Durability Values Research Articles

The Initiation of Polypropylene Oxidation

The rate of primary initiation of PP oxidation with catalytic centers containing transition metals was evaluated. The rate was determined from the retardation period of the oxidation reaction in the fracture sites of stressed PP films with an inhibitor when the retardation period was close to the value of durability. The number of initiation centers was taken into account. For this purpose, the predicted durability of samples was calculated for the concentration of initiation centers of the polymer without additives. Inhibited PP films with various complexone contents introduced to the polymer to deactivate the catalytic centers were studied. The rate of initiation was shown not to change in the presence of the complexone, while the number of centers changed. The comparison of the oxidation kinetics of samples derived from the oxygen absorption using data from this study showed that the macrokinetic parameters were dependent on the number of the initiation centers. Thus, the kinetic regularities were shown to be related to the catalytic activity of initiation centers and also to their concentration.

Development of the erosion durability technique for thin coatings

A novel method has been developed to assess the durability of thin coatings exposed to solid particle erosion. In this test a stream of particles travels from a parallel nozzle to strike a coated surface. The divergence of the stream leaving the nozzle can be described analytically and the flux of particles at any point may thus be predicted. By monitoring the growth in the diameter of the wear scar the critical dose Q c of particles required to remove the coating may be determined and used to describe the durability of the coating. The behaviour of a series of well-characterised titanium nitride PVD coatings on tool steel substrates has been studied. Q c depended on the erosion conditions (particle type, shape, size and velocity) and on the thickness of the coating. The effects of these parameters were systematically investigated and an analytical relationship determined which allows values of durability to be normalised. The work has provided an improved understanding of the properties determined by the erosion durability test and has also suggested methods for tailoring the technique to investigate different aspects of coating performance such as adhesion.

Effects of composition changes on the crystallization behaviour and properties of SiO 2-Al 2O 3-CaO-MgO (Fe 2O 3-Na 2O-K 2O) glass-ceramics

Several glass-ceramic materials located in the SiO 2-Al 2O 3-CaO-MgO(Fe 2O 3-Na 2O-K 2O) system were formulated by using naturally occurring materials and 1 wt% chromite ore as a nucleant. The crystallization behaviour of specimens was investigated by using dilatometric, DTA and XRD techniques. It was found that the replacement of CaO by MgO has a profound effect on the crystallization behaviour of specimens and some of them show almost complete crystallization. After a two stage heat treatment, an aluminium dioxide phase was identified as the sole crystallization product in all specimens. The microstructures were investigated by SEM. It was found that phase separation occurs prior to nucleation of dioxide and the latter phase grows into a fibrous shape. The bending strength of crystallized specimens which range from 31 to 76 MPa depends on the degree of crystallinity and on the porosity of specimens. The hardness and chemical durability values depend only on the amount of crystalline phase.

A survey of the engineering properties of some anhydrite and gypsum from the north and midlands of England

The Permian and Triassic systems in the north and midlands of England contain notable beds of anhydrite and gypsum. These rocks contain small but varying amounts of muddy material which often has some influence on their geomechanical properties. Anhydrite is a strong to very strong rock in terms of both its unconfined compressive strength and point load index, whereas gypsum is of medium strength according to its unconfined compressive strength. Because of the low porosity of these rocks, porosity does not have a significant influence on their strength. However, the strength and hardness of these rocks are strongly correlated. In terms of the slake-durability test, anhydrite has a very high durability and gypsum a high to very high durability, with the stronger rocks yielding higher values of durability. Most anhydrite and gypsum exhibit plastic-elastic-plastic deformation, subsequent plastic deformation occurring at an earlier stage during loading of gypsum than of anhydrite. As far as deformability is concerned, that of anhydrite is very low while that of gypsum varies from low to high. Both rock types experience hysteresis on cyclic loading, that of gypsum being more notable than that of anhydrite and the amount of hysteresis undergone increases with successive cycles of loading and unloading. Anhydrite and gypsum both undergo creep when subjected to constant loading, gypsum being the more prone to creep under constant load.

