ASME 1992 Nadai Lecture—Micromechanics of Inelastic Composite Materials: Theory and Experiment

1993 ◽  
Vol 115 (4) ◽  
pp. 327-338 ◽  
Author(s):  
George J. Dvorak
Keyword(s):  
Composite Materials ◽  
General Procedure ◽  
Local Fields ◽  
Field Analysis ◽  
Plastic Strains ◽  
Inelastic Behavior ◽  
Aluminum Composite ◽  
Plastic Strain Increment ◽  
Multiphase Materials ◽  
Transformation Field Analysis

Some recent theoretical and experimental results on modeling of the inelastic behavior of composite materials are reviewed. The transformation field analysis method (G. J. Dvorak, Proc. R. Soc. London, Series A437, 1992, pp. 311–327) is a general procedure for evaluation of local fields and overall response in representative volumes of multiphase materials subjected to external thermomechanical loads and transformations in the phases. Applications are presented for systems with elastic-plastic and viscoelastic constituents. The Kroner-Budiansky-Wu and the Hill self-consistent models are corrected to conform with the generalized Levin formula. Recent experimental measurements of yield surfaces and plastic strains on thin-walled boron-aluminum composite tubes are interpreted with several micromechanical models. The comparisons show that unit cell models can provide reasonably accurate predictions of the observed plastic strains, while models relying on normality of the plastic strain increment vector to a single overall yield surface may not capture the essential features of the inelastic deformation process.

Transformation field analysis of inelastic composite materials

1992 ◽  
Vol 437 (1900) ◽  
pp. 311-327 ◽  
Keyword(s):  
Composite Materials ◽  
Micromechanical Model ◽  
Preceding Paper ◽  
Local Stress ◽  
Local Fields ◽  
Field Analysis ◽  
Governing System ◽  
Transformation Field Analysis ◽  
Exact Relations ◽  
Inelastic Strains

A new method is proposed for evaluation of local fields and overall properties of composite materials subjected to incremental thermomechanical loads and to transformation strains in the phases. The composite aggregate may consist of many perfectly bonded inelastic phases of arbitrary geometry and elastic material symmetry. In principle, any inviscid or time-dependent inelastic constitutive relation that complies with the additive decomposition of total strains can be admitted in the analysis. The governing system of equations is derived from the representation of local stress and strain fields by novel transformation influence functions and concentration factor tensors, as discussed in the preceding paper by G. J. Dvorak and Y. Benveniste. The concentration factors depend on local and overall thermoelastic moduli, and can be evaluated with a selected micromechanical model. Applications to elastic-plastic, viscoelastic, and viscoplastic systems are discussed. The new approach is contrasted with some presently accepted procedures based on the self-consistent and Mori—Tanaka approximations, which are shown to violate exact relations between local and overall inelastic strains.

Implementation of the transformation field analysis for inelastic composite materials

1994 ◽  
Vol 14 (3) ◽  
pp. 201-228 ◽  
Author(s):  
G. J. Dvorak ◽  
A. M. Wafa ◽  
Y. A. Bahei-El-Din
Keyword(s):  
Composite Materials ◽  
Field Analysis ◽  
Transformation Field Analysis

scholarly journals Effective potentials in nonlinear polycrystals and quadrature formulae

2017 ◽  
Vol 473 (2204) ◽  
pp. 20170213 ◽  
Author(s):  
Jean-Claude Michel ◽  
Pierre Suquet
Keyword(s):  
Order Approximation ◽  
High Stress ◽  
Stress Triaxiality ◽  
Local Fields ◽  
Field Analysis ◽  
Effective Potentials ◽  
Quadrature Formulae ◽  
Highly Nonlinear ◽  
Transformation Field Analysis ◽  
High Stress Triaxiality

