Search Results (43)

This work presents an atomistic investigation of the structural and mechanical properties of Li–Mg alloys with 5, 10, and 20 at.% Mg using Monte Carlo and Molecular Dynamics simulations, elastic constant calculations, and uniaxial tensile tests. Structural equilibration revealed that Mg species promote enhanced relaxation and a tendency to form B2-type ordering. The elastic constants showed that Mg primarily increases the longitudinal stiffness while the shear-related components remained nearly unchanged. Derived mechanical properties confirm this strengthening trend, and comparison with recent experimental data shows good qualitative agreement. Tensile tests showed composition-dependent deformation mechanisms: the 0 and 5 at.% Mg samples underwent complete BCC-to-FCC transformation accompanied by strong stress reduction, the 10 at.% Mg alloy exhibited a similar transition while preserving positive stresses, and the 20 at.% Mg alloy displayed an abrupt shear-band instability that interrupted the transformation. These results provide insights into the role of Mg as an element that enhances the structural stability and mechanical stiffness of Li-Mg alloys, supporting their improved performance as electrode materials. Full article

Understanding the microstructure–property relationship in aluminum extrusions is crucial to leverage their potential in automotive lightweighting. The sensitivity of the processing history to the microstructure and through-thickness variations poses a major challenge since it leads to strong directionality in plasticity and fracture. Reliable characterization of the mechanical response under relevant stress states is crucial for the development of modeling strategies and performance ranking in alloy design. To this end, tensile and 3-point bend tests were performed for an aluminum extrusion produced on a laboratory-scale extrusion press at Rio Tinto Aluminium. Direct measurements of surface strains during bending using stereoscopic digital image correlation revealed that a larger bend angle in the VDA238-100 test does not necessarily imply a higher fracture strain. The T4 sample tested in the extrusion direction sustained a bend angle of 104° compared to 68° in T6 for the same nominal bend severity (ratio of sheet thickness to punch radius), despite comparable major fracture strains of 0.60 and 0.58, respectively. It is proposed that the work-hardening behavior governs the strain distribution on the outer bend surface. The higher hardening rate in the T4 condition helped distribute deformation in the bend zone more uniformly. This delayed fracture to larger bend angles since strain is accumulated at a lower rate. To assess whether the effect of the hardening behavior is manifest at a microstructural lengthscale, microcomputed tomography (μ-CT) scans were conducted on interrupted bend samples. The distribution and severity of damage in the form of cracks on the outer bend surface were distinct to the temper and thus the hardening rate. Full article

Under specific temperature and strain rate conditions, certain materials, such as low-carbon steels and select magnesium and aluminum alloys, experience a localized deformation phenomenon known as the Lüders effect. This behavior manifests as a well-defined yield point, after which the stress–strain response transitions into a plateau phase. Experimentally observed through full-field tests, the Lüders effect appears in the form of a band(s). This manuscript presents, for the first time, a systematic study of interrupted loading on the Lüders phenomenon in AISI 1524 hot-rolled steel, using uniaxial tensile testing combined with digital image correlation (DIC). While similar approaches have been applied to other alloys, no prior work has reported on AISI 1524 steel under unloading–reloading cycles during the Lüders plateau. Interruptions in loading involved unloading at 25%, 50%, and 75% of the total plateau region independently until stress approached zero, followed by reloading at the same rate until failure. Each unloading case was subjected to two tests, alongside two additional control tests where loading proceeded without interruption. Based on the findings of this study, it can be inferred that the Lüders phenomenon in AISI 1524 steel exhibits a decrease in strain intensity upon unloading, along with an extension of the Lüders plateau when interrupted loading occurs up to halfway through the plateau region. However, implementing an interrupted loading regime at three-quarters of the plateau had minimal to no discernible effect on the phenomenon. The majority of samples displayed two Lüders bands, a few exhibited either a single band or three bands, suggesting a complex relationship with material heterogeneity and specific impurities present in each sample. The novelty of this work lies in showing how controlled unloading–reloading cycles alter both the propagation and characteristics of Lüders bands in AISI 1524 steel. Full article

