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Showing papers in "Journal of Materials Science Letters in 1993"


Journal ArticleDOI
Yoshitsugu Kojima1, Kenzo Fukumori1, Arimitsu Usuki1, Akane Okada1, Toshio Kurauchi1 

244 citations



Journal ArticleDOI
TL;DR: In this paper, the authors show that the rate of capillary absorption of water in cement-based materials is anomalous when compared with that of other liquids, including other liquids.
Abstract: The paper shows that the rate of capillary absorption of water in cement-based materials is anomalous when compared with that of other liquids.

100 citations





Journal ArticleDOI
TL;DR: In this paper, the authors describe a newly discovered phenomenon: ductile fracture in cementitious materials, characterized by a very small micro-crack zone at the crack tip, typically of submillimetre scale, low fracture energy of the order of 0.01 kJm -2, and a linear load versus load point displacement curve from a fracture test.
Abstract: This letter describes a newly discovered phenomenon: ductile fracture in cementitious materials. The brittle nature of materials such as concrete and ceramics has prompted the development of various approaches to enhance their fracture toughness. Fibre reinforcement has been the common focus in the toughening of the brittle materials. Two types of fracture have been observed to date in cementitious materials and ceramics: brittle and quasi-brittle fracture. Brittle fracture can be observed, for example, in hardened cement paste material. It is characterized by a very small microcrack zone at the crack tip (Fig. la), typically of submillimetre scale, low fracture energy of the order of 0.01 kJm -2, and a linear load versus load-point displacement curve from a fracture test. Quasi-brittle fracture can be observed in concrete and in most fibre-reinforced cements or concretes (FRC). It is characterized by a bridging process zone in addition to the small microcrack zone at the crack tip (Fig. lb). The bridging action provides additional energy absorption through aggregate and/or ligament bridging in concrete, and through fibre bridging in FRC, in the wake of the crack front. For quasi-brittle materials the fracture energy extends a large range, from 0.1 kJm -2 in concrete to several kJ m -z in the case of FRC. Correspondingly, the process zone size extends from the mm scale to the cm scale. The load versus load-line displacement curve from a fracture test may involve a small non-linear region near the peak load, with a significant post-peak tension-softening behaviour. Research into quasi-brittle materials in the past decade has been extensive (see, for example [1, 2] for a recent collection of papers on the subject). It must be mentioned that the classification of the fracture characteristics for cementitious materials described above may also be applicable to current monolithic and fibre-reinforced ceramics.

72 citations


Journal ArticleDOI
TL;DR: The theory of thermal conductivity of composites is well established as discussed by the authors, and it is shown that any thermal expansion behavior intermediate to those for the individual components can be obtained by the judicious selection of the component volume fractions, as demonstrated by Geiger and Jackson [2] for particulate-reinforced metal-matrix composites.
Abstract: Electronic packaging requires matching the coefficients of thermal expansion of the various materials that make up the package to reduce the magnitude of the stresses which arise from temperature variations, reducing the risk of mechanical failure. Maximizing the thermal conductivity of all materials avoids the build up of excessive temperature. Materials with tailorable coefficients of thermal expansion can be obtained with composite materials. As shown by Turner [1], the coefficient of thermal expansion of a composite is a function of the coefficients of thermal expansion, the bulk moduli and the volume fraction of the components. Generally, the thermal expansion of a composite is dominated by the component with the highest value of bulk modulus. In principle any thermal expansion behaviour intermediate to those for the individual components can be obtained by the judicious selection of the component volume fractions, as demonstrated by Geiger and Jackson [2] for particulate-reinforced metalmatrix composites. Silicon carbide, aluminium nitride and diamond, which also exhibit high values of thermal conductivity, have been used to make discontinuously reinforced aluminium composites. These metal-matrix composites not only permit control of the thermal expansion, but may also enhance the thermal conductivity. The theory of thermal conductivity of composites is well established. In general the thermal conductivity of a composite depends on the values of the thermal conductivity, the volume fraction and the distribution and particle size of each component, as well as on the existence (if any) of an interfacial thermal barrier. The effective thermal conductivity of a continuous matrix with dilute volume fractions of non-interacting spherical inclusions is [3]

