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  • Journal article
    Skamniotis C, Kamaludin MA, Elliott M, Charalambides Met al., 2017,

    A novel essential work of fracture experimental methodology for highly dissipative materials

    , Polymer, Vol: 117, Pages: 167-182, ISSN: 0032-3861

    Determining fracture toughness for soft, highly dissipative, solids has been a challenge for several decades. Amongst the limited experimental options for such materials is the essential work of fracture (EWF) method. However, EWF data are known to be strongly influenced by specimen size and test speed. In contrast to time-consuming imaging techniques that have been suggested to address such issues, a simple and reproducible method is proposed. The method accounts for diffuse dissipation in the specimen while ensuring consistent strain rates by scaling both the sample size and testing speed with ligament length. We compare this new method to current practice for two polymers: a starch based food and a polyethylene (PE) tape. Our new method gives a size independent and more conservative fracture toughness. It provides key-data, essential in numerical models of the evolution of structure breakdown in soft solids as seen for example during oral processing of foods.

  • Journal article
    Mohagheghian I, Wang Y, Zhou J, Yu L, Guo X, Yan Y, Charalambides MN, Dear JPet al., 2017,

    Deformation and damage mechanisms of laminated glass windows subjected to high velocity soft impact

    , International Journal of Solids and Structures, Vol: 109, Pages: 46-62, ISSN: 1879-2146

    Bird strike can cause serious risks to the safety of air travel. In this paper, the aim is to improve design by determining deformation and damage mechanisms of laminated glass windows when subjected to high velocity soft impacts. To achieve this, laboratory-scale impact experiments using bird substitute materials were performed in the velocity range of 100–180 m s−1. An important step forward is that high-speed 3D Digital Image Correlation (DIC) has effectively been employed to extract the full-field deformation and strain on the back surface of the specimens during impact. The finite element simulations were performed in Abaqus/explicit using Eulerian approach and were able to represent successfully the experiments.For the laminated glass structures investigated, the damage inflicted is strongly sensitive to the nose shape of the projectile and most deleterious is a flat-fronted projectile. Two threshold velocities for impact damage have been identified associated with firstly the front-facing and secondly the rear-facing glass layer breaking. The order of the glass layers significantly influences the impact performance. The findings from this research study have led to a deeper and better-quantified understanding of soft impact damage on laminated glass windows and can lead to more effective design of aircraft windshields.

  • Journal article
    P Mohammed MA, Wanigasooriya L, Chakerabarti-Bell S, Charalambides MNet al., 2016,

    Extrusion of unleavened bread dough: experiments and simulations

    , Journal of Rheology, Vol: 61, ISSN: 0148-6055

    An experimental and numerical study on ram extrusion of bread dough was conducted in order to develop predictive models for the pressures involved, as well as the deformation of the extruded dough. Such studies are needed as high pressures can potentially lead to significant degassing, tearing and shearing of the dough and hence poor bread quality; the latter limits the use of extrusion processes which would otherwise be a cost – effective forming process. A laboratory extrusion rig was designed, with dies of varying angles and exit radii. Rate dependent behaviour was observed from tests conducted at different extrusion speeds, and higher extrusion pressure was reported for dies with smaller exit radius or larger die angle. A simulation of extrusion was performed to predict the extrusion pressure as well as the extrudate swell, as a function of die geometry and extrusion rate. A continuum approach was taken in the constitutive model of dough which is a starch filled system in a protein matrix. A nonlinear viscoelastic model combined for the first time with the Mullins model for filled rubbers is found to capture the continuum behaviour well. A Coulomb friction law combined with a maximum shear stress limit was used to describe the contact definition between the extrusion barrel and the dough. Higher die angles and higher extrusion speeds require higher shear stress limit values for the model and the experiments to agree. A possible reason for this is that the shear stress limit depends on maximum strain as well as strain rate imposed during the extrusion process. Static zones were observed both experimentally and numerically. The onset of the static zones was predicted well but quantifying the geometry of the latter needs further studies.

  • Conference paper
    Charalambides M, P Mohammed MA, Wanigasooriya L, 2016,

    Experimental and Numerical Investigation of Ram Extrusion of Bread Dough

    , ESAFORM2106, Publisher: AIP Publishing, Pages: 180004-180004, ISSN: 0094-243X

    An experimental and numerical study on ram extrusion of bread dough was conducted. A laboratory ram extrusion rig was designed and manufactured, where dies with different angles and exit radii were employed. Rate dependent behaviour was observed from tests conducted at different extrusion speeds, and higher extrusion pressure was reported for dies with decreasing exit radius. A finite element simulation of extrusion was performed using the adaptive meshing technique in Abaqus. Simulations using a frictionless contact between the billet and die wall showed that the model underestimates the response at high entry angles. On the other hand, when the coefficient of friction value was set to 0.09 asmeasured from friction experiments, the dough response was overestimated, i.e. the model extrusion pressure was much higher than the experimentally measured values. When a critical shear stress limit, maxW, was used, the accuracy of themodel predictions improved. The results showed that higher die angles require higher maxWvalues for the model and theexperiments to agree.

