[en] Fracture as one of the mechanical properties of materials is structurally dependent. Defects, defect assemblies, grain boundaries and sub-boundaries materials, modify the local stress intensity factors intensively. Brittle fracture prefers to confine to the grain boundary where the specific surface energy is lower than that in the grain. Again, transgranular cracking may occur on the crystal cleavage plane or planes where the local toughness is lowered by dislocation interaction and motion. This paper shows the complexity of the fractal dimension or roughness index of fractured surfaces in materials with metallographic structures or in inhomogeneous media. (author)

[en] The results from a series of tests on steel fiber reinforced concrete at elevated cyclic temperature are presented. The residual compressive strength and ultimate splitting tensile strength were nadir's on specimen ts with no fibers and with 0.5% and 1% plain steel fibers over a temperature range of 300-700 C. concrete was subjected to one, two or three cycles of heating and cooling. In general the exposure to temperature decreased the strength of concrete, although the number of heating cycles seems only to have a secondary effect. The results also show that the steel fiber reinforced concrete performs better than plain concrete. Two equations were suggested to predict the strength of concrete and the results show good agreement with the experimental values. . (authors). 10 refs., 1 tabs. 3 figs

[en] Previous papers on silicon carbide/Ti-15V-3Cr-3Al-3Sn (SCS6/Ti-15-3) composite have explored many aspects of fatigue behavior in this system. However, most of this effort has centered on composites with a 35 volume percent (v/o) fiber content. The objective of this study was to systematically compare the isothermal fatigue behavior of unidirectionally reinforced SCS6/Ti-15-3 composites with significantly different fiber contents. The target fiber contents of interest were 15, 35 and 45 v/o in this study

[en] The physical mechanisms characterizing the breaking of concrete, a brittle material in extension which is heterogeneous, porous and out of equilibrium, are presented. Various modelling paths are presented and discussed to describe material cracking and to calculate the structures. An industrial example in the civil nuclear field illustrates the optimization of concrete and the dimensioning method making it possible to ensure the ductility of the structure. (authors). 42 refs., 13 figs

[en] The fatigue response of a metal matrix composite, SCS-6/Ti-15-3 with the cross-ply lay-up of [0/90]_2s, was investigated under tension-compression cycling condition at room temperature and elevated temperature of 427 C. The fatigue lives for both temperatures were same at higher stress levels in the fiber dominated region, but they were longer at 427 C in comparison to room temperature at intermediate or lower stress levels in the matrix dominated region. This increase was due to the increased ductility of matrix at elevated temperature

[en] A hybrid experimental-numerical approach has been used to measure the fracture resistance of a sandwich structure consisting of a 304 stainless steel/partially stabilized zirconia ceramic-matrix composite crack-arresting layer embedded in a partially stabilized zirconia ceramic specimen. The mode 1 fracture toughness increases significantly when the crack propagates from the ceramic into the ceramic-matrix composite region. The increased toughening due to the stainless steel particles is explained reasonably well by a toughening model based on processing-induced thermal residual stresses. In addition, several experimental modifications were made to the chevron-notch wedge-loaded double cantilever beam specimen to overcome numerous problems encountered in generating a precrack in the small, brittle specimens used in this study

[en] In cooling sintered composites of Al₂O₃-ZrO₂ from their fabrication temperature residual stresses are created as a result of both the difference in thermal expansion between the two phases and the crystallographically anisotropic thermal expansion of the Al₂O₃ phase. In this work the first and second moments of the residual stress distribution have been measured as a function of volume fraction of zirconia from 0.01 to 0.90. The measurement technique used is piezo-spectroscopy based on the optical fluorescence from Cr³⁺ dopants in the alumina phase. For zirconia volume fractions up to 0.35 the average stress accurately fits the predictions given by the upper Hashin bound and this fit provides a value of the average thermal strain in the composites. Using this value, the effective medium approximation produces an excellent description of the average stress over the entire volume fraction. It is shown that the fluorescence broadening due to stress fluctuations lies close to the predicted upper and lower Hashin bounds modified by the restrictions imposed by the principle of maximum entropy. The measured moments and those predicted by stochastic stress analysis compare well suggesting that the stochastic analysis provides a reliable method of calculating residual stress in composites

[en] Very large floating structures (VLFSs) may one day be essential to the study and utilization of the ocean. Some possible applications for VLFSs are ocean ranching homeports. observatories for ocean research, seabed mineral refineries, energy generation platforms. and waste management facilities. A VLFS that is in the conceptual phase, and may one day be based off the coast of Hawaii, has been named Blue Revolution. Candidate materials for Blue Revolution were identified based on criteria of rigidity, strength, and weight. Priority was given to materials that could be used to construct lightweight VLFSs. Major static forces were considered in this preliminary analysis. The best materials were identified as those having low values of density/modulus (ρ/E) and density/strength (ρ/σ). Concrete, metal alloys, organic-matrix composites (OMCs), and metal-matrix composites (MMCs) were evaluated. OMCs and MMCs were generally the best materials based on their very low ρ/E and ρ/σ values

[en] Experimental studies were carried out so as to estimate the influences of temperature and moisture migration on properties of concrete subjected to elevated temperatures. The test pieces were either sealed (up to 175degC) and unsealed (up to 600degC) during temperature exposure, mechanical and thermal properties were studied. The simulated mass concrete mock-up specimens were heated at one side, with maximum temperatures up to 600degC. After heating, the influences of temperature and moisture content on mechanical properties were studied. As a result, it is confirmed that the properties of concrete, subjected to elevated temperatures can be influenced significantly by moisture migration during heating. (author)

[en] Predictions using current micromechanics theories for the effective moduli of particulate-reinforced composites tend to break down at high volume fractions of the reinforcing phase. The predictions are usually well below experimentally measured values of the Young's modulus for volume fractions exceeding about 0.6. In this paper, the concept of contiguity, which is a measure of phase continuity, is applied to Mori-Tanaka micromechanics theory. It is shown that contiguity of the second phase increases with volume fraction, leading eventually to a reversal in the roles of the inclusion and matrix. In powder metallurgy practice, it is well known that at high volume fractions, sintering and consolidation of the reinforcement make it increasingly continuous and more like the matrix phase, while the former matrix tends to become more like the inclusion phase. The concept of contiguity applied to micromechanics theory results in very good agreement between the predicted Young's modulus and experimental data on tungsten carbide particulate-reinforced cobalt