Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Fracture Load Estimations for U-Notched and V-Notched 3D Printed PLA and Graphene-Reinforced PLA plates using the ASED Criterion
Get PDFThis paper addresses the estimation of critical loads in FFF (Fused Filament Fabrication) printed polymers and composites containing notches. Particularly, the analysis is focused on the fracture load estimations of 39 PLA (polylactic acid) and 39 graphene reinforced PLA (PLA-Gr) printed plates containing two different types of notches (U- and V-notches) and combining different plate thicknesses and defect length to plate width (a/W) ratios. The addition of graphene (1 wt.%) increases both the yield stress and the ultimate tensile strength, also reducing the strain at rupture and, thus, generating a material whose behavior is closer to linear elasticity. Among the different assessment tools that may be used to estimate critical loads, this work applies the well-known Averaged Strain Energy Density (ASED) criterion, which compares the averaged strain energy over a certain control volume at the notch tip with the corresponding critical value, the latter being a material property. This approach has a linear-elastic nature, so its application to non-fully linear materials may require the use of specific corrections or calibrations. For the two materials analyzed here, PLA and PLA-Gr, it has been observed that the ordinary linear-elastic ASED criterion provides good estimations for the PLA-Gr material, whereas the pristine PLA, with more evident non-linear behavior, the obtainment of accurate results requires a previous specific calibration of the ASED material parameter
Effect of Granular Waste Compact Disc on Bond Strength between Steel Bars and Surrounding Concrete
Get PDFIn recent decades, researchers have tried to use waste materials as a partial or complete replacement of the gravel ingredients of concrete to reduce environmental impact. One of these materials is electronic waste. The problem of this disposal material, particularly outdated CDs and DVDs, has turned out to be serious. In this study, 36 pull-out cylindrical shape test specimens were used to conduct an ASTM C234-91A-compliant pull-out test to measure the bonding behavior and strength between three sizes of steel bars and concrete with different embedded lengths, including waste disc shreds (CD and DVD) as a partial substitute for fine aggregate. Four groups of modified concrete specimens with different percentages of disc shreds as partial replacements for sand were prepared. The ratio of cement:sand+disc:coarse aggregate:water was 1:2:2.5:0.4. The disc shreds were utilized to substitute partially for fine aggregate in four different weight percentages: 0%, 4%, 8%, and 12%; nevertheless, the cement-to-sand ratio was consistently 2. Results demonstrated that the bond strength is considerably influenced by the bar diameter and the disc shreds (CDs and DVDs) used as a partial replacement for fine aggregate. The bond strength behavior of the modified concrete with disc fibers is comparable with that of traditional concrete. The ACI-318 Code for the bond strength of ordinary Portland cement concrete was modified to calculate the bond strength of this new kind of disc concrete
Damage-failure transition in titanium alloy Ti-6Al-4V under dwell fatigue loads
Get PDFThe role of structural mechanisms responsible for the consequent staging of damage-failure transition as the combination and continuity of ductile and creep kinetics of the structure evolution and the modeling in dwell fatigue regime. Damage-failure transition is considered as critical phenomena, the structural-scaling transition, when the damage develops as specific phase with characteristic stages: nucleation of new phase and the phase growth kinetics. In the case of dwell fatigue, the nucleation stage is associated with slip localization, faceting, voids and microcrack initiation; the phase growth kinetics has the relation to specific non-linearity of the free energy release responsible for the staging of damage-failure transition. Statistically based phenomenological model of damage-failure transition specified the links of macroscopic material parameters with structural parameters responsible for the influence of microstructure on the structure sensitive mechanical properties. The developed conception of modeling of Ti alloys based on the duality of damage kinetics in dwell fatigue loads allowed us to propose the strategy of structural study to provide in perspective the links of structural parameters of /phases with phenomenological parameters responsible for different mechanisms of damage accumulation at LCF and stress hold regimes
The influence of notch connection location on the short-term behaviour of timber-concrete composite beams, modelling of TCC beams and research for optimal locations, a numerical study
