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NDT TESTING TIPS FROM NDTECH - NEWSLETTER #17 - July 2000


This issue of the Newsletter includes:

1. SIMoNET: Structural Integrity Monitoring on the Net.
2. Aging Aircraft: The Graying of Our Skies
3. Publications
4. Acoustic Emission Working Group - 43rd Meeting - Seattle,WA. July
18/19/20, 2000.
5. Ceramics WebBook

**********************************************************************
The NDTech Newsletter is published periodically by NDTech, a consulting
firm offering nondestructive testing, services, and instruments. This
newsletter is distributed by email and covers brief descriptions of some
useful but less publicized radiographic, ultrasonic, penetrant, magnetic
particle, and other NDT methods. You will automatically receive the
newsletter, at no cost. If you wish to be removed from the NDTech
Newsletter, simply reply with "Remove" as the subject.

To find out more about NDTech and its nondestructive testing consulting
services and instrumentation, visit the NDTech website at
http://www.ndtech.net/
**********************************************************************

1. SIMONET- Structural Integrity Monitoring on the NET (report on seminar
UCL NDE Center, 3-30-00)

Introduction to Structural Integrity Monitoring
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr. John Sharp (Cranfield University) explained the background to
structural integrity monitoring (SIM), with particular reference to
offshore applications. In the late 1970's and early 1980's considerable
research was initiated into offshore structure monitoring (Forties,
Heather, Piper Alpha). This included both the use of deck and sub-sea
accelerometers. In addition the first platform to be removed from the North
Sea (West Sole WE) was instrumented before and after removal (in 1978),
with the ability to sever members in situ to establish the effects of
damage on the response. Changes of stiffness were measured, by monitoring
changes to the response spectra. The methods indicated that in low
redundancy platforms removal of a main diagonal member might lead to a 10%
change in response, whereas for a more redundant structure such damage
would only lead to 2-3% change which was comparable with the natural
changes in frequency (~2%). As such it was concluded that structural
monitoring had limited application for detecting reasonable damage in
typical offshore platforms. However, since then there had been considerable
improvements in sensor technology, in computing capacity and the ability to
transmit data onshore.

Acoustic emission (AE) had also been researched in the 1980's, and been
used offshore for example in monitoring crack growth on the Ninian Southern
platform, over a period of 3 years. These cracks had grown around welds at
access windows, many of which needed expensive repair. Monitoring provided
an alternative to repair and the use of AE had proved useful in this
respect.

Full-scale measurements had been made on several offshore platforms
(Magnus, Tern, West Epsilon), with the aim of comparing in-service
performance with design assumptions. In addition to structural monitoring
(using strain gauges, accelerometers) measurements were also made of wind,
wave and current to establish the loading. The results from these had been
valuable in developing improved design methods.

Finally Dr. Sharp indicated the current scope of the SIMoNET web site, and
asked for contributions to this, particularly for relevant papers, details
of meetings, companies in the field and links to other related sites.

Application of Structural Instrumentation for
Performance Verification & Monitoring
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Alan Dougan (Fugro Structural Monitoring) explained his company's long
term involvement in SIM, outlining the background. This included
measurements on offshore structures, bridges and other similar large
installations. He noted that the natural variability in structural response
was around 1.5%. This was compared with measurements on several offshore
platforms. For the Forties structure, FE modelling had shown that a severed
member would lead to a 1-2% change, whereas failure of two neighbouring
members would produce a 4.5% change. Simulation of damage on the eight
legged Ninian North platform, with high redundancy, had shown that loss of
a diagonal member would only produce a 0.5% change, which was not
detectable above the background. As such it had been concluded that the
technique had limited value for monitoring damage in offshore installations.

A severed member had been discovered on the Ninian South platform which
had enabled measurements to be made of its effect (fortunately measurements
had also been made prior to the damage). This showed a 2.5-4% change which
was significant, and in line with the FE predictions.

Mr. Dougan also mentioned full scale offshore monitoring (e.g. Magnus)
where sensors had been installed prior to offshore installation. Comparison
of design and in-service behaviour had shown that the original design was
conservative, and enabled modifications to the topsides to be made without
any strengthening. Similar monitoring of the West Epsilon jack-up (by
Fugro) had been valuable in confirming the design assumptions, particularly
of the foundations.

Structural Monitoring of Large Ship Hulls
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Richard May (BMT, Sea Tech Ltd) described the use of monitoring in the
ship industry. In-service inspection was difficult (large structure, poor
access, limited access time), which made structural monitoring an
attractive alternative. The operational benefits were life extension,
assessment of operational conditions and a record of the structural loads
experienced by the vessel. Cracking from weld defects and corrosion were
some of the main problems. Several commercial monitoring systems were
limited to monitoring global stresses, whereas the problems arose from
concentrated stresses on the hull. BMT had introduced their SMART
monitoring system in 1997, which was now being further developed. Several
different types of display were possible, which were used in real time for
providing warnings etc. British Steel (now Corus) had used the system for
their carriers. The system enabled warnings to be given to slow the vessel
down as a result of high stresses occurring in the structure. The measured
data also provided information on extreme events for insurance purposes.