In this paper, the tensile behavior of the power cable used for charging electric machines was analyzed. It is known that such a cable, consisting of several conductors, polymeric sheaths and textile core wire, can be subjected to mechanical and thermal stresses that lead to failure to operate at the desired parameters or to total interruption of operation. The mechanical stresses to which the cable is subjected are, in general, bending and tensile stresses, with the development of normal stresses, torsional stresses where tangential stresses occur and, possibly, shock stresses produced by several causes. The present paper proposes to determine some mechanical characteristics of the mentioned conductors resulting from tensile stress for testing, using a special device built for this purpose. In order to obtain other mechanical characteristics also, a finite element analysis has been carried out, the results of which are compared with those obtained from the experiment. Another type of determination was also carried out using the tensile device: the variation of the electrical resistance of one of the electrical conductors of the cable during tensile stress was recorded. Full article

Widening existing bridges is an important way to meet the surge in traffic demand, which is often carried out in a way that does not interrupt traffic. To investigate the effect of traffic vibration on the compressive strength of high-strength concrete and the splitting strength of new-to-old concrete interfaces, the initial to final set time of high-strength concrete C60 was first investigated in this article. Then, the traffic disturbance parameters were determined. Later, the compressive strength of C60 concrete at different stages under traffic disturbance parameters was carried out. Finally, the splitting tensile strength of new-to-old concrete specimens at different stages with different loading modes was tested. The test results indicated that the compressive strength of the specimens vibrated for 3 h and cured for 3, 7, and 28 days was increased by 4.3%, 5.7%, and 11.9%, respectively; those of the specimens vibrated for 7 h and cured for 3, 7, and 28 days was decreased by 13.7%, 20.4%, and 19.9%, respectively; the effect traffic vibration on the compressive strength of the specimens vibrated for 5 h was not obvious. When loaded along the old and new concrete joint, the specimens cracked along the joint; the splitting tensile strengths of the specimen at different disturbed stages were significantly decreased. When loaded perpendicular to the joint, the specimens cured for 3 and 7 days still cracked along the joint, and the splitting tensile strengths of the specimen at different disturbed stages were significantly decreased; while the specimens cured for 28 days cracked in the direction perpendicular to the joint, the tensile strengths of the specimens at different disturbed stages were significantly decreased. This study can promote the widening and improvement of existing concrete highways and bridges, which can save resources and improve land use. Full article

Early in fatigue life, fatigue cracks are often initiated at persistent slip bands (PSBs), which play the main role in surface evolution when the components are subjected to cyclic loading. Therefore, this paper aims to study the behavior of the surface development of medium-carbon steel, specifically 42CrMo4 (SAE 4140). Tests were conducted using tension–compression fatigue testing with stress amplitudes set at 30%, 40%, and 50% of the ultimate tensile strength (UTS); a load ratio of R = −1; and a frequency of f = 10 Hz. The ultimate number of test cycles was 2 × 10⁵. The fatigue test specimens with as-machined surface quality (Ra < 100 nm) were tested on a servo-hydraulic push–pull testing machine, and the tests were interrupted a few times to bring the specimens out for surface measuring with a confocal microscope. The linear roughness values of the arithmetic mean deviation (Ra), maximum height (Rz), maximum profile peak height (Rp), and maximum profile valley depth (Rv) were investigated and further used to determine the roughness evolution during cyclic loading (REC) by analyzing the inclinations of the fitting curves of roughness and number-of-cycles diagrams. REC could then be used to estimate and classify the fatigue lifetime. Full article

