Characterization and modeling of strain assisted diffusion in an epoxy adhesive layer

Abstract

In this paper a coupled model for strain-assisted diffusion is derived from the basic principles of continuum mechanics and thermodynamics, and material properties characterized using diffusion experiments. The proposed methodology constitutes a significant step toward modeling the synergistic bond degradation mechanism at the bonded interface between a Fiber Reinforced Polymer (FRP) and a substrate, and for predicting debond initiation and propagation along the interface in the presence of a diffusing penetrant at the crack tip and at elevated temperatures. It is now well-known that FickÕs law is frequently inadequate for describing moisture diffusion in polymers and polymer composites. Non-Fickian or anomalous diffusion is likely to occur when a polymer is subjected to external stresses and strains, as well as elevated temperatures and humidity. In this paper, a modeling methodology based on the basic principles of continuum mechanics and thermodynamics is developed which allows characterization of the combined effects of temperature, humidity, and strain on diffusion coefficients as well as on moisture saturation level, from moisture weight gain data. For tractability, the diffusion governing equations are simplified for the special case of 1-D diffusion subjected to uniaxial strain and a uniform strain gradient. A novel test specimen that introduces a uniform strain gradient is developed, and diffusion test data for an epoxy-based primer/adhesive are presented and employed for complete characterization of material constants used in the model.

Micromechanics of diffusion-induced damage evolution in reinforced polymers

“…In the present context of diffusion-induced damage, we define a normalized tortuosity, n = t c /t m , where t c is the time required for moisture saturation in an RVE with a given f and characteristic dimension (in the diffusion direction) L 2 , and t m is the corresponding time required for moisture saturation in bare matrix with the same characteristic dimension. 5 As per this definition, although the SR-RVE is less clustered ((C v ) SR $ 0.17) than the RC-RVE ((C v ) RC $ 0.25), they exhibit similar tortuosities (n SR $ 9.1, n RC = 9). However, the RC-RVE experiences significantly higher damage (w RC $ 0.31) than the SR-RVE (w SR $ 0.1) (Fig.…”

“…Composites used for dental restoration purposes may experience aqueous service environments that range between strongly acidic to strongly alkaline [3]. Further, the moisture diffusivity itself may be a function of the applied stress, which in turn may affect the stress distribution in the composite [4][5][6]. The absorbed moisture may lead to matrix cracking [7][8][9][10][11] or plasticize the matrix thereby reducing effective stiffness and strength of polymers [7] and their composites [1,2,12].…”

On solvent diffusion in a solid with large dilatation

“…In a previous paper [22], the authors have addressed the case of non-Fickian diffusion in a polymer in the presence of applied strains as well as strain-gradients. In that paper, the authors employed a more complete description of the solvent flux in terms of the gradient of the chemical potential, which, in turn, was derived from a Helmholtz energy potential.…”

“…(20)- (22) are repeated until the solution converges. The typical convergence metric is the Euclidean norm,…”

Simultaneously Effect of Envinronment and Sustained Load on the Degradation of Aluminium Bonded Joint

“…Stress of the adhesive during diffusion can cause a more rapid absorption. [7][8][9][10][11][12]. Moisture diffusion causes a change of adhesive mechanical properties and the failure stress of adhesives reducing with increasing moisture [2,3,13,14].…”