Showing 8 results for Crack
Saremi M., Nouri Delavar A., Kazemi M.,
Volume 2, Issue 4 (12-2005)
Abstract
An investigation of the electrochemical noise generation during Stress Corrosion Cracking (SCC) of 70-30 Brass in Mattson's solution was conducted. The fluctuations of potential and current were monitored. The relationship between potential and current fluctuations has been evaluated in time domain and the obtained data has been analyzed in the frequency domain using Power Spectral Density (PSD). It is shown that 70-30 Brass has characteristic noise behavior during SCC that is step-by-step change in current and potential up to the final stage of fracture, and this may be used for SCC monitoring.
Haddad Sabzevar M., Fredriksson H.,
Volume 3, Issue 1 (6-2006)
Abstract
The hot cracking susceptibility can be determined by establishing the transition temperature between brittle and ductile fracture at high temperature tensile testing of in situ solidified samples. High temperature tensile properties were determined for commercial cathodic pure Cu and Cu- 30%Zn alloy. The transition temperatures for pure Cu and Cu-30%Zn were evaluated from ultimate tensile stress, true strain and area reduction at different testing temperatures. The results show that hot cracking in pure Cu also occurred below and near to its melting temperature. It can be proposed that in this case excess vacancies and vacancy diffusion and condensation are the dominating mechanisms for hot crack formation. The transition temperature for Cu- 30%Zn was much lower than its solidus temperature and this alloy has more susceptibility to hot cracking as compared to pure Cu. The effect of two different cooling rates (15 °C/min and 60 °C/min) on the transition temperature was investigated. The results show that by increasing cooling rate, the transition temperature will increase. The morphology of fracture surfaces for both ductile and brittle modes were evaluated by SEM Two different morphologies, i.e. interdendiritic and intergranual fracture, was found.
A. Hassani, R. Ravaee,
Volume 5, Issue 2 (6-2008)
Abstract
Abstract: To ensure the rail transportations safety, evaluation of fatigue behavior of the rail steel
is necessary. High cycle fatigue behaviour of a rail steel was the subject of investigation in this
research using fracture mechanics. Finite element method (FEM) was used for analyzing the
distribution of the stresses on the rail, exerted by the external load. FEM analysis showed that the
maximum longitudinal stresses occurred on the railhead. To find out about the relation of crack
growth with its critical size, and to estimate its lifetime, the behaviour of transverse cracks to rail
direction was studied using damage tolerance concept. It revealed that transverse crack growth
initially occurred slowly, but it accelerated once the crack size became larger. Residual service
life was calculated for defective segments of the rails. In addition, allowable crack size for
different non-destructive testing intervals was determined the allowable crack size decreased as
the NDT intervals increased.
M. Divandari,, H. Arabi, H. Ghasemi Mianaei,
Volume 5, Issue 3 (9-2008)
Abstract
Abstract: Thermal fatigue is a stochastic process often showing considerable scatter even in
controlled environments. Due to complexity of thermal fatigue, there is no a complete analytical
solution for predicting the effect of this property on the life of various components, subjected to
severe thermal fluctuations. Among these components, one can mention car cylinder, cylinder head
and piston which bear damages due to thermal fatigue. All these components are usually produced
by casting techniques. In order to comprehend and compare the thermal fatigue resistance of cast
Al alloys 356 and 413, this research was designed and performed. For this purpose, several
samples in the form of disc were cast from the two alloys in sand mould. The microstructures of the
cast samples were studied by light microscopy in order to choose the samples with the least
amounts of defects for thermal fatigue tests. The results of thermal fatigue tests showed that the
nucleation of microcracks in Al-356 alloy occurred at shorter time relative to those occurred in Al-
413 alloy under the same test conditions. In addition, the density of micro-cracks in Al-356 alloy
was more than that of Al-413 alloy. The results of fractography on 356 alloy indicated that the
cracks were generally nucleated from inter-dendritic shrinkage porosities and occasionally from
the interface of silicon particles with the matrix. The growth of these micro cracks was along the
dendrite arms. Fractography of 413 alloy fracture surfaces showed that nucleation of microcracks
was often associated with silicon particles.