Effects of BSS and BSS + Irrigation Solutions on Rabbit Corneal Transendothelial Electrical Potential Difference

Measurements of electrical potential difference across isolated rabbit corneal endothelium (transendothelial electrical potential difference, TEPD) were used to evaluate the effect of two commonly used commercially prepared intraocular irrigation balanced salt solutions, BSS and BSS+, together with our own standard bicarbonate-containing control solution (BS). The highest and most durable TEPD values were obtained by using BSS+; TEPD began at 550 microV, peaked at 600 microV 1 h later, and then decreased slowly down to some 300 microV after about 8 h. Gassing BSS+ with an air/5% CO2 mixture was optimal; gassing it with air reduced the TEPD values slightly, by about 10%. On the other hand, perfusion with BSS gassed with air had a rapid and marked adverse effect; the TEPD, which began at some 500 microV, fell down precipitously to about 50 microV after 1 hour. In contrast, perfusion with BSS on the endothelial side with the addition of BS to the stromal side, both sides being gassed with an air/5% CO2 mixture, maintained the TEPD at levels near those obtained with BSS+. We attribute the adverse effect by BSS to the absence of bicarbonate in it. From these and past results, we conclude that BSS cannot be recommended for intraocular use as a properly balanced saline solution.

The Value of Bank Durability: Borrowers as Bank Stakeholders

ABSTRACTWe examine the value of bank durability to borrowing firms. The analysis is based on theoretical models of the asset services view of intermediation which imply that private information and associated relationship‐specific activities are intrinsic to bank lending. We analyze share price effects on firms with lending relationships with Continental Illinois Bank during its de facto failure and subsequent FDIC rescue. We find the bank's impending insolvency had negative effects and the FDIC rescue positive effects on client firm share prices. We conclude that borrowers incur significant costs in response to unanticipated reductions in bank durability and thus are bank stakeholders.

The Value of Bank Durability: Borrowers as Bank Stakeholders

The Value of Bank Durability: Borrowers as Bank Stakeholders

Determination of the relative oxidative stability of petroleum bitumens by thermogravimetry

An isothermal thermogravimetric technique was used to determine the apparent activation energies ( E a) for the oxidative degradation of petroleum bitumens produced from different crude sources and with different histories. The values of E a were found to be different for each bitumen. For a particular bitumen, E a was independent of temperature over the range studied (240–370°C), but increased with increasing fractional conversion (α). A good correlation at low α was established between E a and the durability value for each bitumen. The durability value is a relative measure of oxidative stability derived from an oven aging procedure (100°C) which has been found to be useful in predicting actual sprayed bitumen seal lifetimes in the field.

A Scale Effect in the Durability of Oriented Thin-Wide Polypropylene Films during Oxidation under Load: Fracture Model of Stressed Polypropylene Films

Abstract Studies have been made of the durability of oriented isotactic polypropylene (PP) films depending on their width during intensive oxidation (T = 130°C, P02 = 20 kPa) under load. As the specimen width decreases under low stresses, mean durability is determined thermooxidative destruction rate at the nucleation sites the scale effect takes place. The durability values are found to be discrete multiples of integers for narrow specimens. The conclusion is drawn that the difference in polymeric specimen durability is determined by the concentration of defect zones, rather than by the versatility of their nature. The model of oriented PP films fracture under low-load oxidation conditions is proposed. This model is based on the dependence of durability on a number of oxidation destruction centers which are similar in nature (in the initiation rate) and cause specimen fracture while growing and joining together.

Coal Measures mudrocks: composition, classification and weathering processes

Abstract British Coal Measures mudrocks are dominantly non-marine, mature sediments with a high average clay minerals content of over 75%. A geological classification based on quartz content does not differentiate the dominant durable mudrocks from the non-durable types and overconsolidated clays in the formation. A uniaxial compressive strength greater than 3.6MN/m 2 with a three cycle slake durability value of over 60% is suggested as an appropriate division between durable and non-durable mudrocks of this age. Physical breakdown, which acts as a control on chemical weathering triggered by pyrite oxidation, is considered to be governed by incidence of sedimentary structures, slaking and expandable mixed-layer clay content. Shear strength reduction during post-glacial weathering can be significant. A tentative fully weathered effective stress peak strength for the weakest mudrocks and clays is deduced to be φ′ = 22°( c ′ = 0). Colliery tip investigations indicate that chemical weathering effects on the shear strength of the mudrocks are small. A diagenetic rank factor applies both to peak shear strength and slake durability of mudrocks excavated from UK coal mines.

