Search Results (270)

For the first time, comprehensive investigations into the tensile load-bearing behavior and crack formation of reinforced concrete based on ultrasound are presented. Uniaxial tensile tests are performed on reinforced concrete tension members equipped with embedded ultrasonic transducers. Key mechanical parameters across all ranges of tensile behavior are continuously quantified by recording ultrasonic signals and evaluated with coda wave interferometry. The investigations include member configurations of different lengths to cover different numbers of cracks. For reference, crack patterns and crack widths are analyzed using digital image correlation, while the strain in the reinforcement is monitored with distributed fiber optic sensors. For the first time, a direct proportional relationship between the relative velocity change in ultrasonic signals and crack widths is established in the ranges of crack formation and stabilized cracking. In the non-cracked state, linear correlations are found between the velocity change and the average strain, as well as the length of the specimens. The experimental results significantly enhance the general understanding of the phenomena related to ultrasonic signals in flexural reinforced concrete members, particularly concerning cracking in the tensile zone. Consequently, this study contributes to the broader objective of employing coda wave interferometry to evaluate the condition of infrastructure. Full article

Carbon black (CB)-filled rubber materials are extensively used in civil engineering seismic isolation. However, CB-filled rubber materials often experience mechanical property degradation because of exposure to environmental factors. To better understand the influences of thermo-oxidative, ultraviolet and ozone aging on mechanical property degradation, uniaxial tension and dynamic mechanical analysis (DMA) tests were carried out. In the uniaxial tension tests, the stress strength and elongation decreased with an increase in aging time. In the DMA tests, the effective temperature ranges decreased by 3.4–14%. And the neo-Hookean model was applied to simulate the hyperelasticity of CB-filled rubber materials. The relationship between the elastic modulus (a constant of the neo-Hookean model) and aging time was established, which provided a qualitative relationship between crosslink density and aging time. In addition, the dispersion of the CB aggregate was investigated using an atomic force microscope (AFM). The results indicated that the mechanical property degradation might be closely related to the aggregate diameter. This paper establishes a bridge between the microstructure and mechanical properties of CB-filled rubber materials, which can improve the understanding of the mechanical property degradation mechanisms of rubber materials and the fabrication of rubber components. Full article

In this study, a new fibre combination for an interlayer hybrid fibre-reinforced polymer laminate was investigated to achieve pseudo-ductile behaviour in tensile tests. The chosen high-strain fibre for this purpose was S-Glass, and the low-strain fibre was flax. These materials were chosen because of their relatively low environmental impact compared to carbon/carbon and carbon/glass hybrids. An analytical model was used to find an ideal combination of the two materials. With that model, the expected stress–strain relation could also be predicted analytically. The modelling was based on preliminary tensile tests of the two basic components investigated in this research: unidirectional laminates reinforced with either flax fibres or S-Glass fibres. Hybrid specimens were then designed, produced in a heat-assisted pressing process, and subjected to tensile tests. The strain measurement was performed using distributed fibre optic sensing. Ultimately, it was possible to obtain repeatable pseudo-ductile stress–strain behaviour with the chosen hybrid when the specimens were subjected to quasi-static uniaxial tension in the direction of the fibres. The intended damage-mode, consisting of a controlled delamination at the flax-fibre/glass-fibre interface after the flax fibres failed, followed by a load transfer to the glass fibre layers, was successfully achieved. The pseudo-ductile strain averaged 0.52% with a standard deviation of 0.09%, and the average load reserve after delamination was 145.5 MPa with a standard deviation of 48.5 MPa. The integrated fibre optic sensors allowed us to monitor and verify the damage process with increasing strain and load. Finally, the analytical model was compared to the measurements and was partially modified by neglecting the Weibull strength distribution of the high-strain material. Full article

A novel approach to estimating the absorbed energy (toughness) in a uniaxial tensile test with only knowledge of the microstructure is presented. The flow behavior of each Dual-Phase (DP) steel grade is predicted using idealized Representative Volume Elements (RVEs) up to uniform elongation. To estimate the flow behavior beyond uniform elongation, the stress-modified fracture strain in a non-local damage model was implemented in Abaqus. Damage parameters were calibrated using Finite Element (FE) simulations of purely ferritic tensile specimens. The damage parameters remained unchanged, except for the coefficient of triaxiality. This coefficient was adjusted based on the average triaxiality of ferrite elements at the instability point of the uniaxially loaded RVEs for each DP steel grade. The proposed approach comprises two steps: micron-sized RVEs to predict the flow behavior up to the point of uniform elongation and the average triaxiality and full-scale tensile-test simulations to predict the rest of the curves. The results show that the damage parameters calibrated for high-strain ferrite effectively estimate the absorbed energy during failure in tension tests. This approach is also geometry-independent; varying the geometry of the tensile specimen, including miniature or notched specimens, still yields predicted absorbed energies that are in good agreement with the experimental results. Full article

