Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Investigating the repair of cracks through bacterial self-healing for sustainable concrete in aggressive sulfate attack environments
Full text linkConcrete completely submerged in sulfate solutions has been used as the primary study subject for the durability of concrete subjected to sulfates. On the other hand, empirical data from the field indicates that concrete exposed to sulfates may exhibit physical attack-induced surface scaling above. This study aims to study the two different types of local bacteria, (BS) and (BM), with content of 0%, 0.25%, 1%, 2.50%, and 5.00% by cement weight used in this work under curing in sulfate to examine the efficiency of bacterial self-healing of cracks for sustainable concrete in aggressive sulfate attack environments. The results show that in both curing in freshwater, FW, and sulfate, SUL, the optimum bacteria ratio was 2.5% BM, and the compressive strength improved by 43.34% for FW and 47.65% for sulfate. On the other hand, the results proved that the crack-filling and crack-repairing methods may be considered quicker than conventional methods. Moreover, a detailed conclusion about the preparation and processing of bacteria to provide the most significant content of locally accessible bacteria in Egypt, mainly when using chemical and mineral additives
Long-term development of mechanical properties of concrete with different water to cement ratio and internal curing ability
Full text linkConcretes with water to cement (or binder) ratios of 0.50. 0.40, 0.30 and 0.20 were prepared and long-term mechanical properties were measured. Porous light-weight aggregates (LWA) in dosages of 10 % and 20 % were used for self-curing (internal curing) as a partial replacement of fine aggregates for some concrete types. Two environmental conditions were studied i.e., one under water and the other in foil, which prevents the extensive water exchange with the environment.
Measured strengths at the ages of 28, 91, 365 and 720 days show higher values for the specimens covered in foil than for the specimens stored in water. On the other hand, the presence of LWAs reduces the compressive strength and bending strength of concrete with w/c = 0.30 at the age of 28 days of curing. The tests performed at the ages of 91 days and 1 year show higher flexural strengths than those of specimens cured in foil than those cured in water and those with internal curing
About Measuring the Stress Intensity Factor of Cracks in Curved, Brittle Shells
Full text linkMost techniques of measuring the stress intensity factor (SIF) in the cracking process assume a crack in a planar medium. Currently, there is no effective approach for curved brittle shells, particularly for non-developable cases, i.e., shapes with non-vanishing Gaussian curvature. This paper introduces a novel approach to obtaining material properties related to fracture by experimentally observing weakly curved surfaces. Based on the DIC record of the displacement field around the crack tip, the truncated Williams expansion is fitted to the data adjusted according to the shallow shell equations. The convergence properties of the method are investigated by comparing experimental data of PMMA cylinders to theoretical and numerical predictions. The applicability of the technique to non-developable surfaces is verified. It is demonstrated that robust convergence requires the number of terms in the Williams expansion exceeding 6. For different geometries, the ratio of the data selection radius and the length of the crack should exceed 0.3
Effect of printing process parameters on tensile strength and wear rate of 17-4PH stainless steel deposited using SLM process
Full text linkIn the current work 17-4PH Stainless Steel is deposited using SLM process. It is widely used to build structural parts appropriate for automotive, medical, and aerospace applications. The 17-4 PH SS samples were deposited using technical parameters such as laser power: LP, Scan speed: SS, and hatch distance: HD) were studied to analyze the wear rate and ultimate tensile strength. Fracture and wear track analysis was performed using SEM analysis. The DOE-Taguchi method is applied for the experimental plan and analysis of the parametric contribution with a statistical evaluation technique: Pareto Analysis of variance. The fracture surface morphology of 17-4 PHSS samples at different conditions indicated different failure. 17-4 PHSS samples LP1SS1HD1 condition displayed ductile-brittle fracture followed by LP3SS3HD2 and LP3SS3HD3 conditions displaying ductile failure. The wear features indicate abrasive pits and thin grooves across few areas reduced intensity of wear compared to the extensive wear-out surface observed at conditions. The optimized conditions are validated and recommended to industry personnel for reference
Elastic-viscoplastic deformation models of salt rocks
Full text linkResults of secondary creep tests for salt rock specimens were mathematically described. Elastic-viscoplastic modeling of viscous properties of salt rocks was based on elastoplastic models using a non-associated Mohr-Coulomb plastic flow and an associated volumetric yield criterion. In combination with these models the one-parameter Bingham and Duvaut-Lions as well as the two-parameter Perzyna and Perić viscoplasticity laws were analyzed. It’s been found that all laws being considered reflect an increase in longitudinal deformation of salt specimens during creep. It should be noted though that the yield criteria combined with the Perić law are characterized by relatively simple, stable parametric support and acceptable description of steady-state creep. The use of viscoplastic deformation model makes it possible to point out the fracture regions formed during creep according to a specified strength criterion
Correlation coefficients of vibration signals and machine learning algorithm for structural damage assessment in beams under moving load
