Daiki Shiozawa

Passive Electric Potential CT Method Using Piezoelectric Material for Crack Identification

When the piezoelectric film is glued on the surface of a cracked material subjected to mechanical load, change in electric potential distribution is observed on the surface of the film. Based on this phenomenon, the passive electric potential CT (computed tomography) method can be developed, which does not require electric current application for identifying cracks. This method may be applied to develop an intelligent structure with a function of self-monitoring of flaws and defects. For the crack identification from electric potential distribution, an inverse method based on the least residual method was applied, in which square sum of residuals are evaluated between the measured electric potential distributions and those computed by using the finite element method. Numerical simulations were carried out on identification of a through-thickness transverse crack. It was found that the location and size of the crack can be quantitatively identified by the proposed passive electric potential CT method.

Identification of Delamination Defect in Laminated Composites by Passive Electric Potential CT Method

This paper describes the feasibility of passive electric potential CT (computed tomography) method which does not require electric current application for detection of damage in laminated composites. In this method, piezoelectric film is glued on the surface of composites as a sensor. Electric potential values on the piezoelectric film change due to the strain distribution on the composite, when the composite is subjected to external load. The strain distribution of the cracked body shows a characteristic electric potential distribution. Therefore passively observed electric potential values on piezoelectric film can be used for the defect identification. This method may be applied to develop an intell igent structure with a function of self-monitoring of flaws and defects. An inverse method based on the least residual method was applied to the defect identification from the electric potential distribution. In this inverse method, square sum of residuals are evaluated between the measured electric potential distributions and those computed by using the finite element method. Numerical simulations were carried out on the estimation of location and size of delamination defect in composites. It was found that the location, size and depth of the defect can be quantitatively identified by the passive electric potential CT method.

Evaluation of Fatigue Damage in Short Carbon Fiber Reinforced Plastics Based on Thermoelastic Stress and Phase Analysis

Short carbon fiber composite materials are receiving a lot of attentions because of their excellent moldability and productivity, however they show complicated behaviors in fatigue fracture due to the random fibers orientation. In this study, thermoelastic stress analysis (TSA) using an infrared thermography was applied to the evaluation of fatigue damage in short carbon fiber composites. Second harmonic component of thermoelastic temperature change that is obtained by lock-in processing based on double-frequency against loading frequency was conducted to identify the turbulence in thermoelastic waveform due to fatigue damage evolution. It was found that the portions showing high second harmonic component values coincided with the portions where delamination damages were detected.

Application of infrared camera for steel bridge maintenance

Heavy-duty anticorrosion coating with multiple-layered paints is applied to long-span steel bridge members on the sea. By aging deterioration, the coating is worn from surface year by year. Appropriate repainting programs should be adopted for the maintenance of the bridges according to the evaluation of wear extent. In this study a new nondestructive evaluation technique using short wavelength infrared (SWIR) camera, that enables us to easily detect the wear loss of surface fluororesin coating layer, is developed based on the difference in spectral absorptance between surface fluororesin coating and inner-layer epoxy resin coating.