EML 3004 C CHAPTER 3 Engineers and the

EML 3004 C CHAPTER 3 Engineers and the Real World? Namas Chandra Introduction to Mechanical engineering Chapter 3 -1

EML 3004 C 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 Society’s view of Engineering 3. 2 How Engineers Learn From Mistakes 3. 3 The Role of Failure in Engineering Design: Case Studies 3. 4 Preparing for Failures in Your Own Design Namas Chandra Introduction to Mechanical engineering Chapter 3 -2

EML 3004 C 3. 1 Society’s View of Engineering? q Engineers are not perceived as glamorous but as talented professionals. q Engineers do the impossible as a matter of routine Ø They create science fiction stories into realities Ø Recall Captain Kirk with a flip-box talking to anyone in the world in 1960 >>>> Today’s cell phone Ø Rewind to 1902 • Would you have believed that man would have landed on the moon • Explore another planet Mars q As Engineers, we need to hold ourselves to high standards in expanding the quality of life and maintain Ø Moral and Ethical Standard Ø Clear many popular scientific/engineering misconceptions. Namas Chandra Introduction to Mechanical engineering Chapter 3 -3

EML 3004 C 3. 1 Myth and Perception? q Perception of the public may distort truth. q Do you know? Ø Cell phone communications still need land lines • Hurricanes can affect both equally likely Ø 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 Ø MP 3 music has a better quality than one in regular CD • One is the format and the other storage medium. Ø 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 3004 C 3. 2 How Engineers Learn from Mistakes? q Only he who does nothing makes no mistake (French proverb) q Failure is delay, but not defeat. It is a temporary detour but not a dead-end street. (William Ward) q The fellow who never makes mistakes order from the one who does (Herbert Prochnow) q 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 3004 C 3. 2 Hypothetical Design Competition q Consider a simple hypothetical design competition in EML 3004 C. q The goal is to build a vehicle with an articulated arm that would pick up an opposing vehicle and throw it off the track. q 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 3004 C 3. 2 Scenario 1 q Mike and Heather form a team. q They design a vehicle on paper, draw it Pro-E CAD, test it out using animation software. q They draw all the 58 parts needed for the vehicle q Go to the machine shop, machine all the parts accurately and assemble them perfectly q In one week, they do a mock up test on another vehicle. q 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 3004 C 3. 2 Scenario 2 q Mike and Heather have been working now for more than a month. q After many trials and tribulations, they design an arm capable of lifting objects. q They first use two mouse-trap springs but found power to be inadequate. Needed to replace with battery powers. q They buy electric motors with fine controls. Holes in the arm needed to be re-drilled. Too many wrong holes. q Five weeks past, no working vehicle, project over budget. q When the arm is mounted on the vehicle, it does not fit-needs rework. q When it all fits, during testing the opponent vehicle is lifted but both the vehicles fall of the track. q Abandon the arm concept and redesign with a ram approach. Namas Chandra Introduction to Mechanical engineering Chapter 3 -8

EML 3004 C 3. 2 Welcome to reality! q “If anything can go wrong, it will”- Murphy’s Law q All great discoveries are made by mistake q An expert is one who knows more and more about less and less until he knows absolutely everything about nothing q Experienced engineers know that design never works the first time and are never discouraged by initial failures. q Failures are inevitable part of the design process. q It is better for a defect to surface during the design and testing, rather than in the field. q The best way to avoid field failure is to test, re-test and do some more re-testing. q Computers based virtual testing complement the actual testing but does not replace it. Namas Chandra Introduction to Mechanical engineering Chapter 3 -9

EML 3004 C 3. 2 Case Studies of Engineering Disasters! q Despite great attempts by engineers to weed out design mistakes, they eventually show up and result in catastrophes. q Mistakes are made by engineers who do their best but fail due to lack of prior experience or/and lack of engineering judgment. q Of course, it is easy to pick the flaw in hind sight. Monday morning quarterback!! q Spotting a flaw becomes difficult as the complexity of the system increases. q 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 3004 C 3. 2 Succeed by Averting Failures! q The study of failure is an important part of the engineering design process Ø Studying failures which occur during product testing helps to discover hidden flaws which were not foreseen during the initial design and prototype process Ø Subsequent redesign and adjustment will help to prevent similar failures from occurring once the product has been released to the public q Classic engineering failures Ø Well documented cases where inadequate design or testing resulted in catastrophic failure Ø Caused both loss of life and/or major loss of property Ø The study of these failures helps us to avoid the mistakes of the past Namas Chandra Introduction to Mechanical engineering Chapter 3 -11

