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Design and Implementation of Nondestructive Evaluation Instrument for Acoustic-based Wood Modulus of Elasticity Prediction
Design and Implementation of Nondestructive Evaluation Instrument for Acoustic-based Wood Modulus of Elasticity Prediction
Undergraduate Thesis
Abdurrachman Mappuji
12/329912/TK/39124
Department of
Nuclear Engineering& Engineering Physics
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Wood
Versatile material
Used in various applications
Construction
Furniture
Art
Etc.
Is an anisotropic material
mechanical properties changes with direction along object
Graded by elastic properties e.g. MOE
Indonesia ranked 7th top wood exporters
based on Worlds Richest Country in 2015
Figure 1. Wood StackImage by Aora Smith
Wood Grading
A quantitative measurement of wood strength
Classified wood by its quality
SNI 7973-2013 used MOE as one of grading parameters
Nondestructive evaluations are involved
Quality CodeMOE (MPa)EEminE2525,00012,500E2424,00012,000E2323,00011,500E2222,00011,000E2121,00010,500E2020,00010,000E1919,0009,500E1818,0009,000E1717,0008,500E1616,0008,000E1515,0007,500E1414,0007,000E1313,0006,500E1212,0006,000E1111,0005,500E1010,0005,000E99,0004,500E88,0004,000E77,0003,500E66,0003,000E55,0002,500Table 1. SNI Wood Grading
Modulus of Elasticity
Is the stiffness of a material
Used for wood grading
Some nondestructive evaluations are available
MOE = /
where,
= stress = F/A
= strain = L/L0
Figure 2. MOE illustration
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Nondestructive Evaluation of Wood
Identifying the physical and mechanical properties of a piece wood material w/o altering its end-use capabilities [1]
Types of evaluation
Visual characteristics
Chemical tests
Physical tests
Mechanical tests
[1] Ross, R. J. (Ed.). (2015). Nondestructive Evaluation of Wood (2nd Ed.). Forest Product Laboratory U.S. Department of Agriculture.
Visual characteristics
Color
Presence of defects
Chemical tests
Composition
Presence of treatments
Preservatives (Pengawet)
Fire retardants
Physical tests
Electrical properties
Vibrational properties
Wave propagation
Acoustic emissions
Mechanical tests
Flexural stiffness
Proof loading
Bending
Tension
Compression
Probes/coring
8
Static Flexure Method
Is a simple mechanical evaluation
No advanced-tech equipment required
MOE = Pa(3L2 4a2) / 48I
(a)
(b)
Figure 3. Common static flexure setup (a), and alternative setup (b) [1]
[1] Ross, R. J. (Ed.). (2015). Nondestructive Evaluation of Wood (2nd Ed.). Forest Product Laboratory U.S. Department of Agriculture.
Static Flexure Method
The drawbacks:
Need at least 2 tools i.e. load generator (e.g. an test weight cast iron, electrically induced load) and LVDT position sensor (for measuring the )
Often we need a variable load generator e.g. iron brick with multiple weight, or electrically induced load
(a)
(b)
Figure 4. Iron brick (a), and a wood loaded with electrically induced load (b)
Longitudinal Stress Wave Method (LSWM)
Is a simple physical evaluation wave propagation
Need a computer to perform FFT get resonant freq.
The MOE can be predicted by
MOE = 4f02L2, where
f0 :fundamental resonant frequency
L : length
: density
Figure 5. Longitudinal Stress Wave Method Setup [1]
[1] Ross, R. J. (Ed.). (2015). Nondestructive Evaluation of Wood (2nd Ed.). Forest Product Laboratory U.S. Department of Agriculture.
11
Longitudinal Stress Wave Method
Determining the fundamental resonant frequency
(a)
(b)
Figure H1. LSW in time domain (a), and in frequency domain (b).
12
Longitudinal Stress Wave Method
Performance
[2] Ayutyastuti. (2015). Studi Kelayakan Metode Nondestructive Test Berbasis Akustik untuk Memprediksi Nilai Modulus Elastisitas Kayu. Universitas Gadjah Mada.
