Mechanics of adhesion and friction in stick insects and tree frogs

167 Pages·2008·7.03 MB·English

MECHANICS OF ADHESION AND
FRICTION IN STICK INSECTS AND
TREE FROGS
Dissertation zur Erlangung des
naturwissenschaftlichen Doktorgrades
der Bayerischen Julius-Maximilians-Universität
Würzburg
vorgelegt von
patrick hans drechsler
aus
Böblingen
2008
Würzburg
Eingereicht am:
Mitglieder der Promotionskommission:
Vorsitzender:
Gutachter: Dr.Walter Federle
Gutachter: Dr. Jon Barnes
Tag des Promotionskolloqiums:
Doktorurkunde ausgehändigt am:
PUBLICATIONS
Some ideas and figures have appeared previously in the follow-
ing publications:
2005
Drechsler, P. and Federle, W. ( ). Adhesion and friction in
stick insect tarsal pads. Comparative Biochemistry and Physiol-
141 3 144
ogy, A( /Suppl.):S .
2006
Drechsler, P. and Federle, W. ( ). Biomechanics of smooth
adhesive pads in insects: influence of tarsal secretion on at-
tachment performance. Journal of Comparative Physiology A
192 11 1213 1222
Sensory Neural and Behavioral Physiology, ( ): – .
Federle, W., Barnes, W., Baumgartner, W., Drechsler, P., and
2006
Smith, J. ( ). Wet but not slippery: boundary friction in
tree frog adhesive toe pads. Journal of the Royal Society Inter-
3 10 689 697
face, ( ): – .
iii

