scholarly journals The irreversible thermal expansion of an energetic material

2021 ◽  
Author(s):  
Hervé Trumel ◽  
François Willot ◽  
Thomas Peyres ◽  
Maxime Biessy ◽  
François Rabette
Keyword(s):  
Thermal Expansion ◽  
Residual Stresses ◽  
Volume Fraction ◽  
Energetic Material ◽  
Internal Stresses ◽  
Plastic Yielding ◽  
Initial State ◽  
Expansion Behavior ◽  
Small Volume Fraction

The works deals with a macroscopically isotropic energetic material based on triamino-trinitrobenzene (TATB) crystals bonded with a small volume fraction of a thermoplastic polymer. This material is shown experimentally to display an irreversible thermal expansion behavior characterized by dilatancy and variations of its thermal expansion coefficient when heated or cooled outside a narrow reversibility temperature range. The analysis of cooling results suggests the existence of residual stresses in the initial state, attributed to the manufacturing process. Microstructure-level FFT computations including the very strong anisotropic thermoelastic TATB crystal response and temperature-dependent binder plasticity, show that strong internal stresses develop in the disoriented crystals under thermal load, either heating or cooling. Upon cooling, binder plastic yielding in hindered, thus promoting essentially brittle microcracking, while it is favored upon heating. Despite its low volume fraction, the role of the binder is essential, its plastic yielding causing stress redistribution and residual stresses upon cooling back to ambient.

scholarly journals Effects of added SiO2 nanoparticles on the thermal expansion behavior of shape memory polymer nanocomposites

2018 ◽  
Vol 30 (1) ◽  
pp. 32-44 ◽  
Author(s):  
Mohammad Javad Mahmoodi ◽  
Mohammad Kazem Hassanzadeh-Aghdam ◽  
Reza Ansari
Keyword(s):  
Thermal Expansion ◽  
Shape Memory ◽  
Polymer Nanocomposites ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Shape Memory Polymer ◽  
Polymer Nanocomposite ◽  
Thermal Expansion Behavior ◽  
Interphase Region ◽  
Expansion Behavior

In this study, a unit cell–based micromechanical approach is proposed to analyze the coefficient of thermal expansion of shape memory polymer nanocomposites containing SiO2 nanoparticles. The interphase region created due to the interaction between the SiO2 nanoparticles and shape memory polymer is modeled as the third phase in the nanocomposite representative volume element. The influences of the temperature, volume fraction, and diameter of the SiO2 nanoparticles on the thermal expansion behavior of shape memory polymer nanocomposite are explored. It is observed that the coefficient of thermal expansion of shape memory polymer nanocomposite decreases with the increase in the volume fraction up to 12%. Also, the results reveal that with the increase in temperature, the shape memory polymer nanocomposite coefficient of thermal expansion linearly increases. The role of interphase region on the thermal expansion response of the shape memory polymer nanocomposite is found to be very important. In the presence of interphase, the reduction in nanoparticle diameter leads to lower coefficient of thermal expansion for shape memory polymer nanocomposite, while the variation of nanoparticles diameter does not affect the coefficient of thermal expansion in the absence of interphase. Based on the simulation results, the shape memory polymer nanocomposite coefficient of thermal expansion decreases as the interphase thickness increases. In addition, the contribution of interphase coefficient of thermal expansion to the shape memory polymer nanocomposite coefficient of thermal expansion is more significant than that of interphase elastic modulus.

Residual Stresses Distributions within Thin-Walled Ceramic-Metal Seal

2012 ◽  
Vol 503-504 ◽  
pp. 428-431 ◽  
Author(s):  
Guo Liang Zhang ◽  
Lei Shi ◽  
Da Zhi Jin
Keyword(s):  
Thermal Expansion ◽  
Residual Stresses ◽  
Fem Simulation ◽  
Matrix Composites ◽  
Thermal Expansion Coefficients ◽  
Expansion Behavior ◽  
Metal Seal ◽  
Significant Difference ◽  
Thin Walled ◽  
Typical Configuration

