Dynamic Strain Research Articles

Fatigue life analysis of fillet weld with root gap in bogie tie rod seat under road traffic load

The results of failure analysis on the fillet welds of the tie rod seat in HDX2 type vehicle showed that size of root gap around cracks was usually larger than that observed in the region without cracks. Dynamic strain gauges were used to measure the time-strain curve of the zone surrounding the fillet weld in the locomotive traveling process. Then, a transfer matrix was utilized to calculate the time-strain curve of fillet welds and then a rainflow counting method was adopted to obtain hierarchical load spectra in the traveling process, which was used for predicting fatigue damage of fillet welds and safe service mileage. To reveal the influence of the root gap on the fatigue life of fillet welds, a three-factor and five-level orthogonal scheme was designed by taking the height, width and length of the root gap as variables. The calculation results based on road traffic loads indicated that: (1) When there is no gap at the root of fillet weld, the safe service mileage can meet standard requirements; when there is a gap at the root of the fillet weld, the safe service mileage is significantly shortened; (2) When the width, height or length of the root gap of fillet weld increases, the safe service mileage decreases monotonously. Given the same change in size, effect of the change in height of root gap on safe service mileage is the most significant among the three variables considered; (3) The maximum stress at straight line section of weld path was significantly greater than that at the corner section; (4) An inspection and maintenance program for root gaps of various sizes was developed.

Annealing‐Induced Dynamic Strain Evolution in Cycled High‐Ni Layered Oxides Revealing Latent Lattice Imperfections (Adv. Energy Mater. 36/2023)

Annealing‐Induced Dynamic Strain Evolution in Cycled High‐Ni Layered Oxides Revealing Latent Lattice Imperfections (Adv. Energy Mater. 36/2023)

Dynamic responses of copper and impact velocity of split Hopkinson pressure bar strikers

Copper high-impact analysis is critical for understanding characterization at dynamic strain rates. The dynamic behaviour of any material is influenced by numerous components of a split Hopkinson pressure bar (SHPB), such as striker forms, striker speed, striker length, bar geometry, and so on. There is also a significant information gap in the literature when it comes to determining the behaviour of copper under high strain rates, especially when the SHPB parameters are varied. Using ABAQUS/Explicit 6.14, this paper numerically investigates the dynamic behaviour of copper under different striker bar shapes (circular flat, circular round, and square) and impact velocities (10, 12.5, 15, 17.5, and 20 m/s). To understand the effects of the specimen's shape under high strain rate loadings, the geometry of the copper specimen is also changed from circular to square. Copper's behaviour was found to be positively sensitive to strain rates, and compressive strength increased by 32%. For the common velocity of the striker, the maximum copper strength was found for a circular flat-shaped striker and the minimum for a circular round-shaped striker. The true yield strength and ultimate strength increase by 8% and 3%, respectively, when the shape of the specimen changes from circular to square.

Fiber‐Optic Observations of Internal Waves and Tides

AbstractAlthough typically used to measure dynamic strain from seismic and acoustic waves, Rayleigh‐based distributed acoustic sensing (DAS) is also sensitive to temperature, offering longer range and higher sensitivity to small temperature perturbations than conventional Raman‐based distributed temperature sensing. Here, we demonstrate that ocean‐bottom DAS can be employed to study internal wave and tide dynamics in the bottom boundary layer, a region of enhanced ocean mixing but scarce observations. First, we show temperature transients up to about 4 K from a power cable in the Strait of Gibraltar south of Spain, associated with passing trains of internal solitary waves in water depth <200 m. Second, we show the propagation of thermal fronts associated with the nonlinear internal tide on the near‐critical slope of the island of Gran Canaria, off the coast of West Africa, with perturbations up to about 2 K at 1‐km depth and 0.2 K at 2.5‐km depth. With spatial averaging, we also recover a signal proportional to the barotropic tidal pressure, including the lunar fortnightly variation. In addition to applications in observational physical oceanography, our results suggest that contemporary chirped‐pulse DAS possesses sufficient long‐period sensitivity for seafloor geodesy and tsunami monitoring if ocean temperature variations can be separated.

