Materials Flashcards
State hooke’s law (2)
-The extension of a material is proportional to the load applied to it provided limit of proportionality is not reached
-F=KL
State 3 points which could determine if the material/graph follows hooke’s law (3)
-linear relationship = stress proportional to strain
-young Modulas
-no permemant deformation = after load is removed the material returns to its original shape
Define young modulus (2)
-is a property of material that measures its stiffness or how it responds to deformation
-stress/strain
State 3 main types of mechanical forces that act on a body (3)
1 tensile force
2 compressive
3 shear
Define tensile force (1)
- a force that tends to stretch a material
- increases the length of the material
Define compressive force (2)
- a force that tends to squeeze or crush a material
-will decrease the length of the material
Define shear force (4)
-a force that tends to slide on force of the material over an adjacent force
-shear stress occurs when the forces are not co planar
-the area on which the stress acts is parallel
-shear force causes a material to bend, slide or twist
Define stress (2)
-the ratio between force to cross sectional area of the material
-force/area
Define strain (2)
-the fractional change in a dimension of a material produced by a force
- change in length/ original length
State formula for percentage strain (1)
Change in length / original length x 100
State formula for area of wire (1)
(Pie x d2)/ 4
Convert 1mm2 to m2 (1)
1mm2 = 1x10-6 m2
State formula for shear modulus (1)
Shear stress/shear strain
Define elasticity and give examples (3)
-is the ability of a material to return to its original shape and size on the removal of external forces
-example= lead, plasticine
What type of energy is used in elasticity (2)
If deformation is elastic, all the work is stored as elastic strain energy in the material
Define limit of proportionality (3)
-the point on the graph where extension is no longer proportional to the applied force
-it is the point where the material stops obeying hooke’s law
-just beyond this point the material can behave in a non linear elastic manner
Define non linear elastic manner (1)
The relationship between stress and strain is not proportional
Define linear elasticity (1)
When the material obeys Hooke’s law so stress and strain are proportional
Explain what plasticity means and give examples (3)
-is the property of a material of being permanently deformed by a force without breaking
-it’s when a material does not return no it’s original shape when load is removed
-examples= copper, rubber, polyethene
State the energy transfer when plastic deformation occurs (1)
-if deformation is plastic, work is done to separate the atoms and energy is mostly dissipated as heat
How is plastic deformation used in real like scenarios (3)
-transport design
-crumple zones are designed to deform plastically in a crash
-energy goes into changing the shape of the vehicle
Define elastic limit (2)
-if the applied force is large it is found that material has become plastic and no longer returns back to its original length even after load is removed
-object passed the elastic limit shows plastic deformation
State and explain the behavior of ductile materials and give examples: (3)
-is the ability of a material to be plastically deformed by elongation without fracture
-it enables a material to be drawn out into wires
-examples: mild steel,copper,gold
State and explain the behavior of brittle materials and give examples: (4)
-is a property of a material that can easily break without bending or stretching it
-they have no plastic state
-elastic state followed by immediate failure
-example: glass,concrete,bricks
State and explain the behavior of malleable materials and give examples: (3)
-property of a material where it can be shaped when cold by hammering or rolling it
-capable of undergoing plastic deformation without fracture
-example: lead,gold
State and example the key differences between brittle and ductile materials: (4)
1)Plastic deformation:
Ductile : undergo plastic deformation before failure
Brittle: fractures before undergoing plastic deformation
2) yield point:
Ductile: They have a yield point, they can be stretched or bent without fracture
Brittle: do not show yield point
3) deformation:
Ductile: undergo a lot of deformation before fracture
Brittle: undergo very little or no deformation before fracture
4) toughness:
Ductile: High toughness, they can absorb a lot of energy before fracture
Brittle: Low toughness, they can’t absorb energy before fracture
How can stiffness of a material be determined (1)
By finding the gradient also called as the young modulus = stress/strain
Define yield (1)
The point where the material starts to suddenly stretch without any extra load
Define strength (1)
-measure of resistance of material to deform
How is strength of materials determined (1)
-determined by reading of the ultimate tensile strength also called as breaking stress off the graph
Define UTS or breaking stress (1)
The maximum stress a material can withstand
Define toughness (1)
Measure of the materials ability to absorb energy (using charpys test to measure)
Outline the method of charpys test (3)
-consist of striking a suitable specimen with a hammer on a pendulum arm while the specimen is held securely at each end
-the hammer strikes opposite the notch
-the energy absorbed by the specimen is determined by precisely measuring the decrease in motion of the pendulum arm
Define creep (2)
-it is a high temprature progressive deformation at constant stress.
-it depends on time and temperature
What is creep test used to evaluate (2)
-it is used to evaluate materials for boilers, gas, turbines, jet engines and ovens or any application that involves Hugh temperature under load
-it gives critical data for designing safe and reliable structures in industries where high temperature and stress are common
State the types of advanced materials (4)
-ceramics
-semiconductors
-polymers
-composites
State the types of engineering materials (5)
-semiconductor
-ceramics
-metals
-polymers
-composites
State the structure of metals (2)
-atoms in metals are arranged in a regular, orderly pattern and vibrate in their fixed spaces
State the properties of metals (3)
-conduct electricity
-strong
-ductile
Define ceramics and state examples (2)
-ceramics are compounds formed between metallic and non metallic elements
-most frequently oxides, nitrides like Silicon dioxide, Aluminium oxide
What does traditional ceramics mean (1)
-those compounds of clay minerals as well as cement and glass
State the properties of ceramics (4)
-stiff
-hard
-brittle
-insulators
What does polymers mean, define it (2)
-include familiar plastic and rubber materials
-many of them are organic compounds that are chemically based on carbon, hydrogen and other non metallic elements
What are the properties of polymers (4)
-lightweight
-ductile
-easily processed
-insulators
Define composites and state its properties (2)
-a composite is composed of 2 or more individual materials (metals,ceramics,polymers)
-light and strong
Why do industries use ceramics, what is the goal of it (2)
- is to achieve a combination of properties that is not displayed by any single material
-to incorporate the best characteristics of each of the component materials
State an example of ceramics and explain (4)
Fiberglass
-glass fibers are embedded within a polymer.
-the glass fibers are relatively strong and stuff but also brittle
-whereas the polymer is ductile but also weak and flexible
-which makes fiberglass relatively stiff,strong,flexible and ductile
State the properties of ceramics (3)
-lightweight
-low density
-strong
-excellent thermal properties
Define advance materials (2)
-materials that are used in high technology application
-which include semiconductors, biomaterials, smart materials
State and explain the properties of semiconductors (2)
-electrical properties that are intermediate between electrical conductors and insulators
explain crystalline material (1)
-atoms are self organized in a periodic array
Explain single crystal (1)
-atoms are in a repeating or periodic array over the entire extend of the material
Explain polycrystalline material (1)
-comprised of many small crystals or grains
Explain amorphous (1)
-lacks a systematic atomic arrangement
Which materials are used for making a laptop, can be multiple (3)
Composites: some may use composite materials as they are created by 2 or more materials with different properties
-because it’s high strength and light weight
Polymers: used for various part of the laptop including the keyboard
-because it’s light weight and durable
Metals : for structural components and casings
-because they are durable and High strength
Define modulus of elasticity (2)
-the modulus of elasticity measures an objects resistance to being deformed when stress is applied on it
E = stress/strain
