Showing papers by "Lehigh University published in 1981"

Interpenetrating Polymer Networks and Related Materials

Abstract: To the surprise of practically no one, research and engineering on multi polymer materials has steadily increased through the 1960s and 1970s More and more people are remarking that we are running out of new monomers to polymerize, and that the improved polymers of the future will depend heavily on synergistic combinations of existing materials In the era of the mid-1960s, three distinct multipolymer combinations were recognized: polymer blends, grafts, and blocks Although inter penetrating polymer networks, lPNs, were prepared very early in polymer history, and already named by Millar in 1960, they played a relatively low-key role in polymer research developments until the late 1960s and 1970s I would prefer to consider the IPNs as a subdivision of the graft copolymers Yet the unique topology of the IPNs imparts properties not easily obtainable without the presence of crosslinking One of the objectives of this book is to point out the wealth of work done on IPNs or closely related materials Since many papers and patents actually concerned with IPNs are not so designated, this literature is significantly larger than first imagined It may also be that many authors will meet each other for the first time on these pages and realize that they are working on a common topology The number of applications suggested in the patent literature is large and growing Included are impact-resistant plastics, ion exchange resins, noise-damping materials, a type of thermoplastic elastomer, and many more"

Nonstoichiometry in Undoped BaTiO3

Abstract: Equilibrium electrical conductivity data for large-grained, poly crystalline, undoped BaTiO3, as a function of temperature, 750° to 1000°C, and oxygen partial pressure, 10−20

Stresses in adhesively bonded joints - A closed-form solution

Abstract: The plane strain of adhesively bonded structures which consist of two different orthotropic adherents is considered. Assuming that the thicknesses of the adherends are constant and are small in relation to the lateral dimensions of the bonded region, the adherends are treated as plates. The transverse shear effects in the adherends and the in-plane normal strain in the adhesive are taken into account. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form. A single lap joint and a stiffened plate under various loading conditions are considered as examples. To verify the basic trend of the solutions obtained from the plate theory a sample problem is solved by using the finite element method and by treating the adherends and the adhesive as elastic continua. The plate theory not only predicts the correct trend for the adhesive stresses but also gives rather surprisingly accurate results.

Recent progress in understanding environment assisted fatigue crack growth

Abstract: Metal fatigue has been well recognized as an important cause for failure of engineering structures. In most applications, fatigue damage results from the conjoint actions of the cyclically applied stress and the external (chemical) environment, and is therefore time dependent. Understanding of this load-environment interaction is essential to the formulation of rational life prediction procedures and to the development of realistic materials evaluation and qualification tests. Research over the past 15 years has led to the suggestion that the rate of fatigue crack growth in an aggressive environment, (da/dN)e, is the sum of three components—the rate of fatigue crack growth in an inert environment, (da/dN)r, which represents the contribution of “pure” fatigue, a cycle-dependent component, (da/dN)cf, that requires the synergistic interaction of fatigue and environmental attack, and the contribution by sustained-load crack growth (i.e., stress corrosion cracking) at K levels above K Iscc, (da/dN)scc. Recent fracture mechanics and surface chemistry studies have provided a clearer understanding of the cycle-dependent term, and, hence, a more complete understanding of environment assisted fatigue crack growth. (da/dN)cf results from the reaction of the environment with fresh crack surfaces produced by fatigue, and is a function of the extent of reaction during one loading cycle. For highly reactive alloy-environment systems, this contribution depends also on the rate of transport of the aggressive environment to the crack tip. The experimental basis and the development of models for transport and surface reaction controlled fatigue crack growth are reviewed. Interpretation of the effects of partial pressure of the aggressive environment and cyclic load frequency in terms of surface reaction and transport processes is discussed. Implications in terms of service performance and life prediction procedures are considered.

Solubility of TiO2 in BaTiO3

Abstract: Scanning electron microscopy and electron probe micro-analysis were used to investigate the microstructure of both slow-cooled and quenched polycrystalline BaTiO3 specimens with a small excess of TiO2 (Ba/Ti=0.995 to 0.999) or of BaO (Ba/Ti=1.002 and 1.005). The electron micrographs of polished and etched TiO2-excess BaTiOs samples, and of fracture surfaces of quenched samples, showed a second phase in the grain boundaries and triple-point regions, whereas no second phase was observed in samples having Ba/Ti=1.000. Microprobe analysis of the second phase gave compositions near that of the reported adjacent phase of higher TiO2 content, Ba6Ti17O40. The results indicate that the solubility of TiO2 in BaTiO3 is <0.1 mol%.

