
Saullo G. P. CastroDelft University of Technology | TU · Aerospace Structures and Materials (ASM)
Saullo G. P. Castro
Dr.-Ing.
Design, analysis and optimization of lightweight structures; crashworthiness; post-buckling strength; dynamic behavior.
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126
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Introduction
Additional affiliations
February 2008 - May 2018
February 2012 - December 2014
June 2018 - present
Publications
Publications (126)
The substitution of conventional mechanical fasteners by adhesive joints has been advocated by the aircraft and aerospace industries due to the weight saving potential. Flaws such as debonding of the adhesive layer between the skin and the stiffener may greatly affect the structural behavior of composite panels. Within this context, this work prese...
The following presents a preliminary assessment on the crash characteristics of the Flying-V aircraft, an unconventional configuration consisting of a V-shaped flying wing with an oval cabin cross section, currently being actively researched at TU Delft. Successively, the preliminary assessment is carried out by means of design of experiments, wher...
Design optimisation offers the potential to develop lightweight aircraft structures with reduced environmental impact. Due to the high number of design variables and constraints, these challenges are typically addressed using gradient-based optimisation methods to maintain efficiency. However, this approach often results in a local solution, overlo...
To design crash structures for disruptive aircraft designs, it is required to have fast and accurate methods that can predict crashworthiness of aircraft structures early in the design phase. Axial crushing is one of the key energy absorbing mechanisms during a crash event. In this study, various analytical models proposed for calculation of mean c...
The design and optimisation of aircraft wings are critical tasks in aerospace engineering, requiring a balance between structural integrity, aerostructural performance, and manufacturability. This multifaceted challenge involves the interplay of various disciplines, each with distinct parameters and constraints. Traditional design approaches often...
The study presents deflation constraints that enable a systematic exploration of the design space during the design of composite structures. By incorporating the deflation constraints, gradient-based optimizers become able to find multiple local optima over the design space. The study presents the idea behind deflation using a simple sine function,...
Double-curved composite structures that are manufactured via automated fiber placement, such as pressure vessels, can take advantage of tow steering to reduce weight. This design freedom comes with the cost of adding internal normal stresses to the tow, possibly leading to wrinkles or pull up. The present work investigates tow pull up both experime...
In thermoplastic composite joints with a circular ultrasonic spot weld, the damage growth is located at the interface between the joined components. This means that any damage in these joints is invisible from the outside. This experimental study compares three different in-situ methods to measure the damage growth indirectly. The motivation lies i...
This paper reviews analytical models proposed by Abramowicz et al.[1, 2] and Stefan et al.[3] for the axial crushing of metallic tubular structures with square and circular cross-sections. First, a database of experiments for square and circular tubes was created based on the literature. Subsequently, the predictions obtained using these analytical...
Material properties, geometrical dimensions, and environmental conditions can greatly influence the characteristics of bistable composite laminates. In the current work, to understand how each input feature contributes to the curvatures of the stable equilibrium shapes of bistable laminates and the snap-through force to change these configurations,...
The Flying-V aircraft concept promises better fuel-burn performance over conventional tube-and-wing configurations, integrating the passenger cabin and cargo volume into the lifting surface. However, the wing-fuselage and cockpit windows of the Flying-V are exposed to the flight direction, posing a new challenge to the design and certification of s...
In this paper, an innovative design methodology is proposed to simultaneously optimize the size, layout, and number of stiffeners of a stiffened panel using a gradient-based optimizer. In the proposed method, CAD-based parameterization is used to parameterize the layout of the stiffeners. The location and orientation of each stiffener are controlle...
Modular structures come with the promise of efficient manufacturing and reduced maintenance costs. The amount of modularization is usually limited by weight efficiency, meaning that the minimum weight always lies on the most customized design, where all the structural elements are allowed to be different across the structural domain. This work stud...
The Vibration Correlation Technique (VCT) is a non-destructive method to predict buckling loads for imperfection-sensitive structures. While successfully used to validate numerical models and predict experimental buckling loads, recommendations for defining the VCT experiment are scarce. Here, its sensitivity towards the number of load steps and th...
An innovative design methodology is proposed for the simultaneous layout and sizing optimization of stiffened panels. A computer-aided design (CAD) modelling tool is used to generate the panel geometry and parameterize the stiffeners layout. The same geometric parameterization is used in the gradient-based optimization. Therefore no additional cons...
