Self-Repairing Membranes for Inflatable Structures Inspired by a Rapid Wound Sealing Process of Climbing Plants

A new self-repairing membrane for inflatable light weight structures such as rubber boats or Tensairity constructions is presented. Inspired by rapid self-sealing processes in plants, a thin soft cellular polyurethane foam coating is applied on the inside of a fabric substrate, which closes the fissure if the membrane is punctured with a spike. Experimental tests are carried out with a purpose built setup by measuring the air mass flow through a leak in a damaged membrane sample. It is shown that the weight per unit area of the self-repairing foam as well as the curing of the two component PU-foam under an overpressure influence the repair efficiency. Curing the foam under overpressure affects the relative density as well as the microstructure of the foam coatings. Maximal median repair efficiencies of 0.999 have been obtained with 0.16 g.cm 2 foam cured at 1 bar overpressure. These results suggest that the bio-inspired technique has the potential to extend the functional integrity of injured inflatable structures dramatically.

Deformation of wrinkled membrane inflatable structures under concentrated loads

The axisymmetric deformation of a paraboloidal membrane inflatable structure subjected to a concentrated load at its apex and a uniform internal pressure was analyzed. The wrinkle angle was obtained according to the membrane theory when wrinkles appeared and determined the wrinkle region. The wrinkled deformation was obtained based on the relaxed energy function. The effects of inflation pressure and concentrated loads on the wrinkle angle were analyzed and the deformation was obtained at the apex of structure. According to the numerical analysis, the shape of deformed meridians with wrinkles was obtained.

A simple analytical method for deflation prediction of inflatable structures

The static performance of inflatable structures has been well studied and the dynamic deployment simulation has received much attention. However, very few studies focus on its deflation behavior. Although there are several dynamic finite element algorithms that can be applied to the deflation simulation, their computation costs are expensive, especially for large scale structures. In this work, a simple method based on classic thermodynamics and the analytical relationship between air and membrane was proposed to efficiently analyze the air state variables under the condition of ventilation. Combined with failure analysis of static bearing capacity, a fast incremental analytical method was presented to predict both elastic and post wrinkling deflation process of inflatable structures. Comparisons between simplified analysis, dynamic finite element simulation, and a full-scale experimental test are presented and the suitability of this simple method for solving the air state and predicting the deflation behavior of inflatable structures is proved.

Friction characteristics of confined inflatable structures

The availability of high‐strength fabrics and progress in the development of large‐scale inflatable technology made possible the creation of temporary and quickly deployable structures for protection of underground infrastructure.Inflatable structures are relatively lightweight and portable,and can maintain the required rigidity while in operation.These benefits have prompted the development of inflatable structures for use in confined spaces,such as tunnels and large‐diameter pipes to act as barriers for containing flooding with minimal infrastructure modification.This work presents experimental results obtained from the evaluation of frictional characteristics of the fabric material that constitute the structural membrane of confined inflatable structures developed for protection of underground transportation tunnels and other large conduits.Friction tests at coupon level and slippage tests in a reduced‐scale inflatable structure were performed in order to evaluate the frictional characteristics of Vectran webbings.Tests at coupon level were performed to determine the friction coefficient for different surface types and conditions.Tests with the reduced‐scale inflatable structure contributed to the understanding of the friction characteristics at system level when subjected to different pressurization or depressurization sequences designed to induce slippage.Test results indicate that friction coefficient values at coupon level are about 29 percent higher than values derived from reduced‐scale tests.

Deployment dynamics and topology optimization of a spinning inflatable structure

Inflatable space structures may undergo the vibration of a long duration because of their features of dynamic deployment,high flexibility,and low-frequency modes.In this paper,a topology optimization methodology is proposed to reduce the vibration of a spinning inflatable structure.As the first step,a variable-length shell element is developed in the framework of arbitrary Lagrange-Euler(ALE)and absolute nodal coordinate formulation(ANCF)to accurately model the deployment dynamics of the inflatable structure.With the help of two additional material coordinates,the shell element of ALE-ANCF has the ability to describe the large deformation,large overall motion,and variable length of an inflatable structure.The nonlinear elastic forces and additional inertial forces induced by the variable length are analytically derived.In the second step,a topology optimization procedure is presented for the dynamic response of an inflatable structure through the integration of the equivalent static loads(ESL)method and the density method.The ESL sets of the variable-length inflatable structure are defined to simplify the dynamic topology optimization into a static one,while the density-based topology optimization method is used to describe the topology of the inflatable structure made of two materials and solve the static optimization problem.In order to obtain more robust optimization results,sensitivity analysis,density filter,and projection techniques are also utilized.Afterwards,a benchmark example is presented to validate the ALE-ANCF modeling scheme.The deployment dynamics and corresponding topology optimization of a spinning inflatable structure are studied to show the effectiveness of the proposed topology optimization methodology.