X80 steel plays a pivotal role in the development of oil and gas pipelines; however, its welded joints, particularly the heat-affected zone (HAZ), are susceptible to stress corrosion cracking (SCC) due to their complex microstructures. This study investigates the SCC initiation mechanisms of X80 steel welded joints under practical pipeline conditions with varying levels of cathodic protection. The SCC behaviors were analyzed through electrochemical measurements, hydrogen permeation tests, and interrupted slow strain rate tensile tests (SSRTs) conducted in a near-neutral pH environment under different potential conditions (OCP, −1.1 V_SCE, −1.2 V_SCE). These behaviors were influenced by microstructure type, grain size, martensite/austenite (M/A) constituents, and dislocation density. The sub-zones of the weld exhibited differing SCC resistance, with the fine-grain (FG) HAZ, base metal (zone), welded metal (WM) zone, and coarse-grain (CG) HAZ in descending order. In particular, the presence of coarse grains, low dislocation density, and extensive M/A islands collectively increased corrosion susceptibility and SCC sensitivity in the CGHAZ compared to other sub-zones. The SCC initiation mechanisms of the sub-zones within the X80-steel welded joint were primarily anodic dissolution (AD) under open-circuit potential (OCP) condition, shifting to either hydrogen-enhanced local plasticity (HELP) or hydrogen embrittlement (HE) mechanisms at −1.1 V_SCE or −1.2 V_SCE, respectively. Full article

Thermoplastic composites are continuously replacing thermosetting composites in lightweight structures. However, the accomplished work on the fatigue behavior of thermoplastics is quite limited. In the present work, we propose a numerical modeling approach for simulating fatigue delamination growth and predicting the residual tensile strength of quasi-isotropic TC 1225 LM PAEK thermoplastic coupons. The approach was supported and validated by tension and fatigue (non-interrupted and interrupted) tests. Fatigue delamination growth was simulated using a mixed-mode fatigue crack growth model, which was based on the cohesive zone modeling method. Quasi-static tension analyses on pristine and fatigued coupons were performed using a progressive damage model. These analyses were implemented using a set of Hashin-type strain-based failure criteria and a damage mechanics-based material property degradation module. Utilizing the fatigue model, we accurately foretold the expansion of delamination concerning the cycle count across all interfaces. The results agree well with C-scan images taken on fatigued coupons during interruptions of fatigue tests. An unequal and unsymmetric delamination growth was predicted due to the quasi-isotropic layup. Moreover, the combined models capture the decrease in the residual tensile strength of the coupons. During the quasi-static tension analysis of the fatigued coupons, we observed that the primary driving failure mechanisms were the rapid spread of existing delamination and the consequential severe matrix cracking. Full article

The creep behaviour of as-built additive-manufactured Ti-6Al-4V alloy was studied through small punch creep test (SPCT) experiments at 450 and 500 °C. The couple stress/minimum strain rate deduced from these tests made it possible to draw a Norton plot showing good agreement with tensile test creep results. The microstructure characterisation within the SPCT specimen evidenced the effect of local strain on microstructure evolution. After interrupted creep at 450 °C, in most deformed areas, the as-built martensite structure was fully decomposed to the α + β equilibrium phases, giving rise to a submicron equiaxed grain structure. Full article

Low fracture toughness has been a major barrier for the structural applications of cast Mg-Gd-Y-Zr alloys. In this work, the tensile properties and fracture toughness of a direct-chill-cast Mg-9Gd-4Y-0.5Zr (VW94K) alloy were investigated in different conditions, including its as-cast and as-homogenized states. The results show that the tensile properties of the as-cast VW94K alloy are greatly improved after the homogenization treatment due to the strengthening of the solid solution. The plane strain fracture toughness values K_Ic of the as-cast and as-homogenized VW94K alloys are 10.6 ± 0.5 and 13.8 ± 0.6 MPa·m^1/2, respectively, i.e., an improvement of 30.2% in K_Ic is achieved via the dissolution of the Mg₂₄(Gd, Y)₅ eutectic phases. The initiation and propagation of microcracks in an interrupted fracture test are observed via an optical microscope (OM) and scanning electron microscope (SEM). The fracture surfaces of the failed samples after the fracture toughness tests are examined via an SEM. The electron backscatter diffraction (EBSD) technique is adopted to determine the failure mechanism. The results show that the microcracks are initiated and propagated across the Mg₂₄(Gd, Y)₅ eutectic compounds in the as-cast VW94K alloy. The propagation of the main cracks exhibits an intergranular fracture pattern and the whole crack propagation path displays a zigzag style. The microcracks in the as-homogenized alloy are initiated and propagated along the basal plane of the grains. The main crack in the as-homogenized alloy shows a more tortuous fracture characteristic and a trans-granular crack propagation behavior, leading to the improvement of the fracture toughness. Full article