  • Conference paper
    Kinloch AJ, mohammed IK, Charalambides MN, 2016,

    Modelling the Peeling Behavior of Soft Adhesives

    , 21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy, Publisher: Elsevier, Pages: 326-333

    Peel tests were performed on pharmaceutical drug patches which consisted of a polyester backing membrane supporting an acrylic pressure-sensitive adhesive (PSA) (without and with an anti-fungal drug present) adhered to a polyethylene substrate. Interfacial separation of the PSA from the polyethylene substrate was observed in most cases. Finite element (FE) peeling simulations were conducted which characterized the backing-membrane as an elasto-plastic power-law material, the PSA as a viscoelastic material and the interfacial properties with a cohesive zone model (CZM). The mechanical response of the backing membrane and the PSA were measured from tensile experiments while the rate-dependent cohesive zone parameters, i.e. the fracture energy and maximum stress, were measured directly from poker-chip probe tack tests. The numerical results from the CZM/FE simulations and the experimental values of the peel forces as a function of the peel angle, peel speed and PSA thickness were found to be in good agreement. Two different anti-fungal drugs were added to the PSA and the influence of the drug was investigated using contact angle measurements, tensile tests, dynamic mechanical analysis and peel tests.

  • Journal article
    Williams JG, Atkins AG, Charalambides MN, Lucas PWet al., 2016,

    Cutting science in biology and engineering

    , Interface Focus, Vol: 6, ISSN: 2042-8901

    On 26–27 October 2015, the Theo Murphy international scientific meetingon ‘Cutting science in biology and engineering’ was held at the KavliRoyal Society Centre, Chicheley Hall, Buckinghamshire, UK. The meetingwas organized by Professor Gordon Williams FREng FRS, Professor TonyAtkins FREng, Professor Peter Lucas and Dr Maria Charalambides and itwas enabled through the Royal Society scientific programme. It connectedscientists from diverse backgrounds and disciplines including Biology andMechanical Engineering from around the world.

  • Journal article
    Skamniotis, Patel Y, Charalambides MN, Elliott Met al., 2016,

    Fracture investigation in starch based foods

    , Interface Focus, Vol: 6, ISSN: 2042-8901

    The study of oral processing and specifically cutting of the food piece during mastication can lead towards optimisation of products for humans or animals. Food materials are complex bio-composites with highly nonlinear constitutive response. Their fracture properties have not been largely investigated as yet while the need for models capable of predicting food breakdown increases. In this study, the blade cutting and the essential work of fracture (EWF) methodologies assessed the fracture behaviour of starch based pet-food. Tensile tests revealed rate dependent stiffness and stress softening effects, attributed to viscoplasticity and micro-cracking, respectively. Cutting data were collected for 5, 10 and 30 mm/s sample feed rates, whereas the EWF tests were conducted at 1.7, 3.3 and 8.3 mm/s crosshead speeds corresponding to average crack speeds of 4, 7 and 15 mm/s respectively. A reasonable agreement was achieved between cutting and EWF, reporting 1.26, 1.78, 1.76 kJ/m² and 1.52, 1.37, 1.45 kJ/m² values, respectively, for the corresponding crack speeds. These toughness data were used in a novel numerical model simulating the ‘first’ bite mastication process. A viscoplastic material model is adopted for the food piece, combined with a damage law which enabled predicting fracture patterns in the product.

  • Journal article
    Mohammed IK, Charalambides MN, Kinloch AJ, 2016,

    Modeling the effect of rate and geometry on peeling and tack of pressure-sensitive adhesives

    , Journal of Non-Newtonian Fluid Mechanics, Vol: 233, Pages: 85-94, ISSN: 1873-2631

