Lei Zhenkun

A New Theoretical Model of a Carbon Nanotube Strain Sensor

Carbon nanotubes (CNTs) are potential strain sensors due to their excellent mechanical and spectral properties. A new theoretical model of a CNT strain sensor is obtained by applying the polarized Raman properties of CNTs, which calculates the synthetic contributions of Raman spectra from the CNTs in random directions. By using this theoretical model, the analytic relationship between planar strain components and the Raman shift increment of uniformly dispersed CNTs is obtained, which is applicable for accurately characterizing the strain in random directions on the surface of a measured microsystem.

Whole-field determination of isoclinic parameter by five-step color phase shifting and its error analysis

Abstract Combining color imaging with phase shifting, a technique named five-step color phase shifting is presented to determine the whole-field isoclinic parameter. Relevant theory is derived and explicit conditions for directly determining the isoclinic parameter in the range of [0, π /2] are given. The unloaded light intensity of the model is systematically studied. A color camera recorded five isoclinic images coupled with isochromatics from a plane polariscope with five different settings, respectively. Experiments have been carried out with a circular disk under diametral compression and errors have been analyzed and estimated. This technique utilizes white light, which avoids undefined isoclinics near the locations where the isochromatics exist and will have active effect on experimental stress analysis and structural strength design.

Experimental characterization of interlaminar shear failure in sandwich structures under three-point bending

We applied an improved six-step phase-shifting method in digital photoelasticity to an adhesively bonded aluminum/epoxy/aluminum sandwich structure in order to study interlaminar shear failure behavior. Before and after three-point bending, a self-balanced thermal residual shear stress appeared on the interface because of the difference in thermal expansion coefficients between aluminum faces and epoxy core interlayer. At the beginning of loading, the shear stress in the core layer distributes continuously and forms shear bands tilting at a 45° direction. It then joins with the upper and bottom aluminum faces in order to realize the shear load transfer. As the bending load increases, the maximum interface shear stress occurs near the supports and a partially debonded region appears at the interface. The interfacial shear stress in the partially debonded region decreases rapidly until a shear failure occurs. A load–flexibility curve of the vibration-damping–type sandwich structure agrees well with the theoretical prediction of a laminated beam.

A robust method to measure residual stress in micro-structure

An experimental investigation on the residual stress in porous silicon micro-structure by means of micro-Raman spectroscopy is presented. It is shown by detecting the Raman peak shifts on the surfaces and cross-sections of electrochemical etched porous silicon samples with different porosities that serious residual stresses distribute complicatedly within the whole porous silicon structure. It is proved that micro-Raman spectroscopy is an effective method for residual stress testing on the micro-structures applied in optoelectronics and microelectronics.