Without interrupting the traffic on the old bridge, the connection of the widening bridge will cause disturbance to the concrete in the splicing position. In order to study the anti-disturbance performance of concrete material, the Normal Concrete (NC) material and the Ultra-High-Performance Concrete (UHPC) material were experimentally investigated by the vertical shaking table and X-ray computed tomography scanning. It can be learnt from tests that the compressive strength of NC and UHPC can be increased by about 10% to 20% after disturbance, while the flexural tensile strength and splitting tensile strength of both NC and UHPC can be reduced by about 20% to 25% and 10% to 20%, respectively. The elastic modulus of UHPC is not significantly affected by the vibration disturbance, and that of NC can be increased by about 20%. The setting time difference of the proposed NC material can be controlled within 100 min, and it can improve its anti-disturbance performance. Excessive vibration disturbance affects the internal structure of NC, while it has little effect on the distribution of steel fiber in UHPC. Due to the high cost of UHPC materials, it is recommended to analyze the joint performance requirements before the selection of splicing materials. If the stress requirement is not particularly high, it is still recommended to apply the proposed NC material for the splicing of widening bridge. Full article

For the purpose of splicing widening bridges without interrupting traffic in expressway reconstruction and extension projects, different types of anti-differential disturbance concrete (ADC) were developed. This paper experimentally investigated the mechanical performance of ADC under the influence of traffic–vehicle coupling vibration. The experimental device, with one end fixed and the other end vertically vibrated, was designed to simulate vehicle–bridge coupling vibration on an existing old bridge. Different disturbance degrees were simulated by adopting specimens made with standard molds and integral plate molds. The compressive strength and other performances of normal-type ADC (NADC) and high-performance ADC (HPADC) were tested. Owing to the differential disturbance, the compressive strength of the NADC increased by 10~20%, and that of the HPADC was almost unaffected. The flexural tensile strengths of the NADC and the HPADC were decreased to some extent. NADC and HPADC can both meet the requirement of widening bridge splicing, and the anti-differential disturbance performance of HPADC is superior to that of NADC. Full article

In order to reveal the effect of irradiation damage caused by high-level liquid radioactive wastes on the welded joint of the container, the irradiation-induced microstructure evolution and mechanical properties degradation of the 310S stainless steel welded joints were investigated in this study. For this purpose, the 1.3 MeV ⁶⁰Co and 2 MeV accelerators were used to simulate irradiation experiments on 310S welded joints. The uniaxial tensile tests characterized the specimens' mechanical properties and fracture morphology. The results revealed that elongation was reduced by about 5% of irradiation damage by ⁶⁰Co, and the fracture morphology shows a large number of secondary cracks. In contrast, the elongation was recovered irradiated by the accelerator, and the fracture morphology showed a large number of dimples. Following the interrupted creep deformation, creep fracture tests were conducted for irradiation specimens. The ⁶⁰Co irradiation damage significantly decreases the creep resistance, leading to deformation of creep, which is increased to 1.5 times that of those unirradiated specimens. At the same time, the ductility is seriously degraded for the irradiated creep fracture specimens. As a result, the creep fracture strain of ⁶⁰Co specimens is reduced to 70% of that of unirradiated specimens. Further, ductility reduction was related to the irradiated hardening by ⁶⁰Co, while Nano-indenter hardness was 5.9 GPa, higher by 44% than the unirradiated specimens. The results are shown in an enrichment of Cr, C and P elements at phase boundaries for ⁶⁰Co irradiation specimens, while the magnitude of element segregation increased by the accelerator combination irradiation. Finally, the creep cracking analysis results show intergranular cracking was observed on the surfaces of the irradiated specimens, while the M₂₃C₆ has a primary relationship with the intergranular cracks. The synergic effect of irradiation promoted damage, and element segregation was the primary cause of the intergranular cracking of the 310S welded joints. Full article

