Papers by Keyword: Fracture Behaviour

Abstract: Interpenetrating Phase Composites (IPC) belong to a special category of composite materials, offering great potential in terms of material properties due to the continuous volume structure of both composite components. While manufacturing of metal-ceramic IPC via existing casting and infiltration processes leads to structural deficits, semi-solid forming represents a promising technology for producing IPC components without such defects. Thereby, a solid open pore body made of ceramic is infiltrated with a metallic material in the semi-solid state. Good structural characteristics of the microstructure as the integrity of the open-pore bodies after infiltration and an almost none residual porosity within the composites have already been proven for this manufacturing route within a certain process window. On this basis, the following paper focuses on the mechanical properties such as bending strength of metal-ceramic IPC produced by using semi-solid forming technology. Thereby, the impact of the significant process parameters on these properties is analysed within a suitable process window. Furthermore, a fractographic analysis is carried out by observing and interpreting the fracture behaviour during these tests and the fracture surface thereafter.

Abstract: Nickel based amorphous alloys have been developed in ribbons form by planar flow casting method and were subjected to tensile tests. For this purpose, specimens with calibrated area were obtained by electroerosion cutting method and tested at tensile test with different strain rates. Following the results obtained during the tests, the mechanical properties have been determined and compared and the fracture behaviour has been analyzed by scanning electron microscopy.

Abstract: AZ31 alloy sheets were produced by twin-roll casting (TRC) and sequential hot rolling. Uniaxial tensile tests were used to evaluate the deformation properties of the AZ31 alloy at a strain rate of 7×10^-4s^-1 and a temperature range from room temperature to 400°C. The microstructure evolution and fracture behaviour were observed by optical microscopy and scanning electronic microscope. The results show that the elongation of the AZ31 alloy increases with increasing temperature at a strain rate of 7×10^-4s^-1. The AZ31 alloy begins to exhibit superplasticity at 300°C. The elongation of 497.8% is achieved at 400°C. The deformation of the AZ31 alloy at low temperature is controlled by dislocation motion, and with increasing temperature (above 300°C), grain boundary sliding (GBS) begins to play a dominant role during superplastic deformation.

Abstract: Composite materials (55 vol.% SiC_p/A356) were brazed by filling with a Zn-based alloy with the assistance of ultrasonic waves. 37 vol.% SiC particles composite bonds were produced and their structural features as well as mechanical properties were obtained. The crack initiation and propagation behavior of the composite bonds were examined using in situ SEM and SEM fractographic observations. The shear strength of the brazed bonds containing ~37 vol.% SiC particles was 37% higher than the 55%SiC_p/A356 composites and 48% higher than the un-reinforced bond. There are two mechanisms of crack initiation in metal matrix composite. In the first cracks may initiate at in the eutectic phase in the composite bond. In the second cracks may also initiate due to cracking of the particles.

Abstract: In order to understand the anchorage mechanisms the fracture behavior of jointed rock masses reinforced with rockbolts was compared with those of the jointed rock masses without rockbolts. Firstly the unaixal tensile tests were conducted on the specimens with inclined surface cracks, horizontal through cracks and horizontal a quarter through cracks to investigate the crack growth of the jointed rock masses without rockbolts. The experimental results show the fracture of the specimens without rockbolts belonged to tensile fracture in the catastrophic way under uniaxial tensile conditions. However the experimental results of the specimens reinforced with rockbolts show that rockolts can change the initiation of the pre-existing cracks, incur the secondary cracks and there existed stable crack propagation.

Abstract: The influences of the ways in which the surface cracks were made and fillings in the surface cracks on the fracture behavior of the jointed rock masses were studied by a number of experiments. In the experiments the surface cracks were made in different methods such as placing polyester and aluminum thin plate, cutting. The experiment results show that the surface crack made by placing polyester thin plates and cutting may well simulate the natural cracks in jointed rock masses, but the specimens can’t initiate and fracture through the surface cracks formed by placing aluminum thin plate. In order to study the influences of the fillings in the cracks on the fracture behavior of the jointed rock masses polyester and aluminum thin plates were placed in the surface cracks to simulate different fillings. Compare with the surface crack without fillings those with fillings initiated and coalescence at a higher load. However the influences of fillings on the crack growth were very complex, which required to be studied further.

Abstract: Bulk nanostructured (grain sizes in the range of 50-200nm) and ultrafine structured (grain sizes in the range of 100-500nm) -TiAl based alloys with compositions Ti-47Al (in at%) and Ti–45Al–2Cr–2Nb–1B–0.5Ta (in at%), respectively, have been produced using a combination of high energy mechanical milling of mixtures of elemental powders and hot isostatic pressing at 800 and 1000oC respectively, and the microstructures of the samples have been characterised. At room temperature, the HIPed samples fractured prematurely at tensile stresses in the range of 200-300MPa and showed no ductility, very likely due to the relative high oxygen content (0.6wt%) in the samples and very low tolerance of TiAl based alloys on dissolved oxygen. At 800oC, the HIPed samples showed a yield strength in the range of 55-70MPa, a tensile strength in the range of 60-80MPa, a large amount of elongation to fracturing around 100% and clear strain softening. Examination of the fractured tensile test specimens at room temperature and 800oC showed that the level of the consolidation was fairly high, but the HIPed samples do contain a small fraction of interparticle boundaries with weak atomic bonding. The fracture of the HIPed samples in tensile testing at room temperature and 800oC, respectively, is predominately intergranular, and the large amount of plastic deformation prior to fracture at 800oC is achieved mainly through grain boundary sliding in conjunction with dislocation gliding, in agreement with the deformation mechanisms of nanostructured and ultrafine structured alloys generally agreed by researchers.

Abstract: In this work, the fracture behavior of a multi-layered thin film structure under residual tensile stress is investigated theoretically. Using composite material theory and a modified shear-lag model, the analytical solutions for the distribution laws of the tensile stress developed in the first-layer thin film and the shear stress developed along the interface can be obtained. In addition, the crack density of the first-layer thin film can be derived from the residual stress and the mechanical and geometric parameters of the cracked system. This result also yields a measurement of the residual stress from the crack density and the mechanical and geometric parameters of the system. Finally, a numerical example is presented to show how the crack density varies versus the residual stress.

Abstract: The fracture behavior of a brittle coating on an elastic substrate under residual stress is investigated. Using a mechanical model, the analytical solutions for the distribution laws of the tensile stress developed in the coating, the shear stress developed along the interface and the relationship between the crack density of the coating and the residual stress can be obtained. The analytic relationship between the crack density and the residual stress can also be taken as a new expression to estimate the magnitude of the residual stress. A numerical example is presented to show how the crack density varies versus the residual stress.

Abstract: The design of steel column base plays a very important role in steel structure design. Through large-scale analysis software ANSYS, this paper analyzes the steel column base by finite element numerical simulation nonlinear analysis,and discuss the fracture behavior and restoring force characteristics of steel pipe column in different thickness and axial compression ratio,and the link between the two. The results showed that, (1) the section of most likely break focus on the bottom of vertical load plane in the middle of the steel column base. (2) with the increase of thickness, anti-cracking ability increased gradually.(3) Axial compression ratio of the specimen has little effect for anti-cracking ability relatively. (4) With the increase of anti-cracking ability, the seismic behavior of specimens gets heightened.