Flexural and Peel Properties of High Performance Magnesium/Carbon-Fiber/PEEK Laminated Composites

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1 Key Engineering Materials Vols (24) pp online at (24) Trans Tech Publications, Switzerland Flexural and Peel Properties of High Performance Magnesium/Carbon-Fiber/PEEK Laminated Composites M. C. Kuo 1,2,a and J. C. Huang 1,b 1 Institute of Materials Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan 84 2 Department of Applied Fiber Style, Kun Shan University of Technology, Tainan, Taiwan 7 a muchen@mail.ksut.edu.tw, b jacobc@mail.nsysu.edu.tw Keywords: Mg/carbon-fiber/PEEK laminated composites, Hot pressing, Flexture test, Peel test. Abstract. Mg/Carbon-Fiber/PEEK laminated composites were successfully fabricated through simple hot pressing. The flexural and peel properties of this Mg based laminated composites are examined and analyzed. The flexural stress and modulus along the longitudinal direction are 96 MPa and 54.6 GPa, respectively, suggesting a sufficiently high resistance against bending deflection. The peel strength is around 5 N/mm, superior to that of the epoxy-resin-adhered Al/CFRP laminated composites. Introduction The research and development of high performance structural materials for aerospace and automobile have long been focused on the weight saving and minimal environmental impact. Accordingly, lightweight characteristics in structural materials has become one of the basic requirements for all transportation systems. Because of the low density of ~1.7 Mg/m 3, magnesium alloys have attracted considerable attention and become the promising alloys, competing with Al and Ti alloys, in transportation applications. On the other hand, carbon fiber reinforced aluminum laminates (CARALL) have been developed [1] to offer the superior fatigue crack growth resistance. It is well-known that magnesium alloys can be reinforced by particulates [2-6] and by short fibers [7-9] to form the Mg based metal matrix composites for the purposes of improving their hardness [2-4] and stiffness [2-5], high strain rate superplasticity [6], and creep resistance [7,8]. So far, continuous-carbon-fiber reinforced Mg based laminated composites were mainly fabricated by means of liquid metal infiltration, CVD, powder infiltration and hot-forming [9-11], but none of the resulting composites could fully utilize the fiber properties. It would be interesting to explore the feasibility to laminate the Mg sheet directly with the well established CF/PEEK prepreg, similar to the previous cases developed for the Al base laminated composites. A simple and feasible hot pressing fabrication mean in processing such Mg based laminated composites has been demonstrated previously [12]. The laminated composites were developed for the Mg base alloys, using the widely applied and low-priced AZ31 Mg commercial sheets (Mg-3wt%Al-1wt%Zn-.2wts%Mn), reinforced with the high strength unidirectional CF/PEEK prepreg (designated as APC-2) through hot pressing. Tensile studies on this laminated Mg/CF/PEEK Mg based composites have revealed a high modulus of 75 GPa and a high tensile strength of 932 MPa along the longitudinal direction [12]. And the experimentally measured tensile modulus and strength data along both the longitudinal and transverse directions are all within 9-1% of the theoretical predictions by rule of mixtures, suggesting that the bonding between layers and the load transfer efficiency are satisfactory. To further evaluate the performances of the proposed Mg based laminated composites in practical applications, it is insteresting and necessary to estimate the laminated composite properties under the bending or peel loading. The results are analyzed and compared with previous reports. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, (ID: /1/6,3:17:53)

