16 TH INTERNATIONA CONFERENCE ON COMPOSITE MATERIAS EVAUATION OF THERMA CONDUCTIVITY IN PITCH- BASED CARBON FIBER REINFORCED PASTICS Shinji Ogihara*, Makoto Yaaguchi**, Takahito Chiba**, Junichi Shiizu****, Yoji Okabe**** and Nobuo Takeda****, *Departent o Mechanical Engineering, Tokyo University o Science, Chiba, Japan **Graduate Student, Tokyo University o Science, Chiba, Japan ***Nippon Steel Materials Copany iited **** Departent o Aeronautics and Astronautics, The University o Tokyo Keywords: Theral conductivity, Theral resistance, CFRP, Unidirectional coposite Abstract Theral conductivities in longitudinal and transverse directions o a CFRP unidirectional coposite are evaluated experientally. aser lash ethod is eployed to easure theral conductivity. To discuss the experiental results, rules o ixture predictions and two-diensional steady-state and transient heat transer siulations are conducted. In addition, a heat sink is ade with the CFRP. The heat radiation perorance under natural convection (the theral resistance) is copared with heat sinks ade o aluinu with dierent surace treatent. Eect o heat radiation is discussed both experientally and analytically. Three-diensional steady-state heat transer siulations are perored to copare with the experient result. 1 Introduction Carbon iber reinorced plastics (CFRP) are used in various ields, especially in aerospace engineering, due to their high speciic odulus and strength. Because pitch-based carbon ibers have high theral conductivity, their coposites are expected to be used as heat control aterials [1]. Considering a carbon iber unidirectional coposite, it ay have anisotropy in theral conductivity, that is, it is high in iber direction whereas low in the direction perpendicular to the ibers. Moreover, it is expected that we can develop a aterial with higher theral conductivity. In the present study, theral conductivities in pitch-based carbon iber (YS9A) reinorced epoxy unidirectional coposites with dierent iber volue ractions are experientally evaluated by using the laser lash ethod. To discuss the experiental results, rules o ixture prediction and two-diensional steady-state and transient heat transer siulations are conducted. In addition, a heat sink is ade with the CFRP. The heat radiation perorance under natural convection (the theral resistance) is copared with heat sinks ade o aluinu with dierent surace treatent, that is, with and without aluite treatent. To discuss the experiental results, three-diensional steady-state heat transer siulations are conducted. Experient.1 Materials A pitch-based carbon iber, YS9A (Nippon Graphite Fiber td.), is used. An epoxy resin is used as the atrix aterial. Unidirectional coposites with dierent iber volue ractions (55%, 4%, % and % (neat resin)) are abricated or the theral conductivity easureent by the laser lash ethod. For theral resistance easureent, CFRP heat sink o 55% volue raction is used. Both speciens whose iber directions are parallel and perpendicular to the heater plane are used. Properties o iber and atrix in the present study are listed in Table 1. Table 1 Properties o iber and atrix Theral Speciic heat Conductivity capacity (W/K) (J/gK) Density (g/c3) Fiber 5.837 1.75 Epoxy.6 1.1 1.3 1
SHINJI OGIHARA, Makoto Yaaguchi, Takahito Chiba, Junichi Shiizu Yoji Okabe and Nobuo Takeda. Measureent o theral conductivity by the laser lash ethod Theral conductivities in the unidirectional coposites are easured by using the laser lash ethod. In the ethod, a laser bea is lashed on the top surace o a cylindrical specien (Fig.1). The teperature change at the botto surace o the specien is onitored. Based on the easured teperature history, the haltie t 1/ (tie or the teperature rise up to the hal o the axiu teperature) is deterined, which in turn used to calculate specien theral diusivity, α, by using the ollowing equation. α =.1388 (1) 1/ t where is specien length. The diaeter and the length o the speciens are 1 and 3, respectively. Based on the theral diusivity, theral conductivity can be calculated by using ollowing equation. λ = αcρ () where C is speciic heat capacity and ρ is density. Specien aser pulse Inrared sensing device α =.1388 t α:theral diusivity : Specien length t / :Haltie T ax T ax Fig.1 Principle o the aser Flash Method.3 Heat sinks A heat sink is ade with a CFRP prepreg ade o a carbon iber, YS9A (Nippon Graphite Fiber td.), and Epoxy resin. Prepreg sheets are stacked such that the iber direction is parallel to the in height. The heat sink is ade with integrated olding. The size o the heat sink is shown in Fig.. Coercially available heat sinks o the sae size ade o aluinu alloy (Ryosan Inc.) are also used. Both aluinu heat sinks with and without aluite treatent are used. Properties o each heat sink are shown in Table. 