ME 437 Mechanical System Design

Assignment #2 : Due October 4th

[You may work with one team member]

When faced with real problems most people feel uncertain and consequently unhappy about the task ahead. The bad feeling comes from the fact that you know whatever you do, there is no assurance that you did the perfect thing. Most humans suffer when they can not make perfect decisions or produce perfect results. As designers and engineering problem solvers you have to get used to this and accept it as a fact. In the real world decisions have to me made and deadlines have to be met. Unlike academic problems, the first and often the longest activity required to solve real problems is hard thinking. You basically through the problem into your mind and hope that your mind can synthesize the related elements to solve the problem.

The following problems encourage you to form several hypotheses and evaluate them in order to reach a satisfactory solution. Try to come up with solutions or proposals based on your engineering knowledge. These problems relate to material science therefore a review of the relevant issues is important. In order to guide your review of material science you are required to find answers to the specific questions posed following the problems.

  1. A company uses 15 lb sledge hammer heads made from AISI 1060 steel. To reduce tool replacement costs the company takes badly deformed heads and grinds off the deformed segments. A reground hammer struck a metal plate and a chip from a corner of the hammer flew off and caused facial injury to a worker. A lawsuit was subsequently filed. Investigation showed the chip hardness of Rc 65 while the hammer bulk material hardness should have been between Rc 45 and 55. What do you think was the problem? What is your recommendation to the company?
  1. A 10-inch diameter gear has been fabricated from AISI 1080 steel. The gear blank has been hot-forged, air cooled and then fully annealed for machining the gear teeth. Following machining the gear teeth are flame hardened and quenched to the surface hardness of Rc 55. After being placed in service the teeth begin to deform and the gears fail to mesh properly leading to excessive noise and rough operation. What do you suspect has caused the failure? What changes do you suggest to the manufacturing process or materials for adequate fabrication of the gear?

[While none of the problems are easy, the next problem is more challenging that the rest]

  1. The bearings on a marine engine have been manufactured from AISI 52100 steel that has been austenized, quenched, and tempered to final desired properties. Performance has been adequate for several months. After exposure to a period of subzero temperatures in winter, the engine fails during its first operation. Inspection of the failed bearings reveal brittle fracture characteristics. Measurements of bearing dimensions reveals the bearing dimensions somewhat larger than specifications. What do you suspect to be the cause of the failure? What is your recommendation to the bearing manufacturer?
  1. The frame of a 10-speed bike has been made of cold-drawn alloy steel. As a result of an accident the frame fractured in a characteristically brittle fashion. The frame was repaired through conventional arc welding. Shortly after the repair the frame deformed (bent) under normal use in an area adjacent to the welding. What do you think was the cause of the frame deformation? Was there a better means of repairing the original fracture?

Material science review questions

Answer the following questions using your understanding of the subject (rather than copying from some text). Each question must be answered briefly in no more than two line.

Mechanical / Physical Properties

  1. What is ductility?
  2. What is toughness?
  3. What is meant by strength?
  4. What is the endurance limit?
  5. What is fatigue strength?
  6. What is hardness?
  7. What is meant by hardenability?
  8. What is stiffness?
  9. What is meant by porosity?

Manufacturing Properties

  1. What is meant by machinability?
  2. What characteristics are imortant in measuring machinability?
  3. What characteristics are important in formability?
  4. What is the difference between welding and brazing?

Material Science Fundamentals

  1. What is a polycrystaline metal?
  2. What happens in work hardening?
  3. What is the recrystalization temperature?
  4. What is a solid solution?
  5. What is an intermetalic compound?

Iron-Carbon Phase Diagram

  1. What is a phase diagram?
  2. What is -ferrite?
  3. What is austenite?
  4. What is cementite?
  5. What is pearlite?
  6. What is a cast iron?
  7. Describe the micro-structure of grey cast iron.
  8. Describe the important properties of grey cast irons.
  9. Describe the micro-structure of ductile iron.
  10. Describe the important properties of ductile iron.

Heat Treatment of Steels

  1. What are the objectives of processing heat treatment?
  2. What is full annealing?
  3. What is normalizing?
  4. What is process annealing?
  5. What is spheroidization?
  6. Describe the micro-structure of martensite.
  7. What are the mechancial properties of martensite?
  8. How is martensite formed in practice?
  9. What is the effect of tempering on martensite?
  10. What is retained austenite? [Clue to problem C]
  11. What are the possible problems with retained austenite?
  12. Describe some of the drawbacks of designing heat treated parts.
  13. Name a few surface hardening techniques.

Steel Products

  1. What are the class of steel products known as plain carbon steel?
  2. What is the carbon content of low-carbon steel and what are its major applications?
  3. What is the carbon content of meduim-carbon steel and what are its major applications?
  4. What is the carbon content of high-carbon steel and what are its major applications?
  5. What are the main objectives of adding alloying elements to plain carbon steels?
  6. What are the main alloying elements in AISI 4340 steel? How much carbon does it have?
  7. What are the improved properties of HSLA steels compared to plain carbon steels?
  8. State some of the favorable properties of constructional alloy steels (also known as Quench-and Tempered Structural Steels).
  9. What are free machining steels?
  10. What is the main alloying element of stainless steels?
  11. What are the four classes of stainless steels?
  12. What are the properties of ferritic stainless steels?
  13. What are the properties of martensitic stainless steels?
  14. What are the properties of austenitic stainless steels?
  15. Name some of the engineering application of bronze products.
  16. Name some of the engineering applications of brasses.
  17. What are high temperature superalloys? Examples?