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November 2007
Design engineering can be challenging and
interesting when it comes to addressing durability issues. More
so, if the failure has already occurred and the onus is on the design
department to provide a solution.
Though conventional wisdom prompts the
design engineer to increase the section modulus to reduce extreme fibre
stresses, sometimes, reducing section modulus may prove to be
beneficial in overcoming a failure issue! Sounds puzzling?
Next comes an obvious question. How much
more is the new design better in terms of life expectancy while
addressing cost and efficiency? Fatigue is going to be the theme
of this edition of Newsletter from EGS India. As always, we
welcome your feedback for more improvement in content and layout.
Yours
sincerely
Editor
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"An idea that is developed and put into action is more
important than an idea that exists only as an idea."
- Buddha
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| Finite
Element Thought For The Day |
www.egsindia.com
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| FE analysis results are only as good as the Problem
definition,
modelling strategy, loads and boundary conditions. Saint-Venant's
Principle states that the effect of a load or boundary condition are
localized to the area of their application and their effects are far
removed at distances considerably away. Hence the object area of
interest, while performing FEA, should not be influenced to ensure no
violation of Saint-Venant's Principle. This consideration is very
vital while reviewing the results of an analysis and to ensure accurate
simulations. Next time you apply a constraint, check whether the
FE
model is under-, over- or exactly constrained. Think about it. Need
Answers? Contact EGS India!! |
Contact
us For:
- Product Design
- Finite Element
Analysis
- Analysis to test correlation
- Failure Elimination
- DFMEA
- New Product Development
- Safety Certification
- Computational Fluid Dynamics
- Value Engineering
- GD&T Training
- Training in FEA
- SolidWorks CAD
Software
- Cosmos FEA
Software
- Vibration Problem
Trusted Specialists since 1993
EGS Computers India
Private Limited
Regd. Office:
New No 90 Old No 342 Arcot Road
I Floor
Kodambakkam Chennai 600024 INDIA
Tel : +91-44-24803370 / 2372 0265
Telefax : +91-44-24844227
Branch
Office:
1/1 B. R. Nagar, Trichy Road, Opposite Coimbatore Stock Exchange,
Singanallur Post, Coimbatore 641050 INDIA
Tel: +91 422 231 0268
Email : egsindia@vsnl.com
www.egsindia.com
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Fatigue
Considerations in Design
Fatigue is defined as a
failure at a load much less than the
design load. When a metallic specimen, such as steel, is subjected to a
rotating bending fatigue test, if there is no evidence of failure after
1E07 cycles, it is considered to have infinite life for stated
loading. For softer metals such as Aluminium, the threshold
is
considered at 1E08 cycles. Though majority of designs can be subjected
to uni-axial fatigue considerations, sometimes multi-axial fatigue
calculations are important such as cases involving combinatorial
loading involving
bending and torsion.
Fatigue can
be classified into high-cycle (elastic) and low-cycle
(plastic) regimes. FEA results can be used to compute fatigue
life.
It has been found that such computations are accurate and help in
Remaining Life Assessments for critical components.
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Images
show Cosmos FEA results vis-a-vis
failure in a heat exchanger
Accuracy of Life
Prediction calculations are dependent on understanding
of failure modes, capturing mechanisms of failure in FEA, computing
alternating stresses/ strains, pre-stress/strain considerations and
more importantly material property data such as S-N curves,
mean-correction factors in addition to creep effects, if any. FEA
and
Fatigue calculations have considerably improved Reliability in
aerospace applications wherein critical components are serviced or
replaced
after specified service life. Automotive industry has adopted
fatigue
as an important consideration to address warranty and reliability
challenges. Importance of Fatigue is getting more attention while
addressing Reliability & Warranty Issues.
Need more information? Contact EGS India
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What's
New in CosmosWorks 2008
With Focus on Design and Not
on Tools, CosmosWorks 2008 has set a new Paradigm in Design
Validation Solution.
Design Scenarios:
Design scenarios have been enhanced for greater usability providing
direct cut and paste access to tabular data from programs like MS Excel
and Word. Users can now resize the input window and automatically fill
in Parameter values using linear, exponential, or uniform data fills.
Coordinate system dependent output has been added to the Results
Summary.
Force at Any Location: Point forces can
simply be applied at any location using reference points. This
eliminates manual work and unnecessary geometry modifications, such as
surface splitting.
Trend Analysis:
Trend Tracker provides data to intuitively evaluate the impact of
successive design changes on a base design by allowing users to focus
on relative results instead of absolute. The insight provided by this
data will allow users to zero in on the best design alternatives in
less iteration with more confidence in the value of each feature.
Load/Restraint Advisor:
Choosing appropriate loads and restraints may be the most difficult
task facing design analysis users at all levels. The Analysis Advisor
has condensed the experience of analysis experts into a concise flow
chart format to allow designers and novice users to make informed
decisions on part interactions. A database of common load and restraint
modeling techniques has been added for review allowing customers to
capture best practices for their design challenges.
