Chapter 4 TERMS

Question 1

define brittleness

Answer 1

Relative inability of a material to deform plastically before it fractures.

Question 2

define compressive stress

Answer 2

Compressive force per unit area perpendicular to the direction of applied force.

Question 3

define compressive strength

Answer 3

Compressive stress at fracture.

Question 4

define ductility

Answer 4

Relative ability of a material to elongate plastically under a tensile stress. This property is reported quantitatively as percent elongation.

Question 5

define elastic strain

Answer 5

Amount of deformation that is recovered instantaneously when an externally applied force or pressure is reduced or eliminated.

Question 6

define elastic modulus

Answer 6

(also modulus of elasticity and Young’s modulus)—Stiffness of a material that is calculated as the ratio of elastic stress to elastic strain.

Question 7

define flexural strength

Answer 7

force per unit area at the instant of fracture in a test specimen subjected to flexural loading.

Question 8

define flexural/bending stress

Answer 8

orce per unit area of a material that is subjected to flexural loading.

Question 9

define fracture toughness

Answer 9

The critical stress intensity factor at the point of rapid crack propagation in a
solid containing a crack of known shape and size.

Question 10

define hardness

Answer 10

Resistance of a material to plastic deformation, which is typically produced by an indenta- tion force

Question 11

define malleability

Answer 11

Ability to be hammered or compressed plastically into thin sheets without fracture.

Question 12

define percent elongation

Answer 12

Amount of plastic strain, expressed as a percent of the original length, which
tensile test specimen sustains at the point of fracture (Ductility).

Question 13

define plastic strain

Answer 13

Irreversible deformation that remains when the externally applied force is reduced or eliminated.

Question 14

define pressure

Answer 14

Force per unit area acting on the surface of a material (compare with Stress).

Question 15

define proportional limit

Answer 15

Magnitude of elastic stress above which plastic deformation occurs.

Question 16

define resilience

Answer 16

The amount of elastic energy per unit volume that is sustained on loading and released upon unloading of a test specimen

Question 17

define shear stress

Answer 17

Ratio of shear force to the original cross-sectional area parallel to the direction of the applied force.

Question 18

define shear strength

Answer 18

Shear stress at the point of fracture.

Question 19

define stress

Answer 19

Force per unit area within a structure subjected to a force or pressure (see Pressure).

Question 20

define stress concentration

Answer 20

Area or point of significantly higher stress that occurs because of a structural discontinuity such as a crack or pore or a marked change in dimension.

Question 21

define strain

Answer 21

Change in dimension per unit initial dimension. For tensile and compressive strain, a change in length is measured relative to the initial reference length.

Question 22

define stress intensity

Answer 22

stress intensity factor)—Relative increase in stress at the tip of a crack of given shape and size when the crack surfaces are displaced in the opening mode (also Fracture Toughness).

Question 23

define strain hardening

Answer 23

Increase in strength and hardness and decrease in ductility of a metal that results from plastic deformation.

Question 24

define strain rate

Answer 24

Change in strain per unit time during loading of a structure.

Question 25

define strength

Answer 25

Maximum stress that a structure can withstand without sustaining a specific amount of plastic strain (yield strength); (2) stress at the point of fracture (ultimate strength).

Question 26

define tensile stress

Answer 26

Ratio of tensile force to the original cross-sectional area perpendicular to the direction of applied force.

Question 27

define tensile strength

Answer 27

Tensile stress at the instant of fracture.

Question 28

define toughness

Answer 28

Ability of a material to absorb elastic energy and to deform plastically before fracturing;
measured as the total area under a plot of tensile stress versus strain.

Question 29

define true stress

Answer 29

Ratio of applied force to the actual (true) cross-sectional area; however, for convenience, stress is often calculated as the ratio of applied force to the initial cross-sectional area.

Question 30

define yield strength

Answer 30

The stress at which a test specimen exhibits a specific amount of plastic strain.