Hardness of a material to resist surface abrasion –Ability Difficult to measure Measure the resistance of the surface layer to penetration by an indenter Brinnell Test Vickers diamond test Metals (properties) clean (luster) Solids under ordinary conditions Usually conduct heat and electricity Malleable or hammered –rolled Ductile into wires –drawn Hard/soft Low melting/high melting Polymers solid –Molecular Thermosets usually crosslinked Permanently hard, when heated do not soften but char Superior flexural hardness Thermoplastics Soften when heated their glass temp(tg) harden on cooling –shaped, Superior flexural and impact properties Wood 4
Hardness –Ability of a material to resist surface abrasion Difficult to measure Measure the resistance of the surface layer to penetration by an indenter Brinnell Test Vickers diamond test Metals (properties) clean (luster) Solids under ordinary conditions Usually conduct heat and electricity Malleable –rolled or hammered Ductile –drawn into wires Hard/soft Low melting/high melting Polymers –Molecular solid Thermosets usually crosslinked Permanently hard, when heated do not soften but char Superior flexural hardness Thermoplastics Soften when heated their glass temp(tg) –shaped, harden on cooling Superior flexural and impact properties Wood 4
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