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Showing 30 results for Crack

Barzegar Alamdarit B., Ashrafi Zadeh S.n., Ashrafi Zadeh F.,
Volume 1, Issue 2 (6-2004)

In the current research, the optimum conditions for the electrolytic deposition of TiO2 coatings on titanium pieces were experimentally investigated. Flat pieces of commercially available titanium with dimensions of 50 x20 x3 mm were used as the anode and cathode electrodes. The coatings were applied on the cathode in an electrolyte solution essentially from water and methanol, containing different amounts of TiCI4, and H202. Coatings of sufficient thickness and adequate adhesion to the substrate were obtained at the optimum conditions of theELD process. The latter conditions were electrode gap distance of 3 cm, TiCl4 concentration of 0.005M, H202 concentration of 0.1 M, current density of 35 mA/cm2, methanol/water volume ratio of 9, and pH of the electrolyte in the vicinity of 1.40. Results of XRD analysis revealed the presence of anatase crystals of titanium oxide in the coated layers, where the deposited coating was treated at some temperatures in the range of 400 to 600°C for a period of at least 2 hours. Scanning electron microscopy (SEM) pictures also confirmed the formation of a uniform coating layer with cracked suiface area. At the optimum conditions of the process coatings with thicknesses of up to 10 flm were easily obtained through the application of one to three deposited layers.
Saghafian Larijani H., Rainforth W. M.,
Volume 1, Issue 3 (9-2004)

An AI-7wt%Si-5vol%TiCp was worn against a cast iron disc in a tri-pin-on-disc machine, under dry sliding conditions at the sliding speed of 0.24 m/s and applied loads of 6, 20 and 40 N/pin. Stress-strain (`3-^9) curves were constructed by measuring the microhardness and the equivalent strain gradients in near surface regions on the cross-sectional surface prepared parallel to sliding direction.It was shown that, both the magnitude of plastic strains and the depth of plastic deformed zones increased with the applied load. The material exhibited considerable work softening in addition to work hardening at the highest applied load. The softened layer placed just beneath the mechanical mixed layer (MML), was mostly covered with the fine fractured eutectic Si and TiC fragments most of which were associated with microcracks at Al/Si and Al/TiC interfaces. The results were discussed in terms of some of the current work hardening models.
Mehryab A., Arabi H., Tamizifar M., Seyedein S.h., Razazi M.a.,
Volume 2, Issue 1 (3-2005)

In this research, the mechanism of joining three sheets of metals, i.e. brass-steel-brass, by cold roll welding process has been studied. For this purpose, the two surfaces of steel sheets were roughened with stainless steel wire brush by different amounts, then the brass sheets were put on both sides of the steel sheets, before they were subjected to cold roll process. During rolling, peaks of the asperities on the surfaces of the steel sheet were pressurized, i.e. deformed, much more than that of trough. Hence, more hardening due to formation of higher dislocation density in the peaks regions were detected in comparison to the trough regions. Therefore, due to the differences in the amounts of work hardening occurred during cold rolling in the peaks & trough of the scratches and also due to the nature of the rough surfaces of the steel sheets, which causes the smooth surface of soft brass sheets laied over the rough surface of the steel sheet to be shappend according to the profile of the steel sheet scratches during cold rolling, mechanical locking occurred at the interface of brass & steel sheets. In addition, while the extrusion of brass took place through cracks within the surface of hardend peaks and metal bonding occurred on the contact points of the brass sheet & the vergin steel. Therefore, it seems two mechanisms were in operation is making a suitable joining between the sheets. One was a locking mechanism due to the roughness of the steel sheets & the other was bonding mechanism due to the bonding between the peak points of the scratches &soft brass surface. The strength of the bonded points in the interface were later increased by annealing the composite, so that by annealing the samples within the 500-900°C range for aperiod of 1 1/2 hr the interface strength increase substantially. The results of peeling test indicated that the interface strength of the samples annealed at 700°C or more increased so much that the brass sheet toms during peeling & the fracture did not pass through the interface.
Saremi M., Nouri Delavar A., Kazemi M.,
Volume 2, Issue 4 (12-2005)

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.
Hadian A.m., Abu Fanas S.h.,
Volume 2, Issue 4 (12-2005)

