JST Vol. 21 (1) Jan. 2013 - Pertanika Journal - Universiti Putra ...

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Suriani, M. J., Aidy Ali, S. M. Sapuan and A. Khalina occurs to residual strength degradation method. The failures were caused by the degradation of residual strength to the applied stress. Another approach that has been used by several authors is strain failure criterion which considers the final failure of the composite materials that occurs at the stage of resultant strain that reaches the ultimate static strain (D’amore et al., 1999; Clark et al., 1999). The other method used to predict fatigue life, done by Salvia et al. (1997), is stiffness reduction or degradation which needs another failure condition rather than the total failure of the specimen such as predefined critical number of cycles representing certain damage state. The critical number of the cycles was obtained when a given stiffness loss (predefined) was reached, and then the critical cycle numbers and stiffness reduction were associated. MODELLING FATIGUE IN COMPOSITES Damage Accumulation Damage evolution mechanism is one of the important focuses and also a foundation to predict fatigue life. The mechanical properties of the composite materials show progressive degradation with the increasing of the number of cyclic loading. Two quantitative relations, obtained from a study on a fatigue damage model of composite, are defined by the stiffness degradation rule in the loading direction. The proposed model is as follows: E0 − E( n) ⎛ n B ⎞ D( n) = = 1− ⎜1− ( ) ⎟ E − E ⎝ N ⎠ 4 Pertanika J. Sci. & Technol. 21 (1): 283 - 298 (2013) 0 Where 0 E is the initial Young’s modulus, E f is the failure Young’s modulus, ( ) n E is Young’s modulus of the material subjected to nth cycling loading, n is the cycle, N is the fatigue life, A and B are model parameters, D(n) is the fatigue damage which equals 0 when n=0 and equals 1 when n=N (Wu & Yau, 2009). Shen et al. (1993), in predicting of fatigue life of Boron/Aluminium composite, worked on a technique involving the iteration of damage accumulation and internal stress redistribution. As pointed by Shen et al. (1993), damage accumulation can be determined by applying the fatigue damage evolution law and the redistribution of stress. The characteristics of damage growth in the composite materials have been studied and compared with those of the damage growth in homogeneous materials. The study on the fatigue damage of composite materials of characteristic of damage accumulation in composites materials was done in 2002 by Mao and Mahadevan, who reported that the concept of damage accumulation might be used as a more suitable approach to predict the fatigue life of the structures of composite materials. However, fatigue damage cannot be measured directly. Therefore, for quantitative evaluation of fatigue damage, Young’s modulus or the stiffness of composite materials is often used to evaluate the fatigue damage due to cyclic loading. Fig.3 shows a schematic comparison of damage accumulation in the composite materials and homogeneous materials as a function of fatigue cycle ratio. Fig.3 is plotted in terms of damage index versus cycle ratio, where the damage index is defined as Eq. (3): f A (2)
Aspect of Fatigue Analysis of Composite Materials: A Review Fig.3: Sketched fatigue damage accumulation (Mao & Mahadevan, 2002) 1 1 E D = − (3) E where D 1 is accumulated fatigue damage, E is the Young’s modulus of the damaged material and E 0 is Young’s modulus of undamaged material. The cycle ratio is the number of cycles at a given instant divided by the fatigue life. Mao and Mahadevan (2002) presented a new damage accumulation model to describe the degradations of composite materials. This model accurately explains the rapid damage growth during both the early and final stages of life. The proposed function is of the following form: Pertanika J. Sci. & Technol. 21 (1): 283 - 298 (2013) 0 m m 1 2 ⎛ n ⎞ ⎛ n ⎞ D= q⎜ ⎟ + ( 1−q) ⎜ ⎟ ⎝ N ⎠ ⎝ N ⎠ (4) where D is the normalized accumulated damage; q, m 1 and m 2 are material dependent parameters; n is the number of applied loading cycles, and N is the fatigue life at the corresponding applied load level. The parameters for Eq. (4) are defined as: q = α ⎛ N0 ⎞ −( − ) ⎜ ⎟ 1 1 m m α ⎛ N0 ⎞ A⎜ N ⎟ ⎝ ⎠ A ⎝ N ⎠ (5) β ⎛ No ⎞ 1 = ⎜ ⎟ 2 ⎝ N ⎠ (6) γ ⎛ N ⎞ = ⎜ ⎟ N ⎝ 0 ⎠ (7) 5
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Page 8 and 9: Selected Articles from UPM-Malaysia
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DISCUSSION Y. Yusuf, J. M. Juoi, Z.
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Y. Yusuf, J. M. Juoi, Z. M. Rosli,
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ISSN: 0128-7680 © 2013 Universiti
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Modelling of Motion Resistance Rati
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The Empirical Method Modelling of M
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Assessment of Heavy Metal Pollution
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TABLE 1: Size of mussels in average
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TABLE 5: Heavy metal concentrations
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Physico-Chemical and Electrical Pro
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TABLE 1: (continued) Physico-Chemic
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Norhashila Hashim et al. effectiven
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Statistical Analysis Norhashila Has
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Norhashila Hashim et al. Post-hoc a
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Norhashila Hashim et al. Cubero, S.
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S. Ismail and K. A. Mohd Atan 4 4 p
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S. Ismail and K. A. Mohd Atan The f
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Lemma 1.1 The equation S. Ismail an
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CONCLUSION S. Ismail and K. A. Mohd
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INTRODUCTION Tajau, R. et al. A hig
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Tajau, R. et al. the acrylate’s c
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Tajau, R. et al. double bond) and C
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Tajau, R. et al. Ulanski, P., & Ros
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Aji, I. S., Zinudin, E. S., Khairul
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Aji, I. S., Zinudin, E. S., Khairul
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CONCLUSION Aji, I. S., Zinudin, E.
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D. Bachtiar, S. M. Sapuan, E. S. Za
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TABLE 1: (continue) 4 D. Bachtiar,
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N. Maizatul, I. Norazowa, W. M. Z.
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REFERENCES N. Maizatul, I. Norazowa
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CBIR Using Colour and Shape Fused F
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Toward Automatic Semantic Annotatin
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Issues on Trust Management in Wirel
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Trust Value MF-ID 1 0.8 0.6 0.4 0.2
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A Negation Query Engine for Complex
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REFERENCES A Negation Query Engine
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The Problem Association Rule Mining
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Association Rule Mining threshold t
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Association Rule Mining must be sor
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Association Rule Mining On the othe
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Association Rule Mining Quinlan, J.
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Che Mustapha Yusuf, J., Mohd Su’u
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Az Azrinudin Alidin and Fabio Crest
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Yogan Jaya Kumar, Naomie Salim, Ahm
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REFERENCES Yogan Jaya Kumar, Naomie
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Hasiah Mohamed@Omar, Azizah Jaafar
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The Role of Similarity Measurement
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TABLE 5: Winners MRS The Role of Si
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REFEREES FOR THE PERTANIKA JOURNAL
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Guidelines for Authors Publication
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table should be prepared on a separ
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The Journal’s review process What
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Usability of Educational Computer G
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JST Vol. 21 (1) Jan. 2013 - Pertanika Journal - Universiti Putra ...

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