Identification of Aging Aircraft Electrical Wiring

Woolrich Engineering Consulting Firm

Midterm Report

Group Members: Robert Beremand – Project Manager Chad Hanak – Senior Engineer Melissa Straubel – Senior Engineer

Sponsors: Dr. R. O. Stearman Marcus Scott Kruger

March 7, 2003

Woolrich Engineering Consulting Firm Austin, TX 78705

March 7, 2003 Dr. R.O. Stearman Department of Aerospace Engineering and Engineering Mechanics College of Engineering, University of Texas at Austin Dear Sir: The attached report contains a description of Woolrich Engineering Consulting Firm’s efforts in evaluating wire aging experiments and the effect of aging on the triboelectric effect. Within the report are background information, theory, a description of the experimental setup and laboratory specimen, a list of work that WECF still needs to complete, and a description of the cost analysis. The background information discusses the history of the problem, recommended solutions to the problem, and also presents technical background including the types of wire failures. A description of the triboelectric effect and frequency response are presented in the theory portion of the report. In subsequent sections, descriptions of the wire to be used in our experiments, as well as an explanation of the test setup, are discussed. While we have yet to simulate the aging of the wires, WECF was successful in obtaining wire, an incubator and a freezer, and evaluating the test setup. The attached report contains the first half semester’s work; however, if you have any questions/comments, please feel free to contact us via email at beremand@mail.utexas.edu. Sincerely, Melissa Straubel Robert Beremand Chad Hanak Senior Engineer Project Manager Senior Engineer

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Abstract

The analysis techniques and results developed in this paper were motivated by a need to find a viable method of determining the quality of aircraft electrical wiring. Deteriorating insulation on electrical wiring is considered a significant safety hazard in aviation. An aircraft’s wiring cannot be visually inspected without disassembling the craft, which is not a feasible option. Therefore, an indirect method of gauging the condition of a wire’s insulation is required. This study builds upon the research of previous studies by attempting to use the triboelectric effect in wiring to determine the condition of the wire. The authors hope to find that a wire excited by a vibration of know frequency and amplitude will produce a predictable triboelectric response that varies with the condition of the wire.

Wire specimen aging techniques from previous studies were evaluated and modified to yield better (faster) results. A freezer and an incubator have been acquired for this purpose, but are not yet operational. Consistency problems with the wire analysis test setup used by previous studies have also been addressed, and solutions proposed. Particular attention has been given to reducing the Electro-Magnetic Interference (EMI) between various testing components. The direction of future work has also been noted.

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Acknowledgements

WECF would like to thank our sponsors for this project, Dr. R.O. Stearman and

Marcus Kruger. Dr. Stearman, who is an aerospace engineering professor at the

University of Texas at Austin, has been instrumental in acquiring several major

components for this project. These components include an incubator in which we will

conduct our heat and humidity tests and a freezer in which we will conduct our cold tests.

He has also used personal contacts to assist us in obtaining actual aged wire from an

aviation scrap yard in Dallas. Marcus Kruger, an aerospace engineering graduate student,

has provided his knowledge and guidance in the setup of this project. WECF has met

with him during weekly consultation sessions in which we analyzed the experimental

setup and methods for testing.

WECF would also like to thank Frank Wise, the onsite electrician for the

Aerospace Engineering and Engineering Mechanics Department. He offered his

expertise to assist us in researching and obtaining the wire we will be using in our

experiments.

Without the contributions of these individuals, the work conducted by WECF

would have been incredibly difficult and time consuming.

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Table of Contents

Abstract............................................................................................................................... i Acknowledgements ........................................................................................................... ii List of Tables and Figures ............................................................................................... iv 1.0 Introduction........................................................................................................... 1

1.1 Previous Work................................................................................................... 1 1.2 Methodology ...................................................................................................... 2 1.3 Project Scope ..................................................................................................... 4 1.4 Report Overview ............................................................................................... 4 2.1 Types of Wire Failures ..................................................................................... 6 2.2 Current Methods Used to Detect Faulty Wiring............................................ 6

3.0 Theory .................................................................................................................... 7 3.1 Triboelectric Effect ........................................................................................... 7 3.2 Frequency Response ......................................................................................... 9

4.0 Laboratory Specimen ......................................................................................... 10 4.1 Wire Selection.................................................................................................. 10

5.0 Phase I: Laboratory Aging................................................................................. 12 5.1 Data Collection Cycle ..................................................................................... 12 5.2 Aging Processes ............................................................................................. 13 5.3 Aging Equipment ............................................................................................ 16 5.4 Anticipated Results ......................................................................................... 17

6.0 Age Analysis ........................................................................................................ 19 6.1 Experimental Setup ........................................................................................ 19

6.1.1 Signal Analyzer/Computer........................................................................ 19 6.1.2 Data Acquisition System........................................................................... 20 6.1.3 Amplifier................................................................................................... 20 6.1.4 Electromagnetic Shaker ............................................................................ 21 6.1.5 Electromagnetic Interference (EMI) Reduction........................................ 21

