Sharif Digital Repository

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

This article describes a study on WC–10Co cemented carbides with different percent of grain growth inhibitors. Samples were prepared by the conventional powder metallurgy method, using WC and Co powder and different concentrations of VC and (Ta, Nb)C powder. All samples were processed using a hot isostatic press (HIP) and the effect of grain growth inhibitors on the microstructure and mechanical properties were investigated. Additionally, microstructure and powder particle morphology were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The specimen's microstructure proved that the addition of VC is more effective at suppressing grain growth than... 

An architectural modification method was utilized to improve fracture toughness of discontinuously reinforced aluminum (DRA) composites. Al-DRA composites having a structure similar to that of reinforced concrete were fabricated. The number of reinforcing DRA rods within Al matrix and volume fraction of SiC particles in DRA were altered to evaluate their effect on fracture behavior of these materials. It was found that architectural modification does not have any destructive influence on elastic modulus and yield strength of the composite. Moreover, the success of this method on toughness improvement strongly depends on the occurrence of debonding between Al and DRA regions upon loading  

Artificial neural networks with multilayer feed forward topology and back propagation algorithm containing two hidden layers are implemented to predict the effect of chemical composition and tensile properties on the both impact toughness and hardness of microalloyed API X70 line pipe steels. The chemical compositions in the forms of "carbon equivalent based on the International Institute of Welding equation (CEIIW)", "carbon equivalent based on the Ito-Bessyo equation (CEPcm)", "the sum of niobium, vanadium and titanium concentrations (VTiNb)", "the sum of niobium and vanadium concentrations (NbV)" and "the sum of chromium, molybdenum, nickel and copper concentrations (CrMoNiCu)", as well... 

This paper presents and discusses the effect of maximum size of coarse aggregate on fracture characteristics and brittleness of self-compacting concrete (SCC). Based on an experimental program, a series of three point bending tests were carried out on 86 notched beams, as recommended by RILEM. For all mixes, the parameters were analyzed by the work-of-fracture method (WFM) and by the size effect method (SEM) and consequently a correlation between these methods was obtained which is used to calibrate cracking numerical models. Test results showed that with increase of size of coarse aggregate, (a): fracture energies of GF in WFM and Gf in SEM increase which may be explained by the change in... 

Lamination has been shown to enhance damage tolerance of discontinuously reinforced aluminum (DRA) composites. Doing this technique, DRA layers could be laminated with ductile interlayers. In this research, two types of laminates consisting similar DRA layers and a ductile AA1050 interlayer were fabricated by means of hot roll-bonding. AA6061-5. vol% SiCp and AA6061-15. vol% SiCp composites were considered as exterior layers. Different rolling strains, was applied to control the interfacial strength which was examined by shear test. Toughness behavior of laminates was evaluated by three-point bending test in crack-divider orientation. Based on obtained results, the plastic deformation of... 

In this study, the effect of carboxyl-terminated butadiene-acrylonitrile liquid rubber on fracture toughness of glass-reinforced epoxy composites has been investigated. Fracture toughness tests were conducted in modes I, II and different mixed mode ratios. The data obtained from these tests have been analyzed by using different methods. Results indicated that interlaminar fracture toughness of composite specimens improved considerably through addition of carboxyl-terminated butadiene-acrylonitrile in modes I, II and mixed mode. Interlaminar fracture surfaces of the specimens were also characterized by field emission scanning electron microscope  

Functionally graded aluminum matrix composites (FGAMC) are new advanced materials with promising applications due to their unique characteristics in which composite nature is combined with graded structure. Different architectures of Al6061/SiCp composite laminates were fabricated by successive hot roll-bonding. For FGAMCs, two composite layers as outer strips and a layer of Al1050 as interlayer were applied. To investigate laminate toughness, the quasi-static three-point bending test was conducted in the crack divider orientation. Genetic programming as a soft computing technique was implemented to find mathematical correlations between architectural parameters and experimentally obtained... 

Good knowledge of fracture parameters and cracking behavior of self-compacting concrete (SCC) from early ages until the SCC becomes mature plays an important role in design of SCC structure and also in evaluation of durability and consequently prevention of damage. In this paper, variation of fracture parameters and corresponding ductility behavior of SCC at different ages (e.g. 3days, 7days, 28days and 90days) for SCC mixes with w/c ratios of 0.45 and 0.65 have been experimentally studied. To do so, three-point bending tests were carried out on 120 notched beams. Then, size effect method (SEM) and work of fracture method (WFM) were applied to interpret the results. The results of analyses... 

Addition of spinel (MgAl2O4) to Al2O3-ZrO2 composite inhibits alumina grain growth and produces phase boundaries that leads to formation of a ceramic matrix composite with special mechanical properties such as high temperature superplastic deformation. However, the room temperature mechanical properties of Alumina-zirconia-magnesia spinel composite (AZM) such as fracture toughness were rarely investigated by researchers. In this research the AZM nanocomposite powders were synthesized via the solution combustion method. The dense AZM composite samples were fabricated through gelcasting process. Phase analysis studies were performed on both powder and sintered samples and the effects of spinel... 

