Tensile Stress Measurements Research Articles

Elongational flow opto-rheometry for polymer melts

Polymer melt elongation is one of the most important procedures in polymer processing. To understand its molecular mechanisms, we constructed an elongational flow opto-rheometer (EFOR) in which a high precision birefringence apparatus of reflection-double path type was installed into a Meissner's new elongational rheometer of a gas cushion type (commercialized as RME from Rheometric Scientific) just by mounting a small reflecting mirror at the center of the RME's sample supporting table. The EFOR enabled us to achieve simultaneous measurements of tensile stress σ(t) and birefringence Δn(t) as a function of time t under a given constant strain rate $$\dot \varepsilon _0$$ within the range of 0.001 to 1.0s−1. σ(t) can be monitored upto the maximum Hencky strain ɛ(t) of 7 as attained, in principle, with RME, while the measurable range of the phase difference in the birefringence was 0 to 250 π (0 to 79 100 nm for He-Ne laser light) within the accuracy of ±0.1 π (±31.6 nm) up to ɛ(t) ∼ 4. The performance was tested on an anionically polymerized polystyrene (PS) and a low density polyethylene (LDPE). For both polymers σ(t) first followed the linear viscoelasticity rule in that the elongational viscosity, $$\eta _E (t) \equiv \sigma (t)/\dot \varepsilon _0$$ , is three times the steady shear viscosity, 3η o(t), at low shear rate $$\dot \gamma$$ , but the η E (t) tended to deviate upward after a certain Hencky strain $$\varepsilon (t) = \dot \varepsilon _0 t$$ was attained. The birefringence Δn(t) was a function of both Hencky strain $$\varepsilon (t) = \dot \varepsilon _0 t$$ and strain rate $$\dot \varepsilon _0$$ in such a way that the stress-optical law holds with the stress-optical coefficient C(t) = Δn(t)/δ(t) being equal to the ones reported from shear flow experiments. Interestingly, however, for PS elongated at low strain rates the C(t) vs σ(t) relation exhibited a strong nonlinearity as soon as σ(t) reached steady state. This implies that the tensile stress reaches the steady state but the birefringence continues to increase in the low strain-rate elongation. For the PS melt elongated at high strain rates, on the other hand, C(t) was nearly a constant in the entire range observed. For LDPE with long-chain branchings, σ(t) exhibited tendency of strain-induced hardening after certain critical strain, but C(t) was nearly a constant in the entire range of σ(t) observed.

Tensile stress measurements of dilute polymer solutions containing traces of salts and dyes

Tensile stress studies were made on dilute solutions of poly(ethylene oxide) and polyacrylamide using a fiber spinning apparatus to investigate the interaction of polymer molecules with the flow field. The addition of dyes or metal ions to the solutions has a considerable influence on the tensile stress. These ingredients normally cause contraction of the polymer coils and stiffen the molecular chains. One additive, Congo Red, markedly increased the tensile stress of poly(ethylene oxide) solutions.

Stress and birefringence relaxations of noncrystalline linear polymer

Internal stressses in noncrystalline, linear polymer materials arise from two different sources: deviation of polymer conformation from is equilibrium state and change of intersegment distances. The separation of the two components in stress relaxation by simultaneous measurements of tensile stress and birefringence was carried out over the temperature range from the glassy state to the terminal zone, using three samples of polystyrene with different molecular weights. The master curves and relaxation spectra of the two stress components were constructed from the data. Discussion was given to the relaxation spectra for comformational deformation

Hot electron effects in 2DEGS in Si of low Ndepl

Studies have been made of Si 2DEGS formed on (001) high resistivity ( rho approximately 1000 Omega cm) p-type substrates in the hot-electron region. Thermal population of an excited subband leads to a decrease in resistance in contrast with the increase seen in 2DEGS formed on lower resistivity substrates, and this suggests that mu (Eex)> mu (E0) in these samples, though which of the excited subbands, E'0 or E1, is lowest is not known. Tensile stress measurements indicate that mu (E'0)> mu (E0) and this is attributed to the greater average distance of the electrons from the interface resulting from their weaker confinement in high-resistivity substrates.