Future developments included improved siting of sensors (e.g. to measure
loads on shells), and the simultaneous measurement of ship characteristics
(e.g. speed, course, rpm, shaft torque etc), as well as wind and wave
conditions.

Structural Monitoring of Bridges
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr. Graham Tilly (Gifford & partners) provided some general background to
the monitoring of both steel and concrete bridges. In general monitoring
had several benefits, which included identifying problems during
construction, deciding on operational use of the bridge (e.g. in high
winds), assessment of old bridges for higher loads by using artificial
excitation (e.g. laden trucks), and identifying damage in service. The use
of the method on the Severn Bridge had resulted from a prediction of
fatigue cracking in the hangers, which was detected and repaired.

Giffords had been responsible for monitoring the concrete cable stay
bridge across the Dee, and Dr. Tilly explained this in detail. Some cable
stay bridges had experienced problems in heavy rain and wind, with
vibrations occurring. A range of different sensors and probes had been used
on the Dee Bridge, including thermocouples, accelerometers, load cells,
strain gauges, movement gauges and corrosion probes. Details of some of
these probes were given.

The measurements taken after completion of the installation showed very
good agreement with design calculations. The horizontal and vertical
movements under vehicular loading were 0.85 and 0.9 of the calculated
values, respectively, which was very encouraging. Forces in the stay cables
were 0.84 of the design value, showing that the load was spread more widely
than assumed. The response from the corrosion probes had been limited to
date (as expected), but the drying out of the concrete in the first year of
operation resulted in a higher resistivity being measured, which was
beneficial. The bridge was continuing to be monitored, with benefits to its
operation.

Decision Analysis for Target Fatigue Lives
in Combination with a Monitoring Plan
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sirous Yasseri (Granherne, Brown & Root) outlined the method to calculate
fatigue lives in offshore tubular joints, and related this to high
redundancy, where more than one joint could fail without serious
consequences. He related this to risk based design and showed that the
probability of failure of more than one joint from fatigue was low, and
claimed that this demonstrated that fatigue was a less serious problem than
often considered by the industry. Monitoring provided a valuable input to
detecting fatigue failure, and could reduce the need for standard offshore
diver inspection.

Monitoring Movement in the Channel Tunnel
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Stephen Cargo (Eurotunnel) gave background to the construction of the
Channel Tunnel, and its drainage system. The concrete tunnel linings were
monitored during construction and now during operation, using strain gauges
and stress meters. A trial tunnel built before the current one was used to
try out several different types of gauges. Results to date had shown that
the tunnel had performed well during construction. Access was now more
difficult with trains running. The setting up of 'alert' levels was
difficult in practice, as the right level had to be found.

Monitoring of Cyclic Stresses using ACSM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr. Feargal Brennan (UCL) described the development of a stress
measurement instrument, based on monitoring changes in magnetic
permeability. The probe had many advantages, including being able to
measure through coatings, insensitivity to dry/wet conditions, and ability
to use in a range of temperatures. The testing of the probe was described,
together with the software. Overall the potential for using ACSM had been
demonstrated, and test results had shown good repeatability. Further
development would provide a very useful non-contacting stress monitoring
tool.

Monitoring of Fatigue Damage using ACFM
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr. Raymond Kare (TSC) described the ACFM technique for crack detection
and sizing. It had been used for underwater monitoring, as well as for
cracks in topside structures. The software gave a clear indication of the
presence of cracks. ACFM arrays were now in use, where positioning of the
probe was less critical, and could be used via an ROV. Natee Tantbirojn
described recent laboratory work showing ACFM crack monitoring during
corrosion fatigue tests on high strength Jack-up steels. Overall the
technique offered the potential for monitoring cracks through coatings,
marine growth, and in situations where there was short period for access.

Use of Optical Fibre Technology for Bridge Monitoring
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Professor Laurie Boswell (City University) gave a brief background to a
large BRITE-EURAM project, involving several partners, concerned with the
monitoring of civil engineering structures for improved maintenance, which
included monitoring a Norwegian bridge in due course. City University,
together with Kent University and Shrivenham, also had EPSRC funding for
developing the use of optical fibre techniques for monitoring large
structures, including repair.

Brett McKinley and Yonas Gebremichael described developments in optical
fibre methods, using Bragg gratings. These enabled sensitive measurements
of strain to be made (although the results were also temperature
sensitive). These sensors had many advantages including tolerance of high
temperatures, use in harsh environments, lightweight and small in size and
with the capability to measure a large range of strain. Two methods for
using the fibres were available (wavelength domain, time domain). The
advantages and disadvantages of these were compared. Further development
work was underway, to include temperature compensation, improved bonding of
sensors to a substrate and the use of large numbers of sensors in practice.