Researchers have examined different approaches to improve damage tolerance of discontinuously reinforced aluminum (DRA). In this study, three-layer DRA laminates containing two exterior layers of Al6061-15 vol.% SiCp and an interlayer of Al1050 were fabricated by hot roll bonding. Interfacial adhesion between the layers was controlled by means of rolling stain. The results of shear test revealed that, the bonding strength of laminates was influenced by number of rolling passes. Considering this effect, the role of interfacial bonding on the toughness of laminates was studied under three-point bending in the crack divider orientation. The quasi-static toughness of the laminates was greater... 

Addition of fine zirconia particles in the alumina matrix in order to produce ZTA composite is a well-known method for improving the mechanical properties of alumina ceramics such as flexural strength and fracture toughness. Increasing homogeneity and reducing alumina grain size are two key factors for achieving proper mechanical properties in this ceramic matrix composite. In this work two batches of ZTA powder precursor were prepared through mixing of alumina and zirconia by ball milling and in situ synthesis of ZTA composite via solution combustion method. The bending strength testing samples were fabricated through gel-casting process. The effects of different powder processing methods... 

Ferrite-bainite-martensite triple phase (TP) microstructures with different volume fractions of martensite were obtained by changing heat treatment time during austempering at 300 C. Room temperature impact properties of TP steels with different martensite volume fractions (VM) were determined by means of Charpy impact testing. The effects of test temperature on impact properties were also investigated for two selected microstructures containing 0 (the DP steel) and 8.5 vol.% martensite. Test results showed reduction in toughness with increasing VM in TP steels. Fracture toughness values for the DP and TP steels with 8.5 vol.% martensite were obtained from correlation between fracture... 

The paper describes an experimental research on fracture characteristics of self-compacting concrete (SCC). Three point bending tests conducted on 154 notched beams with different water to cement (w/c) ratios. The specimens were made from mixes with various w/c ratios from 0.7 to 0.35. For all mixes, common fracture parameters were determined using two different methods, the work-of-fracture method (WFM) and the size effect method (SEM). Test results showed that with decrease of w/c ratio from 0.7 to 0.35 in SCC: (a) the fracture toughness increases linearly: (b) the brittleness number is approximately doubled: (c) the effective size of the process zone cf in SEM and the characteristic... 

Damage tolerance improvement has been reported by laminating aluminum alloys and composites by researchers. Three-layer laminates comprising Al6061 outer layers and Al1050 interlayer have been roll bonded in this research. While most of the works done have focused on fracture properties of roll bonded Al laminates in crack arrester geometry, this study explores their behavior in crack divider configuration. Rolling strain is varied to control the interfacial bonding in laminates. The fracture behavior of laminates and the constituent material was examined via three-point bending and impact tests. This study presents significant improvement in damage tolerance of laminates compared to their... 

In this research, the effects of nano-sized MgO in Al2O 3-SiC composites were investigated. The overall changes in the density and mechanical properties of sintered samples (hardness, bending strength and toughness) were evaluated. After mixing, drying and uniaxial compaction of the powders, they were first heat-treated at low temperature in an electric furnace to remove any residuals. They were then heat-treated at high temperature (1700 °C) inside a graphite furnace in argon atmosphere for sintering (at normal and high pressure). The content of MgO in the Al 2O3-10 vol% SiC composite was 0, 500, 1000, and 1500 ppm. Thefracture toughness(KIC)of sintered composite with 10... 

Effect of loading rate on toughness characteristics of hybrid rubber-modified epoxy was investigated. Epoxy was modified by amine-terminated butadiene acrylonitrile (ATBN) and recycled tire. Samples were tested at various loading rates of 1-1000 mm/min. Fracture toughness measurements revealed synergistic toughening in hybrid system at low loading rates (1-10 mm/min); hybrid system exhibited higher fracture toughness value in comparison with the ATBN-modified resin with same modifier content. However, synergistic toughening was eliminated by increasing the loading rate. At higher loading rates (10-1000), the fracture toughness of hybrid system decreased gradually to the level lower than that... 

This article describes a study on WC-10Co cemented carbides with different percent of grain growth inhibitors. Samples were prepared by the conventional powder metallurgy method, using WC and Co powder and different concentrations of VC and (Ta, Nb)C powder. All samples were processed using a hot isostatic press (HIP) and the effect of grain growth inhibitors on the microstructure and mechanical properties were investigated. Additionally, microstructure and powder particle morphology were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The specimen's microstructure proved that the addition of VC is more effective at suppressing grain growth than... 

Effects of pozzolans and fibers on mechanical properties of RCC are addressed. The mechanical properties were evaluated using optimum moisture with different amounts of pozzolans, steel and polypropylene fibers. Using pozzolans, maximum increase in compressive strength was observed to occur between 28 and 90 days of age, rupture modulus was found to decrease; but toughness indices did not change considerably. The influence of steel fibers on compressive strength was often more significant than that of PP fibers; but neither steel nor PP fibers did contribute to increase in the rupture modulus independently from pozzolans. Also, the toughness indices increased when steel fibers were used  

An investigation into the mixed mode fracture of steel fiber reinforced concrete (SFRC) beams with one percent volume fraction of steel fiber is presented. A series of notched beams with different notch depths and locations are tested under three-point bending. The test results for apparent fracture toughness, crack trajectories, and fracture energy are presented. The crack paths for SFRC and plain concrete beams are compared. The apparent fracture toughness values were more scattered for SFRC than for plain concrete. The load-deflection curves were used to obtain the fracture energy. To this end, two methods were utilized for center notched beams, and the results were comparable to each...