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Brittle Materials (brittle + material)
Selected AbstractsFlame-retardant action of red phosphorus/magnesium oxide and red phosphorus/iron oxide compositions in recycled PETFIRE AND MATERIALS, Issue 5 2006F. Laoutid Abstract Red phosphorus was combined with metallic oxides Fe2O3 and MgO to improve the fire properties of recycled PET. Both Fe2O3 and MgO act as co-synergist agents at a total loading of 5 wt%. The analysis by diffraction X of the char formed during combustion shows that transformation of Fe2O3 to Fe3O4 occurs. Fe2O3 favours the oxidation and improves the effectiveness of red phosphorus. It is suggested that MgO interacts with acidic end groups of PET and forms a thermal stable residue. The thermal decomposition of recycled PET containing red phosphorus combined with Fe and Mg oxides was studied by thermal analysis and leads to an increase in char formation. While the incorporation of Fe2O3 in this ternary blend maintains the mechanical properties of PET, the reactivity of MgO leads to a brittle material. The use of reinforcements (talc and glass fibres) to mechanically stabilize the char formed during combustion of ternary blend with Fe2O3 entails a further decrease in heat release rate, nevertheless impact resistance of the material decreases dramatically. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical simulation of the fracture process in cutting heterogeneous brittle materialINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2002H. Y. Liu Abstract The process of cutting homogeneous soft material has been investigated extensively. However, there are not so many studies on cutting heterogeneous brittle material. In this paper, R-T2D (Rock and Tool interaction), based on the rock failure process analysis model, is developed to simulate the fracture process in cutting heterogeneous brittle material. The simulated results reproduce the process involved in the fragmentation of rock or rock-like material under mechanical tools: the build-up of the stress field, the formation of the crushed zone, surface chipping, and the formation of the crater and subsurface cracks. Due to the inclusion of heterogeneity in the model, some new features in cutting brittle material are revealed. Firstly, macroscopic cracks sprout at the two edges of the cutter in a tensile mode. Then with the tensile cracks releasing the confining pressure, the rock in the initially high confining pressure zone is compressed into failure and the crushed zone gradually comes into being. The cracked zone near the crushed zone is always available, which makes the boundary of the crushed zone vague. Some cracks propagate to form chipping cracks and some dip into the rock to form subsurface cracks. The chipping cracks are mainly driven to propagate in a tensile mode or a mixed tensile and shear mode, following curvilinear paths, and finally intersect with the free surface to form chips. According to the simulated results, some qualitative and quantitative analyses are performed. It is found that the back rake angle of the cutter has an important effect on the cutting efficiency. Although the quantitative analysis needs more research work, it is not difficult to see the promise that the numerical method holds. It can be utilized to improve our understanding of tool,rock interaction and rock failure mechanisms under the action of mechanical tools, which, in turn, will be useful in assisting the design of fragmentation equipment and fragmentation operations. Copyright © 2002 John Wiley & Sons, Ltd. [source] Qualitative and quantitative fracture analyses of high-strength ceramicsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 2 2009Marit Řilo The aims of this study were to assess the applicability and repeatability of qualitative and quantitative analyses of the fracture patterns of four different high-strength ceramics. Ten bar-shaped specimens of four high-strength ceramics with different material composition and fabrication methods had been fractured by three-point bending in water (n = 40). Commonly used fractographic patterns for brittle materials, such as mirror and mist, were used to characterize and quantify the fractured surfaces of these specimens. The analyses were performed twice, on separate occasions, by the same operator. Assessment of the association between fractographic patterns and fracture stress was carried out, and repeatability assessments of the measurements were performed. The fracture initiator site and the common fractographic markers surrounding this site were found in all specimens. Statistically significant correlations were found between certain fracture patterns and stress at fracture. The repeatability of the measurements of the different fractographic patterns varied among the materials. Fracture analyses seem applicable as a tool to determine the fracture initiation site and to estimate the force vectors involved in the fracture of dental high-strength ceramics. [source] Suppression of Premature Fracture of Silicon under Three-Point Bending: Role of Nanoscale Localized Deformation of Metallic Multilayered Coating,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Yuan-Ping Li Brittle single crystal Si with and without Au/Cu multilayer coating was investigated via three-point bending test. Load-bearing capacity of the Si coated with the Au/Cu multilayer is improved evidently compared with the bare Si. Especially the nanoscale plastic deformation of the multilayer was observed to be effective in delaying instable crack propagation within the Si. That would shed significant light in toughening methods of brittle materials. [source] Homogenization-based analysis of anisotropic damage in brittle materials with unilateral effect and interactions between microcracksINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 6 2009Q. Z. Zhu Abstract This paper is devoted to micromechanical modeling of induced anisotropic damage in brittle geomaterials. The formulation of the model is