The present study investigates how to apply continuous tow shearing (CTS) in a manufacturable design parameterization to obtain reduced imperfection sensitivity in lightweight, cylindrical shell designs. The asymptotic nonlinear method developed by Koiter is applied to predict the post-buckled stiffness, whose index is constrained to be positive in...
Variable-angle filament-wound (VAFW) cylinders are herein optimized for minimum mass under manufacturing constraints, and for various design loads. A design parameterization based on a second-order polynomial variation of the tow winding angle along the axial direction of the cylinders is utilized to explore the nonlinear steering-thickness depende...
For the last three decades, bistable composite laminates have gained publicity because of their outstanding features, including having two stable shapes and the ability to change these states. A common challenge regarding the analysis of these structures is the high computational cost of existing analytical methods to estimate their natural frequen...
View Video Presentation: https://doi.org/10.2514/6.2022-1331.vid This study presents a method for modelling the aerodynamic performance of a tandem wing long-range eVTOL aircraft at an early design stage. This procedure is applied to the design of the Wigeon eVTOL which has a tandem wing configuration with open rotor distributed propulsion. The pro...
View Video Presentation: https://doi.org/10.2514/6.2022-0256.vid The multi-modal formulation of Koiter's asymptotic method provides a systematic and efficient procedure to evaluate the initial post-buckling behaviour and to assess the nonlinear behavior of structures. This manuscript presents a displacement-based multi-modal formulation of Koiter's...
View Video Presentation: https://doi.org/10.2514/6.2022-1485.vid In aircraft structural design it is of utmost importance to minimise the structural mass while maintaining a durable structure that is able to sustain the design loads for a predetermined number of flight cycles. The present manuscript investigates a methodology for the preliminary de...
View Video Presentation: https://doi.org/10.2514/6.2022-1030.vid The electric aircraft industry is starting to gain traction mainly due to the growing specific energy capacity of new batteries. Within this industry electric vertical takeoff and landing (eVTOL) aircraft serve the urban and regional air mobility market, requiring less infrastructure...
View Video Presentation: https://doi.org/10.2514/6.2022-1029.vid This study proposes a strategy to incorporate control and stability aspects into the preliminarydesign of a tandem-wing, long-range eVTOL aircraft concept. Four operational phases areconsidered: cruise, transition, hover, and ground operation. For cruise, a method to designfor open-lo...
The multi-modal formulation of Koiter's asymptotic method provides a systematic and efficient procedure to evaluate the initial post-buckling behaviour and to assess the nonlinear behavior of structures. This manuscript presents a displacement-based multi-modal formulation of Koiter's method for cylindrical shells, which are structures known for th...
The leading edges of wind turbine blades are adhesively bonded composite sections that are susceptible to impact loads during offshore installation. The impact loads can cause localized damages at the leading edges that necessitate damage tolerance assessment. However, owing to the complex material combinations together with varying bondline thickn...
Novel eVTOL aircraft configurations are picking up momentum in the emerging market of urban air mobility (UAM). These configurations feature electrical power systems and distributed propulsion architectures, both uncommon in current aircraft. As such, the design of eVTOL aircraft lies outside the bounds of current established frameworks and poses m...
The issue of adequate transportation is widespread. Not only are many modes of transportation expensive, but they often require dedicated infrastructure and are prone to traffic and congestion. In an attempt to attenuate this costly problem, an electrical Vertical Takeoff and Landing (eVTOL) aircraft concept, the Wigeon, is proposed after a trade o...
One of the core technologies in lightweight structures is the optimal design of laminated composite stiffened panels. The increasing tailoring potential of new materials added to the simultaneous optimization of various design regions, leading to design spaces that are vast and non-convex. In order to find an optimal design using limited informatio...
The issue of adequate transportation is widespread. Not only are many modes of transportation expensive, but they often require dedicated infrastructure and are prone to traffic and congestion. In an attempt to attenuate this costly problem an electrical Vertical Takeoff and Landing (eVTOL) aircraft concept is proposed. To be precise, three such co...
Available on: Saullo G. P. Castro, & José Humberto S. Almeida Jr. (2021). VAFW cylinders 2020, S1, S2, S4, S8, DIC raw data (Version 2021-03-16) [Data set]. Zenodo. 10.5281/zenodo.4608398. The files contain the raw data obtained with digital image correlation (DIC) of variable-angle filament-wound (VAFW) cylinders. The data is used as an input for...
