Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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A novel procedure for accurately measuring the Mode II fracture toughness of steel fiber reinforced self-compacting concrete
Full text linkMost research on the mode II fracture toughness of fiber-reinforced concrete (FRC) has intentionally avoided bridging fibers at pre-notch surfaces by using a through-thickness crack (TTC) that cuts the entire thickness, including fibers in this region. The objective of the present research is to accurately measure mode II fracture toughness (KIIC) using double-notched cube (DNC) specimens on steel fiber reinforced self-compacting concrete (SFRSCC). The effects of precrack-to-specimen width ratios (a/w), i.e., a/w = 0.3, 0.4, and 0.5, and fiber volume fraction percentage (Vf%), i.e., Vf% = 1% and 1.5% were investigated. A comparison between KIIC measured through specimens having the TTC concept, i.e., the absence of fiber bridging on the surfaces of the pre-notch, and those with the presence of fiber bridging on the surfaces of the pre-notch, i.e., the matrix crack (MC) concept. For greater clarity, the SCC specimens were cast without fibers with (MC/C) or without fiber bridging on the pre-crack surfaces to determine the unique effect of the presence of fiber bridging on the pre-crack surfaces on enhancing KIIC. The results showed that DNC specimens with MC consistently obtained the highest mode KIIC for all values of a/w, indicating the greatest resistance to crack growth. KIIC increased as the a/w ratio increased. MC/C method, i.e., the presence of fibers behind the crack front only, showed more effectiveness on the KIIC than the TTC, i.e., the presence of fibers ahead of the crack front only. In general, the MC is an accurate method for measuring KIIC of FRC
Optimization of austenitic and ferritic steels for deep drawing. Part 1: metallurgical and mechanical analyses.
Full text linkDeep drawing of stainless steels thin sheets is a cold forming process used to produce components with complex geometries at limited costs. Although it seems a simple shaping technique, this technology requires a high level of know-how, essential to optimize parameters and limit production scraps. The choice of stainless steel type also plays a fundamental role, since there are austenitic and ferritic grades with improved chemical composition which should be characterized by a superior deformability when compared to the more common ones. This study investigates the formability of two austenitic and two ferritic stainless steels, AISI 304, 304 mod., AISI 430 and AISI 441, using tensile tests and Erichsen tests. From the former, the mechanical properties and anisotropy coefficients were determined along three sampling directions in respect to the rolling direction. Since the deep drawing is influenced also by some technological parameters such as the lubrication, the punch speed, and the blank-holder pressure, Erichsen tests were performed varying the deformation conditions and an Erichsen index (IE) was determined. The Erichsen samples were also subjected to metallographic and HV0.2 microhardness analyses to study the modification of the microstructure and the consequent impact on the local mechanical properties
Modified multi-scale constitutive model of Aluminum: complex loading with variable thermal conditions
Full text linkDuring manufacturing of parts from metals and alloys through forming and subsequent thermal and mechanical treatments the materials are often subjected to complex loading. In such cases materials significantly change their structure, which determines the operational characteristics of a finished product. Therefore, for digital design of technological processes aimed at improving the functional characteristics of products, it is promising to develop mathematical models that adequately describe the material structure evolution during forming, thermal and mechanical processes including complex loading.
This work considers the previously developed two-level constitutive models of aluminum under complex loading accompanied by temperature variations. The model parameters were calibrated to the experimental data of simple shear loading of aluminum specimens. The resulting deformation curves for aluminum subjected to simulated reversed simple shear loading with temperature variations, as well as loading involving strain-path changes, correspond well to the experimental data. The observed effects arising under the considered complex loading conditions are explained through analysis of the obtained description of the intragranular dislocation slip mechanisms. The study results demonstrate the applicability of multilevel constitutive models for comprehensive descriptions of the effects observed in the material during thermal and mechanical treatments
Effect of contact geometry, loading, material properties and relative slip on the fretting fatigue behaviour of metallic components
Full text linkMetallic structural components, placed in contact with other bodies while experiencing vibrations in operating conditions, are susceptible to fretting, which can have a significant impact on their fatigue performance. Although extensive research has been conducted over the past decades to analyze the effects of various fretting influencing factors (including loading conditions, friction coefficient, relative slip amplitude, contact configuration, surface finishing, material properties, and environmental factors), this area of study remains an active field of investigation.
