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  • 1.
    Burman, Magnus
    et al.
    KTH Royal Institute of Technology, Sweden.
    Stig, Fredrik
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP.
    Zenkert, Dan
    KTH Royal Institute of Technology, Sweden.
    Blister propagation in sandwich panels2019Ingår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 21, nr 5, s. 1683-1699Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper deals with the problem of face/core interfacial disbonds in sandwich panels that are pressurised, i.e. the disbond has an initial fluid pressure that causes the disbond to deform. The problem is often referred to as a blister. The panel with a blister is then subjected to an in-plane compressive load. Four different panels are analysed and tested, having different size disbonds and different initial internal pressure. The cases are analysed using a finite element approach where the blister is modelled using fluid elements enabling the pressure inside the blister to vary as the in-plane load is applied. The analysis uses non-linear kinematics, and in each load step, the energy release rate is calculated along the disbond crack front. This model is used for failure load predictions. The four cases are then tested experimentally by filling a pre-manufactured disbond cavity with a prescribed volume of air. This air volume is then entrapped, and the panel is subjected to an in-plane compressive load. The load and blister pressures are measured throughout the test and compared with the finite element analysis. Surface strains and blister deformations are also measured using digital correlation measurements. The predicted failure loads compare well with the experimental results, and so does the blister pressures, the latter at least qualitatively. © The Author(s) 2019.

  • 2.
    Cameron, Christopher
    et al.
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    Hozić, Dženan
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    Stig, Fredrik
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    van der Veen, Sjord
    Airbus Operations SAS, France.
    A method for optimization against cure-induced distortion in composite parts2023Ingår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 66, nr 3, artikel-id 51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a novel method developed for the optimization of composite components against distortion caused by cure-induced residual stresses. A novel ply stack alteration algorithm is described, which is coupled to a parametrized CAD/FE model used for optimization. Elastic strain energy in 1D spring elements, used to constrain the structure during analysis, serves as an objective function incorporating aspects of global/local part stiffness in predicted distortion. Design variables such as the number and stacking sequence of plies, and geometric parameters of the part are used. The optimization problem is solved using commercial software combined with Python scripts. The method is exemplified with a case study of a stiffened panel subjected to buckling loads. Results are presented, and the effectiveness of the method to reduce the effects of cure-induced distortion is discussed. © 2023, The Author(s).

  • 3.
    Cameron, Christopher J.
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP.
    Saseendran, Sibin
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP.
    Stig, Fredrik
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP.
    Rouhi, Mohammad
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP.
    A rapid method for residual cure stress analysis for optimization of cure induced distortion effects2018Ingår i: ECCM 2018 - 18th European Conference on Composite Materials, Applied Mechanics Laboratory , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Within this paper, the authors present a rapid method for residual cure stress analysis. The method uses a high-fidelity path-dependent cure kinetics analysis subroutine implemented in Abaqus to calibrate values for a linear elastic analysis. The path dependent model accounts for the tool-part interaction, forming pressure, and the changing composite modulus during the rubbery region of matrix curing during an arbitrary cure cycle. Results are used to calculate equivalent lamina-wise coefficients of thermal expansion (CTE) in 3 directions for a linear temperature analysis. The goal is to accurately predict distortions for large complex geometries with a single linear temperature load as rapidly and accurately as possible for use in an optimization framework. A carbon-epoxy system is studied. Simple parts are manufactured using unbalanced layups and out-of-autoclave methods. The resulting distortions are scanned with a 3D scanner and compared with simulation results for the same geometries. Further, a more complicated part is studied to compare the two methods using complex geometry. Results are presented and the accuracy and limitations of the rapid simulation method are discussed with particular focus on implementation in a numerical optimization framework.

  • 4.
    Cameron, Christopher
    et al.
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    Saseendran, Sibin
    RISE Research Institutes of Sweden.
    Stig, Fredrik
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    Rouhi, Mohammad
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer. National University of Singapore, Singapore.
    A rapid method for simulating residual stress to enable optimization against cure induced distortion2021Ingår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 55, nr 26, s. 3799-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a rapid method for residual cure stress analysis from composite manufacturing is presented. The method uses a high-fidelity path-dependent cure kinetics subroutine implemented in ABAQUS to calibrate a linear elastic model. The path-dependent model accounts for the tool-part interaction, forming pressure, and the changing composite modulus during the rubbery phase of matrix curing. Results are used to calculate equivalent lamina-wise coefficients of thermal expansion (CTE) in 3 directions for a linear temperature analysis. The goal is to accurately predict distortions for large complex geometries as rapidly as possible for use in an optimization framework. A carbon-epoxy system is studied. Simple coupons and complex parts are manufactured and measured with a 3 D scanner to compare the manufactured and simulated distortion. Results are presented and the accuracy and limitations of the rapid simulation method are discussed with particular focus on implementation in a numerical optimization framework. © The Author(s) 2021.

