Showing papers in "Journal of Materials Science in 1997"

The immobilization of high level radioactive wastes using ceramics and glasses

Abstract: An overview is given of the immobilization of high level radioactive waste (HLW) and surplus materials from a variety of commercial and defence sources employing glass and ceramic hosts. A number of specific host materials are reviewed, including borosilicate and phosphate glasses, glass-ceramics and crystalline ceramics. Topics covered include wasteform processing and manufacture, in addition to wasteform stability, durability and mechanical behaviour. Although, at the present time, borosilicate glass is the generally accepted first generation wasteform for the immobilization of HLW, the emergence of new sources of radioactive materials requiring immobilization has renewed interest in many of the alternative candidates. These include, in particular, titanate, zirconate and phosphate based ceramics, together with iron phosphate based glasses and basaltic glass-ceramics. The relative merits and limitations of each host material are compared and discussed, with particular reference to processing considerations and to current and likely future requirements.

Indentation brittleness of ceramics: a fresh approach

Abstract: The hardness and brittleness of ceramic materials are interrelated. Hard materials are more apt to fracture in the vicinity of an indentation during a hardness test, while softer materials tend to plastically deform to the indenter shape without fracturing. Measured hardness, in turn, is affected by both specimen deformation and fracture processes. This interrelationship is examined by means of extensive Vickers hardness testing. A new index of brittleness is proposed.

Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres: Part II Analysis of composite microstructure and mechanical properties

Abstract: The microstructure and mechanical properties of polypropylene composites containing flax and wheat straw fibres are discussed. Particular emphasis has been given to determining the nature and consequences of fibre damage induced during melt-processing operations, fibre orientation occurring in mouldings, and possible interfacial adhesion between the matrix and fibres. Compared to unfilled polypropylene, addition of flax and wheat straw caused a significant increase in tensile modulus, particularly, in the case of flax fibres, which also gave higher tensile yield strength and Charpy toughness, despite a lack of interfacial bonding. Tensile strength was increased further through inclusion of 5% by weight of maleic anhydride-modified polypropylene, which was shown to promote adhesion between fibres and matrix.

Room temperature synthesis of crystalline metal oxides

Abstract: Crystalline titanium dioxide powders have been synthesized as either rutile or anatase from aqueous solutions at low temperatures (T≤100°C) and atmospheric pressure. First, a sol is prepared by the hydrolysis of a titanium alkoxide in an acidic solution. The sol is subsequently heated at different rates to produce the different crystalline phases of titanium dioxide. Powder characterization was carried out using X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. In general, the precipitate size was observed to be between 50 and 100 nm. Possible mechanisms involved in determining the crystal variants are discussed.

Theoretical modelling of tensile properties of short sisal fibre-reinforced low-density polyethylene composites

Abstract: The experimentally observed tensile properties (tensile strength and modulus) of short sisal fibre-reinforced LDPE with different fibre loading have been compared with the existing theories of reinforcement The macroscopic behaviour of fibre-filled composites is affected by fibre loading, orientation and length of the fibres in the continuous medium The interfacial adhesion between fibre and matrix also plays a major role in controlling the mechanical properties of the fibre-filled composites In this study, a comparison is made between experimental data and different theoretical models Composite models, such as parallel and series, Hirsch, Cox, Halpin–Tsai, modified Halpin–Tsai and modified Bowyer and Bader, have been tried to fit the experimental data

The formation and control of Laves phase in superalloy 718 welds

Abstract: Weld heat input/cooling rate (affected by welding process, parameters, technique, tooling, etc.) was found to influence the microstructural characteristics and segregational features in alloy 718 welds, with low heat inputs proving beneficial. Laves phase formed in the interdendritic regions of the weld metals as a result of segregation. The morphology and composition of Laves phase depended strongly on heat input/cooling rate and influenced its response to subsequent homogenization post-weld heat treatment. The various factors affecting the formation and control of Laves phase in alloy 718 welds are highlighted.

