scholarly journals Techniques for Identification of Bending and Extensional Elastic Stiffness Matrices on Thin Composite Material Plates Based on Virtual Field Method (VFM): Theoretical and Numerical Aspects

10.5772/18414 ◽  
2011 ◽  
Author(s):  
Fabiano Bianchini ◽  
Eder Lima de Albuquerque
Keyword(s):  
Composite Material ◽  
Elastic Stiffness ◽  
Field Method ◽  
Stiffness Matrices ◽  
Virtual Field

The Effect of Nanotube Waviness and Agglomeration on the Elastic Property of Carbon Nanotube-Reinforced Composites

2004 ◽  
Vol 126 (3) ◽  
pp. 250-257 ◽  
Author(s):  
Dong-Li Shi ◽  
Xi-Qiao Feng ◽  
Yonggang Y. Huang ◽  
Keh-Chih Hwang ◽  
Huajian Gao
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Effective Properties ◽  
High Strength ◽  
Elastic Stiffness ◽  
Field Method ◽  
Effective Field ◽  
Great Promise ◽  
Reinforced Composites ◽  
Stiffening Effect

Owing to their superior mechanical and physical properties, carbon nanotubes seem to hold a great promise as an ideal reinforcing material for composites of high-strength and low-density. In most of the experimental results up to date, however, only modest improvements in the strength and stiffness have been achieved by incorporating carbon nanotubes in polymers. In the present paper, the stiffening effect of carbon nanotubes is quantitatively investigated by micromechanics methods. Especially, the effects of the extensively observed waviness and agglomeration of carbon nanotubes are examined theoretically. The Mori-Tanaka effective-field method is first employed to calculate the effective elastic moduli of composites with aligned or randomly oriented straight nanotubes. Then, a novel micromechanics model is developed to consider the waviness or curviness effect of nanotubes, which are assumed to have a helical shape. Finally, the influence of nanotube agglomeration on the effective stiffness is analyzed. Analytical expressions are derived for the effective elastic stiffness of carbon nanotube-reinforced composites with the effects of waviness and agglomeration. It is found that these two mechanisms may reduce the stiffening effect of nanotubes significantly. The present study not only provides the relationship between the effective properties and the morphology of carbon nanotube-reinforced composites, but also may be useful for improving and tailoring the mechanical properties of nanotube composites.

An efficient seismic modeling in viscoelastic isotropic media

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. T63-T81 ◽  
Author(s):  
Renhu Yang ◽  
Weijian Mao ◽  
Xu Chang
Keyword(s):  
Seismic Waves ◽  
Linear Equations ◽  
Viscoelastic Body ◽  
Elastic Stiffness ◽  
Momentum Conservation ◽  
Stiffness Matrices ◽  
Isotropic Media ◽  
Linear Viscoelastic ◽  
Standard Linear ◽  
Viscoelastic Modeling

Energy is absorbed and attenuated when seismic waves propagate in real earth media. Hence, the viscoelastic medium needs to be considered. There are many ways to construct the viscoelastic body, in which the generalized standard linear viscoelastic body is the most representative one. For viscoelastic wave propagation and imaging, it is very important to obtain a compact and efficient viscoelastic equation. Because of this, we derived a set of simplified viscoelastic equations in isotropic media on the basis of the standard linear solid body and the constitutive relation for a linear viscoelastic isotropic solid. The simplified equations were composed of the linear equations of momentum conservation, the stress-strain relations, and the memory variable equations. During the derivation of the equations, the Lamé differentiation matrix, which has a similar form to the stiffness matrix and indicates the relations between viscoelastic and elastic stiffness matrices, was introduced to simplify the memory variable equations. Analogous to the elastic equations, the simplified equations have symmetrically compact forms and are very useful for efficient viscoelastic modeling, migration, and inversion. Applied to a 2D simple model and the 2D SEG/EAGE salt model, the results show that our simplified equations are more efficient in computation than Carcione’s equations.

scholarly journals Identification of Materials Properties Using Displacement Field Measurement

2011 ◽  
Vol 482 ◽  
pp. 57-65 ◽  
Author(s):  
Marina Fazzini ◽  
Olivier Dalverny ◽  
Sébastien Mistou
Keyword(s):  
Finite Element ◽  
Displacement Field ◽  
Model Updating ◽  
Virtual Work ◽  
Field Measurements ◽  
Element Model ◽  
Field Method ◽  
Element Analysis ◽  
Virtual Field ◽  
Constitutive Parameters

The aim of this work is to identify parameters driving constitutive equations of materials with displacement field measurements carried out by image stereo-correlation during an unidirectional tensile test. We evaluate two identification techniques. The first one is the virtual fields method which consists in writing the principle of virtual work with particular virtual fields. It is generally used in the case of linear elasticity and it requires a perfect knowledge of the model in terms of boundary condition since the virtual fields used must be kinematically admissible. This method allows to determine parameters by a direct and fast calculation, without iterations. The second method is the finite element model updating method. It consists in finding constitutive parameters that achieve the best match between finite element analysis quantities and their experimental counterparts. This method is more adaptable than the virtual field method but it needs to spend more calculation time.

