Jin-Ho Roh

Thermal post-buckling analysis of shape memory alloy hybrid composite shell panels

This paper was performed for the Smart UAV Development program, one of the 21st Century Frontier R&D Programs funded by the Ministry of Science and Technology of Korea

Wrinkling control of inflatable booms using shape memory alloy wires

An inflatable boom is a fundamental structural part of inflatable space structures maintaining the expected configuration of the whole system, supporting external loads and guaranteeing the efficiency of the membrane surface. The inflatable structure is a thin film structure compactly packaged and expanded to the desired configuration by the internal gas pressure. But the structures can be easily distorted and even collapsed by wrinkling. In this study, the behavior of an inflatable boom structure is investigated numerically and experimentally. To achieve a better bending strength, the methodology to control the wrinkling growth and the deformed configuration of the inflatable boom structure with a shape memory alloy (SMA) wire actuator is developed. To understand the nonlinear behavior of an inflatable boom due to wrinkling, the structure is numerically modeled using the ABAQUS finite element program with a wrinkling algorithm developed based on the Miller–Hedgepeth membrane theory. To verify the present analysis method, the inflatable boom made of Kapton film is examined by the bending tests with various internal pressures. To delay the growth of wrinkling that rapidly deteriorates the bending strength of the inflatable boom, a SMA wire actuator is applied. SMA wires are attached on the edge of the inflatable boom and generate a recovery force to remove wrinkling and restore the deformation of the boom.

Nonlinear finite element simulation of shape adaptive structures with SMA strip actuator

In this research, the thermomechanical responses of shape memory alloy (SMA) actuators and their applications in the shape adaptive structures combining strip SMA actuators are investigated. The numerical algorithm of the three-dimensional (3-D) SMA thermomechanical constitutive equations based on Lagoudas model is developed to analyze the unique characteristics of a SMA strip. The Green–Lagrange strain-displacement relationships are adopted to consider the large displacements, large strains, and material nonlinearity. For the numerical results presented in this article, the ABAQUS finite element program has been utilized with an appropriate user supplied subroutine (UMAT) written by FORTRAN for modeling a SMA strip and host elastic structure elements. In this model of a SMA strip, the shape memory effect is restricted to one-way applications. Numerical results show that an SMA strip actuator can generate enough recovery force to deform the host structure and sustain the deformed shape subjected to large external load, simultaneously. But, there are some difficulties found in designing reversible shape adaptive structures with this actuator, even if the SMA strip is coupled to an elastic structure which compels the SMA to recover the initial condition.

Experimental Studies on Active Shape Control of Composite Structures using SMA Actuators

In this article, the experimental modeling and active shape control of hybrid composite structures actuated by shape memory alloy (SMA) wires are presented and discussed. The thermomechanical properties of the SMA wires are experimentally measured. SMA actuators with residual strains are prepared by loading-unloading tensile tests. Hybrid composite structures are established by attaching the SMA actuators on the surface of a graphite/epoxy composite beam and plate by bolt-joint connectors. The first-order numerical model is used to model the response of the hybrid composite structures attached to the SMA actuators. The parameters of the first-order model are experimentally determined and the response is compared with experimental data. For faster and more accurate shape/deflection control of the hybrid composite structure, feedforward and proportional integral derivative (PID) feedback controllers are designed and applied to the hybrid composite structure. The PID feedback controller significantly improves the performance of the SMA actuators.

Finite element analysis of adaptive inflatable structures with SMA strip actuator

The interactions between the inflatable structure and shape memory alloy (SMA) strip actuators are investigated using finite element simulation. The numerical algorithm of the 3-D SMA thermomechanical constitutive equations based on Lagoudas model is implemented to analyze the unique characteristics of SMA strip. For the numerical results presented in this paper, the ABAQUS finite element program has been utilized with an appropriate user supplied subroutine (UMAT) for the modeling SMA strip. In this model of SMA strip, the shape memory effect is restricted to one-way applications. The geometrically nonlinear, updated Lagrangian equilibrium formulation implemented in ABAQUS is used for the numerical model of inflated membrane structures.

Large Deformation Analysis of Inflated Membrane Boom Structures with Various Slenderness Ratios

A comparison of numerical schemes for the nonlinear behavior of inflated membrane boom structures due to the wrinkling is investigated. For a finite element analysis, two different numerical schemes are applied . In t he first scheme, the structure is numerically modeled using membrane elements , and taut, wrinkled and slack membrane states are determined at each load step using the Tension Field theory . In t he second scheme, the structure is modeled with shell elements , and the nonlinear deformation is analyzed using a post -buckling analysis . A comparative study of the wrinkling problems of the inflated membrane boom in bending is carried out. Nomenclature � = stress � = strain D = effective elasticity matrix 2 � = minor principal stress 1 � = major principal strain � = principal angle s F = stretch ing force c F = critical collapse load c M = collapse bending moment

Shape and vibration control of smart composite structures

This research was partially supported by the Smart UAV Development program, one of the 21st Century Frontier R&D Programs funded by the Ministry of Science and Technology of Korea. The authors also acknowledge the support from the National Research Laboratory(NRL) Program.

Wrinkling control of inflatable booms using smart material patch

The methodology to restrain the growth of wrinkling region in inflatable boom is numerically and experimentally investigated. The inflatable boom structure is numerically modeled by using ABAQUS finite element program with membrane elements. To consider the nonlinear deformations of inflatable boom due to wrinkling, the numerical algorithm of wrinkling based on Miller-Hedgepeth membrane theory is developed using user defined material (UMAT) subroutine supported by ABAQUS. The experimental model of inflatable boom is made of Kapton film. To characterize the nonlinear behaviors of inflatable boom, the bending tests for various internal pressures are performed. To delay the growth of wrinkled region and restore the deformed shape of inflatable boom, shape memory alloy (SMA) wire actuator attached on surface of the structure is applied.

Nonlinear Analysis of Inflatable Membrane Structures with Wrinkling Effect

The large deformation of inflatable membrane structure is numerically and experimentally considered in this paper. The numerical algorithm of wrinkling based on Miller and Hedgepeth membrane theory is developed using user material(UMAT) subroutine written by FORTRAN. Wrinkled area and deformed shapes of inflatable membrane structures are investigated by using ABAQUS with UMAT subroutine of wrinkling algorithm.