Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Assessment of fluidity retention, mechanical strength and cost production of blended cement self-compacting concrete using the concept of a performance index
Get PDFConstruction industry consumes a large amount of natural resources and energy and produces high amount of CO2 emissions and waste materials. For more sustainable construction industry, various waste materials are used as natural aggregates substitution or as cement replacement materials. In this paper, marble powder (MP) is used as a substitution to ordinary Portland cement and its effects on some fresh and hardened properties of self-compacting concrete (SCC) are investigated. The tests at the fresh state were slump flow, L-box and sieve segregation. To assess the fluidity retention, slump flow loss was measured after 30, 60 and 90 minutes. At hardened state, two tests were realized: compressive strength and static segregation. The results indicate that adding MP improved the fresh properties, but decreased the compressive strength of SCC. Adding MP allows to maintain the fluidity of SCC until 90 minutes. Production cost can be reduced by using MP. The performance approach showed that a substitution level of MP of 20% is adequate to produce an eco-efficient SCC with high fluidity and acceptable strength
Crack suppression by natural fiber integration for improved interlaminar fracture toughness in fiber hybrid composites
Get PDFIn this paper, the effect of integration of natural fibers in UD carbon fiber is studied. The integration of natural fibers in carbon fiber is made via intra fiber hybridization. Natural fiber hybrid composite samples were prepared for Mode I and Mode II fracture tests. XRD analysis was done for the chosen natural fibres to know the crystallinity index and then compared with Carbon and Glass fibres. The fracture test experimental results, revealed that the effect of Jute fiber integration in UD Carbon epoxy composite was found significant in getting relatively good Mode I and II fracture toughness at the crack initiation without losing its stiffness. In addition to this Kenaf Carbon epoxy composite indicated better crack suppression with 30% higher propagation toughness values as compared other hybrid combinations and pristine composites. It is observed that integration of jute fibers in UD carbon epoxy composites was significant in achieving good mode I and mode II fracture toughness at the crack initiation without losing its stiffness and also kenaf carbon epoxy composites indicated better crack suppression with 30% higher propagation toughness as compared to other hybrid combinations used
Effects of residual stresses on interlaminar radial strength of Glass-Epoxy L-bend composite laminates
Get PDFThe built-in heterogeneity of the composite laminates has been exploited to tailor the stiffness and strength requirements of modern structures to meet the specific functional demands. However, the non-homogeneity in these composites is the root cause for most of their failures. One of the undesirable consequences of the inherited heterogeneity is the development of cure-induced stresses during composite manufacturing. This work aims to investigate the influence of process-induced stresses on interlaminar radial strength in curved composite laminates. Glass-Epoxy (GE) laminates of two different thicknesses were prepared by hand lamination technique using V-shaped tooling and cured under room temperature. The state of residual stresses in GE laminates is varied by post-curing these laminates at different temperatures. Curved bending strength (CBS) and corresponding interlaminar radial stress for delamination of L-bend laminates were evaluated experimentally using four points bending test. The residual stress profile in each GE laminate is experimentally characterized by employing the Slitting method. The results indicate that the residual stresses have a negligible effect on the critical stress for initial delamination in GE laminates. But, the critical stress for delamination was found to be independent of the laminate thickness and increased with higher curing temperatures. The delaminated surfaces of L-bend laminates were studied using a scanning electronic microscope (SEM). The enhancement in the critical stress due to post-curing can be attributed to the improved fiber-matrix interfacial bonding with higher curing temperature
Hybrid phase-field modeling of multi-level concrete gravity dam notched cracks
Get PDFPhase-field models have become a powerful tool to simulate crack propagation. They regularize the fracture discontinuity and smooth the transition between the intact and the damaged regions. Based on the thermodynamic function and a diffusive field, they regularize the variational approach to fracture that generalizes Griffith’s theory for brittle fracture. Phase-field models are capable to simulate complex fracture patterns efficiently and straightforwardly. In this paper, we introduce a hybrid phase-field approach to simulate the crack propagation in laboratory-scale and life-scale structures. First, we apply our methodology to the three-point bending test on notched laboratory beams. Second, we simulate the fracture propagation in a life-size structure: the Koyna gravity dam. We account for the pressure load inside the fracture, and we study the effect of the position and number of initial fractures in the upstream face and the value of the Griffith critical energy release, on the fracture propagation under a flood event. The position of the fracture plays an important role in the final fracture pattern and crest displacements, whereas the value of the Griffith critical energy release alters the onset of the fracture propagation. We conclude that phase-field models are a promising computational tool that may be applied to real engineering problems
Observing the simulation behaviour of Magnesium alloy metal sandwich panel under cyclic loadings
Get PDFThis study aims to investigate the delamination effect of a metal sandwich panel using a four-point bending simulation under continual spectrum loading. The most recent core designs of the sandwich panel have a cavity that can increase vulnerability in terms of bonding strength under constant cyclic loading. The sandwich panel is simulated under constant cyclic loading using different core design configurations, which are rounded dimple, hemispherical dimple, and smooth surface core design. There are two types of conditions used; no pre-stress and pre-stress loads with variable stress ratios based on Gerber stress life theory. Results showed that dimple core design enhanced mechanical behaviour and fatigue life performance about 33% and 5%, respectively, compared to the sandwich panel with a smooth surface core design. It is highlighted that modification on the surface of core design could be beneficial to enhance the bonding strength performance of sandwich panels and prevent early delamination under extreme conditions such as constant cyclic loading. This study is beneficial to enhance the bonding strength for sandwich panels against extreme conditions such as high impact load and continuous cyclic load