This study presents a family of estimates for effective potentials in nonlinear polycrystals. Noting that these potentials are given as averages, several quadrature formulae are investigated to express these integrals of nonlinear functions of local fields in terms of the moments of these fields. Two of these quadrature formulae reduce to known schemes, including a recent proposition (Ponte Castañeda 2015 Proc. R. Soc. A 471 , 20150665 ( doi:10.1098/rspa.2015.0665 )) obtained by completely different means. Other formulae are also reviewed that make use of statistical information on the fields beyond their first and second moments. These quadrature formulae are applied to the estimation of effective potentials in polycrystals governed by two potentials, by means of a reduced-order model proposed by the authors (non-uniform transformation field analysis). It is shown how the quadrature formulae improve on the tangent second-order approximation in porous crystals at high stress triaxiality. It is found that, in order to retrieve a satisfactory accuracy for highly nonlinear porous crystals under high stress triaxiality, a quadrature formula of higher order is required.

Micromechanical Modeling of Multifunctional Composites

2012 ◽  
Author(s):  
Yehia Bahei-El-Din ◽  
Amany Micheal
Keyword(s):  
Composite Materials ◽  
Local Fields ◽  
Field Analysis ◽  
Micromechanical Modeling ◽  
Current Application ◽  
Temperature Changes ◽  
Ambient Temperatures ◽  
Material Development ◽  
Analysis Scheme ◽  
And Performance

In the new generation of aircrafts in which the use of composite materials is ever increasing, smart composites reinforced with active fibers are expected to play a major role in monitoring health and performance of the airframe in addition to their load carrying capabilities. While advancements in material development, e.g. PZT filaments, bring the fabrication of structural components with multifunctionality closer to reality, reliable predictions of their behavior and performance are lacking. In particular, the modeling of damage progression on multiple lengthscales in structural composites is essential in modeling both sensing and/or actuation functionalities. Moreover, temperature changes affect the response of active constituents through changes in thermomechanical fields and/or changes in coupled functions, as for example in pyroelectric materials. These complexities invite a novel modeling approach of the problem. This paper represents a major departure from present approaches, which focus mainly on undamaged, unidirectionally reinforced multifunctional fibrous composites at ambient temperatures. The work presented models multifunctional composite materials and structures on multiscales considering piezoelectric and pyroelectric phenomena. In particular, fibrous laminates with a general layup are considered under membrane forces and bending moments in combination with temperature changes. The solution for the local fields and overall response is determined in terms of a transformation field analysis scheme in which the local stresses or strains that cannot be removed by mechanical unloading are treated as eigen fields applied in an otherwise elastic medium. In the current application, the latter represents an aggregate of unidirectional plies and their phases. The proposed modeling strategy is applied to fibrous laminates subjected to mechanical and/or thermal loads. While the modeling of damage follows the same strategy, it is discussed elsewhere.

Transmission electron microscopy of composite materials

1988 ◽  
Vol 46 ◽  
pp. 1012-1015
Author(s):  
K.P.D. Lagerlof
Keyword(s):  
Composite Materials ◽  
Physical Properties ◽  
Structural Defects ◽  
Structural Composites ◽  
Multiphase Materials ◽  
Structural Reinforcement ◽  
Transmission Electron ◽  
Reinforced Fiber ◽  
Particulate Reinforced Composites ◽  
Definition Of

Although most materials contain more than one phase, and thus are multiphase materials, the definition of composite materials is commonly used to describe those materials containing more than one phase deliberately added to obtain certain desired physical properties. Composite materials are often classified according to their application, i.e. structural composites and electronic composites, but may also be classified according to the type of compounds making up the composite, i.e. metal/ceramic, ceramic/ceramie and metal/semiconductor composites. For structural composites it is also common to refer to the type of structural reinforcement; whisker-reinforced, fiber-reinforced, or particulate reinforced composites [1-4].For all types of composite materials, it is of fundamental importance to understand the relationship between the microstructure and the observed physical properties, and it is therefore vital to properly characterize the microstructure. The interfaces separating the different phases comprising the composite are of particular interest to understand. In structural composites the interface is often the weakest part, where fracture will nucleate, and in electronic composites structural defects at or near the interface will affect the critical electronic properties.

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