Get PDFTimber-concrete composite beams, known as TCC beams, have been widely used in rehabilitation or in new buildings where several types of connections are commonly inserted to ensure partial composite action between the timber joist and the concrete slab. The notched connections represent an effective system due to their strength and ductility and it is simple to cut from timber joists. As a result, a small number is needed for the composite beam to achieve high performance in terms of bending stiffness and load-carrying capacity.This paper aims to develop a FE model for TCC beams with notched connections. It considers realistic interactions between different components.The developed FE model can satisfactorily predict the full range load-mid-span deflection curves and the failure mechanisms.The predictions agree very well with the experimental results reported in the literature, including the stiffness and the load-carrying capacity.After the validation, a numeric study was established, it aimed to research the optimal location of a notch connection between different proposed locations, to figure out which place must be installed to ensure high performance of the TCC beams.As a result of this study, the notch installed at location P3000 was found to be the optimal location to assure the highest bending stiffness. While the maximum carrying capacity was achieved at location P3750
Glass Fiber for Improved Behavior of Light Expanded Clay Aggregate Concrete Beams: An Experimental Study
Get PDFConcrete developed from light expanded clay aggregate (LECA) and glass fiber has good performance, durability, and sustainability. Towards this, the experimental investigation was designed to study cubes, cylinders, and simply supported beams. Four mixtures had LECA volume of 0%, 75%, 85%, and 95% as coarse aggregate replacement and glass fiber content volume of 2% (N, L75, L85, and L95), and the other two mixtures had 75% LECA and glass fiber content of 1% and 1.5% (L75-F1 and L75-F1.5). Results compared to normal concrete showed the weight reduction of samples while adding more glass fiber caused slump reduction in contrast to LECA. Increasing glass fiber volume in the mixture had a negative influence on tensile strength while causing compressive strength enhancement. Moment resistance and energy absorption capacity of L85 were enhanced by 7.5% and 10.3%, respectively. For L75-F1 specimens, the beam stiffness and ductility were enhanced by 14.8% and 14.3%, respectively.  
Fracture behaviour of concrete with different replacement rates of iron tailings sand based on double-K criterion
Get PDFThe article conducts a study on the iron tailings sand concrete's fracture behaviour based on the double-K criterion. Five sets of standard three-point bending beam specimens of concrete with 0%, 25%, 50%, 75% and 100% iron tailings sand replacement river sand respectively were fracture tested, and the P-CMOD and P- ε curves of each set of specimens were measured to determine the pertinent fracture parameters. The specimens were also microscopically tested using scanning electron microscopy and mercury intrusion porosimetry. The results demonstrate that the fracture processes and damage patterns of iron tailings sand concrete and river sand concrete are comparable; the addition of iron tailings sand improves initial cracking load and initial cracking toughness more significantly than unstable cracking load and unstable cracking toughness; the ductility of iron tailings sand concrete is marginally inferior; and the results of microscopic tests demonstrate that the addition of iron tailings sand can improve the morphology and pore structure of the interface transition zone. Therefore, from the assessment of fracture mechanics, iron tailings sand can totally replace river sand in equivalent quantities for concrete preparation, which will provide great potential for the secondary use of iron tailings sand
Multi-level Uncertain Fatigue Analysis of a Truss under Incomplete Available Information
Get PDFWe predict the fatigue life of a planar tubular truss when geometrical parameters, material properties, and live loads are non-deterministic. A multi-level calculation uncertainty quantification framework code was designed to aggregate the finite element method and fatigue-induced sequential failures. Due to the incompleteness of the aleatory-type inputs, the maximum entropy principle was applied. Two sensitivity analyses were performed to report the most influencing factors. In terms of variance, the results suggest that the slope of the curve crack growth rate × stress intensity factor range is the most influencing factor related to fatigue life. Furthermore, due to the application of the entropy concept, the fatigue crack growth boundaries and fatigue crack size boundaries obtained provide the most unbiased fatigue crack design mapping. These boundaries allow the designer to select the worst-case fatigue scenario, besides being able to predict the crack behavior at a required confidence level