Enhancing the properties of dental resin composites is of interest to researchers. The objective of the present investigation was to improve the strength and fracture toughness of dental composites via addition of silicon carbide whiskers and substitution of commonly used filler materials with stabilized zirconia ceramic powder. It was also intended to study the effect of powder- to- whisker ratio on mechanical properties of the resultant composites. The flexural strength and fracture toughness of composite samples with different whiskers loadings were measured. It was found that addition of whiskers to the composites enhances the mechanical properties of the composites. The strength and fracture toughness increased by increasing the amount of whiskers. The flexural strength of a composite having 60wt% whisker and 10wt% zirconia powder was about 210 MPa while that of the composite having only 60wt% ceramic powder was about 110 MPa. The microstructural examinations revealed that reinforcing mechanism was whiskers pull-out as well as crack deflection.
Haddad Sabzevar M., Fredriksson H.,
Volume 3, Issue 1 (6-2006)

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.
G. H. Akbari, M. A. Sheikhi,
Volume 4, Issue 1 (6-2007)

Abstract: Ball mills are used in the last stage of ore processing for grinding raw materials. Forged 70Cr2 alloy steel and Austempered Ductile Iron (ADI) balls are materials from which grinding balls are made for Sarcheshmeh Copper Plant (SCP) ball mills. In the present study wear and impact properties of these two kinds of balls have been investigated. Some balls randomly were selected as samples. They were cut to investigate the cross section under optical and scanning electron microscopes. The microstructure of the sample balls was studied and quantitative measurements of microstructural features were performed. The hardness of different parts of cross sections of balls was measured. The wear resistance of the balls was measured by Pin on Disc method. Repeated dropt test was employed to evaluate impact resistance of the balls. The microstructure of ADI balls consisted of bianitic matrix with graphite nodules and some retained austenite and martensite. Micro cracks and porosities in the cast structure were frequently observed. In the case of forged steel balls the microstructure composed of tempered martensite in outer area and bianitic structure with some tempered martensite in central areas. The wear and impact resistance of forged steel balls were markedly higher than those of ADI balls. The difference was consistent with the differences between the microstructures of the two kinds of balls. Cast structure with microcracks and shrinkage porosities in ADI balls gives rise to lower impact resistance.
H. Ghasemi, M. A. Faghihi Sani, Z. Riazi,
Volume 4, Issue 3 (12-2007)

Abstract: The effect of phase development on peel strength of alumina-copper metalized joint has been investigated. The alumina-copper joint was prepared in three stages. The alumina substrate was, first, metalized at 1500°C in H2-furnace by a new formulation. In the second step, a nickel layer was electroplated on the metalized layer with approximately 10µm thickness. Finally, copper strips were bonded to metalized alumina with Ag-Cu (72-28) filler metal. The peel strength of the joint was 9.5±0.5 Kg/cm which shows approximately 30% increase in comparison to previous works. By study of fracture surface and crack propagation path, it has been concluded that this increase is due to the formation of more spinel phase.
A. Hassani, R. Ravaee,
Volume 5, Issue 2 (6-2008)

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.
William L. Headrick,, Alireza Rezaie, William G. Fahrenholtz,
Volume 5, Issue 2 (6-2008)

gasification (BBLG). One particularly harsh application is linings for gasifiers used in the treatment of black liquor (BL). Black liquor is a water solution of the non-cellulose portion of the wood (mainly lignin) and the spent pulping chemicals (Na2CO3, K2CO3, and Na2S). Development of new refractory materials for the black liquor gasification (BLG) application is a critical issue for implementation of this technology. FactSage® thermodynamic software was used to analyze the phases present in BL smelt and to predict the interaction of BL smelt with different refractory compounds. The modeling included prediction of the phases formed under the operating conditions of high temperature black liquor gasification (BLG) process. At the operating temperature of the BLG, FactSage® predicted that the water would evaporate from the BL and that the organic portion of BL would combust, leaving a black liquor smelt composed of sodium carbonate (70-75%), potassium carbonate (2-5%), and sodium sulfide (20-25%). Exposure of aluminosilicates to this smelt leads to significant corrosion due to formation of expansive phases with subsequent cracking and spalling. Oxides (ZrO2, CeO2, La2O3, Y2O3, Li2O, MgO and CaO) were determined to be resistant to black liquor smelt but non-oxides (SiC and Si3N4) would oxidize and dissolve in the smelt. The other candidates such as MgAl2O4 and BaAl2O4 were resistant to sodium carbonate but not to potassium carbonate. LiAlO2 was stable with both sodium carbonate and potassium carbonate. Candidate materials selected on the basis of the thermodynamic calculations are being tested by sessile drop test for corrosion resistance to molten black liquor smelt. Sessile drop testing has confirmed the thermodynamic predictions for Al2O3, CeO2, MgO and CaO. Sessile drop testing showed that the thermodynamic predictions were incorrect for ZrO2.
M. Divandari,, H. Arabi, H. Ghasemi Mianaei,
Volume 5, Issue 3 (9-2008)

