Secondary Necking Evolution and Strain Hardening Behavior in Tensile Deformation of PEEK

JIANG Xingchen; DENG Yujun; YI Peiyun; PENG Linfa

doi:10.3969/j.issn.1674-6457.2025.11.014

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Journal of Netshape Forming Engineering ›› 2025, Vol. 17 ›› Issue (11) : 152-159. DOI: 10.3969/j.issn.1674-6457.2025.11.014

Intelligent Processing of Advanced Materials

Secondary Necking Evolution and Strain Hardening Behavior in Tensile Deformation of PEEK

JIANG Xingchen, DENG Yujun^*, YI Peiyun, PENG Linfa

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Abstract

The work aims to systematically reveal the necking and strain-hardening behavior of PEEK under high stretching velocities, to provide insights into its long-term stability in complex service environments. Uniaxial tensile tests were performed on Victrex 450G PEEK at various stretching velocities (10-900 mm/min), temperature (25 ℃ and 90 ℃), and initial crystallinity (21.6%, 32.3%, and 35.2%). Full-field strain distributions in the gauge section were obtained using digital image correlation (DIC), enabling quantitative analysis of local necking and secondary necking, as well as characterization of the onset of strain hardening and the strain hardening modulus. Results showed that the uniaxial tensile mechanical behavior of PEEK was significantly affected by temperature and tensile rate, while the initial crystallinity had a limited influence on it. At 25 ℃, PEEK exhibited monotonic hardening under low stretching velocities, while multiple stress peaks and secondary necking appear at high stretching velocities, with the secondary peaks strongly correlated with localized strain concentration. With the increase of the stretching velocity, the onset of strain hardening shifted to higher strains, and the strain hardening modulus increased. At 90 ℃, the multiple stress peaks were attenuated, and stress oscillations occurred at intermediate to high stretching velocities, with amplitudes showing a “first increasing, then decreasing” trend. In conclusion, under high stretching velocities, PEEK exhibits enhanced strain hardening and secondary necking, indicating a complex mechanical response mechanism under extreme service conditions. This finding is of great significance for understanding its structural reliability and service performance.

Key words

poly-ether-ether-ketone (PEEK) / semi-crystalline polymer / necking / strain hardening

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JIANG Xingchen, DENG Yujun, YI Peiyun, PENG Linfa. Secondary Necking Evolution and Strain Hardening Behavior in Tensile Deformation of PEEK[J]. Journal of Netshape Forming Engineering. 2025, 17(11): 152-159 https://doi.org/10.3969/j.issn.1674-6457.2025.11.014

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