Dynamic Deformation Research Articles

Experimental and crystal plasticity finite element study of dynamic shear behavior of CoCrNiSi0.3 medium-entropy alloy

Single-phase CrCoNi-based medium-entropy alloys (MEAs) have garnered considerable attention as a promising class of metallic materials. However, despite this growing interest, the dynamic mechanical response of CrCoNi-based MEAs at high strain rate remains controversial. The dynamic shear mechanical behavior of CoCrNiSi0.3 was characterized through Hopkinson-bar experiment utilizing hat-shaped specimen. In this study, a damage model based on the maximum shear strain of each slip system was chosen to describe the damage initiation and evolution. Combined with this micro-scale damage and dislocation density-based crystal plasticity theory, two constitutive models were proposed to perform predictions of the dynamic shear behavior of CoCrNiSi0.3. The strain rate effect, adiabatic temperature rising, damage evolution, and twin volume fraction during dynamic shear deformation were tracked by investigating the influence of resolved shear stress, dislocation density, texture evolution, and twinning systems shear strain. The presented model effectively predicts the deformation state of specimen, the formation and evolution of Adiabatic Shear Bands (ASBs), and the variations in strain rate and temperature at different locations within the shear region. Adiabatic Shear Bands and texture evolution are caused by the local dislocation density rising and misorientation distributions.

Dynamic mechanical properties and energy dissipation analysis of rubber-modified aggregate concrete based on SHPB tests

The fluctuation of the waveform curves in the Split Hopkinson Pressure Bar (SHPB) test can provide a more intuitive reflection of the material's dynamic deformation process, with different strain rates resulting in varying damage states and σ-ε curves. A Φ120×100 mm size SHPB experiment was conducted to study the dynamic mechanical properties of new rubber-modified aggregate concrete (RAC). Based on the different characteristics of waveform and σ-ε curves, combined with high-speed photography technology, the typical failure modes and dynamic compressive strength of rubber-modified aggregate concrete under different loading rates were analyzed. Furthermore, the energy dissipation capacity and mechanism of rubber-modified aggregate concrete at different stages was discussed. The reflected wave of RAC shows a "double-peak" trend of "first high and then low" instead of "first low and then high" of normal concrete due to its exceptional capacity of energy absorption and dissipation. As strain rate increases, a plateau period appears in the reflected wave before first peak. The evolution process is dominated by the energy storage mechanism until it hits the limit, then by the energy dissipation mechanism. These findings can help us design and use RAC materials under dynamic stress.

An experimental analysis of dynamic deformation and settlement resistance in a novel prestressed railway subgrade

ABSTRACT The dynamic deformation characteristics of track-subgrade systems under moving train loads provide valuable insights for vibration and serviceability assessment of the track-subgrade. This study developed three 1:5 scale track-subgrade models incorporating the novel prestressed subgrade structure and conducted two series of dynamic tests to examine how the heavy-haul train axle loads and prestress levels affected the track-subgrade dynamic deformation. The primary frequency of the subgrade dynamic displacement was observed closely aligned with the input loading frequency of 2 Hz, indicating the validity of the test setup. The track-subgrade dynamic displacement decreased with increasing distance from the loading source, of which the elastic deformation near the subgrade shoulder attenuated by approximately 79% compared to that at the sleeper end. The elastic deformation at the monitoring points approximately linearly increased with the axle load at rates ranging from 0.0018 to 0.0029 mm/t. Conversely, increasing prestress reduced the track-subgrade elastic deformation with average rates of 22.8 and 1.63 μm/100 kPa at the sleeper end and subgrade shoulder, respectively. Furthermore, application of prestress enhanced the track stiffness, with the equivalent track stiffness rising by 16.3% and 17.7% when the prestress increased from 0 to 50 kPa and from 50 to 100 kPa, respectively. The study also showed that the prestressed reinforcement structures could significantly mitigate the cumulative track-subgrade settlement over 60%, comparing the prestressed subgrade with 50 kPa prestress to the unreinforced subgrade, which highlighted the superior deformation resistance of prestressed subgrades under the train loads.

