Session: 04-12-02: Design of Materials and Discovery of Constitutive Models Linking Process-Structure-Property-Performance Relationships

Paper Number: 167567

Evaluation of Flexural Deformation Mechanisms in Inflatable Drop-Stitch Structures 

Inflatable drop-stitch structures offer remarkable potential for lightweight, low cost, portable and rapidly deployable structural components with high bending stiffness and load carrying capacity for use in a variety of aerospace, naval, and military applications. Drop-stitch structures are constructed from pairs of woven fabric skins which, through specialized weaving processes, are tied together by drop stitches. After coating the skins with a polymer coating, the panels are inflated to provide flat panels with remarkable bending stiffness and load carrying capacity. Failure mechanisms include loss of tension of the drop stitch yarns and wrinkling or buckling of the skins. The mechanical performance of these structures is highly sensitive to the inflation pressure, choice of constituent materials and construction parameters. Successful implementation requires detailed experimental characterizations and the development of accurate predictive analytical and numerical models. In particular, the ability to predict the effect of inflation pressure on the mechanical response of drop-stitch structures is critical for effective design of these novel, non-traditional components.

The complex architecture of these structures involves a variety of mechanisms that impact mechanical performance. Upon inflation, the drop-stitch yarns are subjected to tensile stresses and the panel skins experience biaxial stresses that are dependent on the panel’s overall dimensions. Since the panel skins consist of polymer coated fabrics, they exhibit anisotropic elastic behavior that is dependent on the fabric’s weave construction, polymer properties and coating thickness. Upon subsequent bending deformation, the panel skins are subjected to superposed axial bending stresses and sidewall shear stresses. At critical load levels, localized deformation mechanisms including loss of drop-stitch yarn tension and skin wrinkling/buckling are observed. Effective design of these structures requires consideration of these effects when selecting material systems and construction parameters for a specific application.

In this investigation, the deformation behavior of an inflatable drop-stitch panel under four-point bending is examined. An analytical model is developed, taking into consideration the mechanical behavior of the skin material under in-plane biaxial and shear loading.  The effect of localized deformation in the vicinity of the load points are examined, leading to an empirical, pressure dependent model of localized effects. In a parallel numerical investigation, a finite element model of an inflatable drop-stitch panel under four-point bending load is developed and correlated with analytical models and experimental data. Stress distributions associated with the analytical model are derived and compared to the numerical simulation results. The numerical model also provides a tool to evaluate the effects of various deformation mechanisms on the overall response. It is observed that the modeling results are very sensitive to the orthotropic properties of the constituent layers. In particular, the overall bending stiffness of the panel is shown to be highly dependent on the sidewall shear modulus. The findings of this combined experimental and modeling investigation provide insight for designers and guidance for future research into optimizing these structures for specific applications.

Presenting Author: David Taggart University of Rhode Island

Presenting Author Biography: Prof. Taggart is a Professor of Mechanical Engineering at the University of Rhode Island. His degrees include a B.S. in Mechanical Engineering from the University of Delaware, an M.S. in Materials Engineering from Rensselaer Polytechnic Institute, and a Ph.D. in Mechanical Engineering from the University of Pennsylvania. Prof. Taggart's teaching and research interests include mechanics of materials, engineering analysis, computational solid mechanics, theory of elasticity, and experimental solid mechanics. Recent research topics include abrasive waterjet machining, design of minimum weight structures, finite element based topology optimization, and the mechanical behavior of inflatable drop-stitch structures. He is also active in URI’s workforce development programs, focusing on workforce needs in the defense sector.

Authors:

Michael Smith Naval Undersea Warfare Center - Newport Division
Alena Bellon Volkswagen AG
Christopher Hart PacMar Technologies
David Taggart University of Rhode Island