A thermodynamic consistent damage and healing model for self healing materials

et al. 2011

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Self-healing smart materials have emerged into the research arena and have been deployed in industrial and biomedical applications, in which the modelling techniques and predicting schemes are crucial for designers to optimize these smart materials. In practice, plastic deformation is coupled with damage and healing in these systems, which necessitates a coupled formulation for characterization. The thermodynamics of inelastic deformation, damage and healing processes are incorporated here to establish the coupled constitutive equations for healing materials. This thermodynamic consistent formulation provides the designers with the ability to predict the irregular inelastic deformation of glassy polymers and damage and healing patterns for a highly anisotropic self-healing system. Moreover, the lack of a physically consistent method to measure and calibrate the healing process in the literature is addressed here. Within the continuum damage mechanics (CDM) framework, the physics of damage and healing processes is used to introduce the healing effect into the CDM concept and a set of two new anisotropic damage-healing variables are derived. These novel damage-healing variables together with the proposed thermodynamic consistent coupled theory constitute a well-structured method for accurately predicting the degradation and healing mechanisms in material systems. The inelastic and damage response for a shape memory polymer-based self-healing system is captured herein. While the healing experimental results are limited in the literature, the proposed theory provides the mathematical competency to capture the most nonlinear responses.

Section: Experimental Observationsmentioning

confidence: 54%

A theory of anisotropic healing and damage mechanics of materials

Voyiadjis

et al. 2011

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“…Damage healing in thermoset polymer composite structures has become a popular topic recently (Voyiadjis et al 2011). Several healing schemes have been reported in the literature primarily for healing microcracks with narrow opening, including incorporation of external healing agents such as liquid healing agent by microcapsules (White et al 2001), hollow fibres (Pang & Bond 2005) and microvascular networks (Toohey et al 2007), and solid healing agent such as embedded thermoplastic particles (TPs; Zako & Takano 1999;Voyiadjis et al 2012a).…”

Section: Introductionmentioning

confidence: 99%

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

2012

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103

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.

“…The accumulation of the failed chains may result in the loss of the mechanical properties of polymers such as a gradual reduction in the elastic tensile modulus [55,57]. In the case of ductile or low cycle fatigue, the MD damage parameter is constitutively developed by [22,23,54,58] …”

Section: (A) Mechanical Damagesmentioning

confidence: 99%

“…For example, in [54,58] thermodynamic consistent damage models have been developed for glassy polymers and they can be readily applied for the case of ductile MDs in SMPs. The correlation between the damage deformation gradient, i.e.…”

Section: (A) Mechanical Damagesmentioning

confidence: 99%

“…It is obvious that these changes are highly dependent on the thermomechanical cycle conditions. For example, changes in the elastic compressive modulus of an SMP system programmed at room temperature, see [4], notably differs from a system undergoes a high-temperature classical thermomechanical cycle, see [3,54]. Also the free or the constrained recovery process conditions will have a significant effect on the elastic moduli variations, because the rearrangement of the molecular network of SMP is affected by these constraint conditions.…”

Section: (B) Mechanical Damage Induced By Thermomechanical Cyclesmentioning

confidence: 99%

See 1 more Smart Citation

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

2014

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A multi-mechanism-based phenomenological model is developed within the finite deformation kinematics framework for capturing the thermomechanical behaviour of shape memory polymers (SMPs) both during programming and in service. Particularly, the damage mechanisms in SMPs are studied within the continuum damage mechanics (CDMs) framework in which they are classified into mechanical or physical damage, induced during service condition, e.g. fatigue and functional damage induced during thermomechanical cycles, e.g. shape recovery loss. Statistical mechanics is incorporated to describe the initiation and saturation of these deformation mechanisms. The main advantage of the presented viscoplastic model, comparing to the existing counterparts, is its simplicity by minimizing the need for curve fitting, and capability in simulating the nonlinear stress-strain behaviour of amorphous, crystalline or semicrystalline SMPs. The developed viscoplastic CDM model takes into account several distinctive deformation mechanisms involved in the thermomechanical cycle of SMPs, including glass transition loss events, temperature-dependent material properties, stress relaxation, shape recovery transient events and damage effects. The established model correlates well with the experimental results and its computational capabilities provide material designers with a powerful design tool for future SMP applications.