Due to significant difference of thermal expansion coefficients between ceramic and metal, the residual stresses are deemed to be induced into the interior of matrix composites within the ceramic-metal seal systems. Many investigations of the residual stresses distributions on dissimilar solid materials joints so far have been carried out theoretically and experimentally, whereas ones of the residual stresses distributions within the thin-walled ceramic-metal seal systems are rarely performed. In order to obtain information for improving their seal structures in the future, the residual stresses distributions resulted from the thermal expansion behavior in the typical configuration of the thin-walled ceramic-metal seal are investigated by theoretical formulae, experimental observation and finite element method (FEM) simulation in this paper. The changing trends of the computational results of the residual stresses distributions agree with the experimental results of the measurement with X-ray diffractometer. The overall residual stresses are found to increase drastically near the welding interfaces. The highest tensile stress occurs at the outer surfaces of the ceramic near the welding interfaces.

scholarly journals Measurement of Residual Stresses in Metal Matrix Composites

1993 ◽  
Author(s):  
P. K. Wright
Keyword(s):  
Thermal Expansion ◽  
Residual Stresses ◽  
Metal Matrix Composites ◽  
Metal Matrix ◽  
Volume Fraction ◽  
Stress Measurement ◽  
Fiber Direction ◽  
Matrix Composites ◽  
Thermal Expansion Coefficients ◽  
The Matrix

Metal matrix composites (MMC) are expected to develop internal residual stresses on cooling from fabrication due to the large thermal expansion mismatch between reinforcing fibers and the matrix. This work was undertaken to experimentally measure these residual stresses and compare them with analytical calculations in order to clearly establish their levels and dependence on material parameters. Two techniques for residual stress measurement were investigated: 1) Xray diffraction (sin2 psi method) and 2) neutron diffraction. Both techniques gave results in good agreement with analytical predictions for several systems (SCS-6/Ti-24Al-11Nb, W/NiAl, and Al2O3NiAl). The results obtained showed a dependence of residual stresses on thermal expansion coefficients, elastic moduli, volume fraction fibers, and matrix yield strengths. The fibers showed compressive stress states, and the matrix, tension. Average stresses were higher in the fiber direction than transverse to fibers.

Three-dimensional braided composites with zero, negative and isotropic thermal expansion behavior

2020 ◽  
Vol 54 (13) ◽  
pp. 1761-1781
Author(s):  
SA Pottigar ◽  
B Santhosh ◽  
RG Nair ◽  
P Punith ◽  
PJ Guruprasad ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Three Dimensional ◽  
Braided Composites ◽  
Fiber Volume ◽  
Braided Composite ◽  
Expansion Behavior ◽  
Unit Cells ◽  
Composite Configuration

Three-dimensional braided composites with zero, negative and isotropic coefficient of thermal expansion are presented based on an analytical homogenization technique. The configuration of the braided composites is worked out considering the exact jamming condition leading to higher fiber volume fraction. A total of four configurations of three-dimensional-braided composite representative unit cells were analyzed. Among these, two arrangements are 4-axes and the other two are 5-axes. Special emphasis is given on the detailed description of the representative unit cells. Analysis reveals that a three-dimensional-braided composite configuration with thermoelastic isotropic properties having same coefficient of thermal expansion along x-, y-, and z-axes is achievable. As a special case, the homogenization model is used to predict, for the first time, a configuration of braided architecture and material leading to zero coefficient of thermal expansion along x-, y- and z-directions.

scholarly journals Structure and Thermal Expansion of Cu−90 vol. % Graphite Composites

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7089
Author(s):  
Andrej Opálek ◽  
Štefan Emmer ◽  
Roman Čička ◽  
Naďa Beronská ◽  
Peter Oslanec ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Volume Fraction ◽  
Coefficient Of Thermal Expansion ◽  
Pure Copper ◽  
Hot Isostatic Pressing ◽  
Functional Materials ◽  
Electrical Equipment ◽  
Internal Stresses ◽  
Schapery Model ◽  
Graphite Composites

