Micromechanics

About: Micromechanics is a research topic. Over the lifetime, 6000 publications have been published within this topic receiving 162635 citations.

Computational micromechanics of dynamic compressive loading of a brittle polycrystalline material using a distribution of grain boundary properties

Abstract: A two-dimensional finite element model is used to investigate compressive loading of a brittle ceramic. Intergranular cracking in the microstructure is captured explicitly by using a distribution of cohesive interfaces. The addition of confining stress increases the maximum strength and if high enough, can allow the effective material response to reach large strains before failure. Increasing the friction at the grain boundaries also increases the maximum strength until saturation of the strength is approached. Above a transitional strain rate, increasing the rate-of-deformation also increases the strength and as the strain rate increases, fragment sizes of the damaged specimen decrease. The effects of flaws within the specimen were investigated using a random distribution at various initial flaw densities. The model is able to capture an effective modulus change and degradation of strength as the initial flaw density increases. Effects of confinement, friction, and spatial distribution of flaws seem to depend on the crack coalescence and dilatation of the specimen, while strain-rate effects are result of inertial resistance to motion.

Micro-mechanics of crack initiation

Abstract: Prior to the crack initiation, damage is most often localized at a scale below the size of the classical representative volume element of the continuum mechanics. This allows the stress and strain analyses in a component to neglect the strain-damage coupling at macro-scale. At the micro-scale, this coupling plays a very important role which can be emphasized by a two scale element of an elastoplastic damaged micro-element embedded in an elastic or elastoplastic macro-element. The Lin-Taylor hypothesis of strain compatibility allows the determination of the damage at micro-scale by solving the coupled constitutive equations for a given macro-strain history. It is shown how this model may be cast in the form of a post-processor of a finite element code and how a simple damage law coupled with strain constitutive equations replicates the main features of ductile or creep crack initiation, low cycle and high cycle fatigue for the case of a three-dimensional state of stress.

Direct numerical simulation of 3D woven textile composites subjected to tensile loading: An experimentally validated multiscale approach

Abstract: An experimentally validated multiscale computational model for predicting the progressive damage and failure analysis (PDA) of 3D woven textile composites (3DWTCs), is presented. The 3DWTCs are made through a 3D textile weaving process and the dry fiber tows are infused with SC-15 polymer matrix into a single composite material. A thick symmetric configuration of hybridized (carbon, glass and kevlar tows) textile architecture is examined at the entire coupon level to determine the progression of damage under tensile loading and to understand the benefits of hybridization and the resulting performance enhancements. Results also include micro-CT analysis of the laboratory scale coupon to study the effect of microstructure imperfections response. A finite element (FE) model is generated directly from micro-CT data using the software, Simpleware [1]. A three-scale modeling strategy is adopted, where the meso-scale representative volume elements (RVEs) are modeled explicitly in the failure prone gage-area to consider the tow architecture and a 2-layer concentric cylinder (2CYL) [2,3] micromechanics model is used within the fiber tows to consider the fiber/matrix scale and the pre-peak nonlinearity, as caused by matrix microdamage. The analytical subscale model results in a computationally efficient framework for PDA of 3DWTCs.

Multiscale modeling of the effects of nanoscale load transfer on the effective elastic properties of unfunctionalized carbon nanotube-polyethylene nanocomposites

Abstract: A multiscale model is proposed to study the macroscale bulk elastic material properties under the influence of interfacial load transfer at the nanoscale in carbon nanotube?polyethylene (CNT?PE) nanocomposites. Molecular dynamic (MD) simulations are performed to characterize the nanoscale load transfer through the identification of representative nanoscale interface elements which are studied parametrically in terms of the length of the polymer chains, the number of the polymer chains and the ?grip? position. Once appropriate scales of these parameters are deemed to yield sufficiently converged results, the representative interface elements are subjected to normal and sliding mode simulations in order to obtain the force?separation responses at 100 and 300?K for unfunctionalized CNT?PE interfaces. Cohesive zone traction?displacement laws are developed based on the force?separation responses obtained from the MD simulations and are used in continuum level models to determine the influence of the interface on the effective elastic material properties of the nanocomposites using analytic and computational micromechanics approaches. It is found that the inclusion of the nanoscale interface in place of the perfectly bonded interface results in effective elastic properties which are dependent on the applied strain and temperature in accordance with the interface sensitivity to those effects, and which are significantly diminished from those obtained under the perfect interface assumption.