Advanced Functional Materials: SMAs, SMPs, Self-Healing, Chromic, and Electroactive Systems
1. Shape Memory Alloys (SMAs)
Definition
Shape Memory Alloys are metallic materials that can recover their original shape after deformation when exposed to a specific stimulus, usually heat.
The most common example is Nickel-Titanium (Nitinol), known for its shape memory and superelastic behavior.
Mechanism
a. Phase Transformation
SMAs operate through a solid-state transformation between two phases:
- Martensite (low temperature, soft) – Can be deformed easily and retains its shape until heated.
- Austenite
Composite Materials: Types, Advantages, and Uses
Chapter 1: Introduction to Composite Materials
What are Composites?
Composites are materials consisting of two or more constituents. The constituents are combined in such a way that they keep their individual physical phases and are not soluble in each other or do not form a new chemical compound.
One constituent is called the reinforcing phase, and the one in which the reinforcing phase is embedded is called the matrix. Historical or natural examples of composites are abundant: brick made of clay
Read MoreComposite Manufacturing Processes: A Technical Overview
Wet Lay-up / Hand Lay-up
Description: Resins are manually impregnated into fibers, which are in the form of woven, knitted, stitched, or bonded fabrics. This is typically accomplished using rollers or brushes. Increasingly, nip-roller type impregnators are used to force resin into the fabrics with rotating rollers and a resin bath. Laminates are cured under standard atmospheric conditions.
Material Options
- Resins: Any (e.g., epoxy, polyester, vinylester, phenolic).
- Fibers: Any, although heavy aramid
Fiber Composites: Properties and Matrix Comparison
Glass Fiber
- Easily converted into high resistance fibers.
- Easily available and economically achievable.
- Compatible with most manufacturing processes.
- Relatively strong fibers, but stiffness not very high.
- Chemically inert when combined with many plastics.
- Good adhesion with most resins.
- Small thermal expansion.
The basic constituent of glass fiber is silicon, combined with other elements. To avoid surface defects due to abrasion during the wire drawing process, a sizing coating is used.
Carbon Fiber
- Very