Tensile flow and stress–strain behavior over a wide temperature range for poly(butyl methacrylate) with a broad molecular weight distribution

AbstractThe poly(butyl methacrylate) studied is a polymer with a normal molecular weight distribution and a relatively low molecular weight close to Mc, the critical molecular weight from the viscosity–molecular weight relation. The polymer was subjected to uniaxial extension and shear over a temperature range which included Tg. It was found that in the region of Tg an increase in applied stress is accompanied by a decrease both in the temperature shift factor aT and in the activation energy for relaxation and rupture of polymer melts. Close attention is given to the long‐term durability of the polymer. As is expected in the temperature range below Tg, its dependence on the stress is exponential, whereas at temperatures above Tg a power law fits the data. In the latter case a log‐log plot of the long‐term durability versus stress can be represented by two intersecting straight lines which can be replotted as a generalized straight line if the long‐term durability values are normalized by the viscosity.

Electrical ageing of polymeric dielectrics under conditions of suppression of partial discharges

Durability values have been measured for a number of polymer in relation to the strength of constant and variable (50 Hz) electric fields and temperature (193–393 K) under conditions where the level of partial discharges did not exceed 10 −14 Coulomb. Exponential type dependences were obtained for relations between durability and field strength. Some features of the temperature dependence of durability have been detected. The kinetics of electrical breakdown of polymers has been analyzed in a constant field on the basis of concepts of tunnel ionization of macromolecules and subsequent thermofluctuation rupture of macroions in an electric field.

A Search for Procedures for Restoration and Stabilization of 16th and 17th Century Netherlands Atlases Damaged by Green Paint

The Netherlands illuminated atlases of the 16th-17th centureies of the M.E. Saltykov-Shchedrin State Public Library collection have been badly damaged due to the effect of green paint. The browning of the green paint, as well as of the parts of the reverse side of the sheet where the green paint was applied on the foreside, was observed. The brittleness of the paper under the paint increased which resuIted in the fracture of the sheet or losing fragments. The problem was to find a procedure for the conservation of paper and paint and develop proper methods for work with these materials. The paper properties and the paint composition of the atlases were investigated. In most cases the green paint was found to contain the pigment verdigris, which is the salt of copper acetate. Model samples were produced using copper acetate as the pigment of the paint. The change of properties in the process of artificial aging was estimated. The procedure for conservation of the atlases' sheets included the spreading of a protection cover by means of ethylcellulose solution; bleaching with Chloramine B or hydrogen peroxide solution; removal of the ethylcellulose film; stabilization treatment with calcium and magnesium bicarbonate solutions and impregnation with poly(vinyl alcohol) or fluoroplastic solutions; or lamination with tissue-paper. The permanence and durability value of the paper after the treatment was approximated.

Shale rating system and tentative applications to shale performance : Franklin, J A Transp Res Rec, N790, 1981, P2–12

A rating system based on three properties-durability, strength, and plasticity-is proposed. A shale sample is assigned a rating value by first measuring its second-cycle slake-durability index. Rocklike shales that have durability values greater than 80 percent for this index are further characterized by measuring their point load strength. Soillike shales that have durability values of less than 80 percent are further characterized by mearsuring their plasticity index. The shale rating, derived from these test results by using a rating chart, is a continuously variable number in the 0.0-9.0 range. Tentative correlations (trend lines) are proposed that link this rating with aspects of engineering performance such as excavating mehtods (e.g., whether to dig or to blast), foundation properties (e.g., bearing capacities and foundation moduli), embankment construction (e.g., lift thicknesses and compaction methods), and slope stability (e.g., relations between slope height and angle and failure mechanisms).

