PSI - Issue 13

Ahmed Sohail et al. / Procedia Structural Integrity 13 (2018) 1014–1019 Author name / StructuralIntegrity Procedia 00 (2018) 000 – 000

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extra benefit of avoidance of additional constraints. To prevent hour-glassing of the reduced integration elements enhanced stiffness relaxation method is used. To evaluate the damage and constitutive behavior of the hybrid/3D Woven composite Hashin damage criteria was deployed through user subroutine UMAT in ABAQUS/standard. Utilizing the periodicity of 3D woven architecture, suitable periodic boundary condition has been specified on the four vertical faces of the unit cell corresponding to X + , X - and Y + , Y - , The unit cell faces located at Z + and Z - were set free. 2.3. Material Properties The transversely isotropic weft and warp tows and Z-yarns were basically Carbon/Epoxy uni-directional composites in the first architecture, with material properties listed in Table 2. In the case of second (Hybrid) and third (Kevlar) architecture, the material properties for Kevlar fibers are also listed in Table 2. The isotropic epoxy resin matrix was characterized by elastic modulus, E = 3.45 GPa, Poisson’s ratio, v = 0.35. Table 2. Material properties of the transversely isotropic carbon/epoxy (Karahan et al. (2010) and kevlar /epoxy (Huang (2001) fiber tows estimated from Chamis’ model

Elastic moduli (GPa)

Poisson’s ratio

Shear Modulus (GPa)

Elastic Constants

E 1

E 2 = E 3

υ 12 = υ 13

υ 23

G 12 = G 13

G 23

Carbon/Epoxy Kevlar/Epoxy

155 69.8

9.6

0.3

0.49 0.36

5.67 4.36

5.13

7.41

0.33

4.1

X C

Y T 82 20

Y C

S L 90 73

Strength Parameters (MPa)

X T

Carbon/Epoxy Kevlar/Epoxy

2537 1200

1580

236 140

230

3. Results and Discussions

The predicted elastic and strength properties for first configuration (carbon/epoxy tows) of 3D woven composite are presented in Table 3. The results for elastic moduli and strength in warp direction show excellent agreement with the experimental data. However, in the weft direction the results for the numerical simulation have higher values for both, elastic moduli and strength. These variations can be attributed to the ‘arcing’ of the top a nd bottom fiber (weft) tows was not taken into account during numerical simulation and the fiber tows were modeled exactly rectangular shape hence incorporating more material in comparison with the actual specimen.

Table 3. Comparison of longitudinal and transverse elastic moduli presented in Bogdanovich AE et al. (2013) with corresponding results obtained in the present study Exx (GPa) Eyy (GPa) Sxx (MPa) Syy MPa) Present study 58.6 74.5 888 1183.8 Ref. Experimental 60.6 66.9 953 901

After successfully validating the numerical model, three fiber tows have been replaced by Kevlar/epoxy material as explained in the previous section and repeating the numerical simulation under the same condition to find the elastic moduli and strength parameters for the hybrid 3D woven composite. Similarly, for the third configuration (all kevlar) numerical analysis has been accomplished and the results for the tensile properties has been obtained and presented. Table 4 presents the results from numerical analysis for elastic moduli and strength of hybrid and all kevlar configurations. For hybrid configuration, in the weft direction, the fraction of Kevlar introduced is 50% (2 out of 4 tows), the elastic modulus is reduced by 22.6%. In the warp direction the Kevlar tow fraction is ~33%, the elastic modulus is reduced by 18.2%. Similarly, for third configuration where all the fiber tows of 3D woven composite is of Kevlar, the decrease in the weft and warp modulus is 51.7% and 54.1% respectively.