Wednesday, July 1, 2020

Destructive and Non-Destructive test

Destructive test
  • Test on test pieces Damaged after test.
  • Determine mechanical properties of test piece under test.
  1. Tensile test 
  2. Impact Test   
  3. Fatigue Test
  4. Bend test 
  5. Hardness Test 
  6. Creep Test
Non-Destructive Test
  • Test on components. Not damaged after test
  • Determine flaws or imperfection during manufacture (or) service.
  1. Liquid penetrating  
  2. Electrical test method
  3. Ultrasonic method  
  4. Radiographic inspection
  5. Magnetic crack detection

Destructive test
Tensile Test

  • Tensile test is used to determine the behaviour of a material up to its breaking point.
  • A special shape specimen of standard size is gripped in the jaws of a testing machine. A load is gradually applied to draw the ends of the specimen apart such that it is subject to tensile stress up to yield point.
  • The highest value of stress is known as the ultimate tensile stress (UTS) of the material.
Bend Test
  • Specimen is bent through an angle of 180 with internal radius of 1.5 times the thickness of the specimen without cracking at edges.
Impact Test
  • Testing machine basically consists of a pendulum which is raised and allowed to fall, striking and rupturing the specimen.
  • In swinging through its arc of travel past specimen, pendulum assume a lower position at end of its travel due to loss of   energy when it strikes the specimen.
  • Energy given up to the specimen is its impact strength.
Hardness Test
  • Hardness test consist hardened steel ball impressing into metal at given pressure for predetermine time.
  • Load is 3000 kg for steel and 500 kg for soft metals such as brasses and bronzes.
  • Diameter impression indicates the hardness number.
Fatigue Test
  • 'Fatigue' is defined as the failure of a material due to repeatedly applied stress.
  • The specimen is rotated under load in a testing machine. So it is subject to tension and compression stresses alternately.
  • The number of cycles imposed before is recorded.
Creep Test
  • Creep test use to find safe working stress for material working at high temperature
  • It is permanent deformation resulting from loading over long period of time
  • Test piece mount vertically and constant tensile load under constant temperature.
  • Temperature range between 600’C to 1000’C and test period is 1000,10000,100000 hours

Non-Destructive Test
Liquid penetrate test
  • Industrial method, indicate presence crack, lamination lap and surface porosity.
  • Fluorescent dye method and Aerosol dye method.
Fluorescent dye method
  • First, the surface is cleaned using a volatile cleaner and degreaser.
  • Then a fluorescent dye is applied and a certain time allowed for it to enter any flaws under capillary action.
  • Then the surface is wiped clean using the cleaning spray.
  • An ultra violet light is shone on the surface, any flaws showing up as the dye fluorescent.
Aerosol dye method
  • The more commonly used dye penetrant method is similar in application.
  • The surface is cleaned and the low viscosity penetrant is sprayed on.
  • After a set time, the surface is cleaned again.
  • Then a developer is used which coats the surface in a fine white chalky dust.
  • The dye seeps out and stains the developer typically a red colour.
Ultrasonic Test
  • Probe of test equipment transmits high frequency sound waves about 0.5 MHz to 20 MHz which reflected by any flaws in object
  • Reflected sound waves displayed on monitor screen of cathode ray oscilloscope.
  • Suitable for detection, identification and size assessment of a wide variety of both surface and sub-surface defects in materials.
  • Measured thickness of material or to detect internal or surface defects in welds, casting or forging either during manufacture or when in service.
Radiographic Test
  • Image produced on film.
  • X rays and gamma rays are used for inspection of welds, castings, forging and pressure vessels etc.
  • Exposure time for x-rays and gamma rays vary with type of material, thickness and the intensity of rays.
  • Faults in the metal effect the intensity of rays which passes through the material
  • Film exposed by the rays gives the shadow photograph
  • Used on both metallic and nonmetallic material, both ferrous and non-ferrous metal

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