    A model is developed for predicting separation along interfaces of pressure sensitive adhesives. Many authors have used the cohesive zone approach to solve such problems but the parameter calibration of such models remains uncertain. This study reports a novel method for determining such parameters. In addition, it provides crucial evidence for the suitability of the cohesive zone model approach in modelling interface fractures.Peel tests were performed at various rates using specimens which consisted of a polyester backing membrane supporting an acrylic pressure-sensitive adhesive (PSA) adhered to a polyethylene substrate. Interfacial separation of the PSA from the polyethylene substrate was observed. Finite element (FE) peeling simulations were conducted which modeled the backing-membrane as an elasto-plastic power-law material, the adhesive as a viscoelastic material and the interfacial properties with a cohesive zone model (CZM). The material properties of the backing membrane and the pressure-sensitive adhesive were measured from tensile and stress relaxation experiments. The rate-dependent CZM parameters were measured directly from poker-chip probe-tack tests which were performed at pull-off speeds which corresponded to the rates employed for the peel tests. The effect of the PSA thickness and test rate on both tack and peel was investigated experimentally, as well as modeled numerically. Good agreement was found between the experimentally measured and numerically predicted peel forces for different peel angles, speeds and PSA thicknesses. In addition, it was proven that the rate dependence observed in the peel and probe-tack data was dominated by the rate dependence of the interface properties, i.e. the time dependence of the two CZM parameters of maximum stress and fracture energy, rather than the time-dependent bulk viscoelasticity of the PSA peel arm.

  • Journal article
    Hagan EWS, Charalambides MN, Young CRT, Learner TJSet al., 2015,

    The effects of strain rate and temperature on commercial acrylic artist paints aged one year to decades

    , Applied Physics A - Materials Science & Processing, Vol: 121, Pages: 823-835, ISSN: 1432-0630

    Acrylic artist paints are viscoelastic composites containing a high molecular weight copolymer, pigment and a variety of additives. The glass transition temperature of the latex binder is typically slightly below ambient conditions, giving mechanical properties that are strongly dependent on strain rate and temperature. In previous work, the viscoelastic behaviour of custom-formulated latex artist paints was reported for films with known volume fractions of pigment using data from uniaxial tensile tests at different strain rates and temperatures. Secant Young’s modulus and failure strain master curves were constructed for each film through time-temperature superposition, allowing predictions beyond the experimental timescale at a selected reference temperature. A similar analysis is now presented for a small set of commercial artist paints tested at ages of 1 and 27 years. Experimental shift factor values are reported with fits to the Arrhenius, WLF and Vogel Fulcher equations, along with a comparison with published data for acrylic polymers. The tensile results highlight a spectrum of properties that acrylic paints may exhibit—brittle glass to hyperelastic—depending on the conditions during deformation. Strong similarities are shown between products from different manufacturers, and the findings suggest a high degree of stability with age. A method for predicting failure as a function of strain rate and temperature is also presented, and the methodology gives a framework for investigating other artist materials and the factors influencing their mechanical properties.

  • Journal article
    Arora H, Tarleton E, Li-Mayer J, Charalambides M, Lewis Det al., 2015,

    Modelling the damage and deformation process in a plastic bonded explosive microstructure under tension using the finite element method

    , Computational Materials Science, Vol: 110, Pages: 91-101, ISSN: 0927-0256

    Modelling the deformation and failure processes occurring in polymer bonded explosives (PBX)and other energetic materials is of great importance for processing methods and lifetime storagepurposes. Crystal debonding is undesirable since this can lead to contamination and a reductionin mechanical properties. An insensitive high explosive (PBX-1) was the focus of the study.This binary particulate composite consists of (TATB) filler particles encapsulated in a polymericbinder (KELF800). The particle/matrix interface was characterised with a bi-linear cohesive law,the filler was treated as elastic and the matrix as visco-hyperelastic. Material parameters weredetermined experimentally for the binder and the cohesive parameters were obtained previouslyfrom Williamson et al. (2014) and Gee et al. (2007) for the interface. Once calibrated, the materiallaws were implemented in a finite element model to allow the macroscopic response of thecomposite to be simulated. A finite element mesh was generated using a SEM image to identifythe filler particles which are represented as a set of 2D polygons. Simulated microstructureswere also generated with the same size distribution and volume fraction only with the idealisedassumption that the particles are a set of circles in 2D and spheres in 3D. The various modelresults were compared and a number of other variables were examined for their influence on theglobal deformation behaviour such as strain rate, cohesive parameters and contrast between fillerand matrix modulus. The overwhelming outcome is that the geometry of the particles plays acrucial role in determining the onset of failure and the severity of fracture in relation to whetherit is a purely local or global failure. The model was validated against a set of uniaxial tensiletests on PBX-1 and it was found that it predicted the initial modulus and failure stress and strainwell.Keywords: Particulate composites, High volume fraction, Finite Element Analysis,Micromechanics, Fract

  • Conference paper
    Zhang R, 2015,

    Microstructure-property relationships in alumina trihydrate filled poly (methyl methacrylate) composite materials

    , 2015 Global Conference on Polymer and Composite Materials (PCM 2015), Publisher: IOP Publishing: Conference Series, ISSN: 1757-899X

    The mechanical properties (Young's modulus and fracture toughness) of composite made from a poly (methyl methacrylate) (PMMA) matrix filled with alumina trihydrate(ATH) are reported. The experiments were performed using flexural tests and single edge notched bend (SENB) tests. The composites samples were tested at a range of filler volume fractions (34.7%, 39.4% and 44.4%) and mean filler diameters (8 pm, 15 pm and 25 pm). The data of Young's modulus agreed well with the results of Lielens model and finite element analysis (FEA) model.

