Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Assessment of mechanical, fracture and thermal properties of epoxy nanocomposites reinforced with low-concentration nano Boron Carbide (B4C)
Full text linkThis study investigates the effects of low concentration (0.1-0.4 wt.%) nano-boron carbide (B4C) reinforcement on the mechanical, thermal and fracture properties of epoxy nanocomposites. The nanocomposites were prepared via solution casting using ultrasonication to ensure proper dispersion of the nanofiller. The characterisation included Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), tensile, flexural, impact and fracture tests. Results showed significant enhancements in mechanical properties. Tensile strength peaked at 31.2 MPa (71% improvement) for 0.3 wt. % B4C, while modulus increased steadily to 1400 MPa (33% improvement). Flexural tests showed a progressive enhancement in bending strength, exhibiting 70.46 MPa (50% improvement) at 0.4 wt. % B4C. Impact strength surged by 62% at 0.4 wt. % and fracture toughness increased steadily, exhibiting 70% improvement. Thermal analysis revealed a higher glass transition temperature (Tg) and improved stability with B4C addition, attributed to restricted polymer chain mobility. SEM images showed improved fracture resistance, with rougher surfaces and smaller cleavage planes indicating effective energy absorption. Finite element (FE) simulations validated experimental tensile and flexural results, with variations within 15%. Statistical analysis confirmed all improvements were significant (p < 0.05)
Studies on mechanical, fractured surface, wear, and thermal characteristics of TiC reinforced structural grade Al6061 MMCs
Full text linkStir casting technique has been used in the current study to process Al6061 reinforced with TiC particles of different concentrations. The processed compounds' composition of TiC and Al6061 has been verified by Energy Dispersive X-Ray Spectroscopy (EDS) tests. TiC has been added to Al6061 in a range of weight concentrations, including 0, 3, 6, 9, and 12%. To determine the composite material's structure, an optical microscope research was used. It is endeavored to investigate the microstructure, mechanical, wear, and thermal performance of TiC-reinforced composites with varying weight fractions in this study. It was observed that, the strength of the developed composites increased by 51.89% in hardness, 18.47% in tensile strength and 40% in wear rate with the addition of TiC. Also, when compared to the alloy material, TiC particle reinforced Al6061 showed superior thermal characteristics
Strengthening of steel I-Section girder web with depth discontinuity against localized buckling
Full text linkStepped steel girders and beams with a jump in section depth are highly susceptible to local web buckling at the step location. Although tapered steel girders have been studied extensively by researchers, abruptly stepped steel girders have been very rarely investigated. This study uses the finite element method to investigate the local web buckling of stepped steel I-section girders. Firstly, linear buckling analysis is verified against experimental results and the AISC-360 and Eurocode 3 formulae. Then, a case study of stepped steel girder failure during construction is presented and discussed. Finally, the effect of step height, step location, boundary conditions, and adding stiffeners on the local web buckling of stepped girders was investigated. Stepping the girder section was found to cause local web buckling at significantly low loads, reaching only 27% of the original buckling capacity in some cases. Moving the step from the compression flange to the tension flange, or to lower moment locations in the girder, can mitigate the problem. When the step needs to be in the compression flange at high moment points, using a long enough horizontal stiffener was found to almost fully restore the web buckling capacity, while using a vertical one only restores about half of the original buckling capacity. Using both vertical and horizontal stiffeners almost doubles the buckling capacity at the step.
