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Questions and Answers
Why is it important for a professional engineer to select the appropriate type of steel for a specific construction?
Why is it important for a professional engineer to select the appropriate type of steel for a specific construction?
- To simplify the construction process, regardless of material strength.
- To comply with international trade regulations on steel usage.
- To minimize the cost of materials while ensuring the construction is fit for purpose. (correct)
- To ensure the steel matches the aesthetic design of the structure.
A force applied to a body can only change its shape, not its motion.
A force applied to a body can only change its shape, not its motion.
False (B)
What is the defining characteristic of a tensile force?
What is the defining characteristic of a tensile force?
- It causes the material to bend.
- It tends to stretch a material. (correct)
- It tends to slide one part of a material over another.
- It tends to squeeze or crush a material.
What is the unit of force?
What is the unit of force?
Match each type of force with its effect on a material:
Match each type of force with its effect on a material:
In the context of forces acting on a material, what does 'stress' refer to?
In the context of forces acting on a material, what does 'stress' refer to?
What is the correct formula for calculating stress ($\sigma$)?
What is the correct formula for calculating stress ($\sigma$)?
The unit of stress is the ______, which is equivalent to $1 N/m^2$.
The unit of stress is the ______, which is equivalent to $1 N/m^2$.
The cross-sectional area used in calculating tensile stress is the area parallel to the applied force.
The cross-sectional area used in calculating tensile stress is the area parallel to the applied force.
What does 'strain' measure in the context of material properties?
What does 'strain' measure in the context of material properties?
What is the formula for calculating strain ($\epsilon$)?
What is the formula for calculating strain ($\epsilon$)?
Strain is a ______ quantity.
Strain is a ______ quantity.
Percentage strain is calculated by multiplying the strain by 100.
Percentage strain is calculated by multiplying the strain by 100.
Which material property is defined as the ability to return to its original shape and size after the removal of external forces?
Which material property is defined as the ability to return to its original shape and size after the removal of external forces?
What term describes the property of a material being permanently deformed by a force without breaking?
What term describes the property of a material being permanently deformed by a force without breaking?
What is 'Hooke's law'?
What is 'Hooke's law'?
Young's modulus of elasticity is the constant of proportionality between ______ and ______ within the limit of proportionality.
Young's modulus of elasticity is the constant of proportionality between ______ and ______ within the limit of proportionality.
What does a high value of Young's modulus indicate about a material?
What does a high value of Young's modulus indicate about a material?
If a material is stretched beyond its limit of proportionality, what behavior can it exhibit?
If a material is stretched beyond its limit of proportionality, what behavior can it exhibit?
A material that has passed its elastic limit will always return to its original length when the applied force is removed.
A material that has passed its elastic limit will always return to its original length when the applied force is removed.
Which term describes the ability of a material to be plastically deformed by elongation, without fracture?
Which term describes the ability of a material to be plastically deformed by elongation, without fracture?
What is a key characteristic of brittle materials under tensile testing?
What is a key characteristic of brittle materials under tensile testing?
What property describes a material's ability to be shaped when cold by hammering or rolling?
What property describes a material's ability to be shaped when cold by hammering or rolling?
Lead is an example of a ductile material
Lead is an example of a ductile material
What is the effect on a bar of length L which has a coefficient of linear expansion **, that is subjected to a temperature rise of T?
What is the effect on a bar of length L which has a coefficient of linear expansion **, that is subjected to a temperature rise of T?
If expansion is prevented, what does thermal stress equal?
If expansion is prevented, what does thermal stress equal?
A steel prop is used to stabilise a building, the compressive stress in the bar is 30 MPa. What will be the effect if the temperature of the building increases?
A steel prop is used to stabilise a building, the compressive stress in the bar is 30 MPa. What will be the effect if the temperature of the building increases?
If a bar are not constrained, so that it can expand freely, there will be thermal stress
If a bar are not constrained, so that it can expand freely, there will be thermal stress
If solid bar 1 is firmly attached to outer concentric bar 2, and it undergoes a temperature change what is a compatibility consideration?
If solid bar 1 is firmly attached to outer concentric bar 2, and it undergoes a temperature change what is a compatibility consideration?
What are the formula obtained by equilibrium considerations?
What are the formula obtained by equilibrium considerations?
In a tensile test, the specimen is made to standard shapes and sizes
In a tensile test, the specimen is made to standard shapes and sizes
In a typical load/extension graph for a mild steel specimen, which point represents the limit of proportionality?
In a typical load/extension graph for a mild steel specimen, which point represents the limit of proportionality?
On a load/extension graph for a tensile strength test. What does the yield stress give an indication of?
On a load/extension graph for a tensile strength test. What does the yield stress give an indication of?
Which formula is used to determine the ultimate tensile strength (UTS) of a specimen?
Which formula is used to determine the ultimate tensile strength (UTS) of a specimen?
What material property does an increase in the percentage reduction in area relate to?
What material property does an increase in the percentage reduction in area relate to?
When materials such as aluminium alloy and titanium, do not exhibit a definite yield point in their stress-strain curves. Then how can their equivalent yield stresses determined?
When materials such as aluminium alloy and titanium, do not exhibit a definite yield point in their stress-strain curves. Then how can their equivalent yield stresses determined?