In this paper, an experimental campaign reported in the literature, involving Al-4Cu specimens subjected to a partial slip regime cylindrical fretting contact, is examined by means of an analytical methodology developed by the authors. The results obtained through the proposed methodology demonstrate good agreement with the experimental observations in terms of both fatigue life and crack propagation direction. Furthermore, a parametric analysis is carried out to assess the role of different parameters in influencing the fretting fatigue behaviour, providing valuable insights into their effects on crack orientation and component durability
The assessment of the severity of local impact on a pro-bionic composite lattice shell by the use of fiber-optic sensors
Full text linkThe paper considers a pro-bionic lattice shell (PBLS) for civil aviation structures and the problem of getting the parameters of a local low-velocity impact taking the value of residual strain by fiber optic sensors (FOS) installed in PBLS. There was developed a numerical model of an equivalent smooth shell with a detailed part as an impact zone. This detailed part have been constructed from a load-bearing rib containing layers of UD composite, matrix polymer, a protective tab and a skin. The matrix polymer layers and the protective tab had elastic-plastic properties, in the developed numerical model. The UD composite layers and the skin were orthotropic elastic media. FEM calculations showed that the location of FOS directly on the rib surface does not provide the required accuracy of getting impact residual strain. However, FOS installation into elastic-plastic protective tab makes solving the problem. Localized Bragg grating sensors must be installed into the FOS with a high density (every 1-2 cm along the rib) to indicate the impact location, which is technically difficult to implement. Distributed sensors (Brillouin scattering) have an advantage, allowing both to indicate the impact location by residual strain recording and to get possibility calculate later the most important parameter - the impact energy
An Investigation on the Free Vibration Behaviors of Additively Manufactured PA6 Layered Plates: Influences of Stacking Sequence, Infill Ratio, and Boundary Conditions
Full text linkThis study investigates the free vibration behavior of 3D-printed PA6 layered plates by considering the effects of stacking sequence, infill ratio, and boundary conditions. Unlike previous works, this research provides a comprehensive analysis combining experimental pre-analyses and finite element simulations. Nine different plate configurations with infill ratios of 40%, 70%, and 100%, and aspect ratios (a/b = 1, 1.5, 2, and 2.5) were analyzed under clamped and simply supported boundary conditions. The mechanical properties of the printed material were determined through tensile testing, and these properties were used as input for the numerical model developed in ANSYS. Before the vibration analyses, the model was validated by comparing its results with existing literature, showing close agreement. Results showed that higher infill ratios in the outer layers increase natural frequencies due to improved stiffness, whereas a denser core can reduce them due to increased mass. Additionally, increasing the aspect ratio leads to higher natural frequencies. The findings offer valuable insights for improving the vibration performance of 3D-printed PA6 components used in functional parts such as gears, fan blades, and robotic arms
Study on B4C Particulates Size on Mechanical Behavior, Fractured Surface and Optimization of the Wear Parameters of the Al7075 Composites by Statistical Approach
Full text linkAluminum composites with varied weight percentages of 0-2.5 B4C particles and micro- and nanoparticle sizes were fabricated by stir-casting. The material's mechanical and wear characteristics were evaluated. We used dry pin-on-disc wear testing to examine the wear behavior of both micro and nano composites. In the sliding wear trials, different particle sizes (micro and nano), sliding distances (1500 m and 3000 m), and sliding speeds (3 m/s and 6 m/s) were employed. Scanning Electron Microscope (SEM) was utilized in the experiment to examine the materials and microstructures of several composites. Uniform dispersion of the micro and nano particles was readily evident in the SEM image. B4C particle microhardness increased by 16.06 % in nano composites and 10.78 % in micro composites. In a similar way, B4C particles' tensile strength increased by 12.90% in nano composites and 8.78% in micro composites. Taguchi design for experimental technique was applied to a L8 orthogonal array in order to design and ascertain the effects of sliding distance, sliding speed, and particle size on dry sliding wear behavior. ANOVA study showed that the most significant influencing factor on wear resistance was particle size (61.29%), followed by sliding speed (17.27%) as well as sliding distance (14.20%). From the confirmatory tests, the Coefficient of Friction (COF) of the produced composites had a maximum error of 9.09 % and the error of 3.33 % was found in the wear rate which was within the acceptable limit. The wornout surface shows that the composite reinforced with nanoparticles has a smooth wear surface with a finer wear scar
