MechEMat quiz 2

The largest possible value for Poisson's ratio is _______.

0.5

For the stress-strain diagram, which region or point represents elastic behavior?

1

Select the philosophies that address safety in current engineering design practice for structures and machines.

1. allowable stress design 2. load and resistance factor design

Select the general kinds of limit states that apply to structures.

1. strength limit states 2. serviceability limit states

Robert Hooke observed "as the stretch, so the force" in what year?

1678

For the stress-strain diagram, which region or point represents yielding?

2

For the stress-strain diagram, which region or point represents ultimate strength?

4

For the stress-strain diagram, which region or point represents necking?

5

For the stress-strain diagram, which region or point represents fracture?

6

Three bars made of the same material have equal lengths and applied loads. Which bar will elongate the most due to the applied load?

A solid bar with an outside diameter of 8 mm

Three bars made of the same material have equal lengths. Which bar will deform the most due to a 200°C temperature change?

All three bars will elongate the same amount.

Which of the following are not considered live loads? Select all that apply.

Columns, support beams, and plumbing

What are the general types of loads that act on buildings?

Dead, wind, live, and snow loads

Axial deformation in a bar loaded in the axial direction can be reduced by which of the following?

Decreasing the length

_______ means that a material returns to its original dimensions during unloading.

Elasticity

Using the average properties found in the appendix, compare the modulus of elasticity of steel and aluminum.

Esteel > Ealuminum

Using the average properties found in the appendix, compare the modulus of elasticity of steel and plastics.

Esteel > Eplastics

A ductile material will typically fracture at the ultimate strength.

False

According to Saint-Venant's Principal, the stress is uniform where a load is applied on an axial member.

False

All strains in a tension-test specimen that has exceeded the yield point will be fully recovered after the load is removed.

False

Consider a rectangular bar subjected to an axial tension force P. Stress will become less uniformly distributed throughout the bar as the distance from the applied load P increases.

False

Design provisions in ASD are based on probability concepts.

False

Engineering stress accounts for the reduction in a specimen's cross-sectional area during a tension test.

False

Factor-of-safety calculations are limited to stresses.

False

For most metals, Poisson's ratio has a value between 3 and 4.

False

In ductile materials, the fracture stress is typically larger than the ultimate strength.

False

In ductile materials, the yield stress is typically larger than the ultimate strength.

False

It is likely that the largest snow load would occur at the same moment as the extreme wind load and the extreme live load.

False

LRFD focuses on loads that exist at normal or typical conditions, termed service loads.

False

Live loads are loads that are always present in a structure, i.e. self weights.

False

Load-deformation plots are more useful than stress-strain plots.

False

Many brittle materials break in what is termed a cup-and-cone fracture, whereas ductile materials often fracture on a flat surface that is oriented perpendicular to the tensile axis.

False

Material strengths do not change over time due to corrosion.

False

Necking occurs in brittle materials, but not in ductile materials.

False

One way to decrease the strength of a material by stretching and relaxing is called work hardening.

False

Snow loads are known with great certainty.

False

The Poisson effect exhibited by materials causes additional stress in the lateral direction.

False

The initial portion of the stress-strain diagram for most materials used in engineering structures is slightly curved.

False

There is no uncertainty associated with a material used in a structure or machine.

False

Thermal strains should be included in the Poisson's ratio calculation.

False

Typical factors of safety range from 300 to 400.

False

Wind loads are known with great certainty.

False

Axial deformation in a bar loaded in the axial direction can be reduced by which of the following?

Increasing the cross-sectional area

Axial deformation in a bar loaded in the axial direction can be reduced by which of the following?

Increasing the modulus of elasticity

What mechanical considerations do we focus on in mechanics of materials? Select all that apply.

Stiffness, stability, and strength

A structural component is typically considered to have failed if it yields.

True

ASD focuses on loads that exist at normal or typical conditions, termed service loads.

True

Components designed with LRFD should have an acceptably small, but quantifiable, probability of failure.

True

Consider a rectangular bar subjected to an axial tension force P. Stress will become more uniformly distributed throughout the bar as the distance from the applied load P increases.

True

Design provisions in LRFD are based on probability concepts.

True

Engineers seek to produce objects that are sufficiently strong to safely perform their intended function.

