scholarly journals The Thermal Conductivities of Periodic Fibrous Composites as Defined by a Mathematical Model

2017 ◽  
Author(s):  
John Venetis ◽  
Emilio Sideridis
Keyword(s):  
Reasonable Agreement ◽  
Thermomechanical Properties ◽  
Fibrous Composites ◽  
Multilayer Cylinder ◽  
Cylinder Model ◽  
Theoretical Predictions ◽  
The Matrix ◽  
Unit Cells ◽  
Transverse Thermal Conductivity ◽  
Advanced Model

In this paper, a geometric body-centered model to simulate the periodic structure of unidirectional fibrous composites is presented. To this end, three prescribed configurations are introduced to predict in a deterministic manner the arrangement of internal and neighboring fibers inside the matrix. Thus, three different representative volume elements (RVEs) are established. Furthermore, the concept of the interphase has been taken into account, stating that each individual fiber is encircled by a thin layer of variable thermomechanical properties. Next, these three unit cells are transformed in a unified manner to a coaxial multilayer cylinder model. This advanced model includes the influence of fiber contiguity in parallel with the interphase concept on the thermomechanical properties of the overall material. Then, by the use of this model, the authors propose explicit expressions to evaluate the longitudinal and transverse thermal conductivity of this type of composite. The theoretical predictions were compared with experimental results, as well as with theoretical values yielded by some reliable formulae derived from other workers, and a reasonable agreement was found.

scholarly journals The Thermal Conductivity of Periodic Particulate Composites as Obtained from a Crystallographic Mode of Filler Packing

2018 ◽  
Vol 2 (4) ◽  
pp. 71
Author(s):  
John Venetis ◽  
Emilio Sideridis
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Thermomechanical Properties ◽  
Influential Factors ◽  
Particulate Composites ◽  
Closed Form Expression ◽  
Form Expression ◽  
Theoretical Predictions ◽  
Advanced Model ◽  
Theoretical Results

In this paper, an icosahedral non-body-centered model is presented to simulate the periodic structure of a general class of homogeneous particulate composites, by predicting the particle arrangement. This model yielded three different variations, which correspond to three different deterministic particle configurations. In addition, the concept of a boundary interphase between matrix and inclusions was taken into account. In this framework, the influence of particle vicinity on the thermomechanical properties of the overall material was examined in parallel with the concept of boundary interphase. The simultaneous consideration of these two basic influential factors constitutes the novelty of this work. Next, by the use of this advanced model, the authors derived a closed-form expression to estimate the thermal conductivity of this type of composite. To test the validity of the model, the theoretical predictions arising from the proposed formula were compared with experimental data found in the literature, together with theoretical results obtained from several accurate formulae derived from other workers, and an adequate accordance was observed.

scholarly journals The Thermal Conductivities of Periodic Fibrous Composites as Defined by a Mathematical Model

2017 ◽  
Author(s):  
John Venetis ◽  
Emilio Sideridis
Keyword(s):  
Thermal Conductivity ◽  
Mathematical Model ◽  
Periodic Structure ◽  
Geometric Model ◽  
Thermomechanical Properties ◽  
Fibrous Composites ◽  
Transverse Thermal Conductivity ◽  
Thermal Conductivities

In this paper, an advanced geometric model to simulate the periodic structure of unidirectional fibrous composites is presented. This model takes into consideration the influence of fiber contiguity in parallel with the concept of interphase on the thermomechanical properties of the overall material. Next, by the use of this model the authors propose closed – form expressions to estimate the longitudinal and transverse thermal conductivity of this type of composites.

scholarly journals An Upper Bound of Longitudinal Elastic Modulus for Unidirectional Fibrous Composites as Obtained from Strength of Materials Approach

Fibers ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 57
Author(s):  
John Venetis ◽  
Emilio Sideridis
Keyword(s):  
Elastic Modulus ◽  
Upper Bound ◽  
Intermediate Phase ◽  
Analytical Models ◽  
The Novel ◽  
Fibrous Composites ◽  
Strength Of Materials ◽  
Longitudinal Elastic Modulus ◽  
Theoretical Predictions ◽  
The Matrix

In this paper, the authors introduce an upper bound of the longitudinal elastic modulus of unidirectional fibrous composites to strength of materials approach, provided that the fibre is much stiffer than the matrix. In the mathematical derivations resulting in this bound, the concept of boundary interphase between filler and matrix was also taken into consideration. The novel element of this work is that the authors have not taken into account any particular variation law to approach the stiffness of this intermediate phase. The theoretical predictions were compared with those obtained from some accurate analytical models as well as with experimental data found in the literature, and a satisfactory accordance was observed.

