Non-Destructive and Destructive Investigation of MLG Parts of MIG 29 Aircraft (TMP-0165)

Abstract

It is proposed to investigate MLG’s undergone 0, 1885, 2136, 2445 and 2500 landings to arrive at recommendations for life extension methodology and revise limitations to enable formal certification of the aircraft for the extended period/landing. The residual stress profile of the zero landing MLG exhibit wide variation from location to location. The average compressive stress may be considered as around -325 MPa. No set pattern of compressive stresses could be derived from the comparison between the zero landing and with increasing number of landings. However, locations 3, 3’, 4, 5 and 6 indicate a subtle decreasing trend in the stresses. In general, these locations indicate relaxation of stresses with increasing number of landing. Moreover, the residual stresses at all the locations of the investigated five MLG remained compressive. Compressive residual stress field (CRSF) study was found to be varied from location to location of life-expired MLG. The profile at location 4 has shown a decreasing trend, location 5 has nearly flat nature and the profile at location 6 was of initial increasing nature and then decreasing. Moreover, the depths of CRSF (Z0) as well as compressive residual stress at the surface (src) at various locations are in following order: location 4 > location 5 > location 6. The residual stress at the investigated subsurface region remained compressive at location 4 while it changed to tensile at locations 5 & 6. The ultrasonic velocity study on the MLG did not reveal any systematic variation. This may be due to the geometry and the regions of intense stress lying in the regions of at least three different diameters having lap joints. However, ultrasonic velocity measurements indicated that overall shear wave velocity decreases with number of landings. The visual inspection of sliding cylinder shows circumferential damage marks originated due to wear as well as local bluish colouration caused by the local overheating due to abrasion during landing. The microstructure of the base metal shows tempered martensitic structure without any perceptible microstructural changes induced by abrasive heating. The loss of chromium coating thickness due to abrasion seems to be negligible and within the specified range even in the life-expired MLG. Vickers microhardness data of the coating from bluish colouration region shows a slight drop in hardness that may be due local softening of the coating due rise in temperature. The x-ray radioscopy study of the damaged sections shows no discernible changes.