Optimisation of Imperfection-Insensitive Continuous Tow Sheared Rocket Launch Structures

Lincoln, Reece L; Pirrera, Alberto; Groh, Rainer

doi:10.2514/6.2021-0202

Cited by 8 publications

(11 citation statements)

References 31 publications

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“…The fiber angle-to-tow thickness coupling therefore allows unique opportunities for design. For example, by periodically and repeatedly shearing a tow between two orientations along a cylinder's length or across the cylinder's circumference, embedded stiffeners can be manufactured in-situ [7].…”

Section: Introductionmentioning

confidence: 99%

“…Previous work has found that in finite element (FE) predictions RTS cylinders have an increased specific buckling load when compared to their straight-fiber counterparts [8]. When modeled stochastically with Monte Carlo simulations of nonlinear buckling analyses and a dataset of measured geometric imperfections, RTS cylinders also showed a smaller variance and higher mean buckling load when compared to straight-fiber cylinders [7]. As a result, the well-documented sensitivity to geometric imperfections of axially compressed cylindrical shells was shown to be smaller for RTS cylinders.…”

Section: Introductionmentioning

confidence: 99%

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Manufacture and Buckling Test of a Variable-Stiffness, Variable-Thickness Composite Cylinder Under Axial Compression

2023

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Variable-angle tow (VAT) manufacturing methods significantly increase the design space for elastic tailoring of composite structures by smoothly changing fiber angle and ply thickness across a component. Rapid tow shearing (RTS) is a VAT manufacturing technique that uses in-plane shearing (rather than in-plane bending) to steer tows of dry or pre-impregnated fibers. RTS offers a number of benefits over conventional bending-driven steering processes, including tessellation of adjacent tow courses; no overlaps or gaps between tows; and no fiber wrinkling or bridging. Further to this, RTS offers an additional design variable: fiber orientation to tow thickness coupling due to the volumetric relation between tow shearing and the tow’s thickness and width. Previous computational work has shown that through a judicious choice of curvilinear fiber trajectories along a cylinder’s length and across its circumference, the imperfection sensitivity of cylindrical shells under axial compression can be reduced and load-carrying capacity increased. The present work aims to verify these predictions by manufacturing and testing two cylinders: an RTS cylinder and a straight-fiber, quasi-isotropic cylinder as a benchmark. The tow-steered manufacturing process, imperfection measurements, instrumentation, and buckling tests of both cylinders are discussed herein. The experimental tests results are compared against high-fidelity geometrically nonlinear finite element models that include measured geometric and loading imperfections before and during the tests. Finally, a discussion is provided on the outstanding challenges in designing and manufacturing RTS cylinders for primary aerostructures.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Manufacture and Buckling Test of a Variable-Stiffness, Variable-Thickness Composite Cylinder Under Axial Compression

2023

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“…This potential for increased structural performance by embedding stiffening features into a laminate was investigated by Lincoln et al, who studied embedded longitudinal stringers and circumferential hoops on a thin-walled cylinder to decrease structural sensitivity to geometric imperfections under axial compression [15]. Subsequently, Lincoln et al utilized a genetic algorithm to optimize cylinders to identify the potential for structural imperfection insensitivity [16].…”

Section: Introductionmentioning

confidence: 99%

“…Tow-steered structures have thus been the subject of numerous FE studies, however little formal investigation into the most accurate element choice for FE modeling of CTS tow-steered structures exists, due to a widespread continuation of choices taken from AFP studies. When FE modeling CTS structures, authors such as Lincoln et al [15,16], Kim et al [17], Groh and Weaver [18], use degenerated shell elements. This manuscript shall refer to these degenerated shell elements as 'conventional shell elements' (S4 or S4R in Abaqus CAE).…”

