On-Site Hardness Test (MIC 10)

MIC 10 Hardness test is one of the quickest and convenient portable method to determine the hardness of a material on-site. The method of this hardness test is according to the UCI Method (Ultrasonic Contact Impedance). The hardness is measured by detecting the frequency shift of a longitudinal oscillating rod with a Vickers diamond indenter. The diagonal of the indentation is not optically measured, as is usually done, instead the indentation area is electronically detected by measuring the frequency shift.

The shift is proportional to the size of the Vickers indentation. The MIC 10 operates according to the Ultrasonic Contact Impedance (UCI) method of hardness testing, and is standardized according to ASTM A1038. MIC 10 probes use a Vickers diamond indenter that gives you the precision to position it on a tiny point. Indentations produced by the MIC-10 are much smaller than equivalent Rockwell indentations, making this one of the least destructive portable hardness testers available. These attributes make the MIC10 well suited to these typical applications:

• Heat affected zone (HAZ) of welds
• Hardness progression curves
• Fine-grained materials
• Heat-treated materials
• Thin layers and coatings
• Surface hardened parts
• Thin wall pipe
• Difficult to access positions
• Small parts not recommended for testing coarse grained materials.

 

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  Basic Principle UCI MIC10 Hardness Tester

  Conventional Vickers or Brinell hardness testing requires optical evaluation of the area of an indentation produced by its indenter under a specified load. Testing using the UCI (Ultrasonic Contact Impedance) method is not evaluated optically as usual, instead the indentation area is electronically detected by measuring the shift of an ultrasonic frequency.

  A UCI probe consists of a Vickers diamond attached to the end of a metal rod. This rod is excited into a longitudinal oscillation by Piezoelectric transducers. Imagine the rod as a large spiral spring held at one end and free to oscillate at the resonant frequency at the other end. Attached to the free end is a contact plate, the Vickers diamond.

  Now picture the surface of the material to be comprised of a system of smaller spiral springs positioned vertically to the surface with the quantity of these springs representing the elastic properties of the material.

  The diamond’s penetration depth into the material is determined by the material’s hardness with a very hard material having a shallow indentation allowing only a few of these "atomic springs" to contact the diamond resulting in a slight frequency shift. On the other hand if a softer part is tested, the diamond penetration is deeper and the frequency shift is more significantly as additional "springs" are touched. This is the secret of UCI hardness testing: the frequency shift is proportional to the size of the test indentation produced by the Vickers diamond.

  

   

  

   

   

  The graphic below illustrates the relationship of frequency shift to hardness.

  

   

  Selection of MIC 10 Probe based on Applications

  The UCI method is best suited for testing homogeneous materials due to the small size of the indentations created. Five different loads (0.3, 0.8, 1.0, 5.0 and 10 kgf) are employed by the various models of UCI probes. The table below is offered as a general guide to selecting the appropriate probe for a variety of applications.

   

  Load	Advantage or Benefit	Typical Applications
  98 N 10 kgf	Largest indentation requiring only minimal surface preparation	Small forgings & HAZ weld testing
  50 N 5 kgf	Solves most general applications   30mm (1.2 in.) extended length designed for clearing obstacles.   Reduced length to 90 mm (3.5 in.) electronics in separate housing for minimum height.	Induction or carburized machined parts, e.g. camshafts, turbines, HAZ weld testing   Measurement in grooves & gears   Internal Diameter (ID) testing of pipes or tubes
  10 N 1 kgf	Load is easy to apply; provides control to test on a sharp radius   30mm (1.2 in.) extended length designed for clearing obstacles.   Reduced length to 90 mm (3.5 in.) electronics in separate housing for minimum height.	Ion-nitrided stamping dies and moulds, forms, presses, thin walled parts   Bearing raceways & gears     ID testing of pipes or tubes
  8 N 0.8 kgf	Use with urethane fixtures for complex shapes	Finished precision parts e.g. gears, & bearing raceways
  3 N 0.3 kgf	Shallowest indentation	Layers, e.g. copper or chromium layers on steel cylinders (≥40 µm), Copper Rotogravure cylinders, Coatings, Hardened layers (≥20 µm)

   

  Surface preparation for MIC 10 Test Sample

  All hardness test methods require smooth surfaces free of rust, paint, oil or protective coatings. The indentation depth must be large in comparison to the surface roughness. Surface preparation can be performed using a battery driven handheld grinder. However, care must be taken not to alter the surface hardness by overheating or cold working.

  Sizes of the indentations produced can vary greatly due to the extensive range in hardness possible with the MIC 10 and the available probe ranging from 0.3 kgf to 10.0 kgf. It is recommended the surface roughness of approximate 30% of the penetration depth. However, finer surface roughness will provide more accurate and precise result. Refer to table below for estimated surface roughness required as 30% of the penetration depth to the best sand paper grit to be used: 

  Load	Estimated Surface Roughness Required(Ra)	Sand Paper Grit
  98N 10kgf	1.6µm	320
  50N 5kgf	1.6µm	320
  10N 1kgf	0.4µm	500