Groh, Rainer

Kim, Byung Chul (Eric)

Mcinnes, Calum J

Pirrera, Alberto

English

Tow-steered laminates, those in which the fibre angles vary spatially across a ply, have been investigated for improving structural performance under various loading conditions, such as buckling, bending and vibration. When steering tows by the Continuous Tow Shearing (CTS) process, the material is sheared in-plane along a curvilinear reference path. This in-plane shearing generates a non-linear orientation-thickness coupling which can be exploited in design of laminated structures. The thickness change generated by this mechanical coupling allows embedded stiffeners to be laminated into the structure. These embedded stiffeners are termed ‘pseudo-stiffeners’ and have been considered for reducing the imperfection sensitivity of a thin-walled CTS tow-steered cylinder [1]. However, the design and use of these pseudo-stiffeners to act as conventional stiffening features has not been investigated. Previous studies have steered tows continuously across a ply in a chosen direction. This continuous and global dependence of fibre angle on in-plane position has been a barrier for wider adoption of the tow steering concept in industry as it requires specialised and new modelling approaches. For example, as the fibre angles varies continuously, it is not clear how is what the most optimal tow-steered reference paths are for a specific load case. In this work, the concept of ‘local’ tow steering is proposed, where tows are steered across a comparatively shorter length than conventionally defined. This ‘local’ steering approach in conjunction with the CTS process allows for pseudo-stiffeners to be embedded in a tow-steered laminated structure. Hence, instead of attempting to define a non-intuitive curvilinear reference path, one can instead define pseudo-stiffeners through definition of design parameters, such as pseudo-stiffener orientation, in-plane width, out-of-plane thickness and count. Hence, this work utilises the potential of pseudo-stiffener design to propose several novel tow-steered structures of improved structural performance than that possible with conventional straight fibre design. To quantify performance benefits of these pseudo-stiffeners on structures manufactured by the CTS process, a study into the potential improvementsof buckling performance for laminated plates is conducted. Following a classic load case, a simply-supported CTS plate is analysed under uniaxial compression. The effects of pseudo-stiffeners, embedded by locally increasing the laminate thickness through tow steering, are directly compared in performance to an optimum straight fibre design. However, by embedding pseudo-stiffeners through shearing tows a mass increase is also generated. Hence, to allow for a fair comparison of performance between straight fibre and CTS plates, the mass of the tow-steered structure shall be conserved. Firstly, this work will embed pseudo-stiffeners into the optimum straight fibre design to explore the expected further increased structural performance that this design can achieve. Next, an investigation into other more novel designs will be considered. As laminated structures are comprised of multiple layers of material, a CTS laminate can be readily designed such that stacked plies of multiple different steering directions can embed grid-like stiffening patterns, e.g., ortho- and iso-grids. It is expected that these embedded stiffening patterns can allow for increased structural performance. REFERENCES: [1] Lincoln, R. L., Weaver, P. M., Pirrera, A., and Groh, R. M., “Imperfection-insensitive continuous tow-sheared cylinders,” CompositeStructures, Vol. 260, 2021, p. 113445. https://doi.org/10.1016/j.compstruct.2020.113445,URL https://doi.org/10.1016/j.compstruct.2020.113445

