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

2018 ◽  
Author(s):  
John Venetis ◽  
Emilio Sideridis
Keyword(s):  
Elastic Modulus ◽  
Upper Bound ◽  
Theoretical Models ◽  
The Novel ◽  
Fibrous Composites ◽  
Strength Of Materials ◽  
Fiber Concentration ◽  
Longitudinal Elastic Modulus ◽  
The Matrix ◽  
Specific Variation

In this paper, an upper bound of the longitudinal elastic modulus of  unidirectional   fibrous composites is proposed according to strength of materials approach, on the premise that the fiber is much stiffer than the matrix. In the mathematical derivations, the concept of boundary interphase between fiber and matrix was also taken into account and the main objective of this work is the attainment of an upper bound for the interphase stiffness with respect to fiber concentration by volume. The novel element here is that the authors have not taken into consideration any specific variation law to approximate the interphase modulus. The theoretical results arising from the proposed formula were compared with those obtained from some reliable theoretical models as well as with experimental data found in the literature, and a satisfactory agreement was observed.

scholarly journals Thermo-Mechanical Properties of PLA/Short Flax Fiber Biocomposites

2019 ◽  
Vol 9 (18) ◽  
pp. 3797 ◽  
Author(s):  
Laura Aliotta ◽  
Vito Gigante ◽  
Maria-Beatrice Coltelli ◽  
Patrizia Cinelli ◽  
Andrea Lazzeri ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Load Transfer ◽  
Mechanical Performance ◽  
Nucleating Agent ◽  
Flax Fiber ◽  
Analytical Models ◽  
Poly Lactic Acid ◽  
Flax Fibers ◽  
The Matrix

In this work, biocomposites based on poly(lactic acid) (PLA) and short flax fibers (10–40 wt.%) were produced by extrusion and characterized in terms of thermal, mechanical, morphological, and thermo-mechanical properties. Analytical models were adopted to predict the tensile properties (stress at break and elastic modulus) of the composites, and to assess the matrix/fiber interface adhesion. The resulting composites were easily processable by extrusion and injection molding up to 40 wt.% of flax fibers. It was observed that despite any superficial treatment of fibers, the matrix/fiber adhesion was found to be sufficiently strong to ensure an efficient load transfer between the two components obtaining composites with good mechanical properties. The best mechanical performance, in terms of break stress (66 MPa), was obtained with 20 wt.% of flax fibers. The flax fiber acted also as nucleating agent for PLA, leading to an increment of the composite stiffness and, at 40 wt.% of flax fibers, improving the elastic modulus decay near the PLA glass transition temperature.

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 DoubleLex Revisited and Beyond

2019 ◽  
Author(s):  
Xuming Huang ◽  
Jimmy Lee
Keyword(s):  
Symmetry Breaking ◽  
Matrix Models ◽  
Matrix Model ◽  
Upper Bound ◽  
Theoretical Predictions ◽  
The Matrix

The paper proposes Maximum Residue (MR) as a notion to evaluate the strength of a symmetry breaking method. We give a proof to improve the best known DoubleLex MR upper bound from m!n! - (m!+n!) to min(m!,n!) for an m x n matrix model. Our result implies that DoubleLex works well on matrix models where min(m, n) is relatively small. We further study the MR bounds of SwapNext and SwapAny, which are extensions to DoubleLex breaking further a small number of composition symmetries. Such theoretical comparisons suggest general principles on selecting Lex-based symmetry breaking methods based on the dimensions of the matrix models. Our experiments confirm the theoretical predictions as well as efficiency of these methods.

scholarly journals Influence of Alumina Nanofibers Sintered by the Spark Plasma Method on Nickel Mechanical Properties

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 548 ◽  
Author(s):  
Leonid Agureev ◽  
Valeriy Kostikov ◽  
Zhanna Eremeeva ◽  
Svetlana Savushkina ◽  
Boris Ivanov ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Elastic Modulus ◽  
Strength Properties ◽  
Alumina Nanoparticles ◽  
Metal Powders ◽  
Wide Range ◽  
The Matrix ◽  
Spark Plasma ◽  
Average Size

The article presents the study of alumina nanoparticles’ (nanofibers) concentration effect on the strength properties of pure nickel. The samples were obtained by spark plasma sintering of previously mechanically activated metal powders. The dependence of the grain size and the relative density of compacts on the number of nanofibers was investigated. It was found that with an increase in the concentration of nanofibers, the average size of the matrix particles decreased. The effects of the nanoparticle concentration (0.01–0.1 wt.%) on the elastic modulus and tensile strength were determined for materials at 25 °C, 400 °C, and 750 °C. It was shown that with an increase in the concentration of nanofibers, a 10–40% increase in the elastic modulus and ultimate tensile strength occurred. A comparison of the mechanical properties of nickel in a wide range of temperatures, obtained in this work with materials made by various technologies, is carried out. A description of nanofibers’ mechanisms of influence on the structure and mechanical properties of nickel is given. The possible impact of impurity phases on the properties of nickel is estimated. The tendency of changes in the mechanical properties of nickel, depending on the concentration of nanofibers, is shown.

