Materials Science and Engineering A 507(2009)6-12 Contents lists available at Science Direct Materials Science and Engineering A LSEVIER journalhomepagewww.elsevier.com/locate/msea Influence of the strain rate on the mechanical behavior of the 3D needle-punched C/Sic composite Yulong Li*, Tao Suo, Mingshuang Liu School of Aeronautics, Northwestern Polytechnical University, P.O. Box 118, XI'an 710072, People's Republic of china ARTICLE INFO ABSTRACT Compressive mechanical behavior of a 3D needle-punched C/Sic composite at room temp investigated at strain rate ranging from 10-4 to 6.5 x 1031/s using the electronic universal test 15 November 2008 nd the split Hopkinson pressure bar. The experimental results show the strain rate has slig Accepted 7 January 2009 on the mechanical property of the material. The dynamic compression strength obeys the bution with the Weibull parameter m calculated as 8 19. Scanning electron microscope(SI of the fracture surface of specimens tested at various strain rates indicate that the failure pat D needle-punched C/SiC composites material also varies with the strain rate Mechanical properties o2009 Elsevier B V. All rights reserved. Dynamic compression strength Damage angle 1. Introduction matrix. Recently, Fan et al.[14 and Xu et al. [11 analyzed its fri tion performance and suggested that the grain-abrasion was the Carbon fiber-reinforced Sic-matrix composites (C/Sic) have main wear mechanism of the material. The mechanical behavior of such advantages as low density, high ratios of stiffness/ weight 3D needle-punched C/Sic composite under quasi-static loading at temperature conditions, all of which have enabled their extensive that the bending strength vertical to layers was weaker than the pplication in many engineering structures, especially in aeronau- strength parallel to layers, while the compression strength vertical tic and aerospace fields [ 1. The C/Sic composites developed can to layers almost equaled that parallel to the layers. However, to the be grouped into 2D composites and 3D ones. The interface shear best of our knowledge, the dynamic compressive behavior of 3D strength of 2D-C/Sic composites was found by many researchers to needle-punched C/Sic composite has not yet been reported be relatively weak [2-6. To overcome this disadvantage 3D C/Sic In this paper, the uniaxial compressive behavior of a 3D needle- composites were developed [7. Among them, 3D woven C/SiC com- punched C/Sic composite was investigated under both quasi-static posites and 3D needle-punched C/Sic composites were the most and dynamic loadings at room temperature. The failure pattern was widely investigated ones. While the experimental results of the 3D observed via a scanning electron microscope(SEM). woven C/SiC composites exhibit remarkable anisotropy [8-10, the research results of the 3D needle-punched c/SiC composite demon- 2. Experimental procedure strate that its interface shear strength as well as the mechanical erosion resistance could benefit from the special microstructure of 2.1. Material preparation the material [11, 12] Considerable interest has been focused on 3D needle-punched The 3D needle-punched C/Sic composite tested in this study C/SiC composite in recent years. Microstructure and flexural prop- was offered by the State Key Laboratory of Solidification Process erties of a 3D C/SiC composite was examined by Xiao et al.[13]. ing in Northwestern Polytechnical University, Peoples Republic from which the composite was found to be damaged layer by of China. The carbon fiber utilized was T300 carbon fiber from layer with good pseudo-plasticity and that pyrolytic carbon coat- the Nippon Toray Corporation. The quasi 3D reinforced preform ing could moderate the interface strength between C fibers and si was firstly prepared by three-dimensional braided Then isothermal/ isobaric CVI(ICVI)was employed to depo the surface of carbon fiber Corresponding author. TeL: +86 29 8849 4859: fax: +86 29 8849 4859. layer with butane at 850C prior to densification. Finally, methyl mail address: liyulong@nwpueduce (Y Li). trichlorosilane was used for deposition of the Sic matrix to get the 5093/s-see front matter o 2009 Elsevier B V. All rights reserved. 01016 j.msea200901024
Materials Science and Engineering A 507 (2009) 6–12 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Influence of the strain rate on the mechanical behavior of the 3D needle-punched C/SiC composite Yulong Li ∗, Tao Suo, Mingshuang Liu School of Aeronautics, Northwestern Polytechnical University, P.O. Box 118, Xi’an 710072, People’s Republic of China article info Article history: Received 4 May 2008 Received in revised form 15 November 2008 Accepted 7 January 2009 Keywords: 3D needle-punched C/SiC composites Mechanical properties High strain rate Dynamic compression strength Damage angle abstract Compressive mechanical behavior of a 3D needle-punched C/SiC composite at room temperature was investigated at strain rate ranging from 10−4 to 6.5 × 103 1/s using the electronic universal testing machine and the split Hopkinson pressure bar. The experimental results show the strain rate has slight influence on the mechanical property of the material. The dynamic compression strength obeys the Weibull distribution with the Weibull parameter m calculated as 8.19. Scanning electron microscope (SEM) images of the fracture surface of specimens tested at various strain rates indicate that the failure pattern of the material also varies with the strain rate. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Carbon fiber-reinforced SiC-matrix composites (C/SiC) have such advantages as low density, high ratios of stiffness/weight and strength/weight, and failure stress that sustains under high temperature conditions, all of which have enabled their extensive application in many engineering structures, especially in aeronautic and aerospace fields [1]. The C/SiC composites developed can be grouped into 2D composites and 3D ones. The interface shear strength of 2D-C/SiC composites was found by many researchers to be relatively weak [2–6]. To overcome this disadvantage, 3D C/SiC composites were developed [7]. Among them, 3D woven C/SiC composites and 3D needle-punched C/SiC composites were the most widely investigated ones. While the experimental results of the 3D woven C/SiC composites exhibit remarkable anisotropy [8–10], the research results of the 3D needle-punched C/SiC composite demonstrate that its interface shear strength as well as the mechanical erosion resistance could benefit from the special microstructure of the material [11,12]. Considerable interest has been focused on 3D needle-punched C/SiC composite in recent years. Microstructure and flexural properties of a 3D C/SiC composite was examined by Xiao et al. [13], from which the composite was found to be damaged layer by layer with good pseudo-plasticity and that pyrolytic carbon coating could moderate the interface strength between C fibers and SiC ∗ Corresponding author. Tel.: +86 29 8849 4859; fax: +86 29 8849 4859. E-mail address: liyulong@nwpu.edu.cn (Y. Li). matrix. Recently, Fan et al. [14] and Xu et al. [11] analyzed its friction performance and suggested that the grain-abrasion was the main wear mechanism of the material. The mechanical behavior of 3D needle-punched C/SiC composite under quasi-static loading at room temperature was also investigated by Wan [12], who reported that the bending strength vertical to layers was weaker than the strength parallel to layers, while the compression strength vertical to layers almost equaled that parallel to the layers. However, to the best of our knowledge, the dynamic compressive behavior of 3D needle-punched C/SiC composite has not yet been reported. In this paper, the uniaxial compressive behavior of a 3D needlepunched C/SiC composite was investigated under both quasi-static and dynamic loadings at room temperature. The failure pattern was observed via a scanning electron microscope (SEM). 2. Experimental procedure 2.1. Material preparation The 3D needle-punched C/SiC composite tested in this study was offered by the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University, People’s Republic of China. The carbon fiber utilized was T300 carbon fiber from the Nippon Toray Corporation. The quasi 3D reinforced preform was firstly prepared by three-dimensional braided method. Then isothermal/isobaric CVI (ICVI) was employed to deposit a thin pyrolysis carbon layer on the surface of carbon fiber as the interfacial layer with butane at 850 ◦C prior to densification. Finally, methyltrichlorosilane was used for deposition of the SiC matrix to get the 0921-5093/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2009.01.024
Y Li et al./ Materials Science and Engineering A 507 (2009)6-12 Socket Projectle elocity derganc bar High dynamic Fig. 1. The diagram illustration of the split Hopkinson press bar systems 3D-C/SiC composite with density of 1.90 g/cm and open porosity strain rate. The compression strength of the material increases 1609°C from about 350 MPa at the strain rate of 10-4 1/s to 430 MPa at the strain rate of 6.5 x 10 1/s with a relative increment of about 2.2. Experiment procedure 23%. Although remarkable dispersity exists, a close inspection of the experimental results reveals that the compression strength of The specimens were cut from a 3D needle-punched C/Sic com- the material varies linearly with the logarithm of the strain rate(as posite plate to ensure that the loading direction is parallel to the shown in Fig 3). Such phenomenon was also observed for 2D-C/Sic It is believed that microcracks are contributed to the strain rate cylindrical, with a diameter of 5 mm and a length of 4 mm. Both sensitivity of the material. As we known, such defects as micro the quasi-static and dynamic experiments were performed at the cracks caused by the mismatch of thermal expansion coefficients temperature. The strain rates were controlled in the range between the carbon fibers and the sic matrix are unavoidable dur- from1.0×10-4to6.5×1031/s ing the preparation of the composites Under compression loading. An electronic universal testing machine with a maximum load capacity of 10 kN was used to perform the quasi-static experiments. failure of the composites. It should be pointed out that both the The split Hopkinson pressure bar(SHPB), situated in Northwestern nucleation and extension are processes of time dependence.Under Polytechnical University, was used for the high strain rate experi- quasi-static loading. the microcracks have enough time to nucleate ents. A steel pad was employed to restrain the maximum strain and extend. While under dynamic loading, the applied load pulse ithin certain limits so that the fracture surface of the tested spec- is