PSI - Issue 52

66 4 Chenxu Jiang et al. / Procedia Structural Integrity 52 (2024) 63–71 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 Gaussian chains. The series expansion is truncated after the fifth term, and the values of the coefficients C 1 =1/2 , C 2 =1/20 , C 3 =11/1050 , C 4 =19/7000 , and C 5 = 519/673750 . The elastic moduli of the crystalline phase are given in Table 1, which have six independent components. The relatively high stiffness component value C 33 corresponds to the molecular chain direction. The exponents of rate sensitivity coefficient =10 . The reference shear rate ̇ 0 = 0.001 s −1 . The crystalline phase is the orthotropic unit cell, which has eight distinct slip systems. The corresponding slip resistances ( ) at room temperature are given in Table 2. The amorphous phase material parameters are referenced in the reference (Tomita, Tanaka, & Structures, 1995; Wu, Van Der Giessen, & Solids, 1993). The initial bulk modulus is 0 =2000MPa , locking stretch coefficient λ m =7 , the initial shear modulus μ 0 = 35 MPa . Table 1 Elastic moduli of the crystalline phase (Choy & Leung, 1985) C11 [GPa] C12 [GPa] C13 [GPa] C33 [GPa] C44 [GPa] C66 [GPa] 7.0 3.8 4.7 81.0 1.5 1.6

Table 2 Slip resistances of eight slip systems (Bartczak, Argon, & Cohen, 1992)

( ) / [MPa] 8

Slip system (100)[001] (010)[001] {110}[001] (100)[010] (010)[100] {110}〈11̅0〉

Chain slip

20 20

13.3

Transverse slip

20

17.6

3. Finite element model 3.1. Single spherulite model

The crystalline phase consists of orthotropic unit cells. Therefore, each crystal lamellae growth orientation and molecular chain stack direction are calculated separately. The Global coordinate system is defined as shown in Fig. 2a, in which b is the growth direction of spherulite crystal from the spherulite center and coincident with the radial line. φ is the angle between the lamellae growth direction and the X -axis of the Global coordinate system, which ranges from 0° to 360°. Fig. 2b illustrates lamellar surface normal n and molecular chain direction c. ϕ is the angle between n and c, which varies between 20° and 40°(Gautam, Balijepalli, & Rutledge, 2000). In this work, the initial angle of ϕ is set to 35°.

Fig. 2 (a) Global coordinate system in lamellae growth direction (b) Local coordinate system in the inter-lamellae direction

The 2D rectangle size of 20×20 µm and the radius of sheaf of 1 µm were used in the calculation model of a single spherulite, as depicted in Fig. 3 . Different initial orientations of θ were achieved by rotating the principal axis. To