classifying load
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Transcript of classifying load
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Normal Load (Axial load) : Load is perpendicular to the
supporting material.
- Tension Load: As the ends of material are pulled apart
to make the material longer, the load is called a tension
load.
- Compression Load: As the ends of material are pushed into make the material smaller, the load is called
a compression load.
Tension
Compression
Classifying Load
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Shear Load : Tangential load
Classifying Load (cont)
pulling apart
Pressure
Cargo
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Stress-Strain Diagram
A plot of Strain vs. Stress.
The diagram gives us the behavior of the material and
material properties.
Each material produces a different stress-strain
diagram.
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Strain ( ) (e/Lo)
41
2
3
5
Elastic
Region
Plastic
Region
Strain
Hardening Fracture
ultimatetensile
strength
Elastic region
slope=Youngs(elastic) modulus
yield strength
Plastic regionultimate tensile strength
strain hardening
fracture
necking
yieldstrength
UTS
y
12
y
E
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Stress-Strain Diagram (cont)
Elastic Region(Point 12)
- The material will return to its original shape
after the material is unloaded( like a rubber band).
- The stress is linearly proportional to the strain in
this region.
E
: Stress
E : Elastic modulus(Youngs Modulus)
: Strain (in/in)
E or
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Plastic Region(Point 23)
- If the material is loaded beyond the yield strength,
the material will not return to its original shape
after unloading.- It will have some permanent deformation.
- If the material is unloaded at Point 3, the curve will
proceed from Point 3 to Point 4. The slope will bethe as the slope between Point 1 and 2.
- The distance between Point 1 and 4 indicates the
amount of permanent deformation.
Stress-Strain Diagram (cont)
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Strain Hardening
- If the material is loaded again from Point 4, the
curve will follow back to Point 3 with the same
Elastic M odulus(slope).- The material now has a higher yield strength of
Point 4.
- Raising the yield strength by permanently strainingthe material is called Strain Hardening.
Stress-Strain Diagram (cont)
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Tensile Strength(Point 3)- The largest value of stress on the diagram is called
Tensi le Strength(TS)orUltimate Tensile Strength
(UTS)
- It is the maximum stress which the material can
support without breaking.
Fracture(Point 5)
- If the material is stretched beyond Point 3, the stressdecreases as necking and non-uniform deformation
occur.
- Fracture will finally occur at Point 5.
Stress-Strain Diagram (cont)
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A36 Steel
Stress and Strain Diagram
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Material Properties
Strength
Hardness
Ductility
Brittleness
Toughness
Characteristics of Material are described as
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1) Strength
- Measure of the material property to resist deformation
and to maintain its shape
- It is quantified in terms of yield stress or ultimate tensile
strength.
- High carbon steels and metal alloys have higher strength
than pure metals.
- Ceramicalso exhibit high strength characteristics.
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2) Hardness
- Measure of the material property to resist indentation,
abrasion and wear.
- It is quantified by hardness scale such as Rockwell and
Brinell hardness scale.
- Hardness and Strength correlate well because both
properties are related to in-molecular bonding.
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3) Ductility- Measure of the material property to deform before failure.
- It is quantified by reading the value of strain at the
fracture point on the stress strain curve.
- Example of ductile material :
low carbon steel
aluminum
bubble gum
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4) Brittleness
- Measure of the materials inabilityto deform before failure.
- The opposite of ductility.
- Example of brittle material : glass, high carbon steel,
ceramics
Ductile
Brittle
Strain
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5) Toughness-Measure of the material ability to absorb energy.
-It is measured by two methods.
a) Integration of stress strain curve
- Slow absorption of energy
-Absorbed energy per unit volume
b) Charpy test
- Impact toughnesscan be measured.
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- Charpy V-Notch Test
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Charpy V-Notch Test (continued)
- The potential energy of the pendulum before and after
impact can be calculated form the initial and final location
of the pendulum.
- The potential energy difference is the energy it took to
break the material. absorbed during the impact.
- Charpy test is an impact toughnessmeasurement test
because the energy is absorbed by the specimen very
rapidly.
- Purpose : to evaluate the impact toughness as a function of
temperature
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Charpy V-Notch Test (continued)
Temperature (F)Charp
yToughness(lbin)
Brittle
Behavior
Ductile
Behavior
Transition
Temperature
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Charpy V-Notch Test (continued)
- At low temperature, where the material is brittle and
not strong, little energy is required to fracture the material.
-At high temperature, where the material is more ductileand stronger, greater energy is required to fracture the
material
-The transition temperatureis the boundary between brittle
and ductile behavior.
The transition temperature is an extremely important
parameter in selection of construction material.
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High Carbon Steel
Charpy Test
Stainless Steel
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6) Fatigue
The repeated application of stress typically produced by
an oscillating load such as vibration.
Sources of ship vibration are engine,propeller andwaves.
Cycles N at Fatigue Failure
Steel
Aluminum
Endurance Limit: A certain threshold
stress which will not cause the fatigue
failure for the number of cycles.
Aluminum has no endurance limit
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Factors effecting Material Properties
Temperature :
Increasing temperature will decrease
- Modulus of Elasticity
- Yield Strength
- Tensile Strength
Decreasing temperature will:
- decrease ductility
- increase brittlenessEnvironment
- Sulfites, Chlorine, Oxygen in water, Radiation
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