Determining the Strength of Your Materials
In many applications it is useful to know how well a material will resist scratching, deformation, or cutting. Pro Integrity NDT® uses Hardness Testing (HT) to make that determination.
During a hardness test we assess the depth of an indent or incision made by a precisely shaped indentor applied to the test material with a precise amount of force over a specified period of time. When we compare the size of the indent with a similar indent in a known hardness standard we are able to calculate a hardness value for the material being examined. Hardness values can be derived from several scales, including Vickers, Brinell, Knoop, or Rockwell. Hardness testing is appropriate for structural steel, castings, forgings, welds, weld overlays, piping, machined parts and pressure vessels.
We have 2 techniques available to us.
- Telebrineller. A tiny dent is made simultaneously in the material being examined and on the surface of a bar of known hardness, using a hammer and ball bearing apparatus. The diameters of the dents are measured, and the difference in their sizes determines the hardness value of the tested material.
- Ultrasonic Contact Impedance (UCI) A diamond indenter vibrating at ultrasonic frequency is pressed into the material being examined. As it penetrates the material, the frequency of the vibration shifts proportionally. The instrument is calibrated to the frequency shift found during the test of a known hardness standard, and thus the hardness of the tested material can be inferred.
Benefits of this method are:
- Telebrineller deforms a much larger surface area of material, so any errors due to steel crystal structure are minimized.
- UCI leaves a very small testing defect on the surface of machined parts.