Copper–graphite composites are promising functional materials exhibiting application potential in electrical equipment and heat exchangers, due to their lower expansion coefficient and high electrical and thermal conductivities. Here, copper–graphite composites with 10–90 vol. % graphite were prepared by hot isostatic pressing, and their microstructure and coefficient of thermal expansion (CTE) were experimentally examined. The CTE decreased with increasing graphite volume fraction, from 17.8 × 10−6 K−1 for HIPed pure copper to 4.9 × 10−6 K−1 for 90 vol. % graphite. In the HIPed pure copper, the presence of cuprous oxide was detected by SEM-EDS. In contrast, Cu–graphite composites contained only a very small amount of oxygen (OHN analysis). There was only one exception, the composite with 90 vol. % graphite contained around 1.8 wt. % water absorbed inside the structure. The internal stresses in the composites were released during the first heating cycle of the CTE measurement. The permanent prolongation and shape of CTE curves were strongly affected by composition. After the release of internal stresses, the CTE curves of composites did not change any further. Finally, the modified Schapery model, including anisotropy and the clustering of graphite, was used to model the dependence of CTE on graphite volume fraction. Modeling suggested that the clustering of graphite via van der Waals bonds (out of hexagonal plane) is the most critical parameter and significantly affects the microstructure and CTE of the Cu–graphite composites when more than 30 vol. % graphite is present.

How do Impurities Affect the Growth of μc-Si:H?

1998 ◽  
Vol 507 ◽  
Author(s):  
Toshihiro Kamei ◽  
Makoto Fukawa ◽  
Tatsuyuki Nishimiya ◽  
Masao Isomura ◽  
Michio Kondo ◽  
...  
Keyword(s):  
Small Volume ◽  
Volume Fraction ◽  
Defect Density ◽  
Hydrogen Desorption ◽  
Oxygen Impurity ◽  
Surface Hydrogen ◽  
Small Volume Fraction ◽  
Higher Temperature ◽  
Effect Of Oxygen

ABSTRACTUltra clean plasma CVD process opens the doorway to clarify the role of impurities in the growth process of μc-Si:H. A reduction of impurity levels during the growth extends the temperature range for crystalline formation to lower side, i.e., high-crystallinity μc-Si:H formation even at room temperature, substantially reduces midgap defect density at 200°C, and enlarges crystalline grain size at 350°C. These results imply that impurities disrupt crystalline formation even on hydrogen covered surface. The crystalline-to-amorphous transition is induced by a loss of surface hydrogen coverage due to thermal hydrogen desorption at higher temperature of ∼450°C irrespective of the effect of oxygen impurity. Light-soaking experiments for the series of the films from a-Si:H to μc-Si:H films with different crystalline volume fraction indicate that the presence of small volume fraction of crystallite significantly suppresses light induced defect creation under the present light soaking condition of 3SUN 60°C 6hr. These results are explained in terms of preferential recombination of photo-excited carriers in the crystallite.

Microfibres Containing Laminates Prepared by EPD: Microstructure and Fracture Behaviour

2015 ◽  
Vol 654 ◽  
pp. 53-57 ◽  
Author(s):  
Zdeněk Chlup ◽  
Hynek Hadraba ◽  
Daniel Drdlík ◽  
Ivo Dlouhý
Keyword(s):  
Mechanical Properties ◽  
Small Volume ◽  
Volume Fraction ◽  
Fracture Behaviour ◽  
Thin Layers ◽  
Internal Stresses ◽  
Alumina Matrix ◽  
Fracture Properties ◽  
Small Volume Fraction ◽  
Crack Trapping

Recently it was possible to prepare tailored laminates with perfect and strong interface of layers with precise thickness management. Tailoring of ceramic laminates to obtain optimal mechanical properties with enhanced fracture resistance is possible when predictions based on numerical calculations are employed. Extraordinary mechanical properties were achieved via high internal stresses development during material processing. The aim of this investigation can be seen in two directions. The enhanced crack free green bodies through incorporating small volume fraction of micro-fibres to the powders were prepared. Additionally, control of the crack propagation by incorporated directionally oriented micro-fibres both in the volume and in individual layers. In this contribution both alumina and zirconia micro-fibres were used to help eliminate drying defects in the green body stage before sintering. The co-deposition of ceramic micro-fibres and powder led to the preparation of microstructures having unique orthogonal fracture properties. Developed laminate with thin layers created by zirconia micro-fibres in the alumina matrix seems to be the most promising. This type of material exhibited potential of the crack trapping and deflection even when very small amount of micro-fibres was used.