Viscoelastic Analysis of Adhesively Bonded Joints

Abstract: In this paper an adhesively bonded lap joint is analyzed by assuming that the adherends are elastic and the adhesive is linearly viscoelastic. After formulating the general problem a specific example for two identical adherends bonded through a three parameter viscoelastic solid adhesive is considered. The standard Laplace transform technique is used to solve the problem. The stress distribution in the adhesive layer is calculated for three different external loads namely, membrane loading, bending, and transverse shear loading. The results indicate that the peak value of the normal stress in the adhesive is not only consistently higher than the corresponding shear stress but also decays slower.

Acid-Base Interactions in Polymer Adhesion

Abstract: Most polymers and inorganic materials have acidic or basic sites (or both) which can interact to enhance wettability, adsorption, charge-transfer, and adhesion. These interactions, termed “polar” in the past, are independent of dipole moments and occur only when one material has acid groups which can interact with basic groups of the other material. the presence of a third component (solvent, plasticizer, penetrant, etc.) can interfere with adsorption, charge-transfer, or adhesion if the third component has strong enough acid-base interactions with either or both components. Water, a weak acid and a weak base, tends to weaken adhesion of polymers to inorganic materials but not when these have strong acid-base interactions. A quantitative approach to predicting the enthalpy ΔHab of acid-base interactions between polymers and inorganic surfaces is presented based on determining the E and C constants of Drago's correlation for polymers and inorganic surfaces. Preliminary E and C constants are presented for polymethylmethacrylate, for chlorinated polyvinylchloride, for silica surfaces and for iron oxide surfaces.

Energy Dispersive X-Ray Spectrometry

Abstract: The modern energy-dispersive x-ray spectrometer (EDS) coupled with a computer-based multichannel analyzer (MCA) provides a powerful analytical facility in the SEM lab. The purpose of this laboratory is to introduce the student to the basic concepts of energy-dispersive x-ray spectrometry and to examine some of the spectral artifacts inherent in the technique. More details and references can be found in SEMXM, Chapter 5.

The 10A phase in the system MgO-SiO 2 -H 2 O

Abstract: The l0A phase is a unique pressure-dependent hydrous phyllosilicate in the system MgOSiOr-H2O which is stable at pressures between 32 and 95 kbar and temperatures up to 535'C. Although it was previously characterized as a 2rh-octahedral member of the mica family, reexamination of this phase has resulted in a new chemical and structural model represented by the formula [(H3O)2xrIMgyISil"Orr(OH)r]. The results of X-ray powder difraction analysis, thermal analysis, and experiments in which the stoichiometry of oxide starting mixtures was carefully controlled indicate that the structure of the l0A phase is that of a fully trioctahedral 2:l phyllosilicate; it is similar to talc, but contains additional chemically-bound "water" in l2-coordinated sites [(HrO)]IIMg]ISi["O2.(OH[1.The results of infrared spectroscopy, however, indicate that this "water" is best represented as oxonium ions (H.O*) formed by interaction of the l2-coordinated interlayer H2O molecules with certain octahedral-layer hydroxyl groups accordiag to the relation:

High School Dropout: Psychological, Academic, and Vocational Factors.

Abstract: The correlates and presumable causes for dropping out: The phenomenon is more complex than might have been expected.

Rate controlling processes for crack growth in hydrogen sulfide for an alsl 4340 steel

Abstract: Parallel fracture mechanics and surface chemistry studies were carried out to develop further understanding of environment assisted subcritical crack growth in high strength steels. The kinetics of crack growth for an AISI 4340 steel (tempered at 477 K) in high purity hydrogen sulfide have been determined as a function of pressure at room temperature and as a function of temperature at hydrogen sulfide pressures of 0.133 and 2.66 kPa. The kinetics for the reactions of hydrogen sulfide with this steel and the extent of reactions were also determined. Two rate controlling processes have been identified. At the lower pressure, the rate of crack growth varies according to T1/2 and is controlled by the rate of transport of hydrogen sulfide to the crack tip. At the higher pressure, crack growth is controlled by the rate of diffusion of hydrogen into the steel ahead of the crack tip and exhibits an apparent activation energy of about 5 kJ/mol. Embrittlement results from hydrogen that is produced by the reactions of hydrogen sulfide with the steel. These reactions are extremely rapid and are limited in extent, leading to the formation of one to two layers of “sulfide” on the fracture surfaces. The crack growth results are discussed in terms of measured reaction kinetics and published data on diffusion, and in relation to models for transport- and diffusion-controlled crack growth.

