Thermoelastic Forum Vol.1, No.7, May
1996
First Words
The R&D Side
New Products
DeltaTherm 1000 Customer Album
Events
Tid Bits
TSA Primer
Things have been very busy at Stress Photonics this year. Since our last
publication of the Thermoelastic Forum we have been particularly active
placing new DeltaTherm 1000 systems. This is very exciting for us at SP
and in the new "Customer Album" section of this newsletter you
can read about how the excitement has transferred to the new DeltaTherm
owners. If you are not yet familiar with the system you can read about it
in the "New Products" section.
If you get as excited as our customers do about the DeltaTherm 1000 you
will want to pay particular attention to the comment in the "New Products"
article about renting a system. The new Rent-a-Therm program will help you
solve your hot projects right now and introduce you to instantaneous stress
imaging with the DeltaTherm 1000.
At Stress Photonics we are continuously researching thermoelasticity and
IR thermography. The "R&D Side" describes some of the latest
advances in thermoelastic techniques.
By now many of you will have received an invitation to join us at the spring
SEM meeting in Nashville. One highlight of the conference will be the SPATE
Application Working Group meeting and Thermal Methods Round Table discussion
where you can learn more about thermography techniques from experts and
associates. This year SEM has altered it's program and is including oral-only
presentations. This has attracted many more industrial presentations and
has drastically improved the conference. We have included an advance program
with the newsletter. (See the "Events" column for details).
By Jon Lesniak
Stress Photonics has recently released a furnace designed to address the
specific problems of elevated-temperature TSA. Under Air Force funding,
the "Stealth Furnace" was used in combination with the DeltaTherm
1000 stress measurement system to monitor crack growth at elevated temperatures.
Although previous work performed by Enke and Lesniak demonstrated the ability
of TSA to work at elevated temperatures as high as 1100°C (2000°F),
there was not a complete understanding of thermal radiation or the problems
that impede high-temperature testing. Applying TSA to extreme environments
was still very much a black art that would often fail to yield results.
To improve on this, a deeper understanding of the relationship between thermographic
methods and the test environment was necessary.
As seen in the Thermoelastic Stress Analysis Primer provided in this issue,
the Thermoelastic Equation describes that as the specimen temperature rises
so does the differential temperature induced via the thermoelastic effect.
Because of this, the signal-to-noise ratio (S/N) can actually improve as
the temperature increases. The material properties in this equation should
be evaluated at the operating temperature.
Although the thermoelastic effect increases at elevated temperatures, there
are practical considerations that must be addressed. At high temperatures,
pseudo-signals have a greater effect on data, and need to be minimized.
Pseudo-signals are temperature changes that occur in sync with the loading,
and therefore are detected by the DeltaTherm system as thermoelastic signal.
The main causes of pseudo-signals are:
The Stealth Furnace is designed considering all of the potential pseudo-signals
. The furnace is laid out in eight zones six of which control wall temperatures
and two of which control the temperature of the specimen, compensating for
the conduction of heat through the specimen and into the grips. Temperatures
can be controlled to within ±2 C, which is adequate for minimizing
the pseudo-signals described above. Keeping the zonal temperatures similar
solves the problems of thermal gradients, angular motion, and edge effects.
Wall reflections are minimized by the construction and shape of the furnace,
hence the name "Stealth Furnace."
(Contact Stress Photonics for detailed references).
In our last edition of the Thermoelastic Forum, Jon Lesniak described
the development of the DeltaTherm 1000. Stress Photonics is now pleased
to present the DeltaTherm 1000 as a successful new product. A number of
systems have been placed in industrial, government, and university laboratories
across the country (see the "Customer Album" in this Newsletter).
The DeltaTherm's small size, fast imaging speed, and ease of operation combine
to make it a highly productive structural analysis tool. The DeltaTherm
system is simple to setup and operate. It can be unpacked, setup, cooled
down, and collecting data in less than 30 minutes. Thermoelastic stress
maps are formed so fast that a structure can be surveyed for high stress
"trouble spots" in a matter of a few minutes. High quality full-field
stress images are formed in just a minute or two.