Direct measurement of tensile stress (‘‘tack’’) in thin ink films

A printing press tackmeter was built by fitting a pressure sensor into the printing cylinder of a laboratory printing press. This tackmeter has been used to measure pressure profiles of thin (3–14 μm) ink films under printing conditions. We define the maximum tensile stress (or negative pressure) that the ink can withstand in the nip exit before splitting to be the tack of the ink. The tack of inks without dissolved polymer appears to be independent of film thickness. The tack of inks with dissolved polymer resin increases strongly with increased amount of ink in the nip, while pigment and dispersant content have a minor effect on ink tack. This suggests that at high speed, ink tack is mainly characterized by the response of polymer molecules toward rapidly applied stress. No universal correlation was found between the tack and viscous flow properties of the ink.

Conformational changes of linear polymers in the glassy state

Internal stresses in glassy polymer materials arise from two different sources; deviation of polymer conformation from its equilibrium state and change of intersegment distances. These stress components may be separately observed by carrying out simultaneous measurements of tensile stress and birefringence relaxations of polymer films, assuming that they are additive. It is pointed out that the change of intersegment distances occurs first, and conformational deformation is gradually induced if a glassy polymer film is elongated

磁気異方性センサによるレール鋼の非接触応力測定

The magnetic anisotropy sensor (MAS) is based on the phenomenon that steel materials, when brought under application of stress, change in their magnetic anisotropy. The MAS has a small, light probe and is capable of noncontact stress measurement. This paper deals with the experimental result of noncontact stress measurement of rail steel. The specimen was cut from a real 60 kg rail steel. Tensile and compressive stress were applied to the specimen using a fatigue testing machine. Good linearity was disclosed between MAS output voltage and stress of the rail steel over the range of tensile stress measurement 0 to +160 MPa with demagnetization.

Electrical conductivity of elongated polypyrrole film

The mechanical and electrical properties of elongated polypyrrole film have been investigated. The maximum elongation ratio of electrochemically prepared polypyrrole film increased on decreasing the elongation speed and reached 0.55. The simultaneous measurement of tensile stress and electrical resistance of the film during elongation has also been carried out. The approximately constant resistivity of the film by weight or volume was observed during measurement at slow elongation speeds; this provides evidence that the polypyrrole is a low-dimensional conductor. The electrical conductivity of the elongated and relaxed films increased in proportion to the square of the elongation ratio. The films with an elongation ratio of over 0.25 exhibited anisotropy in the conductivity.

Stress Sensitive Property of Fe-base Amorphous Alloy

The high stress sensitivity of Fe-base amorphous alloy was studied. Permeability variation under uniaxial tensile stress measurements showed that the alloy had a saturation magnetostriction of 20 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> and a Young's modulus of 10000 kg/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Permeability variation reached maximum in the neighborhood of 20 kHz, exhibiting the same tendency when the level was varied from 20 to 100 mOe. These results confirm the previous result that magnetization conditions of 20 kHz and 20 mOe are appropriate when making use of stress sensitivity.

Tensile stress measurements on linear and branches low-density polyethylene melts. Interpretation of results with a generalized Maxwell model

Dynamic shear experiments in the linear range of deformation and extensional tests at constant strain rate have been carried out on a linear low-density polyethylene (LLDPE) melt and on two branched low-density polyethylene (LDPE) melts with different amounts of long-chain branching. Both the dynamic shear moduli and the tensile stress obey the time–temperature superposition principle. A simple model based on a nonaffine generalized Maxwell model with two relaxation times is proposed to describe the rheological behavior in elongation of these melts. Close agreement between the model and the experimental data can be obtained by adjusting the two relaxation times and the “slip parameter” of entanglements. The variations of these parameters with strain rate and their relationship with molecular structure are discussed.

