Investigation on the characterization and modelling of Fracture Process Zone behavior in Concrete Beams subjected to Three-Point Loading Tests

The fracture behavior of quasi-brittle materials such as concrete is characterized by the presence of a fracture process zone (FPZ) that precedes the main crack. Within this zone, various mechanisms, including the formation of microcracks, crack deflection, aggregate interlocking, and crack branching, contribute to the complex nature of the fracture behavior. Traditional experimental methods and other techniques often face challenges in fully capturing the micromechanical mechanisms occurring in the fracture process.To address this challenge, numerical models have been developed in the present study to investigate the evolution mechanisms of the FPZ. These models serve as valuable tools for simulating and analyzing the intricate behavior occurring at the microstructural level during the fracture process. By complementing experimental observations, these numerical approaches provide deeper insights into the fracture behavior of quasi-brittle materials and enhance the understanding of material failure. The outcome of present investigation clearly provides the evaluation method of FPZ in concrete beams of different sizes

Evaluation of thinning behaviour under the influence of plastic hardening and surface friction during small punch test

Understanding the deformation response of the material involving thinning under small punch loading is vital to ensure structural integrity. This paper systematically investigates the effects of plastic hardening on the thinning process under different levels of surface friction between the punch, die and specimen. The small punch test conditions are modeled using Finite Element (FE) software of Abaqus. An axisymmetric model with a bi-linear constitutive material model incorporating different plastic hardening slopes is employed. Furthermore, the Coulomb’s friction coefficient between the disc-shaped specimen and the punch as well as the die varies between 0 (frictionless) to 0.7. The study found that the effect of plastic hardening on thinning process is negligible. On the other hand, the effect of thinning at the center of the specimen is significant under frictionless surface conditions. Thinning is observed to be dominant during the membrane stretching and plastic instability deformation stages. As the surface friction increases, the resistance to sliding deformation decreases. As a result, tensile instability is predicted at the location offset from the center of the specimen. Future efforts to model material behaviour and determine mechanical properties using small punch load conditions must consider the effects of friction

Rolling contact fatigue of AISI 440C TiN coated by plasma based ion implantion and deposition

In this work, the microstructural evolution, surface characteristics and wear behavior of high hardness AISI 440C samples coated with a TiN film synthesized at room temperature were investigated. The coating was deposited using a combined process of plasma-based ion implantation and deposition (PBII&D). Rolling contact fatigue (RCF) tests were conducted and compared with those of the uncoated steel. Tests were carried out in a flat washer type testing rig under lubricated pure rolling conditions. The results indicate that the microstructure of the substrates remained unchanged after the deposition process. The application of the coatings produced an increase in the arithmetic average height of the roughness profiles and a change in their skewness. The adhesion of the TiN coating on AISI 440 C proved to be satisfactory. RCF test generated typical fatigue spalls in the uncoated samples. In coated samples partial delamination of the coating occurred along the rolling track. Taking partial delamination of the coating as a failure criterion, it was found that the RCF life of the coated samples was higher than that of the uncoated ones

Numerical study of residual stress fields after double-sided symmetric laser shock peening of blade edge

This paper deals with numerical modelling of the residual stress field formed after laser shock peening of a thin blade edge from TC4. It is shown that the application of double-sided symmetric laser shock peening is an effective way of treatment, as it allows to reduce deformation and geometrical changes caused by laser shock peening in comparison with treatment from one side. The results of numerical modelling obtained by varying the machining parameters (power density, spot shape, number of passes, % overlapping) were used to form a database for further training of the neural network. It is shown which machining parameters lead to compressive residual stresses over the entire thickness of the edge, and which ones induce tensile stresses on the surface

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

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

Studying the fracture surface of brass CuZn37 and aluminum 1100 and their relationship with formability in Single Point Incremental Forming