Mechanics of Gels

1992 ◽  
Vol 271 ◽  
Author(s):  
George W. Scherer
Keyword(s):  
Thermal Expansion ◽  
Fluid Flow ◽  
Time Dependence ◽  
Supercritical Drying ◽  
Time Dependent ◽  
Dependent Behavior ◽  
Expansion Behavior ◽  
Pore Liquid ◽  
Applied Stresses

ABSTRACTThe response of wet gels to applied stresses is discussed, with emphasis on the role of flow of the pore liquid. Even when the network of the gel is purely elastic, the gel exhibits time-dependent behavior that resembles viscoelasticity, which results from fluid flow. The permeability of the gel can be determined from measurement of this time-dependence. Fluid flow also influences the thermal expansion behavior of gels, and can cause severe stresses to develop during supercritical drying, if the autoclave is heated too rapidly.

scholarly journals Design of a Co–Al–W–Ta Alloy Series with Varying γ′ Volume Fraction and Their Thermophysical Properties

2021 ◽  
Author(s):  
N. Volz ◽  
F. Xue ◽  
A. Bezold ◽  
C. H. Zenk ◽  
S. G. Fries ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Volume Fraction ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
Expansion Behavior ◽  
Alloy Series ◽  
Secondary Precipitates ◽  
Tie Line ◽  
Key Parameter

AbstractThe γ′ volume fraction is a key parameter in precipitation-strengthened Co- and Ni-base superalloys and mainly determines the alloys’ properties. However, systematic studies with varying γ′ volume fractions are rare and the influence on thermal expansion has not been studied in detail. Therefore, a series of six Ta-containing Co-based alloys was designed with compositions on a γ–γ′ tie-line, where the γ′ volume fraction changes systematically. During solidification, Laves (C14-type) and µ (D85-type) phases formed in alloys with high levels of W and Ta. Single-phase γ or two-phase γ/γ′ microstructures were obtained in four experimental alloys after heat treatment as designed, whereas secondary precipitates, such as χ (D019-type), Laves, and μ, existed in alloys containing high levels of γ′-forming elements. However, long-term heat treatments for 1000 hours revealed the formation of the χ phase also in the former χ-free alloys. The investigation of the thermal expansion behavior revealed a significant anomaly related to the dissolution of γ′, which can be used to determine the γ′ solvus temperature with high accuracy. Compared to thermodynamic calculations, differential scanning calorimetry (DSC) and thermal expansion analysis revealed a larger increase of the γ′ solvus temperatures and a lesser decline of the solidus temperatures when the alloy composition approached the composition of the pure γ′ phase.

scholarly journals Change of 0.34Cr-1Ni-Mo-Fe Steel Dislocation Structure in Plasma Electrolyte Hardening

Materials ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 1928
Author(s):  
Bauyrzhan Rakhadilov ◽  
Zarina Satbayeva ◽  
Sherzod Ramankulov ◽  
Nurdaulet Shektibayev ◽  
Laila Zhurerova ◽  
...  
Keyword(s):  
Crystal Lattice ◽  
Dislocation Structure ◽  
Volume Fraction ◽  
Internal Stresses ◽  
Shear Stresses ◽  
Initial State ◽  
Α Phase ◽  
Quantitative Characteristics ◽  
Before And After ◽  
Plasma Electrolytic

This work deals with the study of changes in the dislocation structure and quantitative characteristics, as well as morphological components, of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening. According to the electron microscopic studies of the fine structure of 0.34Cr-1Ni-Mo-Fe steel before and after plasma electrolytic hardening, 0.34Cr-1Ni-Mo-Fe steel is a multiphase material containing an α-phase, a γ-phase (retained austenite), and a cementite and carbide phase. It was revealed that, morphologically, the α-phase in the initial state, generally, is present in the form of: lamellar pearlite with a volume fraction of 35%, a ferritocarbide mixture with a volume fraction of 45%, and fragmented ferrite with a volume fraction of 20% of the material. After surface hardening, the morphological components of the structure changed: packet–lamellar martensite with volume fractions of 60% and 40%, 5% and 7% of γ-phase as residual austenite in the crystals of packet–lamellar martensite, 0.6% and 1.5% of cementite in crystals of packet–lamellar martensite, and 0.15% and 0.35% of complex carbide М23С6 in crystals of packet–lamellar martensite, respectively, were observed. The quantitative characteristics of the dislocation structure were estimated by the following calculated indices of packet and lamellar martensite: scalar (ρ) and excess (ρ±) density of dislocations, the value of the curvature-torsion of the crystal lattice (χ), the amplitude of long-range internal stresses (σd), and the amplitude of shear stresses (σL), according to which the plastic nature of the bending-torsion of the crystal lattice was confirmed (σL > σd).

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