Multiple linear regression parameters for determining fatigue-based entropy characterisation of magnesium alloy
Get PDFThis paper presents the development of the multiple linear regression approach based on the stress ratio and applied load that was assessed using entropy generation. The energy dissipation is associated with material degradation to determine the fatigue life with consideration to the irreversible thermodynamic framework. This relationship was developed by predicting a complete entropy generation using a statistical approach, where a constant amplitude loading was applied to evaluate the fatigue life. By conducting compact tension tests, different stress ratios were applied to the specimen. During the tests, the temperature change was observed. The lowest entropy generation was 2.536 MJm-3 K-1 when 3,000N load with a stress ratio of 0.7 was applied to the specimen. The assumptions of the models were considered through graphical residual analysis. As a result, the predicted regression model based on the applied load and stress ratio was found to agree with the results of the experiment, with only 9.3% from the actual experiment. Therefore, the entropy generation can be predicted to access the dissipated energy as an irreversible degradation of a metallic material, subjected to cyclic elastic-plastic loading. Thermodynamic entropy is shown to play an important role in the fatigue process to trace the fatigue life
Numerical Analysis of the Crack Growth Path in the Cement of Hip Spacers
Get PDFThe use of temporary hip prosthesis made of orthopedic cement (spacer) in conjunction with antibiotics became a prevalent method used for prosthetic infections remedy; consequently, this method makes bone cement (PMMA) more fragile. Hence, the necessity of reinforcement incorporation is crucial to strengthen the bone cement. In this study, the finite element (FE) method was used to analyze the spacers behavior. FE model using an implicit integration method was used to simulate the mechanical behavior of the spacer under static loading. In addition, the extended finite element method (XFEM) was also used to investigate the fracture behavior of the non-reinforced and reinforced spacers. The results of this numerical analysis showed that the simulated crack initiation and propagation were in a good accordance with in vivo radiography and in vitro experimental observations. The full-stem reinforcement of 8 mm using reduce significantly the stress intensity factor and, consequently prevent the spacer fracture effectively. The FE models developed in this study contribute to help mechanical designers and engineers for prostheses’ quality and durability improvement.
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Corrosion behavior of Shape Memory Alloy in NaCl environment and recovery maintenance in Cu-Zn-Al sysytem
No full textShape memory effect (SME) and the relation with corrosion behavior of Cu-Zn-Al Smart Memory Alloys (SMAs) were investigated using different techniques: Scanning Electron Microscopy equipped with an Energy Dispersive System, X-Ray Diffraction analysis, Electrochemical Test in NaCl solutions with different concentrations (0.035%, 0.35% and 3.5%), which simulate coastal conditions, mechanical characterization through tensile test and guided bend test.
SMAs are an important class of smart materials able to recover after deformation a pre-imposed shape through a temperature modification. These alloys show great potential, finding several applications in medicine and in different types of industry sectors (aerospace, architecture, automotive etc.). Cu-based SMAs, including Cu-Zn-Al alloys, have lower production costs with respect to Ni-Ti alloys as well as good possibility in seismic and architectural applications. A Cu-Zn-Al alloy with a theoretical composition of 25 wt.% Zn and 4 wt.% Al was produced by casting method.
The aim of this study is to characterize the microstructure, the mechanical properties and the corrosion behavior through different kind of standard corrosion tests of this alloy and to evaluate the effect of corrosion damage on the shape memory recovery capability through a combination of corrosion and thermos-mechanical cyclic test and SEM observatio
Delamination effect on the mechanical behavior of 3D printed polymers
Get PDF This study aims to assess the delamination effect and predict the evolution of damage in 3D printed specimens to investigate the mechanical behavior occurring due to the delamination of the layers of 3D printed thermoplastic polymers. Thus, additively manufactured ABS samples are subjected to tensile tests Made for different thicknesses of specimens by subtracting layer by layer.
The mechanical behavior of the layers and the adherence between the layers are studied in this paper. The deposition of the layers is modeled as a laminated material.
The delamination effect on the resistance of printed material is evaluated experimentally by comparing the mechanical characteristics of homogenously printed specimens, and laminated layers gathered together. Thus, the global resistance is reduced significantly due to the lack of adherence.
Besides, crack growth, and critical intensity factor investigation are based on damage and rupture mechanics theories.
Furthermore, the results allowed us to evaluate the energy behavior of the 3D printed material subjected to static loads and subsequently predict the evolution of the damage and find out the impact of layers' delamination. Indeed, we determined three stages of damage along with the critical life fraction leading to the failure of the specimen
Computer Vision Algorithm for the detection of fracture cracks in Oil Hardening Non-Shrinking (OHNS) die steel after machining process
Get PDFA variant of neural network for processing with images is a convolutional neural network (CNN). This type of neural network receives input from an image and extracts features from the image while also providing learnable parameters to effectively do the classification, detection, and many other tasks. In the present work, U-Net convolutional neural network is implemented on Jupyter platform by using Python programming for fracture surface image segmentation in Oil Hardening Non-Shrinking (OHNS) die steel after the machining process. The results showed that the fracture cracks can be validated by testing with higher accuracy