Strain Distribution Research Articles

Bonding-slip behaviour of steel-concrete interfaces in CFDST members with PBL ribs

The bonding-slip behaviour of different materials of concrete-filled double skin steel tubular members under different interfacial connection structures, such as ribbed plates and ribbed plates with holes, are studied. The failure mode, the bonding force-slip curve and the strain distribution on the slip surface are obtained. The results show that the hollow ratio is inversely proportional to the bonding strength of the interface. The Perfobond leister (PBL) rib enhances bonding performance through increasing the diameter and holes, the effect of excessive hollow ratio on bonding stress is reduced. Different slip interfaces result in various bonding-slip mechanisms. Based on the typical failure modes and bonding-slip mechanism analysis, the bonding strength formulas and bonding stress-slip constitutive models suitable for CFDST members are proposed. A numerical model using a spring element is established by Abaqus for further mechanism analysis, the loading-slip curve and the stress state of the surface are consistent with measured results.

Fully bonded iron-based shape memory alloy for retrofitting large-scale bridge girders: Thermal and mechanical behavior

This study presents a prestressed retrofitting solution for addressing fatigue issues in large-scale steel girders, employing iron-based shape memory alloy (Fe-SMA) strips and adhesive bonding. A comprehensive study encompassing design, experimental tests, and numerical analysis is conducted to develop and validate the proposed solution. A 4200×100×1.5 mm Fe-SMA strip is fully bonded along its entire surface using a two-component epoxy adhesive to a 5300 mm span steel girder. An activation strategy to prestress the Fe-SMA strip is formulated based on a series of finite element (FE) analyses, entailing successive block-by-block heating using a gas torch. Experimental and numerical studies illuminate the full-range thermal and mechanical behavior of the retrofitted girder throughout the activation process. A FE heat transfer analysis with experimental validation reveals the temperature developments and distributions during activation, highlighting a 160 ℃/mm temperature gradient along the adhesive thickness and longitudinal distributions with localized high temperatures. The mechanical behavior during activation, encompassing the effects of thermal expansion, Fe-SMA prestress, and adhesive softening and re-hardening, is interpreted based on experimental and numerical results, showing the evolutions and distributions of deflections, strains, and Fe-SMA prestresses. Static tests and a high-cycle fatigue test up to 3 million load cycles demonstrate the effectiveness and structural integrity of the proposed retrofitting solution.

Full-length strain and damage monitoring for carbon fiber reinforced polymer cable based on optical frequency domain reflectometry

Lightweight, high-strength, corrosion-resistant, and fatigue-resistant carbon fiber reinforced polymer composite (CFRP) cables for cable-stayed or suspension bridges have been considered an excellent alternative to traditional steel cables. In the present paper, optical frequency domain reflectometry (OFDR) technology was applied to realize self-monitoring of the full-length strain and damage of CFRP rod-cable. The full-length axial tensile strain distribution of a 35 m CFRP cable was verified with the tensile test. The strain accuracy was verified to be 1.61 %, with a spatial resolution of ≤ 10 mm and a strain precision of 3.92 με throughout the full-length strain distribution. In comparison to the actual cable force, the cable force distribution, which is based on partial self-monitoring CFRP rods, demonstrates a deviation of approximately 1.6 %. The rod fracture damages in the CFRP cable were identified using wavelet smoothing, resulting in a localization error of ≤ 0.645 m and a quantification error of less than 15 %. According to the present study, methods to determine the cable force distribution and fracture damage for a CFRP cable were proposed.

A simple displacement perturbation method for phase-field modeling of ferroelectric thin film

A displacement perturbation method is proposed for phase-field simulations of the ferroelectric domain structures. A temperature-misfit strain phase diagram is computed to validate this method's accuracy, encompassing rhombohedral, orthorhombic, tetragonal, cubic, and mixed phases by comparing with previous phase-field simulations. The change in free energy density surface with temperature and strain distribution is computed to clarify the mechanism of the mixed phase. The phase diagram, ferroelectric hysteresis, and domain structure all demonstrate that the numerical method of displacement discretization is reliable and practical in solving the time-dependent Ginzburg–Landau equation, consistent with previous simulated and experimental results. This new method offers the advantages of simple programming and easy parallelism, paving the way for advancements in phase-field modeling.

