PSI - Issue 23

Yoshitaka Umeno et al. / Procedia Structural Integrity 23 (2019) 348–353 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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(b)

(a)

Fig. 4: Yield stress as a function of (a) raw strain rate and (b) WLF shifted strain rate. The experimental results are taken from Bauwens Crowet 1974.

Fig. 5: Yield stress as a function of strain rate under various loading modes. The experimental results are from Bauwens-Crowet 1974.

3.3. Effect of Molar Mass on Deformation after Yielding

Figure 6 shows stress-strain relationships obtained with a variety of number-average molar masses, M n . The magnification at a region of relatively small strain (right figure) finds that the molar mass little affects the yield stress. On the other hand, in a region of large strain it is found that stress increases largely after yielding in the model with large molar masses, while stress decreases after yielding in the model with M n = 8.2 kg/mol. The increase in stress after yielding indicates that the material should exhibit ductile fracture because PC molecules tend to attain large stress even after yielding hindering the occurrence of deformation concentration in a small area. In contrast, when molecules cannot hold larger stress than the yield stress, deformation will concentrate in an area of yield initiation, resulting in a rather brittle nature of fracture. Observation of deformation behavior in the simulations revealed that models with larger molar masses exhibited more entanglement of molecular chains. This indicates that entanglement of molecular chains should contribute to transition from brittle fracture to ductile fracture.