Microscopy in the Physical Sciences - Fractography

A Workshop for Middle and High School Teachers

sponsored byTennessee Technological UniversityCenter for Manufacturing ResearchDepartments of Chemical, Mechanical, Earth

Sciences and Curriculum and Instructionand The National Science Foundation

FacultyChris Wilson (Mechanical Engineering)

June 19, 2003

“It’s all a hoax, butit pays the bills.”

My wife.

Falling Down is Part of Growing Up

Rock-a-bye baby

In the tree top.

When the wind blows,

The cradle will rock.

When the bough breaks,

The cradle will fall.

And down will come baby,

Cradle and all.

Jack and Jill went up the hill

To fetch a pail of water,

Jack fell down and broke his crown

And Jill came tumbling after.

Some Never Grow Up (Mini-Baja)

Crack at Weld in Swing Arm

Not Quite The Deacon’s Masterpiece!

Have you heard of the wonderful one-hoss shay,

That was built in such a logical way

It ran a hundred years to a day,

And then, of a sudden, it—ah, but stay,

I’ll tell you what happened without delay,

Scaring the parson into fits,

Frightening people out of their wits—

Have you ever hear of that, I say?

excerpt from Oliver Wendell Holmes

More Serious Motivation

What Will We Learn

How does breaking things make the world better?

What is fracture mechanics? What is fractography? How is microscopy used in understanding

material and structural failure?

Fracture Mechanics is…

…an engineering discipline

describing the behavior of

cracks or crack-like flaws

in materials and

structures under loading.

Fractography

Fracture surface topography Both macroscopic and microscopic features Wide range of magnification and instruments Much work is done with unaided eye or hand

lens

Ranges of Magnification

Microstructural Features in Metals

Microstructural Scale

Mechanisms of Fracture

Transgranular Fracture Ductile fracture by

microvoid coalescence Brittle fracture (cleavage) Fatigue crack initiation

and growth

Intergranular Fracture Grain boundary

separation with microvoid coalescence

Grain boundary separation without microvoid coalescence

Dimple Formation (Ductile)

Cup and Cone Fracture (Ductile)

Polished Copper Cross Section

Dimpled Fracture (Ductile)

Cleavage Features

River Patterns (brittle materials)

Quasi-Cleavage Fracture

Fatigue Striations

6061-T6 Notched Round Bar

Carbon Fiber-Polymer Matrix

0-45 Interface in IM6/3501-6

Ply Rupture Outer Layer

Bleed-out from Natural Pore

Microballoon Experiments

Mimic natural porsity using glass microballoons

Sizes 5 to 60 m Effect of microballoons

on interface strength and stiffness unknown

Microballoons in IM6/3501-6

Filled vs. Broken Microballoons

Some Texts

Understanding How Components Fail by Donald J. Wulpi

The New Science of Strong Materials (or Why You Don’t Fall through the Floor) by J. E. Gordon

The Science of Structures and Materials by J. E. Gordon

Fractography by Derek Hull To Engineer is Human by Henry Petroski

Project Ideas

Component failure investigationsFabrication of fiberglass compositesStatistics of failureConnections with literature and history???

A Final Thought

"I Keep Six Honest..."

I keep six honest serving-men(They taught me all I knew);Their names are What and Why and WhenAnd How and Where and Who.I send them over land and sea,I send them east and west;But after they have worked for me,I give them all a rest.

Excerpt from Kipling’s The Elephant's Child