Materials Test 2

Plastic Deformation occurs easily in a metal that

has a large number of slip systems which depends on the crystalline structure

Critical variables for fracture include

All of the above (Stress, The most severe defect or discontinuity, as characterized by its size and shape, fracture toughness of the material)

A measure of ductility which is also the limit that a material may be cold worked is

%RA (Reduction in area)

A metallic failure that is characterized by slow elsato-plastic deformation at elevated temperature until sudden rupture is

Creep

Fracture Toughness (K)

indicates the ability of a material to absorb energy and is used in fracture mechanics

Failure of brittle materials in tension is usually characterized by

Unstable rapid crack propagation indicated by cleaved chevron markings from the crack initation site and no significant plastic deformation

Jominy Test of a medium carbon steel

Uses hardness testing to determine the depth of hardness for a heat treated steel

The quenched end of the jominy test specimen of a medium carbon steel

is ? with higher strength and hardness as compared to the air cooled end

Strain hardening a metal by cold work

is plastic deformation that occurs at temperatures below re-crystallization

In general for a metal that has been significantly cold worked

The yield strength increases and the ductility decreases

A metal is annealed by heat treating above its recrystalization temp for several hours there is no phase change it is expected that

The grains will increase in size and the effects of prior cold work will be mitigated to result in lower strength but increased ductility

Pressure vessels may be designed using the leak before break criterion this means

the critical crack length is greater than the wall thickness to be self relieving prior to over pressurization rupture

Failure of a ductile material in tension is usually characterized by

substantial plastic deformation and energy absorption

The following operation cannot be done as cold work

Casting (Drawing, extrusion and rolling can all be done via cold work)

The process by which plastic deformation is produced by dislocation motion is called

Slip

The charpy impact test is

a destructive test used to determine DBT based on the ability of a notched specimen to absorb energy as ductile or brittle failure

The fracture surface of cylindrical component which failed ultimately is examined and found to have "clamshell" type markings across approximately 1/3 of the cross section and directional brittle chevron markings across the remaining section it is most li

Fatigue

A large plate is fabricated from 2024 T3 AL that has a plain stress fracture toughness of K=40ksi. The plate is loaded in normal tension. IF the largest defect is an internal crack that is .36in in length determine critical stress that would lead to fract

53,200 psi
Ac=(1/pi)(k/sigma*y)^2

In the previous problem the following assumption is not true

the plate is experiencing shear stress

Jominy Test is a standard test that

characterizes the heat treat-ability of steel by depth of hardness

Ultimate tensile strength is

Greater than tensile yield strength, the maximum engineering stress prior to rupture on the stress strain graph, typically decreased with increasing temp

Fatigue life for a particular metal component may be increased by

Surface treatments such as peening or case hardening

Invar is used as a material of construction for LNG service primarily because

it has a low thermal coefficients of thermal expansion and construction

The following operation cannot be done as cold work

Forging

Failure by thermal shock

does not require external constraint due to the thermal gradient

The thermal conductivity K of a metal

Has a vibration component as well as an electrical component for metals the thermal conductivity is high since the electrical conductivity is high