based on a proper homogenization procedure by taking into account unilateral effects and interactions between microcracks. The homogenization procedure is developed in the framework of Eshelby's inclusion solution and Ponte-Castaneda and Willis (J. Mech. Phys. Solids 1995; 43:1919,1951) estimate. The homogenization technique is combined with the thermodynamics framework at microscopic level for the determination of damage evolution law. A rigorous crack opening,closure transition condition is established and an energy-release-rate-based damage criterion is proposed. Computational aspects on the implementation of micromechanical model are also discussed. The proposed model is evaluated by comparing numerical predictions with experimental data for various laboratory tests on concrete. Parametric studies on unilateral effects and influences of microcracks interactions are finally performed and analyzed. Copyright © 2008 John Wiley & Sons, Ltd. [source] Extrinsic cohesive modelling of dynamic fracture and microbranching instability in brittle materialsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2007Zhengyu (Jenny) Zhang Abstract Dynamic crack microbranching processes in brittle materials are investigated by means of a computational fracture mechanics approach using the finite element method with special interface elements and a topological data structure representation. Experiments indicate presence of a limiting crack speed for dynamic crack in brittle materials as well as increasing fracture resistance with crack speed. These phenomena are numerically investigated by means of a cohesive zone model (CZM) to characterize the fracture process. A critical evaluation of intrinsic versus extrinsic CZMs is briefly presented, which highlights the necessity of adopting an extrinsic approach in the current analysis. A novel topology-based data structure is employed to enable fast and robust manipulation of evolving mesh information when extrinsic cohesive elements are inserted adaptively. Compared to intrinsic CZMs, which include an initial hardening segment in the traction,separation curve, extrinsic CZMs involve additional issues both in implementing the procedure and in interpreting simulation results. These include time discontinuity in stress history, fracture pattern dependence on time step control, and numerical energy balance. These issues are investigated in detail through a ,quasi-steady-state' crack propagation problem in polymethylmethacrylate. The simulation results compare reasonably well with experimental observations both globally and locally, and demonstrate certain advantageous features of the extrinsic CZM with respect to the intrinsic CZM. Copyright © 2007 John Wiley & Sons, Ltd. [source] The Damage Mechanism Route to Better Armor MaterialsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010Donald A. Shockey This paper describes the mechanisms by which brittle materials are penetrated by impacting projectiles, links ballistic performance to fracture behavior, and in turn to microstructure, and suggests a route unexplored previously for achieving better armor materials. Fracture patterns on cross sections through partially penetrated glass and ceramic targets show that deep penetration proceeds by the crushing and subsequent flow of fragments away from the projectile path. Preliminary finite element simulations indicate the likely positive effect of increasing frictional flow resistance of fragments. Tests are envisioned for measuring crush and fragment flow behavior, showing the effects of microstructural variables, guiding mathematical models, and hence leading to a capability to design computationally improved armor materials and structures. [source] A New Analytical Model for Estimation of Scratch-Induced Damage in Brittle SolidsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Xiaoning Jing Scratch tests are of fundamental interest both for understanding machining-induced damage and for evaluating the scratch resistance of brittle materials. An improved blister field model for the scratch process is proposed where the blister field strength is explicitly determined in terms of the material properties, loading conditions, and geometry of the scratch tool. Additionally, one new expanding cylindrical cavity model is implemented to estimate the plastic zone size surrounding the scratch groove. A quantitative evaluation of the damage zone size is conducted by combining the above two models. The predicted damage zone sizes are in good agreement with the results available elsewhere in literature. [source] Characterization of grooves in scratch resistance testingPOLYMER ENGINEERING & SCIENCE, Issue 10 2008Witold Brostow For a number of polymers with different chemical structures and different properties we have determined scratch resistance and sliding wear (15 scratches along the same groove). We have measured cross section areas after scratching, namely the groove and side top-ridge areas. Nanohardness after scratching was determined using nanoindentation testing both inside and outside the scratching and sliding wear grooves. Three modes of sliding wear are seen: plowing, cutting with debris formation, and densification. The dominating mode depends on the material and is reflected in nanohardness. In polycarbonate (PC) the nanohardness inside and outside the groove are practically the same; the indenter just plows the material aside without debris formation or densification. Thus, the old measure of wear as the weight of the debris formed is not usable for PC; grooves are present but there is no loosened material. By contrast, in brittle materials such as polystyrene there is debris formation and nanohardness inside the groove decreases after 15 scratching runs. A third type of behavior is seen in polyethylene and polypropylene, namely densification caused by scratching; as a result, nanohardness inside the groove increases after 15 passes of the indenter. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] | |||||||||||||