The yield and thermoelastic properties of oriented poly(methyl methacrylate)

Oriented sheets of poly(methyl methacrylate) were prepared by drawing to different draw ratios at a range of temperatures near the glass transition temperature. The degree of molecular orientation in these materials was characterized by measuring birefringence, and specimens prepared for measurements of tensile yield stress and shrinkage stress at elevated temperature. The shrinkage stress measurements were carried out by holding specimens at constant length above the glass transition temperature and determining the resulting stress as a function of time. The peak value of stress was found to be a function of birefringence only, independent of draw ratio or draw temperature. The function was linear for a substantial range of birefringence. A further series of specimens was used to measure the tensile yield stress (in the orientation direction) as a function of temperature and strain rate. At each testing temperature it was found that the yield stress correlated uniquely with the birefringence. These results for shrinkage stress and yield stress can both be interpreted through the concept of a frozen-in molecular network, and a semi-quantitative relationship proposed which relates to the anisotropy of the yield stress to the frozen-in network stress. This provides a molecular explanation for the Bauschinger effect observed in oriented polymers.

Measurement of tensile stress at the exit of a printing nip

Measurement of tensile stress at the exit of a printing nip

Prediction and Measurement of Compressive and Tensile Stresses in Coatings of Tic and Tin Chemically Vapour Deposited on Various Substrates

Residual stresses in chemically vapour deposited (CVD) TiC and TiN coatings on various substrates were measured using X-ray diffraction. A quantitative prediction of the vaiue of the strain (and stress) was obtained from the difference in thermal shrinkage between layer and substrate on cooling from the CVD temperature to room temperature. The sign of the strains measured always agreed with the prediction, but in a number of cases the absolute value of the elastic strain measured was smaller than that predicted. For layers on iron and Fe-1.0 wt-%C substrates this difference is caused by strain accommodating processes in the substrate, mainly during phase transformations. For TiN layers on molybdenum and tungsten substrates, strain accommodating processes occur in the layer, and these may originate in the microstructure of the layer.

Behaviour of vacancies during oxidation

AbstractThe behaviour of point defects during oxidation has been re-examined in terms of the process of vacancy injection, the oxide-induced stress, and the oxygen-carbon gas reaction. In zinc and magnesium, the growth of dislocation loops as a function of oxygen pressure for specimens of different orientation is incompatible with the concept of oxidation-induced stress, but is consistent with vacancy injection. In nickel containing carbon, the amount of voiding on oxidation is prolific and is associated with the production of CO2. However, the measurement of oxide-induced tensile stress and the metallographic examination of oxidized single crystals both support a process of vacancy injection rather than vacancy generation by oxide-induced stress. In decarburized nickel, the oxidation rate increases dramatically compared with carbon-containing nickel, because the vacancies produced by oxidation are not required to relieve the stresses set up by the gas pressure arising from the carbon-oxygen gas reaction ...

The Strengthening Mechanism in Consolidated Rapidly Solidified Alloys

ABSTRACTAttempts have been made to study mechanisms of strengthening in the Ni68W22C8B2 and the Ni45CO20 Cr10MO4Fe5B16 alloy systems during their amorphous crysialline transitions. In the Ni68W22C8B2 system where amorphous particulates of varying sizes have been cons Ti a ed at high pressure and low temperature (3.6 MPa, and 673°K respectively), the initial stage of crystallization is marked by transformation of the localized regions of the specimen. These crystallized regions contain microcracks and voids. Microhardness measurements from the consolidated specimens indicate an increasing trend in the microhardness with decreasing particulate sizes. Premature failures of the consolidated specimen during tensile stress measurements have been attributed to the presence of microcracks and voids in these specimens. In the Ni45Co20Crl0Mo4Fe5B16 alloy system isothermal annealing of an initially amorphous alloy has been allowed to produce grains of varying sizes. The tensile stress measurements from these thermally annealed ribbons indicate two distinctly different functional relationships between the strength, σ, and the grain size parameter, λ. In the early stage of transformation where grain reach a maximum growth of up to 400 Å, the functional form of the strength, σ, with the grain parameter, λ, is σ = σ + K Log λ, where σO and K are constants. During latter stages of transformation, where grains larger than 400 Å have been formed, the strength, σ, varies with the inverse square root of the grain sizes. This latter relationship is analogous with the well known Hall-Petch relationships, which describes the strength, σ, as a function of the grain sizes in conventionally processed alloys.

