell H, Osborne J, Charalambides Met al., 2018, Quantifying the differences in structure and mechanical response of confectionery products resulting from the baking and extrusion processes, Journal of Food Engineering, Vol: 238, Pages: 112-121, ISSN: 0260-8774

Extrusion has potential advantages over baking in terms of throughput, asset cost and flexibility. However, it is challenging to achieve through extrusion the “light, crispy” texture of a more traditional baked confectionery. This study compares and contrasts for the first time confectionery products produced through these two processes, i.e. baking and extrusion. The microstructural differences are measured using imaging techniques, i.e. Scanning Electron Microscopy (SEM) and X-Ray Tomography (XRT) whereas mechanical characterisation is used to highlight differences in the resulting mechanical properties. Crucial information is presented which shows that the two technologies result in different mechanical properties and microstructures, even if the level of porosity in the two products is kept constant. In addition, confectionery products whether they are produced through baking or extrusion, have irregular geometries. The latter makes mechanical characterisation a real challenge. Therefore this study also presents rigorous methods for measuring true mechanical properties such that meaningful and valid comparisons may be made. The accuracy of the chosen methodologies is verified through experiments using flat and tubular extruded geometries as well as testing the products in various directions. It was concluded that the manufacturing method and, in the case of extrusion, the initial moisture content influences the microstructure and mechanics of confectionery products, both of which have an impact on consumer sensory perception.

Journal article

Skamniotis C, Patel Y, Elliott M, Charalambides Met al., 2018, Toughening and stiffening of starch food extrudates through the addition of cellulose fibres and minerals, Food Hydrocolloids, Vol: 84, Pages: 515-528, ISSN: 0268-005X

Pet food, one of the largest type of commercial packaged foods, continuously sets new challenges, amongst them the possibility to enhance palatability via adjusting product composition. This will optimise texture perception across consumer groups of diverse chewing capabilities, as well as improve food oral breakdown efficiency with further impact on metabolic health and nutrient bioavailability in the digestive process. Our aim is to pioneer new methods of controlling texture by answering longstanding questions such as the impact of nutrients on the mechanical properties of foods. The impact of cellulose fibres and minerals on the fracture toughness and stiffness properties of starch food extrudates is investigated for the first time through employing tensile tests and two fracture toughness tests namely Essential Work of Fracture (EWF) and cutting, on four different compositions. Fibres alone are found to increase stiffness (stiffening) and toughness (toughening) whereas minerals decrease stiffness (softening) with a minor influence on toughness. Interestingly, fibres and minerals combined maximise toughening at 28% compared to pure starch, due to the synergistic effect of fibre-matrix de-bonding and fibre breakage mechanisms at the crack tip. These new results indicate that texture can be significantly altered through the addition of minerals and short fibres. Such information is critical in the design of products that need to satisfy both nutritional and textural criteria.

Journal article

Mohagheghian I, Charalambides M, Wang Y, Jiang L, Zhang X, Yan Y, Kinloch A, Dear JPet al., 2018, Effect of the polymer interlayer on the high-velocity soft impact response of laminated glass plates, International Journal of Impact Engineering, Vol: 120, Pages: 150-170, ISSN: 0734-743X

The choice of the polymer interlayer is a key consideration for laminated aircraft windshields. Such windshields often employ chemically strengthened glasses and are required to withstand impact by birds, hail-stones and other foreign bodies. In the present study, windshields employing three different polymer interlayer materials were investigated under high-velocity impact by a soft projectile: Thermoplastic Polyurethane (TPU), Polyvinyl Butyral (PVB) and Ionoplast interlayer-SentryGlas® Plus (SGP). Parameters such as the polymer interlayer type and thickness, multi-layering the interlayer and the sensitivity of the behaviour of the windshield to the environmental temperature were studied. The performance was assessed through a series of laboratory-scale impact experiments (using a bird-substitute material) and modelled via finite element simulations (using a smoothed particle hydrodynamics approach). The experimental and numerical results were found to be in good agreement for the three polymer interlayers investigated. The polymer interlayer type was found to have the most significant effect on both the deformation and the failure of the laminated glass windows at room temperature, i.e. 25 °C. However, the influence of the polymer interlayer type became less pronounced at lower temperatures. The novel modelling that has been developed assists in the choice of the best polymer interlayer, including the multi-layering of interlayers, for complex windshield designs.

