Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Multidisciplinary characterisation, weathering patterns, and durability assessment of stone blocks for the conservation of Tamentfoust fort (ex. Rusguniae) in Algiers.
Full text linkThis study investigates the physico-mechanical properties, mineralogical composition, deterioration processes, weathering patterns, and durability of building materials in the Ottoman Fort of Tamentfoust, Algiers, to inform heritage conservation strategies. Stone block samples were taken from a highly damaged wall and, the mechanical and physical characterisation was carried out with through laboratory and on-site methods. These methods included destructive tests (compressive and flexural strength) and non-destructive techniques (Schmidt hammer rebound, ultrasonic pulse velocity, thermal imaging, density, porosity, and capillarity coefficients. Mineralogical and petrographical analyses were conducted using X-ray diffraction (XRD) and X-ray fluorescence (XRF), while durability was evaluated through sodium chloride crystallization and hydrogen chloride ageing tests, with scanning electron microscopy (SEM-EDX) analysing microstructural properties. Weathering forms were assessed and documented using 3D laser scanning, thus generating a weathering mapping for the most damaged facade. The results revealed two stone types: one with high porosity, low strength, and poor durability, and another with high compactness and excellent durability. These findings provide critical insights into material behaviour, enabling tailored preservation strategies for the fort and contributing to the broader field of heritage conservation
A novel approach to estimation of residual strength of laminated polymer composites under compression after impact
Full text linkThis work is dedicated to the experimental study of the influence of preliminary dynamic loading on the residual strength of the laminated polymer composite under compression. A series of low-velocity transverse drop-weight impact tests in a wide range of energies was carried out, followed by quasi-static compression of composite specimens with two reinforcement schemes [0/90]n and [±45]n. Nonlinearity of the obtained dependences of residual static strength on the energy of preliminary dynamic loading has been discovered. It has been noted that there are three characteristic stages on the diagram of fiberglass laminate’s impact sensitivity: area of impact insensitivity; area of reduced bearing capacity; area of achieving the minimum bearing capacity. The identified patterns are consistent with the data on the response of specimens during impact, as well as with specimens’ surface damage after dynamic loading. An anisotropy of the composite's impact sensitivity has been discovered. A novel approach to estimation of residual strength of laminated polymer composites under compression after impact and determination of impact sensitivity thresholds based on the use of mathematical models has been proposed. A new model of residual strength has been developed and tested, its applicability for description of the mechanical behavior of composites with various reinforcement schemes has been demonstrated
A simplified nonlinear model for bamboo-reinforced concrete beams based on lumped damage mechanics
Full text linkBamboo’s renewability may justify bamboo-reinforced concrete (BRC) structures. For practical applications, the accurate description of BRC flexural behaviour is paramount. Lumped damage mechanics is an interesting alternative among some possibilities on nonlinear models since it is based on key concepts of classic fracture and damage mechanics. Therefore, this paper presents a novel lumped damage model for BRC beams. The model’s accuracy is tested with experiments found in the technical literature. Regarding the analysed experiments, the proposed model presents well-fitted results. Finally, the proposed model is feasible for practical applications, even considering structural reliability analysis like Monte Carlo, since it is easy to implement and presents low computational effort
Experimental test on 3D-printing components for Architectural Restoration
Full text linkThe paper investigates the use of 3D-printed components made from Polylactic Acid (PLA) for the restoration of architectural and ornamental elements, focusing on architectural/structural components. The material PLA was chosen for its potentiality in respecting the principles of restoration, recognizability, reversibility and minimum intervention, thanks its visual appearance, very different from typical construction materials, biodegradability and affordability. The paper represents an exploratory study aimed to derive the characteristics of 3D-printed PLA components thought tensile tests on dog-bone samples, and to analyze the behavior of structural components, thought tensile and bending tests on small truss beam samples. Unlike previous works mainly oriented towards aesthetic reproduction, this study focuses on the mechanical performance of PLA components designed for structural integration in restoration projects. The results show that the 3D-printed PLA components exhibit an average tensile strength of 44 MPa and an average Young’s modulus of 1270 MPa, values consistent with literature for fully dense PLA prints, and peak loads of about 6.4 kN in tension and 5 kN in bending for truss elements. Furthermore, this study provides data useful for future numerical modelling of 3D-printed structural elements in PLA, aimed at predicting their structural performance and supporting the design phase
Prediction of the tensile strength of FDM specimens based on Tsai Hill criteria
Full text linkThis study investigates the mechanical behavior of 3D-printed polyethylene terephthalate glycol (PETG) polymer specimens subjected to tensile and shear testing, with a particular focus on the influence of raster orientation and shell contour. Specimens were fabricated using Fused Deposition Modeling (FDM) at three raster angles (0°, 45°, and 90°) and tested using both a mechanical extensometer and a Digital Image Correlation (DIC) system.
The results indicate a significant influence of raster orientation on tensile and shear properties. 0° specimens exhibited the highest tensile strength, as the filament alignment was parallel to the loading direction. In contrast, 45° specimens demonstrated more ductile behavior. While the shell contour had minimal effect on 0° and 45° specimens, it enhanced stiffness and ductility in 90° specimens.
Furthermore, the Tsai-Hill criterion was applied to predict the tensile strength at a 45° orientation.
