TECH 31065 Lecture Notes - Lecture 4: Ultimate Tensile Strength, Ductility, Brittleness
11 May 2018
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Mechanical Properties of Metals
• Strength- resistance of a material to an external force
• Elastic deformation- occurs when a material returns to its original size after the load
has been removed
• Plastic deformation- occurs when a material doesn’t return to its original size after the
load has been removed
Deformation and Elongation
• Yield point- the load required to cause plastic deformation
• Ultimate strength- load required to cause a material to fracture
• Deformation- the percentage of change in the size of a specimen
o Compressive failure
• Elongation- the percentage of change in the size of a specimen
o Tensile failure
Compression Vs. Tension
• Compression- when a material is pressed or crushed
• Tension- when a material is pulled or stretched
Ductility
• Indicates the amount of deformation (elongation) that can occur in tension without
fracture
Brittleness
• Material fracture without deformation or elongation
• Brittle materials do not have impact toughness
• The opposite of ductility
Impact Toughness
• Indicates how much energy is absorbed by a material during fracturing
• Charpy impact- sample is supported on both ends
• Izod impact- sample is supported on only one end
Hardness
• Hardness- a material’s resistance to indentation by a harder material
• Brinell hardness- uses a steel ball indenter
o Read the depth
• Rockwell hardness- read the depth
o B scale- steel ball indenter
o C scale- diamond cone indenter
• Vickers hardness- measures the hardness of a small area of a microstructure
• Knoop hardness- measures the hardness of very small or thin materials
• Materials with high hardness generally have high strength
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Document Summary
Tension: compression- when a material is pressed or crushed, tension- when a material is pulled or stretched. Indicates the amount of deformation (elongation) that can occur in tension without fracture. Brittleness: material fracture without deformation or elongation, brittle materials do not have impact toughness, the opposite of ductility. Indicates how much energy is absorbed by a material during fracturing: charpy impact- sample is supported on both ends. Izod impact- sample is supported on only one end: hardness- a material"s resistance to indentation by a harder material, brinell hardness- uses a steel ball indenter.
