Composite Materials Research Progress

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198 Giangiacomo Minak and Andrea Zucchelli event [47]). The slope variations in all diagrams are associated to events with a high energy content. In fact, as shown in figure 28C, the transitions between Z1 and Z2 and then between Z2 and Z3 are determined by two events with an energy content higher then 1.0 10 -6 J probably caused by fibres breakage. It is also interesting to notice that in the sub-domain Z2 there is a considerable number of events with a high energy content (22 events with an energy higher then 1.0 10 -6 J) probably related to the breakage of quite large number of fibres. This fact was also confirmed by the visual and SEM analysis (figure 23 M-a & M-b, figure 25). Similar considerations can be developed considering the sub-domains Z3 and Z4 with a number of 27 and 100 events with energy content higher then 1.0 10 -6 J respectively, that probably reveal the progressive fibres breaking process. Besides the analysis of the AE information it is interesting to relate the AE diagrams to the mechanical response of the laminate. In particular it is possible to notice that both the first zone Z1 and the second zone Z2 end at the two important load drops. In the sub-domain Z1 the load-displacement diagram has a monotonic increasing trend with an increasing slope and this is a direct consequence of the fact that the system stiffness is increased by the transition from the bending to the membrane behaviour [35]. So this sub-domain characterizes the test phase during which no important damage is induced and the main part of the mechanical energy is stored in the material as strain energy, in fact only a small part of the mechanical energy is dissipated by fibres adjustment or alignments and matrix crack onset. After the first load drop, the sub-domain Z2 begins, where the load displacement diagram is again increasing monotonically, but contrary to what is observed in Z1 the slope is decreasing. This is related to the material damage corresponding to the first load drop. In fact, as noticed by visual inspection and SEM analysis, after the first load drop the fibres breakage and the brittle matrix leakage reduce the local resistance of the laminate. So in the subdomain Z2 the strain energy storing capability of the laminate is reduced if compared with the laminate behaviour in Z1. In the sub-domain Z3 the load-displacement diagram is characterized by a monotonic increasing trend with a consistent decreasing of the slope. After the second load drop delamination and fibre breakages compromise the local out-of-plane resistance of the laminate and the energy storing capability is significantly reduced. The third zone ends when the load reaches a relative maximum value and then it decreases. The sub-domain Z4 is characterized by a slowly decreasing trend of the load with the total penetration of the indenter in the laminate and the AE event are mainly caused by the delamination, matrix cracking and leakage, fibre breaking and bending-pull-out. At the end of the loaddisplacement diagram there is a new increasing trend due to the contact of the support of the spherical indenter with the laminate surface. The physical evidence of the failure modes that happens during the loading history in Z4 can be reconstructed by visual and SEM inspection as shown in figure 23 (H-a& H-b) and figure 24. An example of implementation of the function f(x) for this case study is shown in figure 29 where the strain energy (Es), the cumulative AE event energy (Ea), the load and the f(x) diagrams relative to the same test reported in figure 28 are shown.
Damage Evaluation and Residual Strength Prediction of CFRP Laminates … 199 Es (J) Ea Cumulate (J) f 1.8E+01 1.6E+01 1.4E+01 1.2E+01 1.0E+01 8.0E+00 6.0E+00 4.0E+00 2.0E+00 0.0E+00 Es Load 2.5E-03 0 2 4 6 8 10 12 14 3.0 Displacement (mm) 2.0E-03 Eac CUM Load B 2.5 1.5E-03 1.0E-03 5.0E-04 0.0E+00 2.5E+01 2.0E+01 1.5E+01 1.0E+01 5.0E+00 0.0E+00 Z1 0 2 4 6 8 10 12 14 PII,1 PII,2 PI,1 PI,2 PI,3 ΩAE Displacement (mm) PIII,1 0 2 4 6 8 10 12 14 Displacement (mm) f Load Figure 29. (A) f general behaviour, (B) example of f diagram for an experimental indentation test. In figure 29A the sub-domain Z1,Z2, Z3 and Z4, as previously analysed and in figure 29B the AE domain, ΩAE, are reported. The strain energy diagram, figure 29A, is continuous, Z2 Z3 PIV,1 PII,3 PII,4 PIII,2 Z4 A C 3.0 2.5 2.0 1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 0.0 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Load (kN) Load (kN) Load (kN)
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COMPOSITE MATERIALS RESEARCH PROGRE
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Copyright © 2008 by Nova Science P
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vi Contents Chapter 9 Recent Advanc
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viii Lucas P. Durand scale transiti
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x Lucas P. Durand machine. In paral
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In: Composite Materials Research Pr
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Multi-scale Analysis of Fiber-Reinf
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T300 fibers (Soden et al., 1998; Ag
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1 I L = L : r v Multi-scale Analysi
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I E ⎡0 ⎢ ⎢0 ⎢ ⎢ ⎢ ⎢0
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Applied macroscopic load Correspond
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Optimization of Laminated Composite
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⎧σ x ⎫ ⎡ mE ⎪ ⎪ ⎢ x
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and γ 2 γ 0 Optimization of Lamin
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110 W.H. Zhong, R.G. Maguire, S.S.
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112 Reinforcement: Advanced materia
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130 Yuanxin Zhou, Hassan Mahfuz, Vi
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140 Heat Flow (W/g) Heat Flow (W/g)
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144 Material Yuanxin Zhou, Hassan M
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146 SEM Analysis Yuanxin Zhou, Hass
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Page 164 and 165: 150 Governing Equation For the fibe
Page 166 and 167: 152 ⎧ UU = ⎨ ⎩ ⎧ UD = ⎨
Page 170 and 171: 156 Stress (MPa) 120 80 40 0 Yuanxi
Page 180 and 181: 166 Giangiacomo Minak and Andrea Zu
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Page 202 and 203: 188 A B E (MPa) D 250000 200000 150
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F peak [kN] 16 14 12 10 8 6 4 2 0 D
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Damage Variables in Impact Testing
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276 S.C. Tjong developed in the pas
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278 S.C. Tjong ultrasonic waves gen
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280 S.C. Tjong applications. Goujon
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282 S.C. Tjong nanoparticles were p
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284 S.C. Tjong where DL is lattice
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286 S.C. Tjong stress is temperatur
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288 S.C. Tjong threshold stress res
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290 S.C. Tjong NC Al, and the NC Al
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292 S.C. Tjong (a) (b) Figure 19. T
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294 S.C. Tjong Apart from forming u
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296 S.C. Tjong [29] Saravanan, M.;
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298 braids, 115 broadband, 211 bubb
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300 endothermic, 139 endurance, 32
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302 isostatic pressing, 279, 288 It
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304 piezoelectricity, 261 pitch, 12
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