1 - Deformation of Materials-1
1 - Deformation of Materials-1
1 - Deformation of Materials-1
Plastic Region
Elasticity:
applied on them.
materials.
slip plane
remains same.
Slip occurs when shear stress applied exceeds the critical value.
Critically Resolved Shear Stress:
• Slip occurs when shear stress on the slip plane along the
part.
Twinning
Twinning
twinning plane
Slip Twining
manner.
twinning.
Plastic Deformation of Polycrystalline Materials
grains
strengthening is achieved.
Yield strength
Ductility
Tensile strength
Small amount of cold-working results in a
significant reduction in ductility.
Strain Hardening
deformed
deformation
Fracture
fracture.
1. Ductile:
2. Brittle Fracture:
Instant break
Moderate Ductile Fracture Cup & Cone Fracture
a) Necking
b) Void
nucleation
c) Void growth
and linkage
d) Shearing at
surface
e) Fracture
Voids and internal cracks in the necked region of a polycrystalline specimen of high-
purity copper
Brittle Fracture
Axial Fracture
Shear Fracture
Conchoidal
Brittle Materials
Brittle vs. Ductile
a)Brittle –Small
b)Moderately ductile – Medium
c) Very ductile-large
Trans -granular Fracture
Inter-granular fracture
Ductile fracture Brittle Fracture
material.
• Creep is more severe in materials that are subjected to heat for long
Creep rate decreases with time, the effect of work hardening is more
Forms an early part of the total extension reached in a given time and
Secondary Stage:
Can occur due to necking of the specimen and other processes that
2.Recovery
Factors affecting Creep
Heat Treatment
• Creep resistance of steel is affected by heat treatment.
Grain size
• The major factor in creep is grain size.
• Normally large grained materials exhibit better creep resistance than fine
grained one based on the temperature.
Strain Hardening
Alloying additions
process are:
• Dislocation climb
• Vacancy Diffusion
• In this mechanism, the diffusion of vacancies controls the creep rate but
separates them.
Creep Strength:
Highest stress that a material can withstand without
excessive deformation for a specified time
Creep strength for a component may be the stress that
produces 1% creep for 15000 hours of usage at 900 C
• Loss of strength
• Loss of ductility
• Example: aircraft wings are subjected to repeated loads, oil and gas
pipes are often subjected to static loads but the dynamic effect of
temperature variation will cause fatigue.
• There are many other situations where fatigue failure will be very
harmful.
“fatigue limit”.
Test focuses on the nominal stress required to cause a fatigue
failure in some number of cycles
S-N Curve
Fatigue
• The point at which the curve flattens out is termed as fatigue
stress.
loaded below this stress, then it will not fail, regardless of the
show a fatigue limit; therefore they will fail at any stress and
number of cycles.
• Other important terms are fatigue strength and fatigue
life.
Surface finish:
Temperature:
• Combined stresses
• Metallurgical variables
• Corrosion
Fatigue Failure Process
1. Crack Nucleation
2. Crack Growth
3. Fracture
Fatigue Failure
• Fatigue fracture results from the presence of fatigue cracks,
usually initiated by cyclic stresses, at surface imperfections such
as machine marking and slip steps.