Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Behavior assessment of asymmetrical building with concrete damage plasticity (CDP) under seismic load
Get PDFAccording to the research conducted, the asymmetric multi-storey buildings are complex and suffer from severe damage caused by increased torsional response. This paper addresses the behavior assessment of setback building with irregularity in the plan under severe seismic event such as Kobe earthquake. Using three-dimensional model, the structure is subjected to seismic waves in the three directions through ground accelerations. Nonlinear dynamic procedures have been used by means time-history analysis method. The mechanical model describes physical nonlinear behavior with damage and plasticity showing the regions of cracking propagation, mainly the columns-beams connections and the whole column as well, corroborating the weak column and strong beam concept. The slabs did not present significant failures despite indicating damage regions on the borders of the first floors
Predicting Fatigue Crack Growth Behavior of Coalesced Cracks Using the Global-Local Superimposed Technique
Get PDFThe S-version Finite Element Method (FEM) is known as a global-local superimposed approach that consists of two separate meshes referred to as global and local cracks. The relationship between the energy release rate and the Stress Intensity Factor (SIF) is evaluated to characterize the growth behavior of the fatigue cracks. The SIF is determined using the Virtual Crack Closure Method (VCCM). The cracks propagated in the direction of the loading before coalescing into a single crack. Each crack begins with a length of 10mm and a depth of 3mm. After the crack coalesces, the diameter of the surface crack before it breaks is 28mm, whereas the depth of the crack is 5.3mm. The V-shaped surface crack forms quickly after coalescence occurs and continues to propagate into a massive semi-elliptical surface crack before finally breaking. The result was validated and compared between S-version FEM and the analytical solution. The behavior of the fatigue crack growth shows a good agreement between both methods with small errors. The result indicates that the Root Mean Square Error (RMSE) values before coalescing are 0.1496 with 0.6, and after coalescing is 0.4, the RMSE value is 0.1665. Therefore, it can be stated that the S-version FEM approach can predict the growth of fatigue cracks
Study of the slant fracture in solid and hollow cylinders: Experimental analysis and numerical prediction
Get PDFThis paper is devoted to the numerical and experimental study of ductile fracture in bulk metal forming of the 2017A-T4 aluminum alloy. From an experimental standpoint, the ductile fracture of the 2017A-T4 aluminum alloy is investigated under compressive load. Two cross-sections of solid and hollow specimens are considered. The mechanical behavior and the microstructure of the 2017A-T4 aluminum alloy were characterized. It is found that the well-known barrel shape is obtained when a compressive load is applied. Analyses of fracture topographies show a ductile fracture with dimples under tension and coexistence of ductile fracture with dimples and slant under compression. The classical physically-based Gurson-Tvergaard-Needleman (GTN) model and its extension to incorporate shear mechanisms to predict failure at low-stress triaxiality are considered. These two models have been extended to take into account the thermal heating effect induced by the mechanical dissipation within the material during the metal forming process. The two models have been implemented into the finite element code Abaqus/Explicit using a Vectorized User MATerial (VUMAT) subroutine. Numerical simulations of the forging process made for hollow and solid cylindrical specimens show good agreement with experimental results. In contrast with the GTN model, the modified GTN model incorporating shear mechanisms can capture the final material failure
Artificial neural network based delamination prediction in composite plates using vibration signals
Get PDFDynamic loading on composite components may induce damages such as cracks, delaminations, etc. and development of an early damage detection technique for delaminations is one of the most important aspects in ensuring the integrity and safety of composite components. The presence of damages such as delaminations on the composites reduces its stiffness and further changes the dynamic behaviour of the structures. As the loss in stiffness leads to changes in the natural frequencies, mode shapes, and other aspects of the structure, vibration analysis may be the ideal technique to employ in this case. In this research work, the supervised feed-forward multilayer back-propagation Artificial Neural Network (ANN) is used to determine the position and area of delaminations in GFRP plates using changes in natural frequencies as inputs. The natural frequencies were obtained by finite element analysis and results are validated by experimentation. The findings show that the suggested technique can satisfactorily estimate the location and extent of delaminations in composite plates
Influence of Quenching Agents on Mechanical, Wear, and Fracture Characteristics of Al2O3 / MoS2 Reinforced Al-6061 Hybrid Metal Matrix Composite (MMCs)
Get PDFAluminium (Al) based composites enhance the mechanical and wear behavior by heat treatment. The quenching factors like cooling agent, cooling rate and temperature of cooling are expected to influence the hardness, tensile, and wear behavior of the Al MMCs. This research shows the outcomes of a sequence of experiments to find the wear and mechanical behavior of the Al6061-Al2O3-MoS2 hybrid composites are quenched with different quenching agents. Hardening of the developed hybrid composites was carried out at 510ºC for the time period of 2 hours. Later, the same composite samples were quenched in ice cubes and water separately. Finally, age-hardening was done at 180ºC temperature for 4 hours and then the samples were cooled under room temperature. Heat treated hybrid composites were subjected to evaluate the hardness, tensile, and wear behavior. The outcomes reveal that the heat treatment significantly enhances the wear and mechanical behavior of hybrid composites. High mechanical strength and improved wear characteristics were observed in the hybrid composites which were quenched using ice cubes. The fractured surface of the tensile test samples and the wornout surface of wear test specimens were studied using a SEM analysis
Numerical Analysis of Reinforced Concrete Circular Columns Strengthening With CFRP under Concentric and Eccentric Loadings
Get PDFThe purpose of this study is to explore the numerical behavior of circular RC short columns with different degrees of confinement with CFRP (0%, 25%, 50%, and 100%) wraps under concentric and eccentric loading. The numerical analysis carried out by using an improved concrete plastic-damage model (CDPM) implemented in ABAQUS software for finite element (FE) analysis. The FE model simulated a total of twenty-four numerical specimens. The findings were matched to published experimental test results in the literature. The findings of the FE model and the experimental data were good similar. As a consequence, the model was found to be valid. The numerical results shows that as load eccentricity increased, the load carrying capacity of columns decreased for unconfined specimens, whereas the decline in strength for confined specimens becomes limited as the degrees of confinement ratio increased. In addition, increasing the CFRP confinement ratio improves the column's load-bearing capability at the same load eccentricity
Improvement of crack tip position estimation in DIC images by image processing methods
Get PDFThe study presents and compares an application of two procedures to identify the crack tip location in PVC Sent samples under a uniaxial tensile test based on the image processing method.
