Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Effect of fracture energy estimation on the predictions of mode II behavior of bonded joints using cohesive zone models
Full text linkFracture behavior of adhesive joints is an important topic in structural design of new structural elements or in retrofitting of existing ones. The mechanical models available in literature capable of predicting the failure mode of these junctions are mainly formulated within the cohesive zone model (CZM). Direct approaches for identification of CZM parameters in pure mode II of bonded joints, based on different modelling of strain energy release rate (SERR), are presented. The mode II SERR was determined from experimental results on end notched flexure (ENF) tests. Digital image correlation (DIC) analysis was used to evaluate the shear slip displacements of adhesive layer. The mode II cohesive traction-separation law was identified by numerical differentiation of SERR and best fit equation systems were adopted for an analytical description of cohesive interface behavior. Moreover, the obtained CZM laws were used for predicting the decohesion process by finite element analyses. Global and local responses of ENF test were compared with experimental data in terms of load-displacement and adhesive tangential displacement-time curves, respectively. A more accurate modelling of fracture energy resulted in a sounder agreement of prediction with experimental data
Size Effect in Concrete Beams: A Numerical Investigation Based on the Size Effect Law
Full text linkThe size effect significantly influences the structural design of concrete elements, particularly when applying fracture mechanics principles. As structural dimensions increase, a significant outcome of the size effect is the decline in both strength and ductility. To characterize concrete fracture behavior, various fracture mechanics models have been proposed, integrating material fracture properties that are unaffected by changes in geometry and size. Bažant’s size effect law explains this phenomenon based on the transition from ductile to brittle failure in geometrically similar specimens. When failure is delayed after crack initiation, the size effect is mainly influenced by the energy released during macro-crack propagation. Conventional experimental studies on this phenomenon have typically utilized two-dimensional geometrically similar specimens, though they are often limited by laboratory constraints. While experimental studies on notched concrete beams under three-point bending (TPB) exist, their size is often restricted due to practical challenges in handling large specimens and also numerical modeling of large-scale fracture simulations remains limited due to high computational requirements.
This research proposes an optimized finite element modeling approach to numerically examine the size effect on the fracture characteristics of notched concrete beams subjected to three-point bending (TPB). Beams with depths up to 1000 mm were analyzed using this approach. The numerical findings align well with experimental size-effect data from the literature, exhibiting the expected trends. Furthermore, fitting the results to Bažant’s size effect law demonstrated a strong correlation, validating the accuracy of the proposed numerical model
Effect of the stress state on ultimate strain energy density in the failure of reinforced epoxy resin
Full text linkEpoxy resin reinforced with 10% of TiO2 and pure epoxy resin are taken to exemplify the possibility of constructing a fracture locus for engineering organic polymers as a dependence of ultimate strain energy density in cohesive failure on the stress triaxiality factor in the range and the Lode–Nadai coefficient . The fracture loci are based on the results of compressive testing of cylindrical specimens, tensile and compressive testing of bell-shaped specimens, dishing of thick-walled cup-shaped specimens, shearing of oblique dog-bone-shaped specimens. The tests were performed at 25 and −50 °C. The obtained dependences are approximated by interpolation formulas, and they can be used to predict the failure of structural components made of organic polymer materials mechanically affected under conditions of a complex stress state
Optimization of austenitic and ferritic steels for deep drawing. Part 2: FEM analyses with damage development.
Full text linkDeep drawing of sheet metal is a crucial industrial process due to its high productivity and low cost per unit produced. Stainless steels are ideal for this process, given their high deformability compared to other steels. Despite its apparent simplicity, understanding how the material deforms during deep drawing is essential to predict the final result. From this point of view, simulation via finite element modelling (FEM) represents a rapid and cost-effective alternative to experimental testing. When properly calibrated, FEM models allow for analysing stress and strain distribution, identifying areas at risk of failure, calculating final wall thickness, and optimizing die geometry. This research led to the development of a FEM model capable of simulating deep drawing under different operating conditions, steel types (AISI 304 and AISI 430) and lubrication. The model was calibrated and validated by comparing the numerical results with those obtained from a series of Erichsen tests. To ensure the accuracy of the true stress-strain curves, the steels were thoroughly characterized through tensile tests, Erichsen tests, and metallographic analyses. A specific method was also developed to represent the true stress-strain curve beyond necking, up to physical failure of the steel. The experiment was conducted according to the principles of DoE (Design of Experiments), combined with statistical analysis using the ANOVA technique
Optimizing different damaged reinforced concrete corbel characteristics utilizing CFRP sheets
Full text linkConcrete corbels are short cantilever constructions that may lose their strength over time because of loads that happen over and over again. As an external bonding method for reinforcement, carbon fiber-reinforced polymer (CFRP) strips are utilized to improve performance. This study examines the influence of CFRP strips on the reinforcement and repair of conventional concrete corbels by concentrating on ultimate strength, performance under monotonic loads, and the effects of varying damage ratios during restoration. As part of a study project, nine double-concrete corbels with the same size and reinforcement had to be manufactured and tested. The samples were split into two groups: those with strip wrapping and those with side wrapping. Each group had three corbels that had already been damaged, one corbel that had been reinforced, and control specimens that had not been repaired. The results showed that side-wrapped corbels with CFRP reinforcement exhibited a 19.72% (SCS-0-1) improvement in strength and a 13.73% (RCS-50-1), 18.35% (RCS-60-1), and 4.15% (RCS-70-1) increase in ultimate load. Strip-wrapped corbels showed improvements of 9.86% (RCST-50-2), 5.44% (RCST-60-2), and 0.51% (RCST-70-2), whereas strengthening (SCST-0-2) showed an improvement of 19.72%. Also, specimens wrapped in CFRP showed less ultimate deflection than their un-strengthened counterparts at the same damage levels, which shows that they perform better and last longer
