Showing papers by "Prabhu Rajagopal published in 2013"

Antisymmetric feature-guided ultrasonic waves in thin plates with small radius transverse bends from low-frequency symmetric axial excitation

Abstract: The influence of bends constituting annular polygonal structures on ultrasonic guided waves propagating along their axis is investigated. Considering a single bend as a bent plate connects this problem to the better-understood physics of guided waves in straight plates. Using a three-dimensional finite element simulation validated with experiments, bends in plates are shown to act as features that can concentrate and guide ultrasonic energy along their length. Two interesting feature-guided modes are identified when the bent plate is subjected to “in-plane” or axial excitation applied uniformly along a through-thickness line bisecting the bent edge. Of these, the faster traveling mode has properties similar to, but travels at group velocities lower than, the S0 (fundamental symmetric) Lamb mode in flat plates. This paper however focuses on the slower bend-guided mode that is similar to the A0 (fundamental anti-symmetric) Lamb mode in flat plates. This mode is shown to be more strongly generated in smaller...

Studies on the influence of axial bends on ultrasonic guided waves in hollow cylinders (pipes)

Abstract: Ultrasonic guided waves in hollow cylinders (pipes) are today widely applied as rapid screening tools in the inspection of straight pipe segments in oil, power generation and petrochemical processing industries. However, the characteristics of guided wave propagation across features such as bends in the pipe network are complicated, hampering a wider application of the developed techniques. Although a growing number of studies in recent years have considered guided wave propagation across elbows and U-type bends, the topic is still not very well understood for a general bend angle φ, mean bend radius R and pipe thickness b. Here we use 3D Finite Element (FE) simulation to illumine the propagation of fundamental guided pipe modes across bends of several different angles φ. Two different bend radius regimes, R/λ ≈ 1 and 10 (where λ denotes the wavelength of the mode studied) are considered, exemplifying 'sharp' and gradual or 'slow' bends. Different typical pipe thicknesses b within these regimes are also s...

Ultrasonic waves guided by transverse bends in plates subjected to symmetric axial excitation

Abstract: Inspection of practical plate assemblies is challenging due to the presence of complex features such as bends and corners. The objective is to investigate the influence of bends or curvature in the transverse direction on the propagation of guided waves in plates. A 3D finite element (FE) simulation shows that bends in plates can concentrate and guide ultrasonic energy along the direction of wave propagation. An interesting feature-guided mode that is surprisingly similar to the A0 (fundamental antisymmetric) Lamb mode in normal plates was identified when the bent plate is subjected to 'in-plane' excitation as the generation of this type of mode for a thicknesswise symmetric excitation is unexpected. These results are validated with experiments and discussed using Semi Analytical Finite Element (SAFE) models.