Atul Kumar Agrawal

A study of free surface effects on through cracks using BEM

Abstract The effect of free surfaces on fracture characteristics for elastostatic problems is investigated using three-dimensional boundary element method (BEM). Stress intensity factors (SIFs) are calculated in BEM using traction values at the nodes along the crack front. A close correspondence between K I computed from traction values and J 1 n integral is seen. Thus, it is possible to relate the evaluated state of stress at the crack vertex, where crack front meets the free surface, with a value of SIF. Thickness of boundary layer where free surface effects are predominant is estimated. Also, it is possible to estimate accurately the critical intersection angle of the crack front with the free surface at which square-root singularity is restored at the crack vertex. It may become possible to capture free surface retardation of crack growth accurately in crack propagation studies with the methodology used in this paper.

FREE SURFACE EFFECT ON MOVING CRACK UNDER IMPACT LOADING BY BEM

This paper deals with the implementation of a 3D time-domain boundary integral formulation for a moving center-crack in a finite solid under suddenly applied crack face pressure. The BEM displacement time-domain formulations have, hitherto, been limited to analyzing two-dimensional crack problems, though hypersingular formulations have been used to analyze finite cracks in infinite domains. In this paper, variation of dynamic stress intensity factor (DSIF) along the crack front for a moving, through-thickness straight crack is studied for a finite solid under step loading. The state of stress is evaluated at the crack vertex, where crack front meets the free surface. The effect of free surface on DSIF is investigated. It is possible to estimate accurately the critical intersection angle of the crack front with the free surface at which square-root singularity is restored at the crack vertex under step loading for various speeds of crack propagation. It is also predicted in this work that for high speeds of crack propagation, crack front maintains its straight profile.

A study of free surface effects on through cracks under impact loading

This paper deals with the implementation of a three-dimensional time-domain boundary integral formulation for a center-crack, finite solid under symmetrically applied step loading. The BEM displacement time domain formulations have, hitherto, been limited to analyzing two-dimensional crack problems, though hypersingular formulations have been used to analyze finite cracks in infinite domains. In this paper, variation of dynamic stress intensity factor (DSIF) along the crack front for a stationary, through-thickness straight crack is studied for a finite solid under step loading. The state of stress is evaluated at the crack vertex, where crack front meets the free surface. The effect of free surface on DSIF is investigated. The effect of waves traveling in thickness direction is explained. It is possible to estimate accurately the critical intersection angle of the crack front with the free surface at which square-root singularity is restored at the crack vertex under step loading. A new partitioning scheme is proposed for spatial integration of elastodynamic kernels.

Online condition monitoring of misaligned meshing gears using wear debris and oil quality sensors

This paper aims to investigate the effect of misalignment on wear of spur gears and on oil degradation using online sensors.,The misalignment effect on gears is created through a self-alignment bearing, and is measured using laser alignment system. Several online sensors such as Fe-concentration sensor, moisture sensor, oil condition sensor, oil temperature sensor and metallic particle sensor are installed in the gear test rig to monitor lubricant quality and wear debris in real time to assess gearbox failure.,Offset and angular misalignments are detected in both vertical and horizontal planes. The failure of misaligned gear is observed at both the ends and on both the surfaces of the gear teeth. Larger-size ferrous and non-ferrous particles are traced by metallic particle sensor due to gear and seal wear caused by misalignment. Scanning electron microscope (SEM) images examine chuck, spherical and flat platelet particles, and confirm the presence of fatigue (pitting) and adhesion (scuffing) wear mechanism. Energy-dispersive X-ray spectroscopy analysis of SEM particles traces carbon (C) and iron (Fe) elements due to gear failure.,Gear misalignment is one of the major causes of gearbox failure and the lubricant analysis is as important as wear debris analysis. A reliable online gearbox condition monitoring system is developed by integrating wear and oil analyses for misaligned spur gear pair in contact.