Buckling of Microfibers

1967 ◽  
Vol 34 (4) ◽  
pp. 1011-1016 ◽  
Author(s):  
M. A. Sadowsky ◽  
S. L. Pu ◽  
M. A. Hussain
Keyword(s):  
Elevated Temperatures ◽  
Thermal Characteristics ◽  
Compressive Force ◽  
Theory Of Elasticity ◽  
Primary Objective ◽  
Infinite Length ◽  
Volume Percentage ◽  
Initial Strength ◽  
Surrounding Matrix ◽  
The Matrix

Most composites are fabricated at elevated temperatures and cooled to room temperature. The difference in coefficients of thermal expansion of the fiber and matrix may cause buckling of the slender-shaped microfibers. This would greatly reduce the initial strength of the composites. The primary objective of this paper is to explain qualitatively the basic phenomenon of buckled microfibers in a composite and to present some numerical results in certain ranges of elastic parameters. Our analysis is based on assumptions that (a) the volume percentage of fibers is small so that the mutual interference of fibers is negligible and the matrix surrounding a fiber may be considered as infinitely large; (b) the diameter of the fiber is very small in comparison to its length so that the fiber may be treated as a linear fiber with infinite length; (c) the constituents are homogeneous and isotropic and the classical linear theory of elasticity may be applied; and, (d) in the process of cooling, the fiber is subjected to compression but not twisting moment by the surrounding matrix. The analysis leads to a relation between the pertinent elastic and thermal characteristics of the matrix and microfiber and the compressive force along the axis of the microfiber at the critical moment of incipient buckling. With the knowledge of that relation, it is now possible to know in advance whether or not buckling is to be expected and to avoid such manufacturing methods in which a threat of having buckled microfibers is present.

Microstructural Stability of Stressed Lamellar Eutectics

1995 ◽  
Vol 398 ◽  
Author(s):  
N. Sridhar ◽  
J.M. Rickman ◽  
D.J. Srolovitz
Keyword(s):  
Elevated Temperatures ◽  
Operating Conditions ◽  
Microstructural Stability ◽  
Lamellar Eutectic ◽  
Stability Diagrams ◽  
Flat Interface ◽  
Surrounding Matrix ◽  
Critical Wavelength ◽  
The Matrix ◽  
Enhance Mass

ABSTRACTAt elevated temperatures, stresses enhance mass transport at the microstructural scale and under certain conditions, lead to microstructural instabilities. Using a linear stability analysis, we examine the effect of stresses on the morphological stability of plate-like phases and lamellar eutectic composites. These stresses can be either due to misfit strains and/or due to externally applied loads. We find that for misfitting plates, the nominally flat plate-matrix interface is unstable with respect to the growth of perturbations with wavelengths greater than a critical wavelength, provided that the reinforcing plates are elastically suffer than the surrounding matrix. On the other hand, for stresses generated by externally applied loads, the flat interface is always unstable as long as the plate modulus and the matrix modulus are not identical. In addition, the analysis reveals that misfit strains can either counteract or enhance the destabilizing influence of applied loads depending on the elastic properties of the plate and the matrix. Finally, we have developed stability diagrams that identify material properties and operating conditions required to maintain a stable interface in these lamellar eutectic composites.

A Coupled Temperature-Displacement Numerical Analysis of Hydraulic Press Workspace

2016 ◽  
Author(s):  
Jakub Jirasko ◽  
Antonin Max ◽  
Radek Kottner
Keyword(s):  
Numerical Analysis ◽  
Computational Model ◽  
Automotive Industry ◽  
Elevated Temperatures ◽  
Compressive Force ◽  
Hydraulic Press ◽  
Metallic Materials ◽  
Pressing Force ◽  
Stress Criterion ◽  
The Press

