
Fig. 1.
Composite analysis scales

Fig.2.
Construction of composite pressure vessel type IV
Tab. 1.
Mechanical properties of carbon fibre and resin epoxy
| Carbon fiber T700 (9) | Epoxy resin (9) | ||
|---|---|---|---|
| Properties | Values | Properties | Values |
| Ex[GPa] | 230 | Tensile modulus Em[GPa] | >3,2 |
| Ey, Ez[GPa] | 28 | ||
| Gxy, Gxz[GPa] | 50 | Shear modulus Gm[GPa] | 1,17 |
| Gyz[GPa] | 10 | ||
| vxy, vxz | 0,23 | Poisson’s ratio vm | 0,35 |
| vyz | 0,3 | ||

Fig. 3.
Scan of the actual fibre structure: a) multifiber view, b) single fibre zoom

Fig. 4.
a) RVE with circular fibre: b) RVE with elliptical fibre

Fig. 5.
RVE with actual fibre: a) geometry, b) mesh

Fig. 6.
Numbering of RVE vertices

Fig. 7.
Displacement distributions of RVE: a) tensile in X-direction, b) tensile in Y-direction, c) tensile in Z-direction

Fig. 8.
Displacement distributions of RVE: a) shear in XY-plane, b) shear in XZ-plane, c) shear in YZ-plane

Fig. 9.
Equivalent stress distributions of RVE: a) tensile X-direction, b) tensile Y-direction, c) tensile Z-direction

Fig. 10.
Equivalent stress distributions of RVE: a) shear in XY-plane, b) shear in XZ-plane, c) shear in YZ-plane

Fig.11.
Model displacements to calculate Young's modulus, Poisson's ratio and shear modulus
Tab. 6.
Mechanical properties of carbon epoxy composite
| Properties | Material Designer (Circular fibre) | PBC equations in Mechanical | Difference between actual fibre and circular fibre [%] | ||
|---|---|---|---|---|---|
| Circular fibre | Eliptical fibre | Actual fibre | |||
| E1[GPa] | 139,345 | 139,012 | 138,972 | 142,502 | 2,51 |
| E2[GPa] | 8,242 | 8,195 | 8,291 | 8,612 | 5,09 |
| E3[GPa] | 8,242 | 8,195 | 8,288 | 8,620 | 5,19 |
| G12[GPa] | 4,657 | 4,629 | 4,900 | 5,122 | 10,65 |
| G23[GPa] | 3,943 | 3,936 | 4,454 | 4,153 | 5,51 |
| G13[GPa] | 4,657 | 4,629 | 4,899 | 5,143 | 11,10 |
| v12 | 0,271 | 0,271 | 0,272 | 0,270 | 0,37 |
| v23 | 0,501 | 0,494 | 0,468 | 0,466 | 6,99 |
| v13 | 0,271 | 0,271 | 0,272 | 0,270 | 0,37 |

Fig. 12.
Solid model of composite pressure vessel
Tab. 7.
| Properties | 6061-T6 | PA6 |
|---|---|---|
| Tensile Modulus [GPa] | 68,9 | 1,4 |
| Poisson's ratio | 0,33 | 0,35 |
| Yield Strength [MPa] | 276 | 76 |
| Tensile Strength [MPa] | 310 | - |
Tab. 8.
Mechanical strength properties of carbon epoxy composite
| Properties | Values [MPa] |
|---|---|
| Longitudinal Tensile Strength Xt | 2860 |
| Transverse Tensile Strength Yt,Zt | 81 |
| Longitudinal Compressive Strength Xc | -1450 |
| Transverse Compressive Strength Yc,Zc | -268,5 |
| Shear Strength in fiber plane S12, S13 | 136 |
| Sherar strength out of fiber plane S23 | 87 |
Tab. 9.
Winding angles correspond to variable polar radius for helical layers
| Winding angleα [°] | Total number of layers | Radius of polar openings r0 [mm] |
|---|---|---|
| 10 | 10 | 30 |
| 14,5 | 4 | 42 |
| 19 | 4 | 54 |
| 23 | 4 | 66 |
| 27,5 | 4 | 78 |
| 31,5 | 2 | 90 |
| 36,5 | 2 | 102 |

