CONTENTHardnessGeneral type of hardness testRockwell hardness test
HARDNESS:- Hardness is simply the resistance to plasticdeformation or permanent deformation ofmaterial. The term hardness may also refer toresistance to bending, scratching, abrasionor cutting. Hardness is dependenton ductility, elasticity plasticity, strain,strength,
GENERAL TYPES OF HARDNESS MEASUREMENTThere are three general type of hardnesstest: Scratch hardness test Indentation harness test Rebound hardness test
SCRATCH TEST Scratch hardness is the measure of howresistant a sample is topermanent plastic deformation due tofriction from a sharp object. Theprinciple is that an object made of aharder material will scratch an objectmade of a softer material. In scratch test Moh’s scale are usuallyadopted. This consist of a list of materials
INDENTATION TEST Indentation hardness measures the resistanceof a sample to material deformation due to aconstant compression load from a sharp object. They are primarily used inengineering and metallurgy fields. it is most widely used for measurement ofharness it measure the brinell hardness , Rockwellhardness, Vickers hardness etc.
ROCKWELL HARDNESS TEST The Rockwell Hardness test also uses a machine toapply a specific load and then measure the depth ofthe resulting impression. Rockwell hardness test devised in USA. It is useful for finished material testing . Hardness no. is indicated on dial. Test piece is place on table of the instrument. Indenter is brought into contact with surface of testpiece under light load(minor load). Scale is then adjusted to zero. Major load is applied ,hardness index is read from thescale.
Penetration depth “e” of impression ismessure by instrument. This penetration depth is convert intoharness value appear on dial. Rockwell hardness formula HR = E - e
F0 = preliminary minor load in kgf F1 = additional major load in kgf F = total load in kgf e = permanent increase in depth ofpenetration due to major load F1 measuredin units of 0.002 mm E = a constant depending on form ofindenter: 100 units for diamond indenter, 130units for steel ball indenter HR = Rockwell hardness number
SCALE USE ON DIAL scale being determined by indenter and full load use . Scale A : which is use in conjunction with diamondcone and 60kgf load .it is use for very hard materialsuch as tool steel. Scale B : which is use in conjunction with 1/16 inchdiameter steel ball and 100kgf load.it is use for softmaterial such as copper alloy ,mild steel etc.
Scale C: which is use in conjunction withdiamond cone 120 degree angle and 150load .it is use for hardend steel , hard castiron.
ADVANTAGE/DISADVANTAGE Advantages of the Rockwell hardness include: The direct Rockwell hardness number readouton the dial. Rapid testing time. Can be used for a very wide range of materials. Disadvantages include: Possible errors due to shifting of the sample under testload during test cycle Quality of the indenter has a strong influence on thetest result