Effect of reinforcement layer on dynamic wetting behavior and accumulative deformation of granite residual soil subgrade

This paper contributes to investigate the impact of reinforcement layer on the dynamic wetting behavior and accumulative deformation of granite residual soil subgrade of expressways in southern China. The wetting test combined with vehicle test and vibration test were conducted in two selected test sections with a reinforcement layer (WRL) and without a reinforcement layer (NRL), respectively. The influence of vehicle speed, moving load, repeated loading, and loading number on the dynamic stress, dynamic acceleration, and dynamic displacement of both the NRL and WRL subgrades was explored under different wetting conditions. The impact of the wetting number and traffic loading on the time-domain characteristics of the dynamic response and the accumulative deformation were revealed. The results indicate that the WRL subgrade can effectively reduce the dynamic response compared to the NRL subgrade. The influence depth of the WRL subgrades is 1.3 m, while the influence depth of the NRL subgrades is 3.3 m. Dynamic stress, dynamic acceleration, and dynamic displacement increase with increasing the wetting number, moving load, and repeated loading. The peak values of the dynamic stress and dynamic acceleration time-domain curves for the NRL subgrade are 27 % and 24 % higher than those of the WRL subgrade, respectively. At 3 million loading numbers, the accumulative deformation of the NRL subgrades is 53.7 % higher than that of the WRL subgrade. The dynamic stress, dynamic acceleration, and dynamic displacement of the NRL subgrade are generally higher than those of the WRL subgrade. The predictive models are established to correlate the wetting, dynamic load, and the dynamic response for both NRL and WRL subgrades. The dynamic stress, dynamic acceleration, and dynamic displacement measured in the vibration test are generally higher than those measured in the vehicle test. The research results provide a reference for the design of durability subgrade in granite residual soil regions.

Full-field, frequency-domain comparison of simulated and measured human brain deformation.

We propose a robust framework for quantitatively comparing model-predicted and experimentally measured strain fields in the human brain during harmonic skull motion. Traumatic brain injuries (TBIs) are typically caused by skull impact or acceleration, but how skull motion leads to brain deformation and consequent neural injury remains unclear and comparison of model predictions to experimental data remains limited. Magnetic resonance elastography (MRE) provides high-resolution, full-field measurements of dynamic brain deformation induced by harmonic skull motion. In the proposed framework, full-field strain measurements from human brain MRE in vivo are compared to simulated strain fields from models with similar harmonic loading. To enable comparison, the model geometry and subject anatomy, and subsequently, the predicted and measured strain fields are nonlinearly registered to the same standard brain atlas. Strain field correlations , both global (over the brain volume) and local (over smaller sub-volumes), are then computed from the inner product of the complex-valued strain tensors from model and experiment at each voxel. To demonstrate our approach, we compare strain fields from MRE in six human subjects to predictions from two previously developed models. Notably, global values are higher when comparing strain fields from different subjects ( ) than when comparing strain fields from either of the two models to strain fields in any subject. The proposed framework provides a quantitative method to assess similarity (and to identify discrepancies) between model predictions and experimental measurements of brain deformation, and thus can aid in the development and evaluation of improved models of brain biomechanics.

Application of deep learning for technological parameter optimization of laser shock peening of Ti-6Al-4V alloy

The paper is devoted to the development of the method of laser shock peening (LSP) of metals. To optimize the mode of LSP for Ti-6Al-4V specimens a deep learning model for predicting residual stresses by laser shock peening was developed. A numerical-experimental method was used to carry out the model training, in which an experimental study of the effect of different processing mode on the depth and distribution of residual stresses was carried out. The Johnson-Cook model was used as the governing relationship for modeling the dynamic deformation process. At the second stage, the problem of static equilibrium of a body with a plastically deformed area was numerically solved to determine residual stresses. The results of research on determination of the optimal configuration of the deep learning model showed that when using sinusoidal activation function of the neural network with 4 hidden layers and the number of neurons 10, the best level of accuracy in solving the problem is achieved. The obtained model allows us to optimally determine the LSP mode according to the given limitations of values and depth of residual stresses.

Structure and Mechanical Properties of AlMgSi(Cu) Extrudates Straightened with Dynamic Deformation.

Before artificial ageing, extruded aluminium profiles are subjected to stretching with a small cold deformation in the range of 0.5-2%. This deformation improves the geometrical stability of the extruded product and causes changes in the microstructure of the profile, which leads to the strain hardening of the material after artificial ageing. The work has resulted in the creation of the prototype of an original device, which is unique in the world, for the dynamic stretching of the extruded profiles after quenching. The semi-industrial unit is equipped with a hydraulic system for stretching and a pneumatic system for cold dynamic deformation. The aim of this research paper is to produce advantageous microstructural changes and increase the strength properties of the extruded material. The solution of the dynamic stretching of the profiles after extrusion is a great challenge and an innovation not yet practised. The paper presents the results of microstructural and mechanical investigations carried out on extruded AlMgSi(Cu) alloys quenched on the run-out table of the press, dynamically stretched under different conditions, and artificially aged for T5 temper. Different stretching conditions were applied: a static deformation of 0.5% at a speed of 0.02 m/s, and dynamic deformation of 0.25%, 0.5%, 1%, and 1.5% at speeds of 0.05 and 2 m/s. After the thermomechanical treatment of the profiles, microstructural observations were carried out using an optical microscope (OM) and a scanning electron microscope (SEM). A tensile test was also carried out on the specimens stretched under different conditions. In all the cases, the dynamically stretched profiles showed higher strength properties, especially those deformed at a higher speed of 2 m/s, where the increase in UTS was observed in the range of 7-18% compared to the classical (static) stretching. The microstructure of the dynamically stretched profiles is more homogeneous with a high proportion of fine dispersoids.