Optimizing mechanical properties of AA7075 Metal Matrix Composites reinforced with TiB2 and ZrO2 particulates
Full text linkHybrid metal matrix composites (MMCs), recognized for their superior strength-to-weight ratios and synergistic property enhancements, are emerging as advanced materials capable of mitigating the inherent limitations observed in conventional monolithic composites. While traditional composites offer structural benefits, their susceptibility to creep deformation and abrasive wear restricts their broader applicability. In sectors such as aerospace, automotive, and marine engineering, aluminum-based hybrid MMCs reinforced with ceramic particulates like titanium diboride (TiB2) and zirconium dioxide (ZrO₂) have garnered considerable interest due to their enhanced mechanical integrity and tribological performance. This investigation is an extension of previous work by authors AA7075 MMCs. This work systematically examines the influence of TiB2 (fixed at 5 wt%) coupled with incremental ZrO₂ reinforcement levels (2, 4, and 6 wt%) on the microstructure, mechanical strength, hardness, and wear resistance of AA7075 alloys fabricated via the stir casting process. The study aims to elucidate the compositional optimization of hybrid reinforcements to tailor material properties for high-performance applications. Microstructural analysis revealed an equiaxed grain structure with uniform reinforcement distribution, particularly in AA7075/5% TiB2/4% ZrO2 composition. The addition of reinforcements improved hardness up to 85.45%, increasing from 55 Hv (base alloy) to 102.40 Hv. And, also the yield strength increased from 107 MPa (base alloy) to 123 MPa, an increase of 15%, attributed to the improved particle detachment resistance. Introducing TiB2 and ZrO2 particles remarkably enhanced wear resistance with a wear rate of 155 µm with 10N load due to reinforcements that act as the lubricating agent between the metal matrix and the rotating disc. Among the compositions studied, AA7075/5% TiB2/4% ZrO2 exhibited superior performance, highlighting the potential of tailored hybrid composites for advanced mechanical and tribological applications in automotive, aerospace and marine industries
Advanced algorithms for early detection of first damage during static tensile tests
Full text linkThe Static Thermographic Method (STM) involves analyzing the thermal behavior of a specimen subjected to a quasi-static tensile test. The temperature trend, measured by an infrared camera, follows three phases where the first and second are cooling phases, while the third a heating phase. A limit stress value can be determined, corresponding to the macroscopic stress level at the point of slope change between the first and second phase, indicating the occurrence of initial damage. The onset of plasticity is the reason of fatigue failure; thus, the limit stress can be adopted as a first indication of failure stress level for design purposes. This work aims to objectify the Static Thermographic Method, which currently relies on the operator's experience and skill in identifying the different thermal phases during the static tensile test. Three different algorithms have been developed to determine the best mathematical model for the temperature trend over time, eliminating the subjectivity of data observation
Parameters Optimization for Manufacturing Advanced Self-Reinforced Composites based on Ultra-High Molecular Weight Polyethylene
Full text linkIn this study, the relationships between processing, structure and properties of self-reinforced ultra-high molecular weight polyethylene (UHMWPE) composites fabricated via thermal pressing are investigated. By systematically varying processing temperatures (145, 155, 165, 170, 175,180 °C) and pressures (25 and 50 MPa), we demonstrate that mechanical performance is governed by the interplay between fiber consolidation and the preservation of the oriented crystalline phase. Scanning electron microscopy reveals the presence of residual voids that are independent of the processing parameters, and which lead to interfacial failure and fibrillar fracture morphologies. We identify a critical processing threshold at 165 °C (25 MPa), which yields peak interlayer shear strength (7.8–11.1 MPa), bending strength (102–130 MPa), elastic modulus (23–42 GPa), and Charpy impact resistance (72–95 kJ/m²). Beyond this threshold, however, mechanical performance deteriorates due to fiber remelting and loss of anisotropy, resulting in the composite transitioning to an isotropic UHMWPE matrix. Conversely, elevated pressures fail to improve properties due to insufficient macromolecular interdiffusion, which is the dominant bonding mechanism. These findings establish a processing-structure-property framework for UHMWPE-based self-reinforced composites that balances interfacial adhesion and crystalline alignment, while providing actionable guidelines for engineering high-performance single-polymer materials