Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
Not a member yet
2800 research outputs found
Sort by
Optimization of Vanadium Content for Achieving Higher Wear Resistance and Hardness in High Cr-V White Cast Irons for Ball Tube Mill Liner Application
Get PDFThe liner materials, being used, at present from high Cr cast iron grades in coal fired tube mills are less promising due to lower combination of abrasion wear resistance, hardness and impact toughness properties, thus giving life of only 25,000 to 35,000 hours. In this study, focus was given to develop a high Cr-V cast iron of high abrasion wear resistance with higher hardness and impact strength for ball tube mill liner application. The developed liner possesses high abrasive wear resistance and impact resistance simultaneously for having life of 40,000 to 50,000 hours. This grade was made using induction melting and sand casting method. The casting was heat treated in two stages to achieve higher abrasion wear resistance and mechanical properties. Various tests like chemical analysis, abrasion wear, hardness and impact tests were conducted on the above developed material. Abrasion wear test results show a low wear loss value (2.7 to 4.4 mg/min). Hardness and impact tests show a high combination of hardness (57 to 64 HRC) and impact strength (44 to 57 J/cm2). Prototype tube mill liners were manufactured and tested in a tube mill at 250MW site. Results obtained from site testing are also discussed in this study
Limit load based evaluation of plastic η factor for C(T) specimen with a mismatched weld
Get PDFPlastic η factor is adopted to account crack tip plasticity while evaluating the fracture toughness of the materials as per ASTM E1820. It is valid only for homogeneous materials. The plastic η factor for compact tension geometry (CT) with type 316LN stainless steel weld has been evaluated based on elastic-plastic FE analysis. The incremental elastic-plastic material model with various values for strength mismatch level (M), from 1.2 to 2.2 has been considered for the weld. The weld width (h) parallel to the crack plane is varied from 4 mm to 16 mm. The η values thus obtained are analyzed and the inferences are discussed
Experimental characterization of fiber-reinforced cementitious mortar under tension
Get PDFThis work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poisson’s coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strength is proposed, for both design and numerical modelling purposes
Fatigue reliability assessment of small sample excavator working devices based on Bootstrap method
Get PDFTo evaluate the fatigue reliability of the excavator working device, the fatigue tests of 2 sets of moving arm and bucket rod of medium-sized excavators with self-weight of 26000 kg were carried out. The virtual augmented sample method (VASM) combined with Bootstrap method was used to analyze the reliability of the excavator working device under extreme small samples, and the interval and point estimations of life parameters were obtained. Based on the lognormal distribution of the excavator working device, the reliability evaluation model of the excavator working device was esTablelished, and reliability indexes, such as reliability function, failure distribution function, inefficiency function, reliable life and so on, were obtained. And the results of fatigue safety life under different confidence and reliability were calculated. The evaluation results show that the average failure time of the excavator working device is 5885 hours under the confidence of 75%, which provides an important reference for the design, the safety inspection and maintenance decision of the excavator working device
Experimental characterisation of fatigue crack growth based on the CTOD measured from crack tip displacement fields using DIC
Get PDFThe current work presents an experimental study on the use of the crack tip opening displacement (CTOD) to evaluate its ability to characterise fatigue crack growth. A methodology is developed to measure and to analyse the CTOD from experimental data. The vertical displacements obtained by implementing digital image correlation (DIC) on growing fatigue cracks are used to measure the CTOD. Two fatigue tests at stress ratios of 0.1 and 0.6 were conducted on compact tension (CT) specimens manufactured from a 1 mm thick sheet of commercially pure titanium. A sensitivity analysis to explore the effect of the position selected behind the crack tip for the CTOD measurement was performed. The analysis of a full loading cycle allowed identifying the elastic and plastic components of the CTOD. The plastic CTOD was found to be directly related to the nonlinear zone (i.e., plastic deformation) generated at the crack tip during fatigue propagation. Moreover, a linear relationship between da/dN and ΔCTODp independent of the stress ratio was found. Results show that the CTOD can be used as a viable alternative to the stress intensity factor range (ΔK) in characterising fatigue crack propagation since the parameter considers the fatigue threshold and crack shielding in an intrinsic way
