A Regularized Discrete Laminate Parametrization Technique with Applications to Wing-Box Design Optimization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97055/1/AIAA2012-1519.pd

Design of anisotropic composite shells using an isogeometric approach

Thin-walled composite structures, typically modeled as Cosserat continua during the design phase, are of particular importance in aerospace and automotive applications. At the dawn of industrial scale adoption of advanced fibre placement technology, it became viable to better exploit the directional properties of composite materials. In the recent past, numerous researches were devoted to the design of shells with optimal anisotropy. In the present work, combined stiffness tailoring and shape optimal design is proposed that is naturally facilitated in a non-uniform rational B-spline based isogeometric approach. Spatial variation of stiffness properties is parameterised by means of lamination parameters and the thickness of the shell. Shape changes are easily achieved by modifying selected control point co-ordinates and weights. The method of successive approximations has been employed to solve the optimisation problem. The formulation is separable in terms of sizing variables, however, separability of the shape design problem is not enforced. The design framework is verified through selected compliance minimisation problems.Aerospace Structures & MaterialsAerospace Engineerin

Design of Fiber-steered Variable-stiffness Laminates Based on a Given Lamination Parameters Distribution

Mechanical properties of fiber-reinforced laminated composite materials are directionally dependent. Contemporary laminated composite design aims to make effective use of these directional properties by means of stacking sequence design, selecting the fiber orientation angle of each ply from a predefined set. Automated fiber-placement (AFP) technology can be used to improve the efficacy of composite materials by means of fiber steering. The variation of fiber orientation angles per ply of the laminate yields a variable stiffness (VS) laminate. For optimization purposes it is attractive to design such laminates in terms of lamination parameters (LP), as the number of design variables per point in the structure can be reduced to as little as four dimensionless variables considering balanced symmetric layups, and because many lay-up optimization problems can be made convex by describing them in terms of LPs. VS laminate design in terms of LP requires the obtained LP distribution to be converted into an actual fiber angle design. In a previous study the authors proposed a method to convert VS laminate designs using LPs into fiber angle designs. This method includes a constraint on in-plane curvature, a manufacturing constraint related to AFP. Thickness build-up will occur due to fiber steering. The amount of thickness build-up that results from the obtained fiber angle designs is discussed here as a function of the constraint on fiber curvature. The streamline analogy is used to obtain an estimate for thickness build-up and to determine fiber paths. A square plate loaded in biaxial compression is used to demonstrate the effect of the in-plane curvature constraint on thickness build-up, and several fiber angle designs, thickness distributions and fiber paths are given for this structure.Aerospace Structures & MaterialsAerospace Engineerin

Reboot biomedical R&D in the global public interest

COVID-19 diagnostics, therapeutics and vaccines are powerful reminders: health technologies can help to shape the way in which societies control disease. Challenges in ensuring global, equitable access to these fruits of biomedical research and development (R&D) during the COVID-19 pandemic have highlighted the urgency of reorienting the system towards the public interest. The first step is a clearer articulation of what R&D in the global public interest is. That is what we seek to do here. There are four major concerns about biomedical R&D, despite its impressive technological advances amid profound transformations in how knowledge is generated and used. The first is the lack of medicines in areas where market incentives are inadequate to attract private investment, such as for neglected diseases of poverty, bacterial infections and emerging infectious diseases1. Second is the slow pace of progress in some areas, such as Alzheimer’s disease2. Third is the risk of harm, such as adverse drug reactions. The final concern is restricted access to technologies, caused by high prices, insufficient production or inadequate supply3. These concerns pre-date the emergence of the coronavirus SARS-CoV-2, but the pandemic has underscored the urgency of addressing them. That requires looking beyond just one country or sector. Biomedical R&D is increasingly global. Historically, it was concentrated in the advanced industrialized countries (excluding traditional medicine). Today, there is rapid growth in low- and middle-income countries (LMICs) in capacity, investment and networks. And, as medicines markets have globalized, people on every continent pay for health technologies – either out of their own pockets or through public and private medical insurance. Both public and private interests and investments drive R&D. Research is conducted by public laboratories, universities, private firms (small, medium and multinational), non-profit organizations and health-care facilities (public and private). It is funded by taxpayers, philanthropic foundations, private investors, companies and patients. And it is shaped by public policies and agencies, such as those for intellectual property (IP), regulatory standards, procurement, treatment guidelines and reimbursement. All of these actors can and should reorient the biomedical R&D system to better serve the global public interest (see ‘Checklist for R&D in the global public interest’). Concretely, that means answering three questions: why do R&D? How should it be done, and for whom