ESTIMATION OF WEATHERABILITY FLEXURAL PROPERTIES FOR CFRP SUBJECTED - PDF document

18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS ESTIMATION OF WEATHERABILITY FLEXURAL PROPERTIES FOR CFRP SUBJECTED TO LONG-TERM OUTDOOR EXPOSURE Akira Kudo 1 and Goichi Ben 2* 1 Department of Aerospace Engineering, National Defense Academy, Japan; 2 Department of Mechanical Engineering, College of Industrial Technology, Nihon University, Japan * Corresponding author ( ben.goichi@cit.nihon-u.ac.jp ) Keywords : Weatherability, Flexural strength, CFRP, Outdoor exposure, Accelerated exposure can be predicted, the durability and reliability of Abstract CFRP can be improved. It was known in the past The present paper discusses the degradation papers [1] that the multiple effects of ultraviolet mechanism for weatherability flexural properties of radiation from the solar light, moisture absorption CFRP subjected to outdoor and accelerated and hydrochloric acid absorption decreased the exposures. One of the specimens was made of epoxy strength of GFRP subjected to the outdoor exposure. resin and unidirectional carbon fiber prepregs Specifically, the standing out of fibers owing to the having the fiber orientation angles of 0 or 90 degree reduction of surface resin was reported in GFRP [2] and another specimen was made of the same epoxy and in CFRP [3], [4]. According to the increase of resin only as the matrix of the prepregs. In order to the outdoor exposure period, this phenomenon was clarify the effects of exposure period on the often observed and it seemed to be a cause of the variations of flexural strengths and moduli, matrix strength degradation in both FRP’s. On the other volume fractions, thickness and absorption rate of hand, the strength in the fiber direction in CFRP infrared rays, the complex accelerated exposure test mainly depended on the fiber strength and the fiber was conducted to continue for up 100 cycles and a volume fraction, and it seemed to exhibit no effect direct outdoor exposure has been also conducted to of outdoor exposure. However, it should be made continue for 156 months. It was shown that both the clear whether the degradation of epoxy resin caused weatherability flexural strengths had been calculated by outdoor exposure had an effect on the strength of by results of epoxy resin and thickness change of unidirectional CFRP or not. Since the outdoor CFRP during the exposures. The experimental values exposure test needs long periods to evaluate test of flexural strength could be estimated on the data of [5,6]. outdoor exposure until the 36 months and on the data Aiming at the effects of ultraviolet radiation from of accelerated exposure until the 16 cycles. solar light, moisture absorption and hydrochloric Furthermore, the correlation of the acceleration acid absorption on the degradation of weatherability exposure test to the outdoor ones was demonstrated. strength of CFRP, this paper presents the flexural properties of CFRP subjected to outdoor and accelerated exposure. We used two classes of 1 Introduction specimens. The first class of specimens is two Carbon fiber reinforced plastics (CFRP) are unidirectional CFRP laminates having different fiber utilized in various structures because they have such orientation angles 0 or 90 degree, respectively. The as specific strength, specific rigidity and corrosion second class of specimens is made solely of epoxy resistance. In a wider range of structural applications resin identical in chemical composition to the matrix of CFRP, the materials exposed to complex of the above CFRP laminates. In order to clarify the environmental effects and these effects cause a effects of exposure period on the variation of degradation of CFRP. If weatherability properties flexural strength and modulus, matrix volume 1

