Hybrid Optimization of Curvilinearly Stiffened Shells Using Parallel Processing

Future aerospace vehicles like hybrid wing/body, truss-braced wing, and “double bubble” would have pressurized noncircular fuselage structures and complex wing geometry. Traditional aircraft designs have led to the confidence and experience of designing such structures using the knowledge base built over the years and the resulting rules of thumb. However, there is a lack of experience of load calculations and design of complex, multifunctional, aircraft structural concepts for future aerospace vehicles. Designing such structures will require a physics-based optimization framework. Therefore, a new optimization framework, EBF3PanelOpt, is being developed. Commercial software MD-PATRAN (geometry modeling and mesh generation) and MD-NASTRAN (finite-element analysis) are integrated in EBF3PanelOpt framework using the Python programming environment to design stiffened panels with curvilinear stiffeners. Currently, EBF3PanelOpt optimizes the stiffened panel with curvilinear blade stiffeners, where the loads ar...

Developments in rapid manufacturing techniques such as electron beam freeform fabrication have made it easier to manufacture objects with complex shapes (like panel with curvilinear stiffeners). In this paper, design optimization of stiffened panels is carried out using different types of response surfaces. Placement and sizing variables are optimized using integrated high-performance, commercially available software. The proposed approach has two optimization loops. The sizing optimization is carried out in the first loop through finite element analysis using gradient-based optimization method for different placement variables. In the second loop, optimal placement of stiffeners is carried out using response surfaces. Because of response surface construction using whole design space, the proposed approach does not suffer from getting trapped in a local minima. The proposed approach is applied to square panels subjected to in-plane biaxial and uniform surface pressure loadings. Panel weight is minimized with buckling, displacements, and stress constraints. An approach to perform both placement and sizing optimization of panels with curvilinear stiffeners is also discussed and a surrogate model is developed for placement and shape optimization of stiffeners.

This paper summarizes some numerical results of optimal design study of curvilinear stiffened panels where the reference axes of the stiffeners can be curvilinear. An integrated approach to use different capabilities in relevant fields, such as NURBS, DistMesh, and MSC.NASTRAN, etc., are adopted in the MATLAB environment. Numerical studies on optimal stiffened panel designs of buckling dominant problems are made to look into the effects of certain factors, such as, orientation, spacing, location, and curvature, etc., on the optimal designs. It is observed that curvilinear placement of stiffeners plays the role of orientation, spacing, location and intersection placement of infinitesimal straight stiffeners, and provides an enhanced design space. This enhanced design space may lead to better designs than using straight stiffeners though it is not always so. This work reveals the necessity to use global optimization techniques to perform topology/placement/shape optimization of curvilinear stiffened panels along with size optimization.

The unique tool-less and layer-upon-layer capabilities of additive manufacturing (AM) have largely lessened manufacturing constraints and significantly broadened design freedom. AM offers new opportunities for developing customized products by achieving significant improvements in product performances and lower overall costs. The AM-enabled customization opportunities inevitably challenge traditionally design theories and methodologies (DTMs) that lack design knowledge for AM products. Here, to counteract this limitation, this study presents a novel methodology for constructing knowledge supporting DTMs for AM-enabled customization: customized design for AM (CDfAM). The CDfAM supports two main phases of design for additive manufacturing (DfAM): (1) opportunistic DfAM in a conceptual design phase and (2) restrictive DfAM in an embodiment design phase. In terms of the knowledge construction for the opportunistic DfAM, it is essential to construct knowledge that supports to explore a customized design space enabled by AM’s design freedom from the conceptual design phase. To address the challenge, this study provides a novel method for capturing knowledge of customized AM product behaviors. First, this study proposes an affordance-based DfAM framework by integrating the concept of affordance into three link chain models. Second, an affordance structure is proposed to develop a formal method for representing the knowledge of the customized AM product behaviors utilizing finite state automata. In terms of the knowledge construction for the restrictive DfAM, this study presents a formal method for representing and reasoning customizable modular knowledge of design rules for AM. First, a novel structured modular hierarchy and associated formalisms of AM design rule elements are presented. Second, machine learning is employed to automatically learn design rules from AM data, which leverages the proposed design rule formalisms. A knowledge graph is designed and built to demonstrate the proposed methodology. Case studies with AM products such as a transtibial prosthesis leg and AM data such as ex-situ AM measurement data provide illustrations in this study. The case studies show that the proposed methodology explicitly constructs structured and correlated AM design knowledge of customized AM product behaviors, product geometries, and additive manufacturability constraints. It is also shown that qualified design knowledge in the knowledge graph enhances automation of DfAM decision-making and data-driven knowledge constructions. The proposed CDfAM methodology enables incorporating both customized AM product functionalities and additive manufacturability constraints into product designs. This study provides a foundation for AM knowledge construction and data- and knowledge-driven automation of DfAM decision-making. Validated design rules and representations are expected to contribute to developing international standards on AM design rules.

