Papers by Keyword: Fracture

Abstract: A fibrous monolith cemented carbide with WC-6%Co as cell and WC-20%Co as cell boundaries was produced through hot co-extrusion process in this paper. The density, hardness, transverse rupture strength (TRS) and fracture toughness (K_Ic) of the fibrous monolith cemented carbide were tested, and the fracture and crack propagation were observed by metalloscope and Scanning Electron Microscope. The result shows fibrous monolith structure design could effectively improve the TRS and the K_Ic of WC/Co cemented carbide without a significant decrease of hardness. It is the reason of high transverse rupture strength and fracture toughness that WC-20%Co can absorb more fracture energy in order to slow, prevent, or deflect crack propagation, proved by metalloscope and scanning electron microscope.

Abstract: A fibrous monolith cemented carbide with WC-6Co as cell and WC-20Co as cell boundaries was produced through hot co-extrusion process in this paper. The density, hardness, bending strength and fracture toughness of the fibrous monolith cemented carbide were tested, and the fracture and crack propagation were observed by metalloscope and SEM. The results showed that the bending strength and fracture toughness of the fibrous monolith cemented carbides was remarkably improved 71.91% and 45.7% respectively, while the hardness was slightly decreased 1% compared with WC-6Co composites. It is the reason that the tougher shell WC-20Co with higher bending strength and fracture toughness can absorb more fracture energy, which can slow down and prevent the crack propagating from brittle core WC-6Co.

Abstract: This paper presents results of the investigation of Si₃N₄ ceramic inserts with CVD coatings in turning grey cast iron. The high effectiveness of Si₃N₄ ceramic inserts with multi-layered coating in the finish turning of the grey irons was shown. It was established that at the heart of the wear mechanism of coated Si₃N₄ ceramic inserts there is a chain of relations cutting conditions loading fracture of coating сhipping of ceramic surface layer failure of tools. One of the important features of wear mechanism of these tools is the operational defects formed at the coating substrate interface.

Abstract: This paper based to study of the dynamic and fatigue behaviors with numerical and experimental parts of a composite material manufactured by stacking two layers of E-glass fiber in different angle orientations (0°/90°) immersed in polyester resin with total thickness 1.39mm. In Finite Element Analysis (FEA) using ABAQUS was used to evaluate the maximal (displacement, strain and stress) and the natural frequencies (mode shapes) of composite behavior under crack initiation condition. In the experimental part the laminate plate specimen with two layers is tested under one types of cyclic load in fully reversible tensile at (R=0), the fast fracture occur phenomenon and the fatigue life are presented , the fatigue testing exerted in INSTRON 8801 machine.

Abstract: Effective modeling of ice material behavior requires treatment of both damage and fracture. In this paper, a discussion of local ice damage and fracture processes observed during laboratory-scale indentation experiments conducted on unconfined polycrystalline ice using a spherical indenter is provided. Particular emphasis is placed on the interplay between fracture and extrusion processes corresponding to the failure of ice under a single zone of high contact pressure. Simulations have been conducted using a continuum damage mechanics user-material routine in conjunction with element removal techniques to simulate pressure-softening and discrete fracture processes, respectively. Simulation results provide good agreement with test data and provide important insights into interplay between damage and fracture mechanisms associated with compressive ice failure. Finite element modeling was found to work well for modeling pressure softening effects and for replicating the effects of discrete fracture events. For interactions involving multiple failure events, further work is needed to develop models that account for random aspects of fracture associated with flaw structure, contact geometry and the geometry of individual spalls.

Abstract: Strength data of three advanced ceramics were fitted to the Weibull, normal and lognormal distributions. The three ceramics had similar grain size and varied in binder content. The role of microstructure in the failure mechanism of such ceramics was analysed in terms of the chosen strength distributions. The best-fit distributions were determined using the maximum log-likelihood criteria and a comparison between the best and worst fit was conducted using the Akaike Information Criteria (AIC). Both large and small samples were tested to investigate possible scaling effects for these ceramics. It was found that for two of the three ceramics tested that a lognormal distribution rather then the conventionally used Weibull distribution was preferable in characterising the strength data. A small drop in strength was noticed between large and small samples but this trend was not thought to be a result of scaling rather due to the decrease in binder content.

Abstract: Researched the effect of DNP on mechanical properties of materials with a coarse-grained and fine-grained initial structure of aluminum alloy 2024 - T3, D16 and nano-crystallite titanium VT1-0. It has been shown that self-organization of structures at dynamic non-equilibrium processes is a critical parameter for materials with a nano-structures, since it significantly reduces the strength at the subsequent loading.

Abstract: The role of stress state on the fracture properties of a quasi-brittle material are explored using reactor core Gilsocarbon graphite. The objective of the experiment was to study the initial propagation of cracks. Cruciform specimens have been tested by a biaxial flexural loading method. Pre-slots of 10 mm width and up to a quarter of the depth of the specimen were introduced at the centre of the specimen by electric discharge machining. The slots are located between two through-thickness holes, which are designed to guide crack propagation. A loading jig has been designed and built that allows a range of biaxial loading states to be applied by variation of the length of the loading arms. Clip gauges are used to measure the crack mouth opening displacements. Preliminary tests have studied the fracture of specimens under different loading conditions.

Abstract: Numerical model for fatigue crack propagation within the framework of finite element smeared crack analysis is presented. It concentrates on modeling of fatigue behavior of material under tensile load which causes initiation and growth of cracks in concrete. The fatigue material model is an extension of existing static three-dimensional fracture-plastic material model, and as such it has been implemented into the ATENA Finite Element software package. The developed model has been used to model experiments with high-cycle loading of three point bending concrete specimens tested by collaborating institutions. Analysis results are compared to the measurements.

Abstract: Resistance of tear is an important characteristic of textile materials, especially for fabrics used for personal protective equipment. In this study, a constant force is applied to tear the fabric specimens to obtain the del-zone theoretically. The strain-stress curve for a single yarn is obtained from experiment, and the del-zone is determined by an ancient Chinese algorithm. This combination of ancient Chinese algorithm and actual tearing behavior of woven fabrics provides a noval analysis approach of tearing performance of textile product theoretically.