Material Properties: Metals, Polymers, Ceramics, and Composites
Metals and Metal Alloys
Metallic bonds
Features:
- Ordered crystalline structure
- High electrical conductivity
- High thermal conductivity
- Ductility
- Reflect light (shine)
- Large alloy
- Plastic deformation
- They are tenacious
- Medium elasticity
- Medium voltage
Covalent Bonds: Polymers
Features:
- Material formed by long chains from the union called monomers (basic chain)
- Are not crystal
- Polymer mechanical properties vary
- Bad electrical conductors
- Thermal bad drivers
- Used as an insulator
- Low density
- Low-temperature decomposition
Ionic Bonds: Ceramics
Features:
- Formed by metallic and non-metallic elements
- High-temperature fusion
- The properties are achieved after heat treatment
- Fragile
- Hard
- Low toughness
- Low ductility
- Very sensitive to thermal shock
- Crystal structure
- Thermal and electrical insulators
- Plastic undeformed
- High elasticity
- High tension
- High break
Composite Materials: Ionic-Covalent Link
Features:
- Mixing of two or more materials
- Formed by a parent and other material in it dispersed
- Properties of materials over the form
- Structured in various ways, fibrous, or particles
Types of Chemical Bonds
Ionic > Metal > Covalent > Ionic-Covalent
Ceramic > Metal > Plastic or Polymers
Eelast Ionic > Eelast Metal > Eelast Covalent
Ionic Bond
(Rocks, Gypsum, Lime)
Features:
- Occurs between metallic and non-metallic elements
- Electrostatic type link
- Is produced by an assignment of electrons, electron-negative to positive
- Very high energies of the link
- Non-directional
Covalent Bonds
(Wood, Cork, Bituminous, Asphalt, Plastic)
Features:
- It is produced by the sharing of electrons between pairs of atoms
- Apolar bonding like atoms
- Different atoms, polar bonds
- Is directional
Metallic Bond
Features:
- Each atom contributes one or more valence electrons to the rest of the atoms. This creates a cloud of moving delocalized electrons throughout the crystal.
- The energies of the link are very different
- Non-directional
Secondary Bonds
Features:
- Interaction between a material part of, but not joining each other atoms
- Available in all materials
- They are very weak but very addictive
- There are three types:
- Dipole-dipole
- Concluding dispersion between nonpolar molecules
- Hydrogen bonds
High modulus of elasticity: Very rigid material
Low modulus of elasticity: Very plastic material
Mechanical Properties
Measure the relationship between a force applied to a body and its response.
This is proved by 3 systems:
- Draft to applied forces on the cylinder and stretched uniaxial along the direction of the force
- Compression like traction but compression force that is the counterforce
- Applied parallel wind shear to the surface of the specimen
Plastic Deformation
It is when the material changes shape and does not return to regain its form. Permanent deformation, not recoverable.
Elastic Limit
Tension is to the sort of material that stops elastic behavior and becomes plastic.
Tensile Strength
Tension to which produces a specimen in a generally narrowing in the vain central.
Ductility
Processing capacity of a wireless or material in sheets.
When the length is very high, the material is very ductile.
If the area is very low, the material is very ductile.
Viscoelastic Flow
Variation of deformation measured in time.
Hardness
Measure the strength within a deformable material applies a force on a surface.
Fracture
Measures the separation of a body into two or more pieces in response to an applied voltage.
- Ductile fracture: Plastic deformation before the fracture. Cracks form that slowly propagate and only under the action of an increase in tension.
- Brittle fracture: Little or no plastic deformation before fracture. Cracks extend very fast once they are formed.
Structural Properties
Igneous Rocks
Magma of cooling necessary, depending on the texture of the cooling rate.
- Slow cooling intrusion permits molecules to form a glazed order (Granite)
- Rapid cooling warmly lets no molecules have an orderly structure vitreous (Basalt)
Sedimentary Rocks
Come from the erosion of the igneous rocks of water through.
Accumulates in layers by compression of the own weight sedimentary form.
Can be limestones, shell deposit, silica, or sandstone.
Metamorphic Rocks
Sedimentary or igneous rocks are modified by temperature or pressure.
Modified crystalline structure.
Thanks to pressure and heat, they are generally stronger than the rocks from which they come.
Marble from limestone recrystallization
Quartzite from recrystallization of the sandstone
Slate from shale recrystallization
Fibrous Structure (Wood)
Features:
- Long, formed by cells and hollow, which transports water from roots to leaves to carry out photosynthesis
- The pulp and lignin from photosynthesis make up the wood
- Rapidly growing spring training cell with wide, thin-walled tubes
- Summer cells grow slowly and are small and thicker-walled
- Density differences and color make the annual rings
- Anisotropy call is the directional effect of wood properties
- Longitudinal resistance > radial and tangential
Amorphous Structure (Glass)
Features:
- Ordered silica consists of a liquid form amorphous
- Maintain not as a three-dimensional order in crystalline structure
- The crystallization temperature happens overnight denominated fusion
- Glass = supercooled liquid
- Own opacity
- Transparency because of the amorphous structure
- Amorphous structure due to the rapid cooling
Corrosion
A process by which metal is converted into a metallic compound.
Metal properties are lost, such as:
- Resistance
- Elasticity
- Ductility
- Polished metal
- Electrical and thermal conductivity
It is produced by the oxygen. To avoid this, it is necessary to coat the metal with a layer that prevents oxidation. This can be done by galvanization.
Metals do not have much mechanical strength as iron or steel.
Reinforced Concrete
Features:
Are fragile and have little resistance to driving. That is why the concrete is reinforced with steel bars to give tensile strength.
Ductility and Fragility
Features:
- Prevent deformation alloys plastic easy
- Alloy is the best with carbon
- Steels with low carbon < 0.25% ductility and strength
- Steels high in 1.7% carbon, 0.8 a little more resistant and ductile
High-Strength Steels
Features:
- Are the states to manganese and vanadium
- Steel is a 0.25% carbon making it pliable, distort the structure thereby increasing the resistance of iron
Heat Treatment:
- Standard: To warm up to 850° and slowly cool to weak and ductile
- Tempered: To warm up to 850° and cool quickly to resistance and fragile
- Annealing: To warm up to 225º and slowly cool to strong, tenax
Mechanical Processing:
- Processes incremental resistance steel deformed crystal structure
- Produce atomic dislocations that increase resistance to plastic deformation
- But increases, decreases resistance ductility
- The structure is recovered by standard
- Cold work increases more resistant dislocations
Stress and Strain
Tension = Force per unit area
Elongation or strain = Per unit length contraction
Stress is measured in MPa while deformation does not have the dimensions.
Modulus of elasticity indicates material stiffness is the tension is needed to produce to 100% of deformation.
Fractures
Break the links atoms of a material or evaporator.
The fracture is favored by the presence of tiny microfractures. Material must be at high tension and the cleft is large enough.
Tests
Are read the strength of hard materials whether in durability and toughness, test drive is a ductile material for compression and fragile materials.
Workability
The facility to be mixed concrete release and fill the mold to be compacted and have adequate surface finish.
- Dry 0-2
- Plastic 3-5
- Soft 6-9
- Smooth 10-15
- Liquid > 15
Fatigue
Strength of metals = decreased by means of traction and compression loads of repetitive.
Toughness
Is the energy required to break a material, the greater the surfaces provided under greater stress curve of deformation, i.e. has greater toughness.