Volcanoes indication of volcanoes indication of metal

•Volcanoes indication of •Volcanoes indication of
metal shearing. deformation
– not expansion.
•Thin sheet residual stresses
are much lower in thin sheet
than thicker products.
2008 (C) M. Ramulu
Cold worked hole fracture
Material Properties and % of elongation:
L = 8%
LT = 4%
ST = 3%
•Percent Expansion – 3% - 5%
•Cold Working is not recommended in
materials where cold work expansion exceed
material elongation properties.
2008 (C) M. Ramulu
Cold Working : Effect of Stress
Rule of thumb in Metallic Structure
–A 20% Reduction in Stress Doubles the Fatigue
Life
2008 (C) M. Ramulu

7
HEAT TREATMENT:
Different cooling rates during
quenching cause thermal stresses which can lead to a
residual stress distribution.
2008 (C) M. Ramulu
ASSEMBLY OF COMPONENTS:
Bolted joint with built-in stresses if t
1
is not equal to t
2
.
2008 (C) M. Ramulu
Residual stress distribution and residual stress
intensity factor, K
res
, for a longitudinal welded
infinite plate containing a central through crack.
(a) Residual stress distribution, , across the plate width. (b)
Residual stress intensity factor, K
res
2008 (C) M. Ramulu
Influence of chromium plating and chromium plating
with shot-peening on the axial loaded fatigue behavior of
4130 steel
2008 (C) M. Ramulu
Effects of surface finish on the fatigue limit of steel
2008 (C) M. Ramulu
MEASUREMENT OF RESIDUAL STRESSES
• Analytical Methods: Local strain approach
• Numerical/Computational methods: FEM
• Experimental Methods: There are seven major experimental methods
-The hole drilling Method: typically 1.5-3.0mm deep, strain gages
-Layer removal or Sectioning methods: the curvature
changes/deflections for each layer are measured. Thickness of the layer
removal is 20microns
-X-ray diffraction: Residual stresses cause crystal lattice distortion, and a
measurement of the inter planar spacing of the crystal lattice
indicates the magnitude of the residual stress. The angle of diffraction
is the measured quantity.
-Neutron Diffraction
- Ultrasonic Method: Speed of sound travelling throgh metal is linearly
proportional to the residual stresses
- Magnetic Methods
2008 (C) M. Ramulu

8
Elimination of residual stress
• Plate by plastic bending
• Heat treating (recrystallization):
Approximate temperatures at which stress relief will be significant are:
• 400-450C (750-840F) for Titanium alloys
• 450-500 C( 840-930F) for high temp resistant steels
• 650-800 C (1200-1475F) for high temp resistant Nickel alloys
• 800-900 C ( 1475-1650 F) for superalloys
• Unfavourable residual tensile stresses at the surface can be reduced or reversed into
favourable by peening.
2008 (C) M. Ramulu
Conclusions
• Cold Working can improve fatigue life of
machined parts significantly.
• However, Cold Working requires intensive labor
that adds high cost to the operation b t that adds high cost to the operation, but
engineering & manufacturing can optimize their
process and concurrence engineering to achieve
the lowest cost to achieve highest quality
products.