Research Papers

A Model for Calculating Hyperelastic Material Properties Under Thermal Aging

[+] Author and Article Information
Ahmed G. Korba

Department of Aerospace
Engineering and Mechanics,
The University of Alabama,
Tuscaloosa, AL 35401
e-mail: agkorba@crimson.ua.edu

Abhishek Kumar

Department of Aerospace
Engineering and Mechanics,
The University of Alabama,
Tuscaloosa, AL 35401
e-mail: akumar16@crimson.ua.edu

Guoqin Sun

Department of Mechanical Design and Method,
College of Mechanical Engineering and
Applied Electronics Technology,
Beijing University of Technology,
Beijing 100022, China
e-mail: sguoq@bjut.edu.cn

Mark E. Barkey

Department of Aerospace
Engineering and Mechanics,
The University of Alabama,
Tuscaloosa, AL 35401
e-mail: mbarkey@eng.ua.edu

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received February 2, 2017; final manuscript received June 18, 2017; published online August 9, 2017. Assoc. Editor: Huiling Duan.

J. Eng. Mater. Technol 140(1), 011006 (Aug 09, 2017) (10 pages) Paper No: MATS-17-1036; doi: 10.1115/1.4037170 History: Received February 02, 2017; Revised June 18, 2017

Understanding the degradation of material properties and stress–strain behavior of rubberlike materials that have been exposed to elevated temperature is essential for rubber components design and life time prediction. The complexity of the relationship between hyperelastic materials, crosslinking density (CLD), and chemical composition presents a difficult problem for the accurate prediction of mechanical properties under thermal aging. In this paper, a new and relatively simple mathematical formulation is presented to expresses the change in material properties of hyperelastic materials under thermal aging. The proposed formulation has been applied to a natural rubber (NR). Testing was performed on more than 130 specimens that were thermally aged then subjected uniaxial tension and hardness tests. The aging temperatures ranged from 76.7 °C to 115.5 °C, and the aging times ranged from 0 to 600 h. Based on the recorded experimental data, the NR mechanical properties under thermal aging showed a similar behavior to the rate of change of the CLD with aging time and temperature. Three mechanical properties have been chosen to be studied in this paper: the ultimate tensile strength, the fracture stretch value, and the secant modulus at 11.0% strain. The proposed mathematical formulation is a phenomenological equation that relates the material properties with the change in CLD based on a form of Arrhenius equation. The proposed equation showed promising results compared to the experimental data with an acceptable error margin of less than 10% in most of the cases studied.

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Fig. 1

Tensile test specimen: (a) rubber pad and (b) rubber strip (2 mm × 2 mm squares grid)

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Fig. 2

Unaged engineering stress–strain behavior with average line (Average±10%)

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Fig. 3

Stress–strain behavior for different aging times and temperatures: (a) T = 76.7 °C, (b) T = 82.2 °C, (c) T = 87.8 °C, (d) T = 93.3 °C, (e) T = 98.9 °C, (f) T = 104.4 °C, (g) T = 110.0 °C, and (h) T = 115.5 °C

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Fig. 4

Hardness test data variation with time

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Fig. 5

Crosslinking density behavior with aging time and temperature for NR based on Choi's [2] results: (a) CLD behavior under thermal aging and (b) ΔCLD slope with aging time (K)

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Fig. 6

Graphical representation of Eqs. (2), (10), and (13)

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Fig. 7

USR variation with aging time and temperature; see Table 3

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Fig. 8

Hyperelastic materials typical stress–strain behavior

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Fig. 9

FSR variation with aging time and temperature

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Fig. 10

SMR variation with aging time and temperature

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Fig. 11

Stress–strain behavior of the three random samples for verification

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Fig. 12

SMR error % of Eq. (14) results compared to the measured test data




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