Papers by Keyword: Fracture Toughness

Abstract: The scanning electron microscope (SEM) and optical microscope (OM) were used to study the deformation of TC18 titanium alloy microstructure at 881°C and 896°C. And the basket weave structure fracture mechanism was discussed. The results have been shown: during deformation at 881°C, the TC18 titanium alloy β grain size of about 305μm and the discontinuous grain boundary α phase along the β grain boundary were obtained. With the deformation temperature rising to 896°C, the β grain growth of 510μm and the continuous grain boundary α phase along the straight β grain boundary were obtained. The TC18 titanium alloy fracture toughness decreased from 77.8 MPa·m^1/2 to 65.4 MPa·m^1/2 as the rising of deformation temperature from 881°C to 896°C. The average β grain size is about 305μm and the discontinuous grain boundary α phase leads to the higher fracture toughness of TC18 titanium alloy forging. The fracture mode of fine β grain and discontinuous grain boundary α phase is the transgranular fracture, while the coarse β grain and continuous grain boundary α phase is the intergranular fracture.

Abstract: Hybridization of aluminium matrix composite is with a view to offset the properties deficient in one composite reinforcement. The present investigation involves a comparative study of AA6063 matrix composites with single reinforcement of Al₂O₃, SiC, graphene respectively and various hybridized proportions of the same reinforcements. Physical (density and %porosity) and mechanical (tensile strength, fracture toughness, %elongation, elastic modulus, etc.) properties of composites developed via solidification processing technique were evaluated. The porosity of all the composites falls below the maximum acceptable limit for cast metal matrix composite. Maximum values for UTS, %elongation and absorbed energy at maximum stress was obtained by hybrid composite with 4wt% Al₂O₃, SiC and 2wt% graphene, while the composite with the highest single reinforcement of graphene have the highest value for elastic modulus and fracture toughness. Numerical optimization results show that a matrix and hybrid reinforcements contents of AA6063 (91.413wt.%), SiC (3.679wt.%), Al₂O₃ (0.277wt.%), and graphene (4.632wt.%) respectively, will result in optimal values for the evaluated properties.

Abstract: In order to analyze the effect of insoluble Fe-rich phases on the fracture toughness of high-strength Al-Zn-Mg-Cu alloys, plane-strain fracture toughness test, scanning electron microscopy, finite element analysis and quantitative modeling were used to investigate the fracture toughness of three commercial high-strength Al-Zn-Mg-Cu alloys. The results show that the fracture mode of the three experimental alloys is strongly related to the Fe-rich phases, which are prone to initiate intergranular fracture of the experimental alloys. Finite element analysis proved that the larger the shape factor of the Fe-rich phases, the more sensitive it is to external stress and more prone to secondary cracking, which is consistent with the fracture morphology observation. Quantitative analysis shows that the size, volume fraction and morphology of the Fe-rich phases have a greater influence on the fracture toughness of the high-strength Al-Zn-Mg-Cu alloy. The fracture toughness of the alloy will be improved when the shape factor of the Fe-rich phases is small and close to circular and the volume fraction of the Fe-rich phases is small. The fracture toughness value of the Al-Zn-Mg-Cu alloys can be better predicted when the deviation of the shape and distribution of the Fe-rich phases is considered.

Abstract: The deformation parameters of aluminum alloys during thermal deformation have a significant impact on the alloy's properties. The industrial free forging of the Al-Zn-Mg-Cu alloy was carried out at deformation rates of 10 mm/s and 20 mm/s, respectively, at a deformation temperature of 430°C and a deformation degree of 60% in this study. The microstructure was determined using EBSD, and the mechanical characteristics were examined. According to EBSD observations, the recrystallization fraction of the alloy is nearly identical under both deformation rates; however, the average grain size of the alloy with a deformation rate of 10 mm/s is 10.8 μm larger than that of the alloy with a deformation rate of 20 mm/s. As the deformation rate increased from 10 mm/s to 20 mm/s, the alloy's yield strength and fracture toughness increased. The resistance to fatigue crack propagation, on the other hand, displayed the reverse pattern. That is, the alloy with a 20 mm/s deformation rate had a higher FCP rate than the alloy with a 10 mm/s deformation rate. In summary, the influence of deformation rate on the microstructure and mechanical properties of a high alloy Al-Zn-Mg-Cu alloy was investigated.

Abstract: The purpose of the study was to predict the mechanical and toughness properties of Ni-modified alloy steels by adding 1.55%, 1.75%, and 1.95% of Ni-content to the existing Cr-Mo alloy steel of transmission gear material. Typically transmission gears have been working under severe working situations of loads and rotations. Due to these situations, the properties and qualities of gear materials are highly affected consequently, fatigue failure is instigated. So, improving the mechanical and toughness properties of the existing gear material is very vital and compulsory since these properties have a direct impact on gear fatigue failure. Investigations have been done on determining the mechanical and toughness properties of the Ni-modified Cr-Mo alloy steels, through ANN modeling prediction by associating the complex relation of input (chemical composition, tempering temperature) and output parameters (mechanical and toughness properties), and verified by experimental test approaches. Explored these materials property with ANN modeling and experimental test show that the more Ni-content added to the Cr-Mo alloy steel, the higher the ultimate and yield strength can achieve at every instant of tempering temperature. Likewise, fracture toughness, impact toughness, and percent of retained austenite of these materials were also investigated thoroughly as tempering temperature varies. Thus, a 1.55 % Ni-modified Cr-Mo alloy steel has a higher value of both impact toughness and fracture toughness compared with other Ni-modified alloy steels. Similarly, surface hardness was slightly decreased as the amount of Ni-content added increased at each instant of tempering temperature. Lastly, based on both predicted and experimental results, 1.55 % of Ni-modified Cr-Mo alloy steel showed a better combination of mechanical and toughness properties. Keywords: ANN modeling; Yield strength; Ni-modified; Tempering temperature; Fracture toughness; Surface hardness

