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Temperature, Hardness and Toughness

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Presentation on theme: "Temperature, Hardness and Toughness"— Presentation transcript:

1 Temperature, Hardness and Toughness

2 Temperature Effects on Material Properties
Temperature changes and extremes affect the value of many engineering properties yield, modulus, toughness, corrosion resistance, creep, relaxation, viscosity, shrinkage, solubility…..

3 Temp Effect on Tensile Strength

4 Temp Effect on Other Properties

5 Thermal Expansion Elevated Temperatures excite the electrons at the atomic level of any material The excited atoms can more easily move to a lower energy state and change orientation of atomic planes This leads to dimensional changes in most materials There are exceptions, e.g. InVar, Ni-Cr alloy with a very low energy state that is not easily altered.

6 Temperature vs. Expansion
t is the coefficient of thermal expansion. t is typically a constant.

7 Surface Properties Hardness Impact Energy Scratch hardness
Surface Hardness Impact Energy

8 Hardness - Moh’s Scale Moh scale is a surface scratch resistant scale based on minerals 1 - Talc 2 - Gypsum 3 - Calcite (CaCO3) 4 - Flourite 5 - Apatite 6 - Orthoclase (Feldspar) 7 - Quartz 8 - Topaz 9 - Corundum (or sapphire) 10 - Diamond The Moh scale is a test of scratch resistance, based on empirical relationships developed in mineralogy.

9 Surface Hardness Surface hardness is quantified by determining the energy necessary to cause localized plastic deformation. A specific energy is imparted on a surface of a material and the amount of plastic deformation is quantified in most hardness procedures. Based on theory of plasticity.

10 Types of hardness tests
Brinell ball original hardness test Rockwell , rounded cone most common, (ASTM E18) Hardness values depends on: Method used, Shape of indenter - spherical, pyramidal, diamond shape, etc., Dimensions of indenter, Magnitude of load placed on indenter However, the hardness energy can be converted from one method to another. Vickers pyramid, first micro-hardness test, similar to Brinell, used for thin specimens Knoop diamond pyramid more refined micro-hardness Note: P = Applied load in all tests 120°

11 Use of hardness Surface hardness of heat treated metals
Quality control of heat treatment process Correlated with other properties Yield strength “Brittleness”

12 Impact tests Charpy V-notch - Measure energy required to
rupture specimen Izod V-notch - Same as Charpy but different specimen

13 Use of impact resistance
Quantify resistance to dynamic impacts and crack sensitivity Quantify the “transition temperature” of an alloy (ductile – brittle behavior) Impact Energy, Joules Temperature Ductile Brittle

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