The Notched Strength of Angle-Ply Laminates - TSpace - University

119 Pages·2001·4.06 MB·English

The Notched Strength of Angle-Ply Laminates
Weijia Zhang
A thesis submitted in confonnity with the requirements
for the degree of Master of Applied Science
Department of Chernical Engineering and Applied Chemistry
University of Toronto. Toronto. Ontario. Canada
O Copyright by Weijia Zhang 2001
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ABSTRACT
Notched Strength of Angle-Ply Laminates
Master of Applied Science
300 1
Weijia Zhang
Department of Chernical Engineering and Applied Chemise
University of Toronto
The notched tensile strength of carbon-epoxy and glass-epoxy laminates with
Umm width and 20mm gauge length were studied at different fiber lay-up angles and
quasi-isotropic laminates. Mostly tiber failure was observed for l j0 and 30' laminates.
With angles greater than 45'. fiber failure hardly occured at all.
The photoelastic rnethod was used in the study. The fringe patterns showrd that
the stress distributions in angle-ply laminates were different From those for isotropic
materials. The quasi-isotropic laminates were very similar to isotropic materials.
The results showed that KI, can be measured for both carbon-epoxy and glass-
epoxy angle-ply laminates for fiber angles at 30' or less: and for quasi-isotropic carbon-
epoxy. It still had some validity at 45' or higher. Ki,' s of up to 8 6 ~ ~ a mw" 'e re
observed. Work of fracture estimated therefore would be as high as 740 ~ m " .
ACKNO WLEDGEMENTS
I am \.cry grateful for Professor M.R. Piggott for his supenision. guidance and
encouragement during the course of this work. Thanks to Prof. Coyle and Prof. Yip for
being my cornmittee members for the gradiiate oral. Very special thanks to Jenny Clifford
for her tmly tiiendship. hslp and encouragement.
I am thankful to al1 manbers of the :\d\.ancrd Composite Physiçs and Chsmistn
Ciroiip Iùr their jlipport and friendship. Thanks al1 of ).ou. Jim. blicharl and Jessica for
creating an enjoyablr study environment. It was fun! Also thanks Haihui for helping
scmning the prüphs.
Sprcial thanks to my husband Gang for his undentandine and support. and very
specid thanks to my daughter Jessie. to be so patient and helpful. Momi loves you!
TABLE OF CONTENTS
ABSTRACT
ACKNO WLEDGEMENTS
TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
LIST OF NOMENCLATURE
1. NTRODLrCTIOX
1. I Composite Materials
1.2 Elastic Constants
1.2.1 Laminae
12.2 Laminate
1.3 Strengths
1 2.l Tensile strength
1.32 Shear strength
13.3 Delamination resistance
1.1N otched strength
1.1.1 Fracture mrchanics for isotropic materials
1 .1.2 Fracture mechanics for anisotropic materials
1 .j Photoelastic analysis
1.6 Objective of this study
2. EXPERIMENTAL METHOD
2.1 Materials
2.3 Specimen fabrication
2.2.1 Laminates for tensile test
2.22 Laminates for tensile photoelastic test
7.3 Mec hanicai Test
2.3. l Tensile test
2.5.2. Tensile photoelastic analysis
3. EXPERIMENTAL RESCLTS
3. I Force displacement cunweasn d t'ailure obsen-arions
YS.
3.2 Strength vs. notch dspth
3 -3 Photorlastic fringe pattern
4. DISCL'SSION
4. I Stress intensity factors for angle-pl! laminûtcs
4.2 Efkct of pl!. angle on Ki;lcan d Ci,
4.3 Modelinp Gi,
5. CONCLI;'SIONs
6. RECOMMENDATTOPi
7. REFERENCES
APPENDIX
A. 1 Results of tensile srrength test of angle-ply laminates
A.2 Photorlastic images of angle ply laminates
A 3 T heoretical Calculations of G[,o f angle-plu laminates
LIST OF FIGURES
Fiber direction relative to x-y mes
Symmetric laminate of [k45lS
Effect of fiber orientation on strength for silica-aluminum
Results for glass and carbon 2Omm gauge length specimrns
compared with results obtained by Snell for lOmm s 20mm carbon
tibcr laminates and by Tsai for 63mm x 4.6mm glas .' fiber
laminates
Description of regions in the Bauge area
.-\ngle pl) composite strength mode1 compared with rsperimcntal
results
Symmetric Angle-Plu Larninate Geometp and Stresses
Variation of enrrgy with cnck length
Modes O t' crack de formation
Ratios of unnotched to notched strengths t'or cnrbon-rpos). and
glass cposy laminates
Translarninar liacture toughness test specimen
(a)S tresses ncar the tip of an eliiptic cnck and (b)S tresses at right
angles to the stress applied to an elliptic crack
Photoelastic fiinge patterns around hole in boronl eposy specimen
[Oli-45/0/90], for applird stresses. from left to right 165MPa.
