H.F. Tan

Abnormal frequency characteristics of wrinkled graphene

This paper observes an abnormal phenomenon in the frequency variation of wrinkled graphene. Compared with the pristine case, a slight wrinkle decreases the resonant frequency, while a heavy wrinkle increases the resonant frequency. This observation gave us the idea to tune the wrinkle and work out the frequency variation of graphene. Our results reveal that the frequency shift of graphene may be tuned by wrinkles ranging from 83.8% to 128.6%. The abnormal frequency variation is close to the dominant contributions of the effective mass involved in vibration and the wrinkled stress level. The effective mass involved in vibration governs the decreasing trend of the resonant frequency in graphene which has slight wrinkles. The wrinkled stress level controls the increase in resonant frequency of heavily wrinkled graphene. A modified prediction model is proposed which predicts the abnormal frequency variation and evaluates the resonant frequency of wrinkled graphene within 2% mean difference. Our results will benefit the design of wrinkle-tuned variable-frequency nano-resonators or devices.

Wrinkling Behaviors of Gossamer Structure with Stretched Annulus-Shape under In-Plane Torsion

In this paper, an out-of-plane wrinkling function is constructed and then is introduced to the buckling theory to complete the wrinkling analysis. Two key techniques (initial imperfection and prestress) are then introduced to the shell model to perform the post-wrinkling numerical analysis of the annulus-shaped membrane under in-plane torsion. The numerical analysis is also performed to evaluate the effects of the thickness and structural scale on the wrinkling behaviors. The results indicate that the wrinkling behavior is intensely affected by structural size compared with membrane thickness. Results from analytical models and simulations agree well, and show both are effective to predict detailed wrinkling behavior of gossamer structures accurately.

Vibration Evaluation of Wrinkled Membrane Inflated Beam

Inflated booms are under increasing application in various membrane spacecraft structures. A specific emphasis is often placed on determining static characteristics of inflated beams in bending. There is a lack of knowledge in dynamic conditions, especially for simple and accurate solutions for wrinkled inflated beams. This article deals with the theoretical evaluation on the natural frequencies of wrinkled inflated beams. Three factors, including the inflated pressure, the wrinkles, and the aspect ratio, are introduced into the vibration equation of the beam to predict the first-order natural frequency of the wrinkled inflated beams. The predictions on the first-order natural frequency agree well with the vibration simulations. The parametric studies on the vibration characteristics of the wrinkled inflated beam are performed in the end. Results reveal that the wrinkles decrease the first-order natural frequency of the inflated beam greatly. The first-order frequency of the wrinkled inflated beam is sensitive to the aspect ratio. The results and conclusions are good references to the design and the wrinkling control of the inflated booms.

The interactive bending wrinkling behaviour of inflated beams

A model is proposed based on a Fourier series method to analyse the interactive bending wrinkling behaviour of inflated beams. The whole wrinkling evolution is tracked and divided into three stages by identifying the bifurcations of the equilibrium path. The critical wrinkling and failure moments of the inflated beam can then be predicted. The global–local interactive buckling pattern is elucidated by the proposed theoretical model and also verified by non-contact experimental tests. The effects of geometric parameters, internal pressure and boundary conditions on the buckling of inflated beams are investigated finally. The results reveal that the interactive buckling characteristics of an inflated beam under bending are more sensitive to the dimensions of the structure and boundary conditions. We find that for beams which are simply supported at both ends or clamped and simply supported, boundary conditions may prevent the wrinkling formation. The results provide significant support for our understanding of the bending wrinkling behaviour of inflated beams.

Membrane wrinkling patterns and control with SMA and SMPC actuators

Wrinkling is a main factor affecting the performance of the membrane structures and is always considered to be a failure as it can cause dramatic decrease of shape accuracy. The study of membrane wrinkling control has the analytical and experimental meanings. In this paper, a feasible membrane shape control method is presented. An expression of wrinkle wavelength using stress extremum principle is established based on the tension field theory and the Von Karman large deflection formula which verifies the generation and evolution reason of membrane wrinkles. The control mechanism for membrane wrinkles is developed using shape memory alloy (SMA) and shape memory polymer composite (SMPC) actuators which are attached to the boundaries of the membrane for producing contraction/expansion forces to adjust the shape of the membrane. The whole control process is monitored by photogrammetric technique. Numerical simulations are also conducted using ANSYS finite element software with the nonlinear post-buckling analytical method. Both the experimental and numerical results show that the amplitudes of wrinkles are effectively controlled by SMA and SMPC actuators. The method introduced in this paper provides the foundation for shape control of the membrane wrinkling and is important to the future work on vibration control of space membrane structures.