Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
Not a member yet
2800 research outputs found
Sort by
Numerical modeling of fracture processes of bodies with stress concentrators under conditions of proportional loading, taking into consideration the statistical distribution of ultimate strength and partial loss of load bearing capacity
Full text linkThis work is dedicated to the development of a fracture model for an elastic-brittle solid with statistically distributed strength characteristics of subregions and the application of this model to describe fracture processes of bodies with stress concentrators under biaxial loading. The methodology of numerical modeling of deformation and fracture processes is improved to take into account the partial loss of load bearing capacity and the appearance of local anisotropy. Based on the improved methodology, modified algorithm is developed. The influence of the biaxial loading mode and the dispersion of the ultimate strength distribution on the loading diagrams and the orientation of the macrodefect is considered. The realization of the gradual macrodefect development (localized type of damage accumulation) or its growth through the most weakened damaged areas (mixed type) is revealed. The applicability of the approach to assessing the type of damage accumulation based on the analysis of numerical solutions of boundary value problems within the elasticity theory is demonstrated. The efficiency of the usage of the modified approach to ensure the reliability and safety of critical structures under multiaxial loading is concluded
An experimental study on the rehabilitation performance of CFRP-strengthened bubble deck slabs: effects of void size and preloading levels
Full text linkThis study examines the rehabilitation performance of reinforced concrete bubble deck slabs (with 50 mm and 60 mm voids) strengthened with externally bonded CFRP sheets. Nine specimens were tested: eight bubble slabs (grouped by void size and preloading level) and one solid control slab. Three specimens of each void size were pre-damaged to 50%, 60%, and 75% of their ultimate load before being strengthened with CFRP and retested. One specimen per group remained unstrengthened for comparison. Results show that increasing void size reduces load capacity: the unstrengthened 50 mm and 60 mm void slabs achieved 96.2% and 86.5% of the solid slab’s strength, respectively. CFRP rehabilitation effectively restored structural performance, with 50 mm void slabs recovering up to 98.5% of the control slab’s capacity and exhibiting 25% lower deflection. In contrast, 60 mm void slabs showed lower recovery efficiency, particularly at higher preloading levels SB-6-75 recovered only 82.5% of the control strength. All strengthened specimens failed by CFRP debonding combined with flexural cracking, with no shear failures observed. The study demonstrates that CFRP retrofitting significantly enhances the strength and stiffness of damaged bubble deck slabs, especially those with smaller voids. Void size and pre-damage level are critical factors influencing rehabilitation success
A Three points bending ultrasonic fatigue resistance and vickers hardness of Tlalpujahua clay thermally treated
No full textUltrasonic fatigue at an operating frequency of 20 kHz was conducted on thermally treated clay bricks at 500, 750, and 1000 °C with a holding time of 5 h, using a three-point bending setup to assess their fatigue endurance. A Vickers hardness test was also performed on small clay squares thermally treated at the same temperatures, showing increased hardness values. X-ray diffraction (XRD) analysis was also performed, revealing temperature-induced changes in the clay chemical composition. Specifically, the illite transformation into spinel at 1000 °C contributed to a significant increase in hardness and, consequently, a diminution in fatigue life. A finite element simulation under different applied loads was performed to evaluate the von Mises stress behavior of the clay brick. Considering the change in mechanical properties, such as bulk density, at various temperatures. The simulation results show a corresponding behavior with the values of the Vickers hardness. This study provides a perspective on the relationship between ultrasonic fatigue, Vickers hardness, and thermal treatment
Experimental investigation of the influence of internal defects (voids, wrinkles) on the shear properties of CFRP
Full text linkThe study focuses on examining the impact of internal manufacturing defects (voids and wrinkles) on the mechanical behavior of structural carbon fiber reinforced polymers (CFRP) under shear loading.
Specimens of VKU/VSE1212 material with a [0/90]10 layup were artificially embedded with defects: circular voids (Ø 20 mm) and square voids (20×20 mm) at a concentration (area fraction) of 5.3%, as well as wrinkles increasing thickness by 10%. In-plane shear tests were conducted according to ASTM D7078 using a Vic-3D system for digital image correlation (DIC) to record strain fields.
Results revealed that voids at 5.3% concentration (area fraction) reduced shear strength by 2.2% (from 72.1 MPa to 70.5–70.6 MPa, regardless of geometry, indicating that the defect area, rather than its shape, governs the failure response. The shear modulus of void-containing specimens (~4.48 GPa) did not differ from defect-free specimens (~4.49 GPa). Wrinkles increased the shear modulus to 5.39 GPa due to added layers but reduced strength by ~3% (to 69.9 MPa). DIC analysis confirmed the method’s efficacy for tracking strain localization in defect zones. Failure modes across all specimens involved vertical crack formation between V-notches.