Modeling of the transition from transgranular to intergranular fracture at elevated temperatures in EI698 nickel alloy
Full text linkIn this study, an efficient computational method for modeling the transition from transgranular to intergranular fracture mechanisms based on phase field fracture theory is discussed. Structural heterogeneity of the material is modeled on the basis of Voroni diagrams. Parameters characterizing the mechanical properties of the material for the intergranular and transgranular space are the same for models of continuum mechanics. The location of crack initiation and the crack path in the proposed method controlled by the difference in the values of the critical energy release rate for the intergranular and transgranular spaces for the phase field model. The source code of the created and used finite element is an open source project and available to download from https://github.com/Andrey-Fog/ANSYS-USERELEMENT-PHFLD. The obtained results correlate well with previously conducted fractographic studies
The static and modal analysis of concrete tank filled with water
Full text linkTanks and reservoirs are structural systems designed for storing various liquids, gravels, granular or other bulk materials. Special attention is usually given to the potable water storage. Regarding the increasing scarcity of clean water and the recent lack of it in some regions worldwide, it is essential that these structures have to be carefully analysed and properly designed. Water tanks are significant architectonic works as well. They are typically constructed from steel or reinforced concrete, and most commonly, they adopt the cylindrical shape. Considering their future utilization and regarding other essential circumstances related to the site of their planned placement, they can be situated on the ground, above the ground, partially buried, or fully underground. Due to the expected static and dynamic effects, both static and modal analysis have to be carried out prior to building them up, even within the designing process.
This paper provides the numerical analysis of a cylindrical surface-mounted water reservoir by using the Finite element method in Ansys Workbench. The hydrostatic pressure simulating the water acting to the wall was imposed. The static and modal analysis were carried out for empty and fully filled tank. Mutual comparison of various approaches is provided
Numerical simulation of crack propagation in clinch joints
Full text linkThe mechanical clinching process can be used for the load-bearing structures of thin-walled steel frame halls. Numerical simulation of crack propagation in a clinching joint using finite element method (FEM) software is an important tool for the analysis and prediction of the behavior of materials under load. This study focuses on clinch joints that must withstand high loads and repeated load cycles. Crack propagation in these joints can lead to failure of the entire structure, therefore it is important to understand the mechanisms of crack propagation and predict their behavior. Using specialized software, a numerical simulation of crack propagation was prepared, including modelling of joint geometry, definition of material properties and application of loads. The simulation provides valuable information on the crack propagation process, which allows optimization of the behavior of the whole structure and the reliability of the clinch joints
Experimental and 3D numerical analysis on the effect of specimen thickness on fracture toughness of Al6061-SiC-cenosphere Hybrid composites
Full text linkThis study examines the fracture toughness of Al6061 alloy-based hybrid composites reinforced with silicon carbide particles and cenosphere microspheres. Aluminum alloy Al6061 is widely utilized in structural applications due to its balanced mechanical properties, and its hybridization with SiC and cenosphere reinforcements enhances its performance under critical loading conditions. The effect of specimen thickness on fracture toughness was examined by fabricating compact tension specimens in accordance with ASTM E399 standards, with thickness-to-width ratios ranging from 0.2 to 0.7. Controlled fatigue cracks were introduced, and both experimental testing and finite element simulations were conducted to assess the critical stress intensity factor and crack propagation behaviour across different thicknesses. Results show that the fracture toughness is constant after the B/W ratio of 0.5 and above, states as plane strain fracture toughness. The 3wt% SiC and 6wt% cenosphere in Al6061 shows the highest fracture toughness up to 15.56 MPa√m, due to the effective stress distribution and interfacial bonding. The fractography using the scanning electron microscopy reveals that particle debonding is major failure mechanism, with microcracking in 3wt% cenosphere composites and crack deflection and stress transfer at high reinforcement contents. Experimental results were well matched with the simulation model with ±10% differences, proving its validity
Influence of Silicon Nanosheet (SiNS) on the Toughness of Biphasic Calcium Phosphate (BCP) Composites
Full text linkRecent developments in the field of replacing and generating human tissues have led to a renewed interest in finding alternative materials or composites that enhance the development of these technologies. Therefore, the main goal of the current study was to investigate the effect of adding a nanomaterial with a two-dimensional structure called silicene, which is also known as silicon nanosheet (SiNS) on among the best leaders in biomaterials which are HA and TCP. This investigation has examined the fracture toughness property and flexural strength to explore the importance of adopting the nanomaterials. Through this paper, silicene has been synthesised using chemical reactions and added in various weight ratios of (1,3, and 5) % to BCP composites which are produced with various weight ratios of HA and TCP. Based on the findings, adding SiNS by a percentage ranging from 1% to 3% to the BCP composites increased their toughness, and flexural strength from 33 to 87.64 %, and 15 to 60 % respectively. However, as some percentages climbed and others fell in toughness or flexural strength, the results of the samples containing 5% of SiNS started to differ somewhat.
This is due to that the filler (SiNS) has the capacity to prevent cracks from growing while also preserving crystalline tissue, which makes it a crucial defence against fracture propagation. This increase gave sufficient motivation to adopt this composition and addition in biomedical applications