usually several hundred microseconds, which is insufficient for imens could be preserved. The diagram of the SHPB and the steel the nucleation and extension of microcracks. As the result, higher ad was shown in Fig. 1. According to the one-dimensional elas- compression strength is needed at high strain rates stress wave theory, the strain, stress and strain rate of tested It should be noticed that the catastrophic brittle failure was not specimen can be calculated as observed for the specimens tested at different strain rates. Instead, despite of the decrease of true stress with true strain after the stress reaches its compression strength, the material still possesses a rel- Es = (1) where ER and Er are, respectively, the transmitted and reflected train pulses which can be measured by the strain gages stuck on the input and output bars: Co, E, and a denote the longitudinal elastic wave velocity. Young's modulus and cross-sectional area of 250 the loading bars respectively; Is and As are the length and cross- sectional area of the specimen respectively 3. Experimental results and discussion 10e2 I 100/s 3.1. Experimental results stress vs strain curves of the 3d needle- punched C/Sic at different strain rates. It can be observed 0020.040060080.10.120.140.16 that both the lon strength and failure strain of the 3D True strain needle-punched C/Sic composite increase with applied strain rate, while elastic modulus of the material is almost independent on Fig. 2. The quasi-static and dynamic true stress vs strain curves of the 3D needling-
Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 7 Fig. 1. The diagram illustration of the split Hopkinson press bar systems. 3D-C/SiC composite with density of 1.90 g/cm3 and open porosity 16.09 ◦C. 2.2. Experiment procedure The specimens were cut from a 3D needle-punched C/SiC composite plate to ensure that the loading direction is parallel to the thickness direction of the material. The specimens tested under quasi-static and dynamic loadings at room temperature were both cylindrical, with a diameter of 5 mm and a length of 4 mm. Both the quasi-static and dynamic experiments were performed at the room temperature. The strain rates were controlled in the range from 1.0 × 10−4 to 6.5 × 103 1/s. An electronic universal testing machine with a maximum load capacity of 10 kN was used to perform the quasi-static experiments. The split Hopkinson pressure bar (SHPB), situated in Northwestern Polytechnical University, was used for the high strain rate experiments. A steel pad was employed to restrain the maximum strain within certain limits so that the fracture surface of the tested specimens could be preserved. The diagram of the SHPB and the steel pad was shown in Fig. 1. According to the one-dimensional elastic stress wave theory, the strain, stress and strain rate of tested specimen can be calculated as S = E A AS εT εS = −2C0 lS t 0 εR d ε˙ S = −2C0 lS εR (1) where εR and εT are, respectively, the transmitted and reflected strain pulses which can be measured by the strain gages stuck on the input and output bars; C0, E, and A denote the longitudinal elastic wave velocity, Young’s modulus and cross-sectional area of the loading bars respectively; ls and As are the length and crosssectional area of the specimen respectively. 3. Experimental results and discussion 3.1. Experimental results Fig. 2 shows the true stress vs. strain curves of the 3D needlepunched C/SiC composite at different strain rates. It can be observed that both the compression strength and failure strain of the 3D needle-punched C/SiC composite increase with applied strain rate, while elastic modulus of the material is almost independent on strain rate. The compression strength of the material increases from about 350 MPa at the strain rate of 10−4 1/s to 430 MPa at the strain rate of 6.5 × 103 1/s with a relative increment of about 23%. Although remarkable dispersity exists, a close inspection of the experimental results reveals that the compression strength of the material varies linearly with the logarithm of the strain rate (as shown in Fig. 3). Such phenomenon was also observed for 2D-C/SiC composite [2,15]. It is believed that microcracks are contributed to the strain rate sensitivity of the material. As we known, such defects as microcracks caused by the mismatch of thermal expansion coefficients between the carbon fibers and the SiC matrix are unavoidable during the preparation of the composites. Under compression loading, the nucleation and extension of the microcracks will cause the failure of the composites. It should be pointed out that both the nucleation and extension are processes of time dependence. Under quasi-static loading, the microcracks have enough time to nucleate and extend. While under dynamic loading, the applied load pulse is usually several hundred microseconds, which is insufficient for the nucleation and extension of microcracks. As the result, higher compression strength is needed at high strain rates. It should be noticed that the catastrophic brittle failure was not observed for the specimens tested at different strain rates. Instead, despite of the decrease of true stress with true strain after the stress reaches its compression strength, the material still possesses a relFig. 2. The quasi-static and dynamic true stress vs. strain curves of the 3D needlingpunched C/SiC composites.
