ME Polymers and Composite Materials 2 — Questions and Answers
Question 1: Degree of polymerization (DP) is defined as:
- The molecular weight of a single repeat unit
- The number of repeat units in a polymer chain (Correct answer)
- The ratio of crystalline to amorphous content
- The number of crosslinks per unit volume
Correct answer: The number of repeat units in a polymer chain
The degree of polymerization is the number of monomer repeat units in a single polymer chain, related to molecular weight by DP = M_n / m (repeat unit mass).
Question 2: Which of the following is a thermoplastic polymer commonly used in engineering applications for its high impact strength and transparency?
- Epoxy
- Polycarbonate (PC) (Correct answer)
- Polyester resin
- Phenolic resin
Correct answer: Polycarbonate (PC)
Polycarbonate is a thermoplastic known for high impact resistance, optical clarity, and good thermal stability, widely used in safety glazing and electronic housings.
Question 3: In polymer science, creep refers to:
- Immediate elastic deformation upon loading
- Time-dependent deformation under sustained stress below the yield point (Correct answer)
- Rapid crack propagation through a polymer
- The return of strain after stress removal
Correct answer: Time-dependent deformation under sustained stress below the yield point
Creep in polymers is the slow, time-dependent increase in strain under a constant applied stress, driven by viscoelastic flow of polymer chains.
Question 4: The critical fiber length in a fiber composite is the minimum fiber length required to:
- Prevent delamination of plies
- Allow full load transfer from matrix to fiber so the fiber can reach its tensile strength (Correct answer)
- Keep fiber volume fraction below 60%
- Prevent fiber buckling under compression
Correct answer: Allow full load transfer from matrix to fiber so the fiber can reach its tensile strength
The critical fiber length is the minimum length needed for the shear stress at the fiber-matrix interface to transfer enough load to bring the fiber to its failure stress.
Question 5: Delamination in laminated composite structures most commonly initiates at:
- Fiber-matrix interfaces within plies
- Free edges and ply drop-offs due to interlaminar stresses (Correct answer)
- The center of the laminate under bending
- Sites of fiber waviness
Correct answer: Free edges and ply drop-offs due to interlaminar stresses
Delamination preferentially initiates at free edges, ply terminations, and ply drop-offs where interlaminar normal and shear stresses are highest.
Question 6: Which composite manufacturing process uses vacuum pressure to infuse resin into a dry fiber preform?
- Filament winding
- Autoclave prepreg layup
- Vacuum-assisted resin transfer molding (VARTM) (Correct answer)
- Pultrusion
Correct answer: Vacuum-assisted resin transfer molding (VARTM)
VARTM (Vacuum-Assisted Resin Transfer Molding) uses vacuum pressure to draw liquid resin through a dry fiber preform placed in a one-sided mold under a vacuum bag.
ME Polymers and Composite Materials 2
Degree of polymerization (DP) is defined as: