tailieunhanh - Smart Material Systems and MEMS - Vijay K. Varadan Part 13

Tham khảo tài liệu 'smart material systems and mems - vijay k. varadan part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 362 Smart Material Systems and MEMS c 35 30 25 Ẫ20 s 15 03 15 10 5 0 50 447 .ônođ xv 35 3 20 445 d Figure a Peak voltage generated in the central patch b sensitivity in the central patch c peak voltage generated in the lower patch d sensitivity in the lower patch. is increased along with the distribution of voltage across the length of the patch. However the effect of the intense crack tip stress fields approaching towards this sensor patch could not be captured. This is captured by the other two sensor patches. As the load acts on the beam symmetrically on the geometrically symmetric DCB specimen the delamination axis coinciding with the central longitudinal axis the piezoelectric patches placed above and below the longitudinal axis undergo equal amounts of flexure. Due to this symmetrical stress conditions prevail in these patches and equal amounts of voltage are generated in these patches. Hence the voltage distribution is shown only for the patch in the lower sublaminate. Figure c shows the spatial distribution of the electric voltage along the length of the patch in the lower sublaminate for various lengths of delamination and the abscissa is taken as the surface nodal x-coordi-nate from the fixed end. As can be observed from this figure that when the delamination length is 25 mm in which case the near end of the PZT patch is 20 mm away from the crack tip the strains in the sensor patch seem to be almost uniform along the surface except for a small length towards the near end of the crack tip. Structural Health Monitoring Applications 363 As such it can be inferred that the flexure of the beam is also causing flexure of the sensor patch. When the crack tip is made to approach the sensor patches in the sublaminates the effect of the crack tip stresses causing flexural strains in the PZT patches can also be observed to be causing non-uniform strains and voltages in the PZT patches. When the delamination length is 45 mm the near end of the sensor .