(Invited) Deformable Electronics Based on Strain-Engineered Van Der Waals Materials

Materials exhibit drastically different physical and chemical properties as their dimensionality varies. Atomically-thin van der Waals (vdW) materials possess unique mechanical, electrical, optical, and thermal characteristics, originated from quantum confined low-dimensionality and a lack of dangling bond. In particular, strong in-plane covalent bonding and weak interlayer vdW interaction of two-dimensional (2D) vdW materials enable exceptional combination of mechanical properties, such as high Young’s modulus, high in-plane strength, and ultralow bending stiffness at a level of cell membrane. Moreover, mechanical strain can induce modulation of electronic and phononic band structures of 2D vdW materials more effectively due to mechanical resilience and high surface-to-volume ratio. For these reasons, deformation engineering has garnered substantial interest in mechanics, materials and electronics communities as a new tuning knob for emerging phenomena and functionalities of 2D vdW materials. In this talk, I will discuss deformation engineering of 2D vdW materials – (1) active and dynamic deformation strategies, including in-plane interfacial slippage and out-of-plane structural deformation, (2) deformation strain induced phenomena, and (3) emerging device concepts based on deformation engineering of 2D vdW materials.

Numerical modelling of multiple sclerosis: A tissue-scale model of brain lesions

Multiple Sclerosis (MS) is an autoimmune condition leading to the degeneration of brain tissue, occurring when the immune system attacks the myelin sheath surrounding axons of white brain matter thereby disrupting brain signals. This study aimed to evaluate how MS lesions alter stress distribution through grey and white brain matter with lesions (active, chronic, and inactive). A linear viscoelastic model represents the tissue-scale dynamic deformation and time dependency of brain tissue. A Prony series expansion was used to model viscous effects including stress relaxation. An elastic modulus, within the viscoelastic model, was either reduced by 11 % for active lesions, or increased by 35 % increase for inactive lesions. These material properties were then implemented to model healthy tissue, active, chronically inflamed, and inactive lesions. Finite element analysis enabled stress evaluation in response to a peak cyclic displacement of 0.5 mm (1 % strain) with the healthy model acting as a control model. Chronic lesions had the largest effect on stress induced, in terms of high (171 Pa) and low stress (108 Pa). Inactive lesions induced an increase in stress of 11 Pa with areas of low stress (105 Pa). Active lesions caused the least deviation in peak induced stress (7 Pa). In conclusion, a hierarchy in stress induced across the lesion types has been found, from highest to lowest: chronic, inactive and active, with potential implications for lesion progression. In conclusion, MS lesions within brain tissue should model lesions, avoid assuming homogeneity during degeneration, and should distinguish between active and passive lesions.

Continuous Dynamic Recrystallization and Deformation Behavior of an AA1050 Aluminum Alloy during High-Temperature Compression

Continuous dynamic recrystallization (CDRX) forms a new recrystallized microstructure through the progressive increase in low-angle boundary misorientations (LAGBs) during the hot forming of metallic materials with high stacking fault energy (SFE), such as aluminum alloys. The present work investigates the effect of deformation parameters on the evolution of the dynamic recrystallization microstructures of an AA1050 aluminum alloy during compression at elevated temperatures. The alloy microstructure is investigated at deformation temperatures and strain rates in the range of 300 °C to 500 °C and 0.001 to 0.8 s−1. A well-defined substructure and subsequent DRX grains provide indication that recrystallization can proceed with continued strain under high-temperature compression. At a strain rate of 0.1 s−1, the DRX fraction is observed to be 0.25 at a temperature of 300 °C. This fraction increases to 0.32 as the temperature rises to 400 °C. The recrystallization mechanism is identified by analyzing the flow stress, the evolution of the subgrain misorientation angle, and the distribution of recrystallized grains. The observations of discontinuous dynamic recrystallization (DDRX) and CDRX under various deformation parameters are discussed. Moreover, the main substructure evolution laws observed from the high-temperature compression of an AA1050 Al alloy are summarized.