Interfacing Remote Embedded Sensors for Ultrasonic NDT
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr Alistair McNab (Strathclyde University) described current work to
develop UT transducers for in-situ monitoring of composite materials.
Special interdigital transducers could be used to generate Lamb waves.
Embedded piezo electric plates or fibre wave-guides could be embedded, to
enable sound waves to be generated in areas of interest. Embedded or
surface mounted sensors could be linked by radio waves (wireless
communication), which was an advantage over conventional connection
methods. Overall a prototype system had been developed which was now being
evaluated.

Concluding Remarks
^^^^^^^^^^^^^^^^^^
Professor Dover concluded by saying that it had been a useful workshop. He
encouraged those present to use the web site, and supply information that
could be used to develop the site. Progress on SIMoNET would be presented
at the British Institute of NDT Meeting in the autumn. Further meetings of
this group would be considered by the Steering Committee. Finally he
thanked all those who had presented papers and taken part in the
discussions.


This article is also listed in p.401 in "Insight".
More information about SIMoNET can be obtained from their website,
http://www.simonet.org
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2. Aging Aircraft: The Graying of Our Skies
by Jill Bartel, NTIAC

Unlike fine wine, aircraft do not necessarily improve with age. Eventually
the stresses of take-offs, high-G maneuvers, and land-ings and being
subjected to adverse conditions (such as salt environments) whittle away at
an aircraft's structural integrity. And because this deterioration is
cumulative, the effects only worsen as an aircraft ages.

In 1998 the average age of U.S. Air Force aircraft was 18.8 years, with 41
% of the inventory over 24 years old (including all B-52s, C/KC/EC- 135s,
C- 14 1s, and T-38s) and 53% of the inventory over 15 years old. By 2005,
over 75% of Air Force planes will be over 20 years old. In addition,
changes in the types of missions flown have accelerated the rate of aging
for some types of aircraft, such as the F-16.

Maintenance costs for aging aircraft are significant. In 1997, the Air
Force estimated that the cost of corrosion repair alone was $800 million.
This figure represents a significant burden on C-5. B-52, KC-135, C-141,
and C-130 aircraft.

Speaking at the Aerial Warfare Symposium in February 2000, Secretary of
the Air Force F. Whitten Peters stated that even if all the aircraft now on
the books are delivered as planned, the average age of Air Force aircraft
will increase nine months for every calendar year. He added that operations
and maintenance spending will increase "1 to 2 percent, in real terms,"
every year, because aging aircraft need more service repair. Current
phase-out projections of many USAF aircraft reveal life spans of
unprecedented length. Out to the year 2010, most C/KC-135s, B-52s, C-5As,
C-141s, older C-130s, T-37s, and T-38s (approximately 2400 aircraft) will
still be in service. The average age of all these aircraft will be between
40 and 50 years. The reality of trying to maintain aircraft airworthiness
over an unprecedented 60- to 80-year life span presents a whole new set of
technical problems/issues the original design did not have to meet. Future
operational readiness, availability, and flight safety are at risk. These
aircraft were designed for a finite life span of approximately 20 to 30
years.

One of the most critical aircraft in the U.S. Air Force fleet, in terms of
aging aircraft corrosion, is the nearly 600 C/KC- 135 air-refueling tankers
and special purpose aircraft. With a current average of 35 years, these
aircraft are expected to remain in service until 2040 or beyond. Based on
the current usage rate of approximately 300 flying hours per year, these
planes, when retired, could be as much as five times older than their
design service objective. However, these figures are misleading because
they do not include structural or material degradation due to the
detrimental effects of corrosion.
The primary threats to aging aircraft are widespread fatigue dam-age and
hidden corrosion. Both of these problems degrade the structural integrity
of the aircraft.

Widespread Fatigue Damage
^^^^^^^^^^^^^^^^^^^^^^^^^
The onset of widespread fatigue damage (WFD) in a structure is
characterized by the simultaneous presence of small cracks in multiple
structural details. Where the cracks are of sufficient size and density,
the structure can no longer sustain the required residual strength load
level in the event of a primary load-path failure or a large partial damage
incident. Multiple-site damage and multiple-element damage are subsets of
WFD, where there are multiple cracks either in the same structural element
or in adjacent structural elements. For example, multiple-site damage can
be small cracks in the outer skin around adjacent rivet holes in lap
splices.

