Dynamic Strain Research Articles

Ultrasensitive optomechanical strain sensor

We demonstrate an ultrasensitive optomechanical strain sensor based on a SiN membrane and a Fabry-Perot cavity, enabling the measurements of both static and dynamic strain by monitoring reflected light fluctuations using a single-frequency laser. The SiN membrane offers high-quality-factor mechanical resonances that are sensitive to minute strain fluctuations. The two-beam Fabry-Perot cavity is constructed to interrogate the motion state of the SiN membrane. A static strain resolution of 4.00 nɛ is achieved by measuring mechanical resonance frequency shifts of the SiN membrane. The best dynamic resolution is 4.47 pɛHz-1/2, which is close to that of the sensor using high-finesse cavity and optical frequency comb, overcoming the dependence of ultrasensitive strain sensors on narrow-linewidth laser and high-finesse cavity with frequency locking equipment. This work opens up a promising avenue for a new generation of ultrasensitive strain sensors.

Investigation of dynamic compression properties of lightweight engineered geopolymer composites containing different ceramsites (LW-EGC)

Lightweight engineering geopolymer composites (LW-EGC) can contribute to green building materials products by taking advantage of the advantages of man-made ceramsite and geopolymers. In this paper, an active "sacrifice" method was proposed, which is based on the idea that low elastic modulus ceramsites are preferentially damaged or ruptured during the impact loading process, thus absorbing and dissipating the impact energy. LW-EGC was enhanced by PVA fiber with volume fraction of 2% and multi-walled carbon nanotubes with mass fraction of 0.15%. The dynamic compression properties of LW-EGC containing different ceramsites were studied by using Φ100 mm split Hopkinson pressure bar (SHPB) test device. The compression characteristics of the LW-EGC under an impact load were evaluated, including the strain rate, dynamic stress–strain relationship, elastic modulus, dynamic increase factor (DIF), energy absorption, and failure patterns. The results showed that the dynamic peak stress, dynamic peak strain, DIF, energy absorption and damage degree of LW-EGC all increased with the increase of strain rate, showing obvious strain-rate sensitivity. At high strain rate, the dynamic elastic modulus mainly showed softening effect. At the same strain rate, the impact resistance of LW-EGC-1 containing fly ash ceramsite was the best, and the damage degree of LW-EGC-3 containing shale ceramsite was the lowest. Empirical DIF formulas of the LW-EGC was proposed; the DIF increased approximately linearly with the strain rate in a logarithmic manner.

The 2022–2023 seismic sequence onshore South Evia, central Greece: evidence for activation of a left-lateral strike-slip fault and regional triggering of seismicity

On 29 November 2022, an earthquake of ML 5.0 (Mw 4.8) occurred onshore South Evia Island (central Greece) preceded by a ML 4.7 (Mw 4.6) event. The pattern of relocated aftershocks indicates the activation of a single, near-vertical fault segment, oriented NW-SE at shallow crustal depths (6–11 km). We suggest that both events ruptured a blind, left-lateral strike-slip fault, about 5 km southeast of village Almyropotamos. We observed that a clear foreshock activity (N=55 events) existed before the two moderate events. The impact of the static stress loading on neighboring fault planes diminishes after a distance of 7 km from the November 2022 epicenters, where the static stress falls below +0.1 bar. We further explore triggering relationships between the 29 November events and the late December 2022 moderate events (ML 4.9) that occurred about 60 km toward NW in the Psachna and Vlahia regions of central Evia. We present evidence of possible delayed dynamic triggering of the late December 2022 central Evia sequence, based on marked changes in seismicity rates and on measured peak ground velocities (PGVs) and peak dynamic strains, both exhibiting local maxima in their map distributions. The causes of the delayed triggering may be related to the well-known geothermal field in central/north Evia and the NW-SE strike of the seismic fault.