Influence of deep rolling on the [formula omitted]’-martensite formation in the subsurface, geometrically necessary dislocations and corrosion resistance of austenitic stainless steel AISI 304

The influence of deep rolling (DR) parameters (speed, number of passes and pressure) on the equivalent total strain, α’-martensite formation, ultra-microhardness, microstructure, and corrosion resistance of an AISI 304 austenitic stainless steel was investigated. The results showed that increasing DR speed led to less heterogeneous strain distributions and relatively high ultra-microhardness, despite an overall reduction in strain and α’-martensite content. This increase in hardness was related to the rise of geometrically necessary dislocations (GNDs) density, found to be one of the primary microstructural features influencing mechanical behavior under high DR speed. The increase in the number of passes elevated the intensity and depth of strain, leading to a 70% increase in the content of α’-martensite, ultra-microhardness, and producing severe grain refinement. The GNDs density decreased in the refined grain layer and increased sharply below it. Increased pressure induced similar results relative to the number of passes, with less impact. Improvement in the material properties is achieved through the interaction of parameters that result in an increase in the severity of the DR process, i.e, a reduction in speed and an increase in the number of passes and pressure. For severe DR conditions, the materials corrosion resistance in a 3.5% NaCl aqueous solution was significantly improved, with an increase of up to 2488% in the polarization resistance, as assesssed by electrochemical impedance spectroscopy. In potentiodynamic polarization tests, the corrosion potential increased from an average value of −0.274 to −0.14 V, and the corrosion current density decreased by approximately 300%.

Visualization of strain distribution in rubber bulk during friction

This study employed a digital image correlation method (DICM) to experimentally quantify horizontal strain distribution in silicone rubber bulk during horizontal displacement against a stainless-steel sphere with/without glycerol. The strain distribution at different depth levels was measured by capturing the position of white powders in transparent rubber bulk. The experimental results indicated that each point in the rubber bulk moved while describing a horizontal loop during horizontal displacement depending on the position and lubrication conditions. This caused changes in the horizontal strain during horizontal displacement. These results suggest that the hysteresis term could be caused by changes in the vertical and horizontal strains.

Investigation on failure characteristics of mode II crack in heat-treated granite specimen subjected to dynamic loading

In order to solve the energy crisis, geothermal energy development has been increasingly valued in recent years. In many geothermal engineering projects, hydraulic fracturing can cause many cracks to appear inside the rock mass during the extraction process of dry hot rock. At present, there have been many studies on mode I cracks and mixed mode I/II cracks. In order to ensure the smooth progress of the project, it is necessary to supplement the research on mode II crack rocks in high-temperature geothermal environments. A series of experiments were conducted using the Split Hopkinson Pressure Bar (SHPB) device and cracked granite specimens treated at different temperatures, the failure modes could be tracked by using a high-speed camera. The dynamic experiment was simulated using software coupling. The Grain Boundary Model (GBM) can well describe the force-thermal coupling damage behavior among various crystal particles. Some analyses were conducted on dynamic fracture toughness, failure mode, strain distribution, thermal damage, and changes in the number of cracks. The research results illustrated that high temperatures lead to a decrease in the mode II fracture toughness of granite, an increase in fracture time, and greater susceptibility to damage. High temperature will increase the maximum strain at the moment of failure. It was also found that the proportion of intra-grain cracks increased with the temperature. After 500 °C, the number of cracks generated during the fracture process is inversely proportional to the temperature.

