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The strong influence of relatively small amounts of filler particles, such as carbon black, on the mechanical properties of elastomers has been well known for decades and has significantly contributed to increased use of elastomeric materials in many commercial applications. Even though the use of fillers is ubiquitous, satisfactory understanding and modeling of the micromechanisms by which fillers alter the mechanical behavior of elastomers has still not been realized. In this work the influence of filler particles on the equilibrium stress-strain response has been investigated. First, an experimental investigation probing the behavior of a chloroprene rubber with varied filler content has been performed. The experimental data allowed for a direct evaluation of both a newly developed constitutive model based on the amplification of the first strain invariant, and a number of other models proposed in the literature. A direct comparison with experimental data suggest that the new model generates superior predictions, particularly for large strain deformations. Then, in an effort to examine some of the assumptions that are common in the constitutive modeling and also to try to determine which of the input parameters are most important, a detailed series of micromechanical models were constructed using two- and three-dimensional finite element simulations. The results indicate that the effect of filler particles on the equilibrium behavior of elastomers can be accurately predicted using stochastic three-dimensional simulations suggesting that successful modeling mainly requires a rigorous treatment of the composite nature of the microstructure and not molecular level concepts such as alteration of mobility or effective crosslinking density in the elastomeric phase of the material.

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This article provides an overview of the connection between the microstructural state and the mechanical response of various bioresorbable polylactide (PLA) devices for medical applications. PLLA is currently the most commonly used material for bioresorbable stents and sutures, and its use is increasing in many other medical applications. The non-linear mechanical response of PLLA, due in part to its low glass transition temperature (T g ≈ 60 °C), is highly sensitive to the molecular weight and molecular orientation field, the degree of crystallinity, and the physical aging time. These microstructural parameters can be tailored for specific applications using different resin formulations and processing conditions. The stress-strain, deformation, and degradation response of a bioresorbable medical device is also strongly dependent on the time history of applied loads and boundary conditions. All of these factors can be incorporated into a suitable constitutive model that captures the multiple physics that are involved in the device response. Currently developed constitutive models already provide powerful computations simulation tools, and more progress in this area is expected to occur in the coming years.

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