1/ T t 1/ t Fig. Size o heat sink Table Properties o heat sinks Al Al(A663-T5)- (A663-T5) aluite treatent CFRP (YS9A) Density (g/c 3 ).7.7 1.75 Theral conductivity (W/K) 9 9 7 Mass (g) 44.6 44.8 3.8.4 Measureent o theral resistance Heat radiation perorance was evaluated by easuring theral resistance under the condition o natural convection. The theral resistance R is deined by ( T1 T ) R( / W ) = (3) Q where T 1 is the highest teperature at the botto surace o the heat sink, T is the abient teperature and Q is the heat lux which into the heat sink. The experiental setup used in the present study is shown in Fig.3. A rubber heater was used as a heat source. Heat lux sensors were used to easure the heat lux which lows in to the heat sink, Q. therocouples o type T were used to the teperatures T 1 and T. The easureents were conducted until the syste reaches the steady state. Therocouple logger Notebook coputer DC power source Heat sink Radiation sheet Styrooa Copper Heater Thero-couple (T-type) Heat lux sensor Fig.3 Experiental setup or theral resistance easureent A V
EVAUATION OF THERMA CONDUCTIVITY IN PITCH-BASED CARBON FIBER REINFORCED PASTICS 3 Analysis 3.1 Rules o ixture predictions Theral conductivity o a unidirectional coposite in the iber direction, λ, can be predicted by the rules o ixture as λ λ V + λ V = (4) conducted ro the next expression by using the value o this heat lux. q λ = (6) T / d Where ΔT is the teperature dierence, that is 3-1=, and d is the odel thickness. λ is theral conductivity, V is volue raction and subscripts and denote iber and atrix, respectively. Theral conductivity o a transverse coposite in the iber direction, λ T, can be predicted by the rules o ixture as 3.5μ 1 λ T V = λ V + λ (5) Fiber direction Analytical odels o the rules o ixture are shown in Fig.4. 7μ λ λ Transverse direction iber atrix V 1-V Fig.5 Models o two-diensional steady-state heat transer siulation (FEM) λ λ 1-V V :iber :atrix Fig.4 Models o the rules o ixture prediction 3. Calculation o theral conductivity by twodiensional steady-state heat transer siulation Coposite theral conductivity is calculated by using the two-diensional steady-state heat transer siulation. Finite eleent ethod is applied. Analytical odels are shown in Fig.5. The top edge o the odel is ixed at 3 and the botto edge is ixed at 1, and the right and let edges are therally isolated. Heat lux q was calculated by suing the node heat lux at the botto surace []. The calculation o theral conductivity λ was 3.3 Calculation o theral conductivity by twodiensional transient heat transer siulation Coposite eective theral conductivity is also evaluated by using a two-diensional transient heat transer siulation. In the analysis, the laser lash ethod is siulated. Analytical odels are shown in Fig.6. Finite eleent ethod is applied. To siulate laser lash ethod, the top layer o 3μ thick is set 1 degrees hotter as the initial condition, and the right and let edge are therally isolated. We onitor the teperature rise at the botto edge o the odel which enables us to deterine the haltie t 1/. Based on the haltie calculated, we can deterine the coposite eective theral diusivity. 3
SHINJI OGIHARA, Makoto Yaaguchi, Takahito Chiba, Junichi Shiizu Yoji Okabe and Nobuo Takeda 3.5μ 3.5μ Fiber direction Fig.6 Models o Two-diensional transient heat transer siulation (FEM) To calculate the theral conductivity, coposite eective speciic heat capacity C c and density ρ c are deterined by using the ollowing rules o ixture as C ρ V ρ V C = C + C (7) ρv + ρv ρv + ρv ρ ρ V + ρ V c = (8) 7μ Transverse direction where λ is theral conductivity, V is volue raction and subscripts and denote iber and atrix, respectively. 3.4 Calculation o theral resistance by threediensional steady-state thero-luid analysis The heat radiation perorances o each heat sink are calculated by steady-state thero-luid analysis. To calculate the theral resistance, coposite eective speciic heat capacity C c and density ρ c are deterined by Eq. 7 and Eq. 8. Analytical odels are shown in Fig.7. To siulate the experiental setup, all the coponents, the heater, the heat radiation sheets, the copper and the heat sink, and the styrene oa are odeled. Only the hal part o the experiental setup is odeled due to syetry. iber atrix Fig.7 Model o three-diensional steady-state thero-luid analysis As the initial condition, the odel is set to be 4. The eect o radiation is considered. The eissivities o CFRP, Aluinu alloy with and without aluite treatent are.94,.8, and.13, respectively. The gravitational acceleration was set to be 9.8 /s. The theral resistance is calculated ro Eq. 3. 4 Results and discussion 4.1 aser lash ethod and analytical result Table 3 and Fig.8 shows the experiental results o the unidirectional coposite theral conductivity in the iber direction and results o the predictions o the analysis as a unction o iber volue raction. In the case o iber direction, the theral conductivity increases linearly with increasing iber volue raction. Experiental results o theral conductivity o CFRP agree with the rules o ixture predictions and the predictions o both two-diensional steady-state and transient heat transer analysis. Table 3 Results o theral conductivity in iber direction easureents and analytical predictions Volue raction (%) 55 4 Experient (W/K) 7.44 19.1 91.63 Rules o ixture prediction (W/K) 75.1.16 1.1 Steady-state siulation (W/K) 75.1.16 1.1 Transient siulation (W/K) 71.55 197.44 97.47 4