These results help systematize knowledge on of manufacturing defects on CFRP shear properties and hold practical significance for refining design tolerances in critical components, developing non-destructive testing methods, optimizing manufacturing processes
J-integral evaluation and structural integrity assessment using FAD for SA 312 Type 304 LN steel welded pipes with notch under monotonic loading
Full text linkIn the present study, structural integrity of SA312 Type 304 LN steel welded pipes with through-wall crack under monotonic loading has been assessed using failure assessment diagram (FAD). Plastic capacity utilization and fracture capacity utilization are compared simultaneously using a FAD. Material’s initiation fracture toughness and J-integral evaluated using load-CMOD method were used for evaluating fracture resistance were used for generation of failure assessment diagrams. Various analytical expressions proposed by Zahoor (1989) and Takahashi (2002) were used to evaluate limit load moment (plastic capacity). Various approaches for deriving the failure assessment line were considered in this study viz, BS 7910 2A, BS 7910 2B, and SINTAP. The failure assessment lines constructed using SINTAP, BS 7910 2A level and BS 7910 2B level for SA312 Type 304 LN steel procedures yielded similar results. Limit load moment values from Takahashi were lower and hence resulted in assessment points closer to the failure assessment lines. Structural integrity assessment is very significant in deciding the safety of operation of the piping components
Elasto-plastic truss optimization under geometric nonlinearity using a genetic algorithm
Full text linkThis paper presents an advanced optimization methodology for truss structures, addressing both elasto-plastic design cases—where plastic deformations are controlled within predefined limits—and purely elastic scenarios, in which inelastic behavior is entirely prevented. Plastic deformations are characterized and quantified using the complementary strain energy of residual forces, providing a reliable measure of inelastic response. Additional design constraints related to load-bearing capacity and structural stability are incorporated through penalization terms, while the objective function focuses on minimizing structural weight. Serviceability restrictions are also applied to enhance the robustness of the design. Building on these considerations, the framework integrates material and geometric nonlinear finite element analysis (FEA) with a genetic algorithm (GA), enabling the automated determination of optimal cross-sectional areas for individual bar members within a predefined design domain. To further enhance safety, geometric imperfections are introduced through an integrated automatic strategy. The effectiveness of the proposed technique was validated using two benchmark numerical examples: a 37-bar planar truss and a 25-bar space truss, evaluated under multiple design scenarios. The results highlight the flexibility and reliability of the optimization framework, demonstrating substantial weight savings while fully meeting all structural performance criteria
Influence of laser shock peening on the residual strains and stresses in additively manufactured TC4
Full text linkAdditively manufactured materials possess significant heterogeneities and anisotropies of stiffness and strength properties between the growth and transverse directions. Residual stresses induced by the fabrication and processing stages are critical to the service life of these materials. In this work, an experimental study of the residual stress fields was conducted in samples cut from additively manufactured titanium alloy TC4. The depth profiles of residual elastic strains for various regimes of laser impact treatment were obtained on elementary samples in the form of rectangular plates of 100´20´5 mm. Five treatment regimes were studied by varying the laser power density, the spot shape, and the percentage of overlap. The dependence of relief strains and residual stress levels on the laser energy density was obtained for two laser spot shapes: a 1´1 mm square and a 2 mm diameter circle. The numerical model, validated against experimental data for both as-built and laser-peened states, provides a reliable tool for analyzing the residual stresses and strain in additively manufactured components
The Axial behaviour of Concrete Filled Double Skinned Steel Tubular (CFDST) column with concrete imperfections
No full textConcrete Filled Double Skinned Steel Tubular (CFDST) composite column is preferred over Concrete Filled Steel Tube composite column (CFST) owing to enhanced strength. However, they may possess concrete imperfection due to shrinkage and creep of concrete and the construction practices adopted. Concrete imperfection may lead to overestimation of strength, reduction in ductility, and composite action of CFDST column. This paper discusses axial compression tests conducted on outer circular and square and inner square-shaped CFDST columns with and without concrete imperfections. Parameters considered in the study include i) shape of the outer steel tube, ii) circumferential gap ratio (1.1% and 2.2%), and iii) spherical or rectangular gap ratio (4.4% and 8.8%). Results of the test in terms of strength, ductility, confinement effect, strain profile along the length, and failure modes are studied in depth. It is observed that the circumferential gap ratio has a significant impact on the peak axial load-carrying capacity of CFDST columns. Ductility of CFDST column reduces with an increase in the concrete imperfection gap ratio. While CFDST columns with circular steel tube yield global buckling failure modes, square outer steel tube exhibit local buckling failure modes. New strength reduction factors are proposed to account impact of circumferential and spherical or rectangular concrete imperfections on load carrying capacity estimation of CFDST column
Study of the forming limit of 6063 aluminum alloy perforated sheet under in-plane and out-of-plane stretching conditions
Full text linkThe current investigation deals with the forming process of Perforated Sheet Metal (PSM) process. The goal of the work is to determine by experimental and numerical methods the Forming Limit Diagrams (FLDs) of an Al-Mg-Si aluminum alloy. In order to achieve this objective, Specimens of different widths, obtained by cutting portions from two opposite sides of a circular blank, were used. The FLDs were determined for the two forming tests: MARCINIAK and NAKAZIMA tests. This choice is motivated by the simplicity of the shapes of the blanks and punches used during these tests, but also in order to measure these curves in both flat (MARCINIAK) and curved (NAKAZIMA) zones. A measurement technique using Stereo-Digital Image Correlation (Stereo-DIC) was implemented. For the sake of comparison, the same tests were performed on Non-Perforated Sheet Metal (NPSM). The experimental FLDs were successfully assessed using simulations in Abaqus finite element code. It is namely found that the safe forming region obtained by NAKAZIMA test is higher than that obtained with MARCINIAK test. Furthermore, the maximum tool displacement in NAKAZIMA tests is double that of MARCINIAK tests for all perforated specimens
Fatigue performance of flexible pavements with cement-bound granular material (CBGM)
Full text linkThe article analyzes the fatigue performance of flexible pavement structures incorporating cement-bound granular material (CBGM) as a subbase layer. In current Polish design methodologies, overly conservative and underestimated stiffness modulus values are often assumed for CBGM, neglecting the material’s behavior in the uncracked state. A mechanistic analysis was conducted using the theory of multilayer elastic half-space. Fatigue life was evaluated based on two criteria: Dempsey and De Beer. The results showed that, according to Dempsey’s criterion, only one selected layer configuration would not crack under construction traffic, whereas De Beer’s criterion indicated that none of the analyzed structures should fail. The findings demonstrate a significant reserve in the fatigue life of CBGM layers and highlight the need to revise existing design assumptions, particularly for mixtures of lower strength classes