Crack initiation in engineering thermoplastics resulting from chemical degrdation

Byoung-Ho Choi, Zhenwen Zhou, Alexander Chudnovsky, Kalyan Sehanobish

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Stress Corrosion Cracking (SCC) in thermoplastics usually appears as a microcrack network within a layer of degraded polymer adjacent to the surface exposed to combine action of mechanical stress and chemically aggressive environment. The stage of crack initiation is primarily controlled by chemical degradation. Degradation of polymers is usually manifested in a reduction of molecular weight, increase of crystallinity in semicrystalline thermoplastics, increase of material density, a subtle increase in yield strength, and a dramatic reduction of toughness, i.e., specific fracture energy. An increase in material density, i.e., shrinkage of the degraded layer is constrained by adjacent unchanged material. It results in a buildup of tensile stress within the degraded layer and compressive stress in the adjacent unchanged material due to increasing incompatibility between the two. These stresses sum up with manufacturing and service stresses leading to an increase of the strain energy. At a certain level of degradation, a combination of toughness reduction and increase of the stored elastic energy results in fracture initiation (FI). From an energy consideration, SCC starts, when the release of the stored strain energy due to microcrack network formation compensates the required specific fracture energy. Considering a chain of micro-events leading to fracture initiation on macro scale, the probability of FI is evaluated using the formalism of Statistical Fracture Mechanics (SFM). A critical level of degradation is determined as the degradation at which FI takes place with certainty. The kinetics of the degradation process and the critical level of degradation then determine the time of fracture initiation. Experimental observations and a mathematical model of the described above processes are presented in this work.

Original languageEnglish
Title of host publication11th International Conference on Fracture 2005, ICF11
Pages2220-2225
Number of pages6
Volume3
Publication statusPublished - 2005 Dec 1
Externally publishedYes
Event11th International Conference on Fracture 2005, ICF11 - Turin, Italy
Duration: 2005 Mar 202005 Mar 25

Other

Other11th International Conference on Fracture 2005, ICF11
CountryItaly
CityTurin
Period05/3/2005/3/25

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ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology

Cite this

Choi, B-H., Zhou, Z., Chudnovsky, A., & Sehanobish, K. (2005). Crack initiation in engineering thermoplastics resulting from chemical degrdation. In 11th International Conference on Fracture 2005, ICF11 (Vol. 3, pp. 2220-2225)