Videometric research on deformation measurement of large-scale wind turbine blades

Utilization of wind energy is a promising way to generate power,and wind turbine blades play a key role in collecting the wind energy effectively.This paper attempts to measure the deformation parameter of wind turbine blades in mechanics experiments using a videometric method. In view that the blades experience small buckling deformation and large integral deformation simultaneously, we proposed a parallel network measurement(PNM) method including the key techniques such as camera network construction,camera calibration,distortion correction,the semi-automatic high-precision extraction of targets,coordinate systems unification,and bundle adjustment,etc. The relatively convenient construction method of the measuring system can provide an abundant measuring content,a wide measuring range and post processing.The experimental results show that the accuracy of the integral deformation measurement is higher than 0.5 mm and that of the buckling deformation measurement higher than 0.1mm.

Shear deformable finite beam elements for composite box beams

The shear deformable thin-walled composite beams with closed cross-sections have been developed for coupled flexural, torsional, and buckling analyses. A theoretical model applicable to the thin-walled laminated composite box beams is presented by taking into account all the structural couplings coming from the material anisotropy and the shear deformation effects. The current composite beam includes the transverse shear and the restrained warping induced shear deformation by using the first-order shear deformation beam theory. Seven governing equations are derived for the coupled axial-flexural-torsional-shearing buckling based on the principle of minimum total potential energy. Based on the present analytical model, three different types of finite composite beam elements, namely, linear, quadratic and cubic elements are developed to analyze the flexural, torsional, and buckling problems. In order to demonstrate the accuracy and superiority of the beam theory and the finite beam elements developed by this study,numerical solutions are presented and compared with the results obtained by other researchers and the detailed threedimensional analysis results using the shell elements of ABAQUS. Especially, the influences of the modulus ratio and the simplified assumptions in stress-strain relations on the deflection, twisting angle, and critical buckling loads of composite box beams are investigated.

Mechanical properties of lattice grid composites

An equivalent continuum method only considering the stretching deformation of struts was used to study the in-plane stiffness and strength of planar lattice grid com- posite materials. The initial yield equations of lattices were deduced. Initial yield surfaces were depicted separately in different 3D and 2D stress spaces. The failure envelope is a polyhedron in 3D spaces and a polygon in 2D spaces. Each plane or line of the failure envelope is corresponding to the yield or buckling of a typical bar row. For lattices with more than three bar rows, subsequent yield of the other bar row after initial yield made the lattice achieve greater limit strength. The importance of the buckling strength of the grids was strengthened while the grids were relative sparse. The integration model of the method was used to study the nonlinear mechanical properties of strain hardening grids. It was shown that the integration equation could accurately model the complete stress-strain curves of the grids within small deformations.

Towards Understanding Why the Thin Membrane Transducer Deforms:Surface Stress-Induced Buckling

This study is directed towards a comprehensive exploration on the deformation mechanism of the thin membrane transducer（TMT） caused by surface stress variation.We stress that the biomolecular interaction has changed the magnitude of the surface stress;and when the surface stress exceeds a critical value the TMT will buckle and deform.Based upon Gurtin＇s theory of surface elasticity and principle of finite deformation,we abstract the TMT as a nanobeam with two clamped ends,and the close-formed governing equation set is derived accordingly.A computer code via the shooting method is developed to solve the presented two-point boundary value problem.In succession,the nanobeam deflection and critical parameters for buckling are quantitatively discussed.This investigation lays the theoretical foundation of TMTs;and it is also beneficial to gain deep insight into characterizing mechanical properties of nanomaterials and engineering nano-devices.

Effects of uniaxial compressive strain on the electronic- transport properties of zigzag carbon nanotubes

Recently, substantial attention has been paid to the strain sensitivity of the carbon nanotubes＇ （CNTs＇） electronic properties. In this study, the relationships between the geometric structures and electronic states of zigzag CNTs under uniaxial compressive strain were investigated. We found that different factors dominate the electronic states of zigzag CNTs depending on the strain regions： the initial stage of the strain loading, which lasts until column-buckling deformation begins, and the strain regions corresponding to column- and shell-buckling deformations. Because shell-buckling deformation significantly increases the re-orbital angle, the angle between the π orbital axis vectors of adjacent atoms, strong localization of the density of states （LDOS） occurs in the buckled area. We also analyzed the current able to pass through deformed CNTs using a tight-binding-based Green＇s function approach and determined that the current can be significantly suppressed by applying uniaxial compressive strain. Our method of predicting the electronic state of a deformed CNT based on the π-orbital angle is expected to be useful for predicting the electronic properties of CNT-based electronic devices and sensors.