The analysis is performed on a hydraulic press which is intended for use in the automotive industry and is a part of a production line. The final phase of manufacture of interior and acoustic parts takes place in this press. These interior and acoustic parts are made of sandwich fabric which is inserted into the heated mould of the press and by treatment with a defined pressure (or, more precisely, a defined compression) and temperature, it is formed into its final shape. This press has a frame with four columns and it is not preloaded. Two double acting hydraulic cylinders placed on an upper cross beam exert the compressive force. Due to continuously increasing demands on the accuracy and quality of products not only in the automotive industry, it is necessary to ensure compliance with the accuracy of certain values of machine operation. Especially in this case, the value of accuracy substantially depends on the clamping plates of the press, for which a certain value of flatness is required, both at room temperature and at elevated temperatures. To achieve this accuracy, it is necessary to guarantee sufficient stiffness of the machine to resist the pressing force with the smallest deformation possible. Another crucial factor affecting the accuracy of the machine is heating of the heated clamping plates. Unequal heating of parts of the frame causes additional deformation that has to be quantified and eliminated. The main aim was to verify the design of the press by numerical computation and gather knowledge for modifying the topological design of the press so that it fulfils the required customer parameters of flatness and parallelism for different types of loading. A computational model of the press was created for the numerical solution of a coupled temperature-displacement numerical analysis. The analysis was performed using the finite element method in Abaqus software. The press is symmetrical in two orthogonal planes and the load of the press is considered to be centric. On the basis of these two factors it was possible to carry out the analysis by considering only a quarter of the press. The analysis was used to investigate the effects of static and combined loads from the pressing force and heat on the press. The influence of a cooling circuit located in the press frame for the reduction of frame deformation (and deformation of clamping plates) was investigated. Contacts were defined among individual parts to ensure the computational model had characteristics as close as possible to the real press. The analysis was solved as stationary, on the basis that the cooling of the tool between individual pressing cycles is negligible. The insulating plates are made of a particulate composite material which was considered to have isotropic properties depending on the temperature. For strength evaluation of composite materials all individual components of the stress tensor were examined according to the maximum stress criterion. Hook’s law was considered to be valid for the metallic materials. Von Mises criterion was used to evaluate the strength of the metallic materials. The geometry of the press was discretized using 3D linear thermally coupled brick elements with 8 nodes and full integration (C3D8T). There were approximately 174,000 elements in total. Design procedures for designing a press frame with higher work accuracy (flatness) were proposed with the example of the simplified model of the press table. With these methods it is possible to achieve times higher accuracy than is achieved with conventional method.

ANALYSIS OF PROTEOGLYCAN GENE EXPRESSION IN CONNECTIVE TISSUES BY SEMI-QUANTITATIVE RT-PCR

2001 ◽  
Vol 05 (02) ◽  
pp. 79-88
Author(s):  
K. Dobra ◽  
A. Hjerpe
Keyword(s):  
Rt Pcr ◽  
Connective Tissues ◽  
Surrounding Matrix ◽  
Cell Proliferation And Differentiation ◽  
Extracellular Matrix Components ◽  
Proliferation And Differentiation ◽  
The Matrix ◽  
Quantitative Changes ◽  
Regulatory Functions ◽  
Multiple Samples

Proteoglycans (PGs) are cell-membrane and extracellular matrix components with a wide variety of different functions. In the matrix, they are mainly of structural importance, although some of them have been ascribed specific regulatory functions, such as in the assembly of collagen fibers. PGs on the cell surface act as essential modulators of specific ligand-binding reactions, involving interactions between adjacent cells and between cells and surrounding matrix. Through these interactions they participate in different processes, including cell proliferation and differentiation. Qualitative and quantitative changes in PG expression can therefore be associated with various physiological and pathological conditions. We have optimized the conditions for semi-quantitative evaluation of proteoglycan expression by RT-PCR reaction, using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as reference gene. The relative fluorescence of analyte to reference amplimers can — within certain limits — be used to estimate the amount of target RNA and allows direct comparison of multiple samples. The profile of PG expression obtained in this way can be used to extend our current understanding of the possible functions that can be associated with these complex molecules.