As aircraft get older, clusters of small cracks in subsurface layers and
structural elements other than skin can occur. These can be very hard to
find with NDE because they are more deeply buried in the structure. One of
the most widely publicized accidents attributable to multiple-site damage
was the 1988 incident involv-ing an Aloha Airlines 737 that had accumulated
35,496 flight hours and 89,690 flight cycles: while in flight, the aircraft
lost part of its upper fuselage due to multiple-site damage resulting from
corro-sion and disbonding that was not visible through normal mainte-nance
inspections.

When the onset of WFD occurs, the airframe (or major component of the
airframe) has reached the operational life limit. To preclude unsafe
operations once the onset of WFD occurs, flight restrictions or groundings
are the only options until the affected structure is modified, re-placed,
or the aircraft is retired.

To assist in aircraft fleet planning, it is necessary to be able to
predict when the onset of WFD will occur (i.e., estimate when a sufficient
number and sizes of cracks will degrade the residual strength of the
structure to below the fail-safe design level) and to assess if WFD
concerns will affect a significant part of the fleet. To predict the onset
of WFD, it is necessary to 1) accurately predict the residual strength of
the structure after encountering the primary damage with various sizes of
small WFD cracks in the adjacent intact structure, and 2) predict when
these cracks will occur. The development of analytical residual strength
models for the various structural configurations and materials that are
typical of aircraft is an important technical issue to address in the
characterization of WFD.

Hidden Corrosion
^^^^^^^^^^^^^^^^
Hidden corrosion is the type of corrosion that is not readily and directly
detectable from any surface measurement technique. Hid-den corrosion is
often quantified as thickness reduction, or material degradation from an
electrochemical process. There are several forms of corrosion damage:
general attack; localized corrosion; environmental cracking; and property
degradation. The simplest form of corrosion is general attack when a more
or less uniform loss of material occurs over a surface.

Localized corrosion can take many forms. Pitting is often observed in
metals that are coated or otherwise protected by a surface film, and is
probably associated with damaged or weak spots in the coating. Crevice
corrosion is a special form of pitting occurring at crevices or cracks
formed between adjacent surfaces. Poultice corrosion is similar to crevice
corrosion; however, there is some foreign material on the surface and metal
loss occurs under this covering. Filiform corrosion occurs under organic or
metallic coatings and is characterized by a network of threads or filaments
or corroded material under the surface. Galvanic attack is the result of
two dissimilar metals in contact, which, depending on the surface area of
the metals involved, can lead to a more dispersed metal loss.

Certain physical forms of corrosion can also produce localized damage. One
of these is fretting in which metal is removed by the abrasive action of
one surface moving against other. Vibrating machinery produces fretting,
and damage is characterized by surface discoloration and deep gouges or
pits. Liquid flowing over a surface can cause velocity-related damage
effects. If the flow is turbulent or if the liquid contains particles,
erosion can occur and may accelerate corrosion by removing protective
films. Other velocity-related effects are cavitation damage, caused by the
formation and collapse of bubbles; and impingement attack, caused by
high-velocity flow producing a pattern of localized damage with directional
features.

Some materials subjected to tensile stress in a specific corrosive
environment are susceptible to spontaneous brittle fracture, even though
such materials in a noncorrosive environment may be quite ductile. This
phenomenon, known as environmental cracking, is different from
stress-assisted cracking in which a material, weakened by corrosion damage,
cracks under tensile load. Environmental cracking refers to crack formation
under the combined effects of stress and corrosion. Stress-corrosion
cracking can occur in a mildly corrosive environment under tensile stress
that would not normally be considered excessive. Metal loss is small; and
the cracks, which can be either intergranular or transgranular, tend to be
multiple branched. Hy-drogen embrittlement (a severe deterioration of
ductility) is caused by the presence of atomic hydrogen in a metal matrix.
Embrittlement can also be caused by intergranular penetration of liquid
metals. Such reactions occur only for certain combinations of metals and
liquid agents.

Examples of property degradation or material deterioration are
intergranular and transgranular corrosion, corrosion fatigue, and
dealloying. lntergranular corrosion is a highly localized form of damage in
which attack occurs along a narrow path that tends to follow grain
boundaries. Transgranular corrosion is similar to intergranular corrosion
in that attack is highly localized and follows a narrow path through the
material; however, the paths cut across grains with no apparent dependence
on grain-boundary direction. Corrosion fatigue is a term applied to the
degradation of fatigue life in a corrosive environment. Although similar to
environmental cracking, corrosion fatigue is distinguished by the
morphology of the fractured surface. Dealloying refers to the selective
dissolution of an alloy constituent in a chemical reaction, a process that
alters the chemical and mechanical properties of the material.

NDE Methods of Detection
^^^^^^^^^^^^^^^^^^^^^^^^
The development of NDE technology for aging airframe structures is driven
by structural requirements and cost considerations. Proper application of
currently available NDE technology can offer significant improvements in
diagnostic capabilities and provide characterization of the damage
necessary to develop effective structural repairs. In addition, NDE methods
protect structural safety by detecting, providing quantifiable
characterization, and screening fatigue cracking, stress-corrosion
cracking, and corrosion conditions that are, or could become, a
flight-safety concern.