  • 5.
    Oddy, Carolyn
    et al.
    Chalmers University of Technology, Sweden.
    Ekermann, Tomas
    KTH Royal Institute of Technology, Sweden.
    Ekh, Magnus
    Chalmers University of Technology, Sweden.
    Fagerström, Martin
    Chalmers University of Technology, Sweden.
    Hallström, Stefan
    KTH Royal Institute of Technology, Sweden.
    Stig, Fredrik
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, IVF.
    Predicting damage initiation in 3D fibre-reinforced composites – The case for strain-based criteria2019Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 230, artikel-id 111336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three dimensional (3D) fibre-reinforced composites have shown weight efficient strength and stiffness characteristics as well as promising energy absorption capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforcements suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner. With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. It is shown that the extension of the LaRC05 stress-based failure criteria for unidirectional laminated composites, to this class of 3D-reinforced composite presents a number of challenges and leads to erroneous predictions. Analysing a mesoscale representative volume element does however indicate, that loading the 3D fibre-reinforced composite produces relatively uniform strain fields. The average strain fields of each material constituent are well predicted by an equivalent homogeneous material response. Strain based criteria inspired by LaRC05 are therefore proposed. The criteria are evaluated numerically for tensile, compressive and shear tests. Results show that their predictions for the simulated load cases are qualitatively more reasonable. 

  • 6.
    Stig, Fredrik
    et al.
    RISE - Research Institutes of Sweden (2017-2019), Material och produktion, SICOMP. KTH Royal Institute of Technology, Sweden.
    Hallström, Stefan
    KTH Royal Institute of Technology, Sweden.
    Effects of crimp and textile architecture on the stiffness and strength of composites with 3D reinforcement2019Ingår i: Advances in Materials Science and Engineering, ISSN 1687-8434, E-ISSN 1687-8442, Vol. 2019, artikel-id 8439530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this study is to experimentally determine how the weave architecture and yarn crimp affect the measured tensile stiffness and strength of composites containing 3D textile reinforcement. It is shown that both the stiffness and strength decrease nonlinearly with increasing 3D crimp. The ultimate strength of specimens containing nominally straight yarns and specimens containing crimped yarns can differ more than a factor of 3, and the stress causing onset of damage can be affected even more. Adding nominally straight stuffer yarns into a 3D-woven reinforcement significantly increases the fibre volume fraction, the stiffness, and the strength of the composite. However, since the stuffer yarns are virtually straight and thus stiffer than the warp yarns, they attract the load and reach their strength at relatively lower strain than the warp yarns. The reinforcement architecture varies between the surfaces and the interior of the studied textiles, which has corresponding influence on the local stiffness. The onset of failure is predicted satisfactorily accurate with relatively simple estimations. The ultimate strength is a result of extensive damage progression and thus more dubious to predict. © 2019 Fredrik Stig and Stefan Hallström.

  • 7.
    Stig, Fredrik
    et al.
    RISE Research Institutes of Sweden, Material och produktion, Polymera material och kompositer.
    Hallström, Stefan
    KTH Royal Institute of Technology, Sweden.
    Extended framework for geometric modelling of textile architectures2020Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 244, artikel-id 112239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three dimensional (3D) textiles are finding their way into fibre reinforced composite applications, and for good reasons; they can eliminate the hazard of delamination and enable complex reinforcement shapes. There is therefore a need for engineering methods to simulate these advanced textile structures during the product development phase. This is many times challenging since the textile architecture is truly 3D and not built by layers as in conventional laminated composites. The overall approach is similar as in a method previously presented by the authors, but some steps are changed that enable modelling of textiles containing strongly curved yarns, yet with very good geometric representation. That is essential for reliable simulations of all parts of the 3D reinforced composite materials, which could then be performed at close to authentic meso level resolution. The resulting textile geometries are very similar to the real materials they represent, both in terms of variation of yarn cross section area and shape along the length of the yarns. This is demonstrated by comparison of details between the real materials and the numerical implementations of their geometry.

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