What is hardness on metals?
With regard to metals, hardness has always been a subject matter of a lot dialogue amongst technical other folks, resulting in a wide range of definitions. Hardness properties include such various attributes as resistance to abrasives, resistance to plastic deformation, high modulus of elasticity, top yield level, high energy, absence of elastic damping, brittleness or loss of ductility.
To a metallurgist, hardness is a subject material’s resistance to penetration. In general, an indenter is pressed into the outside of the material to be tested under a selected load for a undeniable time period, and a measurement is manufactured from the scale or depth of the indentation. Hardness isn’t a basic assets of a subject matter, however a response to a selected test means.
Basically hardness values are arbitrary, and there are no absolute requirements for hardness. Hardness has no quantitative price, with the exception of when it comes to a given load carried out in a selected, reproducible approach and with a specified indenter shape. Static indentation checks wherein a ball, cone or pyramid penetrates into the skin of the material being tested are widespread. The courting of load to the world or intensity of indentation is a measure of hardness, reminiscent of that found in not unusual bench-top Brinell, Rockwell, Vickers or Knoop hardness testers.
The different strategies and another way formed indenters used by, as an example, Brinell (HB) and Rockwell (HRC) produce dissimilar responses of the material under check. Conversion tables with regards to e.g. HRC and HB values have to be determined empirically via experimental evaluation of a specific material’s hardness with the other test strategies. There exists no mathematical equation to transfer measurements from one scale to another. To examine the hardness of 2 different samples, each will have to be measured using the similar hardness scale, or a scale will have to be developed to convert from one dimension to the opposite.
Why (Metal)hardness testing?
Materials are primarily tested in manufacturing applications for two reasons: to investigate the properties of a novel material or as a quality check to guarantee that the sample meets a specified specification
How to measure hardness on-site?
Hardness testing equipment that use traditional methods require the test component to be delivered to the testing instrument, which is not always practicable. In-situ hardness tests are now possible thanks to the development of portable testing instruments. One typical method uses a Vickers-diamond tip to measure the frequency shift of a resonating rod, which occurs when the diamond penetrates the test material by applying a specified test load. The frequency shift is measured and converted to a hardness value that is displayed on the LCD. This approach, known as UCI (Ultrasonic Contact Impedance), is used by the MICRODUR instruments.
The rebound/ LEEB method is another well-known principle for portable hardness testers. For example, the DynaMIC and DynaPOCKET detect the velocity of a propelled impact body prior to and after impact on the test material’s surface. The ratio of the two velocities reflects the material’s hardness, which can be transformed into multiple scales using the instrument’s conversion tables for various materials.