MIE 270: Final (Part 2: Composite and Magnetic Materials)

Chapters: 15 and 18 Does not include equations only theory

Composites

Multiphase materials

Composites: Matrix Phase + Dispersed Phase

Matrix helps retain shape and transfers stresses to the reinforcement

Matrix-based Classification

• Polymer-matrix composites (PMC)

  • GFRP (Glass fiber)

  • CFRP (Carbon Fiber)

  • AFRP (Aramid Fiber)

• Metal-matrix composites (MMC)

• Ceramic-matrix composites (CMC)'

• Carbon-Carbon composites

• Hybrid Composites

Reinforcement-Based Classification

• Particle - reinforced

  • Large (concrete)

  • Dispersion (TIny tiny)

• Fiber - reinforced

  • Continuous aligned

  • discontinuous short

    • Aligned

    • Random

• Structural

  • Laminate

  • Sandwich panels

Large-Particle Composites

• Aggregate Size (water-cement)

  • both affect the strength of concrete

• Problems

  • Very weak in tension

  • Thermal expansion

  • Water Permeability

• Reinforced Concrete

  • Rebar/Wired Mesh

  • Fibers

  • Post-tensioning or Prestressing

Dispersion - Strengthened

• Smaller particles

  • d = 10-100nm

• Particles impede the movement of dislocations

  • Restrained plastic deformation

  • σ_y up, σ_ts up, hardening up

• Particles matrix interacuions

  • Strengthening at the atomic or molecular level

• Example

  • Thorial (thorium dioxide) nickel-chromium, for thermal protection systems (TPS)

Fibre - Reinforced

• Critical Fiber Length

  • L < Lc

    • Short Thick fibers

    • low, inefficient stress transmission

  • L > Lc

    • Long thin fibres

    • High Efficiency

Pultrusion

• Fibers pulled through a resin tank (thermosetting resin)

• pass through a steel die performing to the desired shape

• pass through curing die

  • machined to the final part

  • heated to cure resin

Prepreg - Sheets of a composite

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Filament Winding

1. Fibers are positioned in a predetermined pattern to form a hollow (usually cylindrical) shape.

2. Fibers are fed through a resin bath (thermosetting resin)

3. These fibers are then continuously wound onto a mandrel

4. After layering is complete, curing is carried in an oven or room temp

5. Mandrel is removed to give the final product

Con: Can’t get fibers to be longitudinal and is limited to closed convex shapes (cylindrical)

Laminates

• Unidirectional: 0-degree angle between layers

  • notation: [0^o]_{# of layers}

• Crossply: 0 then 90 angle between layers

  • [0^o/90^o]_{# of layers}

• Angle Ply: 45/-45

  • [45^o/-45^o]_{# of layers}

• Multidirectional:

  • [0^o/90^o/45^o/-45^o/]_{# of layers}

Sandwich Panels

• The thickness of the core dictates the overall panel stiffness

• With extremely large bending stiffness, it is lightweight and cost-effective

• The purpose of the face sheets is to carry bending loads

• The core

  • high shear strength of stiffness to withstand the transverse shear stress of buckling

Nanocomposites

• Types:

  • Nanocarbon: can be single-wall carbon nanotubes

  • Carbon nanofibers

  • Nanolayers (layered silicates)

  • Particulate nanocrystals

• Nanoparticle Size

  • decreasing size can eliminate magnetic properties

  • decreasing size, the surface/bulk ratio increases, and surface phenomena dominates

• Applications

  • Increase in mechanical properties

• Challenges

  • It is hard to achieve adequate dispersion

  • price

  • risk of toxic exposure

Magnetic Properties - Concept

• To some extent, all materials are influenced by the presence of a magnetic field.

• Magnetism: the ability of a material to exert attractive or repulsive forces on a material

Magnetic Forces

Generated by electrically charged particles

• Electron Orbital motion

• Electron Spin

Magnetic Field

Distribution shown by lines of forces

Magnetic Dipoles

Think of very tiny magnets that each have north and south poles

Magnetic induction

• Applied Magnetic Field

  • Created by current through a coil

• H

  • Externally applied magnetic field strength

• B (Magnetic Flux density)

  • Is internally applied magnetic field due to the material inside the solenoid

Permeability (mu)

measure of the degree to which a material can be magnetized

Magnetic Moment

As an electron movies in orbit it generates a magnetic moment. This magnetic moment is along the axis of rotation.

