Materials Chapter 6 Recitation Questions

What does yield strength in a material indicate?

The stress level at which plastic deformation begins

What is the typical unit of measurement for stress?

Pascal (Pa)

In a stress-strain curve, what does the area under the curve up to the yield point represent?

Resilience

Which property measures a material's resistance to surface deformation?

Hardness

What type of deformation is non-permanent and reversible in metals?

Elastic deformation

Poisson's ratio is the ratio of which two types of strain?

Lateral strain to axial strain

What is the typical behavior of metals during plastic deformation?

They experience permanent deformation

What happens at the tensile strength point in a stress-strain curve?

The material begins to neck and then fracture

Which test measures a material's resistance to indentation and is often used to assess hardness?

Brinell hardness test

Why are safety factors used in design?

To ensure a margin against unanticipated failure

Which of the following best describes toughness in materials?

The energy absorbed by a material before fracture

What is the relationship between stress and strain in the elastic region of a material?

Stress is proportional to strain

What does the modulus of elasticity (Young's modulus) measure?

The stiffness of a material in the elastic region

In which type of deformation do atoms return to their original positions once the load is removed?

Elastic deformation

What is the primary factor influencing a material's ability to resist plastic deformation?

Yield strength

Which of the following statements is true regarding ductility?

Ductility is measured by percent elongation and reduction in area

What does the term "ultimate tensile strength" (UTS) refer to?

The maximum stress a material can withstand in tension

Which property is most closely associated with a material's resistance to indentation or scratching?

Hardness

Which mechanical test is commonly used to determine the modulus of elasticity?

Tensile test

Why does necking occur in a tensile test of a ductile material?

Due to strain-hardening followed by localized plastic deformation

If a metal rod originally 100 mm long stretches to 105 mm under tensile stress, what is the engineering strain?

0.05

A material with a high modulus of resilience is best suited for which application?

As a spring material

Which of the following materials is expected to have the highest hardness?

Tungsten carbide

In a tensile test, which term describes the permanent deformation after the load is removed?

Plastic strain

A sample undergoes a 3% reduction in area under tensile stress before fracture. Which property does this indicate?

Low ductility

Which of the following best describes why ceramics have low tensile strength?

They are brittle with many surface flaws

What is Poisson's ratio if a metal sample experiences a lateral strain of -0.002 and an axial strain of 0.004?

0.5

A steel bar with a yield strength of 300 MPa is subjected to a load of 6000 N. What minimum cross-sectional area is required to prevent yielding?

20 mm²

A steel beam is required to support a load of 50,000 N without yielding. If the yield strength of the steel is 250 MPa, and a safety factor of 3 is applied, what is the minimum required cross-sectional area for the beam?

0.6 cm²

Which of the following best describes simple tension?

A force applied along the length of the material, stretching it

In which of the following scenarios would you expect to encounter biaxial tension?

A thin metal sheet being pulled equally in two perpendicular directions

What type of stress occurs when a material is submerged underwater, experiencing equal pressure from all directions?

Hydrostatic compression

Which of the following situations is an example of shear stress?

A metal bar twisted by applying a torque at both ends

A column in a building under the weight of the structure above is experiencing which type of stress?

Simple compression

Which property is directly determined from the slope of the initial linear portion of a stress-strain curve in a tension test?

Modulus of elasticity

During a tension test, which point on the stress-strain curve indicates the onset of plastic deformation?

Yield point

If a sample elongates significantly before breaking during a tension test, which property is it demonstrating?

High ductility

What is necking in a tension test?

A localized reduction in cross-sectional area before fracture

In a typical tensile test, which quantity is calculated by dividing the applied force by the original cross-sectional area?

Engineering stress

Which of the following statements is true about engineering strain in a tensile test?

It is the change in length divided by the original length

In a tensile test, a material with a high modulus of elasticity is expected to:

Be very stiff and resist initial deformation

Which of the following materials typically has the highest Young's modulus?

Diamond

Between metals and polymers, which material family generally has a higher yield strength?

Metals

Which material is expected to have the lowest tensile strength?

High-density polyethylene (HDPE)

Comparing ceramics to metals, which of the following statements is true about their Young's modulus?

Ceramics often have a higher Young's modulus than many metals

Which material would generally have the highest ratio of tensile strength to density, making it ideal for lightweight structural applications?

Carbon fiber composite

Compared to metals, how do polymers generally perform in terms of yield strength and Young's modulus?

Polymers have lower yield strength and lower Young's modulus

What happens to a material's strength in the strain hardening region of a stress-strain curve?

The material's strength increases as it undergoes plastic deformation

Which part of the stress-strain curve represents the strain hardening region?

The region immediately after the yield point up to the ultimate tensile strength

In the context of strain hardening, which of the following is true about dislocations within the material?

Dislocations increase, making further plastic deformation more difficult

Which of the following best describes the relationship between stress and strain during the strain hardening region?

Stress continues to increase with strain, but non-linearly

What does the strain hardening exponent (n) describe in a material?

The rate at which stress increases with strain in the strain hardening region

If the strain hardening exponent n=0, what does this indicate about the material?

The material exhibits no strain hardening and deforms plastically without increasing strength

How does the strain hardening exponent (n) affect the shape of the stress-strain curve in the plastic region?

A higher n value results in a steeper curve in the plastic region

In the Brinell hardness test, which type of indenter is typically used?

A steel or carbide ball