6.2 Anticipated Results ......................................................................................... 22 7.0 Work to be Completed........................................................................................ 26

7.1 Acquisitions ..................................................................................................... 26 7.2 Preparation of Experimental Setup .............................................................. 27 7.3 Verification and Testing ................................................................................. 27

8.0 Task Distributions............................................................................................... 28 9.0 Cost Analysis ....................................................................................................... 29 10.0 Conclusion ........................................................................................................... 30 11.0 Works Cited......................................................................................................... 31 12.0 Appendix – Timeline........................................................................................... 32

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List of Tables and Figures Figure 1: Wreckage from TWA Flight 800 [3]

Figure 2: Relative movement between insulating and conducting surfaces induces a

current [5]

Figure 3: Alpha Wire Spools

Figure 4: Data Collection Cycle Comparison

Figure 5: Aged Wire Samples [4]

Figure 6: Freezer Donated by UT-Austin Zoology Department

Figure 7: Signal Analyzer, Amplifier, and shaker [4] Figure 8: Wire/Electromagnetic Shaker System

Figure 9: Differences in Redox Reaction Rates Can Create an Electric Potential Between

Two Materials [7]

Figure 10: Diagram labeling the distribution of tasks

Table 1: Wire Specifications [8]

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1.0 Introduction

Since the 1980s, the Navy and Air Force have documented problems with aircraft

electrical wires exposed to prolonged high heat, moisture, chemicals, and vibration

during aircraft operation. Faulty electrical wire insulation has caused in-flight fires and

electrical failures in addition to control connection failures. This has caused

malfunctions in aircraft spoilers, and has triggered inadvertent autopilot commands, or

disabled the autopilot completely [1].

Similar problems have occurred in the commercial airplane industry. More than

half of the world’s passenger jets contain potentially problematic wire insulation [2].

Two high profile crashes, TWA Flight 800 and Swiss Air Flight 111, were blamed on

faulty electrical wiring.

Figure 1: Wreckage from TWA Flight 800 [3]

1.1 Previous Work

The fall 2002 group performed laboratory aging tests on Alpha 1632 wire

specimens. From the laboratory aging results, the previous group concluded that heat and

humidity tests did not properly age the wire specimens. Visual and touch inspections of

wires aged over 7 ½ weeks showed no changes in the wire’s physical characteristics. The

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group felt that this result was due its inability to increase the temperature imposed upon

the wire specimens above 120°F [4]. The group also felt that the laboratory aging

experiments would be more affective if conducted over a longer amount of time.

Another test was performed by the fall 2002 group in which they exposed the

Alpha wire to saltwater and Jet-A fuel. They concluded that the saltwater and Jet-A fuel

tests successfully simulated the aging of the wire. Visual inspection of wire subjected to

a saltwater solution showed corrosion that tarnished the wire and bonded the copper

strands together. Physically handling the wire revealed that was noticeably more brittle.

Visual inspection of wire submerged in Jet-A Fuel showed that the rubber insulation had

expanded in diameter and length [4].

In the age analysis portion of the group’s project, they were unsuccessful in

identifying a relationship between the aged wire and its triboelectric response. Single

frequency tests were performed on the aged wires, but no trend could be determined from

data points that were taken. The group suspected the inaccurate data were due to

electromagnetic interference attributed to the electromagnetic shaker because of its

proximity to the wire circuit [4].

1.2 Methodology

This study attempts to build on the work of previous design groups who have

examined this problem. In particular, three tasks are being given a great deal of attention:

• Redesigning and validating the age analysis laboratory setup

• Enhancing the thermal wire aging technique and setup

• Searching for qualitative evidence that the triboelectric response of a wire deteriorates

with age by analyzing documented wires collected from aviation scrap yards.

3

Previous design groups, notably BSS Engineering Inc. (the fall 2002 group), reported that

the current age analysis laboratory setup is not capable of consistently reproducing a

characteristic triboelectric response from a nominal piece of wire [4]. Without the

capability to reproduce nominal results in a controlled test setup, the testing of actual

aged wire specimens is of no real value. Thus, it is important for WECF to first modify

and validate the laboratory analysis setup before attempting to generate any triboelectric

response data.

Another difficulty encountered by previous design groups involved the thermal

aging technique employed to deteriorate the wires’ insulation. Past thermal aging

techniques involved placing wires in an environmental chamber in Ernest Cockrell, Jr.

Hall, which is under the administration of the Civil Engineering Department at the

University of Texas at Austin [4]. This technique proved to be ineffective, however,

because ongoing civil engineering experiments that also resided in the chamber required

a constant temperature of 120°F [4]. Such a temperature is well within the operating

range of the wire insulation, and, therefore, did little to deteriorate the insulation over the

7 ½ week duration of the study. In order to more effectively thermally age the wire

specimens, WECF decided it was necessary to obtain their own equipment. This will

remove the constraints that kept the previous design group from successfully thermally

aging their wire specimens.