F. Gulshan, Q. Ahsan,
Volume 10, Issue 2 (6-2013)
Abstract
The probable reasons for evolution of weld porosity and solidification cracking and the structure- property relationship in aluminium welds were investigated. Aluminium plates (1xxx series) were welded by Tungsten Inert Gas (TIG) welding process, 5356 filler metal was used and heat input was controlled by varying welding current (145A, 175A and 195A). The welded samples were examined under optical and scanning electron microscopes and mechanical tests were performed to determine tensile and impact strengths. Secondary phase, identified as globules of Mg2Al3 precipitates, was found to be formed. Solidification cracking appeared in the heat affected zone (HAZ) and porosities were found at the weld portion. The tendency for the formation of solidification cracking and weld porosities decreased with increased welding current.
A. Ait Yala, N. Demouche, S. Beddek, K. Hamid,
Volume 15, Issue 4 (12-2018)
Abstract
Repairing a crack in a structure consists in reducing crack’s tips stresses by transferring loads trough a bridge made of the composite patch and the adhesive. This operation is impacted by four factors: shear modulus of the adhesive, the composite patch’s Young module and the thicknesses of these two materials. The design of experiments method allowed us to determine, the weight of each of the four factors and their interactions as well their best combination to obtain an efficient and lasting repair. The constraints relative to the stiffness ratio and the shear strain were taken into consideration in order to determine the best configuration that allowed the minimization of K.
Jonas Fernando Macedo, Igor Alexandre Fioravante, Roberto Zenhei Nakazato, Heloisa Andréa Acciari, Eduardo Norberto Codaro,
Volume 18, Issue 1 (3-2021)
Abstract
As we all know, corrosion of pipelines by hydrogen sulfide is the most worrying factor in the production and transport of oil and gas. In this work the corrosion behavior of API 5L X70MS and X70MO low carbon steels in hydrogen sulfide environments was investigated. Hydrogen induced cracking and sulfide stress cracking tests were carried out according to NACE TM0177 standard. After testing, blisters and cracks were observed only in X70MO steel, probably due to its lower grain refinement and banded microstructure. Internal cracks seem to be initiated in elongated MnS inclusions. Corrosion process was studied by obtaining potentiodynamic polarization curves, which were registered after open circuit potential measurements, at room temperature. Both steels showed general corrosion in NACE 177A solutions, but the corrosion rate values in H2S-saturated solution were about an order of magnitude higher than those ones in deaerated solution. Hydrogen permeation w::as char::acterized in accordance with ASTM G148 standard. In deaerated H2SO4 solution, permeation measurements were similar for both steels. In H2S-saturated solution, X70 MO exhibited higher hydrogen oxidation current values than X70 MS. H2S seems to promote the reduction of protons and increase the concentration of hydrogen atoms in the solution/steel interface, favoring the diffusion process. As X70MO has a coarse microstructure, it offers more pathways for hydrogen diffusion.
Zahra Rajabimashhadi, Rahim Naghizadeh,
Volume 19, Issue 1 (3-2022)
Abstract
ꞵ-tricalcium phosphate (ꞵ-TCP) and anorthite are the main crystalline components in bone china bodies. The difference in their thermal expansion coefficients causes a decrease in the thermal shock resistance of the body. In this study, anorthite was replaced with bone ash at the bone china body, and the effect of this new composition on different properties of bone china, after curing at 1260 °C for 3 hours, was investigated. The results showed that the physical and mechanical properties of the sample containing 50 wt% anorthite compared to the typical bone china improved and only 8.7% of the whiteness index diminished. Also the microstructure of samples containing Anorthite were observed without thermal crack and almost uniform distribution of Anorthite and quartz crystals in the heterogeneous glass matrix.