Identification and analysis of a reverse dynamic strain ageing in welded joints of C-Mn steels in the secondary circuit welds of nuclear power plants

In an original way, we exploit a restricted region within the dynamic strain ageing domain where a simultaneous increase in strength and uniform elongation has been shown, with increasing free solute concentrations. This unusual reverse dynamic strain ageing was shown to be a marker of the interaction between strain ageing and strain hardening. Analysis, based on a dual experimental and theoretical approach, shows that dynamic strain ageing reduces the ability of the material to exhibit dynamic recovery. This regime operates at very low solute concentrations and saturates above a critical solute concentration. All the results obtained support the dislocations/solutes interactions as the main mechanism.

Numerical Simulation Study of the Vibrational Response of Continuous Arch Tunnels under the Action of Overlying Train Loads

With the rapid development of transportation infrastructure in China, continuous arch tunnels passing under existing operational railways are increasingly encountered. This paper primarily investigates the mechanical response patterns of the lining of continuous arch tunnels under the vibrational loads generated by trains traveling on railways. To this end, a three-dimensional finite element model of the dynamic response of continuous arch tunnels under train vibrational loads was constructed using Midas GTS/NX software. This model explores the patterns of acceleration, dynamic displacement, and dynamic strain responses of continuous arch tunnels under the action of moving train loads. The study reveals that under train vibrational loads, the vertical acceleration, vertical displacement, and strain time history curves at various monitoring points in the continuous arch tunnel exhibit vibrational characteristics. The acceleration, vertical displacement, and dynamic strain increase as the train enters, fluctuate within a certain range, and then decrease to zero as the train exits. Under high-speed train loads, the acceleration peak values at the arch feet and outer sidewalls of the left and right tunnels are larger, with a greater peak value difference. The vertical displacement peak values at the arch shoulders and crown are larger, whereas those at the middle partition wall and base slab are smaller. During the process from the train's entry to its exit, the dynamic strain exhibits a trend of initially increasing, then stabilizing, and finally decreasing to zero, all while displaying vibrational characteristics. The strain response on the tunnel side where the train enters is greater than that on the side where it exits.

Ross Ice Shelf Displacement and Elastic Plate Waves Induced by Whillans Ice Stream Slip Events

AbstractIce shelves are assumed to flow steadily from their grounding lines to the ice front. We report the detection of ice‐propagating extensional Lamb (plate) waves accompanied by pulses of permanent ice shelf displacement observed by co‐located Global Navigation Satellite System receivers and seismographs on the Ross Ice Shelf. The extensional waves and associated ice shelf displacement are produced by tidally triggered basal slip events of the Whillans Ice Stream, which flows into the ice shelf. The propagation velocity of 2,800 m/s is intermediate between shear and compressional ice velocities, with velocity and particle motions consistent with predictions for extensional Lamb waves. During the passage of the Lamb waves the entire ice shelf is displaced about 60 mm with a velocity more than an order of magnitude above its long‐term flow rate. Observed displacements indicate a peak dynamic strain of 10−7, comparable to that of earthquake surface waves that trigger ice quakes.

Impact toughness and dynamic constitutive model of geopolymer concrete after water saturation

The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress–strain curves.

Dynamic compressive behaviors of polyethylene terephthalate fiber reinforced recycled aggregate concrete

AbstractPolyethylene terephthalate (PET) fibers are green, environmentally friendly materials. They mainly come from recycled plastic bottles and other products. The addition of PET fibers to recycled aggregate concrete (RAC) has the potential to reduce concrete damage and increase specimen toughness. In this study, the influences of recycled coarse aggregate (RCA) replacement ratio and fiber volume ratio on the impact response of PET fiber reinforced RAC at various strain rates were experimentally investigated. It was found that the compressive strength, critical strain, and toughness grew with the increasing strain rate, followed by the aggravation of the concrete damage. Owing to the strain rate effect, the failure mode of concrete specimen at a high strain rate was different from that under a quasi‐static loading. This led to the reduction of differences in the dynamic compressive strength between the natural and recycled aggregate concrete at a high strain rate. Although the replacement of natural coarse aggregates with RCAs resulted in the decrease in the dynamic compressive strength, it increased the critical strain of the specimen. To reduce the brittleness of concrete materials, flexible fibers, PET fibers were added into the concrete matrix. It was found that the addition of PET fibers increased the critical strain and significantly reduced concrete damage. The empirical equations were proposed to describe the rate‐dependent dynamic compressive strength, critical strain, and toughness based on experimental data.

