Rate-dependent Effects Research Articles

Being thin-skinned can still reduce damage from dynamic puncture.

The integumentary system in animals serves as an important line of defence against physiological and mechanical external forces. Over time, integuments have evolved layered structures (scales, cuticle and skin) with high toughness and strength to resist damage and prevent wound expansion. While previous studies have examined their defensive performance under low-rate conditions, the failure response and damage resistance of these thin layers under dynamic biological puncture remain underexplored. Here, we utilize a novel experimental framework to investigate the mechanics of dynamic puncture in both bilayer structures of synthetic tissue-mimicking composite materials and natural skin tissues. Our findings reveal the remarkable efficiency of a thin outer skin layer in reducing the overall extent of dynamic puncture damage. This enhanced damage resistance is governed by interlayer properties through puncture energetics and diminishes in strength at higher puncture rates due to rate-dependent effects in silicone tissue simulants. In addition, natural skin tissues exhibit unique material properties and failure behaviours, leading to superior damage reduction capability compared with synthetic counterparts. These findings contribute to a deeper understanding of the inherent biomechanical complexity of biological puncture systems with layered composite material structures. They lay the groundwork for future comparative studies and bio-inspired applications.

Dose rate dependent genotoxic and metabolic effects predict onset of impaired development and mortality in Atlantic salmon (S. salar) embryos exposed to chronic gamma radiation

Release of radionuclides to the environment from either nuclear weapon and fuel cycles or from naturally occurring radionuclides (NORM) may cause long term contamination of aquatic ecosystems and chronic exposure of living organisms to ionizing radiation, which in turn could lead to adverse effects compromising the sustainability of populations. To address the effects of chronic ionizing radiation on the development of fish, Atlantic salmon embryos were exposed from fertilization until hatching (88 days, 550 day-degree) to dose rates from 1 to 30 mGy·h−1 gamma radiation (60Co). The lowest adopted dose rate was similar to the highest doses measured in some water bodies right after the Chernobyl accident (1 mGy·h−1), however, well above current environmentally realistic scenarios (20 μGy·h−1), or the threshold assumed for significant effects on fish population (40 μGy·h−1). Dose dependent effects were observed on survival, hatching, morbidity, DNA damage, antioxidant defenses, and metabolic status. Histopathological analysis showed dose rate dependent impairment of eye and brain tissues development and establishment of epidermal mucus cell layers accompanied by increased DNA damage at doses ≥1.3 Gy (dose rates ≥1 mGy·h−1).At ≥32.8 Gy (dose rates ≥20 mGy·h−1) deformities and developmental growth defects resulted in respective 46 and 95 % pre-hatch mortality. The 10 mGy·h−1 exposure (≥ 12 Gy total dose) caused significantly increased DNA damage, impaired eye development, and both premature and delayed hatching, while no deformities or effect on survival were observed. We observed a dose rate dependent reduction from dose rate ≥ 20 mGy·h−1 (≥ 27 Gy total dose) on antioxidant SOD, catalase and glutathione reductase enzyme activities. The reduction of antioxidant enzyme activities was in line with observed developmental delay and disturbance to time of hatching. Metabolomic profiles showed a clear shift at dose rates ≥10 mGy·h−1 (≥ 12 Gy total dose) in pathways related to oxidative stress, detoxification, DNA damage and repair. Due to gamma radiation exposure, a switch of central metabolism from glycolysis, citric acid cycle and lactate production towards pentose phosphate pathway indicated a rewiring mechanism for increased production of reductive equivalents to maintain redox homeostasis at the expense of energy output and thus embryonic development.

The effect of testing rate on biomechanical measurements related to stalk lodging

BackgroundStalk lodging (the premature breaking of plant stalks or stems prior to harvest) is a persistent agricultural problem that causes billions of dollars in lost yield every year. Three-point bending tests, and rind puncture tests are common biomechanical measurements utilized to investigate crops susceptibility to lodging. However, the effect of testing rate on these biomechanical measurements is not well understood. In general, biological specimens (including plant stems) are well known to exhibit viscoelastic mechanical properties, thus their mechanical response is dependent upon the rate at which they are deflected. However, there is very little information in the literature regarding the effect of testing rate (aka displacement rate) on flexural stiffness, bending strength and rind puncture measurements of plant stems.ResultsFully mature and senesced maize stems and wheat stems were tested in three-point bending at various rates. Maize stems were also subjected to rind penetration tests at various rates. Testing rate had a small effect on flexural stiffness and bending strength calculations obtained from three-point bending tests. Rind puncture measurements exhibited strong rate dependent effects. As puncture rate increased, puncture force decreased. This was unexpected as viscoelastic materials typically show an increase in resistive force when rate is increased.ConclusionsTesting rate influenced three-point bending test results and rind puncture measurements of fully mature and dry plant stems. In green stems these effects are expected to be even larger. When conducting biomechanical tests of plant stems it is important to utilize consistent span lengths and displacement rates within a study. Ideally samples should be tested at a rate similar to what they would experience in-vivo.