True

Factors of safety are established by groups of experienced engineers who write the codes and specifications used by other designers.

True

For most metals, Poisson's ratio has a value between 1/4 and 1/3.

True

For wood, there may be substantial variation in the strength and stiffness of individual boards.

True

Impact loads are typically larger than if the same object was slowly added to the structure.

True

In ductile materials, the fracture stress is typically smaller than the ultimate strength.

True

In ductile materials, the yield stress is typically smaller than the ultimate strength.

True

In order to find the shear stress on a pin in a member, you should use the resultant force on that pin.

True

In professional practice, design procedures must make allowances for many factors that cannot be quantified with great certainty.

True

It is not likely that the largest snow load would occur at the same moment as the extreme wind load and the extreme live load.

True

It is the engineer's responsibility to select and apply the appropriate factor of safety for each design.

True

Many ductile materials break in what is termed a cup-and-cone fracture, whereas brittle materials often fracture on a flat surface that is oriented perpendicular to the tensile axis.

True

Many of the solutions involving the mechanics of materials approach are approximate.

True

Necking occurs in ductile materials, but not in brittle materials.

True

Normal stresses near a discontinuity may be several times the average stress.

True

One way to increase the strength of a material by stretching and relaxing is called work hardening.

True

Serviceability limit states consider excessive deflections, vibrations, and cracking.

True

Structures and machines are designed to withstand loads above what would be expected under ordinary conditions.

True

The Poisson effect applies only to strains caused by stresses.

True

The information obtained from a stress-strain diagram can be applied to all components, regardless of their dimensions.

True

The results obtained from the mechanics of materials approach are quite satisfactory for a wide variety of important engineering problems.

True

The stress-strain diagram provides essential engineering design information that is applicable to components of any shape or size.

True

The type of failure anticipated as well as the history of similar components, the consequences of failure, and other uncertainties are considered in deciding on appropriate factors of safety for various situations.

True

Thermal strains should not be included in the Poisson's ratio calculation.

True

True stress accounts for the reduction in a specimen's cross-sectional area during a tension test.

True

True stress will continue to increase until fracture.

True

Typical factors of safety range from 1.5 to 3.

True

Necking would most likely occur in _______.

a low carbon steel

What does ASD stand for?

allowable stress design

Plastic deformation in a ductile material _______ to a larger region around discontinuities.

allows stress to flow

A material that exhibits little or no yielding before fracture is called a _______ material.

brittle

Using the average properties found in the appendix, compare the compressive strength of wood when it is loaded perpendicular to the grain to when it is loaded parallel to the grain.

comp-perpendicular < comp-parallel

If a solid body is under axial compression, it will _________ in the longitudinal direction.

contract

If a solid body is under axial tension, it will ___________ in the lateral directions.

contract

A material that can withstand large strains before fracture is called a _______ material.

ductile

If a solid body is under axial compression, it will ___________ in the lateral directions.

expand

If a solid body is under axial tension, it will _________ in the longitudinal direction.

expand

Which approach is better for objects with complicated loading and geometry?

finite element method

Examining the Enter your answer in accordance to the question statement _____________ of the deformed system of bars is often necessary to solve for the stress in each bar.

geometry

Failure stresses should be _______ allowable stresses.

greater than

According to Saint-Venant's Principle, localized stresses have _______ effect on the overall behavior of a body.

little

What does LRFD stand for?

load and resistance factor design

Hooke's Law applies to _______. Select all that apply.

normal stress and normal strain & shear stress and shear strain

For _______, the axial deformation in any bar may be assumed equal to the component of the displacement of one end of the bar (relative to the other end) taken in the direction of the unstrained orientation of the bar.

small displacements

The elastic modulus E is a measure of a material's _______.

stiffness

Using the average properties found in the appendix, compare the tensile strength and compressive strength of wood when it is loaded parallel to the grain.

tens-parallel < comp-parallel

Two nearly identical bars are loaded with an axial tension force P. Which bar will elongate the most?

the long bar

If there are multiple force components acting on a pin or bolt, what force should be used to calculate the shear stress on the pin or bolt?

the resultant force

In a deformation diagram, solid lines represent the Enter your answer in accordance to the question statement ___________ configuration of the system, while dashed lines represent the configurations due to applied forces.

unstrained

Which of the following do not cause dead loads? Select all that apply.

wind and people