Predicting the lifetime of CPVC under increasing temperature and crosshead speed
Get PDFCPVC is an increasingly popular material for plumbing pipes and other applications that require strong and temperature-resistant material. This resin is created using a chlorination process, giving it Chlorine levels that range from 63 to 69% and thus a unique set of characteristics that make it ideal for certain applications. CPVC's combination of corrosion-resistance and low installation costs make it a great substitute for copper in environments with non-ambient conditions such as higher temperatures. This makes it an economic choice for many projects that require smaller budgets. With a variety of applications, CPVC provides a great alternative requiring strong and durable material. The aim of this paper is to characterize the mechanical characteristics of chlorinated PVC (CPVC). Tensile tests were carried on the compounds at different temperatures ranging from -20 to 90°C and crosshead speeds from 5 to 500 mm/min. The results were analyzed to determine how crosshead speed and temperature affected on the mechanical characteristics of CPVC specimens. Two damage models are then developed, one model obtained through by adapting the unified theory version and the other quasi-experimental static model based on ultimate stress. These models allow us to evaluate the damage evolution of CPVC samples and to determine the safety and maintenance intervals of this material
Experimental and Numerical Study on Vibration-Based Damage Detection and Localization in Laminated Composite Plates
Get PDFDamage detection in composite materials is crucial for ensuring the safety and reliability of engineering structures. Conventional methods often face challenges in accurately identifying damage in plate-like structures, particularly in scenarios involving multiple damages or small-scale delamination. This study focuses on investigating the detection and localization of delamination in composite plates by employing both experimental and numerical modal analysis. An eight-ply woven Glass-Epoxy composite laminate with and without damage was prepared with the aid of hand lamination technique. Laminate was fixed to a Clamped-Free-Free-Free (CFFF) boundary condition for experimental modal analysis by introducing controlled damage to examine its impact on modal properties. To validate the natural frequencies (NFs) of damaged and undamaged composite laminates, a numerical analysis was conducted using ANSYS Parametric Design Language (APDL). Further, to advance the understanding of using modal shapes and their spatial derivatives for damage localization in composite plates under various damage situations, post-processing of simulation results was conducted using MATLAB. Finite Difference Method has been employed to calculate the derivatives, and a novel damage index (DI) is proposed to enhance damage localization capabilities. The results affirm that the proposed DI is effective and precise in identifying damage in plate-like structures, both for individual and multiple damage scenarios. This research study presents a novel approach for identifying and pinpointing damage in composite plates, thereby making a valuable contribution to the field of structural health monitoring (SHM) application
Finite-element simulation of residual stresses induced by laser shock peening in TC4 samples structurally similar to a turbine blade
Get PDFThis study is devoted to the investigation of residual stresses distribution (RSD) in a TC4 sample treated with laser shock peening. The study placed special emphasis on analyzing the RSD at the part of the samples structurally similar to a turbine blade, which is more frequently subjected to damage during service according to the aircraft statistics. Results of simulation showed that low power density of 1.11 GWt/cm2 could not induce compressive residual stress on the surface of a treated object. Furthermore, increasing the overlapping of laser spots does not improve the situation and still fail to induce surface compressive residual stress at a laser intensity of 1.11 GWt/cm2. The compressive stresses occur only with the rise in power density. Reducing the spot size from 3 mm to 1 mm for the power density of 10 GWt/cm2 results in a 20% increase in the magnitude of compressive residual stress in the area of interest. Moreover, applying 35% overlapping further enhances this value. In addition to increasing the magnitude of residual stress, this approach also leads to a more homogeneous RSD of the treated material