NDT.org : Information : Newsletters : NDTech Newsletter #17

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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_______________________________________________________________________

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_______________________________________________________________________

Neither NDTech nor any person acting on their behalf assumes any liability

resulting from the use or publication of the information contained in this

document, or warrants that such use or publication of the information

contained in this document will be free from privately owned rights.

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