ME 328 Test 1 Review

Which of the following value for percent elongation is commonly used as a cutoff between a "brittle" material and a "ductile" material

0.05

For a common metal, which of the following represents a realistic value for Poisson's Ratio (select all that apply)?

0.3

At a given point in a tensile test of a specimen with an original cross-sectional area of 50 mm2, the applied force (F) is 500 N. What is the engineering stress at this instant?

10 MPa

The stress-strain curve for an alloy steel is shown below. What is the yield strength as defined by the 0.2% strain offset method in MPa.

1550

The stress-strain curve for an alloy steel is shown below. What is the tensile strength of the steel in MPa.

1950

The equations relating engineering stress and strain to true stress and strain are valid over which of the following regions of strain (select all that apply)?

Below the yield strength of a material & Between the yield strength and the ultimate strength of a material

Which of the following is NOT a common hardness test?

Charpy

The Elastic Modulus (E) of a material depends on which of the following (select all that apply):

Composition

The Yield Strength (σy) of a material depends on which of the following (select all that apply):

Composition & Processing & Microstructure

Which two of the properties listed has the strongest influence on the "toughness" of a material?

Ductility & Yield Strength

In the figure below, each circle represents an atom of a given material. The load F is applied in the second image, and the third image shows the resulting atomic structure once the load has been removed. What type of deformation is the material undergoing in the middle image (select all that apply)?

Elastic & Plastic Deformation

In a tensile test, what property is defined as the specimen elongation (displacement) divided by the original gage length?

Engineering Strain

Two methods are commonly utilized to measure the elongation of a specimen in a tensile test--an extensometer or crosshead displacement. Which of the two methods provides a more accurate measure of the elongation of the gage section (Δl)?

Extensometer

A metal becomes weaker after necking.

False

Each Rockwell Hardness test uses the same shape of indenter. Instead, the forces such as the major load and minor load are varied from one scale to the next.

False

Engineering stress and strain are considered to be a more accurate representation of the mechanical properties than true stress and strain.

False

For a very ductile material, the Modulus of Resilience and the Modulus of Toughness will be very close to the same value.

False

Hardness is a mechanical property that is a measure of a material's resistance to elastic, surface deformation

False

On a tensile tester, force is measured via an extensometer.

False

Tensile specimens A and B are made of the same material and experience the same applied force, F. Because specimen B has a larger cross-sectional area, it experiences the highest stress.

False

The 0.2% offset yield strength is defined as the stress at which a material transitions from linear to non-linear behavior.

False

The Modulus of Toughness (UT) is the ability of a material to absorb energy without yielding.

False

The phenomenon of necking--the rapid reduction of the cross-sectional area of a specimen--occurs prior to reaching the tensile strength of the material.

False

Which of the following is the proper calculation for engineering stress?

Force / Original Area

For a large set of data from an actual tension test, which of the following approaches would be best to calculate the elastic modulus (E)?

Least Square Regression of the linear region

Consider the stress-strain curve for brass shown below. Which is larger for this brass tensile specimen: the modulus of resilience or the modulus of toughness?

Modulus of Toughness

Which of the following are NOT a proper unit for engineering stress (select all that apply)?

Newton

Consider the stress-strain curve for brass shown below. The engineering stress decreases after the tensile strength is reached. Does this mean that the brass (the material itself) is becoming weaker after this point?

No

If a material has a strain hardening exponent of 0, this means that the metal will not experience strain hardening.

No

Consider two cylindrical rods (A and B) with a force F applied in tension. Rod A has a smaller cross-sectional area than rod B. Assuming the same force F is applied to each rod and the rods do not yield, which of the following statements is true about the stress at this point?

Rod A has a larger engineering stress than Rod B

Which of the following are NOT necessary to calculate stress and strain for a specimen undergoing a tensile test (select all that apply)?

Specimen Mass

Hardness is most strongly correlated with which of the following?

Tensile Strength

Which type of loading is typically utilized in a tensile test (select all that apply)?

Tension

The Modulus of Toughness is more closely defined as:

The ability of a material to absorb energy until failure

At small values of strain (e.g. less than 1%), true stress and engineering stress are essentially equal to one another.

True

During plastic deformation, atomic bonds both stretch and slip / break.

True

For a specimen in tension, the true stress will always be greater than or equal to the engineering stress

True

For a theoretical material with a Poisson's Ratio of -0.5, if a specimen of the material was pulled in tension, the cross-sectional area of the specimen would increase.

True

For a very brittle material, the Modulus of Resilience and the Modulus of Toughness will be very close to the same value.

True

In tension, true stress always increases as strain is increased.

True

The Modulus of Resilience (UR) is the ability of a material to absorb energy without yielding.

True

The elastic modulus (E) of a material is defined as the slope of the elastic region of the stress-strain curve.

True

The elastic modulus of a material is a function of the stiffness of the bonds between atoms.

True

The tensile strength of a material is defined as the maximum engineering stress supported by a specimen of the material

True

The yield strength of a material is often found using the 0.2% Strain Offset Method.

True

When a metal is loaded beyond the yield strength and then unloaded, the yield strength of the metal increases.

True

True stress has which of the following defintions?

True Stress = Force / Instantaneous Area

Which property is analogous to the "spring constant" for a material?

Young's Modulus

When plotting the raw data output from a typical tension test, which quantities are typically displayed on each axis

x-axis: Elongation (Δl), y-axis: Force (F)