Y Li et al/ Materials Science and Engineering A 507(2009)6-12 三易 1 2 y=10.053x+37258 A Needlimg-punched C/SiC 一7# Trend(Needling-punched C/SiC) 012 te) Fig 4. The true stress vs strain curves of the 3D needling-punched C/SiC composites at the same strain rates under Fig 3. Compression strength vs strain rate curves of the 3D needling-punched C/Sic dispersity of the material. Larger value of m indicates low den- atively high load-bearing capacity. The failure strain of the material sity of defects and low dispersity of the compression strength. believe that the fracture of the SiC matrix may cause a drop in the when o equals ao. It can be seen from Fig. 5 that the dynamic loading capacity of the material after the peak stress; yet pullout compression strength obeys the Weibull distribution. The calcu of the needle-punched carbon fibers demands additional energy lated Weibull modulus m and the characteristic strength ao which in a way results in a higher failure strain of the 3D needle- the 3D needle-punched C/Sic composite are 8.19 and 426. MPa espectively. not occur in Fig. 2, in place of which an obvious strain softening Because of the remarkable dispersity of the compression is observed. While for 2D-C/SiC composites tested by Liu [15]. the strength of the 3D composites, at least three tests were conducted materials fracture quickly after the stress reaches its compress or each experimental condition. The stress-strain curve with the strength. That is to say, the needle failure strength closing to the trend line in Fig. 4 was picked to tive contribution toward the toughness of the 3D needle-punched be presented in Fig. 2 as a typical stress-strain curve of the 3D C/SiC composite As the results, the 3D needle-punched C/Sic com- composites at corresponding experimental condition posite have improved fracture toughness compared with 2D-C 3.3. Observation of failure surface 3. 2. Weibull distribution of the dynamic compression strength The fractures of the failure specimens were observed by using an As the material was prepared using the CVI process, defects optical microscope and JSM6460 SEM Optical images of the frac- as gas-holes are inevitable and the heterogeneous distribution ture surface of the 3D needle-punched C/SiC composite tested at of them may lead to the dispersity of the material strength. (b)respectively. It can be seen that shear failure and delamina- Thus, remarkable dispersity of the compression strength of the 3d tion feature the fracture of the material, which was also observed eedle-punched C/Sic composites tested at the same strain rate under dynamic loading conditions can be observed in Fig. 4.It should be explained that as steel pads were employed to restrain strain within certain limits during experiments on some samples, the failure strain of three samples(4#, 5# and 7#) is only 0.04, while five of other samples have failure strains more than 0.16 strength of the material, the Weibull distribution was applied this study. In the case of 3D needle-punched C/Sic composites, the s three basic constituents, namely, fiber, interphase, and Sic matrix 2-0.5 re essentially brittle and the cracking involves defect-induced random failures. It thus follows that the statistical distribution of the strength of the 3D needle-punched C/Sic composite can be described by Weibull equation as A Needling-punched C/SIC 6.2 where Fo)is a probability function, o the stress applied, oo the scale parameter or characteristic strength, and m is the Weibul Fig. 5. The Weibull distributions of dynamic failure strengths of the 3D needling modulus, the most important parameter which characterizes the punched C/SiC composites
8 Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 Fig. 3. Compression strength vs. strain rate curves of the 3D needling-punched C/SiC composites. atively high load-bearing capacity. The failure strain of the material tested at different strain rates even exceeds 8%. It is reasonable to believe that the fracture of the SiC matrix may cause a drop in the loading capacity of the material after the peak stress; yet pullout of the needle-punched carbon fibers demands additional energy which in a way results in a higher failure strain of the 3D needlepunched C/SiC composite. Thus, catastrophic brittle failure does not occur in Fig. 2, in place of which an obvious strain softening is observed. While for 2D-C/SiC composites tested by Liu [15], the materials fracture quickly after the stress reaches its compression strength. That is to say, the needle-punched fibers may make a positive contribution toward the toughness of the 3D needle-punched C/SiC composite. As the results, the 3D needle-punched C/SiC composite have improved fracture toughness compared with 2D-C/SiC composite. 3.2. Weibull distribution of the dynamic compression strength As the material was prepared using the CVI process, defects as gas-holes are inevitable and the heterogeneous distribution of them may lead to the dispersity of the material strength. Thus, remarkable dispersity of the compression strength of the 3D needle-punched C/SiC composites tested at the same strain rate under dynamic loading conditions can be observed in Fig. 4. It should be explained that as steel pads were employed to restrain the maximum strain within certain limits during experiments on some samples, the failure strain of three samples (4#, 5# and 7#) is only 0.04, while five of other samples have failure strains more than 0.16. To quantify the degree of dispersity of the dynamic compression strength of the material, the Weibull distribution was applied in this study. In the case of 3D needle-punched C/SiC composites, the three basic constituents, namely, fiber, interphase, and SiC matrix are essentially brittle and the cracking involves defect-induced random failures. It thus follows that the statistical distribution of the strength of the 3D needle-punched C/SiC composite can be described by Weibull equation as F() = 1 − exp − 0 m (2) where F() is a probability function, the stress applied, 0 the scale parameter or characteristic strength, and m is the Weibull modulus, the most important parameter which characterizes the Fig. 4. The true stress vs. strain curves of the 3D needling-punched C/SiC composites at the same strain rates under dynamic compression. dispersity of the material. Larger value of m indicates low density of defects and low dispersity of the compression strength. The maximum density of the Weibull distribution can be achieved when equals 0. It can be seen from Fig. 5 that the dynamic compression strength obeys the Weibull distribution. The calculated Weibull modulus m and the characteristic strength 0 of the 3D needle-punched C/SiC composite are 8.19 and 426.4 MPa respectively. Because of the remarkable dispersity of the compression strength of the 3D composites, at least three tests were conducted for each experimental condition. The stress–strain curve with the failure strength closing to the trend line in Fig. 4 was picked to be presented in Fig. 2 as a typical stress–strain curve of the 3D composites at corresponding experimental condition. 3.3. Observation of failure surface The fractures of the failure specimens were observed by using an optical microscope and JSM6460 SEM. Optical images of the fracture surface of the 3D needle-punched C/SiC composite tested at the strain rates of 10−4 and 10−2 1/s are shown in Fig. 7(a) and (b) respectively. It can be seen that shear failure and delamination feature the fracture of the material, which was also observed Fig. 5. The Weibull distributions of dynamic failure strengths of the 3D needlingpunched C/SiC composites.