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.
M. Ghassemi Kakroudi,
Volume 5, Issue 4 (12-2008)

Abstract: Refractory materials containing cordierite (2MgO.2Al2O3.5SiO2) and mullite (3Al2O3.2SiO2) are used as support in furnaces, because of their low thermal expansion properties which confer them a very good ability to thermal shock resistance. Composed of two phases presenting very different CTE (1.5–3×10-6 for cordierite and 4–6×10-6 K-1 for mullite), these materials can develop damage during thermal cycling due to internal stresses. The resulting network of microcracks is well known to improved thermal shock resistance of materials, since it usually involves a significant decrease in their elastic properties. This paper is devoted to the characterisation of the damage generated by this CTE mismatch, thanks to the application of a specific ultrasonic device at high temperature.
Arash Yazdani, Mansour Soltanieh, Hossein Aghajani,
Volume 6, Issue 4 (12-2009)

Abstract: In this research plasma nitriding of pure aluminium and effect of iron elemental alloy on the formation and growth of aluminium nitride was investigated. Also corrosion properties of formed AlN were investigated. After preparation, the samples were plasma nitrided at 550oC, for 6, 9 and 12 h and a gas mixture of 25%H2-75%N2. The microstructure and phases analysis were investigated using scanning electron microscopy and X-ray diffraction analysis. Moreover corrosion resistance of samples was investigated using polarization techniques. The results showed that only a compound layer was formed on the surface of samples and no diffusion zone was detected. Dominant phase in compound layer was AlN. Scanning electron microscopy results showed that nitride layer has particulate structure. These nitrided particles have grown columnar and perpendicular to the surface. It was also observed that the existence of iron in the samples increases the nitrogen diffusion, thus growth rate of iron containing nitrides are higher than the others. Corrosion tests results showed that formation of an aluminium nitride layer on the surface of aluminium decreases the corrosion resistance of aluminium significantly. This is due to elimination of surface oxide layer and propagation of cracks in the formed nitride layer
R. Khoshhal, M. Soltanieh, M. Mirjalili,
Volume 7, Issue 1 (3-2010)


titanium sheets in pure molten aluminum at 750

and X-Ray Diffraction Analysis results, TiAl

intermetallic layer thickness increases slowly at primary stages. After that an enhanced growth rate occurs due to layer

cracking and disruption. Presumably, reaction starts with solving titanium into the molten aluminum causing in

titanium super saturation and TiAl

intermetallic layer which consequently leads to TiAl

energy of intermetallic layer formation and growth was developed by measuring titanium thickness decreases.

In this work, kinetics of intermetallic compounds formation in Al-Ti system was studied by immersingoC, 850 oC and 950 oC. According to Scanning Electron Microscopy3 is the only phase can form at the interface. Observations revealed that3 formation. At this stage, growth may be controlled by aluminum diffusion through3 formation at the interface of Ti-TiAl3. Furthermore, activation

Z. Ghaferi, K. Raeissi, M. A. Golozar,, A. Saatchi, S. Kabi,
Volume 7, Issue 4 (10-2010)


current densities. Electrochemical impedance spectroscopy (EIS) results showed that the codeposition mechanism of

tungsten in Ni-W deposition is the reduction of tungsten oxide which changed to the reduction of tungsten-containing

ion complexes at higher current densities. In Co-W electrodeposition, the tungsten codeposition takes place via

reduction of tungsten oxide, although, the role of tungsten-containing complexes at higher current densities cannot be

ruled out. The surface morphology of Ni-W coatings was crack-free and was strongly dependent on deposition current

density. In addition, higher grain size and lower tungsten content were obtained by increasing the current density. In