Features of strain-strength properties of butadiene-styrene block copolymers under uniaxial stretching

Abstract The strain and strength behaviour of a block copolymer has been studied for various regimes of uniaxial strain at temperatures below the glass transition temperature over a wide range of deformation rates, stresses and deformations. It was shown that the process of polymer creep may be accompanied by its irreversible flow, the viscosity of which is highly sensitive to changes of stress and temperature. It was shown that the durability of block copolymer is described by regularities characteristic of rubbers. However, the formation of material from solutions may considerably change the observed regularities and influence the values of durability and corresponding strength. The regularities found are explained by a change in the two-phase structure of the material under the influence of external force, temperature and method of formation.

Spectrum of durability times of polymer films

A spectrum of durability times (of four individual times) is observed in PETP film samples. Although the average value of durability depends on tensile stress, durability levels do not depend on stress. The time dependence of stress is explained by the fact that with a change in stress the density of levels and therefore, average durability change. It is assumed that it not the propagation of micro-cracks, but the formation of structural defects of another type and transition from one type to another by the action of the stress applied, which is the most important process that takes place in polymer films.

The influence of molecular weight and of polydispersity on the durability of high density polyethylene

The results are given regarding an investigation of durability values and changes in the MW of high density polyethylene fractions over a range of M ν from 4 × 10 4 to 3 × 10 5. Dumbell specimens were stretched in a medium consisting of an aqueous solution of OP-10 emulsifier at 70°. The durability of fractions has been analyzed in relation to the molecular weight values of M w, M ν and M n . It is shown that the dependence of durability on M ν for the fractions differs from that observed for polydisperse specimens. The dual character of the influence of polydispersity on the durability is brought to light, and an attempt to explain this finding has been made.

Possibilities of strength prediction of adhesive joints of polymers by master curve method

In the present work it is shown that the strength, depending on temperature and strain, and durability, depending on temperature and static load, of adhesive joints of polymers with adhesive of elastomer type can be predicted from master curves, drawn according to the principle of temperature–time analogy. Shift factors, determined by the Williams-Landel-Ferry (WLF) equation with universal values of constants, have been used to draw the master curves. It allowed to find relations between reference temperature and glass transition temperature of the adhesive. Their existence can be explained on the basis of free volume theory. Referring to the analogous influence of temperature and the part of the plasticizer inserted into the adhesive, on the strength of adhesive joints the existence of temperature–concentration analogy has been determined on the phenomenological level. Nomograms have been suggested for the calculation of strength and durability values from the master curves. Their application is convenient for repeated usage of master curves.

Hydrodynamic resistance and the heat loss of rotating solids. (Book) : L. A. Dorfman, translated by N. Kemmer, Oliver and Boyd, Ltd., Edinburgh and London, 1963, ix + 244 pages, 63s. For review see Nature, 200 (1963) 820–821

The article describes the method of estimation of the fatigue life under the multi-parameter random loading. This type of loading occurs when the investigated structure is exposed to the complex load in the form of independent random processes. The processes of changing the stress tensor components in the hazardous area are independent random processes. The proposed method is based on calculating of the microplastic deformations. To calculate microplastics, the structural material model built on the description of the diagram of deformation dependence by the Bridge Ramber-Osgood is used. To identify the model of accumulation of damaged conventional, mechanical and fatigue properties of the material are used. The article presents the fundamental equations of the method. The method of accounting of the mean stress is proposed. The adequacy of the approach is confirmed by comparing the calculation results with the experimental data. Under uniaxial harmonic and random loading calculation results using the proposed model coincide with those obtained by traditional methods. In terms of the plane stress state, the difference between the calculated and experimental values of the experimental durability does not exceed 30% which is quite satisfactory for the case of a high-cycle fatigue.

Art in Liberal Education

Liberal education has no place in an authoritarian nor in a purely technological world; only in a humanistic world can it prosper. There are those who prophesy that liberal colleges will have disappeared in America within a decade. While there may yet be time it behooves those who esteem truth and goodness and beauty as durable values to join forces for the perpetuation of the free human spirit.