Single Point Incremental Forming was conducted on Aluminum1100 and Brass CuZn37 to form a hyperbolic truncated pyramid with varying wall angles until the fracture occurs. The formability of the specimens in terms of fracture depth and maximum wall angle was measured; and scanning electron microscopic photography was used to capture the fractured surface of the specimens to perform a fractography analysis. In each specimen's fracture surface, the identification of the voids shape, calculation of the void volume fraction (VVF) and void size, and the classification of the voids have been performed to allow for the identification of the relationship between formability and the microstructure of both materials. Also, the effect of the input parameters on this relationship has been identified. The results showed that when the VVF and the average void size in the fractured surface increase, the formability of the material increases.  And that the optimal SPIF conditions that increase void volume fraction and formability in CuZn37 occur when all input parameters are set to medium levels. For aluminum 1100, the optimal conditions have a low level of feed rate, a high level of tool speed and sheet thickness, and a medium level of tool diameter and step size

A digital twin framework with MobileNetV2 for damage detection in slab structures

In this study, a digital twin framework is proposed for damage detection in a civil structure, which consists of a finite element model, neural networks, model updating methods, and signal processing. To verify the proposed framework, we present a case study of slab structure using deflection measurement as input data. The dynamic characteristics of the physical model are used to calibrate the digital twin model. Damage scenarios are created on the digital twin model. The defection of the damaged slab under static loads is analyzed with two-dimensional discrete wavelet theory (DWT), whereas the diagonal wavelets are used to extract images data set used to train the convolutional neural network (CNN). MobileNetV2 uses transfer learning can reduce the number of trained parameters and hence perform fast convergence. The proposed method gives high accuracy about detection of low-severity damage having the severity less than 10%. There is more than 80% accuracy for predicting the damaged location and its severity. The success of using MobileNetV2 and transfer learning helps to improve the methods further on mobile devices and the potential for more applications. Moreover, the proposed framework does not require the data of the intact structures, leading to much wider applications

Improved flexural behaviour of reinforced concrete beam strengthened using stainless steel wire mesh

The paper presents an experimental investigation of the flexural behaviour of reinforced concrete (RC) beam elements strengthened externally with stainless steel wire mesh (SSWM). SSWM has the potential to be an alternative composite material in place of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) because of advantages such as being cost-effective, having more fire-resistance and corrosion resistance, good bond behaviour with concrete, improve the strength of members, leaving minimal effects on structural aesthetics as it has less thickness and ease in availability. In the present study, SSWM has been wrapped externally over the beams having three different wrapping patterns, including fully wrapped vertical SSWM strips over the beam, partial wrapping of vertical SSWM strips in between the stirrups of the beam and partial wrapping of vertical SSWM strips above the stirrups of the beam, and control beam with no wrapping, each configuration having two test specimens. Results of experimental investigation in terms of cracking load, ultimate load, corresponding deflection, ductility, initial stiffness and energy absorption capacity of different wrapping patterns have been obtained and compared with those of control beam specimens. From the results obtained, it has been demonstrated that the fully wrapped SSWM strip wrapping pattern enhanced the flexural strength of the beam and showed the highest strength gain compared to the other wrapping patterns

Fatigue behavior of pultruded fiberglass tubes under tension, compression and torsion

This work is devoted to an experimental investigation of fatigue behavior of pultruded fiberglass tubes under uniaxial tension, compression and torsion. Static tests were carried out; a presence of postcritical deformation stage during torsion is noted. Regularities of inhomogeneous strain fields evolution are analyzed using digital image correlation method. Fatigue curves are built for four cyclic loading modes: tension-tension, compression-compression, tension-compression and torsion. An analysis of specimens' fractures is carried out, typical damaging mechanisms are revealed. Residual dynamic stiffness data is obtained and studied using a previously proposed fitting model. Results demonstrate model's high descriptive capability and its flexibility to describe two-staged and three-staged stiffness degradation curves. An influence of loading mode on a shape of these curves is found out. Model parameters' dependence on maximum stress value during the loading cycle is studied using the Pearson's correlation coefficient. The necessity of multiaxial fatigue behavior investigation of pultruded fiberglass tubes is concluded