Y Li et al./ Materials Science and Engineering A 507 (2009)6-12 30° Imm (b)10 6 0 Imm Imm (c)1.1×10°1/s 103 Fig. 6. Fractures of the 3D needling-punched C/siC composites under static and dynamic compression. in 3D C/c composite tested at compression load by Xiong et al. 3.4. Comparison with 2D-C/Sic composites [16]. An increase of shear fracture angle of the failed specimens from 35 at the strain rate of 10-4 1/s to about 45 at 10-2 1/s was In this section, in order to display the advantages of the 3D also observed in Fig. 6(a)and(b). Garland et al. [17)and Bi et al. needle-punched C/Sic composite tested in this study, the mechan- [18 proposed that the strain rate effect of the interface strength ical behavior of the material is also compared with that of 2D-C/Sic may contribute to the magnitude of shear fracture angle in fibrous composites tested by liu et al. [15]. The true stress vs strain curves composites. In other words, high compression strength of the 3d of both two kinds of 2D composites with different densification needle-punched C/SiC composite at high strain rates results in a and the 3d composite tested in this study are shown in Fig. 8. It large shear fracture angle. Fig. 6(c) and (d) shows the fracture sur- can be seen that at the same strain rate the compression strength faces of the material tested at the strain rates of 1.1 x 10 and of 3D needle-punched c/Sic composite is higher than that of low 3x 10 1/s respectively. Differing from the failure pattern under densification(LD)2D-C/Sic composite but lower than that of high juasi-static loading condition, the failure mode under dynamic densification(HD) counterpart. It is also interesting to find the ading displays a split pattern the same failure mode was al 3D needle-punched C/Sic composite shows larger failure strain bserved in 3D needle-punched C/C composite loaded at high strain than both kinds of 2D-C/Sic composite As has been proposed in ates [19]. It is also interesting to find one end of the specimens of [15]. the relatively low interface strength of LD 2D-C/SiC compos 3D composite tested at high strain rate broke into pieces. The exact ite resulted in a weak load-bearing capacity. Thus an increase in eason for such phenomenon is not clear at present time. Shear the strength of 2D-C/SiC composite necessitates an increase of its fracture angle of the 3D needle-punched C/Sic composite are not intensity. But it should be pointed out that the increase of inter defined either. sity can also lead to a reduction in inhere low toughness of the The SEM images of the ruptured surface of the specimens tested material [15 By contrast, the carbon fibers needle-punched into at strain rates of 10-4, 10-2. 1.1 x 10 and 3 x 10 1/s are shown in the laminates in thickness direction of 3D composite can lead Fig. 7 respectively. It can be observed from Fig. 7(a)and (b )that a higher interface shear strength. At the same time, the inserted ge number of fibers were pulled out during deformation at strain carbon fibers can also play a toughening effect on the 3D needle- ates of 10-4 and 10-2 1/s, the length of which decreases with the punched C/SiC composites. As the result, the 3D needle-punched increase of strain rate. In contrast, the specimens tested at stra C/Sic composite shows not only high compression strength but rel- rates of 1.1 x 10 and 3 x 10 1/s display smoother fracture surfaces atively high toughness even after the stress reaches its compression (see in Fig. 7(c)and (d). This indicates the number of fragmental strength. Hence it can be concluded that the 3D needle-punched fibers in the 3D needle-punched C/Sic composite under dynamic C/Sic composite possess advantages of both LD and HD 2D-C/Sic ading increases with the strain rate
Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 9 Fig. 6. Fractures of the 3D needling-punched C/SiC composites under static and dynamic compression. in 3D C/C composite tested at compression load by Xiong et al. [16]. An increase of shear fracture angle of the failed specimens from 35◦ at the strain rate of 10−4 1/s to about 45◦ at 10−2 1/s was also observed in Fig. 6(a) and (b). Garland et al. [17] and Bi et al. [18] proposed that the strain rate effect of the interface strength may contribute to the magnitude of shear fracture angle in fibrous composites. In other words, high compression strength of the 3D needle-punched C/SiC composite at high strain rates results in a large shear fracture angle. Fig. 6(c) and (d) shows the fracture surfaces of the material tested at the strain rates of 1.1 × 103 and 3 × 103 1/s respectively. Differing from the failure pattern under quasi-static loading condition, the failure mode under dynamic loading displays a split pattern. The same failure mode was also observed in 3D needle-punched C/C composite loaded at high strain rates [19]. It is also interesting to find one end of the specimens