The technique WECF plans to use to thermally age the wire was a thermal cycling

process. Wire specimens will be placed in the environmental chamber and subjected to a

temperature of 170°F. After 24 hours of heat, the specimens were removed from the

chamber and placed in a freezer for 24 hours. The cycle will then repeat for the duration

of the study. Other aging techniques employed by WECF will be identical to those

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employed by BSS Engineering Inc. One set of wire specimens was soaked in salt water,

and another set was soaked in Jet-A fuel. These techniques were proven to be effective

by BSS Engineering Inc., and, therefore, will be repeated by WECF.

Finally, WECF decided to use wire that had seen years of service in actual

aircrafts to search for qualitative evidence that the triboelectric response of a wire

changes as the wire ages. The limited amount of time in which this study had to be

conducted meant that it would be possible to age wire specimens by only a small amount.

The controlled aging techniques, however, will allow WECF to search for a quantitative

trend that defines the change in the triboelectric response of a wire with time. Since this

result is not at all apparent at present, it was deemed prudent to collect documented wires

of various ages from an aviation scrap yard and analyze their triboelectric responses to

see if a qualitative trend could indeed be observed.

1.3 Project Scope

This report presents the theory behind the triboelectric effect that motivated this

study. The results of previous design groups, and their effects on current undertakings,

are also discussed. All modifications to the previous laboratory analysis setup and aging

techniques are noted in detail. The report culminates with the results and conclusions

arrived at by WECF. Finally, recommendations for further investigations into wire age

analysis are presented.

1.4 Report Overview

In the following sections of this report, WECF will explain the technical

background and theory behind this project, describe the wire we have chosen to use in

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our experiments, and give technical details of the wire aging techniques and experimental

setup. We will also provide a list of the work we plan to complete in the second half of

the semester, as well as a description of the costs we have encountered thus far.

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2.0 Technical Background

2.1 Types of Wire Failures

When wires deteriorate, the insulation can begin to chaff and crack. This may be

a result of prolonged exposure to harsh temperature, humidity, corrosion, and/or vibration.

Kapton wire appears to be particularly vulnerable to this. When the insulation chaffs and

cracks, the risk of electrical fires increases. Also, chaffed and cracked wire insulation

can cause control malfunctions. By far, the most dangerous wire failure is a phenomenon

called "arcing, in which and exposed wire comes in contact with [another] metal object,

[typically] the frame of [the] aircraft or another exposed wire, to create a short circuit" [4].

When this happens, it creates large amounts of heat, which can ignite the insulation. The

fire can then travel down the wire consuming more insulation and exposing more wire.

Obviously, any system in which this occurs will fail. Worse, the affect can potentially

spread to other systems causing them to fail as well [4]. "Other less significant electrical

system problems involve open circuits, bolted short circuits, intermittent open circuits,

and degraded shielding. Nevertheless, even these minor failures could prove to be

catastrophic, should they occur on critical systems" [4].

2.2 Current Methods Used to Detect Faulty Wiring

Unfortunately, there is currently no widely accepted, widely available method for

detecting faulty wiring. Some industry experts believe the triboelectric response may be

usable to determine the condition of a wire.

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3.0 Theory

The theories utilized in this project are the theory of the triboelectric effect and

the theory behind signal response. Both are discussed in the following sections.

3.1 Triboelectric Effect

The triboelectric effect is more commonly known as static electricity. It occurs

when two materials slide against each other. In the case of electrical wiring, the two

materials are the insulating and conducting materials of a wire. As seen in the figure

below, a frictional force from the two materials sliding against each other causes

electrons from one material to separate and reattach themselves to the second material.

This creates a charge imbalance between the two surfaces, and the current induced from

this imbalance creates unwanted noise and interference. To a certain extent, this is

unavoidable in a signal.

Figure 2: Relative movement between insulating and conducting surfaces induces a

current [5]

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The magnitude of the triboelectric effect is dependent upon numerous factors, such as:

• material composition

• the humidity to which the material is exposed

• the strength of the frictional forces

• the rate at which the electrons separate from one material and reattach themselves

to the other

A general equation for the current induced between two materials is [4]:

DMQC

DkMvi

n

+= (3.1)

Where

k = proportionality constant, which is unique to the material M = mass flow rate D = average particle diameter v = particle velocity n = exponent, which is unique to the material Q = charge on contacting particles i = triboelectric signal C = proportionality constant

The relationship given in this equation may be applicable to a straightforward situation,

such as a single particle running along a surface, but is difficult to apply to more

complicated problems, such as quantifying the aged state of a wire with electrical current.

Because these factors will change with the age of the wire, WECF did not find it

necessary to attempt to quantify each parameter. However, we still expect to find a

relationship between the state of the wire and its triboelectric response.

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3.2 Frequency Response

Frequency response is a system’s response characteristics to a wide range of input

frequencies. Frequency response is usually discussed in terms of gain and phase. The

general transfer function of the system is expressed as [4]:

)()(

)( 0

fGfG

fHi

= (3.2)

Where

H(f) = system transfer function )(0 fG = frequency spectrum of the output signal )( fGi = frequency spectrum of the input signal

There are two methods for analyzing the frequency response of a system:

• A single frequency signal is applied to the system and the amplitude of the

resulting output is measured. To determine the gain of the system, which is the

ratio of output and input amplitudes, this process is repeated for a range of

frequencies [4].

