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Critical crack tip stress intensity factor (Kc) measurements were made for polyester resin reinforced with glass chopped strand mat (CSM) and woven roving fabric (WRF). Specimen thickness and initial crack length were varied for centre notched (CN) 100 mm wide? specimens. Some specimens were saturated by immersion in water under pressure. Kc was negligibly affected by specimen thickness and it was concluded that plane strain conditions are not achieved in laminates of normal thickness. Scatter can be reduced by adjusting results to a standard glass content and Kc varies continuously with crack length. The CSM experiments were extended to 915 mm wide specimens which failed at very low nett section stresses but there may be a region in which Kc is roughly constant relative to crack length. In WRF specimens, however, it is the nett section stress which is constant at a value substantially below the UTS. Fatigue crack-growth studies were carried out on CN specimens. The Paris law adequately describes crack growth in CSM specimens at low rates of growth but Forman's law is better at high rates of growth. Neither law is valid for WRF material when dry but the behaviour changes after saturation with water. The crack-growth resistance of both materials is severely reduced by saturation with water.

The chemical states of iron species, produced in manganese phosphate coatings by the immersion of steel in a manganese phosphate bath, were analysed with the help of conversion electron and conventional transmission Mössbauer spectrometry (CEMS and TMS). The modifications of hureaulite by the variation of iron to manganese ratio are discussed with regard to the growth of manganese phosphate coatings. The thermal properties of manganese phosphate coatings and synthetic hureaulite were also investigated by means of differential thermal analysis and the composition analysis of thermal products.

The development of bioglass composites is presented. Stainless steel AlSl 316 L fibres are introduced into bioglass by immersion of premade porous fibre skeletons into molten bioglass. It is shown that this technique is simple and effective in obtaining metal fibre reinforced bioglass. Thermal shock, tensile tests and three-point bend tests all show a marked increase of strength of the composite over the parent glass and a substantial improvement of toughness.

The dynamic mechanical properties of an amine-cured epoxy resin, filled with a range of fillers including glass, carbon, aramid fibres and glass beads, have been determined on a torsion pendulum. The effects of fibre content, orientation and surface treatment on the beta-relaxation near -50° C at 1 Hz have been studied. For carbon and aramid fibre-filled systems, the maximum value of the loss factor appears to be proportional to the volumefraction of resin present; however, for glass-filled systems, the observed loss is slightly larger than expected. This difference is not dependent on surface treatment. Composite samples were exposed to boiling water and the dynamic properties determined after periods of immersion of up to 500 h. The change in loss properties may be explained in terms of the formation of a new loss peak near -30° c. The rate of formation of this loss peak is increased with increasing fibre content and is dependent on the fibre present. It is suggested that this may be caused by the formation of a distinguishable species at the fibre-resin interface formed during the degraditive process. The original dynamic properties of all the systems were recovered on drying the specimens. When systems containing cleaned glass beads are axposed to boiling water, more complex changes are observed. A peak near -8° C appears initially, but this appears to change to a peak near -30° C, similar to that observed for fibre-filled systems on prolonged exposure.

Accelerated water uptake tests have been used to compare the onsets of destruction of the ability to transfer shear stress at fibre/matrix interfaces in epoxy matrix glass reinforced plastic (GRP) manufactured with each of four different fibres. The ability to transfer shear stress has been monitored directly by measurement of stress birefringence through and adjacent to individual fibres. Full theoretical and practical details of the experimental method are given. “S” glass fibres, drawn into an atmosphere of ammonia in an attempt to promote the deposition of primary amines and/or secondary amines, rapidly lose their ability to receive shear stress from the matrix. This is attributed to neutralization of CO2 by NH3 within interfacial pockets of dissolved water, and the associated generation of osmotic pressure. Commercial samples of “S” and “E” glass fibres and “E” glass fibres drawn into an atmosphere of ammonia, all survive much larger water uptakes although, in the case of both kinds of “E” glass fibre, immersion in boiling water eventually gives rise to interfacial pressure pockets. These pressure pockets are also attributed to osmosis, with the role of dissolved solutes tentatively ascribed to the modifying agents present in “E” glass formulations.

