45
46
permeability was proposed. For a more detailed analysis, it is necessary to obtain information on void migrations, such as the void distribution and void displacement speed during the resin flow.
Experimental studies were conducted with unidirectional glass fiber performs to analyze the hysteresis behaviors in a saturated permeability condition depending on the flow rate and viscosity during the LCM manufacturing process. In a 30cs silicone fluid case, the saturated permeability increases as the flow rate increases. In contrast, these values change slightly when decreasing the flow rate. In the 100cs and 350cs silicone fluid cases, the saturated permeability increases when the flow rate increases, like the 30cs case, but it decreases when the flow rate decreases. The decreasing value of the permeability is lower than that in the increasing cases, and this is observed more clearly in the 350cs case.
Because we can observe the void formation and migration in cases involving an increase in the flow rate, voids may affect the saturated permeability change in the increasing cases. Because there was no void migration in the deceasing cases, the saturated permeability change in the decreasing case can be explained by tow deformation.
Dependence of the saturated permeability on the flow rate is affected by the combined effect of voids and tow deformations. Separate experiments and mechanisms which can explain the effects of each factor can be expected to analyze the hysteresis of saturated
47 permeability.
Lastly, the cross-sections of tows injected at different flow rate were investigated.
Horizontal and vertical length of each tow was measured at different locations from the inlet. A higher flow rate results in a longer horizontal and vertical length, which may have been caused by a tow void.
48
References
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49
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53
Figures
Figure 1. Overall approach of the study
54
Figure 2. Viscosity of the engine oil
55
Figure 3. Double-scale glass fiber mat
56
Figure 4. Typical raw pressure data of the pressure measurement
57
0.0 0.1 0.2 0.3 0.4 0.5
0 5000 10000
Q=50 mm3/s
Pressure [Pa]
x (m)
t2 t3 t4 t5 t6 t7
(a) Pressure profiles of 50 mm
3/s
58
0.0 0.1 0.2 0.3 0.4 0.5
0 8000 16000
Q=100 mm3/s
Pressure [Pa]
x (m)
t2 t3 t4 t5 t6 t7
(b) Pressure profiles of 100 mm
3/s
59
0.1 0.2 0.3 0.4 0.5
0 10000 20000 30000
Q=200 mm3/s
Pressure [Pa]
X [m]
t2 t3 t4 t5 t6 t7
(c) Pressure profiles of 200 mm
3/s
60
0.1 0.2 0.3 0.4 0.5
0 30000 60000
Q=400 mm3/s
Pressure [Pa]
X [m]
t2 t3 t4 t5 t6 t7
(d) Pressure profiles of 400 mm
3/s
Figure 5. Pressure profiles of the 50, 100, 200, and 400 mm
3/s
61
0.1 0.2 0.3 0.4 0.5
0.0 0.5 1.0
Normalized Pressure
X [m]
Q=50 Q=100 Q=200 Q=400
(a) Normalized pressure distribution for different flow rates
62
(b) Pressure profile and pressure gradient for saturated and unsaturated flows
Figure 6. Pressure profiles in saturated and unsaturated flows
63
(a) Void content and flexural strength
64
(b) Void content and inter laminar shear strength
Figure 7. Void content and mechanical properties depending on the flow rate
65 (a)
(b)
66 (c)
Figure 8. Flow characteristics of saturated and unsaturated flows
67
(a) Saturated permeability measurement
68
(b) Unsaturated permeability measurement
Figure 9. Permeability measurement methods
69
Figure 10. Pressure profile at different time instants for the saturated flow
(Q
in=100mm
3/s)
70
0.0 0.1 0.2 0.3 0.4 0.5
0 10000 20000 30000
Q=200 mm3/s t2 (exp) t3 (exp) t4 (exp) t5 (exp) t6 (exp) t7 (exp) t2 (model) t3 (model) t4 (model) t5 (model) t6 (model) t7 (model)
Pressure [Pa]
x [m]
(a) Pressure profile for the unsaturated flow with the low flow rate
(Q
in=200mm
3/s)
71
0.0 0.1 0.2 0.3 0.4 0.5
0 30000 60000
90000 Q=400 mm3/s t2 (exp)
t3 (exp) t4 (exp) t5 (exp) t6 (exp) t7 (exp) t2 (model) t3 (model) t4 (model) t5 (model) t6 (model) t7 (model)
Pressure [Pa]
x [m]
(b) Pressure profile for the unsaturated flow with the high flow rate
(Q
in=400mm
3/s)
72
0.1 0.2 0.3 0.4 0.5
0 50000 100000
Pressure (Pa)
x (m)
Va=1% model Va=2% model Va=3% model experiment
(c) Parametric study with different void content values (Q
in=400mm
3/s)
Figure 11. Pressure profile for unsaturated flow
73
Figure 12 Photos at different time instants showing the migration of an air void during the mold filling process
Some voids are stationary because they are blocked between the tows.
