What is the definition of "torsion stress"?
A specific type of shear stress in which one end of a part is secured while the other end is twisted.

Learn more about torsion stress in the class Overview of Properties for Plastics 135 below.


Materials Training


Class Information
Materials Training Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Overview of Properties for Plastics 135
Description:This class describes the mechanical and chemical properties of plastics and addresses how they impact design considerations.
Prerequisites: none
Difficulty:Beginner
Number of Lessons:15
Language:English, Spanish
 
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Class Outline
  • Objectives
  • The Importance of Plastics Properties
  • Behavior of Plastics
  • Mechanical Properties
  • Types of Strength
  • Toughness
  • Hardness
  • Creep
  • Additives
  • Chemical Properties of Plastics
  • UV Radiation
  • Oxidation
  • Cracking
  • Permeability
  • Summary
  
Class Objectives
  • Describe the importance of learning about the properties of plastics.
  • Describe the behavior of plastics.
  • Define mechanical properties.
  • List types of material strength.
  • Define toughness.
  • Define hardness.
  • Define creep.
  • Describe additives used in plastics.
  • Define chemical properties.
  • Describe the effects of UV radiation on plastics.
  • Describe the effects of oxidation on plastics.
  • Describe cracking.
  • Describe permeability.

Class Vocabulary

Vocabulary TermDefinition
abrasion The scraping or rubbing away of material from an object's surface. Abrasion can be tested with a hardness test.
additive Any substance that is added to a material to achieve a desired characteristic. Additives can be added to plastics to achieve a variety of characteristics, including coloring and UV resistance.
Brinell test A hardness test that measures the diameter of a circle formed by the penetration of a 10mm steel ball under a fixed load pressure.
brittle One of the two categories into which a material is placed when tested for toughness. Brittle materials break easily when hit with a load.
carbon black A soot-like residue that is used as a colorant and/or a protector against UV radiation in polymers.
chemical properties The properties that describe a material's ability to withstand attack by solvents, water or other external agents.
composite A plastic that is composed of two or more separate materials. The different materials that make up a composite still retain their respective properties when mixed together.
compressive strength A material's ability to resist a squeezing force.
compressive stress A force that attempts to squeeze or compress a material.
crazing Small, hair-like cracks beneath the surface of a part.
creep The deformation of a material that occurs over time due to the presence of a constant load.
creep rupture The failure to hold a load over time. Creep rupture occurs when the plastic molecules begin to uncoil.
cross-linking The development of primary bonds that form between polymer molecules. Cross-linking helps prevent creep rupture.
crystallinity Polymer molecules that are folded into a tightly repeating and organized structure. Crystallinity helps prevent creep rupture.
damping The ability to resist deformation through vibration. Plastics have a stronger damping capability than metals.
elastic Having the ability to return to an original shape after being stretched or deformed. Elastic materials show a slight to no modulus on the stress-strain curve.
elasticity A measure of a material's ability to reshape itself after it has been stretched or deformed. A rubber band is an example of an object with high elasticity.
environmental stress cracking The stress cracking of plastic due to a combination of both physical and mechanical factors.
filler An inert substance that is added to polymers to fill up space in the plastic part. Fillers are often added to reduce cost, but not alter the properties of the plastic.
flame retardant The ability to resist igniting when exposed to a flame or elevated temperatures.
force The push or pull that gives energy to an object. Force changes an object's motion or state of rest.
free radical A highly-reactive electron that is not strongly bonded. Free radicals can easily react with oxygen, causing oxidation.
hardness A material's ability to resist penetration, indentation, or scratching. Hard materials tend to be very wear resistant.
hygroscopic Plastics that can effectively absorb moisture in the air. Hydroscopic plastics are often used to manufacture plastic food wrap.
impact toughness The amount of energy that a material can absorb from a sudden, sharp blow before it breaks or fractures.
indenter A device used in a hardness test that is pressed into the test material.
inert The state of being non-reactive. Inert substances are often added to polymers to fill up space and save cost.
load The weight or burden that is supported by a material.
marring The infliction of damage to an object. Marring spoils the integrity of an object in some way.
mechanical properties The properties that describe how a material reacts when it is subjected to some type of force.
mineral A naturally occuring compound, like diamond or talc, that is formed through geological processes. Certain minerals are used in the Mohs hardness test.
modulus The slope of a stress-strain curve. The shape of the modulus indicates the stiffness or elasticity of a material.
Mohs hardness test A hardness test that indicates a material's ability to resist scratching. The Mohs hardness test uses various minerals to scratch a material, thus indicating the hardness of the material.
MRI scanner (Magnetic resonance imaging scanner) A medical device used to see the inside of a patient's body. MRI scanners are state-of-the art devices that allow doctors to diagnose the smallest of abnormalities on the body.
oxidation A material's chemical reaction with oxygen. Weakly bonded molecules are more susceptible to oxidation.
permeability A measure of a material's ability to either resist or absorb liquid or gas. Permeable materials absorb water or gas, while impermeable materials do not.
plasticizer A type of additive that adds elasticity to a plastic. Plasticizers can be toxic and should be avoided.
reinforcement A type of additive that increases certain mechanical properties such as toughness or strength.
Rockwell test A hardness test that measures the degree of penetration into a plastic caused by a diamond or other hard material that is applied to the plastic under a fixed load.
scratching The infliction of a shallow cut or mark on the surface of a part. Hardness tests can gauge a plastic's susceptability to scratching.
shear strength A material's ability to resist forces that attempt to cause the internal structure of the material to slide against itself.
shear stress A force that attempts to cause the internal structure of a material to slide against itself.
solubility The measure of a material's ability to dissolve in a solvent.
solubility rating A rating system that gauges a material's ability to dissolve in a solvent. The lower the rating, the less likely the plastic will dissolve in a solvent.
solute A material that is dissolved in a chemical. When testing the chemical properties of plastics, the plastic material is the solute.
solvent A chemical material that attempts to dissolve another material. When testing the chemical properties of plastics, a solvent can be any type of chemical to which the plastic may be exposed.
stiff Not having the ability to return to an original state once having been deformed. Stiff materials show a steep modulus on the stress-strain curve.
strain The ratio of change in a dimension that takes place with a material under stress. Strain is a measurement of stress.
stress A force that attempts to deform an object.
stress cracking Coming apart in two or more places. Stress cracking can occur in plastics for a variety of reasons, including weather conditions, UV radiation, and overbearing loads.
stress-strain graph A graph that describes the relationship between stress and strain. Stress-strain graphs indicate the elastic and plastic regions for a given material.
tensile strength A material's ability to resist forces that attempt to pull it apart.
tensile stress Force that attempts to stretch or pull a material apart.
thermal degradation The breakdown of a material due to overexposure to heat or the sun. Thermal degradation in plastics can be caused by UV radiation.
torsion stress A specific type of shear stress in which one end of a part is secured while the other end is twisted.
tough One of the two categories into which a material is placed when tested for toughness. Tough materials can withstand a greater amount of mechanical force before it breaks.
toughness The measure of a material's ability to absorb mechanical forces before it breaks. Impact toughness is a particular category of toughness.
ultraviolet radiation (UV radiation). Energy transmitted as invisible, yet damaging rays of the sun. UV radiation can cause thermal degradation or other damaging consequences in plastics.
viscoelastic Having both elastic and viscous properties. Plastics are an example of viscoelastic materials.
viscosity A measure of a material's resistance to flow.
viscous Having the ability to resist flow. Honey is a good example of a viscous liquid, while water is not.