Experimental and Computational Study on the Tensile and Flexural Properties of Polylactic Acid filled with Boron Nitride Nanoplatelets
No full textOur research described in this paper focused on fabricating and characterising polylactic acid (PLA) composites reinforced with randomly dispersed boron nitride nanoplatelets (BNNP). The integrated experimental analysis with the Finite Element Method (FEM) computational simulation employed a multiscale modelling approach used to evaluate the effects of BNNP fillers at varying weight fractions (i.e. 0.005% to 0.04%). The simulations utilised Representative Volume Elements (RVEs) with 1 x 1 x 1 μm dimensions, incorporating randomly dispersed BNNP to mimic the realistic composite behaviour. The modulus predicted through the RVE approach was validated against empirical studies and pre-existing micromechanical models to ensure accuracy and reliability. The empirical findings revealed significant enhancements in the modulus of elasticity, tensile strength and flexural strength of the PLA reinforced with BNNP composites exhibiting improvements of 17.43%, 40% and 61% respectively at elevated filler concentrations of 0.005, 0.01,0.02,0.03 and 0.04. The Scanning Electron Microscopy (SEM) analysis of the fracture surfaces indicated a transition from ductile to brittle fracture patterns as the BNNP content increased, underscoring the reinforcing effect of the nanoplatelets. Flexural testing further validated improvements in the material rigidity and resistance to bending. The Finite element analysis (FEA) simulations strongly correlated with the experimental data, with deviations remaining within an acceptable range. This integrated approach underscores the efficacy of BNNP fillers in enhancing the mechanical attributes of PLA, yielding significant perspectives for developing eco-friendly composite materials exhibiting superior performance features
Experimental and theoretical study of used GFRP I-profile composite columns
Full text linkGlass Fiber Reinforced Polymer (GFRP) is a promising alternative to steel due to its high strength, lightweight properties, corrosion resistance, and low maintenance requirements. This study examines the effect of internal GFRP I-sections on the axial load capacity and fire resistance of reinforced concrete (RC) columns. The experimental program consisted of two groups: the first group, conventional RC columns, with one exposed to 500°C for 90 minutes and the other unheated, and the second group, GFRP I-section reinforced columns, similarly tested under fire and control conditions. Results show that GFRP-reinforced columns exhibited a 17% higher axial capacity than conventional RC columns. However, fire exposure reduced the axial strength of GFRP-reinforced columns by 39% compared to unheated specimens and by 14% compared to conventional RC columns. Theoretical axial load capacities were calculated using design codes, and finite element analysis (FEA) validated the experimental results. Additional parameters, including concrete strength, steel yield strength, reinforcement ratio, and GFRP section properties, were analyzed. The strong correlation between experimental, theoretical, and numerical results provides a foundation for developing practical design guidelines for GFRP-reinforced composite columns
Experimental investigation on mechanical behavior of sandwich structures using Digital Image Correlation (DIC)
Full text linkThe aim of this work is to investigate the mechanical behavior of sandwich structures when subjected to edgewise and flatwise compression loadings, using 2D Digital Image Correlation (DIC). These structures are made of Glass Fiber Reinforced Polymer (GFRP) skins with polyurethane foam (PU) core. Initially, the mechanical characterization of each component within the sandwich structure is exanimated. Subsequently, flatwise and edgewise compression tests are conducted on the sandwich panels, in accordance with ASTM C365 and ASTM C364 standards, respectively. Different geometries are studied by testing various lengths of sandwich structures exposed to edgewise compression loads. The DIC technique is applied to analyze and comprehend the deformation and failure mechanisms of GFRP skins and sandwich structures. The results of the present study indicate that the flatwise compression test revealed condensation and densification of PU foam, accompanied by microcracks in GFRP skin. On the other hand, the edgewise compression test on sandwich structures with an equal length-to-width ratio identified several distinct failure modes, including skin-core debonding, shear sliding damage of the skin, and localized buckling. This localized buckling was initially observed in the mid-section of the specimens, followed by skin cracking on both sides, which then propagated across the width of the samples. For other geometric configurations of the sandwich structures, the Euler general buckling mode was observed. The results show that the length of samples has a significant effect on the collapse modes of sandwich structures under edgewise compression
Numerical study of residual stress fields after double-sided symmetric laser shock peening of blade edge