Chemical reactivity of aluminium with boron carbide

Abstract: The chemical reactivity of boron carbide (B4C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000 °C). Al–B4C powder mixtures were cold pressed, heated for 1–450 h under 105 Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B4C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660 °C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al3BC) and to diboride (AlB2). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141 ± 4 K (868 ± 4 °C), the reaction products are Al3BC and AlB2: at temperatures higher than 1141 K, Al3 BC is still formed while Al3B48C2 (β-AlB12) replaces AlB2. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al3BC and a C-poor boride and, finally, the passivation of B4C by Al3BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB12 + L ⇔ AlB2, which has been found to occur at 1165 ± 5 K (892 ± 5 °C).

Fabrication methods for auxetic foams

Abstract: Auxetic materials have a negative Poisson's ratio, that is, they expand laterally when stretched longitudinally. Negative Poisson's ratio is an unusual property that affects many of the mechanical properties of the material, such as indentation resistance, compression, shear stiffness, and certain aspects of the dynamic performance. The unusual mechanical properties of auxetic foams are attributed to the deformation characteristics of re-entrant microstructures. One way of obtaining negative Poisson's ratio is by using a re-entrant cell structure. Auxetic foam was fabricated from a conventional polymeric foam. The fabrication method for making both small and large auxetic foam specimens is described.

Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres: Part I Fibre characterization

Abstract: The microstructure, thermal and mechanical properties of flax and wheat straw fibres have been examined with a view to using these natural fibres as reinforcing additives for thermoplastics. In this regard, the fibres were characterized prior to incorporation into the polymer, using a range of techniques, including SEM, image analysis, thermogravimetric analysis and micro-mechanical tensile testing, at room and elevated temperatures. The thermal and mechanical properties obtained have been discussed in relation to the measured composition and structural form of the fibres.

A review on particulate-reinforced titanium matrix composites

Abstract: The current status of particulate-reinforced titanium matrix composites is reviewed. The different types of reinforcements being used, together with the alternative processing routes, are described. The mechanical properties of these composites are influenced by a wide range of factors. Particulate reinforcements can affect properties by enhancing modulus and strength or by refining the grain size. Mechanical properties such as elastic modulus, low and high temperature strength, fracture toughness and compressive creep are discussed as functions of reinforcement size/shape and volume fraction. The review concludes by underlining the importance of further research in some critical areas to fully realise the industrial potential of these composites.

Yield criteria for amorphous glassy polymers

Abstract: Three amorphous polymers, polymethyl methacrylate, polystyrene and polycarbonate were tested in uniaxial tension, uniaxial compression, plane strain compression and simple shear, over a range of temperatures. In each test, the yield point was precisely determined via residual strain measurements after unloading. With the yield stresses determined for these four different stress states, two pressure dependent shear yield criteria, i.e, the modified Von Mises and the modified Tresca criteria, were checked and compared. It is shown that (i) in each case (material, temperature, initial ageing state), the yield locus is satisfactorily described by either one or the other of the two criteria, and (ii) each criterion can be associated with a specific deformation mode (either homogeneous or localized in shear bands). As for the temperature dependence of the yield stress sensitivity to the hydrostatic pressure, it appears to be related to the glass transition temperature (Tg) and more precisely to the α and β relaxations. Finally, the pressure dependence of the yield stress can be possibly explained as being due to two effects: (i) the influence of pressure on molecular motions leading to yielding and (ii) the influence of pressure on the microstructural state.

Low-temperature synthesized aluminosilicate glasses. Part III Influence of the composition of the silicate solution on production, structure and properties

Abstract: The low-temperature reaction between an aqueous sodium or potassium silicate solution and metakaolinite yields a solid aluminosilicate. The influence of the molar ratios H2O/R2O (between 6.6 and 21.0) and SiO2/R2O (between 0.0 and 2.3) of the silicate solution (R=Na or K) on the aluminosilicate's production, on the reaction stoichiometry and on the aluminosilicate's molecular structure is studied with differential scanning calorimetry, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), cross-polarization MAS NMR, Fourier transform infrared spectroscopy and X-ray diffractometry. The reaction stoichiometry is determined by a one to one ratio for R/Al. H2O/R2O has no influence on the molecular structure of the aluminosilicate. Aluminium in the aluminosilicate is four-fold coordinated for the whole range of silicate solutions investigated. Moreover, Si and Al are homogeneously distributed and the ratio Al/Si in the aluminosilicate is the same as in the reaction mixture if the stoichiometric one-to-one ratio for R/Al is used. If SiO2/R2O in the Na-silicate solution is equal to or higher than 0.8, the low-temperature reaction yields an amorphous aluminosilicate or “inorganic polymer glass”. For smaller values of SiO2/R2O the Na-aluminosilicates are partially crystalline. Thermomechanical analysis and dynamic mechanical analysis indicate that a variation in the composition of the amorphous aluminosilicates can shift the glass transition over a few hundreds of degrees, with a minimum value of 650°C.

