Browsing by Author "Sutcliffe, Michael P. F."

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    Design selection methodology for composite structures
    (Elsevier Science B.V., Amsterdam., 2008-01-01T00:00:00Z) Monroy, Aceves C.; Skordos, Alexandros A.; Sutcliffe, Michael P. F.
    This paper presents a methodology to help designers select a shortlist or optimum design of composite structure from a large number of alternatives, taking into account conflicting design objectives or constraints (e.g. weight and cost). The methodology is based on creating a database containing results from an exhaustive search of a wide range of possible solutions. These results can be viewed using a commercial software selection package, originally written for materials selection. The designer then has freedom to change the selection criteria and required design constraints, to allow interactive selection of the data. The design methodology is illustrated by way of a case study, the design of a reinforced dogbone specimen.
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    Drape optimization in woven composites manufacture.
    (2005-07-01T00:00:00Z) Skordos, Alexandros A.; Monroy, Aceves C.; Sutcliffe, Michael P. F.
    This paper addresses the optimisation of forming in manufacturing of composites. A simplified finite element model of draping is developed and implemented. The model incorporates the non-linear shear response of textiles and wrinkling due to buckling of tows. The model is validated against experimental results and it is concluded that it reproduces successfully the most important features of the process. The simple character of the model results in low computational times that allow its use within an optimisation procedure. A genetic algorithm is used to solve the optimisation problem of minimising the wrinkling in the formed component by selecting a suitable holding force distribution. The effect of regularisation is investigated and the L-curve is used to select a regularisation parameter value. Optimised designs resulting from the inversion procedure have significantly lower wrinkling than uniform holding force profiles, while regularisation allows force gradients to be kept relatively low so that suggested process designs are feasible.
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    Multi-Objective Optimisation of Woven Composite Draping using Genetic Algorithms.
    (2006-03-01T00:00:00Z) Skordos, Alexandros A.; Sutcliffe, Michael P. F.; Klintworth, J. W.; Adolfsson, P.
    This paper presents a draping optimisation scheme based on the integration of a commercial kinematic drape simulation code and a genetic algorithm. The kinematic model allows a fast solution to the drape model which reproduces successfully the distribution of shear over the component surface, while a genetic algorithm drives the optimisation. Various setups of the problem are considered, including single and multiple objective solutions. The efficiency of the methodology is evaluated based on the results of the scheme applied to the draping of a composite pilot helmet.
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    Optimisation of Sheet Forming for Textile Composites using variable Peripheral Pressure.
    (2006-03-01T00:00:00Z) Long, Andrew; Skordos, Alexandros A.; Harrison, Phil; Clifford, Mike; Sutcliffe, Michael P. F.
    This paper addresses optimisation of the sheet forming process for textile composites. A woven carbon/epoxy prepreg helicopter pilot helmet is used to demonstrate both experimental and numerical studies. A novel stamp-forming experimental procedure is developed, where a segmented blank-holder is used to control draw-in, facilitating process control and optimisation. A truss based finite element model, incorporating non-linear fabric shear properties and the occurrence of wrinkling due to tow buckling, is used to simulate forming. The simple basis of the model results in low computational times that allow its use within an optimization procedure. A genetic algorithm is used to solve the optimisation problem, minimizing the wrinkling in the formed component by selecting a suitable peripheral holding force distribution. Optimised designs resulting from the inversion procedure have significantly lower wrinkling than uniform peripheral force profiles.
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    A simplified rate dependent model of forming and wrinkling of pre-impregnated woven composites
    (Elsevier Science B.V., Amsterdam., 2007-05-01T00:00:00Z) Skordos, Alexandros A.; Monroy, Aceves C.; Sutcliffe, Michael P. F.
    A simplified finite element model is developed and validated for the forming/ draping of pre-impregnated woven composites, incorporating the effects of wrinkling and strain rate dependence. The model development builds upon previous work on simulation of fabric draping using a truss representation of the woven material. Tows are modelled by stiff elastic bar elements, and the non-linear rate dependent shear behaviour is incorporated in elastic-viscoplastic elements that follow an appropriate phenomenological constitutive model. Wrinkling due to tow buckling is simulated by allowing the deactivation of tow elements that undergo compressive deformation. The model convergence is tested and its validity is checked against experimental results from the forming of pre- impregnated woven carbon hemispheres. It is found that the model reproduces successfully experimental measurements of shear and wrinkling with a relative error of approximately 4%, while solution times are kept below 60 s on a conventional PC. These features allow potential iterative use of the model within a process optimisation scheme. The sensitivity of the process outcome to process parameters such as blank holder force and forming speed is investigated.
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    Stochastic simulation of woven composites forming
    (Elsevier Science B.V., Amsterdam., 2008-01-01T00:00:00Z) Skordos, Alexandros A.; Sutcliffe, Michael P. F.
    A stochastic forming simulation procedure is developed and implemented to investigate the effect of geometric variability in pre-impregnated woven textiles on manufacturing. Image analysis is used to characterise variability in tow directions and unit cell size in a pre-impregnated carbon/epoxy satin weave textile. It is found that variability in tow orientations is significant, whereas variability in the unit cell size is negligible. Variability in the weft direction is higher than in the warp direction. Highly anisotropic spatial autocorrelation of weft tow orientations is observed with the major direction of autocorrelation normal to the corresponding set of tows. The extent of autocorrelation is 6–20 unit cells. The autocorrelation structure is modelled using a two-parameter stochastic process, the Ornstein–Uhlenbeck sheet, and an efficient parameter estimation technique is developed based on maximum likelihood. The resulting stochastic process is simulated using Cholesky decomposition which is combined with a simplified forming model within a Monte Carlo scheme. The forming model incorporates non-linear strain-rate dependent behaviour and wrinkling due to tow buckling in a truss formulation. Execution of the integrated scheme shows that geometric variability of the woven material has significant influence on the forming process. The coefficient of variation of minimum and average wrinkling strain in the formed component is in the range of 10–20%. Variability affects the results of forming optimisation and it should be taken into account in process design. Although applied to the case of woven textile forming, the stochastic scheme presented in this paper is general and can be applied to any material system with imperfect stru