Accepted Manuscripts

Jin Chul Yun and Seong Jin Park
J. Eng. Mater. Technol   doi: 10.1115/1.4036709
In this study, a representative volume element (RVE) homogenization approach is proposed to predict the transversely isotropic elasticity of a lithium-ion battery (LIB) cell, module, and pack in an electric vehicle. Different RVE models for the LIB jellyroll and module are suggested. Various elastic properties obtained from RVE analyses were compared to the analytic solution. To validate the approach suggested, the elastic responses of two types of homogenized LIB module for various loading cases were compared to the model where all the jellyroll and module components were described fully. Additionally, parametric studies were conducted to determine the relationship between design parameters of the jellyroll components and the elastic behavior of LIB jellyroll and module. The results obtained in this study provide useful information for both LIB cell developers, at the concept design stage, and engineers of electric vehicles who want to predict the mechanical safety of a battery pack.
TOPICS: Elasticity, Lithium-ion batteries, Design, Electric vehicles, Batteries, Safety, Engineers
Najmul H. Abid, Rashid K. Abu Al-Rub and Anthony Palazotto
J. Eng. Mater. Technol   doi: 10.1115/1.4036687
This paper focuses on micromechanical finite element modeling the effects of size and morphology (particularly elongation or aspect ratio along the loading direction) of martensite particles and the ferrite grains on the overall mechanical behavior of dual-phase steels. To capture the size-effect of the martensite particles and ferrite grains, the core and mantle approach is adapted in which a thin interphase of geometrically necessary dislocations is embedded at the martensite-ferrite boundaries. It is shown that as the martensite particles size decreases or their aspect ratio increases, both the strength and ductility of DP steel increase simultaneously. On the other hand, as the ferrite grain size decreases or its aspect ratio increases, the overall strength increases on the expense of the ductility. The conclusions from this study can be used in guiding the microstructural design of dual-phase steels.
TOPICS: Grain boundaries, Ferrites (Magnetic materials), Finite element analysis, Mechanical behavior, Steel, Particle size, Particulate matter, Ductility, Design, Modeling, Elongation, Dislocations, Grain size, Size effect
Ingrid Padilla Espinosa, Wayne Hodo, John S. Rivas Murillo, Arunachalam M. Rajendran and Ram Mohan
J. Eng. Mater. Technol   doi: 10.1115/1.4036588
Cement paste is a material with heterogeneous composite structure consisting of hydrated and unhydrated phases at all length scales that varies depending upon the degree of hydration. In this paper, a method to model cement paste as a multi-phase system at molecular level for predicting constitutive properties and for understanding the constitutive mechanical behavior characteristics using molecular dynamics is presented. The proposed method creates a framework for molecular level models suitable for predicting constitutive properties of heterogeneous cement paste that could provide potential for comparisons with low length scale experimental characterization techniques. The molecular modeling method followed two approaches, one involving admixed molecular phases, and the second involving clusters of the individual phases. In particular, in the present study, cement paste is represented as two-phase composite systems consisting of the calcium silicate hydrate (CSH) phase combined with unhydrated phases tricalcium silicate (C3S) or dicalcium silicate (C2S). Predicted elastic stiffness constants based on molecular model representations employed for the two phases showed that, although the individual phases have anisotropic characteristics, the composite system behaves as an isotropic material. The isotropic characteristics seen from two-phase molecular models mimic the isotropic material nature of heterogeneous cement paste at engineering scale. Further, predicted bulk modulus of the composite system based on molecular modeling is found to be high compared to the elastic modulus, which concurs with the high compression strength of cement paste seen at engineering length scales.
TOPICS: Composite materials, Cements (Adhesives), Molecular dynamics, Stiffness, Modeling, Elastic moduli, Experimental characterization, Bulk modulus, Compressive strength, Mechanical behavior, Anisotropy

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