of 3D composite tested at high strain rate broke into pieces. The exact reason for such phenomenon is not clear at present time. Shear fracture angle of the 3D needle-punched C/SiC composite are not defined either. The SEM images of the ruptured surface of the specimens tested at strain rates of 10−4, 10−2, 1.1 × 103 and 3 × 103 1/s are shown in Fig. 7 respectively. It can be observed from Fig. 7(a) and (b) that a large number of fibers were pulled out during deformation at strain rates of 10−4 and 10−2 1/s, the length of which decreases with the increase of strain rate. In contrast, the specimens tested at strain rates of 1.1 × 103 and 3 × 103 1/s display smoother fracture surfaces (see in Fig. 7(c) and (d)). This indicates the number of fragmental fibers in the 3D needle-punched C/SiC composite under dynamic loading increases with the strain rate. 3.4. Comparison with 2D-C/SiC composites In this section, in order to display the advantages of the 3D needle-punched C/SiC composite tested in this study, the mechanical behavior of the material is also compared with that of 2D-C/SiC composites tested by Liu et al. [15]. The true stress vs. strain curves of both two kinds of 2D composites with different densification and the 3D composite tested in this study are shown in Fig. 8. It can be seen that at the same strain rate, the compression strength of 3D needle-punched C/SiC composite is higher than that of low densification (LD) 2D-C/SiC composite but lower than that of high densification (HD) counterpart. It is also interesting to find the 3D needle-punched C/SiC composite shows larger failure strain than both kinds of 2D-C/SiC composite. As has been proposed in [15], the relatively low interface strength of LD 2D-C/SiC composite resulted in a weak load-bearing capacity. Thus an increase in the strength of 2D-C/SiC composite necessitates an increase of its intensity. But it should be pointed out that the increase of intensity can also lead to a reduction in inhere low toughness of the material [15]. By contrast, the carbon fibers needle-punched into the laminates in thickness direction of 3D composite can lead to higher interface shear strength. At the same time, the inserted carbon fibers can also play a toughening effect on the 3D needlepunched C/SiC composites. As the result, the 3D needle-punched C/SiC composite shows not only high compression strength but relatively high toughness even after the stress reaches its compression strength. Hence it can be concluded that the 3D needle-punched C/SiC composite possess advantages of both LD and HD 2D-C/SiC composites
Y Li et al/ Materials Science and Engineering A 507(2009)6-12 mm x500 SE 5.0V 12 9mm x500 SE(M (a)10-1/s 150v129mmx500sE 15012m×8sEM loum 1.1×1031/ 3.0×1031/s Fig. 7. SEM micrographs of the 3D needling-punched C/SiC composites ruptured surface under static and dynamic compression. Table 1 lists shear fracture angles of both kinds of 2D composite SEM images of the ruptured surface of both kinds of 2D-C/Si and 3D needle-punched C/SiC composite. It can be seen that the composite loaded under quasi-static and dynamic loading condi 3D composite shows larger shear fracture angle under quasi-static tions are shown in Fig 9 respectively. For LD 2D-C/SiC composite, loading than that of LD 2D-C/SiC composite but smaller than that of in Fig 9, pull out fibers can be observed while bundles of fibers were HD 2D-C/SiC composite. As mentioned above, higher compression cut off for HD 2D-C/SiC composite. The smoother fracture surface of strength will lead to larger shear fracture angle. Thus, larger shear HD composites under both quasi-static and dynamic compression fracture angle also indicates excellent compression behavior of the indicates more small cracked fibers. Matrix fragments generated 3D composite which is consistent with above conclusion derived under dynamic compression for both Ld and HD composites. while directly from Fig. 8. for 3D needle-punched C/Sic composite, the fracture surfaces are relative rough and more fibers were pulled out under both quasi static and dynamic loading(see in Fig. 7). This phenomenon can be LD-2D C/SiC(00001 1/s) attributed to needle-punched carbon fibers in thickness direction. b - LD-2D C/SiC(2300 1/s) As proposed in Section 3. 2, the Weibull modulus of the 3D HD2Dc/Sic(0.00011/s) needle-punched C/sic composite is 8.19 while those of the LD and HD-2D C/SiC(850 1/5) HD 2D-C/SiC composites are 8.36 and 5.27 respectively. It is obvious 3 D C/SiC(0.00011/s) that the Weibull modulus of the 3D needle-punched C/Sic compos- 3D C/SiC(000 1/s) ite is comparable with that of Ld 2D-C/Sic composite and higher than that of HD 2D-C/SiC composite As a result, low dispersity is expected for the compression strength of the 3D needle-punched Table hear fracture angles of 2D-CSic composites and 3D needle-punched C/Sic composit Quasi-static loading Dynamic loading True strain 36°(=23001/s) 知应 55°(E=8501
