3004C
CHAPTER EML 3
Engineers and the Real World?
Namas Chandra Introduction to Mechanical engineering
Chapter 3-1
EML 3004C
Objectives
Examine Society's View of Engineering Learn about the Role of Failure in Engineering Design Discuss Classic Design Failures as Case Studies Learn How to Accept and Utilize Failure in Your Own Design
Sections
3.1 3.2 3.3 3.4 Society's view of Engineering How Engineers Learn From Mistakes The Role of Failure in Engineering Design: Case Studies Preparing for Failures in Your Own Design
Chapter 3-2
Namas Chandra Introduction to Mechanical engineering
EML 3004C
3.1 Society's View of Engineering?
Engineers are not perceived as glamorous but as talented professionals. Engineers do the impossible as a matter of routine
They create science fiction stories into realities Recall Captain Kirk with a flip-box talking to anyone in the world in 1960 >>>> Today's cell phone Rewind to 1902
Would you have believed that man would have landed on the moon Explore another planet Mars
As Engineers, we need to hold ourselves to high standards in expanding the quality of life and maintain
Moral and Ethical Standard Clear many popular scientific/engineering misconceptions.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-3
EML 3004C
3.1 Myth and Perception?
Perception of the public may distort truth. Do you know?
Cell phone communications still need land lines
Hurricanes can affect both equally likely
NMR (Nuclear Magnetic Resonance) was renamed to MRI (Magnetic Resonance Imaging) since public fear Nukes
NMR (or MRI) has nothing in common with Nuclear power
MP3 music has a better quality than one in regular CD
One is the format and the other storage medium.
Too many cell phone calls can bring down the entire network.
Cell phones reach the nearest tower and has no influence on the overall network.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-4
EML 3004C
3.2 How Engineers Learn from Mistakes?
Only he who does nothing makes no mistake (French
proverb)
Failure is delay, but not defeat. It is a temporary detour but not a dead-end street. (William Ward) The fellow who never makes mistakes takes order from the one who does (Herbert Prochnow) To make no mistake is not in the power of man; but from their errors and mistakes the wise and good learn wisdom for the future (Plutarch)
Namas Chandra Introduction to Mechanical engineering
Chapter 3-5
EML 3004C
3.2 Hypothetical Design Competition
Consider a simple hypothetical design competition in EML 3004C. The goal is to build a vehicle with an articulated arm that would pick up an opposing vehicle and throw it off the track. Two students are assigned per group and they are supposed to complete the design, construction, operation and ready for the competition in a six week period.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-6
EML 3004C
3.2 Scenario 1
Mike and Heather form a team. They design a vehicle on paper, draw it Pro-E CAD, test it out using animation software. They draw all the 58 parts needed for the vehicle Go to the machine shop, machine all the parts accurately and assemble them perfectly In one week, they do a mock up test on another vehicle. During the test the vehicle lifts the opposing one and throws it off the track.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-7
EML 3004C
3.2 Scenario 2
Mike and Heather have been working now for more than a month. After many trials and tribulations, they design an arm capable of lifting objects. They first use two mouse-trap springs but found power to be inadequate. Needed to replace with battery powers. They buy electric motors with fine controls. Holes in the arm needed to be re-drilled. Too many wrong holes. Five weeks past, no working vehicle, project over budget. When the arm is mounted on the vehicle, it does not fit-needs rework. When it all fits, during testing the opponent vehicle is lifted but both the vehicles fall of the track. Abandon the arm concept and redesign with a ram approach.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-8
EML 3004C
3.2 Welcome to reality!
"If anything can go wrong, it will"- Murphy's Law All great discoveries are made by mistake An expert is one who knows more and more about less and less until he knows absolutely everything about nothing Experienced engineers know that design never works the first time and are never discouraged by initial failures. Failures are inevitable part of the design process. It is better for a defect to surface during the design and testing, rather than in the field. The best way to avoid field failure is to test, re-test and do some more re-testing. Computers based virtual testing complement the actual testing but does not replace it.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-9
EML 3004C
3.2 Case Studies of Engineering Disasters!
Despite great attempts by engineers to weed out design mistakes, they eventually show up and result in catastrophes. Mistakes are made by engineers who do their best but fail due to lack of prior experience or/and lack of engineering judgment. Of course, it is easy to pick the flaw in hind sightMonday morning quarterback!! Spotting a flaw becomes difficult as the complexity of system the increases. A good engineer becomes a great engineer when he/she can spot flaws before the production or operation.
Namas Chandra Introduction to Mechanical engineering
Chapter 3-10
EML 3004C
3.2 Succeed by Averting Failures!
The study of failure is an important part of the engineering design process
Studying failures which occur during product testing helps to discover hidden flaws which were not foreseen during the initial design and prototype process Subsequent redesign and adjustment will help to prevent similar failures from occurring once the product has been released to the public
Classic engineering failures
Well documented cases where inadequate design or testing resulted in catastrophic failure Caused both loss of life and/or major loss of property The study of these failures helps us to avoid the mistakes of the past
Namas Chandra Introduction to Mechanical engineering
Chapter 3-11
EML 3004C
3.2 Hubble Space Telescope!
Hubble Space Telescope
Powered by large solar panels which resembled wings Alternately heated and cooled as they moved in and out of earth's shadow Resulting expansion and contraction cycles caused the solar panels to "flap" Problem caused by not taking operating environment into account during the design phase
Namas Chandra Introduction to Mechanical engineering
Chapter 3-12
EML 3004C
3.2 What went wrong with Hubble?
Perkin-Elmer fabricated mirrors
A pair of calibrated mirrors to direct light on hubble surface Diameter of the mirror is 2.4 m and to be maintained to 0.001 wavelength in micrometers During assembly there were warning signs-Range was falling short; engineers added 1.3 mm spacers to correct the problem. During mock-up test they found spherical aberration but ignored the concern as trivial.
Namas Chandra Introduction to Mechanical engineering Chapter 3-13
EML 3004C
3.2 Tacoma Narrows Bridge!
Tacoma Narrows Bridge
Built across Puget Sound in Tacoma, WA, in 1940 Longest suspension bridge of its day Engineers copied designs used for shorter bridges, and simply lengthened them, without testing for structural integrity Bridge collapsed after less than one year, due to high winds which the structure could not withstand
Namas Chandra Introduction to Mechanical engineering
Chapter 3-14
EML 3004C
3.2 Tacoma Narrows Bridge!
On November 7, 1940, at approximately 11:00 AM, the first Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations. Situated on the Tacoma Narrows in Puget Sound, near the city of Tacoma, Washington, the bridge had only been open for traffic a few months
Source: http://www.civeng.carleton.ca/Exhibits/Tacoma_Narrows/index.html
Namas Chandra Introduction to Mechanical engineering
Chapter 3-15
EML 3004C
3.2 Hartford Civic Center!
Hartford Civic Center
Built in mid-1970's The roof used a novel "space frame" construction which did not require support columns Computer models were used to evaluate the structure and to verify that the roof could withstand all plausible applied loads. The validity of these computer models were never tested using actual structures or prototypes Roof collapsed under a heavy snow load in 1978
Namas Cha...