Evidence of graphitization of diamond-like carbon films during sliding wear

Abstract: Diamond-like carbon (DLC) exhibits excellent wear and friction characteristics. Transmission electron microscopy (TEM) has been used to investigate the substructures of as-deposited DLC and DLC debris after wear testing. The as-deposited DLC was found to consist of a dense, three-dimensional network structure with a medium range order (<3 nm) present. Diffraction pattern analysis showed that DLC was mainly amorphous. Two diffuse diffraction rings with d111=0.21 nm and d220=0.12 nm were observed, suggesting the presence of a short-range cubic diamond structure (sp3). Morphologically, the wear debris was found to be a discontinuous segregation of carbon particles ranging from nano- to micro-size. Diffraction pattern analysis showed that the debris consisted of graphite (sp2) and distorted DLC (sp3). A wear mechanism has been proposed based on the transformation of DLC to graphite. The transformation is related to the frictional energy and includes two stages: hydrogen release from the structure causing lattice relaxation and shear deformation of the DLC structure producing graphite.

The structure of the calcium silicate hydrate phases present in hardened pastes of white Portland cement/blast-furnace slag blends

Abstract: The C-S-H gels present in both water- and alkali-activated hardened pastes of white Portland cement/blast-furnace slag blends have been studied by solid-state 29Si magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and analytical transmission electron microscopy (TEM). Structural data are obtained by NMR for the semi-crystalline C-S-H gels in the alkali-activated systems and extended to the nearly amorphous gels in the water-activated systems by peak broadening; unambiguous chemical analyses are determined in the TEM. The following conclusions apply to both the semi-crystalline and nearly amorphous C-S-H gels: (1) aluminium substitutes for silicon at tetrahedral sites; (2) aluminium only substitutes for silicon in the central tetrahedron of pentameric silicate chains; (3) the results strengthen confidence in dreierkette-based models for the structure of C-S-H. Compositional similarities suggest that these conclusions will be true for OPC/slag blends, and possibly also for OPC/pulverized fuel ash blends indicating that the same structural model applies to C-S-H gels in a wide range of hardened cement pastes.

Dissipation of energy by bulletproof aramid fabric

Abstract: The bullet resistance of laminates comprised of several layers of aramid Armos fabric has been studied. The high bullet resistance of the fabric is caused by the pulling-out of yarns impacted by the bullet. The pull-out zone is cross-shaped, the centre being the impact point. The length and the width of the pull-out zone was determined for each fabric layer. Energy transferred to fibres increases with the volume of the pull-out zone. Water reduces the bullet resistance of laminates owing to reduction of the width of the zone. The length of the pull-out zone is shorter if the transverse displacement of layers is restricted. At a projectile velocity of 420 m s-1, Armos yarns do not break immediately on impact, and the longitudinal wave propagates along the fibre. Friction of yarns in aramid fabric was studied by a yarn pull-out method.

Surface study of a titanium-based ceramic electrode material by X-ray photoelectron spectroscopy

Abstract: The electrochemical behaviours of the Magneli phase titanium oxides with the general formula TixO2x-1 have been investigated. Surface analysis of these ceramic materials was performed using X-ray photoelectron spectroscopy in order to determine the surface composition. It was shown that the surface layers contain mainly TiIV. When these materials are used as an anode for oxygen evolution, in sulfuric acid, the XPS spectrum shows considerable modification in the O1s region, due to an important contribution of hydroxyl groups and the adsorption of sulfate anions.