An IDS camera captures several photos of the PVC surface as part of the image analysis procedure. All relevant data on crack initiation and propagation is collected and assessed using ImageJ software using image processing methods for detecting cracks. However, the second procedure involves a developed algorithm detecting the discontinuity using digital image correlation (DIC) measurement. Although, because of the experimental conditions, the acquisition of images by the digital camera is never perfect. This noise comes from several sources, including the digital camera, image distortion due to lens magnification or lens angle, the shape and size of the pattern, and electronic noise; ... This article discusses image enhancement methods to overcome these objectionable characteristics using and comparing several filters: Gaussian, median, and Unsharp Mask filters. The performance of the Gaussian filter is better than the Median and Unsharp mask filters. This research demonstrates that DIC is an effective technique for monitoring deformation and understanding the failure mechanism with the best-suited filter
Elastic surface crack interaction and its engineering critical assessment within the framework of fitness-for-service standards
Get PDFIn real industrial conditions, it’s common to witness the interaction of multiple cracks such that their stress fields and crack driving forces are disturbed. For coplanar cracks, a greater hazard is expected because of the amplification phenomenon. FFS standards deal with this by proposing interaction rules and idealizing a single bonding flaw for the FAD methodology to be used. The goal of this paper is to analyze the effectiveness of this standards methodology considering twin surface semielliptical cracks on a plate under mode I loading on the interaction range using FE analyses. Results confirm that the amplification phenomena due to the interaction are higher on the interacting crack tip and progressively higher as the coplanar horizontal distance decreases. The loss of constraint was observed to decrease as the coplanar horizontal distance decreased, but little change was observed regarding its parametric angular position. A higher amplification was found at the coplanar horizontal distance on which crack interaction is to be considered meaningful, which indicates inconsistency regarding the interaction criteria used on FFS standards. To conclude, the engineering critical assessment of the bonding flaw proved to be over-conservative as the remaining operational life was observed on the assessment of the interacting flaws
Web post-buckling strength of thin-webbed cellular beams using carbon PFRP profiles
Get PDFCurrently, cellular steel beams are widely used by structural engineers and major companies due to their useful structural applications and serviceable performance. However, these types of steel beams are susceptible to different states of instability and failure mechanisms such as web post-buckling. The aim of this paper is to investigate the effectiveness of using externally bonded pultruded carbon fiber (CFRP) profiles for the strengthening of web post-buckling in thin webbed cellular beams as an alternative to the typical welding technique of reinforcement. A proposed numerical model created with the finite element software ABAQUS capable of capturing the de-bonding and fracture along the adhesive layer between steel and CFRP has been validated using published experimental results. The suggested numerical model is then used to simulate the parametric analysis of using pultruded CFRP T and U sections to strengthen six cellular beams of various sizes. It was found that this novel technique was able to prevent the web post-buckling failure mode or delay it to a grater load with a considerable strength enhancement comparable to control beams
Evaluation of Tensile properties of FRP Composite Laminates under Varying Strain Rates and Temperatures
Get PDFThe present investigation deals with the characterization of tensile behavior of various Fiber Reinforced Polymer composites under Thermo-Mechanical loading. Five different types of Uni-Directional (UD) composites of Carbon, Glass, Carbon-Glass hybrid and Metal Laminates of Carbon & Glass were tested for tensile behavior. Tensile tests were performed at strain rates of 10-3, 10-2, & 10-1 s-1 at Room Temperature,250 0C and 450 0C. Stress-strain relations reveal the strain rate and temperature sensitive behavior of composites. Glass, Glass-Carbon, Glass-metal epoxy composites showed higher peak tensile stress under room temperature with varying strain rates as compared to neat carbon epoxy composites. Also, high strain rate tensile properties such as peak stress and peak strain of Glass-Carbon-Epoxy specimens were 26%, and 60% higher than that of the neat carbon epoxy composite. The failure mechanisms of both the composites were analyzed through scanning electron microscopy. The composites mainly failed due to matrix crack within elastic range under room temperature and failed with significant plastic deformation of matrix and fibers under test temperatures 250 0C and 450 0C. Finally, this study reveals that the continuous phase of metal layer embedded between Uni-Directional Glass and Carbon fiber, based composite system can be tailored to act as an energy-absorbing material system under both elastic and plastic stress strain regimes