Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Determination of the geometric parameters of the defects based on the tomographically obtained data and their influence on the fatigue behavior of the S960 with laser cladded protective layers
Full text linkThis article deals with identifying defects of layered high strength steel materials with the help of tomography measurement. Test samples were made of S960 High Strength Steel to which layers of either aluminium bronze, hardchrome, cobalt alloy or stainless steel were applied by a laser cladding technology. The experimental campaign included a study of morphometric parameters of internal defects in and near the bi-material interface region using X-ray micro-tomography and their potential influence on the fatigue behavior during a three-point bending test
Development and mechanical characterization of eggshell bio-filler based hybrid composites
No full textHybridization of natural fiber composite by incorporating waste- derived fillers has been identified as a promising sustainable technique to develop environmentally friendly and economical composites with enhanced mechanical properties. This study explores the mechanical performance of hybrid bamboo-epoxy composites incorporated with bio filler derived from waste chicken eggshells. Compression molding was employed to develop unfilled and eggshell powder filled bamboo composites by varying eggshell content (2, 4, and 6 wt%) while maintaining constant bamboo fiber wt%. Composites were tested for mechanical properties by performing tensile test, flexural test, and impact test per ASTM standards. Results indicated that eggshell filler inclusion significantly modifies the tensile, flexural, and impact strength properties of base bamboo composite. Adding eggshell filler enhanced tensile and flexural properties which was attributed to improved interfacial bonding and efficient stress transfer. Optimal filler was achieved for composites with 4 wt % eggshell exhibiting 13.5% improvement in tensile strength and 16.4% improvement in flexural strength. While reduction in impact strength observed was attributed to incorporation of inorganic eggshell filler which mainly consists of CaCo3 content. The fractography studies revealed the improved fiber-matrix interaction with the inclusion of filler, reduced fiber pullouts, and failure by fiber breakage supporting the observed experimental results
In-Plane Mixed-Mode Brittle Fracture Assessment of Harsin Marble Using HCSP Specimen
Full text linkThe primary objective of this manuscript is studying the effect of T-stress term (T) on the crack propagation angle (CPA) and fracture toughness of in-plane mixed mode loading by utilizing a generalized form of minimum strain energy density (SED) criterion. The generalized criterion considers the influence of the first non-singular term of the Williams stress field as well as the conventional stress intensity factors (SIFs). A specimen known as a holed-cracked square plate (HCSP) composed of white Harsin marble is used for a wide range of in-plane mixed-mode fracture studies. HCSP is a square plate containing two cracks that are placed along each other in the circumference of a hole at the center of the specimen. The experimental results from mixed-mode fracture test by using proposed geometry are then compared with the results obtained theoretically from the conventional and generalized form of SED. It is demonstrated that the generalized criterion which includes the T, is substantially in agreement with the experimentally observed in-plane mixed-mode fracture results when compared to the SED criterion
Experimental investigation on the fatigue and fracture properties of a fine pearlitic rail steel
Full text linkThis study reports an experimental investigation of the fatigue and fracture resistance of R350HT, a heat-treated pearlitic rail steel with refined microstructure used in rails. Monotonic tensile, rotating bending, linear elastic plane strain fracture toughness, and fatigue crack growth rate tests are presented. The results are used to outline the basic properties and are corroborated by fractographic investigation. This enables the identification of the dominant type of fracture. Regarding fatigue and fracture resistance, the investigated material shows similar properties as other pearlitic rail steels, such as R260. At room temperature, the dominating fracture is of brittle cleavage type, showing some ductile regions associated with pro-eutectoid.
