Constitutive Behavior

Over the last 30 years NRL's Composite Materials and Structures (CMS) group has been developing a data driven system identification inverse approach for characterizing the constitutive behavior of polymer matrix composites (PMCs). The core concept in this approach has been the experimental identification of a dissipated energy density (DED) function. This is achieved through establishing a non-linear optimization scheme for

In our previous paper [1], a constitutive model was developed for the stress-induced martensitic transformation and
reorientation in single crystalline shape memory alloys. The critical condition and evolution equation for the phase transformation
and reorientation were proposed. In this paper, the model proposed in our previous paper [1] is applied to simulate the behavior of
stress-induced phase transformation in a CuZnAl single crystal and reorientation between CuAlNi martensite lattice correspondence
variants. It is found out that the prediction results are consistent with the experimental data reported in the literature.

The recently proposed neo-classical theory for nematic elastomers is a molecular-statistical generalization of classical Gaussian network theory. The resulting free-energy density pre-dicts the phenomenon of soft elasticity—the ability of elastomers to undergo large deforma-tions with zero force and energy cost. The theory, however, suffers from several drawbacks: (i) extreme non-uniqueness as zero applied force corresponds to infinitely many possible deformations, (ii) insufficient moduli to model observed experimental behavior, and (iii) physically, a small, but non-zero, force must be applied. Here we propose an alternative continuum model for nematic elastomers that removes these drawbacks. Motivated by the molecular-statistical theory, we identify microstructural degrees of freedom as well as two independent strain tensors (the overall macroscopic strain plus a relative strain that indicates how the deformation of the elastomeric microstructure deviates from the macro-scopic de...

Although several theoretical and experimental models have been developed for abrasive waterjet machining (AWJM), the exact nature of erosion is not yet understood. This paper presents an attempt to model AWJM using the finite element method (FEM) in order to explain the abrasive particle–workpiece interaction process. Also, the model predicts the depth of deformation as a result of abrasive particle impact. The main objective is to develop an FE model which would enable the prediction of the depth of cut without any cutting experiments. The new model takes into account the precise representation of the constitutive behavior of the workpiece material under AWJ dynamic loading conditions which was ignored in the previous AWJM models. In the present model, forces acting on the abrasive particle need not be initially determined, as in previous AWJM studies, as they are automatically calculated at each time step. The results show that plastic deformation is very localized. Finally, the present FE results are consistent with experimental results.

A continuum damage mechanics model previously developed to model the tensile response of composites has been further enhanced to simulate their nonlinear constitutive behavior under compressive loading. The refinements were based on the behavior of an analog model, which was constructed to represent the complete force—displacement response of a representative volume element of the material. The updated constitutive model accounts for mechanisms considered to be characteristic of compressive damage growth in laminated composites, such as matrix cracking, fiber kinking, and delamination. The constitutive model was implemented in the commercial explicit finite element code, LS-DYNA, and is used here to predict the quasi-static compressive response of open-hole laminates as well as the dynamic axial crushing of braided composite tubes. It is shown that the model adequately captures: (1) the damage growth and local strain fields in open-hole specimens, and (2) the failure characteristics...

A nonlinear model has been formulated to predict the compressive stress-strain behaviour of strand-based wood composites based on the constitutive properties of the wood strands. Prediction models of this type are indispensable for the advancement of wood composite materials, not only for the development of new products but also for specific application design. Ultimately, they can be used to gauge the effect of varying raw material characteristics with limited fabrication and testing of the full scale product, resulting in tremendous savings in cost and time. The model requires, as input, an experimental database of the two-dimensional orthotropic, constitutive properties of 2.5 x 19 mm Douglas-fir strands, as well as small laminated wood composites. A materially nonlinear finite element code with extended capacity to perform Monte Carlo simulations has been developed. The nonlinear constitutive behaviour of the wood strands is characterized within the framework of rate-independent...

... constructs an anxiety hierarchy, a ranked list of stimuli to which the patient reacts with anxiety. ... We should stress that our quarrel is not with the techniques themselves but with the attempt to tie these techniques to principles and concepts from the field of learning. ...

... Permissions & Reprints. Multiresolution analysis for material design. ... The resulting homogenized constitutive relationship can then be applied through a conventional continuum framework to find the resulting material properties such as toughness and strength. ...

From pharmaceutical to mining or traveling desert dunes to earthquakes, granular materials are at the heart of many industries and natural phenomena. Improving the efficiency of the machines handling them or, constructing safer buildings requires a critical understanding of their behavior. However, this is not a straightforward task as opposed to what one might think due to the abundance of particulate matter. From a fundamental point of view, it has been only recently realized that they cannot be easily classified as a solid or liquid or even a gas as they are able to mimic all of these states under slightly different conditions. The challenge of the scientific research today, is to establish the link between the collective behavior and properties of individual particles composing granular materials.Such a relation would enable to characterize them with only a few parameters in contrast to billions of particles typically found in practice. In the first part of this thesis, we study...

A model for the macroscopic mechanical behavior of porous shape memory alloys (SMAs) is presented in this work. The derivation of the model is presented for the general case of a composite with phases undergoing rate-independent inelastic de-formations. Micromechanical averaging techniques are used to establish the effective elastic and inelastic behavior based on information about the mechanical response of the individual phases and shape and volume fraction of the inhomogeneities. An explicit expression for the effective tangent stiffness and an evolution equation for the effective inelastic strain are derived. The results for porous SMAs are obtained using a constitutive model with internal variables for dense SMAs and assuming zero stiffness for the inhomogeneities. A detailed study on the choice of the pore shape is also performed for a random distribution of pores. Finally, the numerical results are compared with experimental data for porous NiTi SMA processed from elemental p...

We report the cloning and characterization in tobacco and Arabidopsis of a Vigna radiata L. (mung bean) promoter that controls the expression of VR-ACS1, an auxin-inducible ACC synthase gene. The VR-ACS1 promoter exhibits a very unusual behavior when studied in plants ...

Nanoindentation data measured on the cell-wall of Al-alloy foams were analyzed to obtain the material properties of the cell wall. Using the obtained material properties, stress-strain curve of the foam in uniaxial compression was constructed by finite element modeling. The model developed for the analysis was a multiple cell model which utilized the unit cells as the basic building block of the foam. Both the in-plane and through-thickness density variations of the foam were considered in the model. The through-thickness density variation which is a function of casting or foaming process was represented using different densities for different foam layers, while the in-plane density variation which arises from internal defects (such as porosities, second phase particle, inclusions etc.) was assumed to follow a statistical probability distribution of Gaussian type. Uniaxial compression test was performed and the finite element analysis result was compared with the experimental result. The numerical model used in the study overpredicted the crushing strength of foams indicating that the model needs to be improved for predicting the real foam properties with better accuracy.