According to the National Materials Advisory Board, the most critical
inspection needs based on the important aging mechanisms include:
* Detection of fatigue cracks under fasteners.
* Detection of small cracks associated with WFD
* Techniques to discover and quantify hidden corrosion without disassembly
of the aircraft.
* Detection and characterization of cracks and corrosion in multi-layer
structures.
* Detection of stress-corrosion cracking in thick sections.

Reliability is one of the most important characteristics of an effective
NDE method. NDE is a statistical process that depends on the inherent
variability of many features including flaw size, orientation, distance of
flaw from surface, surface roughness, and variations in material
properties. A frequently used measure of the reliability of an NDE system
is the probability of detection (POD), which is a conditional probability
defined as the probability that a flaw with given characteristics will be
detected using a given set of inspection parameters. Obviously, a
requirement for an efficient NDE inspection is a high value of POD for the
particular flaw size and geometry.

NDE methods that can be used to detect both widespread fatigue damage and
corrosion in aircraft include eddy current, ultrasonics, radiography,
visual inspection, and acoustic emission. However, visual inspection is
generally not applicable to hidden corrosion. Additional NDE methods that
are used include liquid penetrant to detect WFD and thermal imaging to
detect corrosion.

Eddy current: The properties of eddy currents are heavily influenced by
the electric conductivity and magnetic permeability of the media in which
the currents flow. Defects such as cracks. thickness variations, and
corrosion can change the electrical and magnetic properties of a structure.
Therefore, there will be a localized change in induced eddy currents while
inspecting a defective structure. The detection of defects as small as 0.8
mm (0.03 inch) has been reported, which correspond to cracks that have been
observed beneath typical fastener heads. Additionally, corrosion detection
as low as 2-3% loss of metal in simulated aircraft lap joints has been
reported using pulsed eddy current.

Ultrasonics: A characteristic of traditional piezoelectric ultra-sonic NDE
methods that in many cases may be considered disad-vantageous is the
requirement of a couplant to aid in the transmis-sion of the ultrasonic
sound wave from the source to the structure under inspection. Typically the
couplant is a substance such as water, oil, petroleum, or grease that is
applied to the surface prior to inspection. Crack depths as small as 0.5 mm
(0.02 inch) have been detected using couplant-free laser ultrasonics. The
detection of second-layer fatigue cracks in C-141 aircraft splice joints
has also been reported. In addition, operators have been able to discern
audible changes corresponding to material thinning from corrosion as small
as 4% in a 1.27-mm (0.050-inch) aluminum plate using audilized ultrasonics.

Radiography: Radiographic NDE methods rely on differential absorption
and/or scattering of electromagnetic waves (X-rays or gamma rays) or
nuclear particles such as neutrons. Conventional radiographic techniques
used for NDE are essentially identical to those used in medical X-ray
imaging. Typically, a beam of X-rays is transmitted through an object under
inspection and the resultant energy is detected with a film or
scintillation screen. Cracks with depths of less than 1.3 mm (0.050 inch)
have been detected in a4. I-mm (0.050-inch) aluminum test piece. The
detection of as little as 1.9% material loss due to corrosion has also been
reported. Neutron tomography inspection of an aluminum lap joint from a
salvaged KC-135 aircraft has been reported of being capable of detecting
corrosion as thin as 0.012cm (0.005 inch). In experiments performed on 0.5
1 mm wide by 2.0 mm deep (0.02 inch wide by 0.08 inch deep) slots cut in
aluminum plates, microwaves could detect the cracks whether they are clean,
rust-filled, or paint-covered (one or two layers). Microwaves have also
been reported to detect rust/corrosion on a steel plate under a 4.1-mm
(0.050-inch) layer of paint. This corrosion was undetectable to the naked
eye.

Visual inspection: Visual inspection is used in 80% of the inspections of
large transport category aircraft. Generally, visual inspection provides
the initial indication of defected structures. Inspections are sometimes
conducted with the naked eye, but in many cases visual aids are utilized.
These devices include flexible or rigid borescopes, image sensors, and
magnifications systems. Some devices allow penetration up to 100 feet
(30.5m), in and around complex structure, from the insertion point, which
drasti-cally reduces disassembly requirements.

Acoustic emission: In acoustic emission NDE methods, sensors monitor
structures for characteristic acoustic signals that indicate the onset or
progression of damage or deterioration. This method is passive in that
structures under inspection are not excited with any externally produced
energy such as heat, electromagnetic waves, or ultrasonic waves. In the
case of crack detection, acoustic emissions resulting from crack initiation
and growth are monitored
by piezoelectric transducers. Crack growth in plate-like structures (i.e.,
aircraft skin) often causes the instantaneous frequency of an acoustic
emission signal to increase as a function of time. The ability of acoustic
emission NDE to detect corrosion is limited since most acoustic emissions
caused by the corrosion process have energies below detectable levels.
However, corrosion detec-tion using acoustic emission NDE methods has been
reported for two corrosion states: corrosion initiation and severe
corrosion.