Explore Bristol Research

                          Mcinnes, C. J., Pirrera, A., Kim, B. C., & Groh, R. (2022). Improvedbuckling performance of fibre-steered laminated plates withembedded pseudo-stiffeners. Poster session presented at 25thInternational Conference on Composite Structures, Porto, Portugal.Publisher's PDF, also known as Version of recordLink to publication record in Explore Bristol ResearchPDF-documentUniversity of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only thepublished version using the reference above. Full terms of use are available:http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersCalum J. McInnes, Alberto Pirrera, Byung Chul Kim, Rainer M.J. Groh25th International Conference on Composite StructuresFaculdade de Engenharia da Universidade do Porto20th July 2022Introduction: Tow-Steered Composites2• Compression buckling is pertinent design driver in aerospace plate structures• Tow steering has proven benefits to structural performance • Current state-of-the-art (90° 0°|70° ) promotes load redistribution • Common studies have focused on tow steering by Automated Fibre Placement (AFP)20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersIntroduction: Continuous Tow Shearing3• AFP tow steering prone to inducing real defects on part• In-plane shearing of material tows by Continuous Tow Shearing (CTS) along curvilinear reference paths eliminates potential defects and allows perfect tessellation • CTS process exhibits nonlinear orientation-thickness couplingReference PathThicknessIncrease20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersKey Points41. Current state-of-the-art (90° 0°|70° ) is no longer optimum when tow steering by CTS process2. CTS tow steering allows for up to 𝟏𝟓% increase in buckling performance on a mass-equivalent basis3. Features of manufacturing process can be exploited in structural design20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners5• CTS ply denoted by ∅ 𝑻𝟎|𝑻𝟏𝒏• Linear variation in angle between 𝑇0 at period centre and 𝑇1 at half-period length 𝑑• Unsheared direction ∅ denotes steering direction• Periodicity 𝑛 denotes number of 𝑇1 → 𝑇0 →𝑇1 variations• Additional angles required for ∅ ≠ [𝟎°, 𝟗𝟎°, ∅𝒅]• Maximum allowable periodicity formulated by geometry and manufacturing parameters 𝑻𝟎20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersContext: CTS Ply Design𝐿∅∅𝒅𝒅𝑻𝟎𝑻𝟏𝑻𝟏𝑊Motivation: Problem Definition620th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners• Current state−of−the−art tow−steered ply design being 90° 0°|70° for uniaxial compression buckling [2]• CTS tow steering increases buckling load increases by 147% with accompanying mass increase of + 142%• On a mass-equivalent basis, the optimum straight fibre design ( ±𝟒𝟓° 𝒔) cannot be exceeded𝒎𝑺𝑻 = 𝒎𝑪𝑻𝑺𝒎𝑺𝑻 ≠ 𝒎𝑪𝑻𝑺90° 0°|𝑇1Motivation: Global & Local Tow Steering720th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners• Exploitation of low steering radius 𝒓𝒔 and material tesselability to embed stiffening features and mitigate a non-insignificant structural mass increase• Conventional, ‘global’ steering is a continuous linear variation in fibre angle• Comparatively, ‘local’ steering is angle variation across minimum steering lengthMethod: Finite Element Modelling820th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners• Element-wise angle and thickness computation for section assignment (e.g. ±90 0|70 1 2𝑠)• Loading introduced as unit force on opposing ends with all edges simply supported for linear buckling analysisMaterial Orientation Section ThicknessType equation here.𝑥𝑦𝑇0 𝑇1𝐿𝑊𝑑 𝑑𝑇1∅Reference Path DesignMethod: Objectives91. Explore design space to identify promising configurations for ±∅ 𝑇0|𝑇1𝑛2𝑠2. Identify configurations which exceed mass-equivalent optimum straight fibre ±45° 2𝑠 performance3. Uncover mechanics of variable angle, variable thickness panel design20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersResults: ±∅ 𝟎°|𝑻𝟏𝐦𝐢𝐧 𝒏𝟐𝒔1020th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners• CTS panels are variable angle, variable thickness • Unequal mass comparison identifies compounding benefits• Irrespective of chosen ∅ buckling load always increases with increasing 𝑇1Results: ±∅ 𝟎°|𝑻𝟏𝐦𝐢𝐧 𝒏𝟐𝒔1120th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersLocalGlobalResults: Mechanics of Optimal ±∅ 𝟎°|𝑻𝟏𝐦𝐢𝐧 𝒏𝟐𝒔1220th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners±𝟎° 𝟎°|𝟓𝟎° 𝟏𝟐𝒔±𝟗𝟎° 𝟎°|𝟕𝟎° 𝟏𝟐𝒔Results: ±∅ 𝟎°|𝑻𝟏𝐦𝐚𝐱 𝒏𝟐𝟐𝒔1320th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersLocalGlobalResults – Increased Design Freedom1420th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners1. Objective: Buckling Load Maximisation for Free Longitudinal StiffnessLaminate Steering ൗ𝜆𝑐𝑟𝐶𝑇𝑆 𝜆𝑐𝑟𝑆𝑇 Τҧ𝐴11 𝐴11±0° 0°|50° 1 2s Global 1.04 2.05±0° 70°|0° 5 2s Global 1.10 1.37±90° 70°|0° 5 2s Global 1.12 1.12±0° 70°|0° 10 2s Global 1.14 1.36±90° 0°|70° 10 2s Global 1.15 1.15Results – Increased Design Freedom1520th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners2. Objective: Longitudinal Stiffness Maximisation for Target Buckling LoadLaminate Steering ൗ𝜆𝑐𝑟𝐶𝑇𝑆 𝜆𝑐𝑟𝑆𝑇 Τҧ𝐴11 𝐴11±35° 0°|20° 1 2s Global 1.0 1.40±5° 0°|70° 5 2s Global 1.0 1.43±0° 0°|60° 10 2s Global 1.01 1.69Conclusions & Future Work1620th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-Stiffeners• Current state-of-the-art (𝟗𝟎° 𝟎°|𝟕𝟎° ) is no longer optimum when tow steering by CTS process• CTS tow steering allows for up to 𝟏𝟓% increase in buckling performance on a mass-equivalent basis• Features of manufacturing process can be exploited in structural design• Break steering equality of ∅1 = ∅2 to generate grid-style thickness build-ups for integrated grid-style reinforcement• Extension of boundary and load conditions to other classical panel problems• Meta-heurisitic optimsiation of rich solution spaceAcknowledgements17• This work was supported by the Engineering and Physical Sciences Research Council through the EPSRC Centre for Doctoral Training in Composites Science, Engineering and Manufacturing [grant number EP/S021728/1]• This work was carried out using the computational facilities of the Advanced Computing Research Centre, University of Bristol – http://www.bris.ac.uk/acrc/20th July 2022Improved Buckling Performance of Fibre-Steered Laminated Plates With Embedded Pseudo-StiffenersQuestions?calum.mcinnes@bristol.ac.ukReferences[1] B. C. Kim, K. Potter and P. M. Weaver, "Continuous tow shearing for manufacturing variable angle tow composites," Composites: Part A, vol. 43, pp. 1347-1356, 2012. [2] Gurdal, Z., Tatting, B., & Wu, C. (2008). Variable stiffness composite panels: Effects of stiffness variation on the in-plane and buckling response. Composites: Part A, 911-922.

Improved buckling performance of fibre-steered laminated plates with embedded pseudo-stiffeners

http://hdl.handle.net/1983/426aa789-d10b-4b6a-8c2a-02c9daf984e2

Improved buckling performance of fibre-steered laminated plates with embedded pseudo-stiffeners

Abstract

Similar works

Full text

Available Versions

Explore Bristol Research