Abstract: The room-temperature fatigue-crack propagation behaviour of poly(butylene terephthalate) is strongly influenced by hysteretic heating near the crack tip since the glass transition temperature is just above room temperature. At low frequencies or stress intensities, the crack tip damage zone consists of several layers of crazes. At high frequencies or stress intensities, hysteretic heating causes a drop in yield stress and a large increase in the depth of the crack tip damage layer. At the same time, the increase in the plane stress plastic zones near the free surfaces produces large shear lips which flank the interior craze zone. This transformation results in a crack growth rate transition which appears as a crack deceleration followed by rapid crack acceleration. This thermal transition can be suppressed or delayed by immersion in water or silicone oil to reduce heat build-up in the sample during testing.

The corrosion of E-glass fibres by hydrochloric, hydrobromic, and hydriodic acids has been investigated by measuring the loss of mechanical strength of the fibres following immersion in solutions of the acids. Corrosion is greatest in hydrochloric acid and least in hydriodic acid. Curves of percentage strength retention against concentration show well-defined minima for hydrochloric and hydrobromic acids, but not for hydriodic acid. This phenomenon has been attributed to complex ion formation by metal ions in the glass with chloride or bromide ions in the corroding solution. Spectroscopic evidence suggests that ferric ions play an important role in the corroding process.

Stress-corrosion tests are conducted on aligned short-fibre composites to assess their performance in both air and 1 N H2SO4 environments. The materials used are 3 mm E-glass, AS4 carbon, and their hybrid fibre reinforced epoxy composites. Several crack propagation models are developed to describe different cracking behaviour; the observed composite fracture modes verify these proposed models. Pre-immersion has significant effects onKl-tf and crack arrest of hybrid composites. A comparison of theoretical and experimentalKl-tf curves indicates good agreement of time to failure. The present research has quantified the susceptibility of these composites to environmental attack.

The moisture absorption characteristics of glass fibre-reinforced polyester in simulated deep sea water environments have been investigated. Test panels of unsaturated isopthalic polyester resin reinforced with woven E-glass were prepared by hand lay-up and the mass gain occurring during immersion in sea water pressurized up to 80 MPa was monitored. Moisture ingress followed a modified form of Fick's second law of diffusion. The saturation moisture content was shown to be linearly dependent upon the vapour pressure equivalent of hydrostatic pressure. In the case of diffusivity, a systematic relationship with hydrostatic pressure was not observed.

A Fourier transform interferometric study of phosphate coatings on iron plates using absorption-reflexion techniques indicated the following succession of chemical events on the surface of Armco iron dependent on time of immersion into the standard zinc phosphating solution: (a) activated formation via a redox reaction of an initial layer of hydrated iron oxide/hydroxides and nitrosyl iron complexes containing isolated PO43- (and possibly NO2-) ions in water solution; (b) chemical transformation of the initial layer into a first, adherent and chemically stable layer containing amorphous hydrated iron phosphate and acid iron phosphates; (c) growth of thicker layers progressively enriched of zinc ions, until only hydrated zinc phosphate crystals are deposited in the outer layer. This complex structure of the coating does not undergo significant chemical changes by heating to normal technological temperatures between 150 and 180° C. Only minor changes in water content are shown by the chemical evolution of the infra-red spectra up to such temperatures. Strong changes of the chemical structure of the coating (producing pyro- and metaphosphates) require temperatures higher than 200° C, and coincide with loss of adhesion of the coating to the iron support.

Thin sections of Portland cement clinker have been prepared by ion-beam thinning and examined in the electron microscope. The three most abundant phases, alite, belite and tricalcium aluminate have been identified. Features of interest include unexplained reflections in the diffraction patterns from alite and internally twinned or faulted martensite plates in belite. Hydrate gel coatings are obtained on the silicate phases but not on the aluminate phase, by immersing the thinned clinker in water. Dislocations in the aluminate phase do not appear to affect its reaction with water. On alite, easily observable hydrate coatings are obtained after immersion times as short as 5 min.