EVAUATION OF THERMA CONDUCTIVITY IN PITCH-BASED CARBON FIBER REINFORCED PASTICS Theral conductivity (W/K) 4 3 1 experient (YS9A) rules o ixture prediction (YS9A) steady-state siulation (YA9A) transient siulation (YS9A) 1 3 4 5 6 Fiver volue raction (%) Theral conductivity (W/K) 1.5 1.5 experient (YS9A) rules o iwture prediction (YS9A) steady-state siulation (YS9A) transient siulation (YS9A) 1 3 4 5 6 Fiver volue raction (%) Fig.8 Theral conductivity o CFRP in iber direction as a unction o iber volue raction or CFRP using YS9A.Coparison with the rules o ixture predictions and heat transer siulations (FEM) Table 4 and Fig.9 shows the experiental results o the unidirectional coposite theral conductivity in the transverse direction and results o the predictions o the analysis as a unction o iber volue raction. In the case o transverse direction, the increase in the theral conductivity due to iber volue raction is very sall. The rules o ixture gave lower prediction than the experiental results but the FEM predictions show a air agreeent with the experiental results. Table 4 Results o theral conductivity in transverse direction easureents and analytical predictions Volue raction (%) 55 4 Experient (W/K) 1.17.73.36 Rules o ixture prediction (W/K).58.43.3 Steady-state siulation (W/K).81.59.38 Transient siulation (W/K).8.59.38 Fig.9 Theral conductivity o CFRP in transverse direction as a unction o iber volue raction or CFRP using YS9A.Coparison with the rules o ixture predictions and heat transer siulation (FEM) The anisotropy o the theral conductivity in pitch-based carbon iber reinorced epoxy unidirectional coposites is conired. It is understood that the laser lash ethod is eective to the easureent o the theral conductivity in the direction o the iber. It is also understood the theral conductivity can be predicted by the rules o ixtures, and two-diensional transient heat transer siulation. 4. Experiental and analytical results o theral resistance Fig.1 shows the experiental results o teperatures o T 1. And Fig.11 shows the experiental results o the theral resistance under natural convection using each heat sink and results o the predictions o steady-state thero-luid analysis. As or the CFRP heat sink, the heat radiation perorance is higher than the aluinu heat sink without aluite treatent, and it can be understood that it is the sae heat radiation perorance as the aluinu heat sink with aluite treatent under the natural convection. Moreover, experiental and analytical results show a good agreeent. 5
SHINJI OGIHARA, Makoto Yaaguchi, Takahito Chiba, Junichi Shiizu Yoji Okabe and Nobuo Takeda Teperature ( ) Theral resistance ( /W) 7 6 5 4 3 Al Al-aluite tretent CFRP 1 5 1 15 5 3 Tie (in.) 3 5 15 1 5 Fig.1 Teperature o T 1 Experient Analysis The heat radiation perorance under natural convection is copared with heat sinks ade o CFRP and aluinu alloy with dierent surace treatent, that is, with and without aluite treatent. To discuss the experiental results, threediensional steady-state heat transer siulations are conducted. As a result, the heat radiation perorance is higher than the aluinu alloy heat sink without Aluite treatent, and it is understood that heat sink ade o CFRP is the sae heat radiation perorance as the heat sink ade o aluinu alloy with aluite treatent under the natural convection. Moreover, experiental and analytical results show a good agreeent. Reerences [1] J.Zier, Extended Abstr Progra Bienn Con Carbon.,pp.39-391, 1991. [] Yokota H., Ohta H. and Shibata H. Coputer Siulation or Estiating the Eective Theral Conductivity o Coposite Materials. Japan Journal o Therophysical Properties, Vol.13, pp.4-45, 1999. Al Al-Aluite YS9A Fig.11 Experiental and analytical results o theral resistance 5 Conclusion Unidirectional coposites consisting o a pitchbased carbon iber and epoxy atrix is abricated and theral conductivity in the iber direction and transverse direction with various iber volue ractions is evaluated experientally by using the laser lash ethod. To discuss the experiental results, the rules o ixture prediction and twodiensional steady-state and transient heat transer siulations are conducted. As a result, the experient result o unidirectional coposites is alost corresponding to results o each analysis. Fro this, it is understood the theral conductivity can be predicted by the rules o ixture, and twodiensional transient heat transer siulation. Moreover, the anisotropy o the theral conductivity o unidirectional coposites can be conired. 6