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Sid - ENMA 300 Introduction to Materials and Their...

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ENMA 300: Introduction to Materials and Their Applications Prof. Ankem [email protected] 1105 CHE (Bldg 90) X55219 TAs: Linmaris Santiago [email protected] Yueying Liu [email protected] MIDTERM 2: This Thursday! Material through today Thursday Nov. 5 Focus on material since last midterm (Chapters 5, 6, 7, Ethics and H5-H8) but since material builds on previous material comprehensive questions are possible Similar format to MT 1 Show your work! Use words to explain! Check your equations against the book 2 Crib sheets – Crib sheet one from exam 1; Crib sheet 2: 1 side of an 8” by 11” sheet of paper (erf table will be provided) When you study: Homework, exercises, lectures (review slides should be helpful) then text FINAL EXAM: Mon. Dec 14, 2009 8:00 – 10:00 am 1 ENMA 300 F09 Ankem Lecture 18
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Tensile strength of polymers Depends on type of polymer and temperature (and loading rate). Elastomers typically show a very large amount of nonlinear deformation and then fracture. They tend to exhibit very little, if any, yield due to cross-linking. Semicrystalline polymers may exhibit yield and pseudoplastic deformation due to chain sliding before failure. Brittle behavior can be observed for glassy (uncrystallized TP, networked and highly cross-linked TS) polymers well below T g . Highly aligned polymers networked and highly cross linked polymers and aligned polymers. Chain alignment in TP affects strength and toughness Decreasing measurement T and increasing loading rate have similar effects Relaxation or viscoleastic modulus for polymers – time dependent behavior; Creep: slow plastic deformation at elevated temperature; deformation under constant load; issue for T near or > T g in polymers 2 ENMA 300 F09 Ankem Lecture 18
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General concepts: Types of strength - what should be used when and why Elastic and plastic deformation Strength vs. toughness Units Hardness: Resistance to penetration Good for ranking (screening) and quality control, not a ‘fundamental’ property Typically: - As hardness increases resistance wear resistance and resistance to plastic deformation and cracking in compression increase (as least for metals) - Brittle materials may exhibit cracks at corners of indents (relative indentation toughness) or even crushing Design or safety factors 3 ENMA 300 F09 Ankem Lecture 18
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Review Continued Chapter 8: Focus on deformation mechanisms in metals and polymers as well as temperature effects and means to strengthen them (i.e. prevent or impede deformation).
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