Numerical simulation of frozen wall formation in water-saturated rock mass by solving the Darcy-Stefan problem
Get PDFArtificial ground freezing (AGF) is a common technology of shaft sinking through water-bearing strata. The AGF technique is used to create a frozen wall preventing shaft flooding. An additional factor that makes shaft sinking more complicated is associated with external groundwater flows occurred due to hydrostatic pressure gradients. In this paper, we study the influence of groundwater seepage on the frozen wall formation in fluid-saturated rock mass in the framework of the two-dimensional two-phase Darcy-Stefan problem. The results of numerical simulation of the thermal and hydraulic properties of the sandstone layer at the site of Petrikov Mining and Processing Plant are presented. It has been found that the external groundwater flow has a significant effect on the growth of a frozen wall in the case when the groundwater velocity magnitude is greater than or equal to 50 mm/day. This critical seepage velocity strongly depends on how quickly the water content and rock mass permeability decrease with decreasing temperature, or on the parameters of the rock mass freezing characteristic curve and permeability versus temperature curve. The proper setting of these parameters is a sine qua non for creating adequate mathematical models of heat and mass processes in the artificially frozen water-saturated rock mass
Investigation of Failure Mechanism of Al2O3 Specimens Subjected to Three-Point Bending Test
Get PDFExperimental loading and FEM simulation-based approach at macroscale are utilized to investigate the failure mechanisms of Al2O3 ceramics. Experimental characterization of microstructure is carried out using SEM. Recently the microscale models of representative volume of porous alumina ceramics were built on the basis of grain and pore distribution patterns and subjected to uniaxial loading in order to determine effective mechanical characteristics which are utilized for macroscopic simulation in this work. Pre-fracture behavior of specimens undergoes the Drucker-Prager model with non-associated plastic flow rule. Experimental and numerical simulation fracture patterns show that material exhibits mixed mode I+II of crack propagation. Comparison of experimental data and numerical simulation data gives a good agreement
Crack growth study under thermo-mechanical loads: parametric analysis for 2024 T3 aluminum alloy
Get PDFDue to their severe operating conditions, many industrial components are subjected to complex combinations of cyclic mechanical stresses and thermal pressures. These combinations are responsible for the initiation and propagation of fatigue cracks in these parts, which can lead to failure. Thus, the study of the fatigue strength of these parts in such conditions becomes essential because it allows us to predict the life and safety of components.
This study examines the influence of the load ratio and temperature on the propagation rate of long cracks on the outer surface. The propagation of a fatigue crack in ABAQUS was therefore automatically simulated using an identified Paris law of 2024 T3 aluminium alloy. Therefore, the study of these components' fatigue resistance in such conditions becomes essential to predict the service life and safety of the components
The effect of temperature on low-cycle fatigue of shape memory alloy
Get PDFThe influence of temperature on the fatigue properties of pseudoelastic NiTi under low-cycle fatigue are investigated. Tests were performed under the uniaxial tensile deformation (pull-pull) at 0°С and 20°С which is above the austenite finish temperature. Experimental results indicate that the fatigue life of NiTi alloy increases with the decrease of test temperature from 20°С to 0°С in the case of presenting the results depending on the strain range and Odqvist’s parameter. Regardless the test temperature, with the increase of number of cycles to failure, the stress and strain ranges, as well as the dissipation energy decrease, and the total dissipation energy and Odqvist’s parameter increase. The slope of the fatigue curves of NiTi alloy is greater at the temperature of 0°С in comparison with the 20°С in the case of employing the stress range, strain range, Odqvist’s parameter, and total dissipation energy as the failure criteria, and is less while employing the dissipation energy as the failure criterion
Fatigue crack growth in welded S355 specimens subjected to combined loadings
Get PDFThe paper presents a result of experimental tests of welded S355 specimens subjected to combined bending and torsion loading. In order to analyse how the fillet joints’ shape and the load ratio affect the crack growth, we selected two kinds of the fillet shape: concave and convex, and two load ratios, namely R = -1, 0. Rectangular specimens with stress concentrators in form of the external two-sided blunt notches and fillet welded joint were tested. The test results were compared to experiments conducted on solid specimens without welds