Identification of damage in bars using PZT sensors and regression techniques
A methodology is developed for the identification of defects in solid bars using longitudinal stress wave propagation data in conjunction with regression techniques. For the experimental study, a series of notches of different depths are cut at a fixed acial location of bars. Longitudinal waves are generated within the bars by means of the indirect collinear impact of a surface hardened spherical steel ball on one of the plane ends of the bars. In order to prevent local plastic deformation of the bar ends and to ensure that the waves induced in the bars are plane longitudinal waves, anvils are attached to the impacted ends of the bars. PZT (lead zirconium titanate) tiles of dimensions 5 X 3 mm, which are cut from standard PZT patches of dimensions 30 X 30 mm, are bonded on the surface of the bars and used as strain sensors. It is shown that the use of PZT sensors has several advantages over the use of conventional resistance strain gauges. A regression anaylysis technique is used to relate the strain histories from the notched bars to the strain history form the defect free bar. It is shown that the technique readily indicates the presence and size of a structural defect. In particular, it is shown that the area enclosed by the regression curve increases as the defect size increases.
KeywordsStrain Sensor Lead Zirconium Titanate Strain History Wheatstone Bridge Electrical Resistance Strain
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