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  • 1.
    Bull, Peter Hoaas
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Edgren, F
    Compressive strength after impact of CFRP-foam core sandwich panels in marine applications2004In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 35, no 6-8, 535-541 p.Article in journal (Refereed)
    Abstract [en]

    A plastic micro buckling approach is investigated in order to see whether it can be used to analytically predict the residual strength of carbon fiber sandwich structures. A parametric study on impact damage resistance and residual strength of sandwich panels with carbon fiber-vinylester faces and PVC foam core is conducted. Two sandwich configurations are studied. The first configuration consists of thin faces and an intermediate density core, representative of a panel from a superstructure. The second configuration consists of thick faces and a high density core, representative of a panel from a hull. Two different impactor geometries are used. One spherical impactor and one pyramid shaped impactor are used in a drop weight rig to inflict low velocity impact damage of different energy levels in the face of the sandwich. The damages achieved ranges from barely visible damages to penetration of one face. Residual strength is tested using in-plane compression of the sandwich plates either instrumented with strain gauges or monitored with digital speckle photography.

  • 2.
    Ekh, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Schön, Joakim
    Melin, L. Gunnar
    Secondary Bending in Multi Fastener, Composite-to-Aluminium Single Shear Lap Joints2005In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 36, 195-208 p.Article in journal (Refereed)
    Abstract [en]

    A novel technique to study secondary bending due to the eccentric load path in single shear, composite-to-aluminium lap joints has been developed and used in a parametric study. The method is based on the specimen curvature, which is derived from lateral displacements of the surface. The lateral displacements are measured with an optical measurement system or calculated with the finite element method. It was found that the specimen curvature is equivalent to the secondary bending which is usually measured with strain gauges in the vicinity of the bolt holes. The two most important parameters affecting specimen curvature is the overlap length and the thickness of the aluminium plate in the joints.

  • 3.
    Karlsson Hagnell, Mathilda
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Åkermo, Malin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    A composite cost model for the aeronautical industry: Methodology and case study2015In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 79, 254-261 p.Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel composite production cost estimation model. The strength of the model is its modular construction, allowing for easy implementation of different production methods and case studies. The cost model is exemplified by evaluating the costs of a generic aeronautical wing, consisting of skin, stiffeners and rib feet. Several common aeronautical manufacturing methods are studied. For studied structure, hand layup is the most cost-effective method for annual volumes of less than 150 structures per year. For higher production volumes automatic tape layup (All) followed by hot drape forming (HDF) is the most cost-effective choice.

  • 4.
    Kelly, Gordon
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Bearing strength of carbon fibre/epoxy laminates: effects of bolt-hole clearance2004In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 35, no 4, 331-343 p.Article in journal (Refereed)
    Abstract [en]

    The bearing strength of carbon fibre epoxy laminates manufactured from non-crimp fabric from heavy tow yarn has been investigated. The effects of laminate stacking sequence and geometry on the bearing strength have been determined experimentally together with the effect of initial bolt-hole clearance on the bearing strength at 4% hole deformation and at ultimate load. Significant reduction in bearing strength at 4% hole deformation was found for both pin-loaded and clamped laminates as a result of bolt-hole clearance. It was concluded that the effect of bolt-hole clearance is significant with regard to the design bearing strength of mechanically fastened joints. A three-dimensional non-linear finite element model was developed to investigate the effects of bolt-hole clearance on the stress field in the laminate adjacent to the hole. The magnitude and distribution of stress at the hole was found to be significantly dependent on the level of clearance.

  • 5.
    Schneider, Christof
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Kazemahvazi, Sohrab
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. University of Cambridge, UK.
    Russell, B. P.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Deshpande, V. S.
    Impact response of ductile self-reinforced composite corrugated sandwich beams2016In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 99, 121-131 p.Article in journal (Refereed)
    Abstract [en]

    Corrugated sandwich beams made entirely from self-reinforced poly (ethylene terephthalate) SrPET are manufactured and tested dynamically. The beams are subjected to impact loading at the mid-span using a metal foam projectile and the beam deflection is measured. For sandwich beams with a constant areal mass, beams with a high mass portion in the core webs outperform configurations with a high mass portion in the face sheets (given that the face sheets are thick enough to carry the transversal loads induced by the core webs). Reinforcing the face sheet - core web interface further improves the impact response. The strain rate sensitivity of SrPET has also been investigated. A three-dimensional finite element (FE) model has been developed to simulate the impact event and a good agreement is found with the measured response. It is found that corrugated sandwich beams made from SrPET has competitive impact performance compared to similar sandwich beams with equal mass and geometry out of aerospace grade aluminium and carbon fiber/high performance foam sandwich.

  • 6.
    Zenkert, Dan
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Shipsha, Andrey
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Persson, K.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Static indentation and unloading response of sandwich beams2004In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 35, no 08-jun, 511-522 p.Article in journal (Refereed)
    Abstract [en]

    This paper deals with analysis of foam core sandwich beams subject to static indentation and subsequent unloading (removal of load). Sandwich beams are assumed continuously supported by a rigid platen to eliminate global bending. An analytical model is presented assuming an elastic-perfectly plastic compressive behaviour of the foam core. An elastic part of indentation response is described using the Winkler foundation model. Upon removal of the load, an elastic unloading response of the foam core is assumed. Also, finite element (FE) analysis of static indentation and unloading of sandwich beams is performed using the FE code ABAQUS. The foam core is modelled using the crushable foam material model. To obtain input data for the analytical model and to calibrate the crushable foam model in FE analysis, the response of the foam core is experimentally characterized in uniaxial compression, up to densification, with subsequent unloading and tension until tensile fracture. Both models can predict load-displacement response of sandwich beams under static indentation and a residual dent magnitude in the face sheet after unloading along with residual strain levels in the foam core at the unloaded equilibrium state. The analytical and FE analyses are experimentally verified through static indentation tests of composite sandwich beams with two different foam cores. The load-displacement response, size of a crushed core zone and the depth of a residual dent are measured in the testing. A digital speckle photography technique is also used in the indentation tests in order to measure the strain levels in the crushed core zone. The experimental results are in good agreement with the analytical and FE analyses.

  • 7. Zimmermann, Kristian
    et al.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Siemetzki, M.
    Testing and analysis of ultra thick composites2010In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 41, no 4, 326-336 p.Article in journal (Refereed)
    Abstract [en]

    For the development of a composite main landing gear fitting in carbon fiber reinforced plastics the behavior and performance of Ultra Thick Laminate components is investigated. Material thicknesses exceeds 60 mm. For the purpose of validation a test program is arranged using T-cross sections subjected to multiple load cases. The components are manufactured entirely with non crimped fabrics (NCF) using an adapted open mould manufacturing process. In addition to these T-Sections large full scale subcomponents of the entire fitting are manufactured and tested. As main topic of this paper standard FE methods are investigated and validated for thick structures using the generated test results. Due to the presence of transverse shear and normal stresses a 3D modeling approach is chosen. Transverse shear and normal stresses are indentified as main failure cause and failure is mainly initiated in the curved regions. Solid composite brick elements offer an efficient way to model thick structures. These are incapable of calculating accurate shear stresses on a ply level; usable results are however achieved by discretisation of the component with multiple elements over thickness. In addition stress gradients in the failure region are small; stress variations on a ply level are minimal. Out of plane material properties are not available and initial assumptions are made. Material correction factors (degradation) are introduced and discussed.

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