Damage evolution of coal with a strong bursting liability and 3D measurement method for elastic deformation energy distribution

When coal with a strong bursting liability is disturbed by a load, catastrophic instability disasters and rockbursts can easily occur. Loaded coal with a strong bursting liability undergoes complex damage evolution and failure behavior due to the intricate interplay among loads, gangue, fractures, and the coal matrix. Intuitively quantifying and characterizing the complex discontinuous structural features, deformation fields, and energy fields within coal is the foundation for the scientific analysis and prevention of disaster mechanisms caused by rockbursts. Therefore, studying the distribution and evolutionary processes of deformation fields and energy fields caused by the evolution of discontinuous structures within coal is highly important for the prevention and control of coal mine rockburst disasters and the protection of coal mine safety during mining operations. In this study, a series of X-ray computed tomography (X-CT) tests were conducted on coal specimens with varying gangue contents under uniaxial compressive loading. The X-CT images clearly illustrated the internal damage evolution of coal with a strong bursting liability, revealing fracture propagation, shear bands, and localized failure under varying loading conditions. Image segmentation was employed to quantitatively analyze the development of damage in coal with a strong bursting liability, revealing the influence patterns of gangue content on the prepeak deformation localization and strength of coal. Additionally, using digital volume correlation, the 3D volumetric displacement and strain of loaded impact-prone coal were determined based on the changes in natural speckle images. The nonuniform distribution of strain was mainly caused by the nonuniform distribution of gangue and pore fractures at the microscopic scale, which explains the localized deformation in coal materials. Importantly, this study provides new full-field strain tensor data and a novel method for measuring the elastic deformation energy of the 3D deformation and cracking processes of loaded coal.

Atomistic insights into friction and wear characteristics of M50 bearing steel: a molecular dynamics simulation study

ABSTRACT M50 bearing steel is a typical alloy material widely used in aeroengines due to its high hardness and fatigue life at high temperatures. To reveal the frictional mechanisms and wear behaviours of contact and sliding, a molecular dynamics simulation model consisting of an indenter and substrate is constructed. The results indicate that, during the indentation process, the normal load exhibits a linear relationship with the indentation depth at shallow depths. With further penetration, the substrate generates severe deformations and subsurface damages. Throughout the scratching process, the average friction force exhibits a linear increase with the growing scratching depth, while the coefficient of friction decreases. Surface morphologies and shear strain distributions are analyzed to elucidate plastic deformation and atomic displacement. Moreover, the wear atom shows a linear proportionality to both scratching distance and depth. These findings enhance understanding of frictional properties and atomic wear behaviour of M50 bearing steel during contact and sliding, potentially informing bearing failure prediction and material optimization.

Flexural behavior of historical RC beams strengthened with hybrid FRP sheets

Historical reinforced concrete (RC) buildings are culturally and aesthetically significant and require conservation due to aging. Strengthening RC buildings often requires the use of Fiber Reinforced Polymer (FRP) sheets, however distinct material properties of historical RC buildings have not been systematically considered yet. This study investigates the flexural behavior of historical RC beams strengthened by hybrid FRP sheets. A total of 11 beam specimens with varying FRP sheet configurations were tested using a four-point bending test to assess their flexural behavior, including failure mode, cracking pattern, load-deflection behavior, strain distribution, and ductility. The results showed that hybrid FRP sheets increased the maximum bearing capacity of strengthened specimens up to 30.2 %. An optimal fiber sheet configuration (T-3) is identified. 45-degree incline installation contributes to a 4.5 % increase in the bearing capacity of specimens. The average ductility loss of hybrid FRP sheets strengthened specimen (except for double-layer strengthened specimen) is 42 %, while an increase of sheet layer post adverse effect on ductility. Strain distribution conforms to the plane-section assumption. Additionally, a maximum bearing capacity calculation model was proposed, aiding the understanding of FRP strengthening in historical RC buildings.

Virulent properties and genomic diversity of Vibrio vulnificus isolated from environment, human, diseased fish.

