Micromechanics – Materials Stress Testing

Micromechanics is the analysis of composites or heterogeneous materials at the level of the material’s individual components. Heterogeneous materials (like composites) are formed from multiple clearly distinguishable components (or phases) which each show different material properties. Because the properties can be so variable, micromechanics aims to predict the response of heterogeneous materials based on the geometries and properties of each individual phase. That process is called homogenization.

Homogenization is helpful by allowing for the behavior of a heterogeneous material to be predicted without testing the material. Material testing can be expensive and require many data points like phase combinations, volume fractions, and more. Additionally, because heterogeneous materials are often anisotropic (meaning their properties vary with the direction), continuum micromechanics can be used to predict the properties along each axis of the material. It’s important that these properties can be calculated because they can be difficult to measure experimentally.

Additionally, micromechanics aims to calculate the local stress and strain fields for each phase. That knowledge is incredible important in understanding damage to the material and failure analysis. This type of calculation is usually based on the idea of a representative volume element (or RVE). The RVE is a small sub-volume of a material that is still large enough to contain all of the necessary geometrical information to obtain the appropriate homogenized behavior. This can be done through either numerical or analytical calculation methods.

Both numerical and analytical methods of continuum micromechanics are used often for preliminary and more precise calculations. The most common and basic analytical methods include the Voigt and Reuss methods. The Voigt method is used when strains are constant in a composite and is a rule of mixtures for stiffness components. In contrast, the Reuss method is used when stresses are constant in a composite and is a rule of mixtures for compliance components. On the other hand, numerical methods are often based on finite element analysis (or FEA). FEA approximates composite materials using a single repeating volume element which is studied using carefully determined boundary conditions.

For any application, appropriate structural analyses and calculations need to be completed to ensure that the materials used can withstand the stresses and strains exerted on them by the situation.

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Updated on January 17, 2018

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