Liquid penetrant: Liquid penetrant inspection is capable of detecting a
wide variety of defect sizes independently of the defect orientation and
the geometry of the structure in which they are located. Liquid penetrants
are able to seep into minute surface openings through a capillary process.
This inspection method allows for the detection of surface cracks, laps,
porosity, shrinkage areas, laminations, and similar discontinuities.

Thermal imaging: Thermographic NDE methods are advanta-geous in that
physical contact with a structure under inspection and the use of a
couplant are not required. Furthermore, large-area scans can be performed
rapidly. Corrosion detection was reported from tests performed on a sample
that was constructed by adhesively bonding a 4.1-mm (0.06-inch) aluminum
plate to another plate that was partially corroded, a configuration similar
to lap joints in aircraft. Subsurface corrosion detection was also reported
on a region along a lap splice on a fuselage section of the Boeing 737
testbed at the FAA's Aging Aircraft NDI Center (AANC) in Albuquerque, New
Mexico. The corrosion appeared as somewhat regular light regions in the
resulting image.

Prognosis
^^^^^^^^^
The effective maintenance of aging aircraft is vitally dependent on
implementing effective NDE methods. Although specific needs are focused
primarily on detection and characterization of cracks and corrosion, each
application involves different component geometry and structural
configuration, requiring revalidation and qualification of NDE methods. The
nondestructive detection and characterization of hidden or inaccessible
corrosion is a very difficult problem.

In general, it is not economically feasible to demand that NDE methods
find the smallest defects possible. In the case of cracks, the maximum
allowable defects can be determined from structural integrity assessments.
The understanding of corrosion effects has not yet advanced to this level.
One of the most important issues in corrosion is to understand the
fundamentals of the chemical and electrochemical process.

The 1997 National Materials Advisory Board (NMAB) Report on Aging Aircraft
includes information on the structural problems experienced in many of the
Air Force's aging aircraft. Based on these service experiences, it is
apparent that there are both specific and overarching features to aging
aircraft NDE needs. Specific needs include the development of techniques to
detect 1) fatigue cracks under fasteners, 2) small cracks associated with
WFD, 3) hidden corrosion, 4) cracks and corrosion in multi-layer
structures, and 5) stress corrosion cracking in thick sections.

The NMAB report indicates that in the long term, the current empirical
approach to validation of new NDE methods should be augmented with analytic
approaches to develop reliable, quantitative NDE methods. Emphasis should
be placed on NDE technique design and development aimed at improved
detection reliability and defect characterization, cost-effective
validation and qualification procedures, transferability to a range of
applications, and interdisciplinary coordination with other elements of the
aging aircraft strategy.

For more information about the NDE methods used to detect widespread
fatigue damage and hidden corrosion, see the following NTIAC documents:
NDE of Cracks in Aircraft, by Jacob K. Easter and George A Matzkanin,
NTIAC-SR-98-04, 1998.
NDE of Hidden Corrosion, by George A Matzkanin and Jacob K. Easter,
NTIAC-SR-98-03, 1998.
NDE of Residual Stress in Metals, by H. Thomas Yolken and George A.
Matzkanin, NTIAC-SR-99-01, 2000.
Nondestructive Evaluation (NDE) Capabilities Data Book, 34 Edition, by Ward
D. Rummel and George A. Matzkanin, NTIAC-DB-97-02, 1997.
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3. Publications

Nondestructive Testing Handbook: Leak Testing, Third Edition, Volume 1.
CD-ROM - Charles N. Jackson and Charles N. Sherlock (technical editors);
Patrick 0. Moore (editor). Leak testing uses a variety of techniques to
detect and locate leaks in pressure containment parts, structures,
evacuated components and systems. Leaks can be detected by using electronic
listening devices, pressure gage measurements, liquid and gas penetrant
techniques, spectrometry, thermography and simple soap bubble tests. This
new multimedia CD-ROM, exclusively from the American Society for
Nondestructive Testing (ASNT), includes live searchable text and extensive
cross links, plus all new audio and video files. Power Mac or Windows95/98
is required to run the CD.

This CD-ROM is available from the American Society for Nondestructive
Testing at www.asnt.org. Contact ASNT for price and ordering information.