Polystyrene (PS) is a widely used building insulation material with good mechanical strength and strong temperature adaptability. However, PS itself is highly flammable and displays poor flame retardancy. At present, building fires caused by organic external wall thermal insulation materials prepared from PS represent a new fire hazard. In this study, the addition of an intumescent flame retardant (IFR) to reduce the flammability of PS was achieved. Using melamine (MEL), acrylonitrile-styrene-acrylate (ASA), and phytic acid (PA) as raw materials, a new type of flame retardant (MAP) was prepared by an electrostatic self-assembly method and was introduced to modify PS. Its effect on the flammability of PS composites was also investigated. The flammability of the PS composites was characterized using the limiting oxygen index (LOI) and vertical combustion. The effect of MAP on the morphology of the carbon layer formed from polymer decomposition was studied using scanning electron microscopy (SEM). By adding MAP to a PS/20%N-IFR flame-retardant composite, the flame-retardant property was significantly improved, the limiting oxygen index reached 37, and the vertical combustion reached a V-0 level. The fire performance index (FPI) of the PS/20%N-IFR composite reached 0.0054, which was significantly higher than that of the control PS (0.037) as determined by the cone calorimetry test. The SEM results showed that the introduction of MAP can increase the density of the carbon layer after combustion. The heat release rate for combustion was reduced. In addition, the mechanical properties of the PS/20%N-IFR composites were compared with those with no flame retardant. The tensile strength of the PS/20%N-IFR composite was 26.1 MPa and the elongation of the PS/20%N-IFR composite remained at 2.2%. The PS/20%N-IFR composite displayed better flame retardancy than the untreated material and good mechanical properties. The presence of MAP prevented the heat and oxygen transfer and interrupted the releasing of flammable products, thus protecting the PS from burning. This flame-retardant material may find broad applications in building insulation materials. Full article

Underground pipelines are vital parts to urban water supply, gas supply, and other lifeline systems, affecting the sustainable development of cities to a great extent. The pipeline joint, which is a weak link, may be seriously damaged during natural disasters such as earthquakes. The failure of pipe joints can cause leakage accidents, resulting in system failure and interruption, and even some secondary disasters. Herein, based on uniaxial and plane tensile test results of a T-rubber gasket material, the assembly process and sealing performance of a T-rubber gasket joint of a ductile iron pipe are numerically simulated using the Ogden third-order strain energy density function to fit the material constant. The simulation accounts for severe nonlinearities, including large deformations, hyperelasticity, and complex contacts. The effects of the assembly friction coefficient, assembly depth, and radial clearance deviation of the socket and spigot on the seal contact pressure are analyzed. The results suggest that the entire history of the deformation and stress variations during assembly can be clearly visualized and accurately calculated. For the different friction coefficients, the assembly depth corresponding to the sliding friction condition of the spigot pipe was 74 mm, while the minimum pushing force required to assemble the T-rubber gasket joint of a DN300 ductile iron pipe was 6.8 kN at the ideal situation with a friction coefficient of 0. The effective contact pressure of the rubber gasket seepage surface under various operating conditions is much higher than the normal pressure of municipal pipelines, thus indicating that the rubber gasket joint exhibits the ideal sealing performance. Furthermore, a certain deviation, which is about 20 mm, is allowed for the assembly depth of the rubber gasket joint such that the axial displacement of the pipe joint can be adapted under an earthquake or ground displacement. Full article