Influence of Adhesive Bonding on the Dynamic and Static Strain Transfers of Fibre Optic Sensors

The influence of the bonding procedure (the adhesive type, application procedure, etc.) on the static and dynamic strain transfers of bonded optical fibre sensors is studied theoretically and experimentally at room temperature. The achievable performances with four different types of adhesives (three urethane and one epoxy adhesive), and with different fibre types, are evaluated: acrylate-coated, polyimide-coated, and bare single-mode optical fibres. Static strain measurements, ranging from 20 to 200 µ strain, are performed using both fibre Bragg gratings (FBGs) and optical frequency domain reflectometry (OFDR), and are compared to reference strain-gauge measurements, and to the proposed analytical model, which is developed on the basis of stress equilibrium relations. This model is valid for bonding to all types of linear and elastic materials, as long as there is no sliding between the host material, the adhesive, and the optical fibre. The results agree between the analytical model and the experiments. Regarding the dynamic sinusoidal strain measurements, the studied dynamic range is from 10 to 100 Hz, and only the FBGs are tested. The results demonstrate that the sensitivities of strain sensors based on bonded uncoated fibres or bonded polyimide-coated fibres are comparable to those of strain gauges, and that it is possible to use bonded FBGs for precise dynamic strain measurements.

Blade Strain Peak Localization Method With Single Transducer During Multimode Vibration

Abstract The dynamic strain/stress measurement of blades provides an effective method to anticipate fatigue life and investigate of failure causes. Unlike the blade strain peak is fixed during singlemode, which can be measured by a single transducer, the strain peak distribution changes over time and space during multimode vibration situations. The existing method reconstructs the full-field strain to find the peak point with multiple transducers. In this work, a single transducer-based full-field dynamic strain reconstruction technique is presented to find the strain peak position on rotor blades. First, the mode response is obtained by separating the measured response from a single strain gauge based on Ensemble Empirical Mode Decomposition. Second, based on the strain mode shape from the finite element model, the reconstructed strain transmissibility matrix is created between a single measured location and the full field. Third, the dynamic strain of the blade can be reconstructed at any location and time by combining the separated mode response with the RST matrix. Finally, the strain peak localization is identified according to the distribution of full-field dynamic strain during multimode vibration. The above process is verified by experimental data from rotor blades with the maximum error of reconstructed strain below 12% and three explicitly recognized strain peak positions.

Experiment Study of Stemming Length and Stemming Material Impact on Rock Fragmentation and Dynamic Strain

Stemming length and stemming materials are crucial factors in blasting design, which affect the sustainability of mining. This study investigates the influence of stemming length and stemming material on rock fragmentation, stemming recoil, and surface strain response through 15 small-scale model blasting tests. The results indicate that when using clay as a stemming material, increasing the stemming length facilitates rock fragmentation and reduces the stemming recoil area. The strain measurements show that both tensile and compressive strain peaks on the blasting crater surface increase with the growth of stemming length, while the strain peaks on the upper surface decrease. A comparative analysis of different stemming materials reveals that clay performs the best, exhibiting the highest total weight of fragments, blasting crater size, and fragmentation energy utilization. Strain results indicate that clay stemming generates more significant strain peaks and higher strain loading rates on the blasting crater surface, favoring a more concentrated application of explosive energy on the crater surface and improving rock fragmentation. Sand + clay stemming yields fragments more concentrated in medium-sized particles than clay stemming. If the blasting goal is to increase the utilization efficiency of explosive energy and reduce the hazards of stemming recoil, it is recommended to use clay stemming. In addition, if uniform fragmentation is desired (reducing large and fine particles), a combination of sand + clay stemming can be used. These findings have practical implications for optimizing blasting design and engineering applications.

Dynamic responses of a waste sludge modified by magnesium-cement-based multiphase cementitious material under influences of temperature and moisture cycles

This paper explores the influences of external stress and moisture and temperature cycles on the microstructure and dynamic responses (including the dynamic shear modulus G, damping ratio λ, and accumulative plastic strain εp) of a waste sludge that is modified by magnesium-cement-based multiphase cementitious material. Experimental results show that (i) freeze–thaw (FT), wet-dry (WD), and wet-dry-freeze–thaw (WD-FT) cycles significantly change the soil’s pore system. Intra-aggregate pores gradually evolve into inter-aggregate pores and cracks develop during moisture and temperature cycles. This leads to the degradation of the pore structure and decrease in the soil stiffness; (ii) during the progress of moisture and temperature cycles, the G decreases, and the λ increases. The effects of WD and WD-FT cycles on the G and λ are more significant compared to FT cycles. The G increases with the confining pressure σc while the λ is not sensitive to the σc. The relationships of the G and λ to the deviator stress σd are generally non-monotonic and the turning point of such relationships is influenced by the moisture and temperature cycles; (iii) the εp increases after moisture and temperature cycles and the development of the εp during cyclic loading gradually evolve from plastic shakedown to plastic creep. Predictive models based on decay laws considering stress states are developed to describe the changes in dynamic shear modulus and accumulative plastic strain.

