302 results found
Wang H, Chang L, Mai Y-W, et al., 2018, An experimental study of orthogonal cutting mechanisms for epoxies with two different crosslink densities, INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE, Vol: 124, Pages: 117-125, ISSN: 0890-6955
Wang H, Chang L, Williams JG, et al., 2016, On the machinability and surface finish of cutting nanoparticle and elastomer modified epoxy, MATERIALS & DESIGN, Vol: 109, Pages: 580-589, ISSN: 0264-1275
Millar TM, Patel Y, Wang H, et al., 2016, An investigation of cutting resistance in stretched polymer films, 21st European Conference on Fracture (ECF), Publisher: ELSEVIER SCIENCE BV, Pages: 190-196, ISSN: 2452-3216
An investigation is made into the fracture properties of polymer films and laminates under cutting by a sharp tool and lateral tension under pure shear conditions. The method involves use of a sharp razor blade applied to the crack tip of polymer films which are also stretched orthogonal to the direction of the blade. The reaction force is measured as the cutting tool cuts the material and the force from applying a lateral strain is measured. The analysis and tests assume quasi-static conditions. The method is applied to a polyester film and three polyester laminates.Steady-state cutting forces are observed from cutting tests and loads at crack initiation are observed from lateral stretching tests. With fracture mechanics analysis the energy contributions from cutting and tearing are used to determine apparent fracture properties from the experimental results. It is observed that the cutting and tearing tests yield similar fracture toughness properties for the three tested polyester laminates, despite the different crack tip geometry at the point of crack growth. However, significantly larger fracture toughness values are measured from tearing tests versus cutting tests for the tested polyester film.
Kamaludin MA, Patel Y, Blackman BRK, et al., 2016, Fracture mechanics testing for environmental stress cracking in thermoplastics, Procedia Structural Integrity, Vol: 2, Pages: 227-234, ISSN: 2452-3216
Under the combined influence of an aggressive environment and applied stress, engineering thermoplastics may undergo a phenomenon known as environmental stress cracking (ESC). This can result in adverse effects such as embrittlement and premature failure in service, due to the growth of environmentally-induced cracks to critical sizes, with little to no fluid absorption in the bulk material. Fracture mechanics is proposed as a suitable scheme to study and quantify ESC, with the aim being to obtain characterising data for different polymer-fluid combinations of interest, as well as to develop a reliable fracture mechanics test protocol. In the proposed method, slow crack growth is monitored to assess the effect of a range of applied crack driving forces (K, or alternatively G) on observed crack speeds, as opposed to simply measuring time-to-failure. This paper presents the results of experiments performed on the following materials: linear low density polyethylene (LLDPE) in Igepal solution and high impact polystyrene (HIPS) in sunflower oil. A discussion of the various issues surrounding the data analysis for these long-term tests is also included, as the attainment of consistent and repeatable results is critical for a method to be internationally standardised, which is a goal of the European Structural Integrity Society (ESIS) Technical Committee 4 from whose interest this work is drawn.
Chang L, Patel Y, Wang H, et al., 2016, The Partitioning of Plastic Energy in Cutting Tests, 21st European Conference on Fracture (ECF), Publisher: ELSEVIER SCIENCE BV, Pages: 309-315, ISSN: 2452-3216
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.
Williams JG, Patel Y, 2016, Fundamentals of cutting, Interface Focus, Vol: 6, ISSN: 2042-8898
The paper extends the notion of steady-state cutting of polymers with a sharp tool to scratching. The analysis assumes there is separation at the tool tip (fracture) and the removed layer undergoes plastic shear. Results are presented for three polymers: PMMA, PC and PBT. For the tougher polymer, PC, smooth scratches were obtained and the modified cutting analysis works well provided that the wear on the initially sharp tip is accounted for. For the more brittle polymers, PMMA and PBT, rougher scratches were obtained and this is consistent with the notion that the polymers exhibited micro-cracking ahead of the tool tip, which led to rough surfaces being generated. The results demonstrate that the fracture toughness and the yield stress are controlling parameters in the scratching process and that a sufficiently high value of crack opening displacement COD (greater than about 10 μm) ensures that smooth scratches are obtained, as was the case for PC.
Blackman BRK, Steininger H, Williams JG, et al., 2015, The fatigue behaviour of ZnO nano-particle modified thermoplastics, Composites Science and Technology, Vol: 122, Pages: 10-17, ISSN: 0266-3538
The present paper describes an investigation into the effects on the fatigue behaviour of adding up to 1.00 vol.% ZnO nano-rods with a diameter of 13 nm and an aspect ratio of three to two amorphous styrene acrylonitrile copolymers. Two acrylonitrile contents, i.e. 24% and 34% respectively, were studied. Fracture mechanics based fatigue tests were conducted at 5 Hz and a Paris Law analysis approach was followed. The fatigue threshold increased notably with the addition of the ZnO nano-rods. The increases in toughness were analysed using an analytical model of plastic void growth around the particles and this enabled the surface energy per unit area for the particle-matrix debonding process to be deduced. Good particle distributions were achieved only for very small volume fractions (<0.3%) above which the occurrence of agglomerated particles and consequential toughness declines were observed. In the fatigue threshold region, surface micrographs showed clear evidence of debonding and plastic void growth and the average measured void diameter agreed closely with that predicted by the model.