fraction, thickness and absorption rate of infrared Flexural strength 6 ray, the complex accelerated exposure test was conducted to continue for up 100 cycles and a direct outdoor exposure has been also conducted to continue for 156 months. It was shown that both the 10 70 weatherability flexural strengths have been calculated by results of epoxy resin and thickness change of CFRP during the exposures. The experimental values 138 6 of flexural strength could be estimated on the data of 6 150 outdoor exposure until the 36 months and on the data of accelerated exposure until the 16 cycles. (unit: mm) Furthermore, the correlation of the acceleration exposure test to the outdoor ones was demonstrated. Fig.1 Test plate and flexural specimens 2 Experimental methods Table 2 Conditions of accelerated exposure test 2.1 Specimens of a cycle Table 1 showed the composition and dimension of 63 ± 3 Black panel temperature [ ℃ ] CFRP and epoxy resin plates for the both of Ultraviolet rays period [h] 100 Sunshine exposure tests. After finishing the designated Weather 15 Water spray period [h] exposure period, four sides of the test plates were Test 100 Test period [h] cut off 6 mm from their edges to avoid the 5 Accumulative dose [MJ/m 2 ] 28 specimens as shown in Figure 1. By using these 5 5±1 specimens, the experimental values of flexural Salt concentration [%] 35 ± 2 strength and modulus, thickness, matrix volume Temperature [ ℃ ] Salt Spray fraction and absorption rate of infrared rays were Test 5.6 ～ 6.0 pH-value obtained for the designated periods including the 24 Test period [h] beginning of both of the exposures. Hereafter, the 23 ± 2 Temperature [ ℃ ] specimens are referred as CF0, CF90 and EP, Standard 50 ± 5 Humidity [%] respectively, for shortness. Condition Test period [h] 44 2.2 Exposure test In order to closely simulate the outdoor exposure environment, the accelerated exposure test was executed by the following three stages, namely, a sunshine weather test, a salt spray test and holding at Table 1 Three kinds of specimens Epoxy CF0 CF90 EP CFRP Unidirectional carbon fiber － Reinforcement PAN type [ 0 ] 8 [ 90 ] 8 Matrix Epoxy of bisphenol A type Fig.2 Outdoor exposure in Japan Weathering Test 150 × 70 × 1.0 150 × 70 × 2.0 Size (mm) Center at Choshi-city 2

room temperature. There were conducted to the bending specimen was cut into small pieces condition of accelerated exposure test as shown for measuring the matrix volume fraction. By in Table 2. The total of 168 hours in the three using a method of FTIR, the outer (surface) and stages was determined to be one cycle and the inner layer of the matrix in CFRP was analyzed longest exposure period was 100 cycles. As for and the deterioration degree of the resin was the outdoor exposure test, plates were installed distinguished measuring to the methylene on the weathering rack that was located at an radical of absorption rate of infrared rays area near sea in Choshi City and was shown in subjected to the exposure. Furthermore, it was Figure 2. This exposure test had continued since thought that this variation might explain the February 1996 to 2009. The plates were relation of the flexural strength. sampled at every 6 months from start of experiment to 5 years and every 12 months from 3 Experimental results 6 years to 13 years, respectively. 3.1 Results of CFRP 2.3 Evaluative procedures S  ,0 (  =0,90) was the average values of flexural First, thickness of five specimens expired the strength for the initial period of CF0 and CF90 for designated exposure period was measured at three outdoor exposure test. (S  ,i /S  ,0 ) were the ratios of positions of each specimen and their average values exposure period and they were shown for the were to be used in the following discussion. Next, outdoor exposure month period (X m ) in Figure 3 (a). these specimens were tested by a four point bending In this figure, the flexural strength ratio of the CF0 test in order to get the flexural strengths and specimens decreased slightly and its value was modulus for the designated exposure period. Then, 1.1 1.1 Flexural modulus ratio E ,i /E ,0 ,i / S ,0 CF0 : S 0,0 =2174 MPa  CF0 : E 0,0 =160 GPa  CF90 : S 90,0 =104 MPa CF90 : E 90,0 =8.30 GPa CF0 Flexural strength ratio S 1 1 CF0 CF90 0.9 0.9 CF90 0.8 0.8 0 24 48 72 96 120 144 168 0 24 48 72 96 120 144 168 Outdoor exposure periods X m (month) Outdoor exposure periods X m (month) (a)Outdoor exposure (a) Outdoor exposure 1.1 1.1 Flexural modulus ratio E ,i /E ,0 ,i / S ,0 CF0 : S 0,0 =2174 MPa  CF0 : E 0,0 =160 GPa  CF90 : E 90,0 =8.30 GPa CF90 : S 90,0 =104 MPa Flexural strength ratio S 1 1 CF0 CF0 0.9 0.9 CF90 CF90 0.8 0.8 0 20 40 60 80 100 0 20 40 60 80 100 Accelerated exposure periods X c (cycle) Accelerated exposure periods X c (cycle) (b) Accelerated exposure (b) Accelerated exposure Fig.4 Reults of flexural modulus ratios under outdoor Fig.3 Reults of flexural strength ratios under outdoor and accelerated expusure for CF0 and 90 and accelerated expusure for CF0 and 90 3