EML 3004 C 3. 2 Hubble Space Telescope! q Hubble Space Telescope Ø Powered by large solar panels which resembled wings Ø Alternately heated and cooled as they moved in and out of earth’s shadow Ø Resulting expansion and contraction cycles caused the solar panels to “flap” Ø Problem caused by not taking operating environment into account during the design phase Namas Chandra Introduction to Mechanical engineering Chapter 3 -12

EML 3004 C 3. 2 What went wrong with Hubble? q Perkin-Elmer fabricated mirrors Ø A pair of calibrated mirrors to direct light on hubble surface Ø Diameter of the mirror is 2. 4 m and to be maintained to 0. 001 wavelength in micrometers Ø During assembly there warning signs-Range was falling short; engineers added 1. 3 mm spacers to correct the problem. Ø During mock-up test they found spherical aberration but ignored the concern as trivial. Namas Chandra Introduction to Mechanical engineering Chapter 3 -13

EML 3004 C 3. 2 Tacoma Narrows Bridge! q Tacoma Narrows Bridge Ø Built across Puget Sound in Tacoma, WA, in 1940 Ø Longest suspension bridge of its day Ø Engineers copied designs used for shorter bridges, and simply lengthened them, without testing for structural integrity Ø 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 3004 C 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 3004 C 3. 2 Hartford Civic Center! q Hartford Civic Center Ø Built in mid-1970’s Ø The roof used a novel “space frame” construction which did not require support columns Ø 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 Ø Roof collapsed under a heavy snow load in 1978 Namas Chandra Introduction to Mechanical engineering Chapter 3 -16

EML 3004 C 3. 2 Space Shuttle Challenger! q Space Shuttle Challenger Ø Exploded in 1986 about two minutes after it was launched Ø One of the O-rings used to seal the solid rocket booster failed after it became brittle due to low (below freezing) temperatures on the day of the launch Ø This low temperature failure was unforeseen because the O-ring was never tested at subfreezing temperatures Namas Chandra Introduction to Mechanical engineering Chapter 3 -17

EML 3004 C 3. 2 Hyatt Skywalk Collapse! q Kansas City Hyatt Skywalk Collapse Ø Hanging, two-layer, open-air pedestrian walkway designed to span a lobby atrium Ø The original design required a set of support shafts which could not easily be fabricated Namas Chandra Introduction to Mechanical engineering Chapter 3 -18

EML 3004 C 3. 2 Hyatt Skywalk Collapse! q Kansas City Hyatt Skywalk Collapse Ø Construction engineers modified the original shaft design. While this modification allowed the walkways to be built, it reduced the maximum load that could be supported Ø The reduced capacity of the walkways did not come to light until their collapse during a party, which resulted in over 100 fatalities Namas Chandra Introduction to Mechanical engineering Chapter 3 -19

EML 3004 C 3. 2 Three Mile Island Power Plant! q Three-Mile Island Power Plant Ø Second-worst nuclear accident (Chernobyl was the worst) Ø Flaw in reactor design: an indicator light showed that power had been delivered to a pressure relief valve actuator coil, but could not verify that the valve had actually opened. This is an example of a poor manmachine interface Namas Chandra Introduction to Mechanical engineering Chapter 3 -20

EML 3004 C 3. 2 My personal experience! q Atomic Power Project Construction Ø Design and site engineer Ø Large stainless steel pressure vessel designed, constructed, fabricated and shipped to site Ø During routine hydrostatic testing …. . Namas Chandra Introduction to Mechanical engineering Chapter 3 -21

EML 3004 C CHAPTER 3…concludes Engineers and the Real World? Namas Chandra Introduction to Mechanical engineering Chapter 3 -22