scholarly journals Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2746
Author(s):  
Mingjin Liu ◽  
Jiaxu Luo ◽  
Jin Chen ◽  
Xueqin Gao ◽  
Qiang Fu ◽  
...  
Keyword(s):  
Shear Layer ◽  
Crack Growth ◽  
Isotactic Polypropylene ◽  
Slow Crack Growth ◽  
Crack Growth Behavior ◽  
Polymer Science ◽  
The Past ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

Comparison of Two Ductile Crack Propagation Models of GTN and CZM for Pipe Steel Fracture

2018 ◽  
Author(s):  
Junqiang Wang ◽  
Haitao Wang ◽  
Nan Lin ◽  
Honglian Ma ◽  
Jinlong Wang
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Pipe Steel ◽  
Damage Model ◽  
Crack Tip ◽  
Ductile Crack ◽  
Constraint Effect ◽  
Propagation Models ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

The ductile crack propagation behavior of pressure equipment has always been the focus of structural integrity assessment. It is very important to find an effective three-dimensional (3D) damage model, which overcomes the geometric discontinuity and crack tip singularity caused by cracking. The cohesive force model (CZM), which is combined with the extended finite element method (XFEM), can solve element self-reconfiguration near the crack tip and track the crack direction. Based on the theory of void nucleation, growth and coalescence, the Gurson-Tvergaard-Needleman (GTN) damage model is used to study the fracture behavior of metallic materials, and agrees well with the experimental results. Two 3D crack propagation models are used to compare crack propagation behavior of pipe steel from the crack tip shape, fracture critical value of CTOA and CTOD, constraint effect, calculation accuracy, efficiency and mesh dependence etc. The results show that the GTN model has excellent applicability in the analysis of crack tip CTOD/CTOA, constraint effect, tunneling crack and so on, and its accuracy is high. However, the mesh of crack growth region needs to be extremely refined, and the element size is required to be 0.1–0.3mm and the calculation amount is large. The CZM model combined with XFEM has the advantages of high computational efficiency and free crack growth path, and the advantages are obvious in simulating the shear crack, combination crack and fatigue crack propagation. But, the crack tip shape and thickness effect of ductile tearing specimen can not be simulated, and the CTOA value of local crack tip is not accurate.

Sign in / Sign up

Export Citation Format

Share Document