Matrix/Inter-fibre failure is characterized by the appearance at the fiber-matrix interfaces of small debonds that can progress along them until reaching a certain extension, then, changing their orientation kinking towards the matrix and finally growing through it. The particular case of compressive loading is specially interesting, given the morphology of the interface cracks and the specific angle that the macrocracks form in the matrix.To date, the analysis of this problem at micromechanical level has been carried out mainly by means of Finite Element or Boundary Element models. In this work, the problem is approached from the experimental point of view, observing under the microscope specimens previously tested at different loading levels. Several aspects such as the identification of the phases of the faliure mechanism, the kinking angle, the extension of the interface cracks and the presence of damage as a function of the loading level are studied.

The design methodologies and part shape algorithms for additive manufacturing (AM) are rapidly growing fields, proven to be of critical importance for the uptake of additive manufacturing of parts with enhanced performance in all major industrial sectors. The current trend for part design is a computationally driven approach where the parts are algorithmically morphed to meet the functional requirements with optimized performance in terms of material distribution. However, the manufacturability restrictions of AM processes are not considered at the primary design phases but at a later post-morphed stage of the part’s design. This paper proposes an AM design method to ensure: (1) optimized material distribution based on the load case and (2) the part’s manufacturability. The buildability restrictions from the direct energy deposition (DED) AM technology were used as input to the AM shaping algorithm to grant high AM manufacturability. The first step of this work was to define the term of AM manufacturability, its effect on AM production, and to propose a framework to estimate the quantified value of AM manufacturability for the given part design. Moreover, an AM design method is proposed, based on the developed internal stresses of the build volume for the load case. Stress tensors are used for the determination of the build orientation and as input for the part morphing. A top-down mesoscale geometric optimization is used to realize the AM part design. The DED Design for Additive Manufacturing (DfAM) rules are used to delimitate the morphing of the part, representing at the same time the freeform mindset of the AM technology. The morphed shape of the part is optimized in terms of topology and AM manufacturability. The topology optimization and AM manufacturability indicator (TMI) is introduced to screen the percentage of design elements that serve topology optimization and the ones that serve AM manufacturability. In the end, a case study for proof of concept is realized.

Results from an analytical study of the response of composite shells with cutouts and subjected to internal pressure and axial compression are presented. The analytical results are obtained using a geometrically nonlinear finite element code. Results for axial compression and combined internal pressure and axial compression are presented. The effects of varying internal pressure and cutout size on the prebuckling, buckling, and postbuckling responses of the shell are described. Results indicate that the nonlinear interaction between the inplane load distribution and the out-of-plane displacements near the cutout can significantly influence the structural response of the shell. The results also indicate that these local load distributions and displacements can be affected by the size of the cutout and the internal pressure load. Introduction Many modern aerospace shell structures are designed to support combinations of internal pressure and mechanical loads during their service life. With the increasing need to produce lighter weight aerospace structures, the use of advanced composite materials has become more common in the design of these structures. During operation, flight loads and internal cabin pressure are present in all commercial transport aircraft. Some of these loads may be compressive loads and, thus, it is necessary to investigate the buckling characteristics of these structures. In addition, designers will *Ph.D. Candidate, Composite Structures Laboratory, Department of Aerospace Engineering. Student Member, AIAA. tHead, Structural Mechanics Branch. Fellow, AIAA. ^ Associate Professor, Composite Structures Laboratory, Dept. of Aerospace Engineering. Member AIAA. Copyright ©1998 by Mark W. Hilburger. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. often need to incorporate cutouts or openings in the structure to serve as doors, windows, or access ports. It has been shown by a number of authors that a cutout in a shell structure subjected to axial compression can cause a significant reduction in the buckling load of the shell (e.g., Ref. 1-4). The local response near the cutout in a compression-loaded shell is strongly influenced by the local displacement gradients and the internal load distribution. These local displacements and internal load distribution can be affected by the size of the cutout. Recent studies of the response of cylindrical shells with longitudinal cracks and subjected to internal pressure and axial compression loads (e.g., Ref. 5) indicate that the interaction between the internal pressure load and the axial compression load can have a significant effect on the local response of the structure. The results of an analytical study of the response of composite cylindrical shells with cutouts and subjected to internal pressure and axial compression are presented. First, the governing parameters for the buckling of cylindrical shells with a cutout will be defined. The governing parameters will be used to develop the results of a parametric study presented in the paper. These parameters will help provide insight into the effects of changing geometric and laminate parameters on the buckling response of shells. The parametric study will include three cutout sizes and five internal pressure levels to determine the effects of varying the cutout size and internal pressure loads on the compression response. The predicted results are characterized by load-shortening response curves and contour plots of shell displacements and stress resultants. Finally, design curves based on classical parameters for the buckling of shells with cutouts and subjected to internal pressure and axial compression are presented.