The DeltaTherm system consists of an ultra-sensitive IR camera head, special
image processing electronics, and a laptop computer. Windows 95 compatible
software on the laptop provides an easy-to-use control panel interface that
allows the user to easily manage the collection, storage, and presentation
of data. The software automatically documents system settings, data processing
history, and user's notes for every image.
The array detector technology used in the DeltaTherm is also capable of
high quality thermal mapping. In the "DC" mode, DeltaTherm collects
thermal maps, or IR digital photographs of the target, for documentation
purposes.
System Performance
Frame Rate:
434 frames/s
Specimen Temperature:
0°C to 50°C
(unlimited range with accessories)
Sync Bandwidth:
1-125 Hz
Dewar Hold Time:
5 hours
Thermal Resolution:
2mK full-field (30s acquisition time)
Optics
Array:
128 x 128 InSb, 3-5mm sensitivity
Lens:
25mm, 50mm, 100mm, f/2.3
Other lenses available upon request
Focus Range:
5.0 inches to infinity
Dewar:
Liquid N2
Overall Size:
12 in. long, 7 in. wide, 9 in. high
Weight (dry):
8.4 lb.
Spatial Resolution:
as little as 0.002 in
Electronics
Power:
100 - 250V, 100W
Size:
19 in. wide, 8 in. high, 10 in. deep
Weight:
14 lb.
Video Outputs:
NTSC composite
Computer Interface:
Bidirectional parallel
Stress Photonics is now offering a rental program for customers who would
like to try the DeltaTherm on a project of their own. The system can be
rented on a weekly basis. Rental fees apply toward the purchase of a DeltaTherm
system*. One day of on-site training is required for first time renters.
*75% of rental fees are credited toward a purchase, provided the purchase
is made within two years of the rental.
After receiving a number of requests, Stress Photonics has decided to offer DeltaVision for the Windows platform. DeltaVision is a thermoelastic image processing software package capable of opening both SPATE 9000 and DeltaTherm data files. It provides the user simultaneous high performance processing of multiple data sets. With multiple images on the screen, it is easy to compare various scans and optimally prepare them for presentation. DeltaVision, used in combination with Windows applications (i.e. Word, WordPerfect, Power Point), makes generating and printing reports an easy final step. Windows DV is written in Microsoft's Visual Basic so users can easily make modifications to meet their own needs or have Stress Photonics do the fine tuning. DeltaVision for Windows will be available in July '96.
By Mike Zickel
The DeltaTherm 1000 is in use and performing well in laboratories across
the country.
Elliott Cramer of NASA Langley Research Center's Nondestructive Evaluation
Science Branch (NESB) has been using the DeltaTherm for Non Destructive
Evaluation (NDE) of aircraft structures. He reports being very pleased with
the results, and talks briefly about the inspection of a particular part.
"[We] used the DeltaTherm 1000 to successfully image the stresses in
a door latch assembly experiencing dynamic loading" (shown below) "This
work was done to confirm finite element modeling of the stress distribution
in that part. A series of additional tests and demonstrations of the capabilities
of the DeltaTherm 1000 are being planned for the near future."
Two DeltaTherm 1000 systems are measuring stresses on existing automobile
parts at two separate General Motors facilities, GM NAO Body Test Lab and
Warren Test Lab. Finite Element Analysis (FEA) and DeltaTherm image results
are combined providing a valuable two-pronged assessment of the stresses
in a test part.
Ford Motor Company has used their DeltaTherm for locating hot spots and
for FEA model correlation. Jim Franko of Ford describes a recent experience
using their system. "Thermal Stress Analysis has become a more valuable
technique since the introduction of the DeltaTherm 1000. The speed and simplicity
of the system allows us to help many more programs and everyone on our team
has been excited to use it. In fact the excitement goes beyond our laboratory.