• A random noise signal is applied to the system and its instantaneous response is

measured. This is performed in order to simultaneously test all frequencies in

question. For this method, the frequency response is the ratio of the cross

spectrum and the autospectrum of the input [4].

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4.0 Laboratory Specimen

4.1 Wire Selection

To provide some constancy with the previous work done on this project, we have

decided to continue to work with ALPHA 1632 wire. This wire has rubber insulation and

was initially suggested to previous groups by Frank Wise, the department electrician, as a

type of wire that might deteriorate quickly. We have also decided to cut this wire into the

same size segments. We did purchase red wire to help immediately distinguish from the

black wire used last fall.

In addition, Dr. Stearman has suggested that we test a wire with Teflon insulation,

as Teflon is a more common insulator in industry. Teflon is tougher than rubber. It is

more resistant to corrosion and temperature extremes than rubber. Also, it has a much

lower coefficient of friction, and, therefore, presumably, has a less pronounced

triboelectric effect [8]. ALPHA 5852 was selected for its low price, Teflon coating, and

because its other characteristics seemed to be average. A smaller diameter, higher gauge,

was chosen for the Teflon wire, based on the fact that a narrower wire has a greater

surface area to volume ratio. WECF is confident that this will make it more susceptible

to corrosion than a similar, thicker wire. In addition, we predict that this high surface

area to volume ratio may cause it to have a more pronounced triboelectric effect than a

similar, thicker wire. We tried to find literature to either support or refute this theory, but

were unable to find any. Also, a narrow wire has the added benefit of being less

expensive. This allows us to make longer segments of wire, which we believe should be

beneficial. It stands to reason that shaking a long section of wire would generate more of

a current than shaking a small section of wire.

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ALPHA 1632 ALPHA 5852

Figure 3: Alpha Wire Spools

Some additional specifications for the wires we are using are presented in Table 1.

Table 1: Wire Specifications [8]

Alpha Wire 1632 • Hook-Up wire, Test Lead wire • Copper wire with rubber insulation • 20 Gauge (thick) • Stranded, Tinned Copper • Rubber Insulation • -30o to 90o C

Alpha Wire 5852 • Hook-Up wire • 28 Gauge (thin) • Stranded, Silver-plated Copper • Teflon insulation • -60o to 105o C • Low Friction • High Chemical Resistances

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5.0 Phase I: Laboratory Aging

5.1 Data Collection Cycle

In order to improve the size of our data sets, we deemed it necessary to restructure

the data collection procedures. The fall 2002 wiring group was limited to collecting one

point of data at any given time during the aging processes, because of their collection

methodology. They began aging all their wire segments at the same time. Then,

periodically, they would remove one sample at a time from each aging process, test it,

mark it, and not return it to the aging process afterwards [4]. In order to avoid such

limitations, we will, instead, remove every sample simultaneously at every collection

time. All the samples will be tested, and then returned to the aging process afterwards to

perpetuate the study. In this way, data yield at a given time will be increased ten fold as

there are ten wire samples for each aging process.

Figure 4: Data Collection Cycle Comparison

In addition to increasing the size, and thus the robustness, of the data sets, there

are other side affects of the new method. One positive side affect is that, because the

samples are always returned after testing, there does not need to be a set date for the end

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of the aging process. Thus, the summer group will be able to continue further aging of

the same samples immediately should they choose to do so. A negative side effect will

be the loss of the ability to retest data at a later date. Because the samples are effectively

recycled, there will be no way to recheck the previous conditions of the samples once

they are returned to the aging process. Should a problem in the testing be discovered

later, it will be impossible to correct. Thus, great care must be taken to make sure that

the samples are evaluated correctly before aging is resumed. Also, due to the extra

burden of testing so many samples at once, we will probably be taking data every week

or every other week rather than every half week, as the fall 2002 group did. In addition,

Visual inspections will be impacted by the new procedures. The fall 2002 group would

strip the ends of the insulation off the wire samples when they were removed from aging

[4]. Stripping is necessary to allow the wire samples to be hooked up to electronics. It

also provided visual data of what had happened to the wire underneath the insulation. If

the samples are to be repeatedly used, they must be stripped from the beginning. The

exposed ends will have to be protected with removable covering of some sort, and will

not be a good representation of the rest of the wire. However, there is a simple solution

to this problem. A group of short wire segments, perhaps only two inches, cut from

surplus wire, can be added for the sole purpose of providing visual data. These mini-

samples will be removed one at a time, partially stripped, tagged, and preserved for side

by side comparison. After considering the possible ramifications, it was decided that the

benefits of the new data collection procedures outweighed trade offs.