66 citations






Journal ArticleDOI
Burtrand I. Lee1, L. Burnett1, T. Miller1, B. Postage1, J. Cuneo1 
TL;DR: In this paper, granulated tyre rubbers were incorporated in Portland Type 1 cement pastes to improve the mechanical properties of these composites, including compressive, diametral tensile, and flexural strength under freezing and thawing cycles.
Abstract: Organic polymers or fibres in ordinary Portland cement matrices have been shown to improve the mechanical properties of these composites. Such industrial wastes as fly ash and silica fume have been successfully incorporated into cement. Based on these results and the disposal problem of waste tyres, granulated tyre rubbers were incorporated in Portland Type 1 cement pastes. Results from preliminary experiments in compressive, diametral tensile, and flexural strengths under freezing and thawing cycles are reported







Journal ArticleDOI
TL;DR: The fracture toughness of renal calculi offers a direct measurement of stone resistance to fracture failure during ESWL and is compared with stone fragility obtained from previous studies [7-9].
Abstract: Since the early 1980s extracorporeal shock-wave lithotripsy (ESWL) has become the primary treatment modality for urinary stone disease [1]. Renal stones are fragmented by high-energy shock waves [2] or by the impingement of cavitation microjets [3, 4] into small pieces and are passed spontaneously. Because of the differences in chemical compositions and structural features of renal calculi [5], shock wave-stone interaction during ESWL [6], and thus the efficacy of stone fragmentation, may vary significantly. Clinically, among common stone types, phosphate (struvite and calcium apatite) stones are found to be easy to fragment, whereas uric acid and brushite stones are in the middle range, and calcium oxalate monohydrate and cystine stones are the most resistant types to ESWL therapy [7-9]. To improve the efficacy of ESWL treatment, it is desirable to identify the physical properties of renal calculi that can offer direct correlation with their fragilities during ESWL and thus can be used to guide treatment procedures for more effective stone fragmentation. The fracture toughness of renal calculi offers a direct measurement of stone resistance to fracture failure during ESWL. In this letter we report our results for the fracture toughness of renal calculi of various compositions. A microindentation technique was used to determine stone hardness. An ultrasound transmission technique was used to measure both longitudinal and transverse wave speeds, from which the Young's and shear moduli of stone materials were derived. Based on these measurements and the lengths of crack lines produced by the hardness indentor, the fracture toughness of renal calculi were calculated and compared with stone fragility obtained from previous studies [7-9]. Implications of the measurement results on an improved understanding of the mechanism of stone fragility and on enhancing the effectiveness of stone fragmentation during ESWL are discussed. Six stone specimens with crystal compositions determined by crystallographic analysis (Urolithiasis Laboratory, Baylor College of Medicine, Houston, Texas, USA) were used. The densities of the specimens were determined using a pycnometer (2 ml in capacity) based on ~ Archimedes' principle [6]. Stone specimens were mounted in a self-curing cold-mounting material (Koldmount, VernonBenshoff Co., New York, USA), polished and prepared for microhardness measurement as described in [10]. Ten indentations were made in homogeneous crystalline regions of each specimen using a Vickers indentor at a load of 50 g with a dwell time of 15 s. Since renal calculi are essentially brittle materials, radial cracks (Fig. 1) were formed along the diagonals of the indentation after unloading [10]. The lengths of these crack lines reflect the degree of elastic recovery of the material and can be used to determine the fracture toughness of the stone [11]. We measured the crack length (c) and the size of indentor impression (l), and calculated the fracture toughness (Kic) for the stone material using [11]


Journal ArticleDOI
TL;DR: In this paper, the authors used periodic pulses of potential to obtain uniformly deposited bioactive calcium phosphate coatings on porous titanium substrates, having an average pore diameter of approximately 300 μm.
Abstract: The authors used periodic pulses of potential to obtain uniformly deposited bioactive calcium phosphate coatings on porous titanium substrates. Titanium wire (99.9% purity, O.25 mm in diameter) was used to form porous substrates having an average pore diameter of approximately 300 μm.








Journal ArticleDOI
TL;DR: In this article, the microstructures of the TiB 2 -SiC composites were characterized and the mechanical properties, such as the bending strength at elevated temperatures and fracture toughness, were investigated.
Abstract: Densification of TiB 2 -SiC composites formed in situ was achieved by hot-pressing. The microstructures of the composites were characterized and the mechanical properties, such as the bending strength at elevated temperatures and fracture toughness, were investigated.