Single-cycle, 643 mW average power terahertz source based on tilted pulse front in lithium niobate.

We present the highest, to the best of our knowledge, average power from a laser-driven single-cycle THz source demonstrated so far, using optical rectification in the tilted pulse front geometry in cryogenically cooled lithium niobate, pumped by a commercially available 500 W ultrafast thin-disk ytterbium (Yb) amplifier. We study repetition rate-dependent effects in our setup at 100 and 40 kHz at this high average power, revealing different optimal fluence conditions for efficient conversion. The demonstrated sources with multi-100 mW average power at these high repetition rates combine high THz pulse energies and high repetition rate and are thus ideally suited for nonlinear THz spectroscopy experiments with significantly reduced measurement times. The presented result is a first benchmark for high average power THz time-domain spectroscopy systems for nonlinear spectroscopy, driven by very high average power ultrafast Yb lasers.

Energy-based modeling of rate-independent hysteresis and viscoelastic effects in dielectric elastomer actuators

Dielectric elastomer (DE) transducers are known to exhibit a rate-dependent hysteresis in their force-displacement response, which is commonly attributed to the viscoelastic behavior of elastomer materials and compliant electrodes. In the case of DE materials characterized by low mechanical losses, such as silicone, the mechanical hysteresis often turns out to be practically rate-independent in the low frequency range (sub-Hz), whereas rate-dependent hysteretic effects only become relevant at higher deformation rates. Most of the existing literature focuses on describing DE hysteretic losses using viscoelasticity theory. This approach results in relatively simple dynamic models, which are not capable of describing rate-independent hysteretic behaviors. In this work, we propose a control-oriented modeling framework for both rate-dependent and rate-dependent hysteresis occurring in uniaxially loaded DE actuators. To this end, classic thermodinamically-consistent modeling approaches for DEs are combined with a new energy-based Maxwell-Lion formalization of the hysteretic losses. The resulting dynamic model comprises a set of nonlinear ordinary differential equations, and is capable of simultaneously describe geometric dependencies, large deformation nonlinearities, electro-mechanical coupling, and rate-independent and rate-dependent hysteretic effects. To deal with the large number of involved parameters, a novel systematic identification algorithm based on quadratic programming is also proposed. After presenting the theory, the model is validated based on experiments conducted on a silicone-based rolled DE actuator. Its superiority compared to classic DE viscoelastic models is quantitatively assessed.

Numerical Investigation of the Damage Effect on the Evolution of Adiabatic Shear Banding and Its Transition to Fracture during High-Speed Blanking of 304 Stainless Steel Sheets.

This paper investigates numerically the effect of damage evolution on adiabatic shear banding (ASB) formation and its transition to fracture during high-speed blanking of 304 stainless steel sheets. A structural-thermal-damage-coupled finite element (FE) analysis is developed in LS-DYNA considering the modified Johnson-Cook thermo-viscoplastic model for both plasticity flow rule and damage law, while further, a temperature-dependent fracture criterion is implemented by introducing a critical temperature. The modeling approach is initially validated against experimental data regarding the fracture profile and ASB width. Next, FE simulations are conducted to examine the effect of strain rate and temperature dependence on damage law, while the effect of damage coupling is also evaluated, aiming to highlight the connection between thermal and damage softening and attribute them a specific role regarding ASB formation and transition to fracture. Also, the influence of dynamic recrystallization (DRX) softening is studied macroscopically, while further, a parametric analysis of the Taylor-Quinney coefficient is conducted to highlight the effect of plastic work-to-internal heat conversion efficiency on ASB formation. The results revealed that the implementation of damage coupling reacts to reduced ASB width and provides an S-shaped fracture profile, while it also decreases the peak force and results in an earlier fracture. Both findings are enhanced when accounting further for DRX softening and a higher value of the Taylor-Quinney coefficient. Finally, the simulations indicated that thermal softening precedes damage softening, showing that the temperature rise is responsible for ASB initiation, while instead, damage evolution drives ASB propagation and fracture.

A unified pseudo-elastic model of continuous and discontinuous softening in the finite deformation of isotropic soft solids

Building on a recently devised approach of hyperelasticity with intrinsic softening, a new framework for capturing both continuous and discontinuous softening in the finite deformation of isotropic incompressible elastomers is considered here. The continuous and discontinuous softening effects of interest pertain to the loading and unloading paths, respectively, and the model is developed within the theory of pseudo-elasticity. The performance of the model in capturing these effects is then compared with the deformation behaviour of a variety of elastomers, including a range of hydrogels from truly independent double-network (t-DN) to tough and nanocomposite hydrogels, dielectric elastomers and carbon-black filled rubber specimens, under uniaxial and multiaxial deformations. The model is demonstrated to show a favourable simulation and prediction of the extant experimental data. The application of the model is then extended to capturing the softening behaviour under rate-dependent loading, based on a prior work by the authors incorporating the rate effects directly into the pseudo-hyperelastic model, by assuming that the model parameters evolve with the deformation rate. The capability of the model to capture the rate-dependent effects accurately will be shown by considering the rate-dependent behaviour of two hydrogel specimens. Given the simplicity of the functional form of the model, akin to a standard pseudo-elastic model, the low(er) number of model parameters, the ability to capturing the softening behaviour in the deformation of a wide range of elastomeric materials, and the easy extension for incorporating additional features such as the rate-effects, the proposed model provides another step towards the unification of various complex deformation features into a single modelling framework, for a more universal application to the finite deformation of soft solids.

The effect of anisotropic rate dependency on the deformation response of Ti-6242 during dwell fatigue loading

The α phase of titanium alloys is known to exhibit both elastic and plastic anisotropic mechanical behavior during deformation loading. Recent experimental studies indicate that single crystal rate dependency may also be anisotropic, though these studies are limited in scale and scope. Consequently, we present a study in which anisotropic rate dependency is studied on polycrystalline samples via crystal plasticity finite element (CPFE) simulations, which are compared against previously-published data from electron backscatter diffraction/digital image correlation (EBSD-DIC) experiments. Cold dwell fatigue loading is utilized, owing to the propensity for transient behavior during constant-load dwells, which is hypothesized to be sensitive to the relative rate dependencies on different slip families (i.e., basal, prismatic, and pyramidal) in hexagonal close packed crystals. A suite of CPFE simulations is conducted on polycrystalline samples in which the slip family rate dependency values are parameterized. We analyze simulation results by focusing on the slip activity and accumulation of slip on the various slip families as a function of dwell cycles, as well as the transient effect during singular dwell cycles, for hundreds of crystals simultaneously. Results are further discussed through the lens of findings from EBSD-DIC experiments.

Convenient Method for Large-Deformation Finite-Element Simulation of Submarine Landslides Considering Shear Softening and Rate Correlation Effects

Submarine landslides pose a serious threat to the safety of underwater engineering facilities. To evaluate the safety of undersea structures, it is important to estimate and analyze the sliding processes of potential submarine landslides. In this study, a convenient model for simulating submarine landslide processes is established by using Abaqus Eulerian large deformation technology with an explicit finite element framework. The VUSDFLD Fortran subroutine is used to consider the strain-softening and rate-dependency characteristics of soil shear strength. The proposed method is validated by comparing its results with experimental data and those of mainstream numerical methods. Then, the results of a dynamic analysis of typical potential submarine landslides in the Shenhu sea area are analyzed using the proposed method. Case studies are carried out under different soil shear strength distributions, and the influence of initial stress is also analyzed. The shear strain-softening and rate-dependency effects are highly involved in the runout process. The simulated landslide’s failure mode is consistent with the geophysical interpretation of existing landslide characteristics.

Research on the loading method for lost motion testing of small-sized reducer

Lost motion is utilized to characterize the transmission accuracy of gear reducers and is commonly evaluated through the hysteresis curve method. In examinations of lost motion for large and medium-sized reducers, the default practice is the application of the equal torque gradient loading method. Nonetheless, for small-sized reducers, this approach is deemed inappropriate due to the constraints of the servo motor loading resolution. This study reveals that employing a larger unit torque for equal torque gradient loading can modify the shape of the hysteresis curve and influence the assessment of lost motion. As a result, this paper introduces two innovative loading techniques, namely equal position gradient loading and uniform speed loading, to address the limitations of equal torque gradient loading and reduce the demands on testing equipment. Subsequent experiments validate the issues associated with equal torque gradient loading, confirm the effectiveness of the two new loading techniques, and yield more comprehensive hysteresis curves. It is important to note that all three loading methods are influenced by the loading rate, but the two novel methods can mitigate the effects of loading rate dependency.

Identification and optimization of material constitutive equations using genetic algorithms

The modeling and simulation of engineering materials using constitutive equations requires a large set of optimized coefficients that characterize the hardening or softening behavior. Optimizing this large set of coefficients with multiple constraints is very challenging using conventional optimization methods. This research proposes a novel model-agnostic framework based on genetic algorithms to identify and optimize the set of coefficients of the constitutive equations of engineering materials. The proposed framework demonstrates solution convergence, scalability to available data, and high explainability over a wide range of engineering materials, including titanium-based, iron-based, and aluminum-based alloys. The experimental test data for necessary validation of the computational framework was generated using the MTS fatigue testing machine equipped with a highly sensitive extensometer. The Chaboche unified visco-plasticity material model has been implemented as an example in this study which can deal with both cyclic effects, such as combined isotropic and kinematic hardening, and rate-dependent effects associated with visco-plasticity. The experimentally obtained cyclic response of three different classes of materials was compared with their optimized simulated constitutive equations, and the results were in good agreement. Furthermore, the proposed multi-objective optimization using genetic algorithm methodology avoids local optimality and converges to the optimal solution much faster than commercially available software.

Influence of rail side lubrication and slip rate dependent effects upon the corrugation on the metro small curve track

For investigating the rail corrugation characteristics of metro small curve track under the combined effect of rail side lubrication and slip rate dependence, by developing a three-dimensional vehicle-track coupling numerical model, the wheel-rail (WR) contact stick-slip (SS) characteristics under different transition areas of rail side lubrication in the presence of corrugation were analyzed. Meantime, on the basis of considering the friction slip rate dependence, the SS vibration characteristics under different rail side lubrication conditions were further analyzed to understand the effect mechanism of rail surface friction characteristics on corrugation. The results show that, when there is rail side lubrication, both inner and outer WR systems have the possibility for SS vibration, and the longitudinal SS vibration intensity is greater than the transverse SS vibration intensity; the SS vibration intensity of the inner WR system is greater than that of the outer WR system, indicating that the inner rail is more susceptible to corrugation and the corrugation is more acute. With the expansion of the rail side lubrication range, the standard deviations of longitudinal and transverse adhesion coefficients decrease, illustrating that the expansion of the lubrication range can reduce the SS vibration intensity of WR system. When the co-effects of rail side lubrication and slip rate dependence are considered, the increase of the rail side lubrication range leads to the increase of standard deviations of adhesion coefficients, which may be related to the enhancement of slip effect induced by the increase of the lubrication range. The introduction of slip rate dependent effect can reduce the standard deviation of the WR adhesion coefficient, which demonstrates that the slip rate dependent effect can ease the degree of SS vibration of WR system, thus reducing the probability of corrugation occurrence caused by the SS vibration.

Mechanical Behavior and Failure Mechanism of Rocks under Impact Loading: The Coupled Effects of Water Saturation and Rate Dependence

Mechanical Behavior and Failure Mechanism of Rocks under Impact Loading: The Coupled Effects of Water Saturation and Rate Dependence

High-Performance Flux Tracking Controller for Reluctance Actuator

To meet the ever-increasing demand for next-generation lithography machines, the actuator plays an important role in the achievement of high acceleration of the wafer stage. However, the voice coil motor, which is widely used in high-precision positioning systems, is reaching its physical limits. To tackle this problem, a novel way to design the actuator using the magnetoresistance effect is argued due to the high force densities. However, the strong nonlinearity limits its application in the nan-positioning system. In particular, the hysteresis is coupled with eddy effects and displacement, which lead to a rate-dependent and displacement-dependent hysteresis effect in the reluctance actuator. In this paper, a Hammerstein structure is used to model the rate-dependent reluctance actuator. At the same time, the displacement-dependent of the model is regarded as the interference with the system. Additionally, a control strategy combining inverse model compensation and the disturbance observer-based discrete sliding mode control was proposed, which can effectively suppress the hysteresis effect. It is worthy pointing out that the nonlinear system is transformed into a linear system with inversion bias and disturbance by the inverse model compensation. What is more, the sliding mode controller based on the disturbance observer is designed to deal with the unmodeled dynamics, displacement disturbances, and model identification errors in linear systems. Thus, the tracking performance and robustness to external disturbances of the system are improved. The simulation results show that it is superior to the PