PRESENTATION TOPIC: VICKERS HARDNESS TEST GROUP# 1: NAILA MUSHTAQ MY-044 NIDA SHAKIL MY-032 SADIA GUL MY-048 SUBMITTED TO: SIR USMAN

Hardness is usually defined as Resistance to permanent indentation under static or dynamic loads Energy absorption under impact loads Resistance to abrasion Resistance to cutting or drilling

There are three main types of tests used to determine hardness:

The Vickers hardness test was developed in 1924 by Smith and Sandland. The

test evaluates hardness in a manner similar to Brinell taking the ratio between

the load applied and the surface area of the resulting impression.

It was decided that the indenter shape should be one based on the following :-

To be capable of producing geometrically similar impressions, irrespective of

size

The resulting impression should have well defined points of measurement

The indenter should have high resistance to self deformation.

A diamond in the form of a square based pyramid satisfied these conditions.

It had been established that the ideal size of a Brinell impression was 3/8 of the

ball diameter. As two tangents to the circle at the ends of a chord 3/8 long,

intersect at 136 degrees It was decided to use this as the included angle of the

indenter. The angle was varied experimentally and it was found that the

hardness value obtained on a homogeneous piece of material remained

constant, irrespective of load.

The unit of hardness given by the test is the Vickers Pyramid Number (HV).

The Vickers Pyramid Number (HV) is determined by the ratio Force (applied to

the Indenter) divided by the Area (the surface area of the resulting indentation).

Vickers test method is defined in the following ASTM standard:

ASTM E92:

This test method covers the determination of the Vickers hardness of metallic materials, using indentor in the form of square based diamond pyramid and applied loads of 1 kgf to 120 kgf .

The basic principles of operation of the Vickers hardness test are illustrated in figure where it can be seen that the load is applied to the indentor by a simple weighted lever. In modern equipment the timing mechanism is done electronically.

All Vickers ranges use a 136° pyramidal diamond indenter that forms a square indent.

The indenter is pressed into the sample by an accurately controlled test force. The force is maintained for a specific dwell time, normally 10 – 15 seconds. After the dwell time is complete, the indenter is removed leaving an indent in

the sample that appears square shaped on the surface. The size of the indent is determined optically by measuring the two diagonals

of the square indent.

The Vickers hardness number is a function of the test force divided by the surface area of the indent. The depth of indentation is about 1/7 of the diagonal length. The average of the two diagonals is used in the following formula to calculate the Vickers hardness.

HV = Constant x test force / avg of two diagonal squared

HV = 1.854 x P/d2

HV= {2Psin(θ/2)}/d 2 where θ=136º

HV = 1.854P/d2

The unit of hardness given by the test is known as the Vickers Pyramid

Number (HV) or Diamond Pyramid Hardness (DPH). The hardness number

can be converted into units of pascals, but should not be confused with a

pressure, which also has units of pascals. The hardness number is determined

by the load over the surface area of the indentation and not the area normal to

the force, and is therefore not a pressure.

Method to convert HV to SI units: To convert HV to MPa multiply by 9.807 To convert HV to GPa multiply by 0.009807

The hardness number is not really a true property of the material and is an

empirical value that should be seen in conjunction with the experimental

methods and hardness scale used. When doing the hardness tests the distance

between indentations must be more than 2.5 indentation diameters apart to

avoid interaction between the work-hardened regions

The Vickers number, which normally ranges from HV 100 to HV1000 for metals, will increase as the sample gets harder. Tables are available to make the calculation simple, while all digital test instruments do it automatically. A typical Vickers hardness is specified as follows:

56 HV 5 Where 56 is the calculated hardness and 5 is the test force in kgf.

a) A perfect square indentation is made with a perfect diamond-pyramid indenter would be a square.

b) The pincushion indentation is the result of sinking in of the metal around the flat faces of the pyramid. This gives an overestimate of the diagonal length (observed in annealed metals

c) The barrel-shaped indentation is found in cold-worked metals, resulting from ridging or piling up of the metal around the faces of the indenter. Produce a low value of contact area giving too high value.

Because of the wide test force range, the Vickers test can be used on almost any metallic material. The part size is only limited by the testing instrument's capacity.

Metallurgy is a specialized field where many types of alloys are made using ferrous and non-ferrous metals. Often Vickers hardness testing is used to determine the properties of these combinations of metallic substances.

When using Vickers hardness testing in the process of alloy production, it is only one-step in each part of each process as a pure metal or alloy is produced. This allows the producer to develop a recipe to create the exact formulation to make a uniform product that is consistent every time. Once the Vickers hardness testing specification is determined, the statistics are recorded. This is then added to a list known as a formulary. From these tests and others, the characteristics can be determined to decide if any changes need to be made. Vickers hardness testing helps with this.

It can test thinner sections than any other production test, and the square indentation is the easiest to measure accurately.

It is used where higher accuracy or shallower penetration is necessary, as in: Thin case-hardened parts, .005 to .010 in. Thin materials down to .005 in. Higher finished parts to avoid a removal operation Thin sections, such as tubing Weak structures Plating thickness

Provide a fairly wide acceptance for research work because it provides a continuous scale of hardness, for a given load.

One scale covers the entire hardness range. A wide range of test forces to suit every application. As the indentations can be kept very small, the function ability is retained in

most cases Independency of the hardness value from the test load in the macro range. No erroneous measurement at specimen yield in the direction of action of the

test load. 

The main drawback of the Vickers test is the need to optically measure the indent size. This requires that the test part be highly finished to be able to see the indent well enough to make an accurate measurement.

The test samples should have a smooth surface and be held perpendicular to the indenter. Thus, time consuming to achieve sufficient surface quality.

Slow Testing can take 30 seconds not counting the sample preparation time. Time required for measuring the diagonal lengths. Sensitivity of the diamond indenter to damage. Operator influence on the hardness value.