The influence of microstructure on the failure behaviour of PEEK

In this study, different molecular weight PEEK materials were used to determine the effect of spherulite size on fracture. Melt processing of the PEEK at different temperatures produced samples of different average spherulite size. A permanganic etching technique was used to reveal the spherulites. It was found that for low molecular weight 150P PEEK, the spherulite size increased with melt processing temperature; but, for the higher molecular weight 450G PEEK, the spherulite size remained approximately constant. Also, the average spherulite size was markedly lower for the material of higher molecular weight. The failure behaviour of these samples was studied using a compact tension test. It was found that the fracture toughness of PEEK varied with processing temperature. Also, the average spherulite size of this material had a profound influence on the fracture mechanism.     

Recycling effects on microstructure and mechanical behaviour of PEEK short carbon-fibre composites

The effect of recycling on microstructure and mechanical properties has been evaluated for injection-moulded poly-ether-ether-ketone (PEEK) composites reinforced with 10% and 30% short carbon fibres. Microstructure characterization was carried out by determining fibre length distributions, PEEK molecular weight, and by SEM observations of fracture surfaces before and after processing. These studies reveal degradation of fibres and matrix during recycling. Tensile Youngs modulus and strength, as well as impact strength reductions are presented for recycled composites.     

The influence of alloy composition on microstructure and tensile behaviour of copper-lead alloys

Lead is a soft metal that possesses excellent antifriction and lubricating characteristics and is a desired addition to alloys which find use in friction-critical and low-load-bearing applications. The influence of alloy composition on microstructure, tensile properties and quasi-static fracture behaviour has been studied. Alloy composition, that is, lead content, was observed to have an influence on the size and distribution of lead globules in the copper matrix. The yield strength, ultimate tensile strength and elastic modulus of the alloy decreased with increase in lead content. The ductility of the alloys showed an improvement with increase in lead content. The influence of lead content on quasi-static fracture is discussed in detail.     

The mechanical behaviour of PEEK short fibre composites

Short glass (GF) and carbon fibre (CF) reinforced poly-ether-ether-ketone (PEEK) composites were prepared by injection moulding and then microstructurally characterized. Their mechanical behaviour was determined by two different methods: a classical unidirectional tensile test and an immersion ultrasonic technique. The reinforcing effect of fibres is discussed in the context of the theory of reinforcement of Bowyer and Bader. Interfacial shear strength and critical fibre length at break are calculated for both PEEK/GF and PEEK/CF composites. Examinations of fracture surfaces of uniaxial tensile specimens revealed a higher adhesion of carbon fibres to PEEK matrix in regards to the adhesion concerning glass fibre-PEEK interfaces, which is in agreement with the results provided by the model. Compatibility of ultrasonic and tensile results is reported.     

The mechanical performance and impact behaviour of carbon-fibre reinforced PEEK

The mechanical performance and impact behaviour of carbon-fibre reinforced polyether-ether ketone (PEEK) with a (0, ±45) lay-up has been compared with that of a similar carbon fibre/epoxy laminate. Differences occurred because of the greater shear strength and lower shear modulus of the carbon-fibre reinforced PEEK. When compared with the carbon fibre/epoxy laminate, carbon-fibre reinforced PEEK was more notch sensitive in tension and had a lower undamaged compressive strength. However, after impact, the residual compressive strength was significantly greater for carbon-fibre reinforced PEEK because delamination was less extensive.     

The influence of annealing twinning on microstructure evolution

This paper reports an experimental investigation on the effect of multiple twinning on the interface population in two low stacking-fault alloys. This is an important topic for grain boundary engineering because annealing twinning is the indirect cause of improved intergranular corrosion resistance in this class of materials. Proportions of Σ 3ⁿ (n = 1–5) boundaries were analysed in both a brass specimen and a superalloy specimen where the boundaries had been processed so as to be very mobile and less mobile respectively. When Σ 3 twin boundaries (as distinct from Σ 3 grain boundaries) are discounted, the Σ 3ⁿ distribution for both specimens had a peak at Σ 9, because Σ 3 + Σ 9 → Σ 3 occurs more frequently than Σ 3+Σ 9 → Σ 27. The distributions and reactions between various Σ 3ⁿ values are described and discussed in detail. A novel trace analysis procedure is used to extract information from Σ 3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin Σ 3s. The data show unambiguously that a significant proportion of Σ 3s are not on 111, and these boundaries have on average higher angular deviations from the exact Σ 3 reference misorientation than do other Σ 3s. A population of Σ 3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin Σ 3s, which are pivotal in grain boundary engineering.     

The influence of microstructure on the thermal conductivity of aluminium nitride

Starting from three different commercial powders, AIN materials were densified by pressureless sintering under various temperature and time values in order to investigate the influence of microstructure on thermal conductivity. The influence of the sintering aids (3 wt% Y₂O₃ and 2 wt% CaC₂) and of the forming processes (cold isostatic pressing and thermocompression of tape cast pieces) were also been evaluated. Thermal conductivity increased with the purity level of the starting powder and with an increasing the sintering temperature and soaking time. The highest thermal conductivity values (196 Wm^–1 K^–1) were obtained with the purest powder and high temperature (1800 °C) sintering over long periods (6 h). No influence on thermal conductivity was detected from the forming technique.     

