HW 3 MET 14400 f20

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Aerospace Engineering

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Oct 30, 2023

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Grading instructions: -1 no questions (mark as NQ) -1 overly sloppy (mark as OS) For each answer: -0 if content is similar to key answer and supporting work is shown (where applicable) -1 if content is partially similar to key answer but has some errors -2 if content differs significantly from the key answer Name (last, first) __________________ Collaborators__________________ MET 14400 Materials and Processes II Fall 2020 Homework #3 – 20 points plus 4 bonus points Due at 11:59 pm on BrightSpace, Thursday, October 1 Questions are taken from DeGarmo’s Materials and Processes in Manufacturing by Black and Kohser or pertain to testing labs (flammability, HDT, MFI, specific gravity, hardness, tensile, Izod impact, specular gloss, film opacity). Any additional references should be cited. Each answer is worth two points . Chapter 2 (12 th and 13 th editions) 1. (book #29) How might tensile test data be misleading for a “strain-rate sensitive” material? a. Different materials may have different results based on how sensitive they are to strain rate. For example, some materials may elongate more if the strain rate was increased as compared to other materials which may stay the same no matter the strain rate. 2. (book #31) What are some of the different material characteristics or responses that have been associated with the term hardness ? a. Toughness, brittleness, strength 3. (book #35) Why are there different Rockwell hardness scales? a. To accommodate for a wide range of materials with a wide range of strength 4. (book #42) Describe several types of dynamic loading (minimum of two). a. Sudden impacts or loads that rapidly change, repeated cycles of loading and unloading, and frequent changes in the method of loading. 5. (book #45) What aspects or features can significantly alter impact data a. Changes in the form of the notch, variations in the specimen’s geometry, and different rates or speeds of loading. 1

6. (book #48) Are the stresses applied during a fatigue test above or below the yield strength (as determined in a tensile test)? a. Usually the stress is below the yield strength 7. (book #58). What property changes are typically observed when temperature is increased? a. Strength and ductility Other (lab instructions, presentations) 8. How does the Izod Impact test determine the impact resistance (also called impact energy) of a material? a. The energy is calculated by measuring the height the arm swings after striking the material 9. An unknown polymer material is tested to determine its specific gravity. If the average sample mass is 0.53 grams and the average sample volume is 0.094 cm 3 , what is the material’s density and specific gravity? Assume testing is completed under standard atmospheric conditions. a. P=m/v b. P=.53g/.094cm^3 c. Density=5.64g/cm^3 d. SG=P/P of water e. SG=5.64g/cm^3/1g/cm^3 f. SG=5.64 10. What conditions commonly result in creep? a. Typically materials being subjected to relatively large loads and high temperatures will result in creep Material Property Definitions (1 point each) Vocabulary still matters! : 11. Hardness- The ability for a material to withstand external damage, such as scratching. 12. Toughness – The ability for a material to withstand energy without rupturing 13. Impact resistance – The amount of energy a certain specimen can withstand before rupture 14. Resilience – How much tensile stress a material can take before it becomes permanently deformed 2

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