Room temperature deformation mechanisms of a Fe–Mn–Al–C steel

This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C steel at room-temperature through uniaxial tensile tests, strain rate sensitivity and stress relaxation analysis. Through numerical analysis and microstructural studies, this investigation reveals that increasing strain leads to the formation of low-angle boundaries (LABs) at the vicinity of grain boundaries. Consequently, these LABs play a facilitating role in the stress-assisted diffusion of carbon atoms, thereby triggering the dynamic strain aging (DSA) phenomenon. The evidence for this is substantiated by the strain rate sensitivity coefficient and stress relaxation results obtained from numerical analysis during uniaxial tensile tests. As deformation progresses, the misorientation of LABs increases, influencing the strain hardening behavior. The intensified DSA contributes to enhanced work hardening, while substructure development results in softening, creating a trade-off between these contrasting effects.

Developing empirical formulations to predict residual strength and damages in tension-leg platform hulls after a collision

During service life, a TLP is under potential damage caused by attendant vessel collisions. The influence of local dents on the maximum strength of TLP is a challenge in ocean engineering structures. Proper regulations outside the industrial practices are required to identify and rehabilitate the strength of these structures subjected to collision. Existing design methods require improvement to accurately predict the ultimate strength of TLPs subjected to accidental collision. Thus, it is imperative to develop viable approaches for predicting the residual ultimate strength of such structures. This paper aims to establish practical modeling techniques and equations to predict the residual strength of dented TLPs subjected to combined axial compression and hydrostatic pressure. The proposed computational models employ nonlinear finite element analyses (NFEA) considering the dynamic effects of materials properties such as strain rate and dynamic fracture strain. A series of NFEA of actual TLP with different collision scenarios and parameters were carried out using ABAQUS software. The empirical equations were provided through the database out of the NFEA results. The reliability of derived empirical formulations was compared with NFEA results, existing formulations, and test data.

Physically Based Constitutive Modeling of Dynamic Strain Aging in C45 Steel

Abstract Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification based on physical parameters to the Voyiadjis and Abed (VA) model to account for the effect of DSA in C45 steel. The resulting modified model is then coupled with an energy-based damage model to further capture the effect of material softening. Previously, in VA model, it was assumed that the total activation energy for overcoming the obstacles without external work remains the same which works well in the absence of DSA. However, during DSA, the mobile dislocations are pinned by the diffusing solute atoms. This results in an increase in the total activation free energy needed by the dislocations to overcome the obstacle. Thus, an increase in strength is observed. It is shown in the current work that utilizing the concept of increased solute concentrations at local obstacles, in conjunction with the physical description that the VA model is based upon, successfully captures the phenomenon of DSA in C45 steel. In addition, the metal experiencing softening after reaching its ultimate strength is due to the significant growth of voids and cracks within the microstructure. To capture this behavior, an energy-based damage parameter is incorporated into the proposed model. The coupled plasticity-damage model shows a good comparison with the experimental results.

Detecting gas pipeline leaks in sandy soil with fiber-optic distributed acoustic sensing

Detecting pinhole leaks in long-haul buried gas pipelines is challenging due to weak leak signals and large spans. Fiber-optic distributed acoustic sensing (DAS) technology offers highly sensitive long-distance monitoring. This study evaluates DAS for detecting pinhole gas leaks in pipelines buried in sandy soil. Controlled experiments examined the effects of pipe-to-fiber distance, fiber position, leak direction, gas pressure, and leak diameter. Pressurized gas erodes the overlying soil, forming cavities and fissures that change soil morphology. Gas preferentially diffuses upward; an optical fiber above the pipe has the highest sensitivity regardless of leak direction and should be deployed above pipelines. Two mechanisms produce DAS-recorded leak vibration signals: dynamic soil straining and gas–fiber friction. Vibration energy from dynamic soil motion concentrates at 60–120 Hz while gas–fiber friction exhibits a broader spectral response. Increasing gas pressure or leak diameter increases detected vibration power but decreases peak frequency and proportion generated by soil strain, indicating a shift toward gas–fiber friction as the dominant mechanism. These results inform improved pinhole leak monitoring in buried gas pipelines using DAS technology.