The incidence of Vibrio vulnificus infections, with high mortality rates in humans and aquatic animals, has escalated, highlighting a significant public health challenge. Currently, reliable markers to identify strains with high virulence potential are lacking, and the understanding of evolutionary drivers behind the emergence of pathogenic strains is limited. In this study, we analyzed the distribution of virulent genotypes and phenotypes to discern the infectious potential of V. vulnificus strains isolated from three distinct sources. Most isolates, traditionally classified as biotype 1, possessed the virulence-correlated gene-C type. Environmental isolates predominantly exhibited YJ-like alleles, while clinical and diseased fish isolates were significantly associated with the nanA gene and pathogenicity region XII. Hemolytic activity was primarily observed in the culture supernatants of clinical and diseased fish isolates. Genetic relationships, as determined by multiple-locus variable-number tandem repeat analysis, suggested that strains originating from the same source tended to cluster together. However, multilocus sequence typing revealed considerable genetic diversity across clusters and sources. A phylogenetic analysis using single nucleotide polymorphisms of diseased fish strains alongside publicly available genomes demonstrated a high degree of evolutionary relatedness within and across different isolation sources. Notably, our findings reveal no direct correlation between phylogenetic patterns, isolation sources, and virulence capabilities. This underscores the necessity for proactive risk management strategies to address pathogenic V. vulnificus strains emerging from environmental reservoirs.IMPORTANCEAs the global incidence of Vibrio vulnificus infections rises, impacting human health and marine aquacultures, understanding the pathogenicity of environmental strains remains critical yet underexplored. This study addresses this gap by evaluating the virulence potential and genetic relatedness of V. vulnificus strains, focusing on environmental origins. We conduct an extensive genotypic analysis and phenotypic assessment, including virulence testing in a wax moth model. Our findings aim to uncover genetic and evolutionary factors that drive pathogenic strain emergence in the environment. This research advances our ability to identify reliable virulence markers and understand the distribution of pathogenic strains, offering significant insights for public health and environmental risk management.

Association analysis of antibiotic and disinfectant resistome in human and foodborne E. coli in Beijing, China

The widespread use of chemical disinfectants and antibiotics poses a major threat to food safety and human health. However, the mechanisms of co-transmission of antimicrobial resistance genes (ARGs) and biocides and metal resistance genes (BMRGs) of foodborne pathogens in the food chain is still unclear. This study isolated 343 E. coli strains from animal-derived foods in Beijing and incorporated online data of human-derived E. coli strains from NCBI. Our results demonstrated a relatively uniform distribution of strains from various regions in Beijing, indicating a lack of region-specific clustering. Additionally, predominant sequence types varied between food- and human-derived strains, suggesting a preference for different hosts and environments. Phenotypic association analysis showed that the chlorine disinfectants peroxides had a significant positive correlation with tetracyclines. Many more ARGs and BMRGs were enriched in human-associated E. coli compared with those in chicken- and pork-origin. The quaternary ammonium compounds (QACs) resistance gene qacEΔ1 had a strong correlation with aminoglycoside resistance gene aadA5, folate pathway antagonist resistance gene dfrA17, sul1 and macrolide resistance gene mph(A). The correlation results indicated a significant association between the copper resistance gene cluster pco and the silver resistance gene cluster sil. Coexistence of many resistance genes was observed within the qacEΔ1 gene structure, with qacEΔ1-sul1 being the most common combination. Our findings demonstrated that the epidemiological spread of resistance is affected by a combination of heavy metals, disinfectants and antibiotic use, suggesting that the prevention and control strategies of antimicrobial resistance need to be multifaceted and comprehensive.

Pressure effects on electrochemical and crack driving forces in aluminium-doped LLZO-based all-solid-state lithium metal batteries

This study employed a combination of computational models and experimental techniques to investigate the effects of stacking pressure on the mechanical deformation and electrochemical performance of All-Solid-State Li metal batteries (ASSLBs). The effects of the stacking pressure were studied in Al-doped LLZO-based electrolytes at the electrode/electrolyte interface and within the electrodes. Optical microscopy and digital imaging correlation (DIC) techniques were used to study the strain distributions induced in the Al-LLZO-based electrolyte at different stack pressures. The results show that minimal levels of stack pressure result in low strains within the electrolyte, whereas intermediate increasing pressures increase the interfacial contacts and electrochemical performance of the cells. However, higher stacking pressures result in higher induced levels of local stresses and strains, which are sufficient to cause cracking and degradation of the electrochemical performance. The implications of the results are discussed for the pressure-assisted manufacturing of all-solid-state lithium metal batteries.

