Research Papers

An Experimental Study on Strain Hardening of Amorphous Thermosets: Effect of Temperature, Strain Rate, and Network Density

[+] Author and Article Information
Chuanshuai Tian

Department of Engineering Mechanics,
College of Mechanics and Materials,
Hohai University Nanjing,
Jiangsu 210098, China
e-mail: cstian@hhu.edu.cn

Rui Xiao

Department of Engineering Mechanics,
College of Mechanics and Materials,
Hohai University,
Nanjing 210098, Jiangsu, China
e-mail: rxiao@hhu.edu.cn

Jun Guo

Department of Engineering Mechanics,
College of Mechanics and Materials,
Hohai University,
Nanjing 210098, Jiangsu, China
e-mail: jun2018@hhu.edu.cn

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received April 20, 2018; final manuscript received June 24, 2018; published online July 17, 2018. Assoc. Editor: Junlan Wang.

J. Appl. Mech 85(10), 101012 (Jul 17, 2018) (8 pages) Paper No: JAM-18-1228; doi: 10.1115/1.4040692 History: Received April 20, 2018; Revised June 24, 2018

In this paper, we present an experimental study on strain hardening of amorphous thermosets. A series of amorphous polymers is synthesized with similar glass transition regions and different network densities. Uniaxial compression tests are then performed at two different strain rates spanning the glass transition region. The results show that a more pronounced hardening response can be observed as decreasing temperature and increasing strain rate and network density. We also use the Neo-Hookean model and Arruda–Boyce model to fit strain hardening responses. The Neo-Hookean model can only describe strain hardening of the lightly cross-linked polymers, while the Arruda–Boyce model can well describe hardening behaviors of all amorphous networks. The locking stretch of the Arruda–Boyce model decreases significantly with increasing network density. However, for each amorphous network, the locking stretch is the same regardless of the deformation temperature and rate. The hardening modulus exhibits a sharp transition with temperature. The transition behaviors of hardening modulus also vary with the network density. For lightly crosslinked networks, the hardening modulus changes 60 times with temperature. In contrast, for heavily crosslinked polymers, the hardening modulus in the glassy state is only 2 times of that in the rubbery state. Different from the results from molecular dynamic simulation in literatures, the hardening modulus of polymers in the glassy state does not necessarily increase with network density. Rather, the more significant hardening behaviors in more heavily crosslinked polymers are attributed to a lower value of the stretch limit.

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Grahic Jump Location
Fig. 1

Storage modulus and tan δ of tBA-co-XLS networks with (a) 2 wt %, (b) 10 wt %, (c) 20 wt %, and (d) 40 wt % crosslinker as a function of temperature

Grahic Jump Location
Fig. 2

Comparison the experiments and model predictions of hyperelastic response of amorphous thermosets with (a) 2 wt %, (b) 10 wt %, (c) 20 wt %, and (d) 40 wt % crosslinker

Grahic Jump Location
Fig. 3

Stress response of tBA-co-XLS with 2 wt % crosslinker at strain rates of (a) 0.003/s and (b) 0.0003/s

Grahic Jump Location
Fig. 4

Stress response of tBA-co-XLS with 10 wt % crosslinker at strain rates of (a) 0.003/s and (b) 0.0003/s

Grahic Jump Location
Fig. 5

Stress response of tBA-co-XLS with 20 wt % crosslinker at strain rates of (a) 0.003/s and (b) 0.0003/s

Grahic Jump Location
Fig. 6

Stress response of tBA-co-XLS with 40 wt % crosslinker at strain rates of (a) 0.003/s and (b) 0.0003/s

Grahic Jump Location
Fig. 7

The strain rate-dependent stress response of tBA-co-XLS with 20 wt % crosslinker deformed at (a) 40 °C and (b) 30 °C

Grahic Jump Location
Fig. 8

The stress response as a function of normalized stretch a(λ1) of (a) tBA-co-XLS with 10 wt % crosslinker and (b) at tBA-co-XLS with 40 wt % crosslinker at a strain rate of 0.003/s

Grahic Jump Location
Fig. 9

The strain hardening modulus as a function of temperature for tBA-co-XLS with (a) 2 wt %, (b) 10 wt %, (c) 20 wt %, and (d) 40 wt % crosslinker




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