Manufacturing and mechanical response of nanocomposite laminates

https://doi.org/10.1016/j.compscitech.2004.10.010Get rights and content

Abstract

A newly developed methodology is proposed first to manufacture AS-4/PEEK APC-2 nano-composite laminates. The improvement of mechanical properties of nano-laminates is verified by a series of testings systematically. The achievement of empirical results is highlighted as follows. From tensile tests it is found that the optimal content of nanoparticles (SiO2) is 1% by total wt. The ultimate strength increases about 12.48% and elastic modulus 19.93% in quasi-isotropic nano-laminates. Whilst, the improvement of cross-ply nano-composite laminates is less than that of quasi-isotropic laminates. At elevated temperatures the ultimate strength decreases slightly below 75 °C and the elastic modulus reduces slightly below 125 °C, however, both properties degrade highly at 150 °C (≈Tg) for two layups generally. Finally, after the constant stress amplitude tension–tension (T–T) cyclic testing, it is found that both the stress-cycles (S–N) curves are very close below 104 cycles for cross-ply laminates w/wo nanoparticles, and the S–N curve of nano-laminates slightly bent down after 105 cycles. Whilst in quasi-isotropic laminates, the S–N curve of nano-laminates is always slightly below that of APC-2 laminates through the life.

Introduction

Composite materials have been applied widely, such as civil, defense and aerospace industries, due to their low specific density, high specific strength, stiffness, easy manufacturing, high resistance to fatigue loading and sustaining most mechanical properties at elevated temperature. However, “lighter, thinner, stronger and cheaper” are the goal of materials science and engineering nowadays. With the advent of nano science and technology many developed and powerful countries have made efforts vigorously in related R&D recently. Engineering materials at the atomic and molecular levels are creating a revolution in the field of materials and processing. The discovery of new nanoscaled materials such as nanoclays, carbon nanotubes, and others offer the promise of a variety of new composite, adhesive, coating and sealant materials with specific properties. Thus, we intend to make nanocomposites by using the peculiar physical, chemical and mechanical characteristics of nanoparticles based on the long-term experience in making and testing composite laminates. Also, our lab has been supported by our National Science Council (NSC) for many years, and the research work on the tensile tests, notched effects and T–T fatigue tests of APC-2 composite laminates at room and elevated temperatures is fruitful. The superiority of the APC-2 composite laminates is quite understood, herein, we spread uniformly the nanoparticles into the interfaces of APC-2 composite laminates to produce a new nanocomposite. The focus of this work is to assure the improvement of nanocomposite laminates through mechanical tests. It is a stepping stone to the engineering applications of APC-2 nanocomposites.

The rapid development of nano science and technology not only stimulates the research work rigorously at universities and institutes, but also accelerates the potential applications in many fields. However, in this study we are only concerned with a small part of engineering application, i.e., adding nanoparticles in APC-2 composite laminates to make a significant improvement in mechanical properties due to static and fatigue loadings. Thus, the survey of literature will be limited to the related research in various nanoparticles, composite materials, and their corresponding properties. Some papers are cited for references. Hussain et al. [1], [2] found the mechanical properties are highly increased in Carbon/Epoxy composites by adding Al2O3 particles. Kim [3] revealed the improvement of interface properties by spreading SiC nanoparticles. Lin [4] studied the effect on wear and friction by adding SiC nanoparticles in PEEK. More specially, Schmidt [5], Raming [6] and Sandler et al. [7] investigated the phase transition and interfacial phenomena. For practical purpose, PEEK matrix mixed with nano carbon fibers of 15% by wt. can reach the optimal strength and stiffness as shown in Wang et al. [8]. To be diversified, the micromechanical model of dynamic fracture was established in heterogeneous materials by Zhai [9]. Qi investigated the synthesis of polymer colloids, hollow nanoparticles and nanofibers in [10]. Li presented the manufacturing and processing methods in nano composites, nanometals and semi-conductor particles [11]. Finally, the study of surface adhesion and contact mechanics in micro- and nano-particles was found by Yan [12]. In short, the vision of the development of nanocomposite increases more challenges and potentials, there is still a lot of space to advance in the integration of nano science and technology, e.g., in the combination of research and application.

Section snippets

Experiments

The nanoparticles SiO2 (Wah–Li Co.) possessed the average diameter 15 ± 5 nm, specific surface area 160 ± 20 m2/g, spherical crystallographic and amorphous powder. The prepregs of Graphite/PEEK (ICI Fiberite Co., USA) unidirectional plies were cut, stacked and cured to form APC-2 laminates with fiber volume fraction vf = 61%, Tg = 143 °C and Tm = 343 °C. Our work was to spread nanoparticles uniformly on the face of each ply about totally 1–10% by wt. of laminate. From the tensile tests of cross-ply and

Results and discussion

After a series of mechanical testing systematically we narrowed the limit (1–10% by wt.) and obtained the stress–strain curves of spreading nanoparticles in 5, 8 and 10 plies (1%, 2%, 3% by wt. of PEEK) in cross-ply as shown in Fig. 3 and quasi-isotropic specimens in Fig. 4, respectively. The data listed in Table 1 were the average value of three specimens. It is found that no matter what the stacking sequence the nanocomposite specimen of spreading 10 plies nanoparticles SiO2 1% by wt. (3% by

Conclusion

Our work and findings can be summarized as follows pertinently. The nanocomposite laminates were made by sol–gel method and modified diaphragm method. Adding nanoparticles 1% by wt. is the optimal choice. The ultimate strength and stiffness increase for both layups and the quasi-isotropic is stronger. As the temperature increasing the strength and stiffness reduce for both layups and the worst at 150 °C.The constant stress fatigue testing was performed at room temperature, it is found a little

Acknowledgements

The authors gratefully acknowledge the sponsorship from National Science Council under the Project No. NSC 92-2212-E-110-021, and kind suggestion and discussion with Professors J.C. Huang and M. Chen at the Institute of Materials Science and Engineering, National Sun Yat-sen University.

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