Implementation of interface damage model with friction to concrete-FRP shear connector

The study investigates the application of fibre-reinforced polymer (FRP) composites in constructions of bridges. It highlights the main advantages of using FRP as a building material and points out its suitability for various structural applications. A numerical analysis was performed on different shape modifications of a jigsaw-puzzle type continuous shear connector. For the interface between concrete and FRP, a bilinear cohesive zone model with friction within a variationally based formulation of interface damage has been chosen and tested. This model captures the load displacement relation accounting for a softening region and offering a continuous response of key variables of stress and damage. Findings illustrate reliability of the cohesive bilinear model as a tool for predicting failure and show a promise for applying it in material design, or in design of FRP composite structures, their members and specifications of their construction details

Fatigue performance of flexible pavements with cement-bound granular material (CBGM)

The 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

Study of the forming limit of 6063 aluminum alloy perforated sheet under in-plane and out-of-plane stretching conditions

The 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

Strengthening of steel I-Section girder web with depth discontinuity against localized buckling

Stepped steel girders and beams with a jump in section depth are highly susceptible to local web buckling at the step location. Although tapered steel girders have been studied extensively by researchers, abruptly stepped steel girders have been very rarely investigated. This study uses the finite element method to investigate the local web buckling of stepped steel I-section girders. Firstly, linear buckling analysis is verified against experimental results and the AISC-360 and Eurocode 3 formulae. Then, a case study of stepped steel girder failure during construction is presented and discussed. Finally, the effect of step height, step location, boundary conditions, and adding stiffeners on the local web buckling of stepped girders was investigated. Stepping the girder section was found to cause local web buckling at significantly low loads, reaching only 27% of the original buckling capacity in some cases. Moving the step from the compression flange to the tension flange, or to lower moment locations in the girder, can mitigate the problem. When the step needs to be in the compression flange at high moment points, using a long enough horizontal stiffener was found to almost fully restore the web buckling capacity, while using a vertical one only restores about half of the original buckling capacity. Using both vertical and horizontal stiffeners almost doubles the buckling capacity at the step.

Augmentation method of fatigue data of welded structures based on physics-informed CTGAN

Variable amplitude loading is frequently applied to welded structures in practical engineering, and fatigue failure is a prevalent problem. In recent years, machine learning is a useful technique for predicting fatigue life. However, it is challenging to acquire a sufficient number of reliable training samples for fatigue tests under variable amplitude loading. The machine learning models' accuracy and generalization capabilities are impacted by this. This work introduces a novel data augmentation approach utilizing physics-informed Generative Adversarial Networks (GAN). Data augmentation is accomplished by incorporating the traditional damage model - Ye model  as constraints within the loss function of the Conditional Tabular GAN (CTGAN). The method combines physical laws of damage with CTGAN, which makes generated fatigue data conform to physical characteristics under two-step loading. Then the impact of generated data on model performance is evaluated on four machine learning models and compared to traditional damage models. The experimental results show that generated fatigue data helps machine learning models to get better prediction results compared with traditional models and unaugmented machine learning models, which significantly enhancing the precision of fatigue life predictions

Studies on mechanical, fractured surface, wear, and thermal characteristics of TiC reinforced structural grade Al6061 MMCs

Stir casting technique has been used in the current study to process Al6061 reinforced with TiC particles of different concentrations. The processed compounds' composition of TiC and Al6061 has been verified by Energy Dispersive X-Ray Spectroscopy (EDS) tests. TiC has been added to Al6061 in a range of weight concentrations, including 0, 3, 6, 9, and 12%. To determine the composite material's structure, an optical microscope research was used. It is endeavored to investigate the microstructure, mechanical, wear, and thermal performance of TiC-reinforced composites with varying weight fractions in this study. It was observed that, the strength of the developed composites increased by 51.89% in hardness, 18.47% in tensile strength and 40% in wear rate with the addition of TiC. Also, when compared to the alloy material, TiC particle reinforced Al6061 showed superior thermal characteristics

Predictive modeling of PMMA-based polymer composites reinforced with hydroxyapatite: a machine learning and FEM approach

This research examines the mechanical characteristics of polymer composites (PMMA) that are reinforced with Hydroxyapatite (HAp), with a particular emphasis on the Elastic Modulus and Compressive Strength. The investigation employs a multifaceted approach that integrates experimental methods, micromechanical analysis, and machine learning techniques. Experimental assessments of Elastic Modulus and Compressive Strength were conducted at various HAp concentrations (5%, 15%, and 30%) and were compared with theoretical predictions derived from Representative Volume Element (RVE) and micromechanical frameworks, including Voigt and Reuss bounds. Various machine learning algorithms, such as Feedforward Neural Network (FFNN), Radial Basis Neural Network (RBNN), and Support Vector Machine (SVM), were used to predict the mechanical properties. The RBNN exhibited high accuracy (R² = 0.92; MAE = 0.05) for intermediate HAp levels (20-30%) but displayed instability at the extremes % of reinforcements values . The FFNN consistently provided lower estimates of the properties, whereas the SVM yielded robust and stable predictions that closely matched both experimental and theoretical results with the error of (2-5) % (Result value). This research highlights the effectiveness of integrating micromechanical modeling with machine learning to improve the prediction and comprehension of composite behavior, thereby offering valuable insights for the design and application of advanced materials

An Investigation on the Free Vibration Behaviors of Additively Manufactured PA6 Layered Plates: Influences of Stacking Sequence, Infill Ratio, and Boundary Conditions

This study investigates the free vibration behavior of 3D-printed PA6 layered plates by considering the effects of stacking sequence, infill ratio, and boundary conditions. Unlike previous works, this research provides a comprehensive analysis combining experimental pre-analyses and finite element simulations. Nine different plate configurations with infill ratios of 40%, 70%, and 100%, and aspect ratios (a/b = 1, 1.5, 2, and 2.5) were analyzed under clamped and simply supported boundary conditions. The mechanical properties of the printed material were determined through tensile testing, and these properties were used as input for the numerical model developed in ANSYS. Before the vibration analyses, the model was validated by comparing its results with existing literature, showing close agreement. Results showed that higher infill ratios in the outer layers increase natural frequencies due to improved stiffness, whereas a denser core can reduce them due to increased mass. Additionally, increasing the aspect ratio leads to higher natural frequencies. The findings offer valuable insights for improving the vibration performance of 3D-printed PA6 components used in functional parts such as gears, fan blades, and robotic arms

Analyzing the Effect of Residual Stresses in the Fatigue Life of High Ultimate-Strength Steel Specimens

An analytical model, based on Solid Mechanics, is developed based on a comprehensive analysis of the effect of residual stress on the fatigue performance of cold-drawn steel wires partially yielded specimens. In the experimental part, it was initially assumed that the specimens, taken from the manufacturer's wire spools, did not have appreciable residual stresses. Therefore, a residual stress pattern was imposed on the specimens before the fatigue testing. Nevertheless, it was realized that the number of cycles spent by the specimens up to failure was higher than those predicted by the fatigue/residual stress compound analytical model. Hence, the initial assumption was reviewed, and a prior superficial compressive residual stress was incorporated into the model, most likely generated by cold-rolling manufacturing. The “resistance increase” and the “stress reduction” approaches were suggested to encompass the number of cycles difference, with good results. In addition, the prior level of existing superficial compressive residual stresses was also estimated

The Axial behaviour of Concrete Filled Double Skinned Steel Tubular (CFDST) column with concrete imperfections

Concrete 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