Co-W coatings, no obvious variation in surface morphology was observed except for the fine cracks appeared at

higher current densities. In this system the grain size remained almost constant with increasing current density. The

microhardness values of Ni-W and Co-W coatings decreased due to the increase in the grain size and/or decrease in

tungsten content.

Ni-W and Co-W alloy nanocrystalline coatings were electrodeposited on copper substrate at different

Y. Fouad,
Volume 7, Issue 4 (10-2010)

Abstract: Rotating bending fatigue tests have been performed using smooth specimens of a rolled AZ31 magnesium alloy in laboratory air at ambient temperature. Fatigue strength and characteristic was evaluated and fracture mechanism was discussed on the basis fracture surface analysis. Electrical polishing (EP) as well as deep rolling (ball burnishing (BB)) U-notched specimens were performed on two groups of samples, to evaluate optimum conditions for fatigue life. The microstructure and tensile properties of roll cast (RC) Mg- 3% Al- 1% Zn (AZ31) was investigated. The fatigue strength of 107 cycles around 100 MPa for deep rolling while it was around 40 MPa for Electrical polishing. It was very important to understand the effect of (ball burnishing (BB)) conditions on the hardness of the surface through to the core. The two procedures improved the fatigue performance, but better improve in results were found in ball burnishing. The growth of small cracks initiated at the surface coincided with the FCP characteristic after allowing for crack closure for large cracks, but the operative fracture mechanisms were different between small and large cracks. At the subsurface crack initiation site, smooth facets were always present regardless of applied stress level.
A. Allahverdi, E. Najafi Kani, M. Fazlinejhad,
Volume 8, Issue 4 (12-2011)

Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.
Dr Mohammad Reza Sarmasti Emami,
Volume 9, Issue 3 (9-2012)

This paper presents an experimental and theoretical investigation of the causes of corrosion of stack in a cement plant. In this paper, information related to metallic stack failures are given in the form of a case study in Neka Cement Plant, Mazandaran, Iran. Heavy corrosion attacks were observed on the samples of stack. The failure can be caused by one or more modes such as overheating, stress corrosion cracking (SCC), hydrogen embrittlement, creep, flame impingement, sulfide attack, weld attack, dew point corrosion, etc. Theoretical calculations and experimental observations revealed that, the corrosion had taken place due to the condensation of acidic flue gases in the interior of stack. Also, the chemical analysis of the corrosion deposits and condensates confirmed the presence of highly acidic environment consisting of mostly sulfate ions.
M. Alzamani, A. Shokuhfar, E. Eghdam, S. Mastal,
Volume 10, Issue 1 (3-2013)

Abstract:In the present research, SiO2–TiO2 nanostructure films were successfully prepared on windshields using the sol–gel technique for photocatalytic applications. To prevent the thermal diffusion of the sodium ions from the glass to TiO2 films, the SiO2 layer was pre-coated on the glass by the sol–gel method. The substrates were dipped in the sol and withdrawn with the speed of 6cm/min-1 to make a gel coating film. The coated films were dried for 2 days at 27 °C to allow slow solvent evaporation and condensation reactions due to rapid sol–gel reaction of Titania precursor. Then, the films were annealed at 100 °C for 30min and at the final temperature (500, 700 °C) for 30 min continuously. The structure and surface morphology properties, which are as a function of annealing temperature, have been studied by SEM FE-SEM and XRD. The FE-SEM surface morphology results indicate that the particle size increases from 19 to 42 nm by increasing the annealing temperature from 500 °C to 700 °C. Likewise, XRD illustrate the crystal anatase and rutile as main phases for TiO2-SiO2 films annealed at 500 °C and 700 °C respectively. This procedure resulted in transparent, crack-free SiO2–TiO2 films.
F. Gulshan, Q. Ahsan,
Volume 10, Issue 2 (6-2013)

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.

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