Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Identification of the anisotropic behavior of the laser welded Interstitial Free steel HC260Y subjected to uniaxial tensile tests
No full textThe main purpose of this paper is to study the anisotropicbehavior of laser welded interstitial free steel HC 260Y when it is subjectedto monotonic tensile tests. The specimens were cut in different orientationsaccording to the rolling direction, annealed and finally assembled by laserwelding. The plastic behavior was modelled using an identification strategybased on a behavior law taking into account the anisotropy of this material, ahardening law describing the evolution of the hardening curves and anevolution law. The proposed identification strategy allowed for a goodvalidation of the model. The model was afterwards used to predict thebehavior of the welded material when it is subjected to various solicitations.Finally, the fracture surfaces of the specimens were examined using thescanning electron microscope (SEM) to determine the failure characteristicsunder the tensile loading
A simplified constitutive model for a SEBS gel muscle simulant - Development and experimental validation for finite elements simulations of handgun and rifle ballistic impacts
Get PDFAn original simplified constitutive model is proposed to simulate the effects of ballistic impacts on blocks of synthetic muscle simulant based on mineral oil and styrene ethylene-butylene styrene polymers (SEBS) as a convenient substitute for Fackler ballistic gelatin. The model is based on a quasi-static elastic-plastic model associated with hydrodynamic properties regulated by a polynomial equation of state. The paper illustrates the development and experimental validation of the model to simulate 9x21mm FMJ round-nose, 7.62x39 mm FMJ, and 5.56x45 mm NATO bullets penetrating 145x145x400 mm gel blocks. All material parameters are provided to be implemented in built-in LS-Dyna keywords. The validation confirms the effectiveness of the model and suggests possible further developments. The work also confirms the tested synthetic gel as a valid and convenient substitute for Fackler 10% ballistic gelatin at 4 °C
Couple effects of temperature and fatigue, creep-fatigue interaction and thermo-mechanical loading conditions on crack growth rate of nickel-based alloy
Get PDFThe ambient and high-temperature fatigue crack growth behaviors in C(T) and SENT specimens of Ni-based superalloy for turbine disk application were studied in a wide interval of temperatures 25–750°C using a combination a electro- and servohydraulic test systems and fractographic investigations. The fatigue, creep-fatigue interaction and thermo-mechanical in-phase fatigue (TMF IP) crack growth tests are performed under isothermal and dynamic waveforms loading conditions. The interpretation of the experimental results is given in terms of the traditional stress intensity factors and C-integral as well as new normalized cyclic fracture diagrams. It is found that there are definite temperature-sensitive regions separate for harmonic fatigue and creep-fatigue interaction loading conditions in which the crack growth rate of Ni-based alloy increases sharply. Scanning electron microscopy in longitudinal sections containing cracks revealed the mechanisms responsible for fatigue crack initiation and growth. The couple effect of temperature ranging and isothermal and dynamic waveforms loading conditions on fatigue life was discussed
Experimental and numerical assessment of the location-based impact of grouting defects on the tensile performance of the fully grouted sleeve connection
Get PDFThe presence of grouting defects emanating from construction operations constitutes a major threat to the structural integrity of the grouted sleeve connection of precast concrete members. This work presents a location-based assessment of the impact of grouting defects on the tensile performance of the grouted sleeve connection. Twenty-two specimens with different configurations of defects were subjected to a uniaxial tensile experiment. Corresponding numerical models were proposed, validated and used to conduct a sensitivity analysis of the connection to the defect's location while considering different design confinements of grouting materials. Experimental and numerical studies revealed the following outcome: In consideration of confinement parameters, when the defect of size 3d is located in the mid-span anchorage length, the variation of the sleeve-to-bar diameter (ds/d) from 2.66 (lower design limit) to 3.55 (upper design limit) changed the drop in the ultimate capacity from 19% to 44% below the connection's design requirement. The governing parameters of the grout-bar bond stiffness were the defect's location and degree of confinement. This work proposes a theoretical diagnosis model and a risk assessment catalogue as a promising step toward establishing a computerized diagnosis model of the defective connection to enlighten rational maintenance actions in actual construction
Fabrication, Mechanical and Wear Properties of Aluminum (Al6061)-Silicon Carbide-Graphite Hybrid Metal Matrix Composites
Get PDFIn recent times, the use of aluminum alloy-based Hybrid Metal Matrix Composites (HMMCs) is being increased in aerospace and automotive applications. HMMCs compensate for the low desirable properties of each filler used. However, the mechanical properties of HMMCs are not well understood. In particular, microstructural investigations and wear optimization studies of HMMCs are not clear. Therefore, further studies are required. The present study is aimed at fabricating and mechanical and wear characterizing and microstructure investigating of Silicon Carbide (SiC) and Graphite (Gr) added in Aluminum (Al) alloy Al6061 HMMCs. The addition of SiC particles was in the range from 0 to 9 weight percentage (wt.%) in steps of 3, along with the addition of 1 wt.% Gr in powder form. The presence of alloying elements in the Al6061 alloy was identified using the Energy Dispersive X-Ray Analysis (EDX). The dispersion of SiC and Gr particles in the alloy was investigated using metallurgical microscope and Scanning Electron Microscopy (SEM). The gain in strength can be attributed to the growth in dislocation density. The nature of fracture was quasi-cleavage. The microstructure examination reveals the uniform dispersion of the reinforcement. Density, hardness, and Ultimate Tensile Strength values observed to be increased with increased contents of SiC reinforcement. Besides, wear studies were performed in dry sliding conditions. Optimization studies were performed to investigate the effect of parameters that affecting the wear. The sliding wear resistance was noticed to be improved concerning higher amounts of reinforcement leading to a decrease in delamination and adhesive wear. The predicted values for the wear rate have also been compared with the experimental results and good correlation is obtained