Hydroxyapatite coatings: a comparative study between plasma-spray and pulsed laser deposition techniques

Abstract: A comparative study between hydroxyapatite coatings produced by two different techniques, plasma spray (PS) and pulsed-laser deposition (PLD) was carried out. Plasma spray is currently commercially used for coating dental and orthopaedical implant devices, and pulsed-laser deposition (or laser-ablation deposition) gave good results in the field of high critical temperature superconductive thin films, and is being applied to produce calcium phosphate coatings for biomedical purposes. X-ray diffraction was used to control the crystallinity of the coatings, scanning electron microscopy for the surface and cross-sectional morphology, and the pull test to determine the tensile strength of the coatings. This study reveals that the pulsed-laser deposition technique appears to be a very good candidate to replace the plasma spray in many biomedical applications, because it overcomes most of the drawbacks of the plasma spray.

Transparent conducting lithium-doped nickel oxide thin films by spray pyrolysis technique

Abstract: Nickel oxide (NiO) and lithium-doped nickel oxide films were deposited by the spray pyrolysis technique using NiCl2 and LiCl as starting materials. All the films were greenish-grey in colour and confirmed by X-ray analysis. The best NiO films were obtained when the substrate temperature, Ts=480 °C where a conductivity of 2.1×10-1Ω-1 cm-1 and transparency above 80% in the visible region are achieved. High transparency (above 80%) and highly conducting NiO films were obtained when doped with lithium.

Statistical tensile strength of Nextel TM 610 and Nextel TM 720 fibres

Abstract: The properties of fibre-reinforced composites are dependent not only on the strength of the reinforcement fibre but also the distribution of fibre strength. In this study, the single filament strength of several lots of NextelTM 610 and NextelTM 720 ceramic fibres was measured. Fracture statistics were correlated with the effects of gauge length and diameter variation, and the Weibull modulus was calculated using several different techniques. It was found that the measured Weibull modulus at a single gauge length did not accurately predict either the gauge length or diameter dependence of tensile strength.

Thermal stability of a PCS-derived SiC fibre with a low oxygen content (Hi-Nicalon)

Abstract: The oxygen free Si–C fibre (Hi-Nicalon) consists of β-SiC nanocrystals (≈5nm) and stacked carbon layers of 2–3nm in extension, in the form of carbon network along the fibre. This microstructure gives rise to a high density, tensile strength, stiffness and electrical conductivity. With respect to a Si–C–O fibre (Nicalon NL202), the Si–C fibres have a much greater thermal stability owing to the absence of the unstable SiOxCy phase. Despite its high chemical stability, it is nevertheless subject to a slight structural evolution at high temperatures of both SiC and free carbon phases, beginning at pyrolysis temperatures in the range 1200–1400°C and improving with increasing pyrolysis temperature and annealing time. A moderate superficial decomposition is also observed beyond 1400°C, in the form of a carbon enriched layer whose thickness increases as the pyrolysis temperature and annealing time are raised. The strength reduction at ambient for pyrolysis temperatures below 1600°C could be caused by SiC coarsening or superficial degradation. Si–C fibres have a good oxidation resistance up to 1400°C, due to the formation of a protective silica layer.

Carbothermal synthesis of titanium carbide using ultrafine titania powders

Abstract: The synthesis of titanium carbide (TiC) by the carbothermal reduction of carbon coated titanium dioxide (TiO2), a novel synthesis process, and titanium dioxide (TiO2) mixed with carbon black was investigated. A high surface area (64 m2g-1) TiO2 powder consisting of anatase and rutile phases was used for starting powders. The carbon coated method is a two-step process that utilizes a precursor derived from decomposing propylene (C3H6) and depositing carbon on the TiO2 particles. TiO2 powders were also mechanically mixed with carbon black for comparison. Both starting precursors and mixtures were reacted in a tube furnace for 2 and 4 h at temperatures of 1100°C to 1550°C under 1 l min-1 flowing argon. The TiC powders were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analyser, chemical analysis (oxygen and carbon) and transmission electron microscopy (TEM). The carbon coating process provides high contact area between the reactants which results in a TiC product with lower oxygen content (0.6 wt%), finer particle size (0.1 μm), and uniform shape when synthesized at 1550°C for 4 h.