Nonlinear buckling and postbuckling of heated functionally graded cylindrical shells under combined axial compression and radial pressure

Additive Manufacturing in Finland: Recommendations for a Renewed Innovation Policy

Increasing transportation safety can be observed as one of the biggest engineering challenges. This challenge often needs to be combined with the need to deliver engineering solutions that are able to lower the environmental impact of transportation, by reducing fuel consumption. Consequentially, these topics have attracted considerable research efforts. The present work aims to address the previously cited challenges by maximizing the energy absorption capabilities of hybrid aluminum/composite shock absorbers with minimal thickness and mass. This engineering solution makes it possible to lighten vehicles and reduce fuel consumption, without compromising safety, in terms of crashworthiness capabilities. A numerical sensitivity study is presented, where the absorbed energy/mass (AE/m) and the absorbed energy/total panel thickness (AE/Htot) ratios, as a consequence of low-velocity impact simulations performed on six different shock absorbers, are compared. These hybrid shock absorbers have been numerically designed by modifying the core thickness of two basic absorbers’ configurations, characterized, respectively, by a metallic lattice core, intended to be produced through additive manufacturing, and a standard metallic honeycomb core. This work provides interesting information for the development of shock absorbers, which should be further developed with an experimental approach. Indeed, it demonstrates that, by integrating composite skins with a very light core producible, by means of additive manufacturing capabilities, it is possible to design shock absorbers with excellent performance, even for very thin configurations with 6 mm thickness, and to provide a significant increase in AE/m ratios when compared to the respective equal volume standard honeycomb core configurations. This difference between the AE/m ratios of configurations with different core designs increases with the growth in volume. In detail, for configurations with a total thickness of 6 mm, the AE/m increases in additive manufacturing configurations by approximately 93%; for those with a total thickness of 10 mm, the increase is 175%, and, finally, for those with a total thickness of 14 mm, the increase is 220%.

Deformation of laminated and sandwich cylindrical shell with covered or embedded piezoelectric layers under compression and electrical loading

Purpose Because of the significant differences in the features and requirements of specific products and the capabilities of various additive manufacturing (AM) solutions, selecting the most appropriate AM technology can be challenging. This study aims to propose a method to solve the complex process selection in 3D printing applications, especially by creating a new multicriteria decision-making tool that takes the direct certainty of each comparison to reflect the decision-maker’s desire effectively. Design/methodology/approach The methodology proposed includes five steps: defining the AM technology selection decision criteria and constraints, extracting available AM parameters from the database, evaluating the selected AM technology parameters based on the proposed decision-making methodology, improving the accuracy of the decision by adopting newly proposed weighting scheme and selecting optimal AM technologies by integrating information gathered from the whole decision-making process. Findings To demonstrate the feasibility and reliability of the proposed methodology, this case study describes a detailed industrial application in rapid investment casting that applies the weightings to a tailored AM technologies and materials database to determine the most suitable AM process. The results showed that the proposed methodology could solve complicated AM process selection problems at both the design and manufacturing stages. Originality/value This research proposes a unique multicriteria decision-making solution, which employs an exclusive weightings calculation algorithm that converts the decision-maker's subjective priority of the involved criteria into comparable values. The proposed framework can reduce decision-maker's comparison duty and potentially reduce errors in the pairwise comparisons used in other decision-making methodologies.