Synthesis, Microstructural Characterization, Mechanical, Fractographic and Wear Behavior of Micro B4C Particles Reinforced Al2618 Alloy Aerospace Composites
Get PDFIn the current studies an investigations were made to know the effect of 63 micron sized B4C particles addition on the mechanical and wear behavior of aerospace alloy Al2618 metal composites. Al2618 alloy with different weight percentages (2, 4, 6 and 8 wt. %) of 63 micron sized B4C particles reinforced composites were produced by stir cast process. These synthesized composites were tested for various mechanical properties like hardness, compression strength and tensile behavior along with density measurements. Further, microstructural characterization was carried by SEM/EDS and XRD analysis to know the micron sized particles distribution and phases. Wear behavior of Al2618 alloy with 2 to 8 wt. % of B4C composites were studied as per ASTM G99 standards with varying loads and sliding speeds. By adding 63 micron sized B4C particles hardness, compression and tensile strength of Al2618 alloy was enriched with slight decrease in elongation. Further, wear resistance of Al2618 alloy was enriched with the accumulation of B4C particles. As load and speed on the specimen increased, there was increase in wear of Al2618 alloy and its composites. Various tensile fracture surface morphology and worn surface behavior was observed by SEM analysis
Damage assessment of different FDM-processed materials adopting Infrared Thermography
Get PDFThe use of components obtained through the additive manufacturing (AM) technique has become increasingly widespread in recent years, playing a central role in industrial production, and in particular in some fields such as automotive, biomedical, aerospace and electronics. Among all AM techniques, FDM (Fused Deposition Modelling) represents the most used printing technique to produce polymeric and composite components, thanks to the flexible printing process, the low cost and the diversity of the materials adopted. The aim of the present work concerns the comparison between the mechanical properties of three plastic materials printed with the FDM technique (polylactic acid PLA, polyethylene terephthalate glycol-modified PETG and Acrylonitrile-butadiene-styrene ABS) using an Original Prusa i3 MK3S, by varying the raster angle between 0°, 45° and 90° degrees. Infrared Thermography has been adopted to monitor the temperature evolution during static tensile tests and to assess stress level that can initiate damage within the material. Failure analysis was performed to correlate the mechanical behaviour with the microstructural characteristics of the materials
Numerical investigation on strengthening steel beams with web openings using GFRP
Get PDFThis study presents the first investigation into the use of glass fiber reinforced polymer GFRP to strengthen steel beams with web openings. Based on previous research about the strengthening of steel beams with web perforation using carbon fiber reinforced polymer (CFRP) conducted by one of the contributing authors of this paper, it was decided to investigate the ability of pultruded glass fiber reinforced polymer, which is less expensive than CFRP materials, to strengthen single rectangular web openings of steel beams. The previous published experimental test was used to validate the proposed numerical model developed with the finite element software ABAQUS, capable of acquiring important phenomena such as debonding between FRP and steel material. The validated simulation was then used to operate a parametric study involving four proposed GFRP strengthening techniques and three distinct pultruded GFRP product thicknesses to reinforce the same steel beam used in the earlier experimental test, having a single rectangular opening shape in two separate positions along the span. From these numerical models, an adequate GFRP strengthening arrangement was found and the possibility of using low-modulus FRP materials rather than the more expensive high-modulus FRP materials for strengthening steel beams with web penetration was confirmed
A method and apparatus for inspecting large flat composite parts by using the Infrared LST technique
No full textThe principle of Line Scan Thermography (LST) was used to develop a self-propelled infrared thermographic nondestructive testing device for the inspection of large, relatively flat composite aerospace parts, such as aircraft wings. The design of the unit allowed the suppression of noise from reflected radiation. The new equipment, using the LST method, provided defect detectability similar to that achieved with a classic, static, flash heating procedure, but with a higher rate of testing. Also, the line heating principle ensured more uniform thermal patterns, and the proper choice of scan speed and field of view allows the selection of optimal time delays and the creation of maps of defects at different depths. Defect characterization efficiency was improved by using a trained neural network
The Metallurgical hydrogen as an indicator and cause of damage to rolled steel: Hydrogen diagnostics of fracture
No full textFatigue tests and measurements of the volumetric distribution of metallurgical hydrogen in specimens cut from rolled I-beam 60Sh3 made of steel 10KhSND were carried out. Fatigue tests show a 20% reduction in fatigue limits compared to similar sheet material. On the fractures of the samples, there are flock-like defects in the areas of interface of the flanges of the I-beam, or the so-called zones of difficult deformation. The concentration of metallurgical hydrogen is unevenly distributed and varies from 0.17 ppm to 1.8 ppm. Large concentrations of hydrogen are observed in the zones of difficult deformation, which indicates the hydrogen nature of the metal defects observed at the fracture. The result of mechanical tests and hydrogen diagnostics is a manufacturing defect of rolled products that cannot be corrected. Hydrogen diagnostics using metallurgical hydrogen (without hydrogen charging samples) takes tens of times less time than mechanical tests, and gives an adequate result