Wang H, Chang L, Ye L, et al., 2015, On the toughness measurement for ductile polymers by orthogonal cutting, 7th ESIS TC4 Conference on the Fracture of Polymers, Composites and Adhesives, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 276-286, ISSN: 0013-7944
Rodriguez J, Salazar A, Gomez FJ, et al., 2015, Fracture of notched samples in epoxy resin: Experiments and cohesive model, 7th ESIS TC4 Conference on the Fracture of Polymers, Composites and Adhesives, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 402-411, ISSN: 0013-7944
Williams JG, 2015, The Griffith Medal Lecture: The fracture mechanics of soft solids, 7th ESIS TC4 Conference on the Fracture of Polymers, Composites and Adhesives, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 192-198, ISSN: 0013-7944
Ivankovic A, Conroy M, Kinloch AJ, et al., 2015, Mixed Mode Partitioning in Beam Like Geometries: A Damage Dependent Solution, Engineering Fracture Mechanics, Vol: 149, Pages: 351-367, ISSN: 1873-7315
The current work studies the fracture mode partition in beam-like geometries as a function of cohesive properties. It is observed that the mode mixity exhibits a unique dependence on the cohesive zone length scale, where the lower and upper bounds are given by the local and global partitioning. Based on this observed unique dependency, a new semi-analytical cohesive analysis (SACA) is proposed for partitioning. This partitioning method is applied to previously conflicting experimental data in the literature, and physically consistent results are obtained in each case, suggesting that this novel SACA method can be used to obtain accurate mixed mode partitioning now always.
Zuo K, Blackman BRK, Williams JG, et al., 2015, The mechanical behaviour of ZnO nano-particle modified styrene acrylonitrile copolymers, Composites Science and Technology, Vol: 113, Pages: 9-18, ISSN: 0266-3538
Forte AE, D'Amico F, Charalambides MN, et 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
Williams JG, 2015, Stress at a distance fracture criteria and crack self-blunting in rubber, INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, Vol: 68, Pages: 33-36, ISSN: 0020-7462
Williams JG, 2015, Observations on the Analysis of Mixed Mode Delamination in Composites, 1st International Conference on Structural Integrity (ICSI), Publisher: ELSEVIER SCIENCE BV, Pages: 189-198, ISSN: 1877-7058
Mohammed IK, Charalambides MN, Williams JG, et 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.
Mohammed MAP, Tarleton E, Charalambides MN, et 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.
Mohammed IK, Charalambides MN, Williams JG, et 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
Williams JG, Blackman BRK, Steininger H, et al., 2014, Toughening by plastic cavitation around cylindrical particles and fibres, Composites Science and Technology, Vol: 103, Pages: 119-126, ISSN: 0266-3538
Leevers PS, Horsfall I, Rager A, et al., 2014, High rate fracture toughness testing of thermoplastics, POLYMER TESTING, Vol: 33, Pages: 79-87, ISSN: 0142-9418
Williams JG, Patel Y, 2014, Blunt Cracks and Two Parameter Fracture Criteria, 12th International Conference on Fracture and Damage Mechanics (FDM 2013), Publisher: TRANS TECH PUBLICATIONS LTD, Pages: 13-16, ISSN: 1013-9826
Mohammed IK, Charalambides MN, Williams JG, et 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
Mohammed MAP, Tarleton E, Charalambides MN, et al., 2013, Mechanical characterization and micromechanical modeling of bread dough, JOURNAL OF RHEOLOGY, Vol: 57, Pages: 249-272, ISSN: 0148-6055
Blackman BRK, Hoult TR, Patel Y, et al., 2012, Tool sharpness as a factor in machining tests to determine toughness, Engineering Fracture Mechanics, Vol: 101, Pages: 47-58, ISSN: 0013-7944
Williams JG, 2011, The fracture mechanics of surface layer removal, INTERNATIONAL JOURNAL OF FRACTURE, Vol: 170, Pages: 37-48, ISSN: 0376-9429
Taylor AC, Williams JG, 2011, Determining the Fracture Energy of Structural Adhesives from Wedge-Peel Tests, JOURNAL OF ADHESION, Vol: 87, Pages: 482-503, ISSN: 0021-8464
Mohammed MAP, Tarleton E, Charalambides MN, et al., 2011, A composite model for wheat flour dough under large deformation, 11th International Congress on Engineering and Food (ICEF), Publisher: ELSEVIER SCIENCE BV, Pages: 492-498, ISSN: 2211-601X
Mohammeda IK, Charalambides MN, Williams JG, et al., 2011, Modelling deformation and fracture in confectionery wafers, 11th International Congress on Engineering and Food (ICEF), Publisher: ELSEVIER SCIENCE BV, Pages: 499-504, ISSN: 2211-601X
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