Pseudo-beam method for compressive buckling characteristics analysis of space inflatable load-carrying structures

This paper extends Le van＇s work to the case of nonlinear problem and the complicated configuration. The wrinkling stress distribution and the pressure effects are also included in our analysis. Pseudo-beam method is presented based on the inflatable beam theory to model the inflatable structures as a set of inflatable beam elements with a prestressed state. In this method, the discretized nonlinear equations are given based upon the virtual work principle with a 3-node Timoshenko＇s beam model. Finite element simulation is performed by using a 3-node BEAM189 element incorporating ANSYS nonlinear program. The pressure effect is equivalent included in our method by modifying beam element cross-section parameters related to pressure. A benchmark example, the bending case of an inflatable cantilever beam, is performed to verify the accuracy of our proposed method. The comparisons reveal that the numerical results obtained with our method are close to open published analytical and membrane finite element results. The method is then used to evaluate the whole buckling and the loadcarrying characteristics of an inflatable support frame subjected to a compression force. The wrinkling stress and region characteristics are also shown in the end. This method gives better convergence characteristics, and requires much less computation time. It is very effective to deal with the whole load-carrying ability analytical problems for large scale inflatable structures with complex configuration.

A new method of complicated folded fabric modeling

In order to resolve the complicated folded fabric modeling problem and establish the high quality finite element model for fabric working simulation in aviation or aerospace area,the Fluid Structure Interaction(FSI) method based on Arbitrary Lagrangian Eulerian(ALE) coupling theory was applied for modeling in this paper.An expanded three-dimensional fabric model(a special airbag) was divided into several segments.Then the folded state of each was calculated based on this numerical method.At last,the completely folded finite element model was obtained.This method can effectively simulate the complicated and natural folds,and the quality of model is very high which can greatly improve the success rate of fabric working process simulation.This method also can be guidance for other kinds of folded fabric modeling.

Experimental Investigation of Folding Damage for the Rigidizable Carbon-Epoxy Composites

This paper focused on the folding damage behavior of the space rigidizable materials in terms of 3-1ayer composite membranes. An experimental scheme was presented. The composite membranes were folded between the two plates for a short time, and then the unfolded composite membranes were compressively cured in an oven. By adjusting the displacement of one plate, the folding radius was changed. As expected, the strength and effective modulus of the cured composite membranes drop with decreasing the folding radius. When the strain controlled failure rule is appliedto the composite membranes, a minimal folding radius can be reached, beyond which the membranes will keep intact.Furthermore, folding damage due to folding and unfolding processes was evaluated by a simplified model. Compared with the measured residual strength and effective modulus, calculated results have the same trend. A discrepancy is attributed to neglecting the effects of the transverse fibers and the matrix.

Experiment research on mechanical behavior of the aluminum laminate in the low-high temperature

Aluminum laminate is one kind of the rigidizable composite materials and plays an important role in construction of the inflatable space structure(ISS),which has potential application in space in the future.But the study of the predecessors mainly focuses on the research of the mechanical behavior in the room temperature,for this reason,mechanical properties of the aluminum laminate in low-high temperature have been studied in this paper.The failure mechanism of the aluminum laminate is also analyzed in the microscopic view by JCXA-T33 electron probe.The results show uhat the temperature has significant influence on the strength and Young's modulus of the aluminum laminate.With the increase of temperature,both the strength and Young's modulus of the aluminum laminate decrease.A model between Young's modulus of the aluminum laminate and temperatures is obtained by using Arrhenius equation.The predicted values by the model agree well with the experiment values.

Simulation of 3D parachute fluid–structure interaction based on nonlinear finite element method and preconditioning finite volume method

A fluid–structure interaction method combining a nonlinear finite element algorithm with a preconditioning finite volume method is proposed in this paper to simulate parachute transient dynamics. This method uses a three-dimensional membrane–cable fabric model to represent a parachute system at a highly folded configuration. The large shape change during parachute inflation is computed by the nonlinear Newton–Raphson iteration and the linear system equation is solved by the generalized minimal residual（GMRES） method. A membrane wrinkling algorithm is also utilized to evaluate the special uniaxial tension state of membrane elements on the parachute canopy. In order to avoid large time expenses during structural nonlinear iteration, the implicit Hilber–Hughes–Taylor（HHT） time integration method is employed. For the fluid dynamic simulations, the Roe and HLLC（Harten–Lax–van Leer contact） scheme has been modified and extended to compute flow problems at all speeds. The lower–upper symmetric Gauss–Seidel（LUSGS） approximate factorization is applied to accelerate the numerical convergence speed. Finally,the test model of a highly folded C-9 parachute is simulated at a prescribed speed and the results show similar characteristics compared with experimental results and previous literature.