 
Improving the performance of damage repair in thin-walled structures with analytical data and machine learning algorithms
Full text linkIn the last four decades, bonded composite repair has proven to be an effective method for addressing crack damage propagation. On the other hand, machine learning (ML) has made it possible to employ a variety of approaches for mechanical and aerospace problems and such significant approach is the repair mechanism and hence ML algorithms used to enhance in the present work. The current work investigates the effect of the single-sided composite patch bonded on a thin plate under plane stress conditions. An analytical model was formulated for a single-sided composite patch repair using linear elastic fracture mechanics and Rose's analytical modelling. From the analytical model, the stress intensity factors (SIF) were calculated by varying all possible parameters of the model. Next, ML algorithms were selected, and comparative studies were conducted for the best possible performance and to identify the parametric effects on optimum SIF. Also, the analytical model is validated with existing work, and it shows good agreement with less than 10% error. This study is particularly important for designing the single-sided composite patch repair method based on analytical modelling. Also, it is important to compare ML algorithms with analytical solutions in regression applications
Degradation analysis of dynamic properties for plain concrete structures under mixed-mode fracture conditions via an improved cohesive crack approach
Full text linkThe present work investigates the crack-induced degradation of the dynamic characteristics in plain concrete elements subjected to mixed-mode fracture conditions. Specifically, a discrete fracture model, based on an inter-element cohesive approach, has been improved and implemented into a 2D finite element framework to evaluate the progressive variation of the static and dynamic properties as the damage level increases. The obtained numerical results highlight the effectiveness of the proposed model in determining the load-carrying capacity and the degradation of natural vibration frequencies during damage propagation, demonstrating its applicability in the framework of structural health monitoring
Reuse of sheep wool fibers in the production of ultralightweight foamed concrete: effect of fiber treatment, length, and content on the mechanical properties
Full text linkConcrete is one of the most widely used materials in the world. Still, its production processes, energy consumption, and high use of raw materials make it one of the most environmentally harmful materials. This study aims to enhance the sustainability of concrete by reducing the amount of binder and incorporating secondary materials into the cementitious matrix. The binder reduction is achieved by using a foaming agent that creates a microporous matrix, significantly decreasing the volume of cement in the material. Additionally, reinforcing the material with sheep wool fiber not only improves its mechanical properties but also gives a new purpose to a commonly discarded secondary material. The research specifically seeks to identify the most effective treatments for sheep wool fiber (including non-treated, salt-treated, lime-treated, NaOH-treated, and surfactant-treated fibers), as well as the optimal fiber length (6, 12, and 20 mm) and content (4.5, 9, and 15 kg/m³) for ultralightweight foamed concrete in terms of mechanical strength. The findings demonstrate excellent compatibility between wool fibers and ultralightweight foamed concrete, with fiber-reinforced samples showing up to a 60% increase in flexural strength and up to a 50% increase in compressive strength. Among the various fiber treatments evaluated, surfactant-treated fibers yielded the best results
Critical length parameter of HDPE and its use in fatigue lifetime predictions
Full text linkThe contribution describes the fatigue lifetime predictions of polyethylene notched specimens based on the theory of critical distance. The approach uses the line method, which averages the axial stress over the critical distance. The critical distance is determined from experimental data of Cracked Round Bar (CRB) specimens and specimens with a model notch. From these two sets of experimental fatigue data and corresponding axial stress distributions, the critical distance is determined. The critical distance depends on the number of cycles to failure and notch radius. For this reason, the critical distance is modified by the ratio of stress concentration factors and the modified distance is used for fatigue lifetime predictions of notched specimens with various notch radii. Using this approach significant savings in testing time can be achieved. CRB fatigue tests are commonly used tests for ranking PE pipe grades and are easily available. Adding the fatigue tests of notched specimens with a model notch, the critical parameter can be found, and fatigue lifetime predictions of various notches can be calculated
The influence of plastic flow localization on the surface morphology of aluminum alloy specimens subjected to complex loading
Full text linkThis study investigates the effects of complex (nonproportional) loading on plastic deformation in aluminum alloys (Al-6% Mg), with a focus on understanding surface morphology changes driven by the Portevin–Le Chatelier effect. Mechanical tests on the deformation of thin-walled tubular specimens were carried out on an Instron 8850 two-axis servohydraulic testing system. Quantitative analysis of the lateral surface of the specimens roughness was carried out based on data obtained using a NewView 5010 interferometer-profilometer. Localized plasticity zones in a wide spectrum of spatial scales were determined using the Hurst exponent as a roughness characteristic. The results of measuring changes in the surface geometry of specimens under various programs of complex (disproportionate) loading are presented. A compact representation of data on the specimens surface relief in the form of amplitude-frequency characteristics was obtained using wavelet analysis. The results obtained can be used to assess the surface roughness of products, especially at the final stages of their manufacturing process by plastic deformation
Low-carbon cementitious composite incorporated with biochar and recycled fines suitable for 3D printing applications: hydration, shrinkage and early-age performance
Full text linkIn recent years, the construction industry has witnessed significant advancements in concrete technology, particularly with the integration of 3D printing in cement-based materials. While this innovation offers promising opportunities for the sector, the high binder and fine particle content of 3D printing mixes presents a substantial environmental challenge due to their considerable carbon footprint. To mitigate this impact, strategies often involve substituting portions of the binder or aggregate with waste materials. This article presents a comparative analysis of two promising approaches to reducing the carbon footprint of 3D printing concrete mixes by partially replacing cement with biochar and recycled fines. The study examines the effects of these materials on the rheological properties and early-age hydration processes of the 3D printing mix. A reference mix (REF) was established, followed by the development of eight additional mixes, with four incorporating biochar and four incorporating recycled fines, each replacing 1.25%, 2.5%, 5%, and 10% of the cement volume. The findings indicate that recycled fines have a neutral effect on the spread flow diameter of the mixture but increase initial deformations in printed elements. Conversely, biochar, due to its water absorption capacity, reduces fluidity, enhancing buildability by enabling faster printing with minimal initial deformation. Additionally, replacing up to 2.5 vol.% of cement with either material accelerates the normalized heat flow, contributing to a quicker gain in mechanical properties. However, biochar increases shrinkage deformations within the first 12 hours, while recycled fines mitigate them. Importantly, replacing up to 10 vol.% of cement with these materials does not significantly compromise early compressive strength