The relationship between microstructure and Young’s modulus of thermally sprayed ceramic coatings

Abstract: An idealized model for the microstructure of thermally sprayed ceramic coatings, consisting of the stacking of lamellae a few micrometres thick, has been used to estimate Young’s modulus of the coating perpendicular to the coating plane. A theoretical relationship between Young’s modulus and the microstructural parameters has been established. There are two components of elastic strain of the coating under tensile stress, one arising from localized elastic strain at the regions of real-bonded area between lamellae, and the other arising from elastic bending of the lamellae between bonded regions. The bending component only becomes significant for a percentage bonding ratio between lamellae of less than 40%. The bending strain contribution depends strongly upon geometrical parameters of the coating microstructure. The estimated Young’s modulus for a typical alumina coating, based on quantitative microstructural data, was about 24% of that for the fully dense material. Taking into account the variable proportion of α-Al2O3 and γ-Al2O3 forms in an alumina coating, the comparison of the estimated Young’s modulus with published data gives reasonable agreement for the coating prepared over a wide range of processes and experimental conditions.

A new statistical distribution for characterizing the random strength of brittle materials

Abstract: A new three-parameter statistical distribution is offered for the description of random strength of a brittle material The distribution allows characterization of a wide range of relations regarding the strength-size effect Thus, in contrast to the Weibull distribution, the non-linear character between the logarithm of average strength and the logarithm of the specimen size may be described, while retaining the Weibull function as a limiting case Furthermore, the proposed distribution permits simple evaluation of the necessary statistical parameters by considering all experimental points for different specimen sizes together Experimental confirmation of the strength distribution is illustrated using experimental data on three types of glass fibres at three gauge lengths each

Density gradient effects on aluminium foam compression behaviour

Abstract: The compression properties of an aluminium foam containing a nonuniform density gradient have been examined. Specimens were taken from various locations within the foam slab, and were tested in two directions. Measured foam properties were compared to calculated values using models derived by Ashby and Gibson [1]. The effect of the density gradient on the compression properties and also the energy absorption characteristics of the foam was found to be significant.

Characterization of the intermetallic G-phase in an AISI 329 duplex stainless steel

Abstract: Duplex austenite–ferrite stainless steels are susceptible to a variety of decomposition processes when aged within the intermediate range of temperatures (250–500 °C). One of these phenomena is the precipitation of the intermetallic G-phase. In the present investigation, the crystal structure and the chemical composition of the G-phase, precipitated in the ferritic phase of an AISI329 duplex stainless steel, is studied by electron microdiffraction and energy dispersive X-ray spectroscopy. It is determined that the space group of the G-phase is F 3 with a lattice parameter four times that of the ferritic matrix. The precipitation mechanism of the G-phase showed a synergetic relation with the ferrite decomposition in Cr-rich and Fe-rich domains. Based on the obtained results, the structural proximity of ferrite matrix and G-phase has been studied. Further analysis allows to suggest that the spinodal decomposition leads to an interdomain of a ferritic structure which is thermodynamically unstable and serves as a precursory site to the development of the G-phase by atomic position readjustments inferior to the atomic distances.

Synthesis of ultrafine particles of barium ferrite by chemical coprecipitation

Abstract: A new method to synthesize barium hexaferrite by chemical coprecipitation is described. A mixed precursor was precipitated by addition of a barium salt to a strongly alkaline ferrate (VI) solution. The precursor yielded barium hexaferrite on heating for 6 h at 800 °C; partial transformation was evident even at lower temperatures, from X-ray patterns and Mossbauer spectra. Scanning electron microscopy of the powders fired at 800 °C, showed that the particles were less than 0.5 μm in diameter.

Effect of interlayer anions on the physicochemical properties of zinc–aluminium hydrotalcite-like compounds