The aim of this work was to study the influence of temperature and strain rate on the formability and structure of C22 steel. This study was based on tensile and compression tests. In the case of the compression test, the study of the influence that the process parameters (temperature and strain rate) have on the nonuniformity of the deformation was taken into account. This work presents an experimental analysis of the effects of temperature and strain rate on the mechanical and structural properties of C22 mild steel. Uniaxial tension and compression testing at high temperatures (800 °C, 900 °C, 1000 °C, and 1100 °C) and strain rates 0.001 1/s, 0.012 1/s, and 0.089 1/s for tension and 6.35 1/s, 5.72 1/s, 4.67 1/s and, respectively, 0.106 1/s for the compression hammer and hydraulic press served as the foundation for the studies. Analysis was carried out on how temperature and strain rate affected yield stress, strain to fracture, hardness, and structural evolution. Additionally, the nonuniformity of the deformations obtained at various temperature and strain rate values was examined. The fracture behavior of C22 steel can be enhanced by raising the deformation temperature and lowering the strain rate. In the tensile tests, the study of stress and strain distribution and the variation in the normalized Latham–Cockroft failure criterion was performed by numerical simulation using FORGE^® NxT 4.1 software. Full article

Plastic forming in magnesium alloy sheet products is becoming a hot topic because of its potential in light-weight structural designs. Due to the special anisotropic and tension–compression asymmetrical properties of magnesium alloys, traditional modeling methods based on the von Mises yield criterion and using only uniaxial tensile properties for bending-dominated process simulations are not able to produce accurate predictions. In this study, two kinds of tensile tests (uniaxial and biaxial) and some compressive tests were performed along three material directions to obtain anisotropic and asymmetric properties, based on which the parameters of the Hill48 and Verma yield criteria were obtained. Then, the user subroutine VUMAT was developed, and the roll-forming process for magnesium alloys was simulated with the established anisotropic and asymmetric yield criteria. Finally, a roll-forming experiment on AZ31 magnesium alloy was performed. Compared with the experiments, it was found that roll-forming and springback predictions based on the Verma yield criterion had higher accuracy than those based on the von Mises and Hill48 yield criteria FEM models, which ignore anisotropy and asymmetry. This study provides an important FEM modeling idea that considers not only anisotropy but also asymmetry in the bending-dominated forming processes of magnesium alloys in which tension and compression exist simultaneously. Full article

Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their inherently limited formability and the strong crystallographic textures that form during deformation. This study aimed to comprehensively characterize the ductile fracture behavior of ZM51M Mg alloy round bars under various stress states and to improve the reliability of ductile failure predictions through the application and calibration of multiple uncoupled damage criteria. Tensile and compressive tests were conducted on specimens of varying geometries (dogbone, notched R5, shear, uniaxial compression, and plane strain compression specimens) and dimensions, meticulously cut along the extrusion direction of the round bar. These tests encompassed a wide spectrum of stress–strain responses and fracture characteristics, including uniaxial tension, uniaxial compression, and shear-dominated states. An inverse analysis approach, involving iterative numerical simulation coupled with experimental data, was employed to precisely determine fracture strains from the test results. The plastic deformation behavior was accurately modeled using the combined Swift–Voce hardening law. Subsequently, three prominent uncoupled ductile fracture criteria—Rice–Tracey, DF2014, and DF2016—were calibrated against the experimental data. The DF2016 criterion demonstrated superior predictive accuracy, consistently yielding the most accurate fracture strain predictions and significantly outperforming the Rice–Tracey and DF2014 criteria across the tested stress states. The findings of this work provide significant insights for improving the assessment of formability and fracture prediction in Mg alloys. This research directly contributes to overcoming the challenges associated with their inherent formability limitations and complex deformation textures, thereby facilitating more reliable design and broader adoption of Mg alloys in advanced lightweight structural solutions. Full article

