Level 4 Level 6
Level 5

03 B - MECHANICAL PROPERTIES OF MATERIALS


8 words 0 ignored

Ready to learn       Ready to review

Ignore words

Check the boxes below to ignore/unignore words, then click save at the bottom. Ignored words will never appear in any learning session.

All None

Ignore?
Hardness
RESISTANCE TO INDENTATION BY A MATERIAL. If a material has a good hardness, then it will be resistant to scratching and wear. It is tested by pressing a hard object (sphere, diamond point) into the test material and measuring the size (depth, area) of the indentation.
Hardness tests
Due to a vast difference in hardness of testing materials there are quite a few hardness testing methods out there such as: [1] BRINNELL - indentation by a steel ball. [2] ROCKWELL - Cone or a steel ball penetrates material. [3] VICKERS - diamond indenter. [4] KNOOP - narrow diamond indenter. [5] SCLEROSCOPE - measures rebound of diamond tipped hammer. [6] DUROMETER - measures elastic deformation of rubber. >>> BeeR ViK SaD - {Brinell, Rockwell,] {Vickers, Knoop,} Scleroscope, Durometer >>> BRINNEL AND ROCKWELL PLAY WITH THEIR IRON BALLS, VICKERS AND KNOOP ARE HARD AS DIAMOND, AND SCLEROSCOPE BEATS UP THE RUBBER DUROMETTER WITH A HAMMER.
Temperature effects
Metals get softer and weaker and high temperatures; some get brittle at low temperatures.
Hot hardness
ABILITY OF MATERIAL TO RETAIN HARDNESS AT ELEVATED TEMPERATURES. Steels can be alloyed to increase hot hardness. Ceramics retain much of their hardness at high temperatures. TOOLING MATERIALS NEED HOT HARDNESS.
Recrystallization temperature
TEMPERATURE AT WHICH A METAL RECRYSTALLIZES (FORMS NEW GRAINS), RATHER THAN WORK HARDENS WHEN DEFORMED. Recrystalization, the formation of new strain-free grains is exploited in hot working - the material is heated and then worked, in order to allow for much greater plasticity of metal. Ussually occurs at half of the melting point in absolute units T_c = 0.5*T_m. Usually specified as the TEMPERATURE AT WHICH THE COMPLETE FORMATION OF NEW GRAINS REQUIRES ABOUT 1 HOUR.
Viscosity
RESISTANCE TO FLOW of a fluid material; the thicker the fluid, the greater the viscosity. >>> HONEY IS THICKER THAN WATER
Newtonian fluid
Fluid for which viscosity is a constant property at a given temperature. Most fluid - water, oils, vodka are Newtonian fluids. VISCOCITY = CONST.
Viscoelasticity
STRAIN OF THE MATERIAL AS A FUNCTION OF STRESS AND TEMPERATURE OVER TIME. A combination of viscosity and elasticity, usually in polymers >>> MAGIC PUTTY VISCOELASTES ON A WALL.