Reliability design optimisation of classic composite plates using a CUF-based layerwise approach

Uncertainties in the manufacturing process of structures may arise at any moment of the fabrication chain. In the case of composite structures, such uncertainties may appear in the material elastic properties as a result of the microscale features of such material or even from manufacturing flaws, such as misalignments, fibre waviness, etc. [1] when assembling the final product. As a result of these defects, the structural response of the final structure might be compromised. Therefore, a reliability analysis is needed. In this work, a reliability-based design optimization (RBDO) [2] regarding the linearized buckling behavior of a straight-fibre composite laminate is carried out concerning homogeneous material elastic properties variation. In order to perform such analyses, Carrera Unified Formulation (CUF) [3] is used, according to which structural theories with low-order accuracy to layerwise models can be implemented in a hierarchical and unified manner. These analyses are then used to build a surrogate model based on Polynomial Chaos Kriging (PCK) [4], which substitutes the finite element model and thus accelerates the optimization process. The final scope of the work is to show that layerwise models can help to broaden the design space that other structural approaches may have shrunk, while subjected to the manufacturing constraints that the industry has imposed through the years [5]. References [1] A. Pagani, A.R. Sanchez-Majano. Influence of fibre misalingments on buckling performance of variable stiffness composites using layerwise models and random fields. Mechanics of Advanced Materials and Structures 2020. DOI: https://doi.org/10.1080/15376494.2020.1771485 [2] M. Moustapha, B. Sudret. Surrogate-assisted reliability-based design optimization: a survey and a unified modular framework. Structural and Multidisciplinary Optimization 60, 2157–2176 (2019). DOI: 10.1007/s00158-019-02290-y [3] E. Carrera, M. Cinefra, M. Petrolo, E. Zappino. Finite Element Analysis of Structures through Unified Formulation. Wiley & Sons. 2014. ISBN: 978-1-119-94121-7. [4] R. Schobi, S. Marelli, B. Sudret, UQLab user manual – Polynomial chaos Kriging, Report # UQLab-V1.3-109, Chair of Risk, Safety and Uncertainty Quantification, ETH Zurich, Switzerland, 2019 [5] G.H.C. Silva, A.P. do Prado, P.H. Cabral, R. De Breuker, J.K.S. Dillinger. Tailoring of a Composite Regional Jet Wing Using the Slice and Swap Method. Journal of Aircraft, 1–15. (2019) DOI:10.2514/1.c03509

Stochastic stress analysis and failure onset of variable angle tow laminates affected by spatial fibre variations

The usage of printed composites in the aerospace industry has been steadily increasing over the last years. Especially, 3D printers and automatic fibre placement machines have allowed the introduction of Variable Angle Tow (VAT) composites, which theoretically offer greater tailoring capabilities than classic composite laminates. Nevertheless, the steering of brittle fibres is not flaw-exempt and, in fact, is greatly affected by the printer signature. This manuscript aims to examine the influence of fibre misalignments on the stress and failure index distribution in laminated VAT composites. For doing so, the Carrera Unified Formulation (CUF) is employed to develop layerwise models with unprecedented accuracy. Flaws are introduced at the layer scale by means of stochastic fields and uncertainty analysis is carried out through a Monte Carlo analysis. The random variation (defects) is propagated through the scales and correlated with the stress and failure index distribution. The results show that misalignments greatly affect the in-plane normal stresses, which lately influence fibre tension and compression failure mechanisms

Multi-scale analysis of thermoelastic properties of graphene foam/PDMS composites

In macroscopic applications, the production of graphene foam (GF) can be an attractive way to utilize the combined advantages of graphene sheets and porous materials. The porosity level significantly affects mechanical and thermal properties by changing the specific surface area. In this study, a multi-scale method is used to calculate the coefficient of thermal expansion (CTE) and heat capacity of GF/polymer composites. Molecular dynamics have calculated the properties of 3D GFs. In particular, four types of GF with increasing mass density and decreasing porosity are investigated. The thermoelastic properties are calculated as temperature-dependent for all groups of GF. Mechanics of structure genome (MSG) based on Carrera unified formulation (CUF) is used to calculate the effective properties of the GF/polymer composites. It was found that the composite consisting of GF with the highest density and lowest porosity has the minimum CTE. Also, the heat capacity of the composite depends not only on the heat capacity of the components but also on their Young modulus, CTE, and geometry

Buckling and Fundamental Frequency Optimization of Tow-Steered Composites Using Layerwise Structural Models

Variable-angle-tow (VAT) composite laminates can eventually improve the mechanical performance of lightweight structures by taking advantage of a larger design space compared to straight-fiber counterparts. Here, we provide a scalable low- to high-fidelity methodology to retrieve the tow angles that maximize the buckling load and the fundamental frequency of VAT plates. A genetic algorithm is used to solve the optimization problem in which the objective function is mimicked using a surrogate model. Both unconstrained and manufactured-constrained problems are solved. The surrogates are built with outcomes from numerical models generated by means of the Carrera unified formulation, which enables to obtain straightforwardly different degrees of accuracy by selecting the order of the structural theory employed. The results show both the validity and flexibility of the proposed design approach. It is shown that, although the optimal design fiber angle orientations are consistently similar, discrepancies in the prediction of the buckling load or fundamental frequency can be found between high-fidelity layerwise and low-to-refined equivalent-single-layer models, of which classical laminated plate or first-shear deformation theories are degenerate examples