The influence of cellulose nanocrystals on the microstructure of cement paste

This paper reports the influence of raw and sonicated cellulose nanocrystals (CNCs) on the microstructure of cement paste. A novel centrifugation method is designed to measure the concentrations of the adsorbed CNCs (aCNCs) on the cement surface, and the free CNCs (fCNCs) which are mobile in water. It is found that, the majority of the CNCs (>94%) are aCNCs. More importantly, sonication does not significantly reduce the amount of aCNCs (reduction of less than 2%). We surmise that, after sonication, the aCNCs are primarily dispersed over the cement surface, instead of becoming fCNCs via sonication. Isothermal calorimetry and energy-dispersive X-ray spectroscopy (EDX) results support this theory. The water desorption tests show that the total porosities of cement pastes with raw and sonicated CNCs are 14.8% and 14.4%, which showed a reduction from 16% for the plain cement paste. The porosity reduction is a result of an increase in the degree of hydration. The advantage of sonicated CNCs is they are dispersed, avoiding therefore agglomerates that can lead to pores, voids, and air entrapment. The nanoindentation results show that the reduced indentation modulus on the interfacial regions between cement particles and the low density CSH is increased when CNCs are used.     

Sn含量对TiNbZr合金组织的影响

具有低弹性模量、高强度、不合有毒元素的β型钛合金是目前新型医用钛合金开发的热点。本实验研究了Ti-18Nb-17Zr-xSn（质量分数％，x=0，1，2，3，4，5）合金，通过热处理调整合金显微组织，使用X射线衍射分析相组成，并对合金的硬度进行测试。通过分析，表明锡元素可以促进快冷过程中α″相的形成。在中慢速冷却过程中，锡能够和其它β稳定元素一起共同稳定β相。锡对力学性能的影响要综合考虑锡的固溶强化作用和锡对相的影响。     

The influence of processing on the microstructure of an aluminum-lithium alloy

The intrinsic microstructural features of a thermomechanically processed Al-Cu-Li-Mn-Cd alloy was characterized. The thermomechanically processed material had an unrecrystallized structure with large unrecrystallized grains. The subgrains within the large unrecrystallized grains were fairly uniform in size. Precipitation of fine particles during the thermomechanical treatment suppressed recrystallization from occurring. The major strengthening precipitates were identified by transmission electron microscopy. Precipitate free zones were found to be absent along the subgrain boundaries of the thermomechanically processed material.     

The influence of crystal anisotropy on mechanical behaviour

Anisotropy of crystal structure leads to complications in mechanical behaviour. Robert Cahn, 50 years ago, made valuable contributions through determination of crystallographic features of plastic deformation in large crystals in polycrystalline -uranium. This research area has become increasingly linked with the effects of internal and external stresses on many materials in polycrystalline form comprised of grains with anisotropic crystal structure. The extent of irreversibility of deformation when such materials are subjected to thermal cycles leads to the significance of crystallographic textures but major effects on mechanical behaviour are often apparent where grains are randomly aligned without preferred crystal orientation when small external stresses are imposed. The importance of these features, their main characteristics and their analysis are briefly reviewed     

The dependence of tear behaviour on the microstructure of biaxially drawn polyester film

The structure-property relationship between a biaxially oriented film from poly(ethylene terephthalate) and its fracture behaviour measured using the Trouser Tear method, has been explored. X-ray diffraction (XRD) was used to characterise the orientation distribution of crystalline and non-crystalline material in the plane of the film and compared with the fracture energy, G _c measured in four directions during tearing. The fracture energy averaged over the four directions ranged between 12 and 25 kJ m^–2, and was found to correlate closely to the draw ratio during manufacture and therefore the degree of molecular orientation. However the individual values of G _c displayed a further level of complexity.The expected anisotropic character of the fracture energy was found to change systematically as a function of position across the original width of manufactured film. This feature compared well with the underlying, crystalline orientation distribution and provided strong evidence that under the mode III deformation of the tear test, the fracture mechanism involves the amorphous-crystallite surface boundary.Further support for this mechanism was provided by a simple model which, based on this assumption was shown to predict reliably, the anisotropic character of the film.     

The effect of microstructure and stress state on the fracture behaviour of wood

Based on a general fracture mechanics approach, this paper attempts to correlate macroscopic fracture properties with micromechanical behaviour in wooD. In the first part, the influence of orientation, cell size and other structural features of wood on toughness, fatigue resistance and fracture morphology is described. Subsequently, experimental observations of crack tunnelling effects are reported which, coupled with direct crack tip strain measurements and a verification of the influence of specimen thickness on fracture properties, confirm the existence of stress state variations across a crack front in wood, and the corresponding effects on fracture behaviour. Irreversible crack-tip deformation modes are identified, involving intercellular debonding, cell twisting and buckling, and the role of stress triaxiality is discussed. A strain criteria for the fracture of pre-notched bulk wood specimens is developed, based on an observed linear relationship between notch root radius and crack opening displacement for fracture initiation.     

