Approximations for Warp-Free Laminate Configurations

O’Donnell, Matthew P.; York, Christopher

doi:10.2514/6.2010-2774

Cited by 4 publications

(6 citation statements)

References 3 publications

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“…Classical laminate theory [2] provides a robust method to capture these effects. Changing layup, leads to a range of laminate responses, from those that do not warp [3], to others that display varying degrees of warping [4]. As it is clear that not all non-symmetric layups are alike, we assert that those laminates that display modest levels of warping be considered for design purposes, as symmetric laminates already are, based on their predicted response.…”

Section: Introductionmentioning

confidence: 87%

Reconsidering Laminate Nonsymmetry

O’Donnell

2020

AIAA Journal

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Non-symmetric laminates are commonly precluded from composite design due to perceptions of reduced performance arising from in-and out-of-plane coupling. This coupling introduces warpage during cure -leading to raised stresses, together with diminished buckling and load carrying capacity. However, these reduced performance characteristics are rarely quantified and included in the design process, instead the "symmetric-only" paradigm remains pervasive at the cost of a significantly reduced design space. Warpage is largely driven by mismatch in the coefficients of thermal expansion between sub-laminates located above and below the mid-plane and can be predicted by classical laminate theory. Acknowledging that all symmetric laminates in multi-part structures have build stresses from assembly, we propose that subsets of non-symmetric laminates, that translate to similar raised stress levels, be considered for design. Challenging this "symmetric-only" design paradigm would permit greater design freedom and offer new routes to elastically tailor composite structures. Further analysis of structural performance is assessed in terms of reduced loading and buckling capacity.

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Section: Introductionmentioning

confidence: 87%

Reconsidering Laminate Nonsymmetry

O’Donnell

2020

AIAA Journal

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“…Although in general coupled laminates often exhibit warping when cured, this is readily quantifiable and in many cases the strains associated with flattening are nominal compared to the ultimate capacity of the component. 4 Lamination parameters have been used successfully in many optimisation procedures and recently a two level approach has been used by Bloomfield et al 5 The advantage of using this approach is that the discrete stacking sequence can be solved separately. As part of the current approach an alternative eccentricity function is proposed and its effects discussed.…”

Section: Figure 1: Example Of Skin/stringer Assemblymentioning

confidence: 99%

Debond Resisting Composite Stringers

O’Donnell

Cosentino²

2012

53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials ConferenceSelf Cite

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The following extends existing work done by Cosentino and Weaver on predicting crack initiation in discretely assembled skin/stringer composite panels. This allows for the analysis of fully coupled systems ie. non-zero B matrix. The nonlinear structural behaviour is obtained by means of the von Kármán formulation for moderately large deflections in plates; three-dimensional assemblies are schematized and the effect of eccentricity is included in the simulation. Solutions are calculated by means of a Rayleigh-Ritz approach based on Galerkin's method, and a linear elastic fracture mechanics-based model is used to simulate the crack initiation in the critical regions. Using this method a bi-level optimisation using lamination parameters was performed subject to closed form buckling and debonding constraints. The optimisation was performed with respect to improving the strength and overall load carrying capacity for a fixed geometry. The results show through the use of layup optimisation incorporating flexure-membrane coupling effects debonding can be reduced.

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“…where the thermal curvature changes during cooling from manufacture, ∆κ κ κ th are added to the manufacture tooling radius. The changes in curvature of an anisotropic plate due to thermallyinduced bending moments (M M M th ) and in-plane forces (N N N th ) [3] can be evaluated as…”

Section: Elastic Strain Energymentioning
confidence: 99%

“…These benefits include high specific properties, anisotropic deformation behaviour, ease of manufacturing complex geometries, and new ways of tailoring the residual stress state of the mechanism. This study aims to investigate the effects of thermal prestress, arising from mismatches in thermal expansion coefficients [3], on the behaviour of composite tape springs. This is achieved using extensions of existing analytical approaches that are compared to experimental results and finite element (FE) simulations.…”

Section: Introductionmentioning
confidence: 99%

Thermal Prestress in Composite Compliant Shell Mechanisms
Stacey
¹
,
O’Donnell
²
,
Schenk
³

2018
Volume 5A: 42nd Mechanisms and Robotics Conference
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Due to the anisotropic nature of fibre-reinforced laminates, thermally-induced internal stresses can remain in the material after manufacture. Mismatches between coefficients of thermal expansion are especially prominent in thin shells with fewer plies or large angle variations. Such stresses cause out-of-plane warping and are therefore often deliberately avoided. Utilising their effects on structural behaviour however, can enable stiffness-tailored composite compliant mechanisms. Work detailed in this paper aims to exploit thermal prestress to reduce the torsional stiffness of cross-ply tape laminate springs. An extension of an analytical tape spring model with composite thermal analysis is presented, which shows that thermal effects cause significant changes to the energy landscapes of thin composite shells. Tape springs that would otherwise be monostable structures become bistable and exhibit greater ranges of low-energy twisting when thermally-induced prestress is present. Predicted shell geometries are compared with finite element models and manufactured samples, showing good agreement between all approaches. The limited feasibility of zero torsional stiffness composite tape springs is discussed, as well as wider challenges involved in manufacturing prestressed composite compliant mechanisms such as fibre misalignment and moisture ingress.

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Approximations for Warp-Free Laminate Configurations

Cited by 4 publications

References 3 publications

Reconsidering Laminate Nonsymmetry

Reconsidering Laminate Nonsymmetry

Debond Resisting Composite Stringers

Thermal Prestress in Composite Compliant Shell Mechanisms

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