Available in:
Saullo G. P. Castro, & José Humberto S. Almeida Jr. (2021). VAFW cylinders 2020, S1, S2, S4, S8, stitched imperfections (Version 2021-03-04) [Data set]. Zenodo. 10.5281/zenodo.4581164. The files contain geometric imperfection data of variable-angle filament-wound (VAFW) cylinders. The data is generated by the stitching algorithm desc...
Measuring the geometric imperfections in cylindrical shells is a critical step necessary to create accurate numerical models that can capture the imperfection-sensitive behavior of these structures. Modern composite structures, such as variable–angle filament–wound (VAFW) cylinders, have a unique imperfection signature that is still unknown to the...
This work demonstrates the potential of manufacturing variable-angle composite cylinders via filament winding (FW), called VAFW. The proposed design strategy allows different filament angles along the axial direction by dividing the cylinder into regions of constant angle called frames. Designs using two, four, or eight frames are herein investigat...
Rain-induced leading-edge erosion of wind turbine blades is associated with high repair and maintenance costs. For efficient operation and maintenance, erosion models are required that provide estimates of blade coating lifetime at a real scale. In this study, a statistical rainfall model is established that describes probabilistic distributions of...
Recent research on variable stiffness laminates have shown both numerically and experimentally that further improvement on the buckling performance is possible by incorporating overlaps that result in variable thickness profiles. We present the concept of overlap-stiffened designs that take advantage of the non-linear coupling between the tow steer...
Variable-angle filament-wound (VAFW) cylinders are herein optimized for minimum mass under manufacturing constraints, and for various design loads. A design parameterization based on a second-order polynomial variation of the tow winding angle along the axial direction of the cylinders is utilized to explore the nonlinear steering-thickness depende...
Around the world, many cities suffer from increasing traffic and congestion problems. Vertical takeoff and landing aircraft are a promising technology to alleviate this problem. Due to their ability to overfly obstacles, move independently of ground infrastructure and take off from anywhere, they could allow for very fast door-to-door transport. It...
Previous research has hinted on further improvements of the buckling behaviour of variable-stiffness laminates by incorporating overlaps, resulting in a variable thickness profile that is non-linearly coupled to the steering angles. The present study compares two modelling strategies to consider the variable thickness distribution: 1) as-manufactur...
Rain‐induced leading‐edge erosion (LEE) of wind turbine blades (WTBs) is associated with high repair and maintenance costs. The effects of LEE can be triggered in less than 1 to 2 years for some wind turbine sites, whereas it may take several years for others. In addition, the growth of erosion may also differ for different blades and turbines oper...
Vibration Correlation Technique (VCT) is becoming an established non-destructive method to predict buckling loads for imperfection sensitive structures. While it has been successfully used to validate numerical models and to predict experimental buckling loads, recommendations on how to setup the experimental test for VCT usage are relatively scarc...
Measuring the geometric imperfections in cylindrical shells is a critical step necessary to create accurate numerical models that can capture the imperfection-sensitive behavior of these structures. Modern composite structures, such as variable-angle filament-wound (VAFW) cylinders, have a unique imperfection signature that is still unknown to the...
Cite as: Saullo G P Castro, Jasper Reichardt, Florian Burau, & Emilio Lozano. (2020, July 20). DESICOS Plug-in for Abaqus (Version 2.4.13). Zenodo. http://doi.org/10.5281/zenodo.3951965
There is a great demand for optimization of high performance composite structures, particularly in the aerospace sector. To avoid vibrational resonance in aerospace and naval structures, laminated plates can be designed using fundamental frequency constraints. Composite panels are particularly attractive because the vibration response can be optimi...
Designs taking advantage of fibre-steered laminated manufacturing can optimally vary the stiffness and strength properties of high-performance structural components according to the geometry, loads and boundary conditions. For the stability behaviour of laminates with discontinuities such as local reinforcements and cut-outs, variable stiffness lam...
Automated manufacturing techniques of composite materials such as automated fiber placement (AFP) and continuous tow shearing (CTS) can be configured to produce fibers that follow curvilinear paths, resulting in variable laminate properties that can be tailored to a large range of engineering applications. The present study focuses on the design an...
Recent research on variable stiffness laminates have shown both numerically and experimentally that further improvement on the buckling behaviour is possible by incorporating overlaps that result in variable thickness profiles, with the thickness non-linearly coupled with the local steering angle. We present the concept of overlap-stiffened panels,...
