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Elasticity, plasticity, fracture, creep

Elasticity and plasticity

Materials are classified as plastic or elastic depending on how they respond to an applied force. It is important to note that plastic substances are not necessarily a type of plastic (polymer) they only behave like plastic. Think of them as being like plastic which you will be familiar with.

A rubber band is a material that has elasticity. It returns to its original shape after an applied force is removed, providing that the material is not stretched beyond its elastic limit.

Plasticine is an example of a material that is plastic. If you flatten a ball of plasticine, it will stay flat. A plastic material does not return to its original shape after an applied force is removed.

  • Elastic materials return to their original shape.
  • Plastic materials deform easily and do not return to their original shape.

Fracture, creep and fatigue

Some materials are neither plastic nor elastic. These substances will break or fracture when a large enough force is applied to them. The brittle glass we mentioned earlier is an example.

Creep occurs when a material deforms over a long period of time because of an applied force. An example of creep is the bending of a shelf over time when a heavy object is put on it. Creep may eventually lead to the material fracturing. The application of heat may lead to an increase in creep in a material.

Fatigue is similar to creep. The difference between the two is that fatigue results from the force being applied and then removed repeatedly over a period of time. With metals this results in failure because of metal fatigue.

  • Fracture is an abrupt breaking of the material.
  • Creep is a slow deformation process due to a continuous force over a long time.
  • Fatigue is weakening of the material due to short forces acting many many times.

Elasticity, plasticity, fracture and creep

  1. List the similarities and differences between elastic and plastic deformation.
  2. List the similarities and differences between creep and fracture as modes of failure in material.

Failure and strength of materials

The properties of matter

The strength of a material is defined as the stress (the force per unit cross-sectional area) that it can withstand. Strength is measured in newtons per square metre ( N · m - 2 ).

Stiffness is a measure of how flexible a material is. In Science we measure the stiffness of a material by calculating its Young's Modulus. The Young's modulus is a ratio of how much it bends to the load applied to it. Stiffness is measure in newtons per metre ( N · m - 1 ).

Hardness of a material can be measured by determining what force will cause a permanent deformation in the material. Hardness can also be measured using a scale like Mohs hardness scale. On this scale, diamond is the hardest at 10 and talc is the softest at 1.

Interesting fact

Remembering that the Mohs scale is the hardness scale and that the softest substance is talc will often come in handy for general knowledge quizes.

The toughness of a material is a measure of how it can resist breaking when it is stressed. It is scientifically defined as the amount of energy that a material can absorb before fracturing.

Questions & Answers

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Nomfundo Reply
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Thembi
Ketone
Mpikele
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Ditdot Reply
is a force a internal or external system
Cherish Reply
a force is a external system not internal
Vusimuzi
what is a structural isomer and what is the difference between structural isomer and chain isomer?😥
Mashel Reply
What is Newtons second law in words
Samkelumusa Reply
Guys who's doing Grade 12 physics here?
beatsbyWayBhi
Me
Mpikele
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beatsbyWayBhi
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beatsbyWayBhi
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beatsbyWayBhi
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Mpikele
What is Newtons second law in words?
Samkelumusa
•When a resultant force acts on an object; it causes that object to accelerate in the direction of the net force •This direction is directly propotional to the net force •And inversely propotional to the mass of an object
Sandile
Dankie
Samkelumusa
Anyone who have already wrote the 1st class test?
Gomotsegang
Um Can Anyone Update Me About The First Chapter In Physics Cause At School The Process IS Delaying The Teacher Haven't Arrived Yet
Syanda
Term 1 *Momentum *Vertical Projectile *Newton 2nd Law *Organic Chemistry These are the Chapters for Term one, maybe your teacher might want to start with Chemistry since it's a very long chapter but meanwhile you can start checking those first two
beatsbyWayBhi
Thank You
Syanda
Surecase bro
beatsbyWayBhi
Newtons Second Law State When A Net Force Act On An Object Of A Mass It Accelerates In The Direction Of The Net Force .The Acceleration Is Directly Proportional To The Net Force And Inversely Proportional TO The Mass
Syanda Reply
what is Newton's second law?
Tshilani Reply
When a net force is exerted on an object,the object will accelerate in the direction of the force. The acceleration is directly proportional to the object & inversely proportional to the mass of the object
Mpikele
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Tshilani
rules to naming the IUPAC name
Angel Reply
actually... what is a structural isomer and what is the different between structural isomer and chain isomer ?
Mashel
what are the alkanes
Tumi Reply
methane ethane propane butane pentane hexane heptane octane nonane decane
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Hlogi_
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Lekgotla
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Fanie
what is Newton third law in words
beauty
newtons third law states tht whn body A exerts a force on body B,body B axerts a force of equal magnitude on body A but in opposite direction
Collen
what are the aliphatic compounds
Tumi Reply
Types of collision ad their explanation together with examples
Phuti Reply
what is Definition of length, mass, and time?
Mona Reply
C6H12CLBr WRITE DOWN THE IUPAC NAME OF THE compound
Apex Reply
What is definition of length, mass, and time, within the example and formula?
Mona
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What is impulse and how does it = to momentum
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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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