Flexural behaviour of damaged concrete T-beams reinforced with ultra-high performance concrete filling

To improve the flexural performance of damaged reinforced concrete T-beams, a method of filling ultra-high performance concrete (UHPC) in the damaged area was adopted. Experimental studies were conducted on two UHPC-reinforced concrete T-beams with different lengths of damaged areas and one undamaged concrete T-beam as a reference. Crack distribution, failure modes, cracking loads, flexural capacities, and strain variation of the specimens were analyzed. Subsequently, a nonlinear finite element (FE) model of the UHPC-reinforced T-beam was developed using ABAQUS, and the FE model results were compared with the experimental results to validate the accuracy of the FE simulation method. The results indicated that the two UHPC-reinforced T-beams exhibited a similar flexural failure process to the undamaged T-beam. The longitudinal tensile strain distribution at the mid-span section showed that the composite section formed by the filling of UHPC in the damaged region still adhered the assumption of the planar section. Owing to the excellent bond performance between UHPC and the existing concrete, the main cracks of the UHPC-reinforced T-beams appeared in the chiseled area, and the crack widths of the UHPC-reinforced T-beams under the same load were smaller than those of the reference T-beam. Overall, the reinforcing method of filling UHPC in the damaged region can restore or even enhance the flexural performance of the damaged reinforced concrete T-beams.

Monitoring the phase evolution and fracture behavior of advanced multiphase QP steel using EBSD technique and digital image correlation

A novel multiphase 0.17C-5Mn-0.88Si-0.76Al-0.22Mo-0.06Nb steel was subjected to complex thermomechanical processing schedules to produce quenching and partitioning (Q&P) microstructures. The tests were performed in the Gleeble 3800 simulator applying multiple deformations in a plane state of strain and final deformation was applied at 850 °C. The samples were controlled cooled to 240 °C and 260 °C to produce some martensite fraction and subsequently partitioned at a temperature of 450 °C to enrich austenite in carbon from the supersaturated martensite. Different primary/secondary martensite microstructures containing retained austenite were produced, which were subjected to detailed microstructural and fracture studies using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The mechanical behaviour of the samples was investigated in static tensile tests using sub-sized flat samples. Digital image correlation (DIC) measurements were performed to monitor the strain distribution in a micro scale. Relationships between processing conditions and fracture behaviour were assessed in fractographic tests.

Experimental investigation on the fatigue life and damage mechanism of plain weave composites under biaxial tension–torsion combined fatigue loading

In this paper, the fatigue life and damage mechanism of plain weave composites under biaxial tension–torsion combined fatigue loading (TTF) are experimentally investigated. A biaxial TTF loading spectrum is designed to consider different fatigue frequencies and amplitudes, and an automated multi-module loading method with synchronized acquisition of the digital image correlation (DIC) and the testing machine is proposed. A comprehensive analysis of the experimental results, including fatigue lives, strain distribution, temperature variation, stiffness degradation, and typical damage morphologies at different fatigue cycles, has been conducted by utilizing DIC, infrared thermography (IRT) and computed tomography (CT). It is observed that the superimposed torsional fatigue load results in a rapid reduction in fatigue lives of plain weave composites, accompanied by more significant residual strain, energy dissipation, temperature rise and stiffness degradation. Particularly, the superimposed torsional fatigue loads mainly promote matrix cracking and debonding around the fiber/matrix interfaces, which then accelerates the damage initiations and accumulations of fiber yarns, ultimately leading to a rapid reduction in TTF fatigue lives. This study can provide valuable references for the design and safe application of plain weave composites under TTF loading.

Visual Strain Sensors Based on Fabry-Perot Structures for Structural Integrity Monitoring.

Strain sensors that can rapidly and efficiently detect strain distribution and magnitude are crucial for structural health monitoring and human-computer interactions. However, traditional electrical and optical strain sensors make access to structural health information challenging because data conversion is required, and they have intricate, delicate designs. Drawing inspiration from the moisture-responsive coloration of beetle wing sheaths, we propose using Ecoflex as a flexible substrate. This substrate is coated with a Fabry-Perot (F-P) optical structure, comprising a "reflective layer/stretchable interference cavity/reflective layer", creating a dynamic color-changing visual strain sensor. Upon the application of external stress, the flexible interference chamber of the sensor stretches and contracts, prompting a blue-shift in the structural reflection curve and displaying varying colors that correlate with the applied strain. The innovative flexible sensor can be attached to complex-shaped components, enabling the visual detection of structural integrity. This biomimetic visual strain sensor holds significant promise for real-time structural health monitoring applications.