Small Lead and Indium Inclusions in Aluminium

1991 ◽  
Vol 235 ◽  
Author(s):  
E. Johnson ◽  
K. Hjemsted ◽  
B. Schmidt ◽  
K. K. Bourdelle ◽  
A. Johansen ◽  
...  
Keyword(s):  
Melting Point ◽  
Elevated Temperatures ◽  
Supersaturated Solution ◽  
In Situ Tem ◽  
Initial Growth ◽  
Heating And Cooling ◽  
Moiré Fringes ◽  
The Matrix ◽  
Spontaneous Phase

ABSTRACTIon implantation of lead or indium into aluminium results in spontaneous phase separation and formation of lead or indium precipitates. The precipitates grow in topotactical alignment with the matrix, giving TEM images characterized by moiré fringes. The size and density of the precipitates increase with increasing fluence until coalescence begins to occur. Implantations at elevated temperatures lead to formation of larger precipitates with well developed facets. This is particularly significant for implantations above the bulk melting point of the implanted species. Melting and solidification have been followed by in-situ TEM heating and cooling experiments. Superheating up to ∼ 50 K above the bulk melting point has been observed, and the largest inclusions melt first. Melting is associated with only partial loss of facetting of the largest inclusions. Initial growth of the inclusions occurs by trapping of atoms retained in supersaturated solution. Further growth occurs by coalescence of neighbouring inclusions in the liquid phase. Solidification is accompanied by a strong undercooling ∼ 30 K below the bulk melting point, where the smallest inclusions solidify first. Solidification is characterized by spontaneous restoration of the facets and the topotactical alignment.

Active control of fan noise from high-bypass ratio aeroengines: a numerical study

2001 ◽  
Vol 105 (1053) ◽  
pp. 627-631
Author(s):  
P. Traub ◽  
F. Kennepohl ◽  
K. Heinig
Keyword(s):  
Active Control ◽  
Numerical Study ◽  
Active Noise Control ◽  
Sound Field ◽  
Primary Objective ◽  
Scale Model ◽  
Research Centre ◽  
Infinite Length ◽  
Circular Duct ◽  
Bypass Ratio

Abstract Under the national research project, dubbed Turbotech II, in which MTU Aero Engines, DLR Institute of Propulsion Technology and EADS Corporate Research Centre participate, active noise control (ANC) has been tested with a scale model fan of one metre diameter for a high bypass ratio aeroengine. MTU’s task in this project was to develop a computer code to predict the sound field in the intake duct of the fan-rig by the use of active control. The primary objective of the numerical study was to specify numbers of actuators (loudspeakers) and error sensors (microphones) and their positioning to control the harmonic sound power, radiated upstream to the duct intake. The computer model is based on the geometry of an annular or circular duct of rigid walls and infinite length, containing a subsonic axial uniform flow. The modal amplitudes of the primary sound field are input data. The actuators are modelled by acoustic monopoles. Two control algorithms have been used for achieving the control objective. The first consists simply in the reduction of the in-duct mean squared pressures. The second, so called modal control, is designed to cancel dominant modes selectively. Numerical results are presented using a typical configuration of wall mounted actuators and error sensors in the form of a number of rings uniformly distributed along the length of the intake duct. Guidelines have also been derived to design a favourable configuration of actuators and sensors. The findings of the numerical study are compared with the results of the ANC tests.

scholarly journals High-Resolution Microstructure Characterization of Additively Manufactured X5CrNiCuNb17-4 Maraging Steel during Ex and in Situ Thermal Treatment

2021 ◽  
Author(s):  
Mihaela Albu ◽  
Bernd Panzirsch ◽  
Hartmuth Schröttner ◽  
Stefan Mitsche ◽  
Klaus Reichmann ◽  
...  
Keyword(s):  
Maraging Steel ◽  
Elevated Temperatures ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Matrix ◽  
Powder Particles ◽  
In Situ Heating ◽  
Heating Up