Proceedings of the 1999 International Mechanical Engineering Congress and
Exposition - American Society of Mechanical Engineers (ASME). The
proceedings from this conference, held November 14-19, 1999 in Nashville,
Tennessee, have been published as bound volumes organized by topic and as
individual technical papers. This publication program covers the broad
spectrum of current mechanical engineering topics discussed in the more
than 500 technical sessions at the conference. The topic volumes are:
Aerospace; Advanced Energy Systems; Applied Mechanics; Bioengineering;
Design Engineering; Dynamic Systems and Control; Fluids Engineering; Fluid
Power Systems and Technology; Heat Transfer; Materials Handling;
Manufacturing Engineering; Materials; NDE Engineering; Noise Control and
Acoustics; Pressure Vessels and Piping; and Safety Engineering and Risk
Analysis.

These proceedings are available from the American Society of Mechanical
Engineers at www.asme.org in both print and CD-ROM. See the specific
proceedings titles for price and other information.

Nondestructive Methods for Materials Characterization, (Materials Research
Society Symposia Proceedings, Volume 591) - T. Matikas, N Meyendorf, G.
Baaklini, and R. Gilinore (editors). Characterization of material
properties is critical for understanding the material's mechanical behavior
and design performance under operating conditions. The necessity to
characterize materials for a myriad of applications has spurred the
development of many new methods and instruments. NDE has become an integral
part of materials research, especially micro- and macro-structural
behavior. The topics of the 46 papers in these proceedings include process
control and deformation behavior via X-ray techniques; NDE for fracture,
fatigue, and corrosion; electric and dielectric NDE; structure-sensitive
properties for NDE characterization; NDE for silicon wafers and thin films;
and optical and infrared techniques.

This hardcover book is available from the Materials Research Society, at
www.mrs.org It was published in March 2000 and has 322 pages. The book is
priced at $90 in the U.S., $103 outside the U.S., $78 for MRS members.

Materials Science of Microelectromechanical Systems (MEMS) Devices
(Materials Research Society Symposium Proceedings Series, Volume 546) -
Arthur H. Heuer and S. Joshua Jacobs (editors). This volume documents
symposium reports from the 1998 MRS Fall Meeting in Boston, Massachusetts.
MEMS-the integration of sensors, actuators, and electronics-is one of the
fastest growing areas within microelectronics. It has been enabled by
extension of the technology of silicon-based photolithography to mechanical
devices with small dimensions (microstructurcs and micromechanisms), some
of which have already found significant industrial application. The reach
of MEMS is now extending to materials other than silicon, and the scope of
applications is proceeding beyond the simple physical regime (e.g.,
accelerometers and pressure sensors) to chemical and biological sensors.
The 38 papers in this book are divided into four segments by materials
type: processing and mechanical properties of silicon, the mainstay of
current MEMS technology: LIGA-produced Ni and other metals; SiC, Si3N4,
diamond, PZT, and other ceramics; and plastics and other organic materials.

This hardcover book is available from the Materials Research Society at
www.mrs.org. It was published in March 2000 and has 246 pages. The book is
priced at $85 ut the U.S., $943 outside the US., $74 for MRS members.
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4. Acoustic Emission Working Group - 43rd Meeting
-Seattle,WA. July 18/19/20, 2000.

Tuesday, 18 July, 2000;
Welcome/Orientation: 8:00AM-8:10AM Boeing Commercial Airplane
Group/Acoustic Technology Group

Session 1. Structures: 8:10AM-9:50AM Chair: W.Prosser,
NASA-Langley
McBride,S.;AE Monitoring Systems AE Monitoring of Fatigue
Crack Growth Underneath Rivet Heads In a
Multisite Damage
Enviroment
Carlyle,J.;Carlyle Consulting Inspecting Crane Truss
Booms with AE
Ziola,S.;Digital Wave Corp Advances in Modal AE
Technology for Structural Health Monitoring
Lovejoy,S.;Oregon DoT AE Monitoring of Steel
Reinforced Concrete

Session 2. Vessels and Piping: 10:10AM-11:50AM Chair:
T.Drouillard; Digital Wave Corp
Muravin,G;et.al.;Margan Int. Evaluation of Industrial
Piping Condition by Quatitative AE Method.
Can it Replace
Other NDI Methods?
Mizutani,Y.;et.al.;A.Gakuin University Damage Location on a GRP
Storage Tank via Lamb-Wave Analysis.
Allevato,D.;Stress Engineering AE as a Tool for Predicting
Fitness-for-Service
Akhtar,A,et.al.;Powertech Labs Inc. Structural Integrity of the
Oxide Scale on Steel Surfaces
Shen,W,et.al;Physical Acoustics Corp. AE Detection of Damage In
Reinforced Concrete Conduit

Session 3. Materials: 1:10PM-2:50PM Chair: J.Carlyle,
Carlyle Consulting
Ono,K;University of Cal. Los Angeles AE in Materials Researcg
for the New Century
Yoshida,K;et.al;Univ. of Tokushima Monitoring of
Micro-Cracking During Heating Process of Hydrogen
Ion Doped Germanium
& Silicon Single Crystals by AE Method
Prine,D;Northwestern Univ. lTl AE from Compression Loaded
Stand-Alone Plasma-Sprayed Aluminum
Kubit,M;Oregon Graduate Institute AE from Fretting in Aluminum

