One should consist of the stress-strain curve for the polymer, the there should consist all three curves) Graph of all three curves : Graph of the polymer curve (PEE) : 2. Determine the following mechanical properties from the stress-strain curve for each of the specimens (by graphical method), and summarize these properties in a table. Sample calculation is to be included in the Appendix. Young Modulus 0. 2% yield strength Yield strength Tensile strength Ductility Fracture stress Toughness Properties cows AS Polyethylene Young Modulus (Amp) 22,304. 15 19,269. 34 786. 90 0. 2% Yield Strength (Amp) 895 565 16 Yield Strength (Amp) 815 15. Tensile Strength (Amp) 923. 44 52. 73 29. 46 Ductility (%) 26. 48 39. 73 Fracture Stress (Amp) 749. 22 710. 35 17. 75 Toughness (MS/mm) 59. 61 95. 4 11. 82 3. Compare, contrast and discuss the mechanical properties of these specimens. The COWS specimen is the specimen that has been through a cold-work process. Cold Work is a process to strengthening the materials by increasing the number of the defect and grain boundary, therefore the dislocation motion becomes more difficult and hence, the materials become stronger. This material just goes slightly beyond the yield strength before it breaks. It shows that the material is brittle.
This material has a low toughness. The toughness is measured by the area under the curve Stress versus Strain. From the graph, it shows that the toughness of this material is the lowest compared to the others. The ductility of this material is also low because the material fractures at the low strain. But this material has the highest tensile strength, Young modulus, and yield strength. It is because the material is brittle and strong. The cold work process helps the material to minimize the dislocation process (dislocation caused the material to be ductile) For the AS material, it has the highest toughness.
This material has a high strength, high ductility and high toughness. This material undergoes quiet much beyond the yield strength before it fractures. Its Young modulus, tensile strength, yield strength and fracture strength are only slightly below the COWS material, but it has higher toughness compared to COWS. This material also has a higher ductility. It is proofed by the graph. The area under the AS curve is larger than the COWS’, hence the ductility is higher. Polyethylene material is a ductile material. It has a high ductility. But in this experiment, the measurement is only done in 2 minutes for each material.
The PEE material has not fractured in 2 minutes, so the ductility could not be measured as the area of the material after experiment could not be achieved. This material is ductile because it undergoes much plastic deformation (area after yield strength is called plastic deformation as the material would not back to original length). But, this material has a low toughness and low strength. It can be shown from the graph, this material experiences very low tensile strength, yield strength and fracture strength.