Powder and SLM additively manufactured parts of X5CrNiCuNb17-4 maraging steel were systematically investigated by electron microscopy to understand the relationship between the properties of the powder grains and the microstructure of the printed parts. We prove that satellites, irregularities and superficial oxidation of powder particles can be transformed into an advantage through the formation of nanoscale (AlMnSiTiCr)-oxides in the matrix during the printing process. The nano-oxides showed extensive stability in terms of size, spherical morphology, chemical composition and crystallographic disorder upon in situ heating up to 950°C in the scanning transmission electron microscope. Their presence thus indicates a potential for oxide-dispersive strengthening of this steel, which may be beneficial for creep resistance at elevated temperatures. The nucleation of copper clusters and their evolution into nanoparticles as well as the precipitation of Ni and Cr particles upon in situ heating have as well been systematically documented.

scholarly journals New approach to the formation of organo-inorganic borosyloxane polymer structures

2019 ◽  
Vol 57 (2) ◽  
pp. 35-40
Author(s):  
Alexander B. Zachernyuk ◽  
◽  
Boris A. Zachernyuk ◽  
Ekaterina N. Solovyova ◽  
Vladimir I. Nedelkin ◽  
...  
Keyword(s):  
Boron Oxide ◽  
Sol Gel ◽  
Thermal Characteristics ◽  
Inorganic Materials ◽  
Organic Modifiers ◽  
Synthesis Time ◽  
Transparent Films ◽  
Boric Anhydride ◽  
The Matrix ◽  
Synthetic Approaches

Using sol-gel methods, new synthetic approaches to the preparation of boron-containing organic-inorganic hybrid polymers based on boron oxide (boric anhydride), which is a part of many inorganic materials, have been developed. Previously, such methods were used to obtain amorphous silicate glasses and their use allows introducing various inorganic and organic modifiers into the matrix of silicon dioxide and other compounds at temperatures up to 120 °C. Within the framework of this work: a) the conditions for obtaining saturated solutions of boron oxide in organic solvents were found and it was found that boric anhydride is most completely dissolved in triethyl orthoformiate (approximately 25%) at 110-110 °C retaining its structure; b) by the condensation of boric acid with 1,3-dichlorotetraphenyl disiloxane, functional borcyclosiloxanes were synthesized to further modify boron oxide. The reaction conditions, spectral and thermal characteristics of condensation products were investigated. It is shown the increasing in the synthesis time to 15-18 h, a bicyclic borsiloxane is formed; c) homophasic modification of boric anhydride with monofunctional cyclic borsiloxanes was carried out and it was shown that the formation of Si-O-B bonds at 110-120 °C occurs due to the use of anhydrous sol-gel process. Transparent films are obtained from modified boric anhydride solutions deposited on glass and stainless steel, followed by curing at a temperature of 160-280 °C, that are not subjected to hydrolysis under the action of air moisture and are stable in air up to 600 °C. As a result of the work, the possibility of obtaining a borsiloxane type polymeric structures having an inorganic molecular skeleton modified with organosilicon compounds has been investigated.

scholarly journals Blend of natural waxes as a matrix for aroma encapsulation

2017 ◽  
Vol 15 (2) ◽  
pp. 103-111
Author(s):  
Jelena Milanovic ◽  
Gordana Ilic-Sevic ◽  
Marijana Gavrilovic ◽  
Milutin Milosavljevic ◽  
Branko Bugarski
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Elevated Temperatures ◽  
Thermal Characteristics ◽  
Feed Additives ◽  
Morphological Properties ◽  
Particle Size Range ◽  
Carnauba Wax ◽  
Potential Applications

In this study, the possibility of using a blend of natural waxes (bees and carnauba) for encapsulation of some aroma compounds was investigated. Melt dispersion/melt solidification technique was applied for microbeads production. Since one of the most important characteristics of the particles are the size and shape, particle size distribution as well as morphological properties are tested. Thermal characteristics are also examined as significant properties for thermal behavior at elevated temperatures, important for application of encapsulated particles in food production processes. Different contents of the carnauba wax in the mixture with beeswax are investigated, from 10% to 50% (w/w). Since one of the potential applications of the encapsulated aroma is in feed additives production, the targeted particle size range was under 300 ?m to be suitable for handling and mixing with other powder substances. According to the obtained results, a higher carnauba wax content in the wax blend had an impact on particle size distribution. Also, it had an impact on the surface morphology and thermal properties. The obtained results may contribute to the development of methods of encapsulation of hydrophobic aromas in the natural wax matrix.