5.2 Aging Processes

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The aging processes we will be exploring this semester fall into two general

categories, temperature plus humidity, and corrosion. The fall 2002 group performed

temperature and humidity processes separately. They were unable to realize the desired

results from heat alone, but attributed this to an inability to achieve adequate heat due to

facility restrictions [4]. By acquiring our own equipment, we hope to reach higher

temperatures. We have also decided to examine the effects of cold temperatures. It may

be a coincidence, but both TWA 800 and Swiss Air 111, probably victims of wire failure,

flew in cold conditions [4]. Furthermore, we firmly believe in the potential of cycling

back and forth between temperature extremes. Although the fall 2002 group found only

minimal results from humidity alone, we believe the presence of moisture will be an

important component of the temperature plus humidity aging processes, especially when

cycling between hot and cold [4]. Adding water will generate periods of freezing and

thawing which will apply mechanical aging on a microscopic level. We are very

optimistic about this combination.

The corrosion aging processes will simply involve exposing the wire samples to

corrosive solutions by means of soaking. The two corrosives to be used are the same as

those used by the fall 2002 group, Jet-A fuel and Salt-water solution. Both corrosives

yielded some results. The saltwater solution had corroded the conductor, and fused the

strands together. Also, the wire exposed to saltwater became noticeably more brittle.

Figure 5: Aged Wire Samples [4]

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The Jet-A fuel had a definite visible affect on the rubber alpha wire, particularly in

significant swelling of the insulation [4].

There is a disconcerting potential side affect from using corrosive soaks, and that

is how any residue that might be left behind might alter the triboelectric response. To

illustrate this concern, consider that, to reduce the triboelectric affect, some wires are sold

with graphite lubricant in between the insulator and the conductor. The graphite serves to

reduce friction and therefore reduce the triboelectric effect [9]. Thus, the presence of

another form of matter can alter the triboelectric effect without altering the age of

condition of the wire. Therefore, it may be possible that salt deposits, or residual Jet-A

fuel could upset the data. One solution would be to remove the foreign material before

testing. Salt could probably be partially removed by a brief, fresh water wash or soak.

Jet-A fuel residue might be more challenging to deal with. Fortunately, if residue does

have a significant effect, we believe it should affect the data consistently. Thus, if

residue is important, the initial application would result in a dramatic change, and then a

constant, unchanging affect.

In addition, we plan on having a group of wires that cycle through all the different

tests. We are also considering the possibility of having groups of wires that are under

tension while aging. In an email to the fall 2002 group, Ronald Galvez of the NASA

Integrated Wire group mentioned that wires under tension tend to age more quickly [10].

Though vibration was specifically mentioned as a potential cause of wire

deterioration, it is not being used in our age processes, because it was deemed to difficult

to accelerate the affects.

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5.3 Aging Equipment

Certain Equipment is necessary to age the wires. The corrosive tests merely

require the corrosive agent, and a large enough bucket. Temperature and humidity,

however, require a more elaborate setup.

Several options were examined for a heating element. Commercial, kitchen ovens

were eliminated because one could not be found that was rated safe for continuous use.

Drying Ovens were quickly ruled out because they are designed to remove humidity.

After a good deal of searching, incubators were also ruled out initially, because one could

not be found with sufficient heating abilities. Thus, we began to consider environmental

chambers. The environmental chambers showed some promise. They were capable of

both hot and cold temperatures beyond our needs. Many could control humidity, and

several were programmable. Programmability would be particularly nice as it would

allow the temperature cycling to be automated and, thus, more frequent. Finding

adequate information on the specifications and prices of environmental chambers was

difficult, and could only be accomplished with calls to companies. Unfortunately, we

could not find a model within our reduced budget. Two units were found for about

$7,000, but these were refurbished, and only came with a three to four month warranty.

Even these were too expensive. The UT surplus on Pickle campus was contacted, but

they had had auctions a few weeks earlier, and did not have any useful equipment on

hand.

Fortunately, Dr. Stearman discovered that the Zoology department had and old

incubator and an old freezer that they no longer had a use for. He was able to secure this

equipment for us for free. Furthermore, it was his understanding that the incubator, a

Labline model, was capable of generating the levels of heat desired. Once the freezer,

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formerly used to store dead animals, is cleaned by the university, and a Labline

technician can come out to inspect the incubator, we will be able to take possession of the

equipment.

Figure 6: Freezer Donated by UT-Austin Zoology Department

The freezer is not designed to control humidity, thus, something must be done to

retain moisture during the cold treatment. The most likely option is placing the wires in

small, sealed containers. Also, if wires are to be placed under tension during aging, some

type of apparatus, perhaps a rack, will be needed for that purpose. If we decide to

employ tension, we will seek the advice of Ronald Galvez.

5.4 Anticipated Results

It is expected that, as the wire deteriorates, its material properties will change. As

the insulation loses its elasticity and corrodes, its texture, friction characteristics,

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impedance, and/or ability to retain or absorb charge my change. In addition, the

conductor may corrode or develop cracks, and it material properties could, therefore,

change as well.