Mechanical properties of terrestrial analogs to calcium sulfate veins on Gale crater, Mars

The MSL (Mars Science Lab) Curiosity rover has documented the presence of natural fractures at the Gale crater on Mars. Through the utilization of the ChemCam instrument, the chemical composition of the veins on Mars has been analyzed, revealing their mineralogy as calcium sulfate. However, there is limited knowledge regarding the mechanical properties of these veins, which hinders a deeper understanding of their origin. This work aims to characterize the mechanical properties of gypsiferous Triassic Moenkopi mudrocks as the terrestrial rock analog to Mars. The Digital Image Correlation (DIC) technique was used in tandem with the Indirect Tensile Strength test to acquire the required spatial full-field strain maps for characterizing the fracture propagation with complex geometries in addition to the derived mechanical properties. The effect of the primary vein orientation on the exerted load on the load-strain profile, fracture initiation and propagation, and tensile strength was established. The dynamic spatial horizontal, vertical, and shear strains' progression was distinguished through DIC imaging. The key findings include: (1) Different failure modes were observed in samples with and without calcium sulfate veins, with higher tensile strength perpendicular to lamination; (2) Most samples with veins exhibited reduced tensile strength, except when oriented 90° to the load; (3) Fracture paths were influenced by the orientation angle, with irregular paths at certain angles and more regular paths for centrally located veins; (4) Digital image correlation revealed a fracture process zone before macro-crack initiation and subsequent shear crack propagation; (5) Shear strain accumulation preceded shear crack propagation, with potential initiation of tensile cracks.

Experimental study on the impact response of the polyurea-coated 3D auxetic lattice sandwich panels subjected to air explosion

A series of air explosion experiments were carried out on the 3D polyurea-coated auxetic lattice sandwich panels in order to combine the advantages of auxetic materials and polyurea. The deformation, dynamic strain, and acceleration of the front and back plate were obtained. The results show that the dynamic response of the 3D polyurea-coated auxetic lattice sandwich panel could be divided into four stages: the shock wave action stage, the auxetic effect stage, the overall deformation stage, and the oscillation stage. The “N” type displacement time history of the back plate center due to the auxetic effect is found through the experiments. It is also found that the concave “hat-shaped” deformation mode of the back plate is opposite to the impact direction. This anomalous deformation mode is of great significance for impact protection. Finally, three dynamic response mode of the 3D polyurea-coated auxetic lattice sandwich panel subjected to air explosion is revealed. This study could provide a reference for the shock resistance design of structures.

Diagnosis and Treatment of a Dynamic Strain Vector after a Motor Vehicle Accident

Abstract This report outlines a case of prolonged pain and somatic dysfunction after a motor vehicle accident where a strain-vector was diagnosed in the biofield and successfully treated with the dynamic strain-vector release (SVR) technique. The palpatory diagnostic approach and end-feel of a strain-vector in the biofield described in this case provides guidance for those wishing to incorporate it into clinical practice, particularly in cases where traditional osteopathic techniques are not effective.

Study on the effects of drying–wetting cycles on the dynamic elasticity modulus of weathered red sandstone soil

In this paper, the effect of drying–wetting cycles on the dynamic elasticity modulus of weathered red sandstone soil was studied based on a series of unconsolidated undrained dynamic triaxial tests under different confining pressures and with the help of the Hardin–Drnevich model. The main results from this work as follows: (1) Hardin–Drnevich model can well express the hyperbolic behaviors of dynamic backbone curves of the weathered red sandstone soil exposed to drying–wetting cycles. (2) Both the maximum dynamic elasticity modulus and the dynamic elastic modulus of the weathered red sandstone soil decreased linearly with numbers of drying–wetting cycles under a certain confining pressure. The dynamic elasticity modulus decreased non-linearly with the increase of dynamic strain. (3) The maximum dynamic elastic modulus of the weathered red sandstone soil decreased by 19.62% to 70.91%, 21.16% to 71.07%, and 29.53% to 77.36%, respectively after 3 to 12 drying–wetting cycles under confining pressures of 100, 200, and 300 kPa. The rate at which the maximum dynamic elastic modulus decreases is basically the same under different confining pressures.

