Mechanical Properties of Polymers and Ceramics Print This and Take It to Lab | MSE 201, Lab Reports of Materials science

Download Mechanical Properties of Polymers and Ceramics Print This and Take It to Lab | MSE 201 and more Lab Reports Materials science in PDF only on Docsity! LAB V - MECHANICAL PROPERTIES OF POLYMERS AND CERAMICS PRINT THIS AND TAKE IT TO THE LAB NOTE: THIS LAB WILL MEET IN THE SCIENCE ENGINEERING RESEARCH FACILITY ROOM 103. OBJECTIVE: The objective of this lab is to understand the microstructure of some polymers and correlate them with their mechanical properties. In addition, the variables on the mechanical response of a polymer during a tensile test will be discussed. TIMELINE FOR LABORATORY 0:00 - 0:10 : Description of lab 0:10 - 0:30 : Tensile Testing, Explanation of crystallinity, Cross-linking demonstration (while tests are running) 0:30 - 0:50 : Izod Impact testing 0:50 - 1:00 : Glass Transition Temperature demonstration with racquetball 1:00 - 1:10 : Glass impact demonstration with Prince Rupert Drop 1:10 - End : Review of lab report requirements, Q&A PROCEDURE: Polymer tension samples (dumbbell shape) of LDPE, HDPE, PMMA and TPS are prepared according to ASTM D638. These have a width of 0.5” and a thickness of 1/8” at the center. A 4” gage length is used. 1. Place the LDPE sample into the grips, and set the crosshead speed to 2 in/min. 2. Start the crosshead and record load (lbs) as a function of extension (in). 3. Repeat the test for HDPE, PMMA and TPS. 4. Do additional test on HDPE at 10 in/min and 20 in/min crosshead speed. 5. Obtain load versus extension data for each of the six tensile tests. 6. Five HDPE samples will be impacted at temperatures of 100 oC, 25 oC, 0 oC, -60 oC (dry ice) and -196 oC (liquid nitrogen). The energy absorbed by the impact is recorded on the tester's gauge. REPORT REQUIREMENTS 1. Plot the load versus extension curves for HDPE (all three speeds), LDPE, TPS, and PMMA. calculate the following quantities for the polymers tested: 1. Elastic Modulus; 2. Yield Strength; 3. Percent Elongation at fracture; and 4. Toughness for PMMA and HDPE (20 in./min). Compare results and comment. 2. Calculate the degree of crystallinity (χc) of the samples HDPE and LDPE using the information in the “concepts” section of this handout. Again, make a typed table of your calculation results. 3. How does the degree of crystallinity influence mechanical properties (ductility, strength and modulus)? 4. Why is PMMA transparent? 5. Why is it important to use the same strain rate to compare the properties of two different polymers? Based on the tensile data, how does the strain rate influence the mechanical properties of polymers? 6. Plot the results from the IZOD impact test as a function of temperature, and indicate the ductile-to-brittle temperature range and the glass transition temperature (Tg) of the polymer. Use lines on your plot to show the transition regions, and indicate the approximate Tg. Did the impact strength continually increase at higher temperatures, or did it fall off? Why or why not? 7. Briefly give some design examples of where hardness, Izod, and Charpy data obtained in this lab may be useful. REPORT GRADING: Introduction 5 points Plots 10 points Calculations of properties from data 10 points Deg. of crystallinity calculations 10 points Question 3 (3 parts) 10 points Question 4 5 points Question 5 (2 parts) 10 points Question 6 (5 parts) 15 points Question 7 5 points Conclusions 10 points Format, Flow, Neatness, Clarity, Labels, etc. 10 points Left: A transmission electron micrograph of a 50nm section in a HIPS (High Impact Polystyrene), or TPS (Toughened Polystyrene), showing the multiple inclusion particle structure which results from the bulk polymerization technique. Crystallinity Polymers may be amorphous or semi crystalline. The degree of crystallinity and the morphology of the crystalline material have profound effects on the mechanical behavior of polymers, and since these factors can be varied over a wide range, the mechanical properties of crystalline polymers take on a bewildering array of possibilities. Highly crystalline polymers such as Polypropylene have a complex morphological structure. The polymer chains generally appear to fold into lamellar structures on the order of 100 Å thick, with most chains turning and reentering in the lamella from which they emerged, as illustrated on the figure below: The degree of crystallinity for a polymer is calculated using the known densities for the polymer in its 100% crystalline form and its amorphous form. Once the sample’s density is measured, one can estimate the degree of crystallinity using this formula: Where pc: 100% crystalline density pa: amorphous density p: sample density In the case of polyethylene, these densities have been measured as follows: pc = density of crystalline fraction = 0.989 g/cm3 pLDPE = 0.910 g/cm3 pa = density of amorphous fraction = 0.810 g/cm3 pHDPE = 0.973 g/cm3 You will use the above values to calculate the degree of crystallinity in LDPE and HDPE for your report. Glass Transitions Most polymers are either completely amorphous or have an amorphous like component even if they are crystalline. Such materials are hard, rigid glasses below a fairly sharply defined temperature known as the glass transition temperature (Tg). At temperatures above the Tg, at least at low or moderate rate of deformation, the amorphous polymer is soft and flexible and may even be an elastomer or a very viscous fluid. The mechanical properties of polymers change drastically when the temperature crosses the Tg. For example, the Elastic Modulus may decrease by a factor of 1,000 times as the temperature is raised through the Tg. This behavior can be tested using the IZOD impact test. The impact toughness is measured in foot-pounds, and the ductile-to-brittle transition temperature can be easily inferred from a plot. Lower temperatures tend to decrease the impact strength, and vice-versa. As a polymer nears its melting point, however, partial melting and/or "alpha relaxation" allows the polymer's crystals to become very mobile, and thus a drop in impact strength is sometimes noted. Ceramic Demonstration Samples of "Prince Rupert's Drops" will be shown to the class. You can read about these interesting items here. A demonstration will be performed to show how glass (a ceramic) can withstand impact from a hammer, but violently shatter when a tiny scratch is made on the surface! Above: A "Prince Rupert Drop" of glass. The bulb (C) explodes violently when scratched, or the tip (A) is broken. The bulb has tremendous impact properties, however. BACK TO HANDOUTS PAGE APPENDIX 1 LAB IV DATA SHEET Name:___________________________________________________________________________ Date of Experiment: ___________________________ Section Number: _____________________________ Tensile Experiment Observations: IZOD Impact values: Temperature (oC) Variable IZOD Fracture Energy (ft-lb) Notes: