Topic 4_2 Roughness, Hardness, and Friction Flashcards
How is hardness measure
in terms of the size of an impresson made on a speciman by an indenter of a specified shape when a specified force is applied for a specified time
How does hardness impact wear mechanism
To reduce wear generally increase hardness as hardness is resistance to plastic deformation
What is hardness
secondary property dependent on ductility, elasticity, plasticity, strain and toughness
What is the three principle methods for expressing the relationship between hardness and the size of the impression
Brinell, Rockwell and Vickers
How do you convert between vickers hardness and Mpa
multiply by 9.81 to get MPa
How is brinell hardness calculated
A ball diameter D is forced against a flat plate at a load of W, area of indent is worked out assuming it follows shape of ball
How is rockwell harndess calculated
Conical (120degree) or spherical indenter used
Minor load used initially and depth measurement set to zero
major load applied
machine gives rockwell number directly
How is Vickers hardness calculated
Use a square based diamon pyramid as the indenter (included angle 136 degrees)
Resulting square impression is viewed and measured in an optical microscope
Draw a diagram of vickers harndess test
see powerpoint
What is the general principle of measuring hardness
Plastically deform surface, measure size of indentation, and from that work out corresponding harndess