225MPa and 292 blPa
Photoelastic fnnge patterns of [OIM510/90],b orodepoxy with
cutouts of various shapes. Applied stress: (a) ~ 3 6M1Pa . (b)
n=Xl MPa. (c) o=33 i MPa
Pliotoelastic fringr patterns around 1 27cm crack of [0/+45'90],
graphite kpoxy spccimen at various Ievels of applied stress
Illustration of steel mould for hot press
Illustration of specimen
Principle of retlrction polariscope
Laminatr tensik photoelastic test set-up
Force vs. displacement for glass-rposy laminates with jmm nntch
dcpth
Forcc displaçr.rnent for carbon-epoxy laminares with 5mm
YS.
notch depth
Failed specinisns of anglc-pl! laminate with 5rnm notch depth
Forcr vs. displacement for glass-epoxy laminates with 1 Smm notch
depth
Force vs. displacement For carbon-epoxy laminates with 15mm
notch depth
Failed specimens of angle-ply laminatr with 1 jmm notch depth
Strength of carbon and glass-epoxy laminate with [OI4 vs. notch
depth
Strength of carbon and glass-eposy laminate with [= 1 51, vs. notch
depth
3.9 Strength of carbon and glass-spoxy laminatr with [do], vs. notch
drpth
3.1 O Strength of carbon and çlass-epoxy laminatr with [545], vs. notch
depth
3.1 1 Strength of carbon and glass-epoxy laminate with [=60], vs. notcli
dcpth
3 1 Strength of carbon and glass-epoxy laminatr with [*75], \.S. notch
depth
3.13 Strength of çarbon-epoy laminate with [O.-45.90.-451, notch
YS.
drpth
3-14 Photoelristic fringe patterns of [k 1 5 1, cxbon-cpoq ai 5 m m n imh
drpth: (a)a t 0.45 GPa and (b)a t 0.64 GPa with fnnge orders indicair
3.15 Photoelastic fringe pattems of [k 301, carbon-cposy (a)a t 0.29
GPa aith frinye ordrrs indicated with X m m notch: (b)a t 0.38
GPa with fringr orders indicated at the central rçyion with 2.5 mm
notch: (c) at 0.38 GPa with Fringe orders indicated with 1Omm
notch
3.16 Photoelastic fringc pattems of [r 451, carbon-eposy (a)a t O. 143
GPa with tnnge ordrrs indicated with 3n1m notch: (b)a i 0.19
GPa with finge orders indicated at the central resion with 7.5 mm
notch: (c)a t OGPa afier load was released with 2.3mm notch (d) at
0.05 GPa with 1 Omm notch: (r)a t 0.078 GPa with tnnge orders
indicated with 1 Ornm notch depth
Photoelastis fringe patterns of [k 601, carbon-epoxy at jmrn notch
depth (a) at 0.06 GPa: (b) at 0.1 1 GPa with fringe orders indicated
Photoelastic fringe patterns of [k 751, carbon-epoxy at 5mm notch
depth
Photoelastic fringc patterns of [0.+45.90.-451, carbon-cposy (a)a i
0.15 GPa with lobes direction indicated with 5mm notch: (b)a t
0.24 GPa n ith fringc ordrrs indicated with 5mm notch: (c) at 0.14
GPa with Iobes direction indicated withlOmm notch: (d)3 t 0.40
GPa with fringe ordrrs indicated with 1O mm notch
Load of carbon-epoxy laminate with [0.+45.90.-451, vs. notch
depth
Force distance plot for [O.-45.90.-45 1 , carbon- at the different
notch depths
Stress intensity hctor of carbon-eposy laminate nith [O.-45.90.-
451, t.s. notch depth
Photoelastic imagé ofcarbon -eposy [O. -45.00. -451, at notch
depth (a)j mm at 15.jkN. (b) 1Omm at KjkN and (c) 1 jmm at
7.5kN
Force distance plot for [?15]j carbon-eposy cit the different notch
drpths
Stress intrnsity factor of [? 151, laminate with vs. notch depth
Photoelastic image of [Il5 1, carbon-ciposy at 7.5mrn notch depth
at 16.5kN