Properties of Engineering Materials

Overview Purpose of lab is to familiarize you with basic properties of common engineering materials Density, Young’s modulus, thermal conductivity, coefficient of expansion, modulus of torsion Do simple experiments to find these properties Also become familiar with the physical properties of some common optical materials used in the IR

Young’s modulus Use bars of material set on simple end supports Measure central deflection as a function of applied load Use physical dimensions of bars to calculate Young’s modulus using Beam equation Cantilever beam configuration also work!

Young’s modulus (2) Use Instron machine and find Stress-Strain curve Actual measurement is force-displacement curve Use specimen geometry and convert measured force-displacement to stress-strain

Young’s modulus (2)

Density Measure physical dimensions of bars Calculate volume Measure mass on an electronic scale Density = mass/unit volume Measure a drop of water, small piece of paper Get a feel for how sensitive the scale is

Thermal properties Get a feel for the thermal properties of materials Widely varying set of conductivities, expansions Measure the nominal length of Copper, Aluminum and steel tube Measure the temperature using thermocouple and thermometer Measure the elongation Find CTE and compare to the reference value

Thermal properties

Optical materials Sapphire Al2O3, .14 – 6.5 um, very hard, low expanson, tough CaF2, .13 – 12 um, moderately soft, expansion like Al, good UV mat’l Silicon 1.2 – 15 um, reasonably hard, quite plastic and strong, brittle Germanium 1.8 – 23 um, similar to Silicon but not as tough, n = 4 ZnSe .5 – 22 um, reasonably easy to use but somewhat soft ZnS .5 – 14 um, similar to ZnSe but cheaper, maybe a little less durable

May do modulus of torsion Measure oscillation of torsion pendulum