Modeling of dynamic bubble deformation and breakup in T-junction channel flow

Bubble deformation and breakup due to strain-rate-induced stress is investigated for a laminar flow configuration. The bubble shape is assumed to be a prolate ellipsoid. A new model for bubble deformation under dynamic load is introduced in the form of an ordinary differential equation for the deformation energy. Breakup is identified with a critical value of the deformation. As an application case, the flow in a joining T-junction is considered with the ratio of the volume flow rate being unity and the outflow Reynolds number being 1800. Dilute, dispersed bubbles with a diameter of 0.5 mm are injected. High-speed shadowgraphy is used and bubble parameters are evaluated via image processing. The capillary number is obtained from a single-phase flow simulation providing the instantaneous shear rate at the position of the bubble. The deformation resulting from the proposed model is then compared with the measured deformation for an exemplary bubble trajectory.

Increasing the strength of potato digger elevator rods

Abstract Currently, high-quality steels are used to increase the reliability of potato digging machines and the durability of elevator rods. Recently, new materials, new technologies and non-metallic materials that are not inferior in strength to steel have been used in agricultural machines. Such materials significantly reduce the mass of the working parts. This article examines the deformation of a new elevator rod design due to the action of soil and tuber-bearing mass. The rods, covered with double-cavity rubber profiles, vibrate the component of the potato heap. During vibrations, in addition to static deformations, dynamic deformations occur, depending on the magnitude of the impact force. As a result, it was found that to eliminate the loss of tubers between the bars of the separating elevator, given the maximum deflection value of 0.03 m and the weight of the soil-tuber-bearing mass, the rubber bar must have the following parameters: elasticity model E = 50 N/mm2; rod perimeter 11x11 mm; the maximum jump height of a mass weighing 130 kg is no more than 0.6 m.

Individuals with asymptomatic hallux valgus exhibit altered foot kinematics during gait regardless of their foot posture

BackgroundA flatfoot has been believed to be closely associated with the development of hallux valgus; however, the association is still controversial. Abnormal foot kinematics has been identified as a possible risk factor for the development of hallux valgus, but it remains unclear whether foot posture contributes to abnormal foot kinematics. This is the first study to investigate the differences in foot kinematics during gait between individuals with and without hallux valgus, while controlling for foot posture. MethodsTwenty-five females with hallux valgus and 25 healthy females aged 18 to 22 were recruited. Foot posture was measured using normalized navicular height truncated and the leg-heel angle. Foot kinematic and kinetic data during gait were recorded by a three-dimensional motion capture system. To investigate the characteristics of foot kinematics in individuals with hallux valgus while controlling for foot posture, we used a propensity score matching method. The matching was obtained by using the 1:1 nearest-neighbor procedure and a caliper width of 0.2. FindingsTwelve pairs were matched. Individuals with hallux valgus had significantly increased midfoot dorsiflexion from 56% to 80% during stance phase, rearfoot eversion from 53% to 71%, and forefoot abduction from 5% to 29% compared with control. InterpretationIndividuals with hallux valgus have a flexible foot that cannot suppress the dynamic deformation of the rearfoot and midfoot during gait. To suppress the development of hallux valgus, interventions that aim to prevent dynamic deformations of the rearfoot and midfoot during gait may be necessary, regardless of their static foot posture.

Backcalculation of Elastic Moduli for Layered Media Based on Dynamic Deformation Analysis (Example of Highways)

Backcalculation of Elastic Moduli for Layered Media Based on Dynamic Deformation Analysis (Example of Highways)

A multi-mode stretching apparatus for in situ synchrotron x-ray scattering of polymer materials.

A compact and versatile tensile apparatus for polymer materials is designed and fabricated. Three distinct stretching modes are developed: constant speed, cyclic, and sinusoidal, with adjustable speeds ranging from 0.001 to 120 mm/s. To capture the true strain of the central region, a high-speed camera has been integrated into the apparatus. The temperature of the sample chamber is controlled by flowing air, enabling a homogeneous temperature in the range of RT ∼200 °C. The apparatus is particularly suitable for a synchrotron beamline. The structural evolution of natural rubber during sinusoidal stretching is investigated by in situ wide-angle x-ray scattering. Scattering patterns, force, clamp position, and sample images are saved simultaneously during stretching. Notably, the results reveal a sinusoidal variation in the crystallinity of crosslinked natural rubber when a sinusoidal strain was applied to the sample. The integration of advanced measurement techniques and controlled experimental conditions ensures the acquisition of reliable and accurate data, providing valuable insights into the structural evolution of materials under dynamic deformation conditions.