Session 4. General Application: 3:10PM-4:50PM Chair: W.Hardrath,
Boeing Commercial Airplane Group
Vallen,J;et.al;Vallen GmbH Achieving Improved Location
Accuracy Efficiently
Dunegan,H;Dunegan Engineering Detection/Location of
Meterorite Impact on Space Vehicle Surfaces
Shiotani,T;et.al;Tobishima Corp. AE Activity with Slope
Behavior on a Slope Model of Rock
Hamstad,M;et.al;University of Denver AE Signal Features in Small
Lab. Samples vs. Large Plate Samples
Kouroussis,D;et.al;Physical Acoustics Wind Tunnel Blade AE
Testing Using Pattern Recognition Technique

AEWG Business Meeting Tuesday, 18 July, 2000; 5:00PM-6:15PM

Wed., 19 July, 2000;
Session 5. Information Processing: 8:10AM-9:50AM Chair: R.Blackburn,
Consultant
Tsimogiannis,A;et.al;Physical Acoustic Data Fusion of AE/AU
Results for Damage Evaluation in Concrete
Schlembach,M;University of Illinois Acoustic Emission
Information Resources
Godinez,V;et.al;Physical Acoustics Advances in AE Source
Location Methods for Pressure Vessels
Nordstrom,R;Portland State University Characterizing Rapid
Sequences of Acoustic Emission

Session 6. Materials: 10:10AM-11:50AM Chair: K.Ono,
University of California at Los Angeles
Ohtsu,M;Kumamoto University Damage Mechanics of
Concrete by AE Rate Process Analysis
Prosser,W;et.al;NASA-Langley Comparision of FE Models
and Simulated AE Signals with a Resonant
Sensor in a Tensile
Coupon Specimen
Finkel,P;et.al;Physical Acoustics Characterization of the
Damage and Fracture Mechanisms in Ternary
Ceramic TiSiC2 Using AE
Shiotani,T;et.al;Tobishima Corp. AE Activity with Slope
Behavior on a Slope Model of Rock
Vallen,H;et.al;Vallen GmbH Threshold Independent Crack
Detection During Scratch Testing

Session 7. Industrial Application: 1:10PM-2:50PM Chair: R.Nordstrom,
Portland State University
Clark,E;et.al;University of NE-Lincoln Monitoring Abrasive Flow
Machining (AFM) Process Parameters in
Real-Time Using a
New AE Technique
Dornfeld,D;et.al;Univ. Cal. Berkeley Monitoring Precision
Manufacturing Processes with AE
Godinez,V;et.al;Physical Acoustics AE Characterization of
Cavitation/Detonation in Combustion Engines
Akhtar,A;et.al;Powertech Labs, Inc. Diagnosis of Osteoporosis
Using Acoustic Emission

Session 8. Commerica Presentation: 3:10PM-4:50PM Chair: A.Green,
Acoustic Technology Group
Order to be determined by drawing: Dunegan Eng; Margan Physical
Diagnostic, Physical Acoustics Corp; Vallen-Systeme GmbH.

AEWG:Reception 5:30PM-6:30PM No host bar.
AEWG:Awards Banquet 6:30PM-8:30PM
Banquet Speaker: Jack C. Spanner, Sr.;Co-Founder and
Honorary Member - AEWG

Thursday, 20 July ,2000
Session 9. Tour: 8:30AM-11:30AM
Boeing Engineering Test Lab. Chair: W.Hardrath,
Boeing Commerical Airplane Group

For additional information on the Acoustic Emission Working Group see
website: http://www.aendt.com
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5. Ceramics WebBook
Materials scientists wanting easy access to ceramics data on the
World Wide Web should point their Internet browsers to a new resource: the
NIST Ceramics WebBook at http://www.ceramics.nist.gov/webbook/webbook.htm.
This WebBook contains evaluated data, a guide to data centers and sources,
as well as software tools and other resources useful for materials
research. The Ceramics WebBook has a link to three NIST-developed materials
databases:the NIST High Temperature Superconducting Materials Database, the
NIST Structural Ceramics Database, and the NIST Property Data Summaries for
Advanced Materials. In addition, the Ceramics WebBook links to 22 other
government and academic data centers and Web resources devoted to
biomaterials, ceramics, metals, and composites, as well as chemical and
physical data. Another page of tools and resources provides links to
software tools, a ceramics virtual library, a discussion forum, and
educational sites.
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Citation of trade names and manufactures does not constitute endorsement or
approval of any product.
Copyright 1999 NDTech.

NDTech website: http://www.ndtech.net
Email: info@ndtech.net




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