Section: Introductionmentioning

confidence: 99%

On the Finite Element Discritization of Continuous Tow Sheared Structures

McInnes

Lincoln

Pirrera

et al. 2022

AIAA SCITECH 2022 Forum

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Tow-steered laminates, those in which the fiber angle varies as a function of in-plane coordinates, represent a substantial numerical modeling problem. In the Continuous Tow Shearing (CTS) process, the tows are deformed by in-plane shearing that generates a non-linear orientation-thickness coupling, which needs to be accounted for when analyzing CTS structures. In this manuscript, an investigation into the Finite Element discretization of CTS structures is conducted to ascertain the most appropriate element choice in terms of computational cost and accuracy. First, natural frequency and buckling eigenvalue analyses are conducted on constant-thickness flat plates and thin-walled cylinders ([±45/0/90] s layup), in order to set a baseline. Next, multiple discretization strategies are implemented to investigate a CTS plate and a thin-walled CTS cylinder by means of two-and three-dimensional shell elements, in linear frequency and buckling analyses. Two CTS stacking sequences are considered, with the first ([±0 0|70 10 ] 2s ) having identical steering across plies, and the second with variable steering across plies ([±0 0|70 10 /±90 0|70 10 ] s ) to increase the discretization difficulty. The use of three-dimensional shell elements allows for greater fidelity in representing the geometry of a CTS structure, as they allow the asymmetric thickness build-ups to be discretized accurately. We show that three-dimensional shell elements enable the use of lower mesh resolutions whilst maintaining solution accuracy, in comparison to two-dimensional shell element meshes of the same geometric in-plane resolution. Moreover, a relation between element type and mesh resolution is presented to appropriately align element centroids and nodal coordinates, for two-and three-dimensional shell elements, respectively, with the maxima of a specific thickness distribution.

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“…pressure vessels [28,29], cylinders under bending [30], compression [31][32][33][34][35][36][37] and vibration [33,38], and aircraft wings [39][40][41][42][43][44][45][46], experimental data that can be used to validate different design, modeling and analysis approaches are relatively rare. Therefore, the steps and techniques required for commercial certification of tow-steered composite parts are not as well defined or understood as for established straight-fiber composites.…”

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confidence: 99%

Nonlinear Buckling and Postbuckling Analysis of Tow-Steered Composite Cylinders with Cutouts

Groh

2022

AIAA Journal

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The buckling and postbuckling behavior of two composite tow-steered shells with cutouts of different sizes is assessed using nonlinear finite element (FE) analysis and compared to experimental measurements. The cylindrical shells are manufactured using an automated fiber placement system, where the shells' fiber orientation angles vary continuously around the shell circumference from ±10 degrees on the crown and keel to ±45 degrees on the sides. One shell features thickness variations due to tow overlaps that result from application of all 24tows during each pass of the fiber placement system. The second shell uses the system's tow drop/add capability to achieve a more uniform wall thickness without overlaps. Unreinforced cutouts of two different sizes-the first smaller cutout representing a passenger door on a commercial aircraft and the second larger cutout a cargo door-were machined into each of the two cylinders resulting in a total of four test cases. These cylinders were tested in axial compression and buckled elastically in previous work and are now analyzed using nonlinear FE models to compare bifurcation buckling loads as well as the load-displacement response in the prebuckling and postbuckling regimes. For all four shells analyzed, the prebuckling stiffness, buckling load, and deformation mode sequence throughout the loading-unloading cycle is accurately reproduced by the models. In particular, the shells first buckle locally around the cutouts in a stable (super-critical) manner with only a slight decrease in axial stiffness, which occurs due to the favorable load redistribution facilitated by tow steering. The shells then buckle globally in an unstable (sub-critical) manner with diamond-shaped buckles forming to the left and right (circumferential direction) of the cutouts. The buckling load of all shells with cutouts is at least 82% of the buckling load of the pristine shells without cutouts. Overall, the ability to sustain local buckling phenomena, and the relatively small reductions in global buckling load compared to pristine shells without cutouts, demonstrates the great potential of using tow

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Optimisation of Imperfection-Insensitive Continuous Tow Sheared Rocket Launch Structures

Cited by 8 publications

References 31 publications

Manufacture and Buckling Test of a Variable-Stiffness, Variable-Thickness Composite Cylinder Under Axial Compression

Manufacture and Buckling Test of a Variable-Stiffness, Variable-Thickness Composite Cylinder Under Axial Compression

On the Finite Element Discritization of Continuous Tow Sheared Structures

Nonlinear Buckling and Postbuckling Analysis of Tow-Steered Composite Cylinders with Cutouts

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