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introduction
MPM offers a wide range of analytical and experimental
services in the fields of applied mechanics and fracture mechanics. In
addition to finite element and elastic/elastic-plastic fracture analyses, MPM's
laboratory capabilities can be used to verify model predictions and to test
theories by building prototypes.
Thermal And Stress
MPM employs a variety of numerical and analytical methods
for the thermal and stress analysis of equipment and structures. General
purpose commercial software such as ABAQUS or ADINA can be used or, when
appropriate, special purpose proprietary software such as WELD3 and DYN3D can be
used. Linear elastic, elastic-plastic, and visco-plastic material behavior
can be analyzed. Loading can be thermal, static, or dynamic.
Fracture Mechanics Analysis
Fracture mechanics analysis is used to understand crack
growth and fracture behavior. Crack growth behavior due to fatigue, stress
corrosion, creep, or some combination thereof can be simulated and predicted
with the appropriate software and experimental data. Fracture occurs when
a crack reaches its critical size. The critical crack size depends on the
material's temperature dependent fracture toughness, the location and
orientation of the crack, and the applied loads. Fracture can involve very
little plastic deformation (brittle fracture) or very significant plastic
deformation (ductile fracture). If the material has very high fracture
toughness properties, the final failure may be due to plastic collapse rather
than fracture. Due to the inherent complexities, fracture mechanics
analyses often involve the use of more than one software tool. Simulation
of crack growth via fatigue, stress corrosion, or creep typically requires the
use of special purpose software. On the other hand, general purpose finite
element thermal and stress analysis software can often be used to calculate
critical crack sizes. However, special purpose proprietary software such
as ALT3D can sometimes provide significant advantages over general purpose
finite element software, even in the critical crack size calculations.
With the wide range of analysis capabilities available, MPM can tailor the
analysis approach to the special requirements of the problem. This results
in greater accuracy and efficiency.
Welding Analysis
Many equipment and structural failures occur in or near weld joints.
These failures can be due to poor weld design but are more often due to weld
defects and/or a sensitivity of the weld material to fatigue or stress corrosion
cracking. A common third factor in weld failures is that weld materials
often exhibit lower fracture toughness than the neighboring base metal.
Fatigue and stress corrosion cracking behavior are affected by residual stresses
as well as applied service loads. Since the welding process typically
leaves residual stresses that are on the order of the material's yield stress in
or near the weld, any analysis of crack growth must include the effects of these
stresses. MPM can use the proprietary WELD3 finite element software to
simulate the welding process and to calculate residual welding stresses.
These residual stresses are typically a key input to weld fracture mechanics
analysis.
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