To investigate the degradation mechanisms of the surrounding rock in abandoned mine roadways used for oil storage, this study combined uniaxial compression tests with digital image correlation (DIC), scanning electron microscopy (SEM), and other techniques to analyze the evolution of the rock mechanical properties under the coupled effects of oil–water soaking and initial damage. The results indicate that oil–water soaking induces the loss of silicon elements and the deterioration of microstructure, leading to surface peeling, crack propagation, and increased porosity of the sample. The compressive strength decreases linearly with the soaking time. Acoustic emission (AE) monitoring showed that after 24 h of soaking, the maximum ringing count rate and cumulative count decreased by 81.7% and 80.4%, respectively, compared to the dry state. As the liquid saturation increases, the failure mode transitions from tension dominated to shear failure. The synergistic effect of initial damage and oil–water erosion weakens the rock’s energy storage capacity, with the energy storage limit decreasing by 45.6%, leading to reduced resistance to external forces. Full article

To overcome the limitation of traditional elastic phase field models that neglect plastic deformation in rock compressive-shear failure, this study developed an elastoplastic phase field fracture model incorporating plastic strain energy and established a coupling framework for plastic deformation and crack evolution. By introducing the non-associated flow rule and plastic damage variable, an energy functional comprising elastic strain energy, plastic work, and crack surface energy was constructed. The phase field governing equation considering plastic-damage coupling was obtained, enabling the simulation of the energy evolution in rock from the elastic stage to plastic damage and unstable failure. Validation was carried out through single-edge notch tension tests and uniaxial compression tests with prefabricated cracks. Results demonstrate that the model accurately captures characteristics such as the linear propagation of tensile cracks, the initiation of wing-like cracks under compressive-shear conditions, and the evolution of mixed-mode failure modes, which are highly consistent with classical experimental observations. Specifically, the model provides a more detailed description of local damage evolution and residual strength caused by stress concentration in compressive-shear scenarios, thereby quantifying the influence of plastic deformation on crack driving force. These findings offer theoretical support for crack propagation analysis in rock engineering applications, including hydraulic fracturing and the construction of underground energy storage caverns. The proposed plastic phase field model can be effectively utilized to simulate rock failure processes under complex stress states. Full article

This study proposes a novel unified constitutive model that systematically integrates the microstructure evolution and macroscopic stress–strain response during the hot deformation of a Ni-based superalloy. The proposed model incorporates a suite of microstructural variables, including damage fraction, recrystallization fraction, δ phase content, average grain size, and dislocation density. Furthermore, the model explicitly considers critical macroscopic stress state parameters, specifically the magnitude and orientation of maximum principal stress, hydrostatic stress component, and Mises equivalent stress. A comparative analysis of rheological curves derived from uniaxial tension and compression experiments reveals that the prediction errors of the proposed model are less than 3%. The model is subsequently implemented to investigate the evolution characteristics of the damage accumulation fraction and δ phase content under varying stress directions and initial δ phase contents. An advanced computational framework integrating the finite element method with the proposed constitutive model is established through customized subroutines. The framework exhibits exceptional predictive accuracy across critical regions of disk forging, as evidenced by a close agreement between computational and experimental results. Specifically, the relative errors for predicting recrystallization fraction and average grain size remain consistently below 8% under varying stress–strain conditions. Testing results from four representative regions demonstrate a good alignment of high-temperature tensile properties with the macroscopic stress–strain distributions and microstructure characteristics, thereby confirming the model’s reliability in simulating and optimizing the forging process. Full article

A good combination of strength and fracture resistance is highly desired for the development of high-strength ferrite–martensite dual-phase (DP) steels for automotive application. But the increase in strength is usually compromised by a reduction in fracture resistance, and the guideline for microstructure optimization remains to be established. This study is dedicated to the DP steels with tensile strength above 1 GPa, and the influences of the equiaxed and fibrous morphologies on the mechanical properties were investigated by both the uniaxial tensile tests and the essential work of fracture (EWF) method. The fibrous morphology is efficient in increasing strength due to the ferrite grain refinement effect. Under uniaxial tension, the fibrous DP morphology does not lead to higher fracture strain. But when evaluating with the EWF method, the fibrous DP steels present a superior fracture resistance, which is attributed to the larger crack tip necking. The interpretation of the fracture resistance measurements was substantiated by the detailed damage observations. Therefore, the fibrous DP concept could provide an efficient pathway to improve the combination of strength and fracture resistance. Full article