Wood TypeScientific NameR2 SonokelingDalbergia latifolia Roxb.0.57TeakTectona grandis L.f.0.59SukunArtocarpus altilis0.63AcaciaAcacia mangium0.90MunggurPithecolobium Saman Benth0.90MahoganySwietenia spp.0.95Table 2. The coefficient of determination R2 for the relationship between MOEd and MOEs [2]
13
Longitudinal Stress Wave Method
The problems:
Tools
There is limited instrument implemented this method
Most of the time FFT is performed in a computer
Noise
Friction due to tapping the wood
We dont know whether the recorded signal is representing the longitudinal stress wave (LSW) or not
14
Proposed Solutions
Enhanced the longitudinal stress wave method
Implement method in a semi-automatic device
Proposed Enhanced Method
Detect presence of noise
Measure how much the recorded signal represent the LSW
Using the known characteristics of damped free vibration observing exponential decay of LSW
16
Proposed Enhanced Method
Constraints
We record an acoustic signal with microphone instead of using a sensor attached directly to the wood
Directly calculating exponential decay of LSW is difficult
(a)
(b)
Figure 6. Ideal damped free vibration (a), longitudinal stress wave of observed Sonokeling wood (b)
17
Proposed Enhanced Method
Solutions
Filter the LSW
Use envelope fitting method to derive exponential decay function
(a)
(b)
Figure 6. Envelope fitting of the transient response of an underdamped single-degree-of-freedom system. The illustration (a), the example on the implemented instrument (b)
18
Proposed Enhanced Method
Additional steps
Legend:
Figure 7. Proposed enhanced LSWM
19
Pre-research of the enhanced LSWM
Mahogany #1
Sonokeling #1
(a)
(b)
Figure 8. Recorded LSW of Mahogany #1 wood (a), recorded LSW of Sonokeling #1 wood (b)
Mahogany #1
Sonokeling #1
(a)
(b)
Figure 9. Signal spectrum of recorded LSW of Mahogany #1 wood (a), recorded LSW of Sonokeling #1 wood (b)
Mahogany #1
Sonokeling #1
(a)
(b)
Figure 10. Signal spectrum of filtered recorded LSW of Mahogany #1 wood (a), filtered recorded LSW of Sonokeling #1 wood (b)
Mahogany #1
Sonokeling #1
(a)
(b)
Figure 11. Filtered recorded LSW of Mahogany #1 wood (a), filtered recorded LSW of Sonokeling #1 wood (b)
Mahogany #1
Sonokeling #1
(a)
(b)
Figure 12. Envelope fitting result of LSW of Mahogany #1 wood (a), and LSW of Sonokeling #1 wood (b)
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Design Specification
The purposes of the instrument are,
Record the stress wave
Perform the FFT algorithm
Assisted user to find the f0
Implement the refined method
The wood frequency range
800 4100 Hz
Presentation Outline
The wood frequency range
800 4100 Hz
Instrument Design
Instrument System Design
Software Architecture
User Interface Design
Main navigation
Plot area
Plot toolbar
Pointer position
Setting
Record
FFT
Pick f
Verify
Calc
Open
Implementation Testing
Microphone Test
FFT Test
Soundcard Test
Complete System Test
Data Collection
Soundcard Test
Data Collection
Microphone Test
Data Collection
Microphone Specs
Physical PropertiesSpecificationAudio Jack3.5 mmPlug Diameter3.5 mmFrequency Range0.1 5 kHzSensitivity-64 3 dBLength16 cmWeight12 gData Collection
FFT Validation
Check the implementation
Test implemented routine against various frequency
Damping Information Exploration
Envelope fitting R2envl vs. MOEs and MOEd R2ed
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Physical Implementation
Successfully implemented
Semi-automatic device
Embedded enhanced LSWM
A 0.1 5 kHz microphone
Raspberry Pi 900 MHz clock speed
3.5 resistive touchscreen
12000 mAh power bank
Soundcard Performance Test
Square wave
Soundcard Performance Test
Triangle wave
Soundcard Performance Test
Sine wave
Soundcard Performance Test
Sine wave (cont.)
Microphone Performance Test
Response of the microphone
Microphone Performance Test
SNR of the Microphone
Fast Fourier Transform Validation
Single frequency
Fast Fourier Transform Validation
Dual frequency
Exponential Decay of LSW
We define the following after some experiments:
The order of Butterworth filter is 3
The frequency cutoff of band-pass filter is 100
Analyzing the R2 of the envelope fitting of exactly same wood as researched by Ayutyastuti 2015 and Feliana 2014. We called this coefficient of determination as R2envl.
Compare this distribution with the R2 of the MOEd and MOEs correlation (called R2ed)
Wood TypeR2edPercentage R2envl > 0.95Sonokeling0.5746.67 %Teak0.5956.67 %Sukun0.6343.33 %Acacia0.9060.00 %Munggur0.9063.33 %Mahogany0.9573.33 %Exponential Decay of LSW
Histogram of R2 of Envelope Fitting for Sonokeling (R2ed = 0.57)
Frequency0.50.550.60.650.70.750.80.850.90.951More0100120309140
R2envl
Frequency
Histogram of R2 of Envelope Fitting for Teak(R2ed = 0.59)
Frequency0.50.550.60.650.70.750.80.850.90.951More0000010417170
R2envl
Frequency
Histogram of R2 of Envelope Fitting for Sukun(R2ed = 0.63)
Frequency0.50.550.60.650.70.750.80.850.90.951More0011121254130
R2envl
Frequency
Histogram of R2 of Envelope Fitting for Acacia (R2ed = 0.90)
Frequency0.50.550.60.650.70.750.80.850.90.951More0001022214180
R2envl
Frequency
Histogram of R2 of Envelope Fitting for Munggur (R2ed = 0.90)
Frequency0.50.550.60.650.70.750.80.850.90.951More1000003502190
R2envl
Frequency
Histogram of R2 of Envelope Fitting for Mahogany (R2ed = 0.95)
Frequency0.50.550.60.650.70.750.80.850.90.951More2000000006220
R2envl
Frequency
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Conclusion
A semi-automatic nondestructive evaluation instrument for predicting the MOE of wood called MyWood is successfully designed and implemented. Each building block of the instrument i.e. the sound card, microphone, and the FFT algorithm are well implemented and validated.