Physiological effects of awake prone position in acute hypoxemic respiratory failure

BackgroundThe effects of awake prone position on the breathing pattern of hypoxemic patients need to be better understood. We conducted a crossover trial to assess the physiological effects of awake prone position in patients with acute hypoxemic respiratory failure.MethodsFifteen patients with acute hypoxemic respiratory failure and PaO2/FiO2 < 200 mmHg underwent high-flow nasal oxygen for 1 h in supine position and 2 h in prone position, followed by a final 1-h supine phase. At the end of each study phase, the following parameters were measured: arterial blood gases, inspiratory effort (ΔPES), transpulmonary driving pressure (ΔPL), respiratory rate and esophageal pressure simplified pressure–time product per minute (sPTPES) by esophageal manometry, tidal volume (VT), end-expiratory lung impedance (EELI), lung compliance, airway resistance, time constant, dynamic strain (VT/EELI) and pendelluft extent through electrical impedance tomography.ResultsCompared to supine position, prone position increased PaO2/FiO2 (median [Interquartile range] 104 mmHg [76–129] vs. 74 [69–93], p < 0.001), reduced respiratory rate (24 breaths/min [22–26] vs. 27 [26–30], p = 0.05) and increased ΔPES (12 cmH2O [11–13] vs. 9 [8–12], p = 0.04) with similar sPTPES (131 [75–154] cmH2O s min−1 vs. 105 [81–129], p > 0.99) and ΔPL (9 [7–11] cmH2O vs. 8 [5–9], p = 0.17). Airway resistance and time constant were higher in prone vs. supine position (9 cmH2O s arbitrary units−3 [4–11] vs. 6 [4–9], p = 0.05; 0.53 s [0.32–61] vs. 0.40 [0.37–0.44], p = 0.03). Prone position increased EELI (3887 arbitrary units [3414–8547] vs. 1456 [959–2420], p = 0.002) and promoted VT distribution towards dorsal lung regions without affecting VT size and lung compliance: this generated lower dynamic strain (0.21 [0.16–0.24] vs. 0.38 [0.30–0.49], p = 0.004). The magnitude of pendelluft phenomenon was not different between study phases (55% [7–57] of VT in prone vs. 31% [14–55] in supine position, p > 0.99).ConclusionsProne position improves oxygenation, increases EELI and promotes VT distribution towards dependent lung regions without affecting VT size, ΔPL, lung compliance and pendelluft magnitude. Prone position reduces respiratory rate and increases ΔPES because of positional increases in airway resistance and prolonged expiratory time. Because high ΔPES is the main mechanistic determinant of self-inflicted lung injury, caution may be needed in using awake prone position in patients exhibiting intense ΔPES.Clinical trail registeration: The study was registered on clinicaltrials.gov (NCT03095300) on March 29, 2017.

Majorana spin current generation by dynamic strain

Majorana spin current generation by dynamic strain

Enhanced Mechanical Properties of Al2O3 Nanoceramics via Low Temperature Spark Plasma Sintering of Amorphous Powders.

In this work, Al2O3 nanoceramics were prepared by spark plasma sintering of amorphous powders and polycrystalline powders with similar particle sizes. Effective comparisons of sintering processes and ultimate products depending on starting powder conditions were explored. To ensure near-full density higher than 98% of the Al2O3 nanoceramics, the threshold temperature in SPS is 1450 °C for polycrystalline Al2O3 powders and 1300 °C for amorphous powders. The low SPS temperature for amorphous powders is attributed to the metastable state with high free energy of amorphous powders. The Al2O3 nanoceramics prepared by amorphous powders display a mean grain size of 170 nm, and superior mechanical properties, including high bending strength of 870 MPa, Vickers hardness of 20.5 GPa and fracture toughness of 4.3 MPa∙m1/2. Furthermore, the Al2O3 nanoceramics prepared by amorphous powders showed a larger dynamic strength and dynamic strain. The toughening mechanism with predominant transgranular fracture is explained based on the separation of quasi-boundaries.

Piezoelectric Actuators Placement Using Genetic Algorithm and Active Vibration Control of Smart Plane Frame Structure

A Genetic Algorithm-based optimisation scheme is presented to find the optimum actuator elements infinite element analysis for active vibration control applications. The dynamic strain data is used to reduce the size of search domain for the actuators placement problem. A modal velocity, feedback control is employed to estimate the active damping of piezoelectric actuators. The structural damping index is taken as a fitness function; which directly reflects the status of active damping effect for a given piezoelectric actuator set. Modal preference is attempted by assigning a different weighting factor in the fitness function for desired modes to have better controllability. As an illustration, a 20-member smart plane frame is modeled with d3I based extension-bending piezoelectric actuators using 2-D piezoelectric Timoshenko beam element. It is shown that the vibration of first four elastic modes is actively controlled with optimally, selected four piezoelectric actuators.