10 Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 Fig. 7. SEM micrographs of the 3D needling-punched C/SiC composites ruptured surface under static and dynamic compression. Table 1 lists shear fracture angles of both kinds of 2D composite and 3D needle-punched C/SiC composite. It can be seen that the 3D composite shows larger shear fracture angle under quasi-static loading than that of LD 2D-C/SiC composite but smaller than that of HD 2D-C/SiC composite. As mentioned above, higher compression strength will lead to larger shear fracture angle. Thus, larger shear fracture angle also indicates excellent compression behavior of the 3D composite which is consistent with above conclusion derived directly from Fig. 8. Fig. 8. Comparison of the 3D needling-punched C/SiC composites with low density and high density 2D-C/SiC composites under static and dynamic compression. SEM images of the ruptured surface of both kinds of 2D-C/SiC composite loaded under quasi-static and dynamic loading conditions are shown in Fig. 9 respectively. For LD 2D-C/SiC composite, in Fig. 9, pull out fibers can be observed while bundles of fibers were cut off for HD 2D-C/SiC composite. The smoother fracture surface of HD composites under both quasi-static and dynamic compression indicates more small cracked fibers. Matrix fragments generated under dynamic compression for both LD and HD composites. While for 3D needle-punched C/SiC composite, the fracture surfaces are relative rough and more fibers were pulled out under both quasistatic and dynamic loading (see in Fig. 7). This phenomenon can be attributed to needle-punched carbon fibers in thickness direction. As proposed in Section 3.2, the Weibull modulus of the 3D needle-punched C/SiC composite is 8.19 while those of the LD and HD 2D-C/SiC composites are 8.36 and 5.27 respectively. It is obvious that the Weibull modulus of the 3D needle-punched C/SiC composite is comparable with that of LD 2D-C/SiC composite and higher than that of HD 2D-C/SiC composite. As a result, low dispersity is expected for the compression strength of the 3D needle-punched C/SiC composite. Table 1 Shear fracture angles of 2D-C/SiC composites and 3D needle-punched C/SiC composite. Material Shear fracture angles Quasi-static loading Dynamic loading LD-2D composite 30◦ (ε˙ = 10−4 l/s) 36◦ (ε˙ = 2300 l/s) HD-2D composite 50◦ (ε˙ = 10−4 l/s) 55◦ (ε˙ = 850 l/s) 3D composite 30◦ (ε˙ = 10−4 l/s), 45◦ (ε˙ = 10−2 l/s) –
Y. Li et al./ Materials Science and Engineering A 507(2009)6-12 装 (a)LD 2D-composite(=10-1/s) (E=2 (c)IID 2D-composite(E=10-1/ (d )ID2D-composite(E=850 1/s) Fig. 9. SEM micrographs of the 2D-C/Sic composites with different densification at quasi-static and dynamic loading. 4. Conclusions Education of China(No. 20070699044)and the 111 project(B07050) to the Northwestern Polytechnical University. The authors also In this paper, the uniaxial compressive behavior of 3D needle- thank Professor Laifei Cheng for providing the 3D needle-punched punched CSic composite at room temperature was investigated C/SiC composite. t strain rate ranging from 10-4 to 6.5 x 10 1/s using the elec- tronic universal testing machine and the split Hopkinson pressure references bar technique. Pseudoplasticity due to the fracture of Sic matrix is observed for specimen tested at all strain rates. Although the [11 LT Zhang. LE Cheng Y.D. Xu, Aeronautical Manufacturing Technology 1(2003 compression strength of the material increases with the strain rate, the strain rate sensitivity of the material is considered to be lov [21 M.S. Liu, YL Li, F. Xu, Z J. Xu, LF. Cheng, Materials Science and Engineering A 489(1-2)(2008)120-126 The compression strength of the 3D needle-punched C/Sic compos- [3] G.Y. Guan, G Q Jiao, Z.G. Zhang, Acta Material Composite Sinica 22(4)(2005) m is 8.19, which is comparable with that of the LD 2D-C/SiC com- 14 WG.Pan. GO liao, C.Y. Guan, Journal of the Chinese Ceramic Society 33(11) osites. The needle-punched fibers enhance the toughness of the [51 E.B. Rachid, B Stephane, C. Gerald, Composite Science and Technology 56(1996) 3D needle-punched C/SiC composite. The failure pattern of the 3D 1373-1382 needle-punched C/Sic composite also varies with strain rate. Shear 6 YH. Wan, Y D. Xu, W.G. Pan, Fiber Reinforced Plastics/composites 5(2005 failure and delamination play prominent roles in the fracture pi [7 M D Curry. ]. Kowal, J W. Sawyer, Proceedings of 1st IAF/ AlAA Space Transporta- ess under quasi-static loading whereas a split pattern features tion Symposium, Huntsville, Alabama, April 11-12, 2002, pp 1-29. the failure mode under dynamic loading. Rough fracture surface of [8 W.G. Pa G.Q. Jiao, G Y Guan, B. Wang, Journal Ceramic Society specimens tested is observed at the strain rates of 10-4 and 10-21/s 19) N. Ekabsons,)varna, Mechanics of Composite Ma 37(4)(2001) while relatively smooth fracture surface is observed for those tested at high strain rate. [101 Y Xu, L Zhang, L Cheng, Carbon 36(7-8)(1998)1051-1056 ee of e Acknowledgem olytechnical University, China, 2005. [131 P. Xiao, J.w. Xie, XXiong. Z.Q. Yan, Journal of Central South University (Science This research was supported by the National Natural Science [14)S W Fan, Y.D. Xu, LT Zhang, Material Science and Engineering A 467(1)(2007) Foundation of China(No. 90405016), Doctoral Fund of Ministry of 53-58
Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 11 Fig. 9. SEM micrographs of the 2D-C/SiC composites with different densification at quasi-static and dynamic loading. 4. Conclusions In this paper, the uniaxial compressive behavior of 3D needlepunched C/SiC composite at room temperature was investigated at strain rate ranging from 10−4 to 6.5 × 103 1/s using the electronic universal testing machine and the split Hopkinson pressure bar technique. Pseudoplasticity due to the fracture of SiC matrix is observed for specimen tested at all strain rates. Although the compression strength of the material increases with the strain rate, the strain rate sensitivity of the material is considered to be low. The compression strength of the 3D needle-punched C/SiC composite obeys the Weibull distribution. The calculated Weibull modulus m is 8.19, which is comparable with that of the LD 2D-C/SiC composites. The needle-punched fibers enhance the toughness of the 3D needle-punched C/SiC composite. The failure pattern of the 3D needle-punched C/SiC composite also varies with strain rate. Shear failure and delamination play prominent roles in the fracture process under quasi-static loading whereas a split pattern features the failure mode under dynamic loading. Rough fracture surface of specimens tested is observed at the strain rates of 10−4 and 10−2 1/s while relatively smooth fracture surface is observed for those tested at high strain rate. Acknowledgements This research was supported by the National Natural Science Foundation of China (No. 90405016), Doctoral Fund of Ministry of Education of China (No. 20070699044) and the 111 project (B07050) to the Northwestern Polytechnical University. The authors also thank Professor Laifei Cheng for providing the 3D needle-punched C/SiC composite. References [1] L.T. Zhang, L.F. Cheng, Y.D. Xu, Aeronautical Manufacturing Technology 1 (2003) 24–32. [2] M.S. Liu, Y.L. Li, F. Xu, Z.J. Xu, L.F. Cheng, Materials Science and Engineering A 489 (1–2) (2008) 120–126. [3] G.Y. Guan, G.Q. Jiao, Z.G. Zhang, Acta Material Composite Sinica 22 (4) (2005) 81–85. [4] W.G. Pan, G.Q. Jiao, G.Y. Guan, Journal of the Chinese Ceramic Society 33 (11) (2005) 1321–1325. [5] E.B. Rachid, B. Stephane, C. Gerald, Composite Science and Technology 56 (1996) 1373–1382. [6] Y.H. Wan, Y.D. Xu, W.G. Pan, Fiber Reinforced Plastics/Composites 5 (2005) 20–24. [7] M.D. Curry, J. Kowal, J.W. Sawyer, Proceedings of 1st IAF/AIAA Space Transportation Symposium, Huntsville, Alabama, April 11–12, 2002, pp. 1–29. [8] W.G. Pan, G.Q. Jiao, G.Y. Guan, B. Wang, Journal of the Chinese Ceramic Society 33 (2) (2005) 160–163. [9] J.N. Ekabsons, J. Varna, Mechanics of Composite Materials 37 (4) (2001) 287–298. [10] Y. Xu, L. Zhang, L. Cheng, Carbon 36 (7–8) (1998) 1051–1056. [11] Y. Xu, L. Zhang, L. Cheng, Journal of Aeronautical Materials 27 (1) (2007) 28–32. [12] Y. Wan, Preparation and mechanical properties for C/SiC composites and components, Dissertation for a Degree of Engineering Master, Northwestern Polytechnical University, China, 2005, pp. 28–30. [13] P. Xiao, J.W. Xie, X. Xiong, Z.Q. Yan, Journal of Central South University (Science and Technology) 38 (3) (2007) 381–385. [14] S.W. Fan, Y.D. Xu, L.T. Zhang, Material Science and Engineering A 467 (1) (2007) 53–58
Y Li et al/ Materials Science and Engineering A 507(2009)6-12 [15] M.S. Liu, Y L Li, L Tao, F Xu, Z. Xu, LF Cheng, Acta Material Composite Sinica [18]x Bi, Z. Li, P.H. Geubelle, J. Lambros. Mechanics of Materials 34(7)(2002) 24(5)(2007)90-96. [16] x. Xiong, B Y Huang, P. Xiao, Journal of Central South University(Science and [19] Q-L Yuan, YL Li, H ]. Li, S.P. Li, L]. Guo, Journal of Inorganic Materials 22(2) Technology)35(5)(2007)702-706. Beyerlein, L.S. Schadler, Composite Science and Technology 61 2001)2461-
12 Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 [15] M.S. Liu, Y.L. Li, L. Tao, F. Xu, Z.J. Xu, L.F. Cheng, Acta Material Composite Sinica 24 (5) (2007) 90–96. [16] X. Xiong, B.Y. Huang, P. Xiao, Journal of Central South University (Science and Technology) 35 (5) (2007) 702–706. [17] B.D. Garland, I.J. Beyerlein, L.S. Schadler, Composite Science and Technology 61 (2001) 2461–2480. [18] X. Bi, Z. Li, P.H. Geubelle, J. Lambros, Mechanics of Materials 34 (7) (2002) 433–446. [19] Q.L. Yuan, Y.L. Li, H.J. Li, S.P. Li, L.J. Guo, Journal of Inorganic Materials 22 (2) (2007) 311–314