2 1154 Advances in Engineering Plasticity and Its Applications Experimental Procedures The Fabrication of Mg/CF/PEEK Mg Based Laminated Composites. The Mg/CF/PEEK Mg based laminated composites were successfully fabricated as described in our previous report [12]. The AZ31 sheets 2 mm in initial thickness were hot rolled into a final thickness of ~.6 mm. The polymer prepreg material used was the AS-4 continuous carbon fiber reinforced PEEK prepreg, designated as APC-2 and fabricated by the ICI/Fiberite Company, USA. The APC-2 prepreg contains ~61 vol% or ~68 wt% continuous AS-4 carbon fiber (with a diameter of ~7 µm and density of ~1.77 Mg/m 3 ) in the PEEK polymer matrix. Forming of the Mg/APC-2 composite was conducted by means of hot pressing with a stacking sequence of AZ31/APC-2/AZ31/APC-2/AZ31 in an unidirectional array. It is estimated that the volume fractions of AZ31, carbon fiber, and PEEK in the resulting Mg/CF/PEEK composite are 61%, 24%, and 15% in volume, respectively. Figure 1 shows the construction of the Mg/CF/PEEK laminated composite mm CF/PEEK prepreg thickness.5-.6mm AZ31 Sheet thickness.5-.6 mm Fig. 1 Schematic drawing of the Mg based laminated composite, layers 1, 3 and 5 are Mg and layers 2 and 4 are APC-2 (with 4 foils). The longitudinal (L) direction is indicated. Flexural and T-Peel Tests. The flexural properties of the Mg/CF/PEEK laminated composites were explored by the three-point bending tests in this study according to the ASTM D79-2 specification. The dimensions of specimens were 1 mm in length, 12.7 mm in width, and 2.8 mm in thickness. The longitudinal and transverse specimens of the Mg/CF/PEEK laminated composites were both tested, with a span-to-depth ratio of 28:1 at a strain rate of 1.7x1-4 s -1. T-peel tests of the Mg/CF/PEEK composites were conducted according to the specification of ASTM D In order to reveal the bond strength between the Mg and APC-2 layers, a three-layer Mg/APC-2/Mg laminate was specially fabricated for this purpose. The thicknesses of the AZ31 Mg and APC-2 prepreg were both about.6 mm. The longitudinal and transverse specimens of the Mg/CF/Mg laminates were both tested. The crosshead speed of 4.2 mm/s was applied, corresponding to a bond separation rate of 2.1 mm/s. To examine the bonding characteristics, the tested specimens were observed by optical microcopy (OM) or scanning electron microscopy (SEM). Results and Discussions Flexual Properties. It is well-known that the hybrid laminated composites exhibit highly anistropic characteristics and cause a mismatch in mechanical properties between individual laminae within the laminate. Such anistropic natures could in turn produce delamination initiation and propagation. The three-point bending loading for the current composite beam can provide the information such as the apparent interlaminate shear strength (ILSS). According to the specification of ASTM D79-2, the flexural stress σ f can be estimated by

3 Key Engineering Materials Vols σ f = 3PL/2bd 2, (1) where P, L, b, and d are ultimate load, free span, width and depth of the beam tested, respectively. And the flexural strain ε f can be also determined by ε f = 6Dd/L 2. (2) Flexural Stress, MPa 1 Flexural Stress at Break 96 MPa Flexural Stress MPa Flexural Modulus 54.6 GPa Fig. 2 The flexural stress and flexural modulus of the Mg/CF/PEEK Mg based laminated composite along the longitudinal direction. Flexural Stress, MPa Max. Flexural Stress 318 MPa Flexural Stress, MPa Flexural Modulus 36.5 GPa Fig. 3 The flexural stress and flexural modulus of the Mg/CF/PEEK Mg based laminated composite along the transverse direction. Figures 2 and 3 show the flexural stresses and moduli of the longitudinaland transverse specimens of the laminated Mg/CF/PEEK composites. As shown in Fig. 2, the flexural modulus, stress and strain along the longitudinal direction of the Mg based laminated composite are 54.6 GPa, 96 MPa and.3, respectively. These high flexural stress and modulus might be due to the sound interfacial bonding between Mg and APC-2. On the other hand, the flexural modulus, stress and strain along the transverse direction of the Mg based laminated composite are 36.5 GPa, 318 MPa and.7, respectively. It is obvious that the carbon fibers

1156 Advances in Engineering Plasticity and Its Applications arrayed in the longitudinal configuration could impart significant contribution in carrying the load, and effectively enhancing the

The flexural properties revealed are basically a reflection from the behavior of the AZ31 Mg sheets, similar to the tensile case observed previously [12].