CONTENTS
1 introduction 1
11 1
. Theories of adhesion and friction
111 2
. . Theories of adhesion
112 7
. . Theories of friction
113 8
. . Theories of peeling
114 10
. . Viscoelasticity
12 11
. Biology of animal attachment
121 12
. . Adhesion and locomotion
122 13
. . Animal attachment structures
13 17
. Biomechanicsofsmoothattachmentpads
131 18
. . Role of pad secretion
132 20
. . Frictional anisotropy
133 23
. . Mode of detachment
2 material and methods 27
21 27
. Study animals
211 27
. . Stick insects
212 27
. . Tree frogs
22 29
. Single pad force apparatus
23 31
. Labview control program
24 31
. Data analysis
25 32
. Friction force measurements
251 32
. . Anisotropy
252 33
. . Amount of pad secretion
253 33
. . Normal force
254 34
. . Humidity
255 34
. . Velocity
256 35
. . Static friction
257 35
. . Frictionforcemeasurementsintreefrogs
26 35
. Adhesionforcemeasurementsinstickinsects
261 36
. . Role of pad secretion
262 38
. . Mode of detachment
27 42
. Centrifuge apparatus
28 44
. Statistics
3 results 47
31 47
. Frictionforcemeasurementsinstickinsects
i
contents
ii
311 47
. . Anisotropy
312 51
. . Role of pad secretion
313 52
. . Normal force
314 53
. . Humidity
315 54
. . Velocity
316 55
. . Static friction
32 57
. Adhesionforcemeasurementsinstickinsects
321 57
. . Role of pad secretion
322 61
. . Mode of detachment
33 81
. Frictionforcemeasurementsintreefrogs
331
. . Possiblecontributionofsurfacetension
83
forces to shear stress in tree frogs
4 discussion 87
41 87
. Frictional anisotropy
42 88
. Role of pad secretion
421
. . Role of pad secretion for attachment to
88
smooth and rough substrates
422 90
. . Roleofpadsecretionforfrictionforces
43 94
. Mode of detachment
5 summary 99
6 zusammenfassung 101
a appendix 103
a1 103
. Material and methods
a11 labview 103
. .
a12 matlab 106
. .
a2 107
. Results
a21 107
. . Adhesion single leg
a22 126
. . Contacttimeandsurfaceroughness
a23 127
. . Scaling of whole body forces
bibliography 128
acknowledgments 145
curriculum vitae 149
erklärung 151
LIST OF FIGURES
11
Figure . ExplanatorydiagramofHertzandJKR
3
models.
12 5
Figure . ExampleofHertzandJKRcurves.
13
Figure . Explanatory diagram of wet adhesion
5
model.
14 9
Figure . Stribeck diagram.
15 10
Figure . Explanatorydiagramofpeelingmodel.
16
Figure . Models of viscoelasticity (Kelvin-Voigt
11
and Maxwell model).
17 14
Figure . Varietyofinsectadhesiveorgans.
18
Figure . Morphology of stick insect pretarsus
14
(Carausius morosus).
19
Figure . Ultrastructure of transversal section of
the arolium cuticle of Carausius moro-
15
sus.
110
Figure . Scanningelectronmicroscopeimageof
16
stick insect arolium.
111 17
Figure . Morphologyoftreefrogtoepads.
112
Figure . Diagram of different amounts of secre-
20
tionpresentbetweenpadandsubstrate.
113 21
Figure . Diagram of friction forces.
114
Figure . Chainmodelshowingtheeffectofprox-
imal and distal movement on peeling
22
angle.
21 28
Figure . Immobilizationofstickinsecttarsus.
22 28
Figure . Immobilization of tree frog.
23
Figure . Experimental setup for measuring ad-
hesion and shear stress of insect adhe-
31
sive pads.
24
Figure . Simplified diagram of movement pat-
37
tern for consecutive pull-offs.
25
Figure . Calculation of work of adhesion using
39
peelingmodel(perpendicularpull-off).
26
Figure . Calculation of work of adhesion using
40
peelingmodelwithcircularcontactarea.
27 43
Figure . Centrifuge apparatus.
iii
iv List of Figures
31
Figure . Anisotropy example curves of friction,
48
areaandshearstressforadhesivepads.
32
Figure . Anisotropy of friction, area and shear
49
stressforimmobilizedadhesivepads.
33
Figure . Velocityanddirectiondependencedur-
50
inganisotropicfrictionmeasurements.
34
Figure . Shear stress measurement in single ad-
52
hesive pads of Carausius morosus
35
Figure . Influence of normal force on friction
53
force,contactareaandshearstress.
36 54
Figure . Influenceofhumidityonshearstress.
37
Figure . Singlepadfrictionforceandshearstress
at four different velocities with “accu-
55
mulated” secretion.
38 2
Figure . Friction force during and min after a
56
slow sliding movement.
39
Figure . Comparison of remaining shear stress
with little and accumulated secretion
57
twominutesaftermovementhadended.
310
Figure . Consecutive,alternatingpull-offsofCa-
rausiusmorosusadhesivepadsfromglass
59
androughaluminiumoxidesubstrates.
311
Figure . Effect of contact time and secretion on
pull-offforcesfromaroughandasmooth
60
epoxy surface.
312
Figure . Example of stick insect’s single leg de-
tachment measurement with different
61
normal forces.
313
Figure . Results of stick insect’s single pad de-
tachmentexperimentsanalysingthein-
63
fluenceofnormalforceandvelocity.
314
Figure . Scaling of stick insect’s single leg pull-
71
offforcesplottedagainstbodymass.
315
Figure . Scaling of stick insect’s single leg pull-
off forces plotted against contact area
A 72
F .
0
316
Figure . Scaling of stick insect’s single leg pull-
off forces plotted against contact area
A 73
F .
max
List of Figures v
317
Figure . Summaryofstickinsect’ssinglelegscal-
ingcoefficientsusingOLSandSMAre-
74
gressions.
318
Figure . Scalingresultsofstickinsectwholebody
80
measurements(centrifugetechnique).
319
Figure . Shear stress measurement in single toe
pads of Litoria caerulea (example data
85
and boxplots).
320
Figure . Exampledatasettoestimatefluidheight
between frog toe pad and substratum
86
using non-linear regression.
41
Figure . “Footloose” arolium moving in proxi-
88
mal and distal directions.
42
Figure . Schematicdiagramillustratingtheadhesion-
enhancing role of insect pad secretion
90
on a rough substrate.
43 95
Figure . Proposedviscoelasticdetachmentmodel.
1 labview
Figure A. Flowchart diagram of control
104
program.
2 labview 105
Figure A. Frontpanelof controlprogram.
3
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
transformed pull-off force versus nor-
115
malforceanddetachmentvelocity.
4
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
A
transformedcontactarea F versusnor-
0
116
malforceanddetachmentvelocity.
5
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
A
transformed contact area F versus
max
116
normalforceanddetachmentvelocity.
6
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
F /A
transformedforcepercontactarea P F
0
versus normal force and detachment
117
velocity.
7
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
1
transformed work of adhesion WOA
versus normal force and detachment
117
velocity.
8
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
2
transformedworkofadhesionWOA
mean
versus normal force and detachment
118
velocity.
9
Figure A. Interaction plot showing the main ef-
fects and two-way interactions of log
2
transformedworkofadhesionWOA
max
versus normal force and detachment
118
velocity.
LIST OF TABLES
11
Table . Overviewofadhesionmodelsandtheir
24
implications on scaling.
31
Table . Two-way within-subject ANOVA table
testing the influence of surface rough-
ness,secretionandcontacttimeaswell
58
as their interaction.
32
Table . SummaryofTwo-wayANOVAsanalysing
the influence of normal force and ve-
locity on dependent variables in stick
insect’ssinglelegdetachmentmeasure-
62
ments.
33
Table . Scaling of stick insect’s single adhesive
pads pull-off force against body mass
m 65
using OLS regression.
34
Table . Scaling of stick insect’s single adhesive
pads pull-off force against contact area
A 66
F using OLS regression.
0
vi