Mechanical Properties of Metals

Question 1

(True or False) Tensile tests are not standard because they are easier to perform; also, for most materials used in structural applications, very little additional information is obtained from compressive tests.

Answer 1

False (standard)

Question 2

(True or False) Compressive tests are used when a material’s behavior under small and permanent (i.e., plastic) strains is desired, as in manufacturing applications, or when the material is brittle in tension.

Answer 2

False (large and permanent)

Question 3

(True or False) The mechanical behavior of a material reflects its response or deformation in relation to an applied load or force.

Answer 3

True

Question 4

If a load is static or changes relatively slowly with time and is applied uniformly over a cross section or surface of a member, the mechanical behavior may be ascertained by a simple (blank) test, that are most commonly conducted for metals at room temperature.

Answer 4

Stress – Strain Test

Question 5

(True or False) Examples of torsion are found for machine axles and drive shafts as well as for twist drills. Torsional tests are normally performed on cylindrical solid shafts or tubes. A shear stress τ, is a function of the applied torque T, whereas shear strain γ is related to the angle of twist, φ in the figure earlier.

Answer 5

True

Question 6

(True or False) A stress–strain test typically takes several minutes to perform and is destructive; that is, the test specimen is permanently deformed and usually fractured.

Answer 6

True

Question 7

For each test a very small diamond indenter having pyramidal geometry is forced into the surface of the specimen.

Answer 7

Knoop and Vickers Microindentation Hardness Tests

Question 8

There are three principal ways in which a load may be applied.

Answer 8

Tension, Compression, and Shear

Question 9

As in Rockwell measurements, a hard, spherical indenter is forced into the surface of the metal to be tested. The diameter of the hardened steel (or tungsten carbide) indenter is 10.00 mm (0.394 in).

Answer 9

Brinell Hardness Tests

Question 10

Is defined as the load F divided by the instantaneous cross-sectional area Ai over which deformation is occurring (i.e., the neck, past the tensile point).

Answer 10

True Stress

Question 11

The (blank) is the stress at the maximum on the engineering stress–strain curve This corresponds to the maximum stress that can be sustained by a structure in tension; if this stress is applied and maintained, fracture will result.

Answer 11

Tensile strength TS (MPa or psi)

Question 12

Are of concern to a variety of parties that have differing interests. It is imperative that there be some consistency in the manner in which tests are conducted and in the interpretation of their results.

Answer 12

Mechanical Properties

Question 13

(Blank) is a variation of pure shear, wherein a structural member is twisted in the manner of the figure shown. (Blank) produce a rotational motion about the longitudinal axis of one end of the member relative to the other end.

Answer 13

Torsion; Torsional forces

Question 14

Is a function of the orientations of the planes upon which the stresses are taken to act.

Answer 14

Stress State

Question 15

For most metallic materials, elastic deformation persists only to strains of about 0.005. As the material is deformed beyond this point, the stress is no longer proportional to strain (Hooke’s law, ceases to be valid), and is permanent, nonrecoverable, or (blank) occurs.

Answer 15

Plastic Deformation

Question 16

A test that can be used to ascertain several mechanical properties of materials that are important in design.

Answer 16

Tension Test

Question 17

(True or False) It is necessarily to involve an understanding of the relationships between the microstructure of materials and their mechanical properties. Materials are frequently chosen for structural applications because they have desirable combinations of mechanical characteristics.

Answer 17

True

Question 18

The stress corresponding to the intersection of this line and the stress-strain curve, as it bends over in the plastic region, is defined as the (blank).

Answer 18

Yield Strength

Question 19

Is a measure of the degree of plastic deformation that has been sustained at fracture.

Answer 19

Ductility

Question 20

Is used instead of design stress. This stress is based on the yield strength of the material and is defined as the yield strength divided by a factor of safety, N.

Answer 20

A safe stress or working stress

Question 21

Constitute the most common method used to measure hardness because they are so simple to perform and require no special skills.