Bending and Shear Deformation Effects in Lap Joints

Abstract: The problem of stress distribution in adhesive joints where two orthotropic plates are bonded through a flexible adhesive layer is analyzed. The effect of bending the adherends on the stresses in the adhesive layer is very significant. However, the transverse shear deformations of the adherends have, in general, very little influence on the adhesive layer stresses; therefore these shear strains of adherends can be neglected in many practical cases. The maximum transverse normal stress in the adhesive is, in general, larger than the maximum longitudinal shear stress.

Influence of absorbed moisture on fatigue crack propagation behaviour in polyamides

Abstract: The effect of plasticization on the fatigue crack propagation response in polyamides was examined by conducting fatigue tests on specimens of nylon 66 (N66), nylon 6 (N6) and nylon 612 (N612) which had been equilibrated at various levels of absorbed water. In N66 and N6, crack growth rates decreased as the water content was increased to about 2.5wt%; with increasing moisture content, FCP rates increased and at saturation (8.5 wt% H2O) FCP rates were higher than those observed in the dry polymer. Crackgrowth rates in N612 decreased monotonically as the water content increased to saturation (3.2 wt% in this polyamide). These results were interpreted in terms of the competition between enhanced crack-tip blunting and lowering of the specimen modulus. Crack-tip blunting was believed to dominate fatigue behaviour at low water contents (⩽2.5wt%) and contributed to reduced FCP rates. The higher crack-growth rates observed at higher moisture levels were believed to be caused by reductions in material stiffness.

Determination of tensile strength of soils by unconfined-penetration test

Abstract: This paper describes the factors affecting the test procedures and methods for preparation of test specimens for determination of tensile strength of soils by unconfined-penetration (UP) method. Correlation of tensile strength with other soil constants and strength parameters, such as Atterberg limits, activity, toughness index, unconfined compressive strength, cohesion, and friction angle, are presented. Theoretical explanations of this method and the conventional split-tension test by use of the limit analysis concept are discussed.

Boole's Algebra Isn't Boolean Algebra

Abstract: To Boole and his mid-nineteenth century contemporaries, the title of this article would have been very puzzling. For Boole’s first work in logic, The Mathematical Analysis of Logic, appeared in 1847 and, although the beginnings of modern abstract algebra can be traced back to the early part of the nineteenth century, the subject had not fully emerged until towards the end of the century. Only then could one clearly distinguish and compare algebras. (We use the term algebra here as standing for a formal system, not a structure which realizes, or is a model for, it—for instance, the algebra of integral domains as codified by a set of axioms versus a particular structure, e.g., the integers, which satisfies these axioms.) Granted, however, that this later full degree of understanding has been attained, and that one can conceptually distinguish algebras, is it not true that Boole’s “algebra of logic” is Boolean algebra?

An Assessment of A-C and D-C Potential Systems for Monitoring Fatigue Crack Growth

Abstract: Electrical potential techniques for crack length measurements have been used for over 15 years to monitor subcritical crack growth. These techniques, based on the changes in electrical resistance of a specimen with crack extension, utilize either a d-c or, more recently, an a-c measurement system. The d-c and a-c systems are described, and the operating characteristics of two specific systems are discussed. A description of the empirical calibration of a specimen using these systems is included. Operating data are included for crack length measurements in a steel compact tension specimen. The d-c system, operated at a current of 10 A, had a crack length resolution of 0.013 mm. The a-c system, employing a lock-in amplifier as a tuned amplifier to provide noise rejection, can be operated at a much lower current of 0.75 A and provided a crack length resolution of 0.010 mm. By design, the a-c system would reject thermal (d-c) electromotive force introduced into the measurement circuit, whereas the d-c system had no such capability. Both systems, however, would be sensitive to changes in resistivity of the material with temperature. In materials of high magnetic permeability, alternating current is not uniformly distributed through the specimen thickness and tends to be concentrated near the specimen surface. The consequences of this "skin effect" in relation to crack length measurements are discussed. Operating procedures that assist in reducing noise and improving measurement sensitivity in both systems are described.

