# 7.1 Failure and strength of materials  (Page 3/3)

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## Alloying

An alloy is a mixture of a metal with other substances. In other words, alloying involves adding impurities to a metal sample. The other substances can be metal or non-metal. An alloy often has properties that are very different to the properties of the substances from which it is made. The added substances strengthen the metal by preventing dislocations from spreading. Ordinary steel is an alloy of iron and carbon. The carbon impurities trap dislocations. There are many types of steel that also include other metals with iron and carbon. Brass is an alloy of copper and Zinc. Bronze is an alloy of copper and tin. Gold and silver that is used in coins or jewellery are also alloyed.

## Tempering

Tempering is a process in which a metal is melted then quickly cooled. The rapid cooling is called quenching. Usually tempering is done a number of times before a metal has the correct properties that are needed for a particular application.

## Sintering

Sintering is used for making ceramic objects among other things. In this process the substance is heated so that its particles stick together. It is used with substances that have a very high melting point. The resulting product is often very pure and it is formed in the process into the shape that is wanted. Unfortunately, sintered products are brittle.

## Steps of roman swordsmithing

• Purifying the iron ore.
• Heating the iron blocks in a furnace with charcoal.
• Hammering and getting into the needed shape. The smith used a hammer to pound the metal into blade shape. He usually used tongs to hold the iron block in place.
• Reheating. When the blade cooled, the smith reheated it to keep it workable. While reheated and hammered repeatedly.
• Quenching which involved the process of white heating and cooling in water. Quenching made the blade harder and stronger. At the same time it made the blade quite brittle, which was a considerable problem for the sword smiths.
• Tempering was then done to avoid brittleness the blade was tempered. In another words it was reheated a final time to a very specific temperature. How the Romans do balanced the temperature? The smith was guided only by the blade's color and his own experience.

## Failure and strength of materials

1. List the similarities and differences between the brittle and ductile modes of failure.
2. What is meant by the following terms:
1. vacancies
2. dislocations
3. impurities
4. grain boundaries
3. What four terms can be used to describe a material's mechanical properties?
4. What is meant by the following:
1. cold working
2. annealing
3. tempering
4. introduction of impurities
5. alloying
6. sintering

## Summary

1. Hooke's Law gives the relationship between the extension of a spring and the force applied to it. The law says they are proportional.
2. Materials can be classified as plastic or elastic depending on how they respond to an applied force.
3. Materials can fracture or undergo creep or fatigue when forces are applied to them.
4. Materials have the following mechanical properties to a greater or lesser degree: strength, hardness, ductility, malleability, brittleness, stiffness.
5. Materials can be weakened by have the following problems in their crystal lattice: vacancies, dislocations, impurities, difference in grain size.
6. Materials can have their mechanical properties improved by one or more of the following processes: cold working, annealing, adding impurities, tempering, sintering.

## End of chapter exercise

1. State Hooke's Law in words.
2. What do we mean by the following terms with respect to Hooke's Law?
1. elastic limit
2. limit of proportionality
3. A spring is extended by 18 cm by a force of 90 N. Calculate the spring constant for this spring.
4. A spring of length 8 cm stretches to 14 cm when a load of 0,8 N is applied to it.
1. Calculate the spring constant for the spring.
2. Determine the extension of the spring if a load of 0,7 N is applied to it.
5. A spring has a spring constant of $-150$  N.m ${}^{-1}$ . By how much will it stretch if a load of 80 N is applied to it?
6. What do we mean by the following terms when speaking about properties of materials?
1. hardness
2. toughness
3. ductility
4. malleability
5. stiffness
6. strength
7. What is Young's modulus?
8. In what different ways can we improve the material properties of substances?
9. What is a metal alloy?
10. What do we call an alloy of:
1. iron and carbon
2. copper and zinc
3. copper and tin
11. Do some research on what added substances can do to the properties of steel. Present your findings in a suitable table.

25 element of physics
an object will remain at rest or move at a constant velocity unless acted upon a net force
thank you
Thabiso
law of inertia
Joan
an object resisting the change in velocity.
Thabiso
What is a molecule
a molecule is a simplest structure unite of an elements
Else
thank you
Thabiso
Plz remind me the 1st Newton's law
Thabiso
Define the term functinal group of an organic compound
a single atom or a group of atoms which is responsible for the property and function of an organic compound
Shandre
thanks😊
Kamvelihle
What's the relationship between intensity and the current?
yu are Spi.ke spanish hola ele
Rolamf
cómo se llama el video donde disquete salgo yo
Rolamf
The intensity doesn't effect the current.
Mosa
what does the word emitted mean?
to be ejected or released
Khathutshelo
Ok thanks
Mwinga
Released
Mosa
what are the hooke laws
what's that
Mosa
what do really asked in exam
questions
Kamvelihle
lmaooo
itsssjust
Which equation do u wanna balance
Rifumo
i tried to write it but my phone just can't write it Cr2 O72-(aq) + H2S (aq) Cr3 (aq) + S(s)
Brian
show is the equation
Pride
us
Pride
hello. what is the difference between a primary, secondary and tertiary alcohol
primary the C=bonded to 1 Carbon atom.... secondary=bonded to 2 carbon atoms tertiary=bonded to 3 carbon atoms
Christina
Christina
thanks Christina
Baningi
My pleasure
Christina
Thank you Christina. This is very helpful 😀👍👍💯
Thokozani
💯💯
Thokozani
Anytime Thokozani
Christina
How to calculate pH?
Thabo
thank you guys i didn't know about the primary, secondary and tertiary alcohols
Brian
thank you Christina
Brian
Hey guys which topic does AC nd DC generator falls
Phumelele
electrodynamics
Christina
thank you
Phumelele
can somebody help me with functional isomers
function isomer has the same molecular formula but different functional group
Thokozani
what's momentum
the product of an objects mass times velocity. it is mainly prevalent in collisions.
tyrique
momentum
Sesethu
in order to produce an interference pattern, the waves used must be what?
Methane contains C and H. This compound is
ketones's functional group
Why does the carboxyl group have acidc properties?
carboxylic acids
tyrique