Fig.13.
Composite thickness distribution at dome section for first 8 helical layers
Tab. 10.
Layup configuration
| Number of layers | Angle [°] | Quantity |
|---|---|---|
| 2 | 10 | x2 |
| 3 | 90 | |
| 1 | 14,5 | |
| 1 | 19 | |
| 3 | 90 | |
| 1 | 23 | |
| 1 | 27,5 | |
| 3 | 90 | |
| 1 | 31,5 | |
| 1 | 36,5 | |
| 3 | 90 | |
| 2 | 10 | x2 |
| 3 | 90 | |
| 1 | 14,5 | |
| 1 | 19 | |
| 3 | 90 | |
| 1 | 23 | |
| 1 | 27,5 | |
| 3 | 90 | |
| 2 | 10 | x1 |

Fig. 14.
Finite element mesh on 3D tank model

Fig. 15.
Thickness distribution of composite at dome part in 3D model: a) Wang method, b) numerical model

Fig. 16.
Quality of finite elements mesh graph: a) aspect ratio, b) element quality, c) skewness d) Jacobian ratio

Fig. 17.
Boundary conditions

Fig. 18.
Distribution of resultant: a) displacement b) strain

Fig.19.
Distribution of Huber von-Mises stress in a) closed boss b) open boss [MPa]

Fig. 20.
Distribution of Huber von-Mises stress in the polyamide liner [MPa]

Fig. 21.
Puck failure distribution: a) fibre, b) matrix
Tab. 11.
Maximum values of damage index for each winding angle layer
| Angle [°] | Fiber failure | Matrix failure |
|---|---|---|
| 10 | 0,329 | 0,836 |
| 14,5 | 0,266 | 0,695 |
| 19 | 0,238 | 0,715 |
| 23 | 0,210 | 0,636 |
| 27,5 | 0,185 | 0,620 |
| 31,5 | 0,182 | 0,582 |
| 36,5 | 0,182 | 0,603 |
| 90 | 0,385 | 0,544 |

Fig. 22.
Hashin failure distribution: a) fibre, b) matrix
Tab. 12.
Maximum values of damage index for each winding angle layer
| Angle [°] | Fiber failure | Matrix failure |
|---|---|---|
| 10 | 0,774 | 0,795 |
| 14,5 | 0,442 | 0,629 |
| 19 | 0,448 | 0,760 |
| 23 | 0,496 | 0,665 |
| 27,5 | 0,509 | 0,603 |
| 31,5 | 0,472 | 0,596 |
| 36,5 | 0,446 | 0,622 |
| 90 | 0,384 | 0,598 |