Rigid latticed steel frames: two large-scale tests and failure predictions

1987 ◽  
Vol 14 (5) ◽  
pp. 602-613 ◽  
Author(s):  
John S. Ellis
Keyword(s):  
Cross Section ◽  
Large Scale ◽  
Static Load ◽  
Yield Criterion ◽  
Elastic Stiffness ◽  
Free Standing ◽  
Stiffness Matrices ◽  
Failure Loads ◽  
Uniform Cross Section ◽  
Large Scale Tests

This work is concerned with the predictions of failure under static load for two identical free-standing latticed cantilever frames. Each structure was 3 m high and consisted of three storeys with panel points 1 m apart; in plan it was 1 m2; its diagonals were at 45° in the form of St. Andrew's cross; all joints were welded and were considered rigid. The four bases were bolted to the laboratory floor and the static load was applied at the top as two compressive horizontal forces parallel to the sides of the structure. The individual members were all solid mild steel round rods; the verticals were of uniform cross section of 25.4 mm in diameter with a slenderness of 157; the horizontal cross-arms were of uniform cross section of 19 mm in diameter; and the diagonals were of uniform cross section of 15.9 mm in diameter. The diagonals were cut at their mid-lengths and welded to give a flush joint.The total horizontal loads that caused failure of the two structures were 79.6 and 79.2 kN. In both cases failure occurred by the sudden buckling of one of the bottom-storey vertical legs, inwards towards the centre of the structure. Also upon failure, the diagonals in the bottom storey of the compression face buckled inwards and the compression diagonal of the side contiguous to the buckled leg also buckled.Three elastic stiffness matrices were used to predict the failure loads: (1) linear with yield criterion, 116 kN; (2) stability with change in sign of the total potential energy, 66 kN; and (3) bowing with the criterion of maximum curvature of the load–deflection curve, 80 kN. The failure loads of the two structures were thus accurately predicted by the bowing matrix. Key words: latticed rigid frames, large-scale tests, bowing matrix, steel.

Elastic constants and Debye temperature of polycrystalline Y1Ba2Cu3O7−x

1987 ◽  
Vol 2 (6) ◽  
pp. 786-789 ◽  
Author(s):  
H. M. Ledbetter ◽  
M. W. Austin ◽  
S. A. Kim ◽  
Ming Lei
Keyword(s):  
Composite Material ◽  
Elastic Constants ◽  
Building Block ◽  
Oxygen Vacancies ◽  
Mass Density ◽  
Characteristic Temperature ◽  
Material Model ◽  
Elastic Stiffness ◽  
Ultrasonic Methods ◽  
Apparent Stiffness

Using ultrasonic methods, the quasi-isotropic elastic stiffnesses of void-containing Y1Ba2Cu3O7−x were determined By a composite-material model, these were corrected to the void-free state. From these, the Debye characteristic temperature was calculated. All the elastic stiffnesses fall well below those of polycrystalline BaTiO3, an approximate crystalstructural building block of Y1Ba2Cu3O7−x. The low apparent stiffness may result from oxygen vacancies, which soften interionic forces. Also, it may result from microcracks, which reduce elastic stiffness without lowering mass density.

scholarly journals Mori–Tanaka Formalism-Based Method Used to Estimate the Viscoelastic Parameters of Laminated Composites

Polymers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 2481
Author(s):  
Mostafa Katouzian ◽  
Sorin Vlase
Keyword(s):  
Composite Material ◽  
Least Squares Method ◽  
Mean Field ◽  
Field Method ◽  
Engineering Practice ◽  
Computation Method ◽  
Creep Tests ◽  
Compliance Matrix ◽  
Viscoelastic Composite ◽  
Viscoelastic Composite Material

The paper establishes the mechanical properties of a viscoelastic composite material reinforced with fibers, where the fiber is transverse isotropic and the matrix is isotropic (a common case met in engineering practice). A computation method using the Mori–Tanaka mean field method has been developed in order to apply on viscoelastic materials. Using this procedure, the time-dependent response of a viscoelastic composite material can be determined. Schapery’s nonlinear constitutive equation is also used in the compliance matrix determination of the composite material under investigation. Nonlinearity factors were determined by creep tests at different values of stresses and temperatures and for different materials, based on the least squares method. The results obtained experimentally and their comparison with the theoretically obtained values show a good agreement between experiment and calculation.

Parametric Instability of Laminated Composite Doubly Curved Shell Panels Subjected to Hygrothermal Environment

2011 ◽  
Vol 383-390 ◽  
pp. 3212-3216
Author(s):  
S. K. Sahu ◽  
M. K. Rath ◽  
R. Sahoo
Keyword(s):  
Dynamic Stability ◽  
Degrees Of Freedom ◽  
Parametric Instability ◽  
Laminated Composite ◽  
Elastic Stiffness ◽  
Composite Shells ◽  
Stiffness Matrices ◽  
Different Temperatures ◽  
Doubly Curved ◽  
Laminated Composite Shells

The dynamic stability behavior of laminated composite shells subjected to hygrothermal loadings are studied in the present investigation. A simple laminated model is developed for the vibration and stability analysis of laminated composite shells subjected to hygrothermal conditions. A computer program based on FEM in MATLAB environment is developed to perform all necessary computations. An eight-node isoparametric element is employed in the present The analysis with five degrees of freedom per node. Element elastic stiffness matrices, mass matrices, geometric stiffness matrix due to mechanical and hygrothermal loads and load vectors are derived using the principle of minimum potential energy. Quantitative results are presented to show the effects of curvature, ply-orientation, degrees of orthotropy and static load factors of laminate on dynamic stability of composite shells for different temperatures and moisture concentrations.

scholarly journals Upscaling the elastic stiffness of foam concrete as a three-phase composite material

2018 ◽  
Vol 110 ◽  
pp. 13-23 ◽  
Author(s):  
M. Ben Youssef ◽  
F. Lavergne ◽  
K. Sab ◽  
K. Miled ◽  
J. Neji
Keyword(s):  
Composite Material ◽  
Elastic Stiffness ◽  
Foam Concrete ◽  
Three Phase
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