Journal article

Charalambides M, Li-Mayer J, Martinez M, Lambros Jet al., 2018, Determination of Mixed-Mode Cohesive Zone Failure Parameters Using Digital Volume Correlation and the Inverse Finite Element Method, 17th International Conference on Fracture and Damage Mechanics

Conference paper

Zhang R, Li-Mayer J, Charalambides M, 2018, Development of an image-based numerical model for predicting the microstructure-property relationship in alumina trihydrate (ATH) filled poly(methyl methacrylate) (PMMA), International Journal of Fracture, Vol: 211, Pages: 125-148, ISSN: 0376-9429

Particulate composites are found in a wide range of applications. Their heterogeneous microstructure affects their bulk behavior and structural performance, however tools for predicting this important structure-property relationship are still lacking. In this study, a numerical method that can provide predictions of the mechanical response of a particulate polymeric matrix composite as a function of volume fraction and particle mean diameter is presented. The work is derived for an alumina trihydrate filled poly(methyl methacrylate) but the methodology is generic and can be used for any particulate composite. Representative Volume elements are determined through images obtained from scanning electron microscopy. The model takes into account the possibility of failure through interface debonding as well as cracks through the matrix. The model predictions for the modulus and fracture strength of the composites are validated through independent experiments on the composite. The numerical results are also used to qualitatively explain the trends measured regarding the fracture toughness of the composites. Compared to other literature on particulate composites, our study is the first to report accurate stress–strain distributions as well as fracture predictions whilst all the necessary model parameters defining the failure criteria are all derived through independent experiments. This paves the way for a relatively simple methodology for determining structure-property relationships in composites design, enabling smarter material utilization and optimal mechanical properties.

Journal article

Kinloch AJ, Rizi K, Mohammed IK, Charalambides MN, Murdan K, Xu Ket al., 2018, A systematic approach to the formulation of anti-onychomycotic nail patches, European Journal of Pharmaceutics and Biopharmaceutics, Vol: 127, Pages: 355-365, ISSN: 0939-6411

Nail patches have a potential role as drug carriers for the topical treatment of nail diseases such as onychomycosis, a common condition. Our aim was therefore to develop a systematic and novel approach to the formulation of a simple drug-in-adhesive ungual patch. Twelve pressure-sensitive adhesives (PSAs), four backing membranes, two release liners and three drugs were screened for pharmaceutical and mechanical properties. From this initial screening, two PSAs, two drugs, one backing membrane and one release liner were selected for further investigation. Patches were prepared by solvent-casting and characterised. The patches had good uniformity of thickness and of drug content, and showed minimal drug crystallisation during six months of storage. Meanwhile, the drug stability in the patch upon storage and patch adhesion to the nail was influenced by thenature of the drug, the PSA and the backing membrane. The reported methodology paves the way for a systematic formulation of ungual nail patches to add to the armamentarium of nail medicines. Further, from this work, the best patch formulation has been identified.

Journal article

Skamniotis CG, Elliott M, Charalambides MN, 2017, On modeling the large strain fracture behaviour of soft viscous foods, Meeting of the Institute-of-Non-Newtonian-Fluid-Mechanics (INNFM), Publisher: AIP Publishing, ISSN: 1070-6631

Mastication is responsible for food breakdown with the aid of saliva in order to form a cohesive viscous mass, known as the bolus. This influences the rate at which the ingested food nutrients are later absorbed into the body, which needs to be controlled to aid in epidemic health problems such as obesity, diabetes, and dyspepsia. The aim of our work is to understand and improve food oral breakdown efficiency in both human and pet foods through developing multi-scale models of oral and gastric processing. The latter has been a challenging task and the available technology may be still immature, as foods usually exhibit a complex viscous, compliant, and tough mechanical behaviour. These are all addressed here through establishing a novel material model calibrated through experiments on starch-based food. It includes a new criterion for the onset of material stiffness degradation, a law for the evolution of degradation governed by the true material’s fracture toughness, and a constitutive stress-strain response, all three being a function of the stress state, i.e., compression, shear, and tension. The material model is used in a finite element analysis which reproduces accurately the food separation patterns under a large strain indentation test, which resembles the boundary conditions applied in chewing. The results lend weight to the new methodology as a powerful tool in understanding how different food structures breakdown and in optimising these structures via parametric analyses to satisfy specific chewing and digestion attributes.