Abstract: The usage of joints between composites and metals has gained significant importance in the recent years and it is the need of the industry that new and improved methods of joining the composites and metals be introduced. In this study, the joint between the carbon fibre reinforced plastic composite and the aluminium metal has been improved with the help of the multi walled carbon nanotubes to reinforce the epoxy adhesive. Knowledge of the interlaminar behaviour regarding the composites is very important as this is the most common type of failure faced by them. Furthermore, the best method for the uniform and fine dispersion of carbon nanotubes in the epoxy is also discussed. In this research, two different types of composite metal joint samples were tested using the mode 1 fracture toughness test to study the interlaminar behaviour of the reinforced epoxy and the double cantilever beam specimen was used to carry out the tests according to the ASTM standards.

Abstract: The article is devoted to tribological studies of a ceramic composite with a zirconia-based die in order to replace carbide wire drawing dies with ceramic. Sliding friction was done according to the scheme finger-disk without lubrication and with lubrication. The wear rate and friction coefficients were determined, on the basis of which it is proposed to produce portage dies-blanks from zirconium ceramics. The influence of sintering temperature on the mechanical properties of ceramics, especially cracking resistance, was studied. The optimum sintering temperature was determined by the criterion of fracture toughness. The formation of defects after the final firing was investigated. It was found that sintering at a temperature of 1600 ° C is more promising. An trial batch of zirconium ceramic dies showed positive results in the process of drawing copper wire in industrial situations.

Abstract: The aim of the current study is to design multiaxial forging (MAF) schedules in order to achieve submicron-grained (<1μm) structure in a microalloyed (MA) steel as well as an interstitial-free (IF) steel, which could impart a good combination of yield strength and tensile ductility. At the same time, an effort has been made to evaluate the fracture toughness characteristics by conducting 3-point bend tests and computing the K_Q, K_ee and J-integral values of ultrafine grained (UFG) samples and correlating them with the microstructure, besides evaluating the other mechanical properties. Fatigue strength in the high cycle fatigue (HCF) regime were also investigated and fracture mechanisms analyzed and comparison established between differently processed samples. The microstructural analysis was performed using transmission electron microscopy (TEM) and Electron backscatter diffraction (EBSD) and results corroborated with the mechanical properties. Superior combinations of yield strength (YS), ductility (% El.), fracture toughness (K_ee) and high cycle fatigue strength (σ_f) were obtained under certain conditions, i.e., i) MA steel: intercritical (α+γ) phase regime (~A_r1) controlled and 15-cycle multiaxially forged (MAFed) (YS=1027MPa, %El.=8.3%, σ_f=355MPa and K_ee=90MPa√m), and ii) IF steel: ferritic region (<A_r1) controlled 18-cycle MAFed (YS=881MPa, %El.=11.2%, σ_f=255MPa and K_ee=97MPa√m). In the case of MA steel, an enhancement of the fatigue and fracture toughness properties can be ascertained following the formation of uniformly distributed nanosized fragmented cementite (Fe₃C) particles (~35nm size) present in the submicron sized (average ~280nm size) ferritic microstructure. In contrast, in the case of IF steel, this is ascribed to the development of submicron sized ferrite grains (average ~320nm) along with a high density of dislocation substructures. These fine dislocation cells/substructures along with the nanosized Fe₃C particles could effectively block the initiation and propagation of cracks and thereby enhance the fatigue endurance and fracture toughness of the steel. Superior fracture toughness along with high mechanical properties in submicron-grained condition render the two steels highly useful for high-strength structural applications.

Abstract: The microstructure and fracture surfaces were investigated for five Fe₃Al – based iron aluminides doped by different alloying elements (Nb, Zr + C, Cr) or without addition. Generally, iron aluminides are considered as brittle material at room temperature, therefore the type and distribution of secondary phases affect the fracture behaviour. The influence of present secondary phase particles on impact toughness at room temperature was evaluated in comparison to binary alloy. The type and the volume fraction of particles affect the value of impact toughness significantly – these values decrease with increasing volume fraction of precipitates. On the other hand, the solid solution strengthening improves impact toughness.

Abstract: This paper deals with the determination of parameters of the interlaminar failure of the CFRP composite laminate in mode I using numerical simulation with cohesive elements. Knowledge of these parameters is crucial to enable prediction of interlaminar strength of laminates using numerical simulations based on the finite element method with cohesive elements. There are several standardized experimental measurements for determining mode I parameters but not all that are needed for numerical simulations. However, the determination of these parameters and their evolution during cohesive failure is very problematic even if the experimental data is available. This paper deals with the design of a methodology for how to determine these parameters using the fitting process of experimental measurement and numerical simulation. The experimental measurements were done on double cantilever beam specimens according to ASTM standards. The numerical simulations were performed in the Siemens Simcenter software with NX Nastran solver. The numerical model with the obtained parameters shows very good agreement with the experimental measurements. compared to the average experimental values and the analytical calculation, the difference of fracture toughness is up to 1.6 %