A viscoplastic theory of shape memory polymer fibres with application to self-healing materials

Abstract

The difficulty in healing structural damage is that most existing schemes need external help to bring the fractured surfaces in contact before healing can occur. To facilitate the existing schemes to heal macroscopic cracks, we envision that the cracked surfaces can be brought in contact through constrained shape recovery of a shape memory polymer (SMP) fibre-reinforced grid skeleton that is embedded in thermoset polymer matrix, similar to stitch a cut in the human skin by suture. In this study, we show that polyurethane SMP fibres can be hardened through cyclic cold-drawing programming, which makes them suitable for reinforcement and healing in thermoset polymer composites. We characterized the microstructure of the SMP fibres, which provides fundamental understanding of the effect of programming on the degree of crystallinity and molecular orientation. Then, a micromechanical multiscale viscoplastic theory is developed to predict the thermomechanical behaviours of the SMP fibres, including the cyclic hardening and stress recovery responses. The proposed theory takes into account the stress-induced crystallization process and the evolution of the morphological texture based on the applied stresses. The cyclic loading and the thermomechanical responses of the SMP fibres confirm the capabilities of the proposed model in capturing these phenomena.

Three-dimensional constitutive model for shape memory polymers using multiplicative decomposition of the deformation gradient and shape memory strains

“…Two-way shape memory, i.e., reversible deformation behavior in response to an on-off stimulus, has also been demonstrated using one-way SMPs and bias loads (Chung et al, 2007;Hong et al, 2010;Pandini et al, 2012). Due to these fascinating properties, SMPs are promising for use in many applications, including aerospace devices , self-healing medical materials (Li and Shojaei, 2012;Xu and Li, 2010), smart biomedical stents (El Feninat et al, 2002;Kim et al, 2010a;Reese et al, 2010), fiber-reinforced SMP composites (Lan et al, 2014;Tan et al, 2014;Zhang et al, 2015), particle-reinforced SMP composites (Hong et al, 2008), metal-SMP composites (Wang and Li, 2011), Alloy-SMP composite (Qiao et al, 2013), and 4D printings (Ge et al, 2014;Ge et al, 2013;Yu et al, 2015).…”

“…For example, the temporarily fixed shape of SMPs has ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T 5 been modeled using their crystallization behavior (Barot and Rao, 2006) and, in particular, strain-or stress-induced crystallization processes (Barot et al, 2008;Li and Shojaei, 2012;Rao and Rajagopal, 2001;Richard and Lisa Mauck, 2008;Westbrook et al, 2010). Shape memory has also been modeled on the temperature-induced changes in SMP microscopic structures Srinivasa, 2013, 2014;Gu et al, 2015;Nguyen et al, 2008;Nguyen et al, 2010;Srivastava et al, 2010;Westbrook et al, 2011;.…”

Thermomechanical constitutive modelling of shape memory polymer including continuum functional and mechanical damage effects

“…Thermomechanical modelling of SMPs has been extensively studied in the literature [4,5,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Most recently Qi and co-workers [25] reported the influence of programming conditions on shape fixity and free shape recovery and developed a unified model for shape memory behaviours.…”

“…It is noted that programming may not need the typical heating and cooling process. Programming can also be conducted at temperature below the transition temperature such as cold compression programming for amorphous thermosetting SMPs [4] or cold-drawing programming for semicrystalline thermoplastic SMPs [5][6][7].…”

Healable thermoset polymer composite embedded with stimuli-responsive fibres

“…In the second step, thermoplastic particles (TPs) that were pre-embedded in the shape memory polymer matrix melted, diffused and bonded the closed cracks through molecular entanglement. However, as indicated by Li & Shojaei [9], this system requires a shape memory polymer as the matrix. However, in engineering structures, conventionally used thermosetting polymers do not have shape memory capability.…”