scholarly journals The Algebraic Degree of Phase-Type Distributions

2010 ◽  
Vol 47 (03) ◽  
pp. 611-629
Author(s):  
Mark Fackrell ◽  
Qi-Ming He ◽  
Peter Taylor ◽  
Hanqin Zhang
Keyword(s):  
Lower Bound ◽  
Upper Bound ◽  
Polynomial Algorithm ◽  
Algebraic Degree ◽  
Nonnegative Matrices ◽  
Stieltjes Transform ◽  
Special Cases ◽  
Phase Type ◽  
Phase Type Distributions ◽  
The Matrix

This paper is concerned with properties of the algebraic degree of the Laplace-Stieltjes transform of phase-type (PH) distributions. The main problem of interest is: given a PH generator, how do we find the maximum and the minimum algebraic degrees of all irreducible PH representations with that PH generator? Based on the matrix exponential (ME) order of ME distributions and the spectral polynomial algorithm, a method for computing the algebraic degree of a PH distribution is developed. The maximum algebraic degree is identified explicitly. Using Perron-Frobenius theory of nonnegative matrices, a lower bound and an upper bound on the minimum algebraic degree are found, subject to some conditions. Explicit results are obtained for special cases.

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.

A Yield Criterion of Porous Materials With Anisotropy Caused by Geometry or Distribution of Pores

1991 ◽  
Vol 113 (4) ◽  
pp. 425-429 ◽  
Author(s):  
T. Hisatsune ◽  
T. Tabata ◽  
S. Masaki
Keyword(s):  
Velocity Field ◽  
Porous Materials ◽  
Upper Bound ◽  
Volume Fraction ◽  
Yield Criterion ◽  
Longitudinal Direction ◽  
Axisymmetric Deformation ◽  
The Other ◽  
The Matrix ◽  
Spherical Cells

Axisymmetric deformation of anisotropic porous materials caused by geometry of pores or by distribution of pores is analyzed. Two models of the materials are proposed: one consists of spherical cells each of which has a concentric ellipsoidal pore; and the other consists of ellipsoidal cells each of which has a concentric spherical pore. The velocity field in the matrix is assumed and the upper bound approach is attempted. Yield criteria are expressed as ellipses on the σm σ3 plane which are longer in longitudinal direction with increasing anisotropy and smaller with increasing volume fraction of the pore. Furthermore, the axes rotate about the origin at an angle α from the σm-axis, while the axis for isotropic porous materials is on the σm-axis.

Fabrication and Mechanical Properties of Dense/Porous β-Tricalcium Phosphate Bioceramics

2007 ◽  
Vol 330-332 ◽  
pp. 907-910
Author(s):  
Fa Ming Zhang ◽  
Jiang Chang ◽  
Jian Xi Lu ◽  
Kai Li Lin
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Exponential Growth ◽  
Weight Bearing ◽  
Area Ratio ◽  
Sectional Area ◽  
Cross Sectional ◽  
The Matrix ◽  
Porous Bioceramics

Attempt to increase the mechanical properties of porous bioceramics, a dense/porous structured β-TCP bioceramics that mimic the characteristics of nature bone were fabricated. Experimental results show that the dense/porous structured β-TCP bioceramics demonstrated excellent mechanical properties with compressive strength up to 74 MPa and elastic modulus up to 960 MPa, which could be tailored by the dense/porous cross-sectional area ratio obeying the rule of exponential growth. The interface between the dense and porous bioceramics is connected compactly and tightly with some micropores distributed in the matrix of both porous and dense counterparts. The dense/porous structure of β-TCP bioceramics may provide an effective way to increase the mechanical properties of porous bioceramics for bone regeneration at weight bearing sites.

Investigation of Thermochemical Hydrogen Production via the Novel Thermo-Mechanical Stabilized Iron Oxide-Zirconia Porous Structure

2013 ◽  
Author(s):  
Ayyoub M. Mehdizadeh ◽  
Kelvin Randhir ◽  
James F. Klausner ◽  
Nicholas AuYeung ◽  
Fotouh Al-Raqom ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Porous Structure ◽  
Chemical Reactivity ◽  
Thermal Reduction ◽  
The Novel ◽  
Concentrated Solar Energy ◽  
The Matrix ◽  
Unique Method ◽  
Laboratory Scale Reactor ◽  
The Stability

In this study we have developed a unique method for synthesizing very reactive water splitting materials that will remain stable at temperatures as high as 1450 °C to efficiently produce clean hydrogen from concentrated solar energy. The hydrogen production for a laboratory scale reactor using a “Thermo-mechanical Stabilized Porous Structure” (TSPS) is experimentally investigated for oxidation and thermal reduction temperatures of 1200 and 1450 °C, respectively. The stability and reactivity of a 10 g TSPS over many consecutive oxidation and thermal reduction cycles for different particle size ranges has been investigated. The novel thermo-mechanical stabilization exploits sintering and controls the geometry of the matrix of particles inside the structure in a favorable manner so that the chemical reactivity of the structure remains intact. The experimental results demonstrate that this structure yields peak hydrogen production rates of 1–2 cm3/(min.gFe3O4) during the oxidation step at 1200 °C and the 30 minute thermal reduction step at 1450 ° C without noticeable degradation over many consecutive cycles. The hydrogen production rate is one of the highest yet reported in the open literature for thermochemical looping processes using thermal reduction. This novel process has strong potential for developing an enabling technology for efficient and commercially viable solar fuel production.

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