The Stress versus Strain (Tensile) Test

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來自 University of California, Davis 的課程

Materials Science: 10 Things Every Engineer Should Know

846 個評分

University of California, Davis

Materials Science: 10 Things Every Engineer Should Know

846 個評分

We explore “10 things” that range from the menu of materials available to engineers in their profession to the many mechanical and electrical properties of materials important to their use in various engineering fields. We also discuss the principles behind the manufacturing of those materials. By the end of the course, you will be able to: * Recognize the important aspects of the materials used in modern engineering applications, * Explain the underlying principle of materials science: “structure leads to properties,” * Identify the role of thermally activated processes in many of these important “things” – as illustrated by the Arrhenius relationship. * Relate each of these topics to issues that have arisen (or potentially could arise) in your life and work. If you would like to explore the topic in more depth you may purchase Dr. Shackelford's Textbook: J.F. Shackelford, Introduction to Materials Science for Engineers, Eighth Edition, Pearson Prentice-Hall, Upper Saddle River, NJ, 2015

從本節課中

Dislocations Explain Plastic Deformation / Stress vs. Strain -The “Big Four” Mechanical Properties

Welcome to week 2! In lesson three we will discover how dislocations at the atomic-level structure of materials explain plastic (permanent) deformation. You will learn to define a linear defect and see how materials deform through dislocation motion. Lesson four compares stress versus strain, and introduces the “Big Four” mechanical properties of elasticity, yield strength, tensile strength, and ductility. You’ll assess what happens beyond the tensile strength of an object. And you’ll learn about a fifth important property – toughness.

The Stress versus Strain (Tensile) Test3:54

The “Big Four” Mechanical Properties3:25

Focusing on Strength and Stiffness4:04

Beyond the Tensile Strength4:09

Focusing on Ductility1:47

A Fifth Parameter – Toughness2:14

與講師見面

James Shackelford
Distinguished Professor Emeritus
Department of Chemical Engineering and Materials Science

Hello again from the teaching laboratories here in Campor Hall.

In this segment, we're going to talk about stress versus strain and

a set of mechanical properties that come from that simple experiment

are extremely important in understanding the basic structural integrity of so

many of the materials that we use in everyday life.

[MUSIC]

So now I'm doing a stress strain experiment, which gives us, as I said,

the big four mechanical properties of a very

important understanding of the nature of the structural materials that we

use very broadly throughout the engineering profession.

Especially metallic samples.

We'll be defining Elastic modulus, Yield strength,

Tensile strength, and Ductility or Strain at failure.

And in doing so, we're going to see that we begin by simply measuring,

in this Instron machine, the load on the sample,

as we pull it slowly in uniaxial tension, and

monitor the increasing length as a result of that pulling of the sample.

So, we'll first of all monitor the load versus length.

And then by dividing the load by the cross section area of the sample and

the length by the initial length of the sample under zero load,

will convert that load elongation curve into a stress string curve.

And then as we monitor that stress strain curve in its various aspects,

first of all a straight line portion with the slope that we call the elastic

modulus and that slope is a definition

of the Famous Hooke's law that many of you have seen in various engineering courses.

That the stress is directly proportional to the strain in that

elastic deformation region.

And then that's followed by the nonlinear breaking away from elastic deformation,

and the beginning of plastic deformation.

And that point of breaking away is defined as the E of the strength.

And then the ultimate tensile strength is sometimes simply called tensile strength.

And then as the sample is taken to complete failure and

breaks, that total amount of elongation at that point of

break is the elongation of failure or the ductility.

And so now let's do the experiment.

We're going to take a sample again, through elastic deformation,

plastic deformation to ultimate failure, and our teaching assistant, Andrew,

is going to operate the Instron machine.

So, Andrew, let's begin.

[MUSIC]

[SOUND] And there you have it.

We've measured elastic modulus, yield strength, tensile strength,

and elongation of failure all in one fairly simple experiment.

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