8.1ME 340: Materials & Design

CHAPTER 8 (ch. 3 in ref.1)

ENGINEERING MATERIALS AND THEIR PROPERTIES

8.2ME 340: Materials & Design

MATERIALS – are the food of design

This chapter presents the full shopping menu or list

Successful product=-good value for money.-Gives pleasure to user-Uses best material for job-Fully exploits their potential-brings out their flavor

Don’t forget though that it is not materials we are after it is certain profile of properties that can be provided by any given material

8.3ME 340: Materials & Design

CLASSES OF ENGINEERING MATERIALS

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Each material can be thought of as having a set of attributes; it’s properties

We consider property-profile

And the material name is the identifier for a particular property profile

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The bulk modulus gives the change in volume of a solid substance as the pressure on it is changed,

For isotropic elastic solids

Data books list values for all 4 properties We will use eqn. 3.2 for E values

8.7ME 340: Materials & Design

STRENGTH of a solid: f Requires careful definition

For METALS 0.2% offset yield strength

POLYMERS

Stress at which Stress-strain curves become

Markedly non-linear:typically at strain of 1%

ft2.1~f

c

tff

c to 1510CERAMICS

Crushing strength

Fracture strength

8.8ME 340: Materials & Design

8.9ME 340: Materials & Design

When difficult to grip specimen (e.g. ceramics)

Larger by ~1.3 than test in tension

WHY???

8.10ME 340: Materials & Design

8.11ME 340: Materials & Design

8.12ME 340: Materials & Design

Hardness = load/projected area

INCORRECT, What is correct eqn.??

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8.14ME 340: Materials & Design

8.15ME 340: Materials & Design

Cyclic loading fatigue limit or fatigue life.Fatigue ratio f dimensionless quantity (f /y)

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8.17ME 340: Materials & Design

Service temperature And softening temp

Kinetic factorUnits: s-1 Reference stress

Thermal shock in K

1/3Tm or 2/3 Tg

8.18ME 340: Materials & Design

Kp=parabolic rate constant

8.19ME 340: Materials & Design

WET CORROSION More complicated and is measured on a a scale , rather than a rate equation.