Full text linkThis paper presents a novel method of assessing structural damage in beams exposed to moving loads via acceleration signals through experimental studies. In this study, beams are supported on both ends, and their dynamic response to moving loads is assessed. The raw signal has been improved using a random decrement technique. Take measurements from different locations and calculate correlation coefficients between them, then use these as features to evaluate the structure. In order to create a reliable and potential framework for predicting damage efficiently, these features are used as input variables to the machine learning model. The proposed methodology exhibits promising results in accurately discerning and predicting damage in beam structure. It demonstrates a high level of precision to subtle changes in structural integrity when trained by machine learning on the statistical feature extracted from acceleration signals. As a result of this research, methods for detecting structural damage can be made more reliable and efficient by employing machine learning techniques. Additionally, structures operating in dynamic environments can benefit significantly from the proposed methodology
Metastability, adiabatic shear bands initiation and plastic strain localization in the AMg6 alloy under dynamic loading
Full text linkNew conception of adiabatic shear bands (ASB) and adiabatic shear failure mechanisms are proposed as special type of critical phenomen, structural-scaling transition, in the ensembles of microshears, governed by the characteristic non-linearity (metastability) of stored (free) energy of solid with mesodefects. Corresponding free energy release kinetics provides experimentally observed ASB induced staging of plastic strain localization and transition to adiabatic shear failure. ASB staging follows to collective properties of microshears ensemble given by the self-similar solutions of evolution equation providing spatial-temporal microshears localization, momentum transfer and damage localization. The criticality of ASB induced plastic strain localization and failure allows us to avoid the discrepancy in the interpretation of ASB effects as thermo-plastic instability in the balance of the stored energy and structural DRX transformation. The microshear ensemble is considered as the second phase and initiation of collective modes provide different staging according to the metastability decomposition and ASB scaling properties following to the self-similar solutions. Self-similar nature of microshears collective modes providing the ASB dynamics is analyzed as the mechanism of steady plastic wave front unversality in shocked materials. The dynamic split Hopkinson pressure bar tests were conducted with AlMg6 alloy combined with “in-situ” imaging of temperature kinetics by CEDIP Silver 450M high-speed infrared camera with conclusion of the secondary role of thermoplastic instability at the ASB staging. The microstructural study performed by an electron microscopy revealed the correlated behavior of the ensemble of defects, which can be classified as a structural transition and precursor of ASB induced strain localization and failure. The modeling reflecting the links of self-similar solutions in microshear ensembles with relaxation properies and damage localization was applied for the comparative analysis of ASB staging and temperature dynamics given be the infrared imaging. 
Shapley additive explanation on machine learning predictions of fatigue lifetimes in piston aluminum alloys under different manufacturing and loading conditions
Full text linkVarious input variables, including corrosion time, fretting force, stress, lubrication, heat-treating, and nano-particles, were evaluated by modeling of stress-controlled fatigue lifetimes in AlSi12CuNiMg aluminum alloy of the engine pistons with different machine learning (ML) techniques. Bending fatigue experiments were conducted through cyclic loading with zero mean stress, and then experimental data was predicted by five different ML-based models. Moreover, when the optimal ML prediction model was found, it was analyzed using the Shapley additive explanation (SHAP) values method. Results illustrated that extreme gradient boosting (XGBoost) had superior data for estimations, with average training coefficients of determination of at least 63% and 90%, respectively for fatigue lifetime and its logarithmic value. The SHAP values interpretation of the XGBoost model revealed that fretting force, stress, and corrosion time were the most significant inputs in estimating the logarithm values of fatigue lifetimes, respectively
The influence of technological defects on the mechanical behavior of CFRP during buckling under compression based on DIC data and acoustic emission
Full text linkThe research focuses on examining the impact of technological defects, specifically "dry-spot" and "wrinkles," on the mechanical behavior and buckling resistance of structural composites. The investigation of the buckling phenomenon was carried out through a compression test on a thin plate fabricated from carbon-fiber-reinforced polymer (CFRP) laminate. This test was performed using a specialized fixture designed in accordance with ASTM 3410 standard. For the analysis, the study employed a three-dimensional digital optical system, Vic-3D, in conjunction with the AMSY-6 acoustic emission system.
The research showcases findings from acoustic emission signals that verify the shear-based mechanism of buckling in plates constructed from CFRP featuring "dry-spot" type defects. In the case of "wrinkles" defects, it was observed that transverse shear transpires at the stress concentration points created by the "excess" layers
Residual stress determination by blind hole drilling and local displacement mapping in aluminium alloy aerospace components
Full text linkThe determination of residual stresses by combining blind hole drilling and optical interferometric measurement of relief deformation is re-visited to evaluate its applicability to aerospace structures. The experimental methodology involves drilling a deep blind hole and evaluating the hole diameter increments in the principal strain directions using electronic speckle-pattern interferometry (ESPI). This is followed by the determination of the principal residual stress components via the solution of the inverse correlation problem. The study presents the pathway to overcoming one of the primary obstacles in residual stress determination, namely, the optimization of the measurement and interpretation procedures to obtain reliable results. It can be concluded from the analysis of the problem that the formulae connecting the raw experimental data and to the sought residual stress component values lead to a well-posed inverse problem. This makes it possible to obtain estimations of the measurement uncertainty. High density fringe patterns from ESPI provide a rapid and reliable method for residual stress determination, as illustrated using examples of approximately 160 MPa stresses in irregular zones of thick-walled structures