The objective of this study is to develop failure-limit material models for Aluminum 6061-T6, A36 Carbon Steel, 304 Stainless Steel, and Nitronic 60 metals, based on parameters of plastic equivalent strain (failure strain) and stress triaxiality. The research is conducted in two parts. This paper presents Part One of the study. In Part One, custom-designed test specimens undergo controlled uniaxial tension and compression testing at ambient temperature. These tests are performed at quasi-static speeds using Universal Testing Machines (UTMs) in accordance with ASTM E8 and ASTM E9 standards. Experimental data, specifically engineering stress–strain and force–displacement curves, are recorded from the onset of loading until specimen fracture, or in the case of compression tests, until the capacity of the testing machine is reached. In Part Two, the emphasis shifts to the calibration of Finite Element Analysis (FEA) models of the custom-designed test specimens. Plastic equivalent strain and the corresponding stress triaxiality values at failure are extracted from each test specimen for the given metal. These values are then systematically plotted onto a single graph to construct the failure-limit curve, which delineates the boundary conditions for material failure. This approach will facilitate the development of a comprehensive material property definition that correlates plastic equivalent strain with stress triaxiality at failure for Aluminum 6061-T6, A36 Carbon Steel, 304 Stainless Steel, and Nitronic 60 metals. Full article

Ultrasonic vibration (UV) has been employed in various plastic forming processes due to its special effect known as acoustoplasticity. Mostly, UV is applied along the longitudinal direction in experimental investigations. However, very few studies have focused on normal UV-assisted uniaxial tension, which is more similar to the loading state of sheet metal in actual forming processes. Herein, normal UV-assisted tension tests on a TA1 thin sheet are performed to study its mechanical properties and microstructure evolution. The macro-mechanical behavior is demonstrated by stress–strain curves under different ultrasonic amplitudes and strain rates. Fracture morphology and microstructure evolution are characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) to reveal the UV softening mechanism at the micro level. The results show that the stress reduction induced by UV reaches 20% when the ultrasonic amplitude is 13.9 μm. Fracture mode changes from ductile fracture to brittle fracture with increasing amplitude. Microstructure examinations show that low-angle grain boundary (LAGB) fraction, kernel average misorientation (KAM), and geometrically necessary dislocation (GND) density in the samples experiencing normal UV-assisted tension are all decreased, leading to a reduction in deformation resistance. The inverse pole figures (IPFs) further reveal that the plastic deformation mechanism of the TA1 thin sheet is diversified with the superposition of normal UV. Full article

An experimental campaign based on multiaxial tests is carried out to characterize the ductile behavior of 17-4PH steel and a Ti6Al4V titanium alloy, and to calibrate numerical ductile damage models, accordingly. This study aimed to identify a minimal set of four specimen types to ensure the robust tuning of the damage models, using only a conventional uniaxial machine for testing. Two different shear–tension candidate geometries are identified, modified, and used together with cylindrical and notched bar specimens to evaluate material plastic strain at fracture under several stress states, characterized by different triaxialities and Lode angles. Finite element analysis and digital image correlation techniques are used to identify local data not directly measured from the tests. Three recent ductile damage models are calibrated using the experimental data. The accuracy of the proposed approach is validated and presented for the two alloys, by comparing the results with calibrations performed on the same materials using more conventional multiaxial tests. It is shown that the new methodology is effective, and how either one of the two shear–tension geometries in addition to tensile tests could replace, with the same level of accuracy, typical more complex calibration procedures involving tests that require dedicated facilities. Full article

As a common rebar connector in prefabricated projects, the grouted sleeve connection (GSC) affects structural performance during fire and seismic events. However, the combined impact of both factors may alter GSC performance, although most studies concentrate on high temperature or loading schemes. Few quantitative models are available for predicting the mechanical characteristics of post-fire GSCs under unidirectional tension, let alone cyclic loading. In this study, 18 GSC specimens were made and subjected to heating, water cooling, and cyclic loading. Thermal and mechanical loads caused rebar fracture below 400 °C, but pullout failure occurred beyond 400 °C. GSC performance declined as temperature and loading cycles increased. Based on this test and several previous investigations, predictive models with guaranteed rates for GSC performance after high temperature by water cooling under uniaxial and cyclic loading were constructed. According to the predictive models, the four parameters (including yield strength, ultimate strength, elastic modulus, and ultimate strain) of the GSCs using HRB400 rebars can be obtained. Full article