Abstract: Zinc–aluminium hydrotalcite-like compounds (ZnAlAn-–HT) with a Zn/Al atomic ratio 2.0 and An- = CO2-3, Cl-, NO-3 and SO2-4, were synthesized by coprecipitation under low supersaturation. Their physicochemical properties were studied using powder X-ray diffraction (PXRD), infrared (IR) and laser Raman (LR) spectra, thermogravimetry (TG), differential scanning calorimetry (DSC), evolved gas analysis (EGA), 27Al MAS NMR, BET surface area and pore-size determination. The PXRD of the synthesized samples showed that the crystallinity was affected by the nature of the anions present in the interlayer space. The IR and LR studies revealed that except the NO-3 ion, the symmetry of these interlayer anions was reduced upon intercalation. The TG, DSC and EGA results showed two or three stages of weight loss corresponding to the removal of the interlayer water, structural water and the anion, respectively. The activation energy, Ea, for the decomposition process was found to decrease in the order ZnAlCO3–HT>ZnAlSO4–HT>ZnAlCl–HT>ZnAlNO3–HT. Formation of a pentacoordinated Al (AlV) in addition to the octahedral (AlVI) and tetrahedral Al (AlIV) was the special feature noticed in the 27Al MAS NMR of the calcined samples. Thermal calcination around 500 °C resulted in the formation of non-stoichiometric ZnO whose crystallinity decreased in the order ZnAlNO3–CHT>ZnAlCl–CHT>ZnAlSO4–CHT>ZnAlCO3–HT while their extent of solid solubility was found to be the reverse. The crystallinity of the calcined samples was also correlated with surface area and pore-size determination.

Effect of sintering conditions on resistivity and dielectric properties of Ni-Zn ferrites

Abstract: Resistivity and dielectric properties of the nickel-zinc ferrite composition, Ni0.65Zn0.35Fe2O4, have been studied near different sintering conditions to optimize the sintering schedule for a specific application. Variable sintering parameters in the study include sintering temperature in the range from 1150 to 1300°C and sintering time with 1 h, 2 h and 4 h durations at each sintering temperature. The results indicate that the decrease of resistivity is linear and less rapid upto a sintering schedule of 1250°C/2 h, and thereafter any increase either in sintering temperature or in sintering time causes a rapid decrease of resistivity due to the increased volatilization of zinc from the samples at these temperatures/times. Possible mechanisms contributing to conduction processes in ferrites are discussed in explaining the obtained results.

Preparation of aluminium-fly ash particulate composite by powder metallurgy technique

Abstract: Aluminium-fly ash mixtures containing different weight percentages of fly ash were prepared and compacted at pressures from 138–414 MPa. The compacts prepared at 414 MPa were sintered in nitrogen atmosphere at 600, 625 and 645°C, respectively. The time of sintering ranged from 0.5–6 h. The densification parameter and the green densities of the compacts were determined as a function of compacting pressure and fly ash weight per cent. Density, hardness and strength of the sintered compacts were determined as a function of weight per cent of fly ash particles. Volume changes during sintering of green compacts were also evaluated as a function of increasing fly ash weight per cent. Microscopic studies of green and sintered compacts were done to study the effectiveness of sintering. Green and sintered density of the compacts were found to decrease with increasing weight per cents of fly ash. Sintering results in slight decrease in density and increase in volume of green compacts within the range investigated. Strength of the sintered compacts decreased with increasing weight per cent of fly ash under the present experimental conditions; however, the hardness was found to increase slightly up to 10 wt% fly ash, beyond which it decreased.

Fatigue fracture mechanisms and fractography of short-glassfibre-reinforced polyamide 6

Abstract: An adaptation to existing failure models for fatigue fracture of short-fibre-reinforced thermoplastics is presented. This was based on results using some new experimental methods. These results led to the conclusion that cracks in glassfibre-reinforced polyamide 6 (conditioned to equilibrium water content) remain bridged by plastically drawn matrix material and/or fibres until just prior to final fracture. In this article, emphasis will be on the fractographic evidence for the existence of this failure mechanism. Also some other phenomena in glassfibre-reinforced polyamide will be mentioned. Apart from the normal fractographic investigations, specimens were cryogenically fractured after fatigue, revealing the structure of damage, before failure. Both fracture surfaces were compared, showing that only a small fraction of the fibres is broken in fatigue; mostly the fibres are pulled out. The mechanism consists of the following steps: damage begins with void formation, mainly at fibre ends; these voids coalesce into small cracks. These cracks, however, do not grow into one full crack, but the crack walls remain connected at several points. This is contrary to the fracture mechanism for the dry as-moulded material. When the material is dry as moulded, the matrix material cracks, without showing much ductility, and no bridges are formed.