Measurement of the tensile strength of a powder bed by a swing method measuring instrument

The measurement of the tensile strength of a powder bed has been carried out by means of the swing method measuring instrument, which has been developed by the authors. The effects on the void fraction and the moisture content have been investigated. From the stress—displacement curves obtained directly with this instrument, the work required for the tensile breakage of the powder bed was calculated. The most interesting problem is the application of the measurement of tensile stress to the design of powder treatment processes. The floodability of fine powders has been discussed empirically but theoretical bases are not sufficient for the evaluation of the potential floodability. The following dimensionless number, namely the ratio of the cohesive force to the gravity force on a single particle, ▪ was found to give a good correlation with the empirical floodability index evaluated by Carr's method.

Critical current behavior in bending and tensile stressed Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn composites at temperatures below 4.2 K

Critical current measurements were obtained on bronze-diffused reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn multifilamentary conductors as a function of mechanical stress loads and applied transverse magnet fields up to 13 T for temperatures in the range between 4.2 K and 1.9 K. To simulate the winding handling of reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn wires for superconducting magnets, operated in normal or superfluid helium the effects of room temperature bend strain on current carrying capacities of monolithic and flat cable conductors were investigated by controlled winding processes using mandrels with various diameters. The results show a field-dependent degradation in critical current with increasing bend strain for both conductor types. Only a very small precompression effect (< 0.5%) on critical current is observed. At higher strain, beginning at 0.4%, the critical current decreased rapidly, reaching at 13 T by more than 50% at a bending strain of 0.9% calculated on overall conductor cross section. Both optical and scanning electron microscopy were used to examine the samples before and after testing. Additional data on the mechanical properties (tensile stress-strain diagrams) of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn samples are presented, along with some preliminary critical current versus uniaxial tensile stress measurements at 2.2 K and 4.2 K, respectively. First results indicate that the increase in critical current at 2.2 K is relatively larger (about 25%) than that at 4.2 K. This fact is interesting for Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn magnets cooled with superfluid helium to obtain a broad strain tolerance.

Determination des contraintes dans les depots electrolytiques au moyen des diagrammes de kossel

Electrodeposits of Ni have been investigated by means of Kossel diagrams and electron diffraction patterns. The epitaxial relation observed on single-crystal copper substrate was of the (100) Ni/(100) cu type. A face centered tetragonal structure of Ni was found by the tensile stress measurements.

Separation of Filler Particles from the Matrix in a Particulate-Loaded Composite Subjected to Tensile Stress

Abstract Simultaneous measurements of tensile stress, longitudinal strain, and transverse strain were obtained on particulate-filled composites. The matrix was a flexible epoxy polymer. Small glass spheres were used as filler in various volume ratios up to 0.35. The spheres were pretreated as follows: clean, coated with a parting agent, coated with either of two silane coupling agents. The volume-expansion behaviors of these four systems of composites showed differences attributed to matrix-filler separation and subsequent vacuole formation. Stress-strain behaviors were especially sensitive to this dewetting process. These two types of data, obtained simultaneously and considered together, thus provide valuable information about interface adhesion.

Mechanical anisotropy of oriented polymers

Measurements of tensile and shear yield stress have been made on strips cut at various angles to the draw direction from films of drawn amorphous poly(ethylene terephthalate). The data were well fitted by a criterion of the von Mises type but with modifications to allow for the anisotropy of the samples and also for a built-in compressive stress in the draw direction. In the tensile experiments a sharp neck is usually formed at an angle to the tensile direction and this angle is predicted with good accuracy by an application of the theory of plastic potential.