Design Insight Plots:
Design Insight plots show the most effective portions of the modeled
geometry in carrying the applied load thus allowing users to make
informed decisions about feature shape and innovative design
alternatives.
Free Body Diagram Plots:
Expanding on the popularity of computed free-body forces, COSMOS users
can now review the load distribution in their parts and assemblies
using intuitive free-body diagrams.
Pressure Vessel Design Study:
Pressure vessel design studies help users to combine the effects of
multiple independent loading scenarios, such as dead weight, internal
pressure, thermal or seismic loading. Users can easily calculate
dynamic stresses using SRSS (Square Root of the Sum of the Squares)
method.
NAFEMS Verification Problems in Tutorials:
NAFEMS, the international association for the engineering analysis
community, has developed a series of benchmarks to verify the quality
of analysis results. The results of many of these benchmarks have been
included as tutorial problems to allow users to better understand the
COSMOS results.
Many
more functionalities have been added to Cosmos FEA for user-friendly
design validation and faster product design iterations.
Interested in CosmosWorks? Contact EGS India
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| Did
You Know?
Here is an interesting anecdote on how
Theory and Observation go hand-in-hand. Herr
Hiemenz, a doctoral student of Ludwig Prandtl - a reknowned Fluid
Mechanics Expert, was experiencing
unsteady fluctuations while studying a flow around a cylinder in a
channel. Observing the experiment, Theodore von Karman, a graduate
assistant of Prandtl, studied the phenomenon and came up with the
vortices calculations over a weekend. When the work, which by then had
come
to be known as the von Karman vortices, was published at a meeting in
Paris, Henri Bernard, another famous Fluid Sciences Expert, had
mentioned that he had photographed the
vortices even earlier and they were un-symmetric. von Karman promptly
made quick calculations on the back of an envelope and was on his feet
explaining the difference and suggested that the street be called
'Boulevard de Bernard" in Paris. Later, von Karman admitted, in his
autobiography, that the inspiration for the study of the phenomenon and
subsequent hypothesis came from an ancient 14th Century painting of St.
Christopher in Bologna, Italy, carrying Infant Jesus across a
water-body, wherein the vortices were depicted around the Saint's
feet !! Now, an observation leads an artist to depict a natural
phenomenon which goes on to inspire a scientific assistant in putting
together the theory that later helps the world solve its fluid
engineering problems !!
While
receiving the First Prestigious National Medal of Science from
President Kennedy, at age 81, von Karman politely shook off the
proffered aid, saying, "Mr President, one does not need help going
down, only going up."
Recent studies have shown that insects
such as bees borrow energy from the vortices
that form around their wings during flight. Vortices inherently create
drag. Insects can recapture some of this energy and use it to improve
speed and maneuverability. Insects rotate their wings before starting
the return stroke, and the wings are lifted by the eddies of air
created on the downstroke. The high frequency oscillation of insect
wings means that many hundreds of vortices are shed every second.
However, this leads to a symmetric vortex street pattern. (Souce:
Wikipedia)
We
remember, with gratitude, von Karman for having helped us, at EGS
India, to solve an interesting fluid-induced vibration problem, using
Cosmos FloWorks, involving a tall column for a renowned Petro-Chemical
customer. The inspiration for this article came from discussions with
Dr. Madhu Ganesh, General Manager - Technology Development, ELGI
Equipments Limited, Coimbatore, India, specializing in
CFD as applied to compressors.
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Thermax Limited
develops Design Process Automation for Chillers using SolidWorks
Cooling and
Heating Division of Thermax Limited, has been one of the
First Users of SolidWorks since 1998. By automating the design
process
using SolidWorks with integrated API functionality, Thermax has shown
the way towards rapid product design with drawing release thereby
reducing the design cycle time which is bound to reduce the time to
market for their Chillers. Configuration Manager inside
SolidWorks has
been used in an innovative way with Design Tables and Excel Integration
to produce a huge
variety of configurations of their design resulting in over 60% saving
in time while eliminating errors and re-work. |
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| SolidWorks Innvoation Days
sees convergence of Engineering Community at Chennai and Coimbatore
A rare opportunity was utilized by Engineers to deliberate on the Theme
- Design with Vision during the Innovation Days program. In
addition
to new functionalities in SolidWorks 2008 and Cosmos 2008, case studies
presented by Wheels India Limited, Chennai, on benefits of Cosmos for
Wheel Design and Design Process Automation by Thermax Limited, Pune,
using SolidWorks, provided deep insight into how Engineering
Organizations can benefit in bringing their products to market faster.
Innovation
Day at Coimbatore saw a huge response from the Engineering
Community. Benefits of the usage of SolidWorks was detailed by
Penta Auto towards Auotomotive Handling Equipment design and
development. Importance of GD&T for Qualitative Designs using
SolidWorks was presented by EGS India.
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