scholarly journals Prediction of Effective Thermal Conductivities of Four-Directional Carbon/Carbon Composites by Unit Cells with Different Sizes

2021 ◽  
Vol 11 (3) ◽  
pp. 1171
Author(s):  
Chang Xu ◽  
Zhihong Sun ◽  
Guowei Shao
Keyword(s):  
Carbon Fiber ◽  
Longitudinal Direction ◽  
Unit Cell ◽  
Carbon Composites ◽  
Temperature Boundary ◽  
The Matrix ◽  
Unit Cells ◽  
Experimental Values ◽  
Different Diameters ◽  
Thermal Conductivities

Two-unit cells developed to predict the effective thermal conductivities of four-directional carbon/carbon composites with the finite element method are proposed in this paper. The smaller-size unit cell is formulated from the larger-size unit cell by two 180° rotational transformations. The temperature boundary conditions corresponding to the two-unit cells are derived, and the validity is verified by the temperature and heat flux distributions at specific positions of the larger-size unit cell and the smaller-size unit cell. The thermal conductivities of the carbon fiber bundles and carbon fiber rods are measured firstly. Then, combined with the properties of the matrix, the effective thermal conductivities of the four-directional carbon/carbon composites are numerically predicted. The results in transverse direction predicted by the larger-size unit cell and the smaller-size unit cell are both higher than experimental values, which are 5.8 to 6.2% and 7.3 to 8.2%, respectively. In longitudinal direction, the calculated thermal conductivities of the larger-size unit cell and the smaller-size unit cell are 6.8% and 6.2% higher than the experimental results, respectively. In addition, carbon fiber rods with different diameters are set to clarify the influence on the effective thermal conductivities of the four-directional carbon/carbon composites.

Failure Mechanisms of Particulate Two-Phase Composites

1998 ◽  
Vol 529 ◽  
Author(s):  
T. Antretter ◽  
E D. Fischer
Keyword(s):  
Residual Stresses ◽  
Crack Growth ◽  
Opening Angle ◽  
Geometrical Parameters ◽  
Two Phase ◽  
Absolute Size ◽  
The Matrix ◽  
Unit Cells ◽  
Angle Criterion ◽  
Probability Of Fracture

AbstractIn many composites consisting of hard and brittle inclusions embedded in a ductile matrix failure can be attributed to particle cleavage followed by ductile crack growth in the matrix. Both mechanisms are significantly sensitive towards the presence of residual stresses.On the one hand particle failure depends on the stress distribution inside the inclusion, which, in turn, is a function of various geometrical parameters such as the aspect ratio and the position relative to adjacent particles as well as the external load. On the other hand it has been observed that the absolute size of each particle plays a role as well and will, therefore, be taken into account in this work by means of the Weibull theory. Unit cells containing a number of quasi-randomly oriented elliptical inclusions serve as the basis for the finite element calculations. The numerical results are then correlated to the geometrical parameters defining the inclusions. The probability of fracture has been evaluated for a large number of inclusions and plotted versus the particle size. The parameters of the fitting curves to the resulting data points depend on the choice of the Weibull parameters.A crack tip opening angle criterion (CTOA) is used to describe crack growth in the matrix emanating from a broken particle. It turns out that the crack resistance of the matrix largely depends on the distance from an adjacent particle. Residual stresses due to quenching of the material tend to reduce the risk of particle cleavage but promote crack propagation in the matrix.

Macro- to Atomic-Scale Tailoring of Si3N4 Ceramics to Enhance Properties

2005 ◽  
Vol 287 ◽  
pp. 233-241 ◽  
Author(s):  
Paul F. Becher ◽  
Gayle S. Painter ◽  
Naoya Shibata ◽  
Hua Tay Lin ◽  
Mattison K. Ferber
Keyword(s):  
Electronic Device ◽  
Atomic Level ◽  
Atomic Scale ◽  
Fracture Properties ◽  
Beta Particles ◽  
Preferential Segregation ◽  
Nitride Ceramics ◽  
Theoretical Predictions ◽  
The Matrix

Silicon nitride ceramics are finding uses in numerous engineering applications because of their tendency to form whisker-like microstructures that can overcome the inherent brittle nature of ceramics. Studies now establish the underlying microscopic and atomic-scale principles for engineering a tough, strong ceramic. The theoretical predictions are confirmed by macroscopic observations and atomic level characterization of preferential segregation at the interfaces between the grains and the continuous nanometer thick amorphous intergranular film (IGF). Two interrelated factors must be controlled for this to occur including the generation of the elongated reinforcing grains during sintering and debonding of the interfaces between the reinforcing grains and the matrix. The reinforcing grains can be controlled by (1) seeding with beta particles and (2) the chemistry of the additives, which also can influence the interfacial debonding conditions. In addition to modifying the morphology of the reinforcing grains, it now appears that the combination of preferential segregation and strong bonding of the additives (e.g., the rare earths, RE) to the prism planes can also result in sufficiently weakens the bond of the interface with the IGF to promote debonding. Thus atomic-scale engineering may allow us to gain further enhancements in fracture properties. This new knowledge will enable true atomic-level engineering to be joined with microscale tailoring to develop the advanced ceramics that will be required for more efficient engines, new electronic device architectures and composites.