Intercritically Annealed Medium-Manganese Steel: Insights into Microstructural and Microtextural Evolution, Strain Distribution, and Grain Boundary Characteristics.

Aluminum-incorporated medium-manganese steel (MMnS) has potential for lightweight transport applications owing to its impressive mechanical properties. Increasing the austenite volume fraction and making microstructural changes are key to manufacturing MMnS. However, the grain boundary character and strain distribution of intercritically annealed low-density MMnS have not been extensively scrutinized, and the effects of crystallographic texture orientation on tensile properties remain ambiguous. Therefore, in this study, the microstructure, microtexture, strain distribution, and grain boundary characteristics of a hot-rolled medium-Mn steel (Fe-0.2 C-4.3 Al-9.4 Mn (wt%)) were investigated after intercritical annealing (IA) at 750, 800, or 850 °C for 1 h. The results show that the 800 °C annealed sample exhibited the highest austenite volume fraction among the specimens (60%). The duplex microstructure comprised lath-type γ-austenite, fine α-ferrite, and coarse δ-ferrite. As the IA temperature increased, the body-centered cubic phase orientation shifted from <001> to <111>. At higher temperatures, the face-centered cubic phase was oriented in directions ranging from <101> to <111>, and the sums of the fractions of high-angle grain boundaries and coincidence-site-lattice special boundaries were significantly increased. The 800 °C annealed sample with a high austenite content and strong γ-fiber {111}//RD orientation demonstrated a noteworthy tensile strength (1095 MPa) and tensile elongation (30%).

Investigating the efficiency and reliability of different lap-splice configurations in NSM BFRP rods for strengthening RC beams

The use of near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement has shown great promise for flexural and shear strengthening of reinforced concrete (RC) members. However, the continuity of NSM FRP rods is often interrupted due to length constraints, necessitating lap splices to transfer forces between spliced rods. The performance of lap splices depends on design configuration factors, including anchorage shape, splice length, and connection method. This research describes an experimental investigation into the bond behaviour and failure mechanisms of various lap splice designs for NSM basalt FRP (BFRP) rods in RC beams. The parameters investigated were end anchorage shape (straight or Embedded Through-Section (ETS) anchors), and connection type (overlay rods or face-to-face with FRP sheet wrap). A total of 8 simply supported RC beams strengthened with different NSM BFRP lap splice configurations were tested under four-point bending. The load-deflection response, strain distribution, and failure modes were evaluated. Test results showed that beams with NSM FRP rods with ETS anchors exhibited higher bond strength and ductility than face-to-face connections. The outcomes of this study can help optimize lap splice design and detail provisions for NSM FRP systems in future strengthening applications.

Strength of Composite Pressure Insulators for High Voltage Circuit Breakers: An Experimental and Numerical Investigation.

Glass fiber-reinforced composite cylinders, capable of withstanding internal pressure generated during service, are increasingly utilized as insulators in high voltage circuit breakers. Different testing procedures have been suggested by various standards to assess the pressure resistance of these components. Due to its simplicity and cost-effectiveness, the split-disk testing method is the most widely used for evaluating the hoop strength of pressure cylinders during the development and verification phases. However, the method presents several aspects, such as those related to the influence of specimen geometry and friction, which require further examination since they may impact the outcome of the experimental tests. The investigation, carried out by a combination of experimental testing and finite element analyses, shows that the friction between the specimen and the semi-disks has a noteworthy effect on the hoop load applied to the specimen. Almost constant load distributions along the hoop direction, representative of the real operating conditions in a pressurized cylinder, can be achieved via proper lubrication of the contact surfaces. Furthermore, FE analyses demonstrate that the notch geometry suggested by specific standards (short notch) is not capable of inducing a uniform strain distribution in the notched region. A different notch geometry (long notch) is proposed in the study to attain a more uniform strain field over the reduced area region. The experimental results indicate that the strength measured on the short notch specimens is higher than that determined on the long notch specimens, thus confirming the significant influence of strain distribution on the strength properties measured with the split-disk method.