Electron spin

an inherent rotation or spin that electrons have, and it contributes to their overall magnetic properties. Denoted as mu s the magnetic moment is directed along the spin axis.

Net Atomic Magnetic Moment

Sum of all electrons (both spin and orbital)

Fundamental magnetic moment: Bohr Magneton

Types of Magnetism

• Diamagnetic

  • X_m < 0

  • mu_r <= 1 (just below)

  • B < B_o

  • No Magnetic Dipole orbital

• Paramagnetic

  • X_m > 0

  • mu_r >= 1

  • B > B_o

  • weak Magnetic Dipole spin

• Ferromagnetic

  • X_m»0

  • mu_r»1

  • B = mu_oM M = X_r

Diamagnetic (Magnetic Responses)

Paramagnetic (Magnetic Responses)

Ferromagnetic (Magnetic Responses)

Diamagnetic Material

• Have no unpaired electrons, hence magnetic moments are all canceled out

• Weakly repelled by H

• i.e. Au, Ag, Cu, Pb, water, humans, etc.

Paramagnetic Material

• Have some unpaired electrons, hence magnetic moments are present

• Weakly attracted by H

• They lose their magnetization in the absence of a magnetic field

• i.e., Al, Ca, Mg, Ti, etc.

Ferromagnetic Material

• Spin of all electrons are parallel

• Net(spin) magnetic moment

• Coupling interactions: Magnetic moments of adjacent atoms to align

• Domains: Mutual spin alignment happens over large volume regions

• Strongly attracted by H

• can be permanently Magnetized

Antiferromagnetic Material

• Coupling between adjacent atoms and ions occur in other materials too, but not parallel

• aligned in opposite directions, so that the moments cancel out

• Material has no net magnetic moment

Ferrimagnetic Material

• Cubic Ferrites (Fe₃O₄)

• Some ceramics show permanent magnetization

• non-parallel spin-coupling interactions

  • There is net magnetic moment since there is incomplete cancellation of the spin moments.

• Good electrical insulators

• M_s = Magnetic Saturation, Smaller than in ferromagnets

Magnetic Saturation

• When you increase H beyond a level, increase in magnetization plateau

Domains in Ferro and Ferri-magnetic Materials

• Before applied H

  • Mutual alignment of all magnetic dipole moments

• After

  • At Ms , a single domain is oriented with H

Magnetic Hysteresis

The tendency of a material to retain its magnetization even after the removal of an external magnetic field. It causes a lag between the changes in the applied magnetic field and the resulting magnetization.

Soft Magnetic Materials

• Low energy loss

• High initial magnetic permeability

• Low H conductivity

• Can easily be magnetized and demagnetized with low energy loss

Hard Magnetic Materials

• High energy loss

• High resistance to demagnetization

• Low magnetic permeability

• High Hc, Br, Bs (Saturation magnetic flux density)

Effects of Temperature on Magnetic Properties 1

• When temp increases, the magnitude of thermal vibrations of atoms increases, aligned directions turn to random directions and don’t get magnetized easily.

• Ferro, AntiFerro, Ferri magnetic materials

  • Thermal motions counteract coupling forces between adjacent atoms or dipole moments causing dipole misalignment.

• Ms is max when T = 0K

Effects of Temperature on Magnetic Properties 2

• At Temp above Tc (curie)

  • Ferro and Ferri magnetic materials become paramagnetic

• Tc (^oC)

  • Fe 768

  • Co 1120

  • Ni 335

• For antiferromagnetic materials

  • Tneel (equivalent to Tc)

Magneto strictive

• Magnetostrictive: A property of certain materials that exhibit a change in shape or dimensions when subjected to a magnetic field.

• used as Sensors

Super Conductivity

The phenomenon where certain materials exhibit zero electrical resistance when cooled below a critical temperature, allowing for the efficient flow of electricity.

Meissner Effect

A phenomenon where a superconductor expels magnetic fields from its interior when cooled below its critical temperature, causing it to levitate above a magnet.