Posted tagged ‘rubber’

POISSON’S RATIO

August 23, 2011

01-PoissonRatio-isotropic linearly material-youngs modulus, bulk modulus, shear modulus, auxetic materials

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.


For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.


01-poissons ratio-calculate simple stress and strains-engineering mechanics

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

01-poissons ratio-strain changes

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.

POISSON'S RATIO

August 23, 2011

01-PoissonRatio-isotropic linearly material-youngs modulus, bulk modulus, shear modulus, auxetic materials

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.


For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.


01-poissons ratio-calculate simple stress and strains-engineering mechanics

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

01-poissons ratio-strain changes

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PLASTIC-2

August 23, 2011

What are Plastics?

Plastics are a material that is made up mainly of macromolecules, that can be made fluid by the action of heating and pressurizing, and that can be processed into end products with any useful shape you want to make.

01-plastic products-plastic household products-Chemical-in-Plastics-to-Cause-Breast-Cancer

Classification of Plastics

Plastics can be classified into:

1. Thermoplastics and Thermo sets
2. Amorphous Thermoplastics and Crystalline Thermoplastics
3. Commodity Plastics and Engineering Plastics

Thermoplastics Vs Thermo sets


01-thermo plastics vs thermosets-difference between thermo plastics and thermosets

Thermoplastics Elastomer

• TPE – thermoplastic elastomer
• Resemble rubber at room temperature
• Can be melt-processed like other thermoplastics
• Become elastic like rubber when cooled

Amorphous Thermoplastics Vs. Crystalline Thermoplastics

01-Amorphous thermoplastics-crystalline thermoplastics

Thermo sets Classifications

01-thermo sets-thermo sets classifications- thermo setting plastics-examples of thermo sets

Commodity Plastics Vs Engineering Plastics

01-difference between commodity plastics and engineering plastics-examples of commodity plastics, examples of engineering plastics

PLASTIC

August 23, 2011

Plastics are excellent materials with unique and very useful properties. You can produce just about anything you can imagine using plastics.

01-Plastics-food-containers-durable plastic products-plastic boxes

Characteristics of Plastics

01-plastics-characteristics of plastics-plastic parts-various plastic products

History Of Plastics:

1. Before Plastics—Age of the Natural Resins

  • Rubber—Tough elastic substance (light cream or dark amber
    colored) from the milky juice (sap) of rubber tree
  • Ebonite—Hard black rubber; natural rubber + sulfur
  • Gutta-Percha—Dark brown substance like natural rubber
  • Shellac—dark-brown material from lac insects

2. Bakelite—The First True Synthetic Plastics

  • Leo Hendrik Baekeland invented Bakelite from coal
  • Bakelite helped make 20th century “The Age of Electricity”

01-Reaction to produce plastics-plastic formation-industrial plastic manufacturing-plastic production methods3. Industrialization of Major Plastics

Year Type of plastics Note
1872 Celluloid (Hyatt, USA) Semi-synthetic
1910 Phenolic resin, “Bakelite” (Baekeland, USA) From coal
1931 Polymethyl methacrylate (PMMA) (Rohm and Haas, Ger-many) From coal
1935 Polyvinyl chloride (PVC) (IG Farben, Germany) From coal
1935 Polystyrene (IG Farben, Germany)

From oil

1938 Nylon 6 (IG Farben, Germany)
1939 Nylon 66 (DuPont, USA) From coal
1939 High-pressure low-density polyethylene (LDPE) (ICI, Eng-land)
1953 Polyethylene terephthalate (PET) (DuPont, USA)
1953 Low-pressure high-density polyethylene (HDPE) (Montecatini, Italy) Ziegler catalyst
1955 Medium-pressure high-density polyethylene (HDPE) (Phillips, USA) Phillips catalyst
1957 Low-pressure high-density polyethylene (HDPE) (Hoechst, Germany) Ziegler catalyst
1959 Polypropylene (Montecatini, Italy)
1977 Linear low-density polyethylene (LLDPE) (UCC, USA)
1991 Metallocene very-low-density polyethylene (VLDPE) (Exxon, USA) Metallocene cata-lyst

4. Concept of High Molecular Weight Compounds & Polymers

  • Herman Staudinger, German chemist, proposed a new theory that several thousands of reactive units bonded together in chains and form giant molecules to make up cellulose and rubber
  • In 1920, Staudinger proposed calling such materials: high molecular weight compounds, macromolecules, or polymers.

5. Nylon—The First Tailor-Made Plastics

  • 1931 – Fiber 66 was produced, later called Nylon 66 in 1938