Conference paper

Charalambides M, Skamniotis, Elliott M, 2017, On modelling the large indentation fracture behaviour of incompressible soft viscous food structures, Physics of Fluids, Vol: 29, Pages: 121610-1-121610-14, ISSN: 1070-6631

Mastication is responsible for food breakdown with the aid of saliva in order to form a cohesive viscous mass, known as the bolus. This influences the rate at which the ingested food nutrients are later absorbed into the body, which needs to be controlled to aid in epidemic health problems such as obesity, diabetes, and dyspepsia. The aim of our work is to understand and improve food oral breakdown efficiency in both human and pet foods through developing multi-scale models of oral and gastric processing. The latter has been a challenging task and the available technology may be still immature, as foods usually exhibit a complex viscous, compliant, and tough mechanical behaviour. These are all addressed here through establishing a novel material model calibrated through experiments on starch-based food. It includes a new criterion for the onset of material stiffness degradation, a law for the evolution of degradation governed by the true material’s fracture toughness, and a constitutive stress-strain response, all three being a function of the stress state, i.e., compression, shear, and tension. The material model is used in a finite element analysis which reproduces accurately the food separation patterns under a large strain indentation test, which resembles the boundary conditions applied in chewing. The results lend weight to the new methodology as a powerful tool in understanding how different food structures breakdown and in optimising these structures via parametric analyses to satisfy specific chewing and digestion attributes.

Journal article

Skamniotis CG, Charalambides MN, Elliott M, 2017, Chewing as a forming application: A viscoplastic damage law in modelling food oral breakdown, 20th International ESAFORM Conference on Material Forming, Publisher: AIP Publishing, ISSN: 1551-7616

The first bite mechanical response of a food item resembles compressive forming processes, where a tool is pressed into a workpiece. The present study addresses ongoing interests in the deformations and damage of food products, particularly during the first bite, in relation to their mechanical properties. Uniaxial tension, compression and shear tests on a starch based food reveal stress-strain response and fracture strains strongly dependent on strain rate and stress triaxiality, while damage mechanisms are identified in the form of stress softening. A pressure dependent viscoplastic constitutive law reproduces the behavior with the aid of ABAQUS subroutines, while a ductile damage initiation and evolution framework based on fracture toughness data enables accurate predictions of the product breakdown. The material model is implemented in a Finite Element (FE) chewing model based on digital pet teeth geometry where the first bite of molar teeth against a food item is simulated. The FE force displacement results match the experimental data obtained by a physical replicate of the bite model, lending weight to the approach as a powerful tool in understanding of food breakdown and product development.

Conference paper

Butt S, Charalambides M, Mohammed IK, Powell Het al., 2017, A Comparison of the Mechanical and Sensory Properties of Baked and Extruded Confectionery Products, 20th International ESAFORM Conference on Material Forming, Publisher: AIP Publishing, ISSN: 1551-7616

Traditional baking is the most common way of producing confectionery wafers, however over the past few decades, the extrusion process has become an increasingly important food manufacturing method and is commonly used in the manufacturing of breakfast cereals and filled snack products. This study aims to characterise products made via each of these manufacturing processes in order to understand the important parameters involved in the resulting texture of confectionery products such as wafers. Both of the named processes result in brittle, cellular foams comprising of cell walls and cell pores which may contain some of the confectionery filling. The mechanical response of the cell wall material and the geometry of the products influence the consumer perception and preference. X-Ray micro tomography (XRT) was used to generate geometry of the microstructure which was then fed to Finite Element (FE) for numerical analysis on both products. The FE models were used to determine properties such as solid modulus of the cell walls, Young’s modulus of the entire foam and to investigate and compare the microstructural damage of baked wafers and extruded products. A sensory analysis study was performed on both products by a qualified sensory panel. The results of this study were then used to draw links between the mechanical behaviour and sensory perception of a consumer. The extruded product was found to be made up of a stiffer solid material and had a higher compressive modulus and fracture stress when compared to the baked wafer. The sensory panel observed textural differences between the baked and extruded products which were also found in the differences of the mechanical properties of the two products.

Conference paper

Chong HM, Mohammed IK, Linter B, Allen R, Charalambides MNet al., 2017, Mechanical and microstructural changes of cheese cracker dough during baking, LWT- Food Science and Technology, Vol: 86, Pages: 148-158, ISSN: 0023-6438

Baked food snacks constitute an important market as a popular consumer product. The mechanical properties of cheese cracker dough at different stages of baking have been investigated as they can relate to the product's texture. The change in mechanical properties during baking was measured whilst the corresponding changes in microstructure were recorded using cryo-SEM at several interrupted baking conditions. The initial modulus of the dough increased with baking time due to starch melting or gelatinisation, melting of fat globules and evaporation of water. Simultaneously gas cells were found to begin forming. The data derived from the uniaxial compression, tension and shear experiments showed that the dough exhibited a rate dependent behaviour at all stages of baking with a power law index of approximately 0.2. Rheometric tests under dynamic heating conditions were also performed and it was found that the modulus decreased significantly, from 150 kPa to 10 kPa, with the initial rise in temperature. This study provides useful data for understanding the evolution of microstructure and rheology during the baking process and its impact on the texture of the final product.

Journal article

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