Chp.7 Material Failure

Question 1

What is Ductile Fracture?

Answer 1

A mode of fracture attended by extensive gross plastic deformation. (non-sudden, preferred)

Question 2

What is Brittle Fracture?

Answer 2

Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation. (Sudden, un-desired)

Question 3

What is a transgranular fracture?

Answer 3

Fracture of polycrystalline materials by crack propagation through the grains.

Question 4

What is an intergranular fracture?

Answer 4

Fracture of polycrystalline materials by crack propagation along grain boundaries.

Question 5

Define fracture mechanics?

Answer 5

A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.

Question 6

What is a stress raiser?

Answer 6

A small flaw (internal or surface) or a structural discontinuity at which an applied tensile stress will be amplified and from which cracks may propagate.

Question 7

What is fracture toughness Kc?

Answer 7

The measure of a material’s resistance to fracture when a crack is present.

Question 8

What is plane strain?

Answer 8

The condition, important in fracture mechanical analyses, in which, for tensile loading, there is zero strain in a direction perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.

Question 9

What is plane strain fracture toughness KcI?

Answer 9

For the condition of plane strain, the measure of a material’s resistance to fracture when a crack is present.

Question 10

What is notch toughness (impact energy)?

Answer 10

A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductile-to-brittle transition behavior of a material.

Question 11

What is Fatigue?

Answer 11

Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses.

Question 12

What is Fatigue Limit?

Answer 12

For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail.

Question 13

What is Fatigue Strength?

Answer 13

The maximum stress level that a material can sustain without failing, for some specified number of cycles.

Question 14

What is Fatigue Life?

Answer 14

The total number of stress cycles that cause a fatigue failure at some specified stress amplitude.

Question 15

What is Thermal Fatigue?

Answer 15

A type of fatigue failure in which the cyclic stresses are introduced by fluctuating thermal stresses.

Question 16

What is Corrosion Fatigue?

Answer 16

A type of failure that results from the simultaneous action of a cyclic stress and chemical attack.

Question 17

How is Thermal Stress caused?

Answer 17

When a material is restrained and experiences thermal expansion, that restraint caused the material to mold into its restraint.