Furthermore, it is expected that these changes will be reflected somehow in the

triboelectric response. The changes should exhibit definite trends that, hopefully, can be

eventually related to the condition of the wire.

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6.0 Age Analysis

Once aged sections of wire have been acquired, either through laboratory aging or

from aviation scrap yards, their triboelectric response must be obtained. This is done by

exciting the wire with a known harmonic vibration and measuring its open-circuit

electrical output. This electrical output is the triboelectric response of the wire, and is

expected to vary with both the condition of the wire and the frequency of the excitation

vibration.

6.1 Experimental Setup

The experimental setup has four major components: signal analyzer/computer,

data acquisition system, signal amplifier, and electromagnetic shaker. The components

are connected in the manner utilized in a previous study by Steinbarger, et al [4].

6.1.1 Signal Analyzer/Computer

A Dell computer controls the entire experiment through the interface of IDEAS, a

laboratory measurement and analysis program. The IDEAS program is used to generate a

known harmonic signal that excited the wire. The electric response from the wire is then

acquired by the program, plotted, and analyzed. Two types of signals will be generated

by IDEAS, and the wire’s responses analyzed: a periodic function of known frequency

and amplitude, and a random noise vibration consisting of many periodic signals with a

range of frequencies. The former signal is useful to determine the effect of a wire’s

physical condition on its triboelectric response at a given frequency. That is, the manner

in which a wire’s triboelectric response varies as the wire deteriorates. The latter signal

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is used to determine the frequency response of a wire. The purpose here is to determine

whether or not the frequency response of a wire varies with the wire’s physical condition.

6.1.2 Data Acquisition System

The Hewlett Packard 3566A/67A Data Acquisition System serves as the interface

between the computer and the wire/electromagnetic shaker setup. The device is

necessary to convert the digital signal that the computer generates to the analog signal

that is needed to operate the electromagnetic shaker. Additionally, the analog signal

generated by the triboelectric response of the wire must be converted into a digital format

before it can be sent to the computer.

Figure 7: Signal Analyzer, Amplifier, and shaker [4]

6.1.3 Amplifier

The analog signal output by the data acquisition system is not powerful enough to

operate the electromagnetic shaker. Thus, the signal has to travel through a MB

Electronics 125V Power Amplifier. Following the precedent set forth by Steinbarger, et

al, the amount of amplification is kept constant and all changes in the amplitude of the

excitation signal are made via the IDEAS interface [4].

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6.1.4 Electromagnetic Shaker

The electromagnetic shaker is powered directly by the signal output from the

power amplifier. It vibrates in the axial direction according to the amplitude and

frequency specified in the IDEAS interface. A stinger is used to protect the shaker by

indirectly connecting it to the wire specimen under examination. Should the motion of

the system approach the safety limits of the shaker, the stinger will fail before the shaker

is harmed.

6.1.5 Electromagnetic Interference (EMI) Reduction

A previous study by Steinbarger, et al, has suggested that electromagnetic

interference (EMI) may have originated from and influenced the various components of

their test setup [4]. It is believed that this interference generated a large amount of noise

that was erroneously incorporated into the response signal from the wire. Such an effect

would help to explain why the group was not able to reproduce a response from a single

wire specimen with any acceptable degree of accuracy. Consequently, several methods

for reducing EMI in the laboratory area are utilized for this study.

First, the data acquisition system and the power amplifier were separated in

order to limit the effect an electromagnetic field generated by one unit might have on the

other. During the aforementioned study, these two units were located one on top of the

other. The data acquisition system, amplifier, and shaker will all be placed inside

grounded foil enclosures as a means of shielding them from EMI. This was suggested by

many sources, including the Alpha Company, which provided the wire that is being used

for this study [6]. Alpha also suggested shielding the wire itself with fully encompassing,

22

grounded foil. We are, therefore, considering placing the wire inside a section of PVC

pipe, which will be wrapped with grounded foil. The PVC also provides us with the

straight and rigid platform, desirable for shaking the wire. We are still researching

whether aluminum foil or copper foil would be the better option. An electromagnetic

field (EMF) meter will be purchased for the purpose of verifying the absence of EMI in

the vicinity of the testing equipment.

6.2 Anticipated Results

Exhaustive analysis of the mechanics behind the triboelectric effect in a wire have

led Woolrich Engineering to model the excited conductor/insulator interface in a wire as

an AC voltage source. The shaker transfers kinetic energy into the wire system, a portion

of which is transmitted to the conductor/insulator interface as friction. A rough

approximation of this friction energy can be derived from the analyzing the work done by

the insulation as it moves past the conductor a length dx , as illustrated in Fig. 3.

Figure 8: Wire/Electromagnetic Shaker System

dx

Shaker

Wire

V

L

R

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The force normal to the surface of the conductor is equal to the hoop stress applied by the

insulation multiplied by the surface area of the conductor. The force of friction is then

given by multiplying the normal force by the coefficient of kinetic friction. Then the

energy imparted on the system by friction is given by the frictional force multiplied by

the relative axial displacement of the two objects, dx . This result is summarized by the

following equation:

6.1

This energy input causes electrons to be stripped from both the insulation and the

conductor. Much like a redox reaction, one of the materials loses electrons at a faster rate

than the other given the same rate of energy input [7]. This idea is illustrated by Fig. 4,

where the magnesium electrode is clearly more negative than the copper electrode.