Modeling and characterization on electroplastic effect during dynamic deformation of 5182-O aluminum alloy

The coupling effects of electrical pulse, temperature, strain rate, and strain on the flow behavior and plasticity of 5182-O aluminum alloy were investigated and characterized. The isothermal tensile test and electrically-assisted isothermal tensile test were performed at the same temperature, and three typical models were further embedded in ABAQUS/Explicit for numerical simulation to illustrate the electroplastic effect. The results show that electric pulse reduces the deformation resistance but enhances the elongation greatly. The calibration accuracy of the proposed modified Lim−Huh model for highly nonlinear and coupled dynamic hardening behavior is not much improved compared to the modified Kocks−Mecking model. Moreover, the artificial neural network model is very suitable to describe the macromechenical response of materials under the coupling effect of different variables.

Modelling of Brake Pad Disc with emphasis on dynamic analysis and deformation of structure.

Modelling of Brake Pad Disc with emphasis on dynamic analysis and deformation of structure.

Influence of aggregate content and strain rate on dynamic behaviour and energy consumption characteristics of concrete

Concrete's dynamic performance and energy dissipation are critical areas of interest that are significantly influenced by strain rate and aggregate content. This study investigated concrete's dynamic deformation, strength development and energy dissipation characteristics from specimens containing 0, 32%, 37% and 42% aggregate. These specimens were subjected to impact compression tests using a split Hopkinson compression apparatus, which allowed the effects of strain rate and aggregate content on the deformation, strength and energy dissipation of the concrete to be analysed. The results show that the concrete exhibits deformation hysteresis under impact loading, with splitting tensile failure as the predominant damage mechanism. Dynamic strength was more sensitive to strain rate than aggregate content. The dynamic increase factor (DIF) varied with aggregate content at different strain rates. The extent of specimen damage significantly influenced the energy distribution ratio, with absorbed energy showing a more pronounced strain rate effect than transmitted and reflected energy. Conversely, the amount of transmitted energy had a more pronounced impact on aggregate content than the amount of absorbed and reflected energy.

Adhesion switchable transition on bio-inspired Janus surface for multi-directional droplet manipulation

Achieving precise and rapid droplets manipulation in versatile directions transport remains a considerable challenge, however adhesion switchable transitions deemed to be rather serviceable. Here, a double-sided microplate array (DMPA) with bio-inspired Janus surfaces, is proposed to fulfill adjustable adhesion through surface wettability switching and microplate dynamic deformation, thereby executing the droplet multi-dimensional manipulation in response to dynamic magnetic field. The triple-coupled bio-inspired Janus surfaces are newly designed with a convex hull and striped structure respectively, inspired by the respiratory ciliary motion and surface properties of lotus and rice leaves. Leveraging variation in superhydrophobicity and low adhesion of convex hull side on Janus surface, diverse droplet directional transports are achieved in plane, such as high-speed horizontal transport (120 mm/s and 500 µL), anti-gravitational climbing (inclined by 15°), and selective droplet orientation. The adhesion switchable transition of surface striped structure on other side is predominated by solid–liquid contact lines evolution resulting from microplate bending deformation, realizing droplet capture/release for long-distance multi-dimensional transport. Concurrently, a magnetic-responsive droplet switch is developed based on multi-directional droplet manipulation, demonstrating enormous potential for practical application.

Simulation of Soluble and Bound VEGF-stimulated in vitro Capillary-like Network Formation on Deformed Substrate.

Capillary plexus cultivation is crucial in tissue engineering and regenerative medicine. Theoretical simulations have been conducted to supplement the expensive experimental works. However, the mechanisms connecting mechanical and chemical stimuli remained undefined, and the functions of the different VEGF forms in the culture environment were still unclear. In this paper, we developed a hybrid model for simulating short-term in vitro capillary incubations. We used the Cellular Potts model to predict individual cell migration, morphology change, and continuum mechanics to quantify biogel deformation and VEGF transport dynamics. By bridging the mechanical regulation and chemical stimulation in the model, the results showed good agreement between the predicted network topology and experiments, in which elongated cells connected, forming the network cords and round cells gathered, creating cobblestone-like aggregates. The results revealed that the capillary-like networks could develop in high integrity only when the mechanical and chemical couplings worked adequately, with the cell morphology and haptotaxis driven by the soluble and bound forms of VEGF, respectively, functioning simultaneously.