bonding and composite fabricator Interview Questions and Answers

1. What is the difference between thermoset and thermoplastic resins?

   • Answer: Thermosets undergo irreversible chemical changes when cured, forming a rigid structure that cannot be melted and reshaped. Thermoplastics, on the other hand, can be repeatedly melted and reshaped without undergoing chemical changes.

2. Explain the process of layup in composite fabrication.

   • Answer: Layup involves manually placing layers of reinforcement material (fibers) onto a mold, often impregnated with resin. This is done meticulously to achieve the desired fiber orientation and thickness, ensuring the final composite part meets strength and stiffness requirements.

3. What are the different types of fiber reinforcement used in composites?

   • Answer: Common fiber reinforcements include carbon fiber, fiberglass (E-glass, S-glass), aramid fiber (Kevlar), and basalt fiber. Each offers different strength, stiffness, and cost properties.

4. Describe the importance of proper surface preparation before bonding.

   • Answer: Proper surface preparation is crucial for achieving a strong bond. This typically involves cleaning, degreasing, and sometimes etching the surfaces to remove contaminants and create a mechanically and chemically sound interface for the adhesive.

5. What are some common adhesive types used in composite bonding?

   • Answer: Epoxy resins, polyurethane adhesives, cyanoacrylates (super glues), and structural acrylics are commonly used. The choice depends on the materials being bonded, the required strength, and environmental conditions.

6. Explain the concept of void content in composites and its impact on properties.

   • Answer: Void content refers to the presence of air pockets within the composite material. Voids significantly reduce the strength and stiffness of the composite, making it more susceptible to failure.

7. What are the different curing methods for composite materials?

   • Answer: Common curing methods include oven curing, autoclave curing (high pressure and temperature), room temperature curing, and UV curing.

8. How do you ensure proper resin-to-fiber ratio in composite fabrication?

   • Answer: Accurate weighing of resin and hardener, using pre-impregnated materials (prepregs), or employing specialized resin transfer molding (RTM) techniques help control the resin-to-fiber ratio.

9. What safety precautions are necessary when working with composite materials and resins?

   • Answer: Respiratory protection (masks), eye protection (goggles), gloves, and proper ventilation are crucial. Some resins are toxic and require specific handling procedures.

10. Describe the process of quality control in composite fabrication.

    • Answer: Quality control involves inspecting materials, monitoring the layup process, ensuring proper curing, and performing non-destructive testing (NDT) such as ultrasonic inspection or X-ray inspection to detect defects like voids or delaminations.

11. What is a prepreg?

    • Answer: A prepreg is a pre-impregnated fiber reinforcement material. The reinforcement fibers are already coated with resin, simplifying the layup process.

12. Explain the concept of fiber orientation in composite design.

    • Answer: Fiber orientation significantly affects the mechanical properties of the composite. Careful planning of fiber orientation optimizes the strength and stiffness in the desired directions.

13. What is the purpose of a release agent in composite molding?

    • Answer: A release agent prevents the cured composite part from sticking to the mold, allowing for easy removal.

14. What are some common defects found in composite structures?

    • Answer: Voids, delaminations, porosity, fiber misalignment, and improper cure are common defects.

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