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MCET 210
Final
| Question | Answer |
|---|---|
| How are free volume, specific volume, density, and crystallinity related? | Free volume and specific volume increase when density and crystallinity decrease, and vice versa. |
| What is the effect of increased strain rate on a stress-strain curve? | Increased strain rate results in a higher stress at a given strain, making the curve steeper. |
| What happens on a molecular level during elastic deformation? | Intermolecular forces are stretched, but molecules return to their original positions when stress is removed. |
| What happens during plastic deformation on a molecular level? | Molecular chains slip past each other, leading to permanent deformation. |
| Why is understanding polymer properties important for application design? | Required properties dictate polymer selection based on toughness, flexibility, and environmental resistance. |
| What factors influence the crystallinity of a polymer? | Cooling rate, molecular structure, and the presence of impurities or additives. |
| How does increased crystallinity affect polymer properties? | Increased crystallinity results in higher density, stiffness, and tensile strength but lower toughness. |
| What are the differences between bioabsorbable and biodegradable polymers? | Bioabsorbable polymers are absorbed by the body, while biodegradable polymers degrade into natural substances. |
| What structural features make a polymer biodegradable? | Hydrolysable bonds, oxygen/nitrogen in the backbone, and lower crystallinity. |
| What are the pros and cons of mechanical recycling? | Pros: Energy-efficient, cost-effective. Cons: Degradation of material properties over cycles. |
| Define viscoelastic materials. | Materials exhibiting both viscous and elastic behavior, dissipating energy while partially recovering shape. |
| What is stress relaxation? | The decrease in stress under constant strain over time. |
| How can you compensate for stress relaxation in part design? | Increase part dimensions or use materials with higher relaxation resistance. |
| What factors affect the rheological properties of polymers? | Molecular weight, temperature, polymer structure, and the presence of additives. |
| How are shear stress, shear rate, and viscosity related to flow rate in a polymer channel? | Viscosity = Shear stress / Shear rate; flow rate depends on cross-sectional area and length of the channel. |
| How can you distinguish between swelling/dissolution and chain scission? | Swelling/dissolution changes physical size; chain scission reduces molecular weight and increases brittleness. |
| What changes can avoid polymer degradation during processing? | Lowering temperature, reducing shear, or using stabilizers. |
| What additive might be used to improve UV resistance in a polymer part? | UV stabilizers. |
| How does fiber reinforcement affect tensile properties? | Introduces anisotropy, increasing tensile strength in the flow direction but decreasing it transversely. |
| How can you identify weld lines in a fiber-reinforced injection-molded part? | They appear where polymer flow fronts meet, often at weak points near gate locations. |
| How do you calculate the modulus of a composite in longitudinal loading? | Use the rule of mixtures: Ec = Vf*Ef + Vm*Em |
| How can you determine if a composite part will fail under longitudinal loading? | Compare the applied stress to the calculated yield stress in the longitudinal direction. |
| What is the deformation of a composite under a given stress? | Use Hooke's Law: Delta L = Stress*L / E |
Created by:
Tsar Pasta
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