Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Mechanical Properties of SiC Nanoparticle-Reinforced Al-2024 Alloy
Full text linkThis study investigates the mechanical properties of Al-2024 alloy reinforced with SiC nanoparticles, highlighting the effectiveness of ultrasonic-assisted stir casting in achieving uniform dispersion of the nanoparticles. The aim is to enhance the material's inherent limitations in hardness and overall mechanical performance under demanding conditions by incorporating SiC nanoparticles. The experimental investigation explores varying SiC content (1%, 2%, 3%, and 4%) and its relationship with tensile strength and hardness. The results indicate a substantial 31% enhancement in hardness and a 25% improvement in tensile strength, demonstrating the effectiveness of nanoparticle reinforcement. Furthermore, several strengthening mechanisms were found to be important contributors to yield strength, including the Orowan mechanism, dislocation strengthening, and grain refinement strengthening. A maximum variation of 13% between the experimental and predicted yield strength of the Al2024-SiCnp composite confirms the reliability of the predictive models employed. Overall, the results support SiC nanoparticles' ability to improve Al-2024 composites' mechanical characteristics for cutting-edge engineering uses
Dynamic damage analysis of carbon fiber reinforced polymer composite pressure vessels
Full text linkThis study investigates spall damage and failure in Carbon Fiber-Reinforced Polymer (CFRP) pressure vessels under explosive internal loading using stimulated electric discharge. Analytical modeling, validation with published experimental data, and explicit numerical simulations were employed. A Coupled Eulerian–Lagrangian (CEL) framework in Abaqus/Explicit captured the dynamic-impact shock propagation, using continuum shell (SC8R) elements for the vessel, solid (C3D8R) for the PMMA insert, and Eulerian (EC3D8R) for copper-wire vapor. Intralaminar failure was modeled using the Hashin criterion, while interlaminar damage was captured using the energy-release-rate-tuned Virtual Crack Closure Technique (VCCT). Results demonstrated high-accuracy agreement with experiments in terms of free surface velocity and failure stresses, with minor discrepancies attributed to wire alignment, material model limitations, and wave reverberations. These findings highlight the reliability of the integrated modeling framework and support improved design and risk-mitigation strategies for composite pressure vessels, advancing safety and cost-efficiency through refined material characterization and structural assessment
A study on the crack presence effect on dynamical behavior of higher-order Quasi-3D composite steel-polymer concrete box section beams via DQFEM
Full text linkThis paper presents a dynamic and critical buckling analysis of the presence of a crack of steel-polymer concrete composite beams modelled using a refined quasi 3D beam theory. The beam model is a hollow steel box section filled with a composite concrete material. The presence of the crack is assumed on both inner concrete core and outer steel layer box, incorporating its effects into the mechanical behavior of the beam. The governing equations for the box beam are derived using the Differential Quadrature Finite Element Method (DQFEM) combined with Lagrange’s principle. The study investigates the natural frequencies and critical buckling loads of steel-polymer concrete composite beams under various crack location and crack depth. Validation is performed by comparing the results with numerical methods and experimental results available in the literature, demonstrating high accuracy. The findings of this research provide valuable insights into the dynamic and stability behavior of box-section beam with composite infill, offering practical guidelines for the design of material-based structures in engineering applications
Realization of introducing non-woven veil on interlaminar radial strength of Glass Epoxy L-Bend composites
Full text linkThis study investigates the effect of interleaving non-woven veils and their surface areal density on the curved beam strength (CBS) and interlaminar radial stress (ILRS) of glass/epoxy L-bend composite laminates. Carbon veils with areal densities of 15, 20, and 30 g/m2 , and glass veils with 25 and 30 g/m2 were used as interleaving materials. The L-bend laminates, both interleaved and non-interleaved, were fabricated using the compression moulding technique. A four-point bending test was employed to evaluate the influence of veil interleaving and areal density on CBS and ILRS. The experimental results demonstrated that interleaving with carbon and glass non-woven veils significantly affects the performance of curved laminates. Notably, the CBS of the glass/epoxy laminate improved by 88% and 17% for specimens interleaved with 15 g/m2 carbon and 30 g/m2 glass veils, respectively. Furthermore, the ILRS of carbon veil-interleaved laminates showed a strong dependence on the veil’s areal density. In contrast, interleaving with glass veils did not exhibit a significant effect on ILRS. Finally, the fracture surfaces of the tested laminates were examined using scanning electron microscopy (SEM) to identify the various failure modes in the curved region and to understand the underlying fracture mechanisms
Experimental field analysis of damage-failure transition in composite material with a stress concentrator under cyclic loading (application of DIC and X-ray tomography techniques)
Full text linkPredicting the failure of carbon fiber composites remains a challenge due to the complex evolution of damage, where the collective behavior of defects like pores and microcracks dictates material strength. The objective of this work is to elucidate the transition from damage accumulation to final failure under cyclic loading by analyzing the integral structural characteristics of the material. A methodology combining microtomography and digital image correlation (DIC) was employed to monitor damage evolution in situ. The analysis of DIC-derived strain fields during block cyclic loading pinpointed the critical transition stage to failure. Furthermore, Bayesian Gaussian Mixture models were used for threshold segmentation and cluster analysis, revealing that mechanical loading induces distinct populations of small and large pores. The main results show that while the overall pore orientation distribution remains consistent, the clustering and ordering of pores evolve differently under cyclic loads compared to quasi-static conditions. Specifically, unloaded samples exhibit three distinct pore clusters based on orientation, a structure that is altered by cyclic loading through pore expansion and coalescence, which ultimately reduces specimen strength. These insights advance the understanding of damage criticality in composites and provide a foundation for developing more accurate predictive models