Mechanism of high temperature mechanical properties enhancement of Ni-based superalloys repaired by laser directed energy deposition: Microstructure analysis and crystal plasticity simulation

The high-temperature tensile and fatigue performance play a crucial role in the applications of repaired Ni-based superalloys by Laser directed energy deposition (LDED). This work investigates the effect of microstructure on the high temperature (650 °C) mechanical behaviors of GH4169 superalloys repaired by LDED with the microstructure characterizations and crystal plasticity modelling. Results indicate that the solution and aging heat treatment (STA) is necessary to homogenize the distributions of precipitations. Microstructure characterizations and crystal plasticity modelling imply that the plasticity deformations occur mainly in columnar dendrites of fusion area and twin grains of substrate, which enhance the tensile strength and elongation rate of repaired area and demonstrates comparable characteristics with the casting alloy. At the same time, the existence of the Laves phase and carbide cannot eliminate the dynamic strain aging phenomenon of repaired material. Similarly, under high stress levels (850– 950 MPa), the fatigue performance of repaired material is primarily influenced by the plastic deformation and exhibits similarity to that of the substrate; however, under low stress levels (650– 750 MPa), it is primarily influenced by the presence of defects, resulting in an obviously longer fatigue life for the substrate.

Cyclical hydraulic pressure pulses reduce breakdown pressure and initiate staged fracture growth in PMMA

Using unique experimental equipment on large bench-scale samples of Polymethylmethacrylate, used in the literature as an analogue for shale, we investigate the potential benefits of applying cyclical hydraulic pressure pulses to enhance the near-well connectivity through hydraulic fracturing treatment. Under unconfined and confined stresses, equivalent to a depth of up to 530 m, we use dynamic high-resolution strain measurements from fibre optic cables, complemented by optical recordings of fracture development, and investigate the impact of cyclical hydraulic pressure pulses on the number of cycles to failure in Polymethylmethacrylate at different temperatures. Our results indicate that a significant reduction in breakdown pressure can be achieved. This suggests that cyclic pressure pulses could require lower power consumption, as well as reduced fluid injection volumes and injection rates during stimulation, which could minimise the occurrence of the largest induced seismic events. Our results show that fractures develop in stages under repeated pressure cycles. This suggests that Cyclic Fluid Pressurization Systems could be effective in managing damage build-up and increasing permeability. This is achieved by forming numerous small fractures and reducing the size and occurrence of large fracturing events that produce large seismic events. Our results offer new insight into cyclical hydraulic fracturing treatments and provide a unique data set for benchmarking numerical models of fracture initiation and propagation.

Dynamic and Energy Consumption Characteristics of Sandstone Ring Specimens under Dry and Wet Cycling

The aim of this study was to examine the effects of sandstone ring specimens with different inner diameters on dynamic compression mechanical characteristics after dry and wet circulation. To carry out our study, we subjected a sandstone ring specimen with a 50 mm outer diameter and a 0~25 mm inner diameter to 10 cycles of dry and wet circulation. Afterward, we recorded the specimen’s basic physical parameters and used a split-Hopkinson pressure bar (SHPB) test device to perform an impact compression test. Following dry and wet circulation, our results showed that the mass loss rate increased and the volume expansion rates and density decreased with the increase in the inner diameter of the sandstone ring sample. Simultaneously, with the increase in the inner diameter of the specimen ring, the dynamic compressive strength of the specimen presented an exponential negative correlation, the dynamic elastic modulus presented a quadratic negative correlation, and the dynamic peak strain presented a quadratic positive correlation. Concurrently, the average particle size of the specimen decreased, and the degree of breakage increased with the increase in the sandstone sample’s inner diameter. Regarding the energy analysis performed in this study, the sandstone ring sample’s energy dissipation increased, and its kinetic performance evidently weakened with the increase in the ring sample’s inner diameter. The results of this study have certain reference values for the construction and maintenance of natural cavity rock and underground hard rock roadways.

