Composite Materials Research Progress

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196 Giangiacomo Minak and Andrea Zucchelli In this case, referred to the back side of a medium damage level lamina, matrix-fibre debonding is evident and the tensile fibre fracture surfaces are orthogonal to their axis and widely separated. Load-displacement curves for the three damage levels are reported in figure 26 while the maximum load, maximum displacements and total strain energy recorded in each test can be found in figure 27. Acoustic emission analysis of the transversal load test A parametric AE analysis was performed considering the acoustic energy, the cumulative events and the cumulative counts per event. As an example, in figure 28 these three AE parameters are plotted together with the respective load-displacement diagrams. For the AE diagrams reported in figure 28, the ΩAE is defined in the displacement range [0.7; 11.1] mm. It is interesting to notice the presence of the FFD that represents a phase of the test during which no damages are induced in the laminate (i.e. [0; 0.7]mm). The diagrams of cumulative events and cumulative counts versus the displacement are characterized by a general monotonic increasing trend, a quite similar shape and, for each diagram, at the same displacement value there are significant slope variations. In particular from figure 28A and figure 28B, inside the ΩAE, it is possible to notice a first part of the cumulative events and counts diagram characterized by low values and a smooth trend and dominated by AE events with a low number of counts and a low AE event rate. In figure 28 this first test phase has been identified in an AE sub-domain marked as Z1 limited, for the considered example, in the displacement range of [0.7; 6.3] mm. Considering also the energy diagram, figure 28C, it is possible to observe that only one event in Z1, at the displacement value of 3.6 mm, has an appreciable acoustic energy (over 3.0 10 -6 J) and from the statistical analysis it was observed that only 5 events have an energy over 1.0 10 -6 J, that can be considered typical for fibres breakage in bending. The sub-domain Z1 is physically dominated by material adjustment (especially fibre alignment) and by matrix deformation and matrix crack onset that are typically related to AE events with a small number of counts and low energy content [47]. The presence of few AE events with a high value of energy (over 1.0 10 -6 J) can be physically related to the breakage of some fibres as was previously noticed by the SEM image (figure 23) even if probably the energy content of these events in most cases should be low since these fibres are not loaded in tension. So during this first test phase (Z1) no significant damage is induced to the material, as it was noticed during the visual inspection of laminate surfaces, a small hemispherical mark in the matrix is appreciable (figure 23 L-a & L-b), and as pointed out by means of the SEM image, figure 24, a certain amount of fibres are broken. After this first phase there is a considerable increase of the AE activity represented by increased values of the slope in both cumulative event and counts diagrams. The test phase characterized by a high AE activity presents two other slope variations that can be used to define three other sub-domains: Z2 over the displacement range [6.3; 7.2] mm, Z3 over the displacement range [7.2; 8.1] mm and the Z4 over the displacement range [8.1; 11.1] mm. It is important to point out, as initially noticed, that all the slope variations in the cumulative event and counts diagram correspond to the same indenter displacement values. This is mainly related to the fact that, generally, the damage growth inside the material causes an increase of the total AE activity (events with an increased rating and an increased number of counts per
Damage Evaluation and Residual Strength Prediction of CFRP Laminates … 197 Event CUM Count CUM Eac (J) 1.0E+04 9.0E+03 8.0E+03 7.0E+03 6.0E+03 5.0E+03 4.0E+03 3.0E+03 2.0E+03 1.0E+03 0.0E+00 3.0E+05 2.5E+05 2.0E+05 1.5E+05 1.0E+05 5.0E+04 Event CUM Load 0 2 4 6 8 10 12 14 4.5E+05 Displacement (mm) 3.0 4.0E+05 3.5E+05 Count CUM Load B 2.5 6.0E-04 5.0E-04 4.0E-04 3.0E-04 2.0E-04 1.0E-04 0.0E+00 Z 1 Z 2 Z 3 Z 4 0.0E+00 0.0 9.0E-04 8.0E-04 7.0E-04 0 2 4 6 8 10 Eac Displacement (mm) Load 12 C 14 3.0 2.5 Ω AE 0 2 4 6 8 10 12 14 Displacement (mm) Figure 28. Main AE parameter and load diagram versus displacement; (A) cumulate of AE events, (B) cumulate of AE counts per event, (C) AE energy of each event. A 3.0 2.5 2.0 1.5 1.0 0.5 0.0 2.0 1.5 1.0 0.5 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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4 x 10 5 4 3 2 1 Compliance (Nmm) 0
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3.5 3 2.5 2 1.5 1 Optimization of L
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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
Page 160 and 161: 146 SEM Analysis Yuanxin Zhou, Hass
Page 162 and 163: 148 Yuanxin Zhou, Hassan Mahfuz, Vi
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
Page 184 and 185: 170 ⎟ ⎞ ⎠ s ⎜ ⎛ ⎝ = a E
Page 202 and 203: 188 A B E (MPa) D 250000 200000 150
Page 204 and 205: 190 D D 1.0 0.9 0.8 0.7 0.6 0.5 0.4
Page 218 and 219: 204 Conclusion Giangiacomo Minak an
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Damage Variables in Impact Testing
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F peak [kN] 16 14 12 10 8 6 4 2 0 D
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Eletromechanical Field Concentratio
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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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306 67, 69, 70, 71, 72, 73, 84, 94,
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