  • Journal article
    Forte AE, D'Amico F, Charalambides MN, Dini D, Williams JGet al., 2015,

    Modelling and experimental characterisation of the rate dependent fracture properties of gelatine gels

    , FOOD HYDROCOLLOIDS, Vol: 46, Pages: 180-190, ISSN: 0268-005X
  • Conference paper
    Mohammed IK, Charalambides MN, Williams JG, Rasburn Jet al., 2015,

    Modelling Deformation and Fracture in Confectionery Wafers

    , International Conference of Computational Methods in Sciences and Engineering (ICCMSE), Publisher: AMER INST PHYSICS, Pages: 289-292, ISSN: 0094-243X

    The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.

  • Conference paper
    Mohammed MAP, Tarleton E, Charalambides MN, Williams JGet al., 2015,

    A Micromechanics Model for Bread Dough

    , International Conference of Computational Methods in Sciences and Engineering (ICCMSE), Publisher: American Institute of Physics, Pages: 305-309, ISSN: 0094-243X

    The mechanical behaviour of dough and gluten was studied in an effort to investigate whether bread dough canbe treated as a two phase (starch and gluten) composite material. The dough and gluten show rate dependent behaviourunder tension, compression and shear tests, and non-linear unloading-reloading curves under cyclic compression tests.There is evidence from cryo-Scanning Electron Microscopy (SEM) that damage in the form of debonding between starchand gluten occurs when the sample is stretched. A composite finite element model was developed using starch as fillerand gluten as matrix. The interaction between the starch and gluten was modelled as cohesive contact. The finite elementanalysis predictions agree with trends seen in experimental test data on dough and gluten, further evidence that debondingof starch and gluten is a possible damage mechanism in dough.

  • Journal article
    Kinloch AJ, Mohammed IK, Charalambides MN, 2014,

    Modelling the interfacial peeling of pressure-sensitive adhesives

    , Journal of Non-Newtonian Fluid Mechanics, Vol: 222, Pages: 141-150, ISSN: 1873-2631

    Peel tests were performed using specimens which consisted of a polyester backing membrane supporting an acrylic pressure-sensitive adhesive adhered to a polyethylene substrate. Interfacial separation of the PSA from the polyethylene substrate was observed. Finite element (FE) peeling simulations were conducted which modelled the backing-membrane as an elasto-plastic power-law material, the adhesive as a viscoelastic material and the interfacial properties with a cohesive zone model (CZM). The material properties of the backing membrane and the pressure-sensitive adhesive were measured from tensile and stress relaxation experiments. The cohesive zone parameters were calculated analytically from the peel test data, as well as being measured directly from independent poker-chip probe tack tests. The numerical results from the CZM/FE simulations and the experimental values of the peel forces as a function of the peel angle were found to be in good agreement.

  • Journal article
    Mohammed IK, Charalambides MN, Williams JG, Rasburn Jet al., 2014,

    Modelling the microstructural evolution and fracture of a brittle confectionery wafer in compression

    , INNOVATIVE FOOD SCIENCE & EMERGING TECHNOLOGIES, Vol: 24, Pages: 48-60, ISSN: 1466-8564
  • Journal article
    Tantideeravit S, Charalambides MN, Balint DS, Young CRTet al., 2013,

    Prediction of delamination in multilayer artist paints under low amplitude fatigue loading

    , ENGINEERING FRACTURE MECHANICS, Vol: 112, Pages: 41-57, ISSN: 0013-7944
  • Journal article
    Mohammed IK, Charalambides MN, Williams JG, Rasburn Jet al., 2013,

    Modelling the deformation of a confectionery wafer as a non-uniform sandwich structure

    , JOURNAL OF MATERIALS SCIENCE, Vol: 48, Pages: 2462-2478, ISSN: 0022-2461
  • Journal article
    Mohammed MAP, Tarleton E, Charalambides MN, Williams JGet al., 2013,

    Mechanical characterization and micromechanical modeling of bread dough

    , JOURNAL OF RHEOLOGY, Vol: 57, Pages: 249-272, ISSN: 0148-6055
  • Conference paper
    Tarleton E, Charalambides MN, Leppard C, 2012,

    Image-based modelling of binary composites

    , 21st International Workshop on Computational Mechanics of Materials (IWCMM), Publisher: ELSEVIER SCIENCE BV, Pages: 183-186, ISSN: 0927-0256

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