Some voids move along the resin flow and their speed is greater than
74
Figure 13. Experimental data of pressure profile for the unsaturated flow with inter-bundle voids (Q
in=50 mm
3/s)
0 2000 4000 6000 8000 10000 12000
0 0.1 0.2 0.3 0.4 0.5
t2 (exp) t3 (exp) t4 (exp) t5 (exp) t6 (exp) t7 (exp) Zone I: Dominant liquid
flow (small void fraction)~(dP/dx)
sat
Zone II: Sudden pressure drop due to high air flow rate (void migration)
Zone III: Decreased negative pressure gradient due to high void fraction (void accumulation at the flow front)
75
-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6
0 10 20
Qg [mm3 /s]
x [mm]
t2 t3 t4 t5 t6 t7 Void flow rate
(a) Estimated void flow rate (Q
in=50 mm
3/s)
76
0.1 0.2 0.3 0.4 0.5
0 6000 12000
Pressure [Pa]
x [m]
t2 (exp) t3 (exp) t4 (exp) t5 (exp) t6 (exp) t7 (exp) t2 (model) t3 (model) t4 (model) t5 (model) t6 (model) t7 (model) Q=50mm3/s (with void)
(b) Comparison between the model and experimental result (Q
in=50 mm
3/s)
Figure 14. Modeling of porous media flow with channel void
77
Figure 15. Ratio of unsaturated permeability to saturated permeability for constant flow rate injection
0 0.2 0.4 0.6 0.8 1 1.2
0 100 200 300 400 500
t7 (exp)
t7 (model)
78
Figure 16. Ratio of unsaturated permeability to saturated permeability for constant inlet pressure injection
Void content ø
T,a=0,
Mass sink q
T=0
79
0 3000 6000 9000
0 30000 60000 90000
pressure (Pa)
time (s)
sensor 1 sensor 2 sensor 3 sensor 4 sensor 5 sensor 6 sensor 7 sensor 8
Figure 17. Raw data of the continuous saturated flow pressure measurement
80
0 700 1400
0.0032 0.0034 0.0036 0.0038
permeability (mm^2)
flow rate (mm^3/s)
increasing Q decreasing Q
(a) Permeability behavior of 30cs silicone fluid depending on flow rate
81
0 600 1200
0.0028 0.0029 0.0030 0.0031
permeability (mm^2)
flow rate (mm^3/s)
increasing Q decreasing Q
(b) Permeability behavior of 100cs silicone fluid depending on flow rate
82
0 300 600 900
0.0029 0.0030 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036
permeability (mm^2)
flow rate (mm^3/s)
increasing Q decreasing Q
(c) Permeability behavior of 350cs silicone fluid depending on flow rate
Figure 18. Permeability behavior of silicone fluids depending on flow rate
83
Figure 19. Void in the saturated flow and void migration whenincreasing the
flow rate
84
Figure 20. Locations of the specimens for observation of tow deformation
85
Figure 21. Horizontal and vertical length of tow deformation
86
A B C D
1.45 1.50 1.55 1.60 1.65
Horizontal length [mm]
Location
200mm^3/s 50mm^3/s
(a) Horizontal length of tows
87
A B C D
0.35 0.42 0.49 0.56 0.63
Vertical length [mm])
Location
200mm^3/s 50mm^3/s
(b) Vertical length of tows
Figure 22. Horizontal and vertical length of tow depending on location and flow
rate
88
Tables
Table 1. Properties of epoxy resin
Properties KFR-130/KFH-140 Mixing ratio (resin :hardener, wt%) 100 :30
Density (g/cm3, ISO 1657) 1.0~1.2 Viscosity (cps, ISO 2555) 250~350 Curing temparature (℃) 75
Pot life (min, ISO 9514) 200
Table 2. Properties of silicone oil
Model No. Specificgravity 25℃
Viscosity 25℃ (Pa s)
Surface tension (mN/m)
KF-96-30cs 0.955 0.02865 20.7
KF-96-100cs 0.965 0.0965 20.9
KF-96-350cs 0.97 0.3395 21.1
Table 3. Properties of fiber reinforcement and injection liquid
Fabric microstructure properties Liquid properties Tow length, a
T 1.6 mm Viscosity, 0.20 Pas
Tow height, bT 0.5 mm Surface tension, 0.03 N/m
Tow volume fraction, VT 0.6429 Contact angle, 30 Fiber volume fraction of tow, V
f,T 0.6222 Fiber volume fraction of fabric, V
f 0.4
89
액상성형공정의 이중구조를 가지는 다공성 매질에서의 불포화 유동양상
서울대학교 대학원 기계항공공학부 김 성 하
요약(국문초록)
액상성형 공정은 경제적이면서도 다양한 형상의 복합재료 제품을 제작할 수 있는 공정이다. 액상성형 공정을 이용하여 우수한 기계적 물성을 가지고 있 는 복합재료를 제작하기 위해서는 수지이송성형과 같은 공정을 이용하여 연 속 장섬유 형태의 프리폼을 강화재로서 사용하는 것이 필요하다. 금형 안의 프리폼에 수지를 주입하는 과정은 다공성 매질을 흘러가는 유동으로 볼 수 있고, 대부분의 프리폼은 조밀한 부분과 그렇지 않은 부분의 이중구조를 가 지는 다공성 매질 형태로 되어 있다. 이중구조를 가지는 다공성 매질에서는 유동선단에서 수지의 유속의 차이로 인하여 기공이 형성되고, 이렇게 생성 된 기공은 전체적인 유동에 영향을 주게 된다. 다공성 매질을 흐르는 유동