The influence of boron content on the fine microstructure of pyrolytic graphite

A study of the fine microstructure of boronated pyrolytic graphite was made utilising optical and X-ray diffraction techniques. The influence of boron content on the laminar structure, the lattice parameter, the lattice strain, the particle size, and the flexural strength of pyrolytic graphite was studied. Significant changes in the behaviour of all investigated parameters were observed in the 0.50 to 0.75 wt % boron range. A mechanism relating these changes to the appearance of a boron carbide deposit is hypothesised.     

The influence of surface microstructure on the scratch characteristics of Kevlar fibers

In this work, nanoindentation and nanoscratching experiments are combined with atomic force microscopy to investigate the relationships between contact geometry, apparent friction, and deformation modes of two grades of Kevlar^® (Dupont) fiber—Kevlar KM2 and Kevlar 49. Changes in the relative angle between the scratching probe and the fiber surface, often termed as the attack angle, result in changes in deformation mode, which correlate with the changes in the apparent friction. As attack angle increases, the observed deformation modes of the fiber surface change from a smoothing of the surface, often termed as ironing, to fibrillation, in which the fibrils break and coalesce in front of the progressing probe. A mixture of these two modes occurs at intermediate attack angles. When fibrillation occurs, material pile-up forms in front of the progressing probe. This pile-up introduces an additional component to the frictional response that is largely responsible for an increase in apparent friction with an increasing attack angle and/or scratch length. The level of friction associated with fibrillation is measured to be up to approximately three times higher than previously reported for Kevlar yarn–yarn friction. Fibrillation of Kevlar KM2 occurs at larger attack angles as compared to Kevlar 49, which is believed to be related to a near-surface region of reduced modulus and hardness previously observed in KM2 fibers. A detailed discussion of the measured response is given based on the interactions between the scratching probe and the fibrillar network and the resulting deformation mechanisms.     

Mo含量对牙科用Ti-Mo合金显微组织及性能的影响

采用LZ5型离心铸钛机制备了4种Ti-Mo（5％、10％、15％和20％（质量分数）Mo）合金，研究了其显微组织和力学性能，并对其在Hank’S溶液和0．9％NaCl溶液中的耐蚀性进行了研究。研究结果表明：Ti-5Mo合金由等轴的α相组成，Ti-10Mo合金由等轴的β相和针状的α相组成，Ti-15Mo和Ti-20Mo合金由单一的等轴β相组成。力学性能测试结果表明，随着Mo含量的增加，Ti-Mo合金的压缩强度降低，塑性增强。耐蚀性研究结果表明，Hank＇s溶液中Ti-10Mo合金的自腐蚀电位较高，且易钝化；0．9％NaCl溶液中，Ti-5Mo合金的自腐蚀电位较高。Ti-20Mo合金易钝化且钝化区间较宽，两种腐蚀介质中Ti-15Mo合金的钝化膜较稳定。     

The influence of high-energy impacts on the microstructure of synthesized metal ceramics

On the example of the metal-ceramic alloy of titanium carbide (TiC) with nickel-chromium (Ni-Cr) binder, the comparative analysis of the influence of different high-energy impacts on the dispersion of the internal structure and phase composition of the synthesized metal ceramics 70 vol % TiC + 30 vol % (Ni-Cr) has been performed for the first time (self-spreading high-temperature synthesis (SSHTS) under pressure, preliminary mechanical activation (MA) of metal components of the initial powder mixture titanium-carbon-nickel-chromium binder, subsequent MA of the whole powder mixture, and intense plastic deformation of the synthesis product). It has been demonstrated that, under intense plastic deformation with extrusion of the high-temperature synthesis product, there a metal-ceramic structure forms containing particles of the nanosized carbide phase of the stoichiometric composition.     

The influence of microstructure on thermal response of glass ionomers

This study was designed to determine the dimensional changes caused by thermal stimuli of glass ionomers with different glass/matrix ratios. Four cylindrical specimens were made for each of four powder/liquid ratios (3:1, 2.5:1, 2:1 and 1.5:1) for a conventional luting glass ionomer, two high viscosity restorative glass ionomers and a restorative resin-modified glass ionomer. The thermal characteristics were determined using a thermal mechanical analyzer (TMA) by heating the samples from 25 °C to 70 °C at 10 °C per minute. All glass ionomers and the resin-modified glass ionomer lost water on heating. The results of the thermal response of these materials were explained in terms of the opposing effects of thermal expansion and desiccation on heating. The contraction on heating of glass ionomer and related materials was found to relate to the glass/matrix ratio but not directly proportional to it. Materials with lower P/L ratios contracted the most when heated to 70 °C. The water loss from conventional and resin-modified glass ionomer with different glass/matrix ratios compensated for their thermal expansion and led to a minimal dimensional change when heated up to 50 °C. This outcome may be interpreted as an example of smart behaviour of these materials.