These findings contribute to a deeper understanding of the anisotropic behavior of 3D-printed materials and highlight the importance of raster orientation in optimizing mechanical performance
Parametric study on the effect of anchor’s geometry on the stress distribution and crack initiation direction in a concrete body
Full text linkThis work deals with investigations of the stress field distribution around a steel anchor embedded in a concrete. Tensile loading - pulling force of the steel anchor is considered, which is very often connected to concrete cone failure. Numerical simulations via finite element method were performed to obtain results for a large extent of geometrical configurations. In accordance with the basic idea of the maximum tangential stress criterion, the angle where this stress reaches its maximum was determined. The influence of selected geometrical parameters of the system on these angles was analyzed and it was found out that they can significantly affect the angle of the maximum tangential stress and consequently the shape of the cone failure. It was observed that the circumferential crack propagation is flatter with increasing length of the steel anchor’s embedment and with increasing anchor’s outer radius. The results obtained numerically agree sufficiently with experimental results especially when the crack direction is compared. Conclusions presented within this research are important for both design and assessment of anchor/concrete systems subjected to tensile loading
An experimental study into the net cross-sectional failure of damaged plates with holes for different steel grades and temperatures
Full text linkThis study reports an experimental investigation on the applicability of the net cross-sectional resistance rules of Eurocode 3 for steel plates with different bolt-hole configurations and steel grades, when relatively small fatigue cracks are present at the edge(s) of the holes. Previous studies have confirmed that the considered design rule is on the safe side. Moreover, part of this safety margin accounts for the potential occurrence of relatively small fatigue cracks.
Two steel grades are considered, namely S275JR and S700MC. Therefore, in addition to previous studies, a relatively high steel grade is considered. Moreover, some tests were carried out on cooled specimens to get an impression of the effect of low temperatures on the failure mechanism. The experimental results demonstrate that relatively small cracks (<1 mm) have a negligible practical influence on the measured ultimate resistance of the plates. Furthermore, the failure assessment diagram is found to be suitable to predict the critical condition in the presence of cracks with length and shape as found in the experiments, also for relatively high steel grades
Coupling crystal plasticity and microstructure in SLM manufactured 316L parts: model development and experimental assessment
Full text linkAdditive manufacturing is extensively used for the production of complex-shaped parts from metals and polymers. Because of the influence of various physical factors, the structure of materials processed under different processing conditions may vary considerably, altering their properties. Application of a multi-level crystal plasticity approach helps explicitly describe the structure of materials at different scale levels. It makes possible the evaluation of basic mechanical properties of the samples fabricated by layer-wise laser melting. In this work, a two-level statistical constitutive model is suggested for calculation the main mechanical characteristics (elastic modulus, offset yield stress) of the AISI 316L stainless steel samples produced by selective laser melting. The model explicitly considers the grain structure and texture of metal parts, twinning defects, and residual stresses in the as-build structure of materials. Under predefined loading conditions, the primary mechanism of inelastic deformation is through intra-granular slips of edge dislocations. Thus, the mechanism of material hardening has been described by a modified form of the Hall-Petch law, where the boundaries of grains and original twins are counted as effective barriers to dislocations. All model parameters are properly identified based on own experimental data and the data found in literature. The elastic moduli and yield stresses are calculated at different residual deformations and are found to be in fair agreement with experiments
Studying the fracture surface of brass CuZn37 and aluminum 1100 and their relationship with formability in Single Point Incremental Forming
Full text linkSingle Point Incremental Forming was conducted on Aluminum1100 and Brass CuZn37 to form a hyperbolic truncated pyramid with varying wall angles until the fracture occurs. The formability of the specimens in terms of fracture depth and maximum wall angle was measured; and scanning electron microscopic photography was used to capture the fractured surface of the specimens to perform a fractography analysis. In each specimen's fracture surface, the identification of the voids shape, calculation of the void volume fraction (VVF) and void size, and the classification of the voids have been performed to allow for the identification of the relationship between formability and the microstructure of both materials. Also, the effect of the input parameters on this relationship has been identified. The results showed that when the VVF and the average void size in the fractured surface increase, the formability of the material increases. And that the optimal SPIF conditions that increase void volume fraction and formability in CuZn37 occur when all input parameters are set to medium levels. For aluminum 1100, the optimal conditions have a low level of feed rate, a high level of tool speed and sheet thickness, and a medium level of tool diameter and step size
Impact of tool rotational speed on friction stir welded joints of AA2014-T6/AA5052-H32: synthesis, microstructural, mechanical and fractographic behaviour
Full text linkThis study examines the changes in microstructure and mechanical properties of friction stir-welded (FSW) dissimilar joints between AA2014-T6 and AA5052-H32 aluminium alloys, with an emphasis on optimizing tool rotation speed for enhanced joint quality. FSW is performed at three different tool rotation speeds (860, 1160, and 1460 rpm) while maintaining a constant welding speed and tool tilt angle of 40 mm/min and 1°, respectively. The joint created at an optimal rotation speed of 860 rpm exhibits outstanding mechanical properties, with an ultimate tensile strength (UTS) of 211 ± 1.0 MPa, a yield strength of 181 ± 1.5 MPa, and an elongation of 16.1%. The joint efficiency, in comparison to the aluminium alloy AA5052-H32, is 93.8%, indicating minimal strength loss relative to the parent material. Vickers hardness tests across the weld cross-section reveal a maximum hardness of 156 ± 1.5 HV in the stir zone, closely matching the hardness of the stronger AA2014-T6 base metal. Fractographic analysis of the FSW joint made at 860 rpm indicates a predominantly ductile failure mode with micro-dimple fracture surfaces, whereas higher tool rotation speeds exhibit brittle characteristics with circular voids and tear ridges