In the present work, a geometrically nonlinear finite shell element is first presented to predict nonlinear dynamic behavior of piezolaminated functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shell, to enrich the existing research results on FG-CNTRC structures. The governing equations are developed via an improved first-order shear deformation theory (FSDT), in which a parabolic distribution of the transverse shear strains across the shell thickness is assumed and a zero condition of the transverse shear stresses on the top and bottom surfaces is imposed. Using a micro-mechanical model on the foundation of the developed rule of mixture, the effective material properties of the FG-CNTRC structures, which are strengthened by single-walled carbon nanotubes (SWCNTs), are scrutinized. The effectiveness of the present method is demonstrated by validating the obtained results against those of other studies from literature considering shell structures. Furthermore, some novel numerical results, including the nonlinear transient deflection of smart FG-CNTRC spherical and cylindrical shells, will be presented and can be considered for future structure design.

Science and engineering have been instrumental in advancing the progress of humanity and are the key enablers that are shaping our very present and the future, improving our health and living standards, allowing humanity to leave the planet, walk on the moon, and explore distant stars and galaxies. Additive manufacturing (AM) or 3D printing is the latest technological marvel in manufacturing that is compelling us to think differently about how we design and manufacture parts and components, the location where the parts are being manufactured, the supply chains, environmental impact of manufacturing and sovereign capability. AM is now being perceived as a disruptive technology because of the benefits and opportunities it offers over the long-established traditional manufacturing technologies. It is a relatively young technology, some 30 years since the invention of the first 3D printer, compared to conventional subtractive technologies that have been around for centuries. Mainstream AM has in fact only been around the last 5 to 10 years as both the 3D printing technology and feedstock materials have evolved and become more robust, cheaper, and reliable giving manufacturers the necessary level of confidence to adopt them in serial production. The level of activity in AM is at an all-time high as various stake holders, company executives, investors, researchers, and government agencies try to predict its trajectory. Global organizations of all types are attempting to understand the role they can play in the AM space. This chapter presents an overview of AM and its enormous potential in the advancement of chemical sciences and engineering. In-depth discussion of fundamental and applied aspects of each individual AM technology and how they relate to chemical sciences and engineering are presented in subsequent chapters. To date AM has seen greater adoption by the aerospace, defense, and biomedical industries and to somewhat lesser degree in the chemical manufacturing and processing industries. Introduction of AM practices in this sector can improve the efficiencies of existing chemical processing technologies, allow sophistication of existing processes for manufacturing of new products, improve process economics, and address complex challenges and demands of our modern society such as environmental compatibility, reduction in wastes and emissions and localized production. AM in chemical sciences has enormous potential in process intensification which enables efficient heat and mass transfer, large reduction in the footprint of chemical manufacturing and processing and reduce environmental pollution.KeywordsAdditive manufacturing3D printingRapid prototypingCustomizationChemical manufacturingProcess intensificationEnergy storageReactors

Additive manufacturing (AM) processes, such as Fused Filament Fabrication (FFF), enable the production of lightweight parts with high stiffness-to-weight ratios, making them highly suitable for a wide range of engineering applications. However, ensuring the mechanical reliability of these components, particularly for load-bearing purposes, requires systematic mechanical testing of well-designed specimens to asses their suitability. While the tensile properties of additively manufactured materials have been extensively studied, the compressive behavior of components produced via AM, particularly those made from thermoplastic materials, remains comparatively underexplored and insufficiently characterized in the existing body of research. Among these materials, polylactic acid (PLA)—a biodegradable thermoplastic derived from renewable resources—has gained prominence in AM applications. Recent studies have investigated the compression properties of PLA in reinforced materials; however, the focus has primarily been on solid, semi-solid, or porous specimens. These investigations largely overlook thin-walled structures, which are integral to weight-saving designs and commonly feature in topology-optimized structures. Understanding the mechanical behavior of monolayers, the fundamental building blocks of most AM components, is essential for accurately predicting the overall performance of multilayer structures. Monolayers represent the smallest, most basic structural elements of AM parts, and their properties directly influence the behavior of the final, more complex assemblies. Establishing a methodology that correlates monolayer properties with those of multilayer components could significantly streamline testing procedures. By performing mechanical tests on monolayers, instead of on more intricate multilayer specimens, manufacturers could reduce testing complexity and cost while accelerating the development process. The current literature reveals a gap in the design and analysis of thin-walled AM specimens, especially monolayers, under compressive loads. Specifically, the design of monolayer or thin-walled AM compression specimens without infill has not been thoroughly explored. This article addresses this gap by investigating the design and testing of AM monolayer compression specimens produced using FFF of PLA. Three distinct specimen geometries are considered—circular, helicoidal, and S-shaped—to evaluate their potential for understanding and predicting the compressive behavior of AM monolayer structures.