Papers by Keyword: Fracture Surface

Abstract: The present work describes the study of mechanical properties anisotropy of two binary alloys namely, Ti-8Nb and Ti-12Nb in hot rolled condition. These alloys were unidirectionally hot rolled to 80 % reduction at 800 °C and subsequently air cooled. The alloys Ti-8Nb and Ti-12Nb consist of mainly α and α″ phases, respectively and small volume fractions of β phase in hot rolled condition. Both the alloys exhibit non-basal main texture components. The ODF plots display weak, continuous and inhomogeneous [0001]||ND and [001]||ND fibres for the alloys Ti-8Nb and Ti-12Nb, respectively. In plane anisotropy (A_IP) and anisotropy index (δ) were calculated from tensile results. Finally, an attempt has been made to correlate in plane anisotropy and yield locus to that of texture present in the hot rolled materials.

Abstract: Polylactide (PLA)-based wood plastic composites (WPCs) were manufactured by extrusion blending followed by injection molding. The fracture surfaces created from the impact test were recorded with SEM. Fractal analysis has been used to calculate the fractal dimension of the fracture surfaces with four different fractal analysis techniques. Then, the correlation between the fractal dimension of the fracture surfaces and its impact strength of the PLA-based WPCs was investigated by the linear regression. The results showed that there is a positive correlation between the impact strength and the fractal dimension.

Abstract: The influence of forming process on mechanical properties and microstructure of high strength microalloyed steel has been studied in this research. All samples selected from 90º and 180º of pipes in transverse and longitudinal orientations after UOE forming. The steel was supplied as a hot rolled plate with accelerated cooling. Microstructure of the micro alloy steel was various combinations of acicular ferrite, granular ferrite and M/A phases. Charpy impact fracture toughness tests were carried out in -50 °C to 0 °C. Minimum and maximum yield strength appears in the 180º and 90º of pipe in longitudinal and transverse orientations respectively. Increasing in the yield strength related to minimum amount was about 5.8 % after UOE forming. Comparison between yield strength after and before forming appears increased about 6.9 % due to forming. With decreasing in the test temperature from -50 °C to 0 °C, fracture energy decrease up to 0.9 % that it’s very little and relinquishment. However for samples that fractured in the temperature of -50 °C difference between highest and lowest energy was about 5.9 %. Charpy test results appear that fine M/A phase not a major factor on decrease of upper shelf energy, if homogenize distributed in the acicular ferrite matrix.

Abstract: In this research, fatigue behaviour of Ti-6Al-4V alloy was investigated for smooth and notched specimens with stress concentration factor(K_t) 3.6 and 4.1. This investigation was conducted for various diameter bars having different ultimate strength.Rotating bending fatigue test at R= -1 was emploied for this research. Notch sensitivity data was compared with those of steels. The result indicated that the presence of notch in this alloy has a different amount of sensitivity when the notch specimens were subjected to high cycle fatigue (HCF) and low cycle fatigue(LCF) tests.The notch sensitivity of this alloy was shown generally to be much lower than steel alloys with similar ultimate strength values. Therefore,considering the low sensitivity to notch of this alloy, can be recommended for applications with the presence of notch such as biomedical application

Abstract: Fatigue deformation behavior of the commercially pure iron containing micro-voids at grain boundaries (GBs) were investigated under total strain amplitude control, and fatigue fractures were quantitatively characterized by fractal analyses. The cyclic response curves of the CP iron show an initial softening stage within early several cycles followed by a continuous cyclic hardening. No stress saturation phenomenon was found. Pre-existence of micro-voids at GBs spurs intergranular cracking to become a common damage mode besides transgranular cracking along slip bands. Quantitative analyses of fracture surface demonstrate that the value of fractal dimension D of the scanning profile in the crack growth zone is the largest as compared to those in the crack source zone and final rapid fracture area, almost regardless of the applied strain amplitude. This phenomenon was discussed in terms of the tortuosity of crack propagation path.