It is reasonable to use a value that is twice that for the stress at the limit of proportionality as the stress at the elastic limit.
It is reasonable to use a value that is twice that for the stress at the limit of proportionality as the stress at the elastic limit.
Match key stresses to their description:
Match key stresses to their description:
Which has both magnitude and direction?
Which has both magnitude and direction?
The centre of gravity refers to:
The centre of gravity refers to:
When forces all acting in the same plane, but not at the same time, they are called coplanar.
When forces all acting in the same plane, but not at the same time, they are called coplanar.
Flashcards
What is elasticity?
What is elasticity?
The quantity expressing the ability of a material to return to its original shape after deformation.
What is Stress?
What is Stress?
The force per unit cross-sectional area within a material.
What is Strain?
What is Strain?
How much a material deforms under stress, expressed as change in dimension over original dimension.
What is Tensile force?
What is Tensile force?
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What is Compressive Force?
What is Compressive Force?
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What is Shear Force?
What is Shear Force?
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What is Limit of Proportionality?
What is Limit of Proportionality?
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What is Stiffness?
What is Stiffness?
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What is Ductility?
What is Ductility?
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What is Brittleness?
What is Brittleness?
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What is Malleability
What is Malleability
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What is Hooke's Law?
What is Hooke's Law?
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What is Young's Modulus?
What is Young's Modulus?
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What is Load/Extension graph?
What is Load/Extension graph?
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What is Elastic limit?
What is Elastic limit?
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What is waist/Neck?
What is waist/Neck?
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thermal stresses?
thermal stresses?
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What is Compound bar?
What is Compound bar?
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What is Proof Stress?
What is Proof Stress?
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What is Scalar?
What is Scalar?
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What is Vectors?
What is Vectors?
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What is Coplanar forces?
What is Coplanar forces?
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What is Concurrent
What is Concurrent
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What are different ways of determining coplaner forces?
What are different ways of determining coplaner forces?
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What is equilibriam?
What is equilibriam?
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What is stable equiblibriam?
What is stable equiblibriam?
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What is unstable equilibriam?
What is unstable equilibriam?
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What is neutral equilibriam?
What is neutral equilibriam?
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Study Notes
Effects of Forces on Materials
- A good understanding of material properties is essential in engineering, particularly in mechanical, manufacturing, aeronautical, civil, and structural fields.
- Steels for submarine pressure hulls are about five times stronger than those used in building construction.
- Engineers need to consider both the performance and cost of materials in construction and manufacturing.
Introduction to Force
- Applying force causes a change in a body's shape or motion or dimensions.
- The unit of force is the newton (N).
- Changes in dimensions from applied forces are often imperceptible.
Mechanical Forces
- 3 types of mechanical force can act on a body :- tensile, compressive, and shear.
Tensile Force
- Tension is a force stretching a material
- Examples include a crane rope holding a load, stretched rubber bands, and a tightened bolt.
- Tensile force increases the length of a material
Compressive Force
- Compression is a force squeezing/crushing a material
- Examples include a bridge support pillar, the sole of a shoe, and a crane jib.
- Compressive force decreases the length of a material
Shear Force
- Shear force slides one face of a material over an adjacent face.
- Examples include a rivet holding plates, a guillotine cutting metal, and forces on beams or transmission joints.
- Shear force can bend, slide, or twist material.
Defining Stress
- Stress is the ratio of applied force (F) to cross-sectional area (A)
- Represented by σ (Greek letter sigma), measured in Pascals (Pa) where 1 Pa = 1 N/m².
- Tensile and compressive forces use cross-sectional area at right angles to the force direction.
- Shear force uses cross-sectional area parallel to the force direction
- The Greek letter tau, Ï„, symbolizes shear stress
Defining Strain
- Strain is the fractional change in a material's dimension due to force
- For tensile/compressive forces, it's the ratio of length change to original length
- Represented by ε (Greek epsilon)
- Calculated as ε = x/L, where x is the change in length and L is the original length.
- Strain is dimensionless but often expressed as a percentage
- For shear force, strain is symbolized by y (Greek letter gamma)
Elasticity and Plasticity
- Elasticity describes a material's ability to return to its original shape after forces are removed.
- Plasticity is when a material is permanently deformed by a force without breaking.
- Examples of elastic materials: mild steel, copper, polythene and rubber (within load limits).
- Examples of plastic materials: lead and plasticine
Hooke's Law
- Hooke's Law states that within the limit of proportionality, extension is proportional to applied force.
- Mathematically, stress = (a constant) × strain.
Young's Modulus
- Young's modulus of elasticity (E) is the constant of proportionality between stress and strain.
- Represents a materials stiffness - its resistance to deformation under stress.
- E is expressed in Pascals
- E = stress/strain
Stiffness
- Material stiffness relates to Young's modulus: higher E implies higher stiffness
- Material stiffness is force divided by extension
Thermal Stress and Strain
- Thermal strain (ε) from temperature change (T) is ε = αT (where α is the coefficient of linear expansion).
- Thermal stress (σ) is σ = –αTE.
- If expansion is prevented, compressive stress develops
Compound Bars
- Compatibility means considering displacements when analysing compound bars.
- Equilibrium must also be considered
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