4 1156 Advances in Engineering Plasticity and Its Applications arrayed in the longitudinal configuration could impart significant contribution in carrying the load, and effectively enhancing the bending resistance of the laminated composite. However, those in the transverse configuration seem to be a minor role. The flexural properties revealed are basically a reflection from the behavior of the AZ31 Mg sheets, similar to the tensile case observed previously [12]. In comparison with the CF/PEEK prepreg polymer composite, the Mg/CF/PEEK Mg based composite shows a slightly lower flexural and tensile modulus and strength along the longitudinal direction, but appreciably higher modulus and strength along the transverse direction, due to fact that Mg is still much stronger than the PEEK matrix. To account for the large differences in the flexural properties along the longitudinal and transverse directions, the fractured specimens were carefully examined, as shown in Fig. 4. In Fig. 4, it suggests that the interface bonding between Mg sheet and APC-2 prepreg is sufficiently strong. The failure behavior in the longitudinal specimen was found to be of multiple modes and an overall failure phenomenum. Carbon fibers were broken and delaminated inside the APC-2 layer of the laminated composite. The outer Mg layer was completely fractured, and the inner Mg layer was squeezed convexly. The interface just adjacent to the failure position of the outer Mg layer showed no apparent delamination. However, delamination occurred at the inner layer counterpart. In contract, the fractured phenomena in the transverse configuration are significantly different to those of the longitudinal countpart, as shown in Fig. 4. It is a more simple failure behavior. The composite showed much higher flexural strain, and until flexural strain of.7 only the outer Mg sheet APC-2 layers were fractured. The carbon fibers in the outer APC-2 layer of the transverse specmen were simply separated each other. Overall, the interface bonding between APC-2 and Mg appears to be sufficient, as evident from the current flexural and previous tensile tests [12]. Fig. 4 Photographs of the fractured Mg/CF/PEEK laminated composites for the longitudinal and transverse configurations of carbon fibers. The loading direction is indicated. Peeling Properties. It was proposed [12] that the interfacial bonding strength between the APC-2 prepreg and the Mg sheet would be strongly affected by the surface treatment during the fabrication processes. It is meaningful to estimate the interfacial bonding strength of the current laminated composites and to compare with the epoxy-resin-adhered Aluminum/CFRP composites [13]. In this study, the T-peel method was adopted to determinate the interfacial strength. For the T-peel specimens, the right-angled tabs were adhesively bonded to the ends of the Mg/APC-2/Mg laminated composites. The APC-2 layer contains five foils of the APC-2, or CF/PEEK, prepregs with the carbon fibers undirectionally stacked within the PEEK matrix. The peel strengths was determined to be 6.63 N/mm, as shown in Fig. 5. These values are lower than the diffusion or fusion bonding in metallic systems (~3 N/mm)

Key Engineering Materials Vols. 274-276 1157 [14], but superior to adhesive bonding of the epoxy-resin-adhered untreated-aluminum/cfrp composites (~2.5 N/mm) [13].

And this can be attributed by the sound interfacial bonding characteristics between the Mg sheet and the APC-2 prepreg. In comparison of the pretreatments of Mg foil with or without CrO 3, Fig.

63 N/mm Peeling Force, N/mm 5 4 3 2 1 5 1 15 2 Elongation, mm Displacement, mm Fig. 5 Result of the peeling test conducted on the Mg/CF/PEEK laminated composites. (c) Fig.

5 Key Engineering Materials Vols [14], but superior to adhesive bonding of the epoxy-resin-adhered untreated-aluminum/cfrp composites (~2.5 N/mm) [13]. The OM micrographs taken from the peeled specimens show that there are many carbon fibers stuck on the Mg foil after peeling, Fig. 6. And this can be attributed by the sound interfacial bonding characteristics between the Mg sheet and the APC-2 prepreg. In comparison of the pretreatments of Mg foil with or without CrO 3, Fig. 6 and, it is apparent that the Mg foil pretreated with CrO 3 etchant shows much better interfacial bonding characteristics. 7 6 Max. peeling force, 6.63 N/mm Peeling Force, N/mm Elongation, mm Displacement, mm Fig. 5 Result of the peeling test conducted on the Mg/CF/PEEK laminated composites. (c) Fig. 6 OM micrographs taken from the peel-tested specimens: Mg layer without CrO 3 etching, Mg layer with CrO 3 etching, and (c) APC-2 layer. The lighter-contrasted PEEK resin adhered on the Mg phase is evident in and on carbon fibers in (c), and the broken carbon fibers stuck on the Mg phase in. High Performance Room Temperature Mechanical Properties. In combining with our previous tensile results, the current Mg based laminated compoiste overall appears to be a promising high performance and light weight structural material possessing high specific mechanical properties, as compared in Table 1.

