MECHANICAL TESTING OF METALLIC MATERIALS Outline

• Testing • Tensile Testing • Impact Testing • Fatigue Testing • Creep Testing • Wear Testing

22-Jan-11 11111 2 MATERIALS PROPERTIES

Design Engineer - Materials properties

Materials Properties

CHEMICAL MECHANICAL PHYSICAL DIMENSIONAL Composition Hardness Density Size Crystal structure Strength-ductility Thermal Shape Bonding Impact Electrical Microtography Fatigue Magnetic Creep wear

SERVICE LIFE

22-Jan-11 11111 3 LT/HT/RT HARDNESS TESING

• Hardness is resistance of material to plastic deformation caused by indentation Deeper or larger impression

Softer materials

most brasses easy to machine cutting nitrided plastics Al alloys steels file hard tools steels diamond

22-Jan-11 increasing hardness11111 4 HARDNESS

Tribologist : – high hardness desirable to reduce plastic deformation and wear in bearings

Machinist : - low hardness preferable for easy and faster machining

Fracture mechanics : – hard material – brittle – engineer undesirable under impact loads

Metal forming : – low hardness preferable for engineer cold rolling 22-Jan-11 11111 5 BASIC PRINCIPLE

• Principle of hardness test method :

- forcing an indenter into the sample surface followed by measuring dimensions of the indentation (depth or actual surface area of the indentation)

22-Jan-11 11111 6 TYPES OF HARDNESS MEASUREMENTS

There are three general types of hardness measurements 1) Scratch hardness • The ability of material to scratch on one another • Important to mineralogists, using Mohs’scale 1= talc, 10 = diamond • Not suited for annealed = 3, martensite = 7.

2) • Major important engineering interest for . • Different types : Brinell, Meyer, Vickers, Rockwell hardness tests.

3) Rebound or dynamic hardness • The indentor is dropped onto the metal surface and the hardness is expressed as the energy of impact 22-Jan-11 11111 7 CLASSIFICATION HARDNESS TESING

-Depending on the loading force value & the indentation dimensions

• Macro-hardness tests

• Micro-hardness tests

• Nano-hardness test

22-Jan-11 11111 8 HARDNESS TESING

Macro-hardness tests : - the most widely used methods for rapid routine hardness measurements

- indenting forces in macro-hardness tests are in the range of 50N to 30000N

• Brinell hardness test

• Rockwell hardness test

• Vickers hardness test

22-Jan-11 11111 9 BRINELL HARDNESS TEST

- One of the oldest tests Static test that involves pressing a hardened steel ball (10mm) into a test specimen while under a load of

3000 kg load for hard metals, 1500 kg load for intermediate hardness metals 500 kg load for soft materials

BALL PRESSED INTO THE SURFACE

INDENTATION PRODUCED IN 22-Jan-11 SURFACE 11111 10 BRINELL HARDNESS TEST

If the BHN value is higher, then the material is said to be harder

where BHN = the Brinell hardness number P = the imposed load in kg D = the diameter of the spherical indenter in mm

22-Jan-11d = diameter of the resulting11111 indenter impression in mm 11 BRINELL HARDNESS TEST

• Rules of thumb – 3000 kg load should be used for a BHN of 150 and above

– 1500 kg load should be used for a BHN between 75 and 300

– 500 kg load should be used for a BHN less than 100

– The material’s thickness should not be less than 10 times the depth of the indentation

22-Jan-11 11111 12 BRINELL HARDNESS TEST

• Brinell Test can not be used : very soft or very hard materials (Indentation becomes equal to the diameter of the ball or No or little Indentation)

Accurate measurement : -impression should be a diameter between 0.25D and 0.50D

22-Jan-11 11111 13 BRINELL HARDNESS TEST

• Limitation of Brinell Hardness Test :

Materials with hardness upto 450HBN with steel ball

Materials with hardness upto 600 HBN with carbide ball – Brinell numbers greater than 650 should not be trusted because the diameter of the indentation is too small to be measured accurately and the ball penetrator may flatten out .

22-Jan-11 11111 14 Brinell Test Method

• Advantages – Well known throughout industry with well accepted results – Tests are run quickly (within 2 minutes) – Test inexpensive to run once the machine is purchased – Insensitive to imperfections (hard spot or crater) in the material

• Limitations – Not well adapted for very hard materials, wherein the ball deforms excessively – Not well adapted for thin pieces – Not well adapted for case-hardened materials

– 22-Jan-11Heavy and more expensive than11111 other tests 15 ROCKWELL HARDNESS TESTING

Rockwell Hardness Test : - widely used method (accuracy, simplicity and rapidity) -there are two types of Rockwell tests

(i) Rockwell: - the minor load is 10 kgf,

the major load is 60, 100, or 150 kgf.

(ii) Superficial Rockwell: -the minor load is 3 kgf and

major loads are 15, 30, or 45 kgf.

In both tests, the indenter may be either a diamond cone or steel ball, depending upon the characteristics of the material22-Jan-11 being tested. 11111 16 ROCKWELL HARDNESS TESTING (ASTM18) Principal of the Rockwell Test 1. The indenter moves down into position on the part surface

2. A minor load is applied and a zero reference position is established (10kg) 3. The major load is applied for a specified time period (dwell time) beyond zero 4. The major load is released leaving the minor load applied

- The Rockwell number represents the difference in depth from the zero reference position as a result of the applied major load. Deeper22-Jan-11 indentation 11111 Softer material 17 ROCKWELL HARDNESS TESTING

Rockwell Indenters:

hardened steel ball Diamond cone or

Rockwell hardness numbers are always quoted with a scale symbol representing the indenter and forces used. The hardness number is followed by the symbol HR and the scale designation. Ex ; 64 HRC= Rockwell hardness number of 64 on Rockwell C scale .

81 HR30N22-Jan-11 = Rockwell superficial11111 hardness number of 81 on 18 Rockwell 30N scale. Superficial hardness test : Initial force : 29.4 N

22-Jan-11 11111 19 ROCKWELL HARDNESS SCALES

Superficial hardness test : Initial force : 10kg

Note: The diameter of the balls arise from standard sizes in inches, 1.588mm being 1/16in,22-Jan-11 3.175mm being 1/8in, 6.350mm being11111 1/4in, and 12.70mm being 1/2in 20 ROCKWELL SUPERFICIAL HARDNESS SCALES

Superficial hardness test : Initial force : 29.4 N

Note: N scales are used for materials that if thick enough would have been tested22-Jan-11 on the C scale, the T scales for11111 those on the B scale 21