Concerning the origin of charge at the polystyrene particle/water interface

Abstract: The electrophoretic mobility behavior of well-characterized polystyrene latex particles, carrying one type of surface functional endgroups, has been studied as a function of pH. At low pH, the interaction of protons with the functional endgroups increased in the order: Hydroxyl > carboxyl > sulfate; at high pH the order of interaction was reversed; and at intermediate pH no interactions were observed. The particles of the polystyrene latexes in their different forms at the intermediate pH range, dispersed in deionized water, all exhibited the same mobility irrespective of the functional endgroup. The origin of charge in these systems is explained as being the result of either the preferential adsorption of hydroxyl ions or an electron - injection mechanism due to the overlap of local intrinsic molecular - ion states in polystyrene and water. At low concentrations of functional endgroups, the surface properties of the polystyrene latexes are largely dependent upon the hydrophobic nature of the sur...

Oxide Scale Formation on Iron-Chromium Alloys in Elevated Temperature Air Environments

Abstract: Oxide scales formed on metals at elevated temperatures may be different, both chemically and structurally, from the scales on the metal once it has cooled to room temperature. This paper discusses Raman spectroscopy instrumentation for the in-situ identification of scales formed on metal surfaces exposed to gaseous environments. The results of an experimental program to characterize scales formed on two commercial iron-chromium alloys, AISI 446 and 502, in air and oxygen environments are also presented.

Thermoplastic interpenetrating polymer networks of a triblock copolymer elastomer and an ionomeric plastic. I. Rheology and morphology

Abstract: The thermoplastic interpenetrating polymer networks (IPNs) are combinations of two physically crosslinked polymers. Thermoplastic IPNs were prepared by combining polymer I, an SEBS triblock elastomer with polymer II, an ionomer prepared from a random copolymer of styrene, methacrylic acid, and isoprene (90/10/1 by volume). Neutralization of the acid groups to form the ionomer was carried out on a Brabender Plasticorder. Two subclasses of the thermoplastic IPNs were identified. Chemically blended systems, prepared by a sequential polymerization method, were compared with compositionally equivalent mechanically blended systems prepared by melt blending the separately synthesized polymers. The chemically blended thermoplastic IPNs (CBT IPNs) exhibited lower melt viscosities than compositionally equivalent mechanically blended thermoplastic IPNs (MBT IPNs). Moreover, the melt viscosities of many of the CBT IPNs were even lower than that of either homopolymer component, leading to an explanation in terms of an unusually low value of the rubbery modulus front factor. Although both types of thermoplastic IPNs underwent a phase inversion during neutralization of polymer II, the phase inversions were often incomplete. Morphological studies revealed that more equal dual phase continuity existed in the MBT IPNs than in the CBT IPNs after ionomer formation.

Poly(n-butyl acrylate) polystyrene interpenetrating polymer networks and related materials. ii: aspects of molecular mixing via modulus-temperature studies

Abstract: The glass transition, rubbery modulus, and tensile behavior of poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks (IPN's), semi-1 IPN's, and their corresponding random copolymer networks were studied as a function of both composition ratio and crosslink density. Two temperatures were selected for analysis: 25°C, halfway between the two transition temperatures, and at 160°C., in the rubbery plateau region. The modulus data at 25°C were compared with wellknown composite models. The moduli of the IPN's and semi-1 IPN's lie close to the Davies model in the polymer II rich region but follow the Budiansky model in the polymer I rich region. In one interpretation of the Coran-Patel model, a phase inversion takes place around ϕ2 = 0.8, which is higher than the composition at which the phase connectivity of polymer II begins to appear, ϕ = 0.5, via electron microscopy studies. The rubbery modulus behavior of the full and semi-1 IPN's follow the equation of Siegfried, et al. reasonably well, which considers the deformation effect of polymer I in terms of the rubber elasticity front factor. The stress-strain behavior of both the full and semi-1 IPN's was similar to that of toughened plastics at polymer II rich compositions, and to that of reinforced elastomers at polymer I rich compositions.