Sorptions of methylene chloride and methylene chloride/n-heptane liquid solutions in poly(aryl-ether-ether-ketone) (PEEK) are analysed and interpreted assuming multiple transport mechanisms. The presence of the highly interacting methylene chloride is responsible for anomalous sorption behaviours. PEEK films immersed in methylene chloride poor n-heptane solutions sorb by non-ideal Fickian diffusion, while limiting Case II and diffusion controlled swelling accompany equilibration in progressively richer methylene chloride solutions. The optical microscopy observation of cryogenically fractured samples conditioned in pure liquid methylene chloride at 5, 20 and 36 ° C for different times, revealed the presence of a sharp moving front. Differential scanning calorimetry (DSC) indicates that the glass transition temperature of the penetrated shells was always lower than the treatment temperature. The high levels of solvent swelling and plasticization were probably responsible for the crystallinity detected in DSC thermograms and wide angle X-ray scattering (WAXS) diffractograms of the solvent treated and initially amorphous samples. The differences of WAXS diffractograms of samples crystallized by immersion in methylene chloride at 5 and 36 ° C for various times and by thermal treatment are discussed. Increasing levels of crystallinity were induced in the samples equilibrated in progressively richer methylene chloride solutions.

The effects of moisture and surface finish on the mechanical and physical properties of the interfacial bond between the carbon/phenolic (C/P) and glass/phenolic (G/P) composite materials are presented in this paper. Four flat panel laminates were fabricated using the C/P and G/P materials. Of the four laminates, one panel was fabricated in which the C/P and G/P materials were cured simultaneously. It was identified as the cocure. The remaining laminates were processed with an initial simultaneous cure of the three C/P billets. Two surface finishes, one on each half, were applied to the top surface. Prior to the application and cure of the G/P material to the machined surface of the three C/P panels, each was subjected to specific environmental conditioning. Types of conditioning included: (a) nominal fabrication environment, (b) a prescribed drying cycle, and (c) a total immersion in water at 71 ‡C. Physical property tests were performed on specimens removed from the C/P materials of each laminate for determination of the specific gravity, residual volatiles and resin content. Comparison of results with Shuttle Solid Rocket Motor (SRM) nozzle material specifications verified that the materials used in fabricating the laminates met acceptance criteria and were respresentative of SRM nozzle materials. Mechanical property tests were performed at room temperature on specimens removed from the G/P, the C/P and at the interface between the two materials for each laminate. The double-notched shear strength test was used to determine the ultimate interlaminar shear strength. Results indicate no appreciable difference in the C/P material of the four laminates with the exception of the cocure laminate, where a 20% reduction in the strength was observed. The most significant effect occurred in the bondline specimens. The failure mode was shifted from the C/P material to the interface and the ultimate strength was significantly reduced in the wet material. No appreciable variation was noted between the surface finishes in the wet laminate.

Abstract: Polymethyl methacrylate (PMMA) film bonded by 4-META dental adhesive resin to mild steel was used as a specimen to study the mechanism of water permeation into the adhesive interface. Degradation of the adhesion interface after immersion in water was investigated by measurement of peeling area after imposing thermal stress using liquid nitrogen. The amount of water penetrated at the interface was calculated from the solution to Fick's second equation. The degradation at the interface is discussed with respect to the water content. Water enters the interface by diffusion through the resin rather than by passage along the interface. The interface is broken by water when the water content at the interface reaches 48% of the equilibrium water concentration of PMMA. Observation through the PMMA film shows no change in the mild steel surface at 48% equilibrium water concentration; at 95% water content many small white spots appear on the surface. The surface colour gradually changes to black due to the formation of corrosion products.