An elastic harmonic inclusion near a rigid harmonic inclusion loaded by a couple

2019 ◽  
Vol 84 (3) ◽  
pp. 555-566
Author(s):  
Xu Wang ◽  
Liang Chen ◽  
Peter Schiavone
Keyword(s):  
Rigid Inclusion ◽  
Elastic Inclusion ◽  
Complex Loading ◽  
Solution Procedure ◽  
External Loading ◽  
Surrounding Matrix ◽  
The Matrix ◽  
Mapping Techniques ◽  
Loading Parameter ◽  
Harmonic Inclusion

AbstractWe use conformal mapping techniques to solve the inverse problem concerned with an elastic non-elliptical harmonic inclusion in the vicinity of a rigid non-elliptical harmonic inclusion loaded by a couple when the surrounding matrix is subjected to remote uniform stresses. Both a size-independent complex loading parameter and a size-dependent real loading parameter are introduced as part of the solution procedure. The stress field inside the elastic inclusion is uniform and hydrostatic; the interfacial normal and tangential stresses as well as the hoop stress on the matrix side are uniform along each one of the two inclusion–matrix interfaces. The tangential stress along the interface of the elastic inclusion (free of external loading) vanishes, whereas that along the interface of the rigid inclusion (loaded by the couple) does not. A novel method is proposed to determine the area of the rigid inclusion.

scholarly journals Attractiveness of thermally different, uniformly black targets to horseflies: Tabanus tergestinus prefers sunlit warm shiny dark targets

2019 ◽  
Vol 6 (10) ◽  
pp. 191119 ◽  
Author(s):  
Gábor Horváth ◽  
Ádám Pereszlényi ◽  
Tímea Tóth ◽  
Szabolcs Polgár ◽  
Imre M. Jánosi
Keyword(s):  
Field Experiments ◽  
Elevated Temperatures ◽  
Thermal Characteristics ◽  
Optical Characteristics ◽  
Degree Of Polarization ◽  
Small Scale ◽  
Host Animal ◽  
Reflected Light ◽  
Scale Models ◽  
Imaging Polarimetry

From a large distance tabanid flies may find their host animal by means of its shape, size, motion, odour, radiance and degree of polarization of host-reflected light. After alighting on the host, tabanids may use their mechano-, thermo-, hygro- and chemoreceptors to sense the substrate characteristics. Female tabanids prefer to attack sunlit against shady dark host animals, or dark against bright hosts for a blood meal, the exact reasons for which are unknown. Since sunlit darker surfaces are warmer than shady ones or sunlit/shady brighter surfaces, the differences in surface temperatures of dark and bright as well as sunlit and shady hosts may partly explain their different attractiveness to tabanids. We tested this observed warmth preference in field experiments, where we compared the attractiveness to tabanids ( Tabanus tergestinus ) of a warm and a cold shiny black barrel imitating dark hosts with the same optical characteristics. Using imaging polarimetry, thermography and Schlieren imaging, we measured the optical and thermal characteristics of both barrels and their small-scale models. We recorded the number of landings on these targets and measured the time periods spent on them. Our study revealed that T. tergestinus tabanid flies prefer sunlit warm shiny black targets against sunlit or shady cold ones with the same optical characteristics. These results support our new hypothesis that a blood-seeking female tabanid prefers elevated temperatures, partly because her wing muscles are more rapid and her nervous system functions better (due to faster conduction velocities and synaptic transmission of signals) in a warmer microclimate, and thus, she can avoid the parasite-repelling reactions of host animals by a prompt take-off.

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