Theoretical and numerical modeling of the effect of damage and dynamic strain aging on the plastic response of C45 steel alloys

A constitutive model for C45 steel alloys is proposed in this work by integrating the effect of damage and a specific phenomenon, so-called dynamic strain aging. For damage modeling, an energy-based isotropic damage model is implemented within a frame of continuum damage mechanics. The total stress is decomposed into athermal and thermal elements. The former includes the additional term for dynamic strain aging. This term is conceptually inspired by the probabilistic nature of dynamic strain aging, and its derivation is micromechanics-based. Both athermal and thermal components are defined as a function of temperature, equivalent plastic strain, and equivalent plastic strain rate because the occurrence and characteristics of dynamic strain aging are dependent on these factors. A finite element solution for the developed model is addressed additionally to further investigate the characteristics of plastic-damage behaviors and dynamic strain aging. The numerical results are compared to the experiments and theoretical predictions for its validation. The modified model developed in this work has largely reduced the number of fitting parameters compared to the previous model originally developed by the authors in 2019. Nevertheless, predictions from the proposed model still capture the experimental data accurately.

Dynamic deformation and meso-structure of coarse-grained saline soil under cyclic loading with freeze-thaw cycles

The cumulative deformation properties of subgrade soil under cyclic traffic loads are critical for optimizing pavement structure design and ensuring long-term highway structural performance. This study aims to investigate the coupling effect of freeze-thaw cycles and cyclic loads on the cumulative deformation behaviors and meso-structure of coarse-grained saline soil (CGSS) subgrade filling in high-cold areas. Dynamic triaxial tests and computed tomography (CT) scanning were conducted to analyze the CGSS under different working conditions. The research focused on the dynamic deformation development and damage evolution under varying freeze-thaw cycles and load amplitudes. The research results show that the cumulative deformation behavior of CGSS under cyclic loading is relatively sensitive to the freeze-thaw process. The cumulative dynamic strain increases as the freeze-thaw cycles, with a critical freeze-thaw cycle number of five. The stable cumulative dynamic strain curve exhibits clear three-stage characteristics when plotted in semi-log coordination, with critical loading cycles at 20 and 1,000. After 10–100 loading cycles, the cumulative strain curve quickly shows failure. The CGSS’s low density and pore regions greatly increase after a freeze-thaw cycle. The rise in dynamic stress amplitude notably affects the bonding between soil particles and crystalline salts. The coupling effect of the freeze-thaw cycle and dynamic activity exacerbates the deterioration of soil structure, resulting in variations in CT values within the scanning layer in the final state.

Experimental study and crystal plasticity modeling of additive manufacturing IN718 superalloy considering negative strain rate sensitivity behavior

Revealing underlying mechanisms of IN718 superalloy's negative strain rate sensitivity behavior at elevated temperatures is significantly important for its further applications in extreme conditions. This work investigates the microstructural mechanisms of the temperature-dependent strain rate sensitivity using experimental methods and crystal plasticity characterization model. Firstly, Electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) techniques are utilized to observe microstructural characteristics of additively manufactured IN718 alloy at different temperatures. The influence of solute precipitation and dislocation slip interaction on the mechanical properties is discussed. Subsequently, the representative volume element (RVE) model is constructed by using acquired orientation, grain size, and dislocation density data. Finally, the crystal plasticity model incorporating dynamic strain aging and dislocation density evolution is developed to characterize the relationship between strain rate sensitivity and temperature. The model can effectively simulate the transition of strain rate sensitivity of additive manufacturing materials. The results indicate that the increase in dislocation pinning caused by intensified carbon element precipitation at high temperatures is the primary reason of the strain rate sensitivity change observed in IN718 metal materials. The carbon precipitated at the dislocation nucleus induces serration flow in IN718 superalloy under high strain. This study contributes to understanding and characterizing the microscopic mechanisms of deformation in metal materials subjected to thermal environments.