Figure 9: Differences in Redox Reaction Rates Can Create an Electric Potential Between Two Materials [7]

( ) dxrLE khoop µπσ 2=

24

Thus, there is a net movement of electrons from one material to the other. This will

either create a surplus or dearth of negative charge in a localized area of the conductor.

Since the charge has remained the same in the parts of the conductor that are not

experiencing vibration, an electric potential now exists along the conductor. This will in

turn induce a current. As the motion resulting from the shaker changes direction, the rate

of energy addition into the system decreases, and the potential between the insulation and

the conductor can no longer be maintained. The local equilibrium is reestablished,

creating an electric potential in the conductor that is opposite in polarity from the original

potential. This causes current to be induced in the opposite direction, thus creating

alternating current.

Based on the above discussion, and the friction energy equation derived earlier, it

is expected that the amplitude of the voltage induced as a result of the triboelectric effect

will vary with the coefficient of kinetic friction, and the rate at which each material loses

electrons, given a specified rate of energy addition ( insulationR and conductorR ). Thus,

6.2

Woolrich Engineering believes that the material constants in the above equation

will change in a predictable manner as a wire ages, and so the voltage should also vary

with the age of the wire. WECF hopes to find an empirical formula that describes this

variation in the voltage produced through the triboelectric effect as a function of a wires

age/physical condition.

( )

= conductorinsulation

k RRdt

dEVV ,,µ

25

WECF will also check to see whether or not the triboelectric effect-generated

frequency response of a wire varies with the age and physical condition of a wire. It is

not clear what to expect from this part of the study.

26

7.0 Work to be Completed

In contrast to the first half of this study, which was focused on research and

design, the next month and a half will be oriented toward verifying the test setup and

generating results. There are also a few items that must be acquired.

7.1 Acquisitions

Woolrich Engineering Consulting Firm (WECF), with the assistance of Dr. R. O.

Stearman, has acquired a freezer and an incubator (capable of varying heat and humidity)

free of charge from the Zoology Department at the University of Texas at Austin.

However, these units are not yet ready to be used for the purpose of aging wire

specimens. The freezer was used to hold biological specimens, and so must be sterilized

and inspected by University authorities. The incubator must be inspected by a technician

from Labline (the incubator’s manufacturer) before it is put back into service.

Foil and cardboard boxes must be purchased for the construction of shielded

enclosures for the various laboratory devices used in the age analysis test setup. PVC

pipe will be needed for the enclosure for the wire. Additionally, an EMF meter must be

purchased in order to verify that EMI is not influencing the experimental results. WECF

was unable to find an EMF meter with the desired range in frequencies that could

interface with a computer, so real-time monitoring of EMI will be required during

triboelectric testing.

Finally, aged wire samples must be acquired from an aviation scrap yard in

Dallas. Dr. R. O. Stearman has arranged for WECF to obtain this wire free of charge,

along with the operational history of the specimens. The history of the wire will be used

27

in conjunction with lab tests performed at the University of Texas at Austin to look for

qualitative trends in the aged dependence of a wire’s triboelectric response. A member of

WECF will likely travel to Dallas to pick up the wire in mid-to-late March.

7.2 Preparation of Experimental Setup

This is probably the highest priority going into the second half of the study. The

wire to be used for controlled aging experiments by WECF has recently arrived on site,

and must be cut into sections and possibly twisted into pairs. The EMI shielding

enclosures must be constructed and properly grounded. Additionally, a testing stand

must be constructed to hold each wire specimen in a uniform fashion while the

electromagnetic shaker vibrates it.

7.3 Verification and Testing

Once everything is physically in place, a new wire specimen will be tested for its

triboelectric response to a harmonic input of known frequency and amplitude. After a

short time period, the wire specimen will be tested again to verify the previous results.

Assuming the results are identical, within a reasonable tolerance, the specimen will be

removed from the testing apparatus and the IDEAS program shutdown. Shortly

thereafter, the same specimen will be reinserted into the testing apparatus and the IDEAS

program restarted. The specimen will be tested with the same excitation signal as was

previously used, and the resulting response compared with the first two experiments.

Assuming the results agree with each other, a new specimen from the same wire spool as

the first, and possessing identical dimensions, will be subjected to the same test.

Assuming the response of this second wire specimen agrees with that of the first to a

reasonable degree of accuracy, the test setup will have been verified. At this point,

evaluation of actual aged wire specimens can begin.

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8.0 Task Distributions

At the start of our project, WECF elected Robert Beremand as our project

manager. His responsibility includes organizing the team and its work, making sure all

components of the project are being implemented. All three members of WECF

contribute equally to the project, though each specializes in one of two major segments –

wire aging and age analysis. These technical areas were divided so as to increase the

proficiency of the work performed by the team. Robert Beremand is responsible for

researching and designing the laboratory aging tests. The design of the test setup and

analysis of the process we will assume to acquire a signal response are the responsibility

of Chad Hanak and Melissa Straubel. All members of WECF contribute and participate

equally to the project, and all are present during each of these phases.

Project Manager: Robert Beremand

• Research of lab aging • Design of lab aging

processes

Senior Engineer: Melissa Straubel

• Design of test setup for age analysis

Senior Engineer: Chad Hanak

• Analysis of signal response method

Figure 10: Diagram labeling the distribution of tasks

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9.0 Cost Analysis

The laboratory experiments and tests to be conducted in the second half of the

semester will require a minimal budget. WECF was fortunate to obtain an incubator

from the Zoology Department at no cost. They have also donated a freezer which we will

use for cold tests. Obtaining these two pieces of equipment at no charge has greatly

reduced our cost. The Jet-A fuel and saltwater solutions to be used for lab aging have

been left over from previous teams. Also, the Aerospace Engineering Department at the

University of Texas at Austin already possesses the laboratory equipment necessary for

age analysis: a signal analyzer, a data acquisition system, a wave amplifier, and a shaker.

The only purchase WECF has made thus far is that of the wire itself. One 1000 ft

spool of Alpha Wire 5852 was purchased at $120.90. Also, five 100 ft spools of Alpha

Wire 1632 were purchased at $36.88 for each spool. Our cost purchases, therefore, total

$305.30.

WECF is still researching electromagnetic field detectors. We will need to

purchase one for the age analysis portion of our project, and we expect the cost of this to

be between $100 and $200. Finally, we will need to obtain, foil, card board and PVC

pipe to construct the shielding enclosures, but these are all relatively inexpensive items.

Therefore, the total cost to conduct this project is relatively inexpensive.

30

10.0 Conclusion

Significant progress has been made in the area of test setup research and design,

as well as in the procurement of necessary materials. The only major item that has not

yet been acquired is the used airplane wire from the aviation scrap yard in Dallas. A

member of WECF, along with Dr. Stearman, will make the trip from Austin to Dallas to

pick up this wire sometime before the end of March. Now that the test setup has been

redesigned in order to provide more consistent testing results, it must be physically

assembled and its operation verified so that testing of the wire specimens can begin.

WECF is optimistic that the changes made to the test setup and wire aging procedures

will significantly augment the ability to generate a useful qualitative (and hopefully

quantitative) relationship between a wire’s age/physical condition and its triboelectric

response.

31

11.0 Works Cited

[1] Furse, C. & Haupt, R. (2001). “Down to the Wire.” IEEE Spectrum Online. http://www.spectrum.ieee.org/WEBONLY/publicfeature/feb01/wire.html (25 January 2003).

[2] Stoller, G. “Wired For Trouble.” USA Today. 09 November 1998. pgs 1B-3B. [3] Barr, E. “TWA Flight 800: What Happened to the 747?” Free Republican.com. http://www.freerepublican.com/forum/a3873a5167f9b.htm (3 March 2003). [4] Steinbarger, S., Bryant, D., and Shinagawa, Y. “Identification of Aging Aircraft

Electrical Wiring.” ASE 463Q Final Report. 6 December 2002. pgs 33-38. [5] Stearman, R. (2003). “A Study on the Insitu Identification of the Aging of Aircraft

Electrical Wiring.” (Project Quad-Sheet) University of Texas at Austin. [6] “Technical Data: Shielding.” Alpha Wire Company.

http://www.alphawire.com/pages/342.cfm (6 March 2003). [7] Clark, J. (2002). “An Introduction to Redox Equilibria and Electrode Potentials.”

Chemguide. http://www.chemguide.co.uk/physical/redoxeqia/introduction.html#top (6 March 2003).

[8] "Hook-Up Wire" Alpha Wire Company. http://www.alphawire.com/pages/pdf/176.pdf (6 March 2003). http://www.alphawire.com/pages/pdf/173.pdf (6 March 2003). [9] "High Resistance Measurements" http://216.239.33.100/search?q=cache:KBNb-PoWQ8sC:www.keithley.com/kei_assets/downloads/6584.PDF+graphite+wire+triboelectric+friction&hl=en&start=8&ie=UTF-8 (cached in www.google.com, site presently down) [10] NASA email to wiring group of fall 2002. Located in WRW 202

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12.0 Appendix – Timeline

Date Jan. 13 - 31 Feb. 1 - 15 Feb. 16 - 30 Mar. 1 - 15 Mar. 16 - 31 April 1 - 15 April 16 - 30 May 1 - 14Objective Group Meetings Preliminary Presentation Research Write Introduction Introduction Due Continue Research Evaluate Progress Write Mid-semester Report Mid-Semester Presentation Edit Mid-Semester Report Mid-Semester Report Due Continue Research Lab and Age Analysis Setup Data Collection and Analysis Final Report & Presentation Preparation Final Presentation Write Final Report Final Report Due

Note: indicates important dates