The test shows that the instruments able to accommodate any waveforms and able to work in a range of 800 4100 Hz which includes the frequency range of the longitudinal resonant frequency of the wood.
Conclusion
We introduced a novel method to measure how much the recorded LSW represent actual LSW. The method involves conventional LSWM method with additional band-pass signal filtering with resonant frequency as the center frequency of the filter, and the envelope fitting method.
We assessed the longitudinal stress wave data from previous researches and found an important parameter called R2envl which is the coefficient of determination of envelope fitting in our damping ratio calculation method. We found that if we record a longitudinal stress wave and we perform our damping ratio calculation method and get a low R2envl, it means that there is a high probability that our data is not representing the longitudinal stress wave signal and we need to repeat the recording procedure of LSWM.
Presentation Outline
Introduction and Motivation
Nondestructive Evaluation of Wood
Instrumentation Design & Tests
Results and Discussion
Conclusion
Future Work
Q & A
Recommendation
In this research, we are not exploring the possibility of using the damping factor, h, that has been calculated using our procedure to define a refined model of measuring the MOE. A depth study about this area may enrich our knowledge of nondestructive evaluation of wood.
We test the implemented designs microphone with a flat response speaker. A further research which test the proposed designs microphone with tuning fork or a standardized calibrator will be appreciated.
DEMO
Thank you
Q & A
dB used in most of this research
dBFS- dB Full Scale
0 dBFS represents the highest possible level in digital gear. All other measurements expressed in terms of dBFS will always be less than 0 dB (negative numbers).0 dBFS indicates the digital number with all digits ="1", the highest possible sample.
The lowest possible sample is (for instance for 16 bit audio):0000 0000 0000 0001, which equals -96 dBFS. Therefore the dynamic range for 16-bit systems is 96 dB. For 20-bit digital audio it is 120 dB. For 24 bit digital audio it is 144 dB.Full-scale input level is the analog input voltage level that will cause the A/D converter to just equal full scale with no clipping on either positive or negative peaks.
Output full scale is defined as the analog output voltage produced while playing a 997 Hz digital full-scale sine wave, assuming the THD+N is less than -40 dB relative to the signal level.
The dynamic range of a digital system is the ratio of the full scale signal level to the RMS noise floor.
JimPrice.Com. (2007). Understanding dB. Retrieved March 23, 2017, from http://www.jimprice.com/prosound/db.htm
Least Square
Least Square
Start
RH < 20%
Place the wood in
the base with a
support on its
end.
Tap the wood in
one end
Record tap sound
(signal) with a
microphone at the
other end.
Find natural
frequency (f) with
frequency
analyzer
Insert fto the
formula
MOE = 4f
2
L
2
Finish
Perform drying
treatment
YES
NO
Perform
Butterworth band-
pass filter at f
x, where xis
obtained an
optimal solution
by trial and error
At the time
domain do
envelope-fitting
(obtained R
2
)
R
2
> = y, where yis
obtained optimal
solution by trial
and error
Make sure
the support is
strong and
does not
shift. Make
sure the next
tap is strong
enough but
not too hard.
YES
NO
Sensor:
Microphone
Sensor:
Microphone
Woods
longitudinal
stress wave
Signal
Conditioning:
A/D Converter
Signal
Conditioning:
A/D Converter
Microprocessor:
Software for User
Interface and Digital
Signal Processing in
RPi
Microprocessor:
Software for User
Interface and Digital
Signal Processing in
RPi
User
Interface:
Touchscreen
Display
User
Interface:
Touchscreen
Display
User
MyWood
Function
Generator
Soundcard
Oscilloscope
Raspberry Pi
Audacity
Software in
RPi
Host
Computer:
Remote
Desktop
Function GeneratorSoundcardOscilloscopeRaspberry PiAudacity Software in RPiHost Computer:Remote Desktop
Transducer:
Flat Speaker
Air:
5 cm gap
Microphone
Tested
Soundcard
Raspberry Pi
Host
Computer:
Remote
Desktop
Audacity
Software in
RPi
Frequency
Generator
Software in
Host
Computer
Transducer:Flat SpeakerAir:5 cm gapMicrophoneTested SoundcardRaspberry PiHost Computer: Remote DesktopAudacity Software in RPiFrequency Generator Software in Host Computer