We regularly receive visitors from the design and CAE development teams
who are anxious to learn from the scans. I feel we have created a learning
environment with much more interaction between testing and CAE because the
system allows us to say 'what if' and obtain immediate answers.
For example, we were verifying stress distributions in a floorpan for the
sole purpose of FEA validation. We reported finding concentrators in areas
that were not reported by the FEA analysis so the modeler visited our lab
to find out why. In less than an hour we convinced the modeler that our
output was real and together determined why his model wasn't demonstrating
the same results. He was so excited that we could help him improve his work
that he asked us to demonstrate our capabilities to his entire work group."
Our newest additions to the DeltaTherm Customer Album are Cleveland State
University's Civil Engineering Laboratory and Sandia National Laboratories
in Albuquerque, New Mexico.
Caterpillar, Inc. rented a DeltaTherm system for experimental stress analysis
of engine components. Darrin Johnston of CAT emphasized that, "The
system is useful for locating high stress areas and correlating FEA models."
Thermosense XVIII, a conference at SPIE's 10th Annual International AeroSense
Symposium, was held April 10-12 in Orlando, FL. On the exhibition floor,
Stress Photonics was a part of NASA-Langley's Technology Transfer display,
which highlighted a mutually beneficial relationship between NASA and SP.
Interest in both TSA and NDE drew many visitors to the booth where Stress
Photonics had a "live" DeltaTherm demonstration.
Jon Lesniak and Dan Bazile presented a paper entitled, "Forced-Diffusion
Thermography Technique and Projector Design," which generated much
interest and added to the number of visitors who stopped by SP's TSA demonstration.
The Thermal Methods Technical Division of SEM is sponsoring a technical
paper session as well as a Thermal Methods Round Table Discussion. The discussion
will be held in conjunction with the SPATE Application Working Group (SAWG)
meeting. See page 8 in the enclosed program for details.
While you're at SEM, make sure to visit the Stress Photonics booth on the
trade show floor where we will be demonstrating the DeltaTherm 1000.
The conference will be held in Nashville, Tennessee, June 10-14 at the Sheraton
Music City Hotel.
Stress Photonics DeltaTherm Seminar
By Brian Bartel
In February 1996, Stress Photonics co-sponsored a course at Defiance Testing
and Engineering Services in Westland, MI. Representatives from eight companies
in the Detroit area attended, including:
Atoma Interior Systems, The Budd Company, Chrysler Corporation, Dana Corporation,
Defiance Testing and Engineering Services, Ford Motor Company, General Motors,
US Manufacturing Company.
The four-hour course consisted of a classroom lecture, a group discussion,
and hands-on laboratory time. Sample data was collected from a simple hole-in-plate
specimen and a rod-end manufactured by Defiance. Attendees left the course
with a good working knowledge of the DeltaTherm system's capabilities, existing
applications, and future directions.
Attending a seminar is an excellent way to become acquainted with the DeltaTherm
1000 system and with Thermoelastic Stress Analysis. If you would like to
see a DeltaTherm seminar organized in your area send in a reader response
card or just give us a call.
Thermoelastic Stress Analysis (TSA) produces a full-field stress map by imaging temperature changes with a sensitive infrared camera. All materials, whether solid, liquid or gas, change temperature when compressed or expanded. In solids, stresses cause small temperature changes described by the thermoelastic equation
To provide accurate measurements, the temperature changes induced by
the thermoelastic effect are repeated and time-averaged during a continuous
dynamic loading, usually provided by a closed-loop hydraulic load frame.
A special infrared camera, known as a differential thermographic system,
correlates the load-induced IR signals with the reference signal from the
load system. This allows a thermal resolution of 1.0mK, which translates
to the following stress resolutions:
Stress sensitivity is similar to that of a common strain gage.