Temperature dependence of tensile mechanical properties and work hardening behavior in direct laser deposited austenitic stainless steel 316L

Austenitic stainless steel 316 L is widely used in various industries due to its good mechanical properties at elevated temperatures (up to 600 °C), excellent corrosion resistance, and relatively low cost. However, there is lack on investigations of high-temperature properties of direct laser deposited (DLD) 316 L alloy. In the present investigation, tensile tests were performed at temperatures ranging from 20 to 1000 °C to study the effect of temperature on mechanical properties and work hardening behaviour. It was found that DLD-processed 316 L alloy has minor anisotropy of mechanical properties and work hardening behaviour at elevated temperatures higher than 200 °C. A gradual decrease in yield stress accompanied by a slight altering of ductility in the temperature range between 200 °C and 700 °C is caused by the dynamic strain ageing effect. At higher temperatures, a rapid decrease in mechanical properties is observed. Strength properties of the DLD alloy are lower in comparison with selective laser melted alloy but higher than those of wrought alloy up to 900 °C. Stress-strain curves of the material has shown stage-by-stage work hardening behaviour, depending on the test temperature. Dilatometric tests revealed a linear increase in the coefficient of thermal expansion (CTE) during heating up to 670 °C for the longitudinal sample and up to 770 °C for the transverse one. Then a non-linear growth of the CTE was observed due to diffusion-controlled transformation of the delta-ferrite to austenite.

Micromechanical response of an electrodeposited NiP metallic glass by pillar compression under extreme conditions

In this work, the mechanical properties of pulse electrodeposited amorphous nickel phosphorous (NiP), with ∼16 wt% P, was investigated for an improved understanding of the deformation behavior of metallic glasses at extreme conditions, particularly at the microscale. Upon decreasing the temperature to sub-ambient, both the yield strength and the shear band density increase. While the change of yield strength with temperature can be well explained by a cooperative shear model, the increase in the number of shear bands can be related to an increase in potential sites for activation of shear transformation zones due to the enhanced structural heterogeneity at lower temperatures. This, however, hinders the percolation of deformation units and leads to a decrease in the shear band propagation speed, from ∼50 nm/s at 295 K to ∼20 nm/s at 195 K. By testing micropillars across seven orders of magnitude in strain rate, a two-stage strain rate sensitivity is observed, from nearly negligible at the quasi-static range (m1 = 0.001 ± 0.002 for 10−3 s−1 to 10−1 s−1) to highly positive at dynamic high strain rate range (m2 = 0.02 ± 0.004 for 1 s−1 to 1000 s−1). This transition implies a change in the yield-controlling process, from the diffusion-assisted relaxation at quasi-static conditions to the rate of energy barrier crossing of shear transformation zones at high strain rates. These findings highlight several distinctive features of microscale metallic glasses, including the reduced shear band velocity at sub-ambient temperature and the two-stage strain rate sensitivity.

Analysis of Dynamic Mechanical Properties and Energy Consumption of Fractured Sandstone under Dynamic–Static Combination Conditions

Under dynamic loads, such as blasting, excavation, or quarrying, rocks with fissures are the first to sustain damage, leading to instability in the engineering rock mass. To investigate the kinetic properties of fractured rocks, fractured coal mine sandstone specimens underwent impact compression tests using a dynamic–static combination SHPB (split Hopkinson pressure bar) test device at different loading rates under combined dynamic and static conditions. The damage characteristics of the specimens were analyzed from an energy point of view. The results show that under the dynamic and static combined condition, when five impact loading air pressures are used for loading at different impact rates, the trends of the dynamic stress–strain curves of prefabricated fissured rock samples under various impact pressures were discovered to be similar and were mainly categorized into three main stages of elasticity, yield, and destruction; the specimen’s dynamic compressive strength increases according to a power function relationship; as the average strain rate increases, the dynamic strain increases linearly and the dynamic modulus of elasticity increases in a quadratic relationship, all of which show a significant strain rate effect. The incident energy is a power function of the loading rate. The reflected, transmitted, and absorbed energies by the sample increase with the incident energy. The degree of the sandstone specimen fragmentation gradually grows with increasing impact loading rate and incident energy, as evidenced by a decrease in the scale of the fragments. The absorbed energy in the sample is mainly used for the deformation damage of the rock, and the more intense the fragmentation of the specimen, the more absorbed energy is required.

