Effect of molecular structure of curing agents on cyclic creep in highly cross‐linked epoxy polymers

Abstract

Ratcheting behavior of highly–cross‐linked epoxy polymers was investigated considering the effect of molecular structure of curing agents by molecular dynamics simulations. Cyclic loading–unloading simulations at two different frequencies were conducted using atomistic models for epoxies cured by aliphatic and aromatic curing agents, triethylenetetramine (TETA) and diethyltoluenediamine (DETDA), respectively. Different ratcheting strain evolutions, dihedral angle stress accumulations, and stiffness variations were observed during the cyclic deformation simulations depending on the molecular structure of curing agents. The epoxy cured by DETDA exhibited a more rapid increase of ratcheting strain and a decrease of the stiffness toward the loading direction. Structural analyses were carried out by observing the orientation order parameter of the monomers, radius of gyration, and free volume evolution to understand the ratcheting strain behaviors and stiffness variations at atomistic scale. The structural analyses revealed that irreversible dihedral angle transitions near the benzene ring of the curing agent DETDA were responsible for low ratcheting resistance and stiffness degradation during the cyclic deformations. Whereas, the aliphatic curing agent TETA, which does not exhibit any stress possession by the irreversible dihedral angle change, was revealed to be advantageous for the ratcheting resistance and stiffness variation of the epoxy polymers.

Uniaxial Tensile Creep Behavior of Epoxy-Based Polymer Using Molecular Simulation

“…From Figure 5 , the yield strength of the resulting epoxy resin model is 206.64 MPA, and the corresponding strain is 0.052. It should be pointed out that the yield strength 206.64 MPa of epoxy resin simulated here is slightly lower than the 264.26 MPa reported in previous studies, which may be due to the fact that the cross-linking degree of the model established using the method of representative monomer in this paper is slightly lower than that of the previously reported model (81.3%) [ 16 ]. At the same time, through postprocessing to fit the points obtained in the linear stage of the stress-strain curve in the tensile process, we found that the Young’s modulus of the epoxy resin system was 4.390 ± 0.251 GPa, with the final fitting degree R 2 equaling 0.98.…”

“…By finding the correlation between the steady-state creep rate and steady-state void nucleation rate, they considered that secondary creep is heavily driven by void nucleation, while tertiary creep is driven by void growth and coalescence. Hyungbum Park et al [ 16 ] conducted the cyclic loading–unloading simulations at two different frequencies using atomistic models for epoxies cured by aliphatic and aromatic curing agents, triethylenetetramine (TETA) and diethyltoluenediamine (DETDA), respectively. They studied the structure and found that irreversible dihedral angle transitions near the benzene ring of the curing agent DETDA were responsible for low ratcheting resistance and stiffness degradation during the cyclic creep deformations.…”

Addressing diffusion behavior and impact in an epoxy–amine cure system using molecular dynamics simulations

“…Figure 1a-d show the chemical structures of diglycidyl ether of bisphenol F (DGEBF), triglycidyl p-aminophenol (TGAP), 3,3′-diamino diphenyl sulfone (3,3′-DDS), and polyether sulfone (PES) composing the epoxy systems, respectively. The Polymer Consistent Force-Field (PCFF) 45 was used to describe the DGEBF, TGAP, 3,3′-DDS, and PES because the PCFF has been used to successfully describe a resin and curing agent in epoxy systems [33][34][35][36] . The total energies (E total s) of molecular structures of the epoxy systems were calculated using Eq.…”

“…Computational materials science techniques have been efficiently used to investigate the structural morphologies and diffusion properties of polymers in organic systems [26][27][28][29][30][31][32] . Other authors have recently investigated the mechanical properties of epoxy resin with curing agents [33][34][35][36][37] and the phase separation of epoxy systems [38][39][40][41] using computational materials science. Research into mechanical properties such as tensile and compressive stress-strain curves, Young's modulus, shear modulus, glass-transition temperature (T g ), and the phase separation of toughening agents with epoxy resin and curing agents is critical to achieving detailed atomic-level understanding of their behaviors.…”

Sound Velocities in Graphene-Based Epoxy Nanocomposites

“…In particular, when employing the technique based on exploiting the structure or dynamics of entire polymer chains to estimate the interphase thickness, the value from about 2 to 3 Rg is usually obtained [42]. For the DGEBAepoxy resins, the value Rg ~ 12 -14 nm has been obtained [44].…”