Fig. 23.
Tsai Wu criterion failure distribution
Tab. 13.
Maximum values of damage index for each winding angle layer
| Angle [°] | Failure |
|---|---|
| 10 | 0,759 |
| 14,5 | 0,547 |
| 19 | 0,678 |
| 23 | 0,498 |
| 27,5 | 0,536 |
| 31,5 | 0,566 |
| 36,5 | 0,581 |
| >90 | 0,580 |
Tab. 14.
Strain values in the most loaded elements
| Failure criteria/strain | εxx | εyy | εzz | εxy | εxz | εyz |
|---|---|---|---|---|---|---|
| Puck fibre | 7,986 · 10−3 | –1,011 · 10−2 | 2,073 · 10−3 | –9,570 · 10−5 | 2,034 · 10−4 | 6,786 · 10−4 |
| Puck matrix | 4,521 · 10–3 | 2,370 · 10−3 | –3,099 · 10−3 | –8,194 · 10−3 | –8,872 · 10−3 | 3,176 · 10−3 |
| Hashin fibre | 2,230 · 10–3 | –6,224 · 10−3 | –5,999 · 10−3 | 1,383 · 10−2 | 1,201 · 10−3 | 8,919 · 10−3 |
| Hashin matrix | 4,522 · 10−3 | 2,370 · 10−3 | –3,098 · 10−3 | –8,194 · 10−3 | –8,875 · 10−3 | 3,171 · 10−3 |
| Tsai Wu | 4,521 · 10−3 | 2,370 · 10−3 | –3,099 · 10−3 | –8,194 · 10−3 | –8,872 · 10−3 | 3,176 · 10−3 |
Tab. 15.
Displacement conditions for walls
| Surface X = 0 | Surface Y = 0 | Surface Z = 0 |
|---|---|---|
| u(0,y,z) = εxy 1 ε.xzz v(0,y,z) = εyyy + εyzz w(0,y,z) = εyzy + εzzz | u(x, 0, z) = εxxx + εxzz v(x, 0, z) = εxyx + εyzz w(x, 0, z) = εxzx + εzzz | u(x,y,0) = εxxx + εxyy v(x,y,0) = εxyx + εyyy w(x,y,0) = εxzx + εyzy |
| Surface X = Lx | Surface Y = Lx | Surface Z = Lx |
| u(Lx,y,z) = εxxLx + εxyy + εxzz v(Lx,y,z) = εxyεx + εyyy + εyzZ w(Lx,y,z) = εxzLx + εyzy + εzzz | u(x, Ly, z) = εxxx + εxyLy + εxzz v(x, Ly, z) = εxyx + εyyLy + εyzz w(x, Ly, z) = εxzx + εyzLy + εzzz | u(x,y,Lz) = εxxx + εxyy + εxzLz v(x,y,Lz) = εxyx + εyyy + εyzLz w(x,y,Lz) = εxzx + εyzy + εzzLz |

Fig. 24.
Stress distributions for maximum Puck fibre failure criterion strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 25.
Stress distributions for maximum Puck matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 26.
Stress distributions for maximum Hashin fibre failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 27.
Stress distributions for maximum Hashin matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 28.
Stress distributions for maximum Tsai Wu failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 29.
Stress distributions for maximum Puck fibre failure criterion strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 30.
Stress distributions for maximum Puck matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 31.
Stress distributions for maximum Hashin fibre failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 32.
Stress distributions for maximum Hashin matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 33.
Stress distributions for maximum Tsai Wu failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 34.
Stress distributions for maximum Puck fibre failure criterion strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 35.
Stress distributions for maximum Puck matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 36.
Stress distributions for maximum Hashin fibre failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 37.
Stress distributions for maximum Hashin matrix failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix

Fig. 38.
Stress distributions for maximum Tsai Wu failure criteria strains: a) Equivalent Huber von-Mises stress for RVE, b) normal X-direction stress for fibre, c) Equivalent Huber von-Mises stress for matrix
Tab. 16.
Maximum stress results from dehomogenisation for different fibre geometries
| Failure criteria | Stress limit [MPa] | Circular fibre | Eliptical fibre | Actual fibre | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| fibre | resin | RVE | fibre | resin | RVE | fibre | resin | RVE | fibre | resin | |
| Puck fibre | 4900 | 80 | 1868 | 1832,9 | 89,9 | 1795,4 | 1760 | 90,5 | 1923 | 1820 | 133,4 |
| Puck matrix | 1104,8 | 1128,1 | 57 | 1027,4 | 1067 | 55,1 | 1095,6 | 1133,6 | 76,3 | ||
| Hashin fibre | 676,1 | 553,2 | 154,4 | 680,9 | 563,35 | 177,2 | 1110,7 | 580,2 | 238,3 | ||
| Hashin matrix | 1104,9 | 1128,2 | 57 | 1107,9 | 1120,3 | 53,9 | 1188,9 | 1204,5 | 138,7 | ||
| Tsai wu | 1104,8 | 1128,1 | 57 | 1107,8 | 1120,2 | 54 | 1188,8 | 1204,4 | 138,7 | ||