The inhibition of copper corrosion by polybenzimidazole and mercaptobenzimidazole at room and high temperature was assessed by in situ surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV). It was found that a very compact protective layer, produced by immersion in polybenzimidazole and mercaptobenzimidazole mixture solutions, showed better anticorrosive performance than each single inhibitor component even at high temperatures. This synergetic effect of the two components was explained by the physico-chemical mechanism of corrosion inhibition of polymeric coatings. Meanwhile, the results implied that the SERS active substrate prepared by the HNO3 etching method was particularly useful for in situ characterization of many problems in high-temperature surface chemistry which otherwise could not be accomplished by the usual SERS active substrates.

The effects of time, temperature and pH on the leaching rates of an La2Zr2O7 waste form were studied. The leaching rates of each constituent measured in deionized water and an alkaline solution (pH=10) were less than about 10-5g m-2d-1 at 90 °C and were smaller than those in an acid solution (pH=1) by one order of magnitude. It was found that the leaching rate of zirconium obtained after immersion for 34 days decreases with increasing temperature in an acid solution. This exceptional phenomenon is attributed to the formation and decomposition of zirconium complexes with CO32-ligands.

The effects of water and NaCl solutions on four different automotive epoxy adhesives bonded on electrodeposited zinc-iron steel substrate were investigated as a function of the degree of microhardness change in the adhesives under water and NaCl solution immersion tests. On the basis of the microhardness measurements, it was found that the soft and elastic adhesives were more susceptible to adhesive softening, swelling and microdamages than the hard and brittle adhesives upon exposure to the test solutions. The degree of microhardness decrease in the adhesives increased with the concentration of the NaCl solution. In the presence of sodium chloride, the same degree of microhardness decrease was obtained in the adhesives although less water was absorbed from the NaCl solution than from the distilled water. In addition, delamination of the adhesives from the steel substrate was observed after each microhardness measurement. Oxygen was found to play an important role in the process of adhesive delamination, although it had no effect on the change in the microhardness of the adhesives.

The physical techniques of polarizing microscopy, including the quantitative measurements of small optical retardations, have been used to investigate elastic fields adjacent to short carbon fibres in epoxy resin composites. The elastic fields associated with shear stress distribution along the fibre-matrix interface have been employed to monitor the initiation of interface debonding during hot (100 °C) water uptake. By examining the development of stress birefringence during resin swelling in the resin adjacent to individual fibres, the differences in the durability of interfacial bonding and the fibre failure modes for differently coated fibres have been obtained. The results show that the state of self-stress in model composites, comprising a single carbon fibre in a film of epoxy resin, can, by immersion in hot distilled water, be enhanced to such an extent that the axial tension in the fibre can be sufficient to initiate fibre fracture. The results also show that, for fibres that have been given certain proprietary surface treatments, the fibre fractures by different failure modes.

The deleterious effects of water on the physico-chemical aspects of the durability of adhesively bonded aluminium joints has been investigated. Emphasis was placed on analytical techniques that lead to the better understanding of changes induced at the metal/epoxy interface by the presence of water. Analytical techniques such as contact angle measurements, X-ray photoelectron spectroscopy and X-ray diffraction were practical in obtaining information on the chemical composition and structure of the samples. Chemical conversion-coated samples were found to be much more stable in wet conditions compared to samples without conversion coating. The surface structure on the adherend, after extensive immersion times, was found to consist of a compact layer of bayerite with traces of gibbsite. The calculations of interfacial energy, ?sl, and work of adhesion in dry and wet conditions, WA and WAl were carried out to evaluate the maximum bond strength. It was found that the durability of the bond in the presence of water was quite high for the XD4300/6061-T6 joint systems.

Experiments have been carried out to assess the fracture behaviour of potato tuber parenchyma tissue from two different varieties (cvs. King Edward and Record) in three different turgor states (turgid, fresh and flaccid). Methods included wedge-penetration fracture tests, razor-blade cutting tests, ball indentation tests and compression tests. Turgor was manipulated by immersion of fresh tissue in osmotica of known concentration, and assessed by means of cell pressure probing. No significant differences in properties were ascribed to the difference in variety. Changes in water status were responsible for appreciable changes in the fracture properties of the tissue. Values of compressive Young's modulus and work of fracture were combined to predict critical crack lengths for different turgor states under given levels of applied stress below the yield stress.

