Module 11: 0.2% Offset Yield Stress

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En provenance du cours de Georgia Institute of Technology

Mechanics of Materials I: Fundamentals of Stress & Strain and Axial Loading

478 notes

Georgia Institute of Technology

Mechanics of Materials I: Fundamentals of Stress & Strain and Axial Loading

478 notes

This course explores the topic of solid objects subjected to stress and strain. The methods taught in the course are used to predict the response of engineering structures to various types of loading, and to analyze the vulnerability of these structures to various failure modes. Axial loading with be the focus in this course. ------------------------------ The copyright of all content and materials in this course are owned by either the Georgia Tech Research Corporation or Dr. Wayne Whiteman. By participating in the course or using the content or materials, whether in whole or in part, you agree that you may download and use any content and/or material in this course for your own personal, non-commercial use only in a manner consistent with a student of any academic course. Any other use of the content and materials, including use by other academic universities or entities, is prohibited without express written permission of the Georgia Tech Research Corporation. Interested parties may contact Dr. Wayne Whiteman directly for information regarding the procedure to obtain a non-exclusive license.

À partir de la leçon

Stress-Strain Diagrams, Material Properties, and Shear Stress and Strain

In this section, we will develop stress-strain diagrams, discuss material properties, and look more in depth at shear stress and strain.

Module 9: Tension Test and Stress-Strain Diagram10:00

Module 10: Internal Properties and Hooke’s Law4:52

Module 11: 0.2% Offset Yield Stress3:14

Module 12: Strain Hardening/Permanent Set1:42

Module 13: Poisson’s Ratio6:58

Rencontrer les enseignants

Dr. Wayne Whiteman, PE
Senior Academic Professional
Woodruff School of Mechanical Engineering

[SOUND] Hi, this is module 11 of Mechanics of Materials I.

Today's learning outcomes are to continue to define and

discuss the material properties associated with stress-strain diagrams, and

to define and identify what we're going to call the 0.2% offset yield stress.

So here again is our typical stress strain diagram and then I've got the stress

strain diagrams for three materials, one of the materials is steel.

Again as I've mentioned before, its typically used for

machine parts, shafts maybe as in the dry shafts of cars, et cetera.

And it's a ductal material so it has a lot of strain before,

it allows for a lot of strain before it fractures.

The other material is aluminum, one of the other materials is aluminum.

It has been typically used in the past for

aircraft frames although now we're seeing a lot more composites in aircraft frames.

The strength to weight ration in aluminum is better than steel,

although steel is stronger.

So that strength to weight ratio is a reason they use in aircraft because

you can get a lot of strength for

less weight, that's what you want to have in an aircraft type application.

And you're starting actually to see aluminum used in cars and

pickups these days.

And then finally the third material I have is stress-strain curve four is magnesium.

It's a low density metal about two thirds that of aluminum.

It has good corrosion resistance.

It has good high temperature properties and

it's used in electronic applications and some other specialty applications.

So, here's the stress strain diagram for the three typical materials.

We've talked a lot about steel where we have a pretty well defined yield point,

where we start to get plastic yielding.

Some materials, like the aluminium here and

the magnesium don't have a well defined yield point.

Remember the yield stress is the low stress that starts to

produce permanent deformation.

So if we can't easily identify that, for those types of materials,

we typically use what's called the 0.2% offset yield stress, so

here's a graph of a depiction of what I mean by yield stress.

As we go up the stress strain curve we go up to a point

where if we backed off we would have 0.2% permanent set or permanent offset.

And that's then called the offset yield stress, and

that's the type of definition we'll use for yield stress, again for materials like

aluminum, magnesium, where there's not a well defined yield stress point.

So let's again have you do a worksheet on your own.

I want you to find the approximate 0.2% Offset Yield Stress for

the aluminum curve on this graph, and I've got the solution in the module handouts.

[MUSIC]

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