Answer 21

Rockwell Hardness Tests

Question 22

A structure or component that has plastically deformed, or experienced a permanent change in shape, may not be capable of functioning as intended. It is therefore desirable to know the stress level at which plastic deformation begins, or where the phenomenon of (blank) occurs.

Answer 22

Yielding

Question 23

Is a mechanical term that may be used in several contexts. For one, blank (or more specifically, fracture blank) is a property that is indicative of a material’s resistance to fracture when a crack (or other stress-concentrating defect) is present.

Answer 23

Toughness

Question 24

Properties of materials are ascertained by performing carefully designed laboratory experiments that replicate as nearly as possible the service conditions.

Answer 24

Mechanical Properties

Question 25

Hardness tests are performed more frequently than any other mechanical test for several reasons:

Answer 25

1. They are simple and inexpensive—ordinarily no special specimen need be prepared, and the testing apparatus is relatively inexpensive.
2. The test is nondestructive—the specimen is neither fractured nor excessively deformed; a small indentation is the only deformation.
3. Other mechanical properties often may be estimated from hardness data, such as tensile strength.

Question 26

(True of False) The output of such a tensile test is recorded as load or force versus elongation. The load–deformation characteristics are dependent on the specimen size.

Answer 26

True

Question 27

Is a measure of a material’s resistance to localized plastic deformation

Answer 27

Hardness

Question 28

Is the capacity of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered.

Answer 28

Resilience

Question 29

(True or False) Stresses that are computed from the tensile, compressive, shear, and torsional force states act either parallel or perpendicular to planar faces of the bodies.

Answer 29

True

Question 30

A machine is designed to elongate the specimen at a constant rate and to continuously and simultaneously measure the instantaneous applied load and the resulting elongation.

Answer 30

Tensile Testing Machine

Question 31

Deformation in which stress and strain are proportional is called.

Answer 31

Elastic Deformation

Question 32

Is conducted in a manner similar to the tensile test, except that the force is compressive and the specimen contracts along the direction of the stress.

Answer 32

Compression Test

Question 33

Key mechanical design properties are:

Answer 33

Stiffness, Strength, Hardness, Ductility, and Toughness.

Question 34

Gauge length is used in ductility computations; the standard value is?

Answer 34

50 mm (2.0 in)

Question 35

(True or False) The output of such a tensile test is recorded as load or force versus elongation. The load–deformation characteristics are not dependent on the specimen size.

Answer 35

False (dependent)

Question 36

(True or False) The degree to which a structure deforms or strains depends on the magnitude of an imposed stress.

Answer 36

True

Question 37

For most metals that are stressed in tension and at relatively low levels, stress and strain are proportional to each other through the relationship

This is known as (blank), and the constant of proportionality E (GPa or psi) is the (blank).

Answer 37

Hooke’s law; Modulus of Elasticity or Young’s Modulus.

Question 38

(True or False) The greater the modulus, the stiffer the material, or the smaller the elastic strain that results from the application of a given stress.

Answer 38

True

Question 39

(True or False) It has been assumed that elastic deformation is time independent—thatis, that an applied stress produces an instantaneous elastic strain that remains constantover the period of time the stress is maintained. It has also been assumed that upon release of the load, the strain is totally recovered—that is, that the strain immediately returns to zero.

Answer 39

True

Question 40

In most engineering materials, however, there will also exist a time-dependent elastic strain component—that is, elastic deformation will continue after the stress application, and upon load release, some finite time is required for complete recovery. This time-dependent elastic behavior is known as (blank) and it is due to time-dependent microscopic and atomistic processes that are attendant to the deformation.

Answer 40

Anelasticity

Question 41

A parameter termed (blank) is defined as the ratio of the lateral and axial strains.

Answer 41

Poisson’s ratio

Question 42

For metals, the anelastic component is normally small and is often neglected. However, for some polymeric materials, its magnitude is significant; in this case it is termed (blank).

Answer 42

Viscoelastic Behavior.