Type 302 stainless steel samples were subjected to a U-bend test in a normal sulphuric acid bath at room temperature. The passive layers which subsequently grew on both sides of the sample, were studied by Auger electron spectroscopy. Each strained sample was immersed and passivated in a sulphuric acid solution under a voltage of +450 mV/SCE and the anodic current density was studied as a function of the immersion time. The results obtained show that the anodic current density is higher for the strained specimens than for the unstrained specimen. Thus, passivation occurs more rapidly for an unstrained sample than for strained samples. There is also clear evidence that the decrease in the anodic current density is more rapid for an elastically strained sample than for a plastically strained one. The influence of the tensile and compressive stresses on the composition of the passive films was studied by comparing the elemental Auger depth profiles. The results obtained show that oxidation is more important on the tensile stressed side than on the compressive stressed one, whether the samples were elastically or plastically strained. Similarly, the width of the region affected by the chromium enrichment was enhanced by tensile straining and reduced by compressive straining, whether the samples were elastically or plastically strained.

The quenching rate required to “freeze-in” high temperature states depends on the resolution attained in the observational technique used and on the kinetics of the property changes that may occur in the sample. For a successful quench, heat must be removed before observable changes occur. Heat loss during travel to the quench bath must be minimized as this lowers the certainty of the quenched-in temperature state, while the heat removal rate after immersion in the quench bath should be maximized. The required quench rate will determine the necessary sample size and quench medium. Quenching has been experimentally evaluated for a propelled “insulating envelope” sample transfer quench device. Results are used to determine optimum conditions for effective quenching. A procedure is established to guide the choice of sample size and quench medium to attain an adequate quenching rate.

A previous investigation (J. Mater. Sci.22 (1987) 1707) has shown that nylon polymers are susceptible to stress cracking by aqueous calcium chloride at slightly elevated temperatures (50° C). In the present study, the nylon-salt interactions were investigated using thin films of both nylon 6 and nylon 6,6. Chemical, thermal, infrared and dynamic mechanical analyses were performed along with tensile property determinations. Weight gain measurements indicated that above 50° C large increases in sorption occurred for films immersed in either aqueous calcium, lithium, or magnesium chlorides. Both salt ions and water were absorbed at the elevated temperature. In contrast to these results, the data for sodium chloride indicated that only water was absorbed at all temperatures. The sorption process was shown to be physically reversible since the absorbed salt could be removed by immersion in pure water. Moreover the sorption of the salt solution at 100° C did not produce chemical degradation or significant crystallization of the nylons. At higher temperatures the absorbed salt did modify the recrystallization behaviour and increase theTg of the nylons. Significant reductions in tensile modulus were observed for nylon films equilibrated in the salt solutions and tensile elongations at rupture were increased. The effect of increasing temperature and salt type on the sorption process parallels the previously observed stress-cracking activity of the aqueous salt solutions. It is therefore suggested that a plasticization-like mechanism is responsible for the salt-induced crazing of the crystalline nylons.

Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to follow the changes that occur on the surfaces of silver sheets when reacting with sulphide solutions of pH 12. The results obtained enabled conclusions to be drawn about the nature of the Ag2S films. Immersion in dilute sulphide solutions (? 3 × 10-4 M) resulted in highly irregular films that were interrupted by shallow depressions (cavities). Inside these cavities AES analysis proved the existence of massive carbon species, the presence of which delayed healing of the cavities by the formation of Ag2S film, thus allowing the silver metal interface to continue in contact with the solution oxygen. This explains why silver electrodes maintain the Ag/Ag2O potential while immersed in dilute sulphide solutions. Equilibration of silver with more concentrated sulphide solutions (5 × 10-4 to 5 × 10-3 M) effected healing of the cavities through the formation of a continuous Ag2S film. Once this continuous film is formed, the metal interface is no longer accessible to the solution oxygen. At this point the transition of potential from Ag/Ag2O to Ag/Ag2S occurs.