Abstract: In the present study, the effect of cooling condition on hot tearing tendency and hot tearing fracture surface morphology were investigated. Results show that, the hot tear fracture surface characteristics are nearly similar under different cooling conditions. The hot tear surface exhibits two main features; the brittle region and the ductile region. The results also indicate that cooling condition has multifaceted effects on hot tearing phenomenon. Increasing cooling rate increases the thermal gradient, which raises the hot tearing tendency; concomitantly it decreases the grain size and dendrite arm spacing which increases the strength of the material. The occurrence of hot tearing phenomenon under different cooling conditions is discussed and evaluated based on the competition between these opposing factors during the solidification process.

Abstract: The tested samples by adding 1.0% nano-copper powder and Fe-base powder mixed with globe grind violently are sintered at 600, 650, 700, 750, 800, 850°C, and keeping temperature 30 minutes and 1, 2, 3, 4 hours at 600°C. The nano-copper morphology changes of impacting fracture surface are observed by scan electrical microscopy (SEM). The results showed that the nano-copper particles occur adsorption rapidly, diffusion and dissolution at Fe-base powder particle interface with increasing sintering temperature at the same keeping temperature times and extending keeping temperature times at the same sintering temperature. The nano-copper particles grow up by reunite and existing unconventional growimg up critical temperature Tc. The nano-copper particles dissolve at the nano-Fe powder surface at the lower sintering temperature, and decreasing the sintering temperature to 920°C.

Abstract: Ti-TiAl multi-layered materials have been prepared by electron beam physical vapor deposition technique. The tensile behavior of samples at room temperature and high temperature was tested, and then the deformation mechanism at different temperature was analyzed according to the fracture surface. The results show that the tensile curves hot-pressed samples have a broad step during the plastic deformation process, and the breaking strain of the sample has been increased for a wide-range. The presence of Ti layers have led to the cracks stagger along the inter-laminar interface or the layer due to which micro laminate expresses a good characteristic of delayed fracture. With the increase of temperature, the bulk modulus and yield strength of multi-layered Ti-TiAl have been increased abnormally due to the anomalous yield strengthening behavior of TiAl intermetallic.

Abstract: The present work aims to study the hydrogen embrittlement process in API 5L X60 and API 5L X80 steels. The tests were performed using two kinds of hydrogen sources to work with two conditions of hydrogen damage: environmental hydrogen embrittlement and internal hydrogen embrittlement. The mechanical behavior of API 5L X60 and API 5L X80 steels in tensile tests, with and without hydrogen, were studied. Under environmental hydrogen embrittlement conditions, the API 5L X60 steel presented a softening process observed by the decrease in yield strength and increase in its deformation. The API 5L X80 steel was more susceptible to the phenomenon due the deformation decrease of hydrogenated samples. In notched samples, both steels were susceptible to embrittlement as shown by the decrease in elongation. Under internal hydrogen embrittlement conditions, in both steels the changes in deformation were significant and can be attributed to changes in the hydrogen trapping due to the hydrogenation process used, the chemical composition and microstructure. It was observed that the fracture surface morphology of hydrogenated samples of both steels was ductile by microvoids coalescence, and that the distribution of dimples per unit area was higher in the API 5L X60 steel. It can be concluded, as reported in the literature, that the reversible hydrogen trapping observable in environmental hydrogen embrittlement is more damaging than irreversible hydrogen trapping, observable in internal hydrogen embrittlement.

Abstract: The present research is undertaken to study the influence of Li on the tensile properties of Al-15%Mg2Si metal matrix composite. The tensile test results show that adding 0.15%Li to the composite raises the UTS and elongation values, insignificantly. In the point of fracture behaviour of the composite, the addition of 0.15%Li converts the fracture behaviour from brittle, with cleavage facets, to ductile, with fine ductile dimples.