An Edge Dislocation in a Three-Phase Composite Cylinder Model With a Sliding Interface

2002 ◽  
Vol 69 (4) ◽  
pp. 527-538 ◽  
Author(s):  
X. Wang ◽  
Y.-p. Shen
Keyword(s):  
Edge Dislocation ◽  
Arbitrary Point ◽  
Circular Inclusion ◽  
Composite Cylinder ◽  
Phase Form ◽  
Sliding Interface ◽  
Three Phase ◽  
Cylinder Model ◽  
The Matrix ◽  
Perfect Interface

An exact elastic solution is derived in a decoupled manner for the interaction problem between an edge dislocation and a three-phase circular inclusion with circumferentially homogeneous sliding interface. In the three-phase composite cylinder model, the inner inclusion and the intermediate matrix phase form a circumferentially homogeneous sliding interface, while the matrix and the outer composite phase form a perfect interface. An edge dislocation acts at an arbitrary point in the intermediate matrix. This three-phase cylinder model can simultaneously take into account the damage taking place in the circumferential direction at the inclusion-matrix interface and the interaction effect between the inclusions. As an application, we then investigate a crack interacting with the slipping interface.

Characristics of Shape Memory Composites Combined with Shape Memory Alloy and Shape Memory Polymer

2013 ◽  
Vol 705 ◽  
pp. 169-172
Author(s):  
Xue Feng ◽  
Li Min Zhao ◽  
Xu Jun Mi
Keyword(s):  
Shape Memory ◽  
Room Temperature ◽  
Shape Recovery ◽  
Volume Fraction ◽  
Shape Memory Polymer ◽  
Young Modulus ◽  
Thermomechanical Properties ◽  
The Matrix ◽  
Shape Memory Composites ◽  
Shape Fixity

In order to develop high functionality of shape memory materials, the shape memory composites combined with TiNi wire and shape memory epoxy were prepared, and the mechanical and thermomechanical properties were studied. The results showed the addition of TiNi wire increased the Young modulus and breaking strength both at room temperature and at elevated temperature. The composites maintained the rates of shape fixity and shape recovery close to 100%. The maximum recovery stress increased with increasing TiNi wire volume fraction, and obtained almost 3 times of the matrix by adding 1vol% TiNi wire.

scholarly journals Transition from a uni- to a bimodal interfacial charge distribution in $$\hbox {LaAlO}_3$$/$$\hbox {SrTiO}_3$$ upon cooling

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. Zwiebler ◽  
E. Di Gennaro ◽  
J. E. Hamann-Borrero ◽  
T. Ritschel ◽  
R. J. Green ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Oxygen Vacancies ◽  
Depth Distribution ◽  
Atomic Layer ◽  
Electric Transport ◽  
X Ray ◽  
Theoretical Predictions ◽  
Unit Cells ◽  
Field Effect Devices ◽  
Interfacial Charge

Abstract We present a combined resonant soft X-ray reflectivity and electric transport study of $$\hbox {LaAlO}_3$$ LaAlO 3 /$$\hbox {SrTiO}_3$$ SrTiO 3  field effect devices. The depth profiles with atomic layer resolution that are obtained from the resonant reflectivity reveal a pronounced temperature dependence of the two-dimensional electron liquid at the $$\hbox {LaAlO}_3$$ LaAlO 3 /$$\hbox {SrTiO}_3$$ SrTiO 3  interface. At room temperature the corresponding electrons are located close to the interface, extending down to 4 unit cells into the $$\hbox {SrTiO}_3$$ SrTiO 3  substrate. Upon cooling, however, these interface electrons assume a bimodal depth distribution: They spread out deeper into the $$\hbox {SrTiO}_3$$ SrTiO 3  and split into two distinct parts, namely one close to the interface with a thickness of about 4 unit cells and another centered around 9 unit cells from the interface. The results are consistent with theoretical predictions based on oxygen vacancies at the surface of the $$\hbox {LaAlO}_3$$ LaAlO 3  film and support the notion of a complex interplay between structural and electronic degrees of freedom.

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