Material behavior computer modeling

Segmental Behavior. The understanding of segmental behavior is clearly a critical factor in many of the frontiers discussed, both because synthetic capability has broadened the potential array of new materials and because this understanding is a vital key in predicting the physical behavior and uses of polymeric materials. With computer modeling, significant improvements in this area can be achieved. 

Fig. 7 gives an example of such a comparison between a number of different polymer simulations and an experiment. The data contain a variety of Monte Carlo simulations employing different models, molecular dynamics simulations, as well as experimental results for polyethylene. Within the error bars this universal analysis of the diffusion constant is independent of the chemical species, be they simple computer models or real chemical materials. Thus, on this level, the simplified models are the most suitable models for investigating polymer materials. (For polymers with side branches or more complicated monomers, the situation is not that clear cut.) It also shows that the so-called entanglement length or entanglement molecular mass Mg is the universal scaling variable which allows one to compare different polymeric melts in order to interpret their viscoelastic behavior. 

Avoiding structural failure can depend in part on the ability to predict performance of materials. When required designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied upon previously. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. This information is supported by stress-strain behavior data collected in actual materials evaluations. 

The computational methods have replaced the oversimplified models of material behavior formerly relied on. However, for new and very complex product structures that are being designed to significantly reduce the volume of materials used and in turn the product cost, computer analysis is conducted on prototypes already fabricated and undergoing testing. This computer approach can result in early and comprehensive analysis of the effects of conditions such as temperature, loading rate, environment, and material... 

There is an increased use of flammability tests, which measure fundamental properties as opposed to tests that simulate a specific fire scenario. The former can be used in conjunction with mathematical models to predict the performance of a material in a range of fire scenarios. This approach has become feasible due to the significant progress that has been made in the past few decades in our understanding of the physics and chemistry of fire, mathematical modeling of fire phenomena and measurement techniques. However, there will always be materials that exhibit a behavior that cannot be captured in bench-scale tests and computer models. The fire performance of those materials can only be determined in full-scale tests. 

Materials in the macroscopic sense follow laws of continuum models in which the nanoscale phenomenon is accounted for by statistical averages. Continuum models and analysis separate materials into solids (structures) and fluids. Computational solid mechanics and structural mechanics emphasize the analysis of solid materials and its structural design. Computational fluid mechanics treats material behaviors that involve the equilibrium and motion of liquid and gases. A relative new area, called multiphysics, includes materials systems that contain interacting fluids and structures such as phase changes (solidification, melting), or interaction of control, mechanical and electromagnetic (MEMS, sensors, etc.). 

Fig. 6 Plot of membrane tension t as a function of dilation for a wide range of copolymer amphiphiles as extracted from MD simulations. The computational models, derived from systematic coarse-graining (black symbols), show nearly the same dilational behavior marked by the solid line. The slope of the line, ka, is very close to experimental measurements performed on giant vesicles 0colored symbols). Experimental data for a dimyristoyl phosphatidylcholine lipid membrane are also shown. The point of membrane lysis as observed experimentally for selected lipid and polymersome systems is also shown in the plot with green and red stars, respectively. Reprinted by permission from Macmillan Publishers Ltd Nature Materials, Ref. [85], copyright (2004)...

Many fundamental properties are themselves amenable to computation if suitable models are available. However, experimental data is required in order to verify the models and establish reliability estimates. Research of this nature is not commonly performed on a sufficiently wide scale to improve the predictive ability of many important models of material behavior. Additional emphasis must be placed on acquiring this information to meet the requirements of the revolution in materials design... 

Because these developments are focused on intended applications in other fields and not problems of LMFR design there are significant differences in design lives, service conditions, materials, manufacturing practices, etc. The types of structures differ. The impact of these differences on such design information as constitutive models, material failure modes and models, and structural failure modes and consequences are sometimes difficult to assess. However, computer modeling, structural analyses methods, and analytic methods to understand materials behavior have advanced greatly in some of these non nuclear areas. 

The accuracy of the simulation results is given mainly by the accuracy of the material model. In the last years, the scientific research is oriented in developing of new material models able to describe the material behavior (mainly the anisotropic one) as accurate as possible (Barlat et al. 2004 Banabic 2010 Banabic et al. 2010). The computer simulation of the sheet metal forming processes needs a quantitative description of the plastic anisotropy by the yield locus. 

A. Saigal, E.R. Fuller, S. Jahanmir, Modeling of Residual Stresses and Mechanical Behavior of Glass-Infiltrated Spinel Ceramic Composites, Computational Modelling of Materials, Minerals and Metals Processing, (ed M. Cross, J.W. Evans and C. Bailey), TMS, (2001). 

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