6 1158 Advances in Engineering Plasticity and Its Applications Summary 1. The Mg/CF/PEEK Mg based laminated composites were successfully fabricated through a simple hot pressing method. This promising method can fabricate high performances and low density laminated composites in terms of tensile as well as flexural properties. 2. The flexural modulus, stress and strain along the longitudinal and transverse directions of the Mg based laminated composite are 54.6 GPa, 96 MPa and.3; and 36.5 GPa, 318 MPa and.7, respectively. The current laminated composite shows sufficiently high resistance to bending deflection. 3. Multiple fracture modes are observed in the longitudinal flexural specimen, while a more simple behavior is seen in transverse counterpart. 4. The peel strength of the Mg/APC-2/Mg laminate is superior to that of the epoxy-resin-adhered Al/CFRP laminated composites. 5. Pretreatment of the Mg sheets with or without CrO 3 etching shows significant differences in terms of the resulting interfacial bonding between Mg and APC-2. Table 1 Comparison of the current Mg based composites with other metallic alloys in terms of the specific tensile and flexural modulus (GPa/Mg/m 3 ) and maximum strength (MPa/Mg/m 3 ) along the longitudinal and transverse directions Properties Mg/CF/PEEK Mg alloy Al alloy Ti alloy Steel (long./trans.) (AZ91) (661) (Ti-6Al-4V) (14) E tensile /d 44/ E flexural /d 32/ UTS tensile /d 548/ UFS flexural /d 565/ Acknowledgement The authors gratefully acknowledge the sponsorship from National Science Council of Taiwan, ROC, under the project number NSC E References [1] C. T. Lin and P. W. Kao: Acta Mater. Vol. 44 (1996), p [2] M. Gupta, L. Lu, M. O. Lai and H. H. Lee: Mater. Research Bulletin Vol. 34 (1999), p [3] W. C. Harrigan Jr. : Mater. Sci. Eng. Vol. A244 (1998), p. 75. [4] D. J. Towle and C. M. Friend: Mater. Sci. Tech. Vol. 9 (1993), p. 35. [5] S. Lim and T. Choh: J. Japan Light Metals Vol. 42 (1992), p [6] H. Watanabe, T. Mukai, T. G. Nieh and K. Higashi: Scripta Mater. Vol. 42 (2), p [7] E. G. Wolff, B. K. Min and M. H. Kural: J. Mater. Sci. Vol. 2 (1985), p [8] F. Chmelik, J. Kiehn, P. Lukac, K. U. Kainer and B. L. Mordike: Scripta Mater. Vol. 38 (1998), p. 81. [9] A. A. Baker: Mater. Sci. Eng. Vol. 17 (1975), p [1] A. A. Baker, M. B. P. Allery and S. J. Harris: J. Mater. Sci. Vol. 4 (1969), p [11] P. W. Jackson, D. M. Braddick And P. J. Walker: Fiber Sci. and Tech. Vol. 5 (1972), p [12] M. C. Kuo, J. C. Huang, M. Chen and M. H. Jen: Mater. Trans. Vol. 44 (23), p [13] K. Y. Rhee and J. H. Yang: Composites Sci. Tech. Vol, 63 (23), p. 33.

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Global Journal of Engineering Science and Research Management

Global Journal of Engineering Science and Research Management INVESTIGATION OF IMPACT BEHAVIOR OF CORRUGATED POLYMER SANDWICH STRUCTURE M. Nusrathulla * 1 Dr. M. Shantaraja 2 * 1 Research scholar in the Department of Mechanical Engineering, at UVCE, Bangalore. India.