Papers by Keyword: Fracture Characteristic

Abstract: The compressive properties of Mg-3Al-2Zn-2Y alloy at room temperature at strain rates in range of 0.001s^-1~4800s^-1 were investigated. To the alloy compressed at 1300s^-1, its basal and non-basal slip produce the mixed dislocation configuration including parallel, bended and tangled dislocation. There is significant twinning in the alloys compressed at 1800s^-1 and 4800s^-1. The flow stress and ultimate trength show the strain rate hardening behavior at the range of 0.001s^-1~1800s^-1. There appears localized deformation zones formed with recrystal grains and twin crystals in the alloy compressed at 4800s^-1, whose mechanical properties are lower than those of alloy compressed at 1800s^-1.

Abstract: SiC filament was prepared by Chemical Vapour Deposition method using W wire as the substance material. The combination between W wire and SiC became a key element influencing tensile strength of SiC. In this paper, tensile fracture morphology of SiC filament was analyzed, from which interface combination between SiC and W wire was discussed under different deposition temperature and the influence of interface layer’s thickness on final tensile of SiC filament was given. How to control the thickness of interface layer is a key factor for improving performance of SiC filament.

Abstract: CH3SiCl3-H2-Ar system was adopted to prepare SiC Filament of high tensile strength by high-frequency induction during Chemical Vapor Deposition (CVD) method. Room-temperature tensile strength of SiC filament prepared under different temperature was test. Crystal structure, surface morphology and fracture character of SiC filament was analyzed with “X-ray diffractometer and scanning electron microscope. Influence of temperature to final tensile behavior of SiC filament was discussed synthetically. The result shows that tensile strength is very sensitive to temperature. From 1000°C to 1400°C, tensile strength increases and then decreases as temperature increases. At 1200°C, tensile strength reaches its max value, the reason ofwhich is composed of three parts. The first one is that the deposited product is β-SiC. The second one is that surface of SiC filament is smooth. The third one is that fracture surface shows ductile dimples fracture, brittle fracture and cleavage fracture patterns. 1200°Cis considered as one reasonable temperature in our laboratory to prepare SiC filament.

Abstract: The behaviour of a propagating crack when an interface is present is a key feature in composite materials. This interaction usually predetermines final fracture behaviour of the material. In case of ceramic based composites (particle, fibre reinforced, laminates etc.) knowledge about properties of the interface and/or interlayer is usually unknown due to difficulties associated with their experimental determination. The aim of this work is to indicate a possible way for the determination of interface characteristics suitable as inputs for numerical calculations. The introduced testing methodology was tested on spinel composite ceramics reinforced by unidirectional SiC fibre. The adopted method for fracture toughness determination is using a chevron notch technique. Additionally, fractographical techniques were used when interpreting the measured values.

Abstract: The overall mechanical characterization of hot-pressed hexagonal boron nitride (h-BN) based ceramics was performed. Hardness, flexure strength and fracture toughness (KIC) measurements were carried out using Vickers indentations, 3-point bending tests and SEVNB method, respectively. The fracture characteristics of hot-pressed h-BN ceramics were investigated by analyzing fracture surfaces using scanning electron microscope (SEM). The hardness, ranged from HV = 0.20GPa to HV = 0.25GPa, which was higher in the surfaces parallel to the hot-press direction due to the perpendicular alignment of the basal planes of the h-BN platelets to the hotpress direction. The fracture toughness and flexure strength values were determined to be 2.6 MPa.m1/2 and 0.14 GPa, respectively. A single KIC value was obtained since a slight variation of the fracture toughness was observed with the orientation of h-BN. The microstructural observations of h-BN grains indicated completely brittle fracture with intergranular voids and microcracks revealing a mixed mode of fracture.

Abstract: Rock masses usually contain intermittent joints. The existence of joints not only significantly affects the static properties of rock masses, but also their dynamic response and stability under blast waves. The present study focuses on investigating the fundamental fracture characteristics of intermittent jointed rock masses subjected to blast loading. A series of blasting tests were conducted on organic glass samples. The results are analyzed in order to obtain the characteristics of initiation, propagation and coalescence of wing cracks in rock bridges. The study indicates that the fracture behavior of intermittent jointed rock masses may be significantly affected by the preliminary static stress fields, the density and filling states of rock joints, the incident angles of blast waves relative to the joints, and the amplitudes of incident waves. From visual observation, three initiation modes and four coalescence modes of wing cracks are suggested. Finally, a comparison has been made between the fracture characteristics of intermittent jointed rock masses under single static stress field and that of under blast loading.

Abstract: In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. A standard CT specimen was used to obtain fracture resistance curves. However the fracture resistance curve by the standard CT specimen was very conservative to evaluate the integrity of the structure. Also the fracture resistance curve was affected by the specimen geometry, crack plane orientation, reverse cyclic loading and dynamic strain aging. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen. For these purpose, fracture tests using the real-scale pipe specimen and standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. From the result of the pipe and the standard CT specimen tests, it was observed that the fracture resistance curve of the standard CT specimen test was conservative compare to that of the pipe specimen test.