Finite element approaches for static and dynamic analysis of partially wrinkled membrane structures

In the past few years, there has been an increasing interest in the use of large and extremely lightweight tensioned membrane structures for spacecraft applications. Typical uses include sunshields, parabolic reflectors, concentrators, and solar sails. Due to complex and/or changing load and boundary conditions, these structures can experience situations for which localized buckling (wrinkling) occurs within the membrane. This behavior is not possible to analyze using conventional finite element codes.; This thesis discusses the development of modeling techniques for the static and dynamic analysis of partially wrinkled membrane structures using a constitutive model that accounts for the “overcontraction” and change in load path within the membrane in an averaged sense. This constitutive model has been successfully used and verified in the past on several static membrane problems with regular boundary and loading conditions that were amenable to closed form solutions.; In the present thesis, this constitutive model is introduced into two different commercially available finite element codes to enable the analysis of realistic membrane structures that involve complex shapes and loading conditions. The analysis method, which involves an iterative procedure to determine the extent and shape of the wrinkled region(s) and then modify the element material properties accordingly, is referred to as the Iterative Membrane Properties (IMP) method. In one case the IMP method was implemented external to the finite element code, while the in the other case the IMP method was implemented internally via a modifiable material property subroutine.; In addition to the IMP approaches, an approximate Cable Network Modeling approach was studied to enable preliminary dynamic studies of partially wrinkled membrane structures. This approach was successfully applied to a realistic problem, NASA's NGST sunshield. The analysis was used in the design of a tenth scale test article, and its accuracy was validated by tests.; Extensive parametric studies using the internally applied IMP approach resulted in a procedure to identify the condition under which wrinkles impact the in-plane and out-of-plane stiffness of a membrane structure, and thus the conditions for which an approximate method can be used with success. Also, in order to demonstrate its versatility, the IMP method was successfully used to model the inflation of initially flat membrane shapes into partially wrinkled, doubly curved membranes. Finally, a reanalysis of the NGST sunshield, replacing the approximate cable network with membrane elements using the IMP approach, demonstrated the IMP method's applicability to dynamic as well as static problems.