Lecture 3: SolidWorks 2 - Testing

Professor Erik Cheever

Remember… Wizards available (Hicks 212) from 7:00-9:00 Wednesdays Thursday 9/17

Mouse Escape: 2nd floor of Hicks at 4:15. MATLAB part from SolidWorks Lab 1 is due (moodle) Department Picnic

Monday 9/21 – Mouse Escape report due (moodle) Thursday 9/24 – Robot arm file and report due (moodle) Plan to attend a study session sometime – just to see what

they are like… See http://www.swarthmore.edu/wizards.xml for schedule.

…or just drop by to say “hi” to Ann in Hicks 308.

The big picture… This week

Lecture - Testing parts with Solidworks Summer Opportunities Lab – Iterative design for optimization

Next week – Soldering and MATLAB. Subsequent weeks in lab – more SolidWorks, Soldering and

MATLAB. Leading up to making a laser pointer robot arm.

Testing parts with SolidWorks SolidWorks uses Finite Element Method (FEM)

Analysis It is hard to calculate forces on shapes that are

complex, so… split the object up into thousands of smaller

objects of simple shape, assume everything behaves linearly, get a computer to solve.

This technique is also used in computer simulations

of heat transfer, fluid dynamics, electronics…

The FEM Mesh

From http://www.algor.com/news_pub/cust_app/monkey_skull/default.asp

Variable Mesh Sizes

FEM Mesh fro fluid flow around pipes.

From http://www2.imperial.ac.uk/ssherw/vortexflows/people/Tim_Kendon/fig/mesh_Vr8.89_B1.53_fsf_Re100_LES.png

Corners concentrate stress (1)

http://varifrank.com/images/314028020_29d914723f_o.jpg

The Early De Havilland Comet (with square windows) – the first commercial jet liner. The windows were square to differentiate them from a ship’s porthole.

Corners concentrate stress (2)

http://www.owlnet.rice.edu/~msci301/CometCrash.jpg

After Several flights the planes had tendency for explosive decompression

Corners concentrate stress (3)

http://www.geocities.com/CapeCanaveral/Lab/8803/p5cyp07.jpg

Round windows!

http://www.plane-spotter.com/ScanAvPhoto/Dan-AirLondon_Comet4.jpg

A later model Comet (with round windows)

Bicycle Design

Stresses on a bicycle are asymmetric because drive train is on right side of bicycle.

During a sprint a bike might have 3 mm of movement on one side and 1 mm on the other.

So bike is either too strong on one side (so material can be removed), or two weak on the other (so material can be added, or cross section changed).

Localized forces Traditional design Asymmetric Design

(using AI to add and remove material)

This week’s lab From this, to this,

using this.

. . . SolidWorks Demo . . .

The Hyatt Regency Kansas City Basic Walkway Design • Walkway on 2nd, 3rd and 4th floors cross the atrium. • 3rd and 4th floor walkways were suspended from roof;

2nd floor walkway suspended from 4th floor walkway.

Images from: http://azurebrooke.com/deviation.htm

As originally designed As built

Constraints – design 1

Loads – design 1

Stress – design 1

Maximum Stress is 4.16*107

Stress (close-up) – design 1

Stress (extreme close-up) – design 1

Note triangular regions due to computer analysis

Deflections – design 1

Maximum Deflection is 5.34*10-3

Loads – design 2

Simplified Analysis of designs

Image from: http://azurebrooke.com/deviation.htm

Stresses – design 2

Maximum Stress is 8.34*107

About twice as much as before (4.16*107)

Adding levels of walkways compounds the problem

Stresses (close-up) – design 2

Deflections – design 2

Maximum Deflection is 7.17*10-3

About 50% more than before (5.34*10-3)

Fourth floor walkway beam

Image from: http://ethics.tamu.edu/ethics/hyatt/hyatt2.htm

Fourth floor beam (close-up)

Image from: http://ethics.tamu.edu/ethics/hyatt/hyatt2.htm

Third Floor Beam

Image from: http://ethics.tamu.edu/ethics/hyatt/hyatt2.htm

Note slight buckling due to insufficient design

An Engineer's Responsibility Engineers have a tremendous responsibility to

insure the safety, health, and welfare of the public.

The public well-being can be maintained only if engineers follow all codes and standards, and uphold their professional obligations.

Safety during the construction phase of projects will help to insure the ultimate safety of the completed structure.

Adapted from: http://www.mech.utah.edu/ergo/pages/Educational/safety_modules/KC/

Facts About Case As originally designed, the walkways were barely

capable of holding up the expected load, and would have failed to meet Kansas City building requirements.

The fabricator did not want to thread entire rod to install the washer and the nut.

The fabricator claimed to receive phone approval for engineering change.

The engineering firm declared they had not received the phone call, but their plans were altered to reflect change.

Adapted from: http://www.mech.utah.edu/ergo/pages/Educational/safety_modules/KC/

Who was responsible? Original design was marginal. A lack of communication between the designer and

fabricator is one contributor to the failure of walkways.

The engineering firm did receive revised drawings during construction and stamped them with their engineering review seal, authorizing construction.

The revised design was significantly less capable of holding up the required forces, and was not designed in accordance with the Kansas City building code.

Adapted from: http://www.mech.utah.edu/ergo/pages/Educational/safety_modules/KC/

Consequences 114 people were killed and over 200 injured. Engineers found guilty of gross negligence,

misconduct, and unprofessional conduct in the practice of engineering.

Many principals lost engineering licenses. Expensive legal suits settled out of court. Several firms went bankrupt.

Adapted from: http://www.mech.utah.edu/ergo/pages/Educational/safety_modules/KC/