Full text linkThis paper deals with numerical modelling of the residual stress field formed after laser shock peening of a thin blade edge from TC4. It is shown that the application of double-sided symmetric laser shock peening is an effective way of treatment, as it allows to reduce deformation and geometrical changes caused by laser shock peening in comparison with treatment from one side. The results of numerical modelling obtained by varying the machining parameters (power density, spot shape, number of passes, % overlapping) were used to form a database for further training of the neural network. It is shown which machining parameters lead to compressive residual stresses over the entire thickness of the edge, and which ones induce tensile stresses on the surface
Experimental and numerical analyses of stiffness and fatigue properties of a spring element for mounts with tunable stiffness made of C85S+QT sheet steel
Full text linkMounting stiffness has an important impact on a system’s structural dynamics and also on the durability of many structures. Mounts with tunable stiffness allow adapting a system’s structural dynamic behavior. Furthermore, they can be used to emulate elastic behavior of adjacent structures in test benches for components and substructures, e.g. for designing simplified, but accurate fatigue tests. For these applications, the tunable mounts themselves need to have sufficient fatigue strength. In this paper, results of experimental fatigue tests with such mounts are reported, providing material and geometry related fatigue data for four different configurations. Based on these experimental results, numerical parameter studies and analytical correlations, fatigue strength and stiffness approxima-tions are proposed for a wider range of geometries. This enables efficient pre-dimensioning of the tunable mounts starting from basic requirements
Reduction of Cracks in Concrete Slabs by Incorporating Synthetic Polypropylene Fiber
Full text linkIn Peru, research on cracking in concrete slabs has been limited, partly due to the perception that cracks do not pose an immediate problem. However, their cumulative effect over the long term can compromise structural durability, highlighting the need for further study. This research was conducted according to the recommendations of ASTM C1579, which establishes procedures for evaluating shrinkage cracking in concrete mixes with and without fiber reinforcement. The main objective was to determine the optimal proportion of polypropylene synthetic fiber that maximizes the reduction in the appearance and formation of cracks. Three dosages were evaluated: DM-01 (500 g/m³), DM-02 (1000 g/m³), and DM-03 (2000 g/m³), compared to a reference concrete (MP) during a 35-day curing period. The results indicated that dosage DM-02 (1000 g/m³) exhibited the best performance, with reductions of 18.41% in average crack thickness, 11.46% in total crack length, and 32.43% in the number of cracks compared to the control concrete. Furthermore, the Mann-Whitney U test applied to DM-02 and MP showed that the average crack thickness at 28 days (p = 0.073) showed a trend toward statistical significance, suggesting a possible reduction in crack thickness with the addition of fibers. In contrast, mixes DM-01 and DM-03 showed heterogeneous results, without substantial improvements in any of the variables; in particular, DM-03 registered an increase in crack thickness. It is concluded that a moderate fiber dosage (DM-02) is the most suitable option, since both a deficiency and an excess of fiber can compromise the material's effectiveness against cracking
Modified elastic-plastic model: implementation algorithm and comparison of computational efficiency with the elastic-viscoplastic model
Full text linkThe most important element of mathematical models of thermomechanical processing of metals and alloys is the constitutive model. In recent decades, multilevel physically-oriented constitutive models (CMs) have found widespread application. The first two-level model was the rigid-plastic theory of J. Taylor,a rigorous mathematical justification of which was developed by J. Bishop and R. Hill (TBH type models). The main disadvantage of this model is the uncertainty of the choice of active slip systems when more than 5 systems are activated. Despite this, the TBH models have become widespread, and its basic provisions have been preserved in many later developments. It seems that limiting the number of active slip systems to 5 has no physical justification and is determined only by the numerical procedure for implementing the model.
Since the 1970s, elastic-viscoplastic models have emerged; it has been shown that as the velocity sensitivity parameter tends to zero, the macroparameters determined in the modeling converge to a solution using an elastic-plastic model. However, the system of equations becomes rigid, requiring the use of implicit schemes and extremely small time steps, which significantly reduces the computational efficiency. The paper proposes a modification of elastic-plastic model of the TBH type, in which a procedure for overcoming the above-mentioned drawback is proposed. To compare the computational efficiency of the elastic-plastic and elastic-viscoplastic models, a series of numerical experiments was carried out