Koiter's asymptotic method enables the calculation and deep understanding of the initial post-buckling behaviour of thin-walled structures. For the single-mode asymptotic analysis, Budiansky (1974) presented a clear and general formulation for Koiter's method, based on the expansion of the total potential energy function. The formulation from Budia...
Previous research has hinted on further improvements of the buckling behaviour of variable-stiffness laminates by incorporating overlaps, resulting in a variable thickness profile that is non-linearly coupled to the steering angles. The present study compares two modelling strategies to consider the variable thickness distribution: 1) as-manufactur...
The issue of leading edge erosion (LEE) of wind turbine blades (WTBs) is a complex problem that reduces the aerodynamic efficiency of blades, and affects the overall cost of energy. Several research efforts are being made at the moment to counter erosion of WTBs such as-testing of advanced coating materials together with development of high-fidelit...
Koiter's asymptotic method enables the calculation and deep understanding of the initial post-buckling behaviour of thin-walled structures. For the single-mode asymptotic analysis, Budiansky (1974) presented a clear and general formulation for Koiter's method, based on the expansion of the total potential energy function. The formulation from Budia...
A reliability-based optimization framework is introduced and used to design filament-wound cylindrical shells with variable angle tow. Seven design cases are investigated to enable a comparison between constant-stiffness and variable angle tow designs, also considering effects of thickness variation created due to overlapping tow paths, determined...
When loading experiments are repeated on different samples, qualitatively different results can occur. This is due to factors such as geometric imperfections, load asymmetries, unevenly stressed regions or uneven material distributions created by manufacturing processes. This fact makes designing robust thin-walled structures difficult. One numeric...
The leading edge of a fiber composite wind turbine blade (WTB) is prone to erosion damages due to repeated rain droplet impact during its service life. Such damages are critical to the blade’s aerodynamic as well as structural performance, ultimately resulting in substantial repair costs. An effective design of a coating material for WTB is necessa...
Abstract Aircraft structural analysis is a process that involves several engineers working concurrently to analyze in detail all structural elements of an airframe, as well as the behavior of the aircraft structure as a whole. The airframe has to be decomposed in its major components such as fuselage sections, wings and control surfaces to allow th...
This paper presents a novel damage mechanics based failure model enabling the prediction of low cycle fatigue life and residual strength of isotropic structures under multiaxial loading. The approach herein proposed does not discretize every load cycle but instead takes an envelope loading whereby the numerical load remains constant at a maximum lo...
The supersonic aeroelastic stability of tow-steered carbon reinforced composite panels, in each layer of which the fibers follow curvilinear paths, is assessed. A structural model based on the Rayleigh–Ritz method, combined with the aerodynamic piston theory, is derived to represent the aeroelastic behavior of rectangular plates under different bou...
The increasing need for automatic mesh generation has led to the development of efficient triangulation algorithms that are able to discretize any 2D or 3D domain. Modern finite element formulations based on strain smoothing techniques (SFEM) provide enhanced convergence properties, preventing yet the stiffening behavior of triangular meshes. Recen...
The use of morphing structures aims to increase aerodynamic efficiency, decreasing fuel consumption and aircraft overall weight. Within this context, piezoelectric materials are of great interest in the design of smart structures because the piezoelectric effect is reversible , allowing them to work both as sensors and as actuators. The present wor...
Geometric imperfections and lower-bound methods used to calculate knockdown factors for composite cylindrical shells: This chapter provides a general overview of the important role that geometric imperfections play on degrading the load carrying capacity of cylindrical shell structures. The developments carried out during the European Project DESIC...
Thin-walled structures are widely used in aerospace, offshore, civil, marine and other engineering industries. Buckling of such thin-walled imperfection sensitive structures is a very important phenomenon to be considered during their design phase. Existing design guidelines, being the most known the NASA SP-8007 for cylinders dated from the late 1...
This work investigates the effects of temperature in the shape memory alloy hybrid composites (SMAHC) cylindrical stiffened panels’ aeroelastic stability. The SMAHC is modelled using a micromechanical formulation embedding carbon fiber, SMA wire and resin to the same lamina and taking into account the martensite/austenite phases of transformation i...
Stability and Vibrations of Thin-Walled Composite Structures presents engineering and academic knowledge on the stability (buckling and post buckling) and vibrations of thin walled composite structures like columns, plates, and stringer stiffened plates and shells, which form the basic structures of the aeronautical and space sectors. Currently, th...