Consecutive shock waves and fatigue loads: action invariants as optimization parameters under Laser Shock Pinning
Full text linkThe criteria for optimizing shock-wave modes to increase the fatigue life of aircraft engine alloys are discussed with reference to laser shock peening (LSP). They are based on the self-similarity of plastic wave fronts and the kinetics of fatigue cracks related to the Swegle-Grady power law of structured plastic wave fronts and the Paris power law of fatigue crack advance. It is shown that the self-similar patterns and the power-law relationships of structured wave fronts at shock pulse amplitudes of 1-10 GPa and strain rates of 105-109 s-1 correspond to “action invariants” that determine the dissipative properties (stored energy) of materials caused by multiscale defect development. The relationship between the “action invariants” of structured plastic waves, the fatigue crack kinetics and the structural scaling invariants is shown using the 3D data of qualitative fracture surface profilometry. The methodological principles for studying material behavior under successive shock-wave and fatigue loads have been developed to optimize LSP processes and thus to ensure maximum fatigue life
Diagnostics and experimental analysis of 3D printed concrete structural elements
Full text linkThis study investigates the structural behaviour of elements produced by extrusion-based 3D concrete printing (3DCP). Six full-scale columns with intentional imperfections were tested in three-point bending and subsequently analysed through fragment testing. Compressive strength (16.6–32.2 MPa), flexural tensile strength (1.96 MPa parallel vs. 1.27 MPa perpendicular), ultrasonic pulse velocity, bulk density, and water absorption were measured. The results confirmed pronounced anisotropy and strong correlations between physical and mechanical properties. A simplified FEM model, calibrated with fragment data, reproduced global stiffness but not brittle delamination. The combined methodology offers a basis for diagnostics and quality control of 3DCP elements
The effect of energy director on ultrasonic consolidation of multilayered composites (laminates) made from unidirectional PEEK/CF prepregs
Full text linkThe study aims at assessing the effects of the ultrasonic consolidation parameters and the insertion of energy directors from the commercially available polyetheretherketone film ~250 µm thick on the structure and mechanical properties of the layered composites (laminates). Commercially available polyetheretherketone-based prepregs reinforced with tapes of unidirectional carbon fibers were ultrasonically consolidated with and without energy directors from neat polyetheretherketone film using an ‘UZPS-7’ ultrasonic welding machine. The laminates without the energy directors consisted of 16 prepreg layers, while 7 and 6 layers of the prepregs and the energy directors, respectively, included the other ones to ensure similar thicknesses during subsequent interlaminar shear strength tests. In the laminates with the energy directors, prolonging the ultrasonic duration allowed for the prepreg interfaces to be virtually blurred, increasing the interlaminar shear strength value up to the maximum level of 60 MPa. With the energy directors, excessive melting and spreading of the polymer occurred at the prolonged ultrasonic durations, increasing the number of discontinuities at the layer interfaces, including delamination and the impregnation of the prepregs with the excessive binder. The ultrasonic duration of 800 ms was the most rational, as it enabled to reduce the damaging effect of applied ultrasonic vibrations on the joined layers (prepregs), increasing the interlaminar shear strength value above 50 MPa
Application of perforated PEEK framework for improving strength of a bases of removable complete denture for maxilla
No full textThe paper presents the results of computer simulation of a hybrid removable complete dentures (RCD) of a maxilla and analysis of its stress–strain states (SSSs) under typical operational loads. For improving their strength and stiffness, it was proposed to reinforce a base made of polymethylmethacrylate (PMMA) with a perforated framework (technological holes for enhancing adhesion) made of polyetheretherketone (PEEK). In total, the SSS for 10 different models were analyzed, simulating the presence or absence of a reinforcing framework as well as its perforation, location in the base, adhesion between the components, and the deformation of the alveolar ridge. The key difference of the conducted computer simulation was the application of a virtual support of the RCD. Its deformation imitated changes in the alveolar ridge height, as well as the presence of more rigid areas corresponding directly to both alveolar ridge and a torus. The SSSs for the FE-models were calculated by the finite element method using the ‘ABAQUS’ software package. The effect of the PEEK framework position on the mechanical properties of the RСD was assessed. It was shown that the main reason for the base’s failure was its bending under the applied loads. However, the load-bearing capacity of the RСD could be increased by 20–40% by embedding of the PEEK framework as an additional layer of the base dome. The effect of variation in the base support conditions, simulating the degradation of the alveolar ridge caused by the bone tissue resorption, was analyzed. It was found that the load-bearing capacity of the RСD could vary within 10% in such cases. The perforation in the PEEK framework did not reduce significantly the mechanical properties of the RСD, but its adhesion to the PMMA base exerted a decisive effect on the operational performance
Analyzing the Effect of Residual Stresses in the Fatigue Life of High Ultimate-Strength Steel Specimens
No full textAn analytical model, based on Solid Mechanics, is developed based on a comprehensive analysis of the effect of residual stress on the fatigue performance of cold-drawn steel wires partially yielded specimens. In the experimental part, it was initially assumed that the specimens, taken from the manufacturer's wire spools, did not have appreciable residual stresses. Therefore, a residual stress pattern was imposed on the specimens before the fatigue testing. Nevertheless, it was realized that the number of cycles spent by the specimens up to failure was higher than those predicted by the fatigue/residual stress compound analytical model. Hence, the initial assumption was reviewed, and a prior superficial compressive residual stress was incorporated into the model, most likely generated by cold-rolling manufacturing. The “resistance increase” and the “stress reduction” approaches were suggested to encompass the number of cycles difference, with good results. In addition, the prior level of existing superficial compressive residual stresses was also estimated