Dynamic mechanical behavior of sandstone with filled joints at varying angles under coupled triaxial static and dynamic loading

Natural or artificially formed rock composite structures with consecutively filled joints at varying angles are frequently disturbed by coupled static and dynamic loads. Understanding the impacts of the confining pressure and joint angle on the dynamic mechanical behavior of rocks is important for the stability of rock mass engineering structures. In this study, seven joint angles and four confining pressures were considered. Dynamic triaxial compressive tests of sandstone with consecutively filled joints were conducted using a split Hopkinson bar (SHPB) apparatus. The test results showed that varying degrees of “strain rebound” phenomena were observed in the stress–strain curves, implying that the jointed samples in the failure stage could still store more elastic energy, which may trigger rock burst accidents in practical engineering. Moreover, the dynamic compressive strength and elastic deformation modulus were proportional to the confining pressure, but showed a trend of slight decrease followed by a noticeable increase with an increase in the joint angle from 0° to 90°. The combined effects of axial pre-stress and confining pressure resulted in different trends in the dynamic peak strain. The plastic deformation moduli of samples with smaller joint angles were insensitive to changes in the confining pressure and smaller joint angles, whereas those of samples with larger joint angles were sensitive to changes in the confining pressure and larger joint angles. In addition, the experimental tendency of the dynamic compressive strength under coupled triaxial static and dynamic loading was in good agreement with the theoretical derivation.

Reconsideration of the dislocation arrest model for dynamic strain aging in C-bearing high Mn steel with low stacking fault energy

In the present study, we investigated the behavior of type A serration in the tensile flow curves measured at temperatures ranging from 273 K to 323 K with a strain rate of 1 × 10−3 /s, using high Mn steels with varying N contents. As a result, it was found that the critical engineering strain for the onset of type A serrations (ecA) increased with an increase in the N content at a given tensile temperature. This finding could not be explained by the conventional dislocation arrest model, which has been used to account for type A serrations occurring in C-bearing high Mn steels without N. Therefore, we attempted to explain the result by introducing the dynamic formation of obstacles to dislocation slip, such as mechanical twins and Lomer-Cottrell locks, during tensile deformation, a factor not considered in the conventional dislocation arrest model. However, the specific reason for the increase in the ecA value due to the addition of N was not elucidated. Therefore, we modified the dislocation arrest model based on the concept that the combination and cross-slip of screw partial dislocations, which accumulate at the obstacles, become more favorable due to an increase in stacking fault energy resulting from the addition of N. The modified dislocation arrest model successfully explained the influences of not only N content but also strain rate and tensile temperature on the ecA value in both C-bearing high Mn steels with and without N.

Flexural fatigue properties of concrete based on different replacement percentage of natural sand with manufactured sand

Compression and flexural fatigue tests were conducted on concrete specimens with varying strengths under different replacement percentages of natural river sand (R-sand) with manufactured sand (M-sand) at 0%, 30%, 70%, and 100%. The objective was to compare and analyse differences in fatigue damage of concrete across different replacement percentages. Findings were made that when the replacement percentage of M-sand was 30% and 70%, the concrete exhibited higher fatigue life, irrespective of any variations in compressive strength. The fatigue life of concrete with a compressive strength of 30 MPa could be increased by an average of 20%–30% compared to concrete with a compressive strength of 50 MPa, and this increasing trend reached its peak when the replacement percentage of M-sand was in the range of 30%–70%. In order to enhance the prediction of fatigue life for concrete subjected to varying replacement percentages of natural sand with M-sand and to elucidate the evolution process of fatigue damage in M-sand concrete, dynamic strain gauges and DIC methods were employed. This enabled determination of the cycle-varying maximum strain and residual strain during the fatigue process across different replacement percentages. The findings indicate that the addition of M-sand can significantly delay the degradation of dynamic elastic modulus (E), with this effect being enhanced by over 15%. The fatigue damage was defined based on fatigue deformation modulus; therefore, a new fatigue damage model was established. It was observed that this new model improved accuracy by up to 6.1% compared to the traditional fitted model in this test. Finally, the effects of different replacement percentages of natural sand with M-sand on the brittle transition of concrete were analysed at the microscopic level. This analysis involved a combination of microhardness testing and examination of the interfacial transition zone and hydride map of concrete under a scanning electron microscope across different replacement percentages of natural sand with M-sand.