Mechanical Engineering

RADIOGRAPHY TEST INTRODUCTION : Industrial radiography is a nondestructive test method that uses X-rays or Gamma rays to show the presence and certain characteristics of internal discontinuities in solid materials. The method is based on the ability of X-ray or Gamma-ray radiation to penetrate solids, to a degree that varies with such factors as wave length of the radiation, and type and thickness of the material part of the radiation penetrates the material and part is absorbed. The amount absorbed and the amount transmitted are a function of the thickness of the material. Where a void or discontinuity exists, there is essentially less material to absorb the radiation. This creates a different in absorption, a difference that registers on photographic emulsions. The result is a shadow picture called a radiography Radio-graphic Sources : The common gamma ray radio-graphic sources : Cobalt - 60 Cesium - 137 Iridium - 192 Thulium - 170 Gamma Ray Radiography : Gamma rays ar...

MAGNETIC PARTICLE EXAMINATION (M.P.I.) INTRODUCTION This method is used for detecting cracks and other discontinuities open to surface or sub surface in ferromagnetic materials. Fine magnetic particles are applied to the surface of a part which has been suitably magnetized. The particles are attracted to regions of magnetic non-uniformity associated with defects and discontinuities, thus producing indication which are observed visually. PRINCIPLE When a piece of metal is placed in a magnetic field and the lines of magnetic flux get intersected by a discontinuity such as a crack or slag inclusion in a casting, magnetic poles are induced on either side of the discontinuity. The discontinuity causes an abrupt change in the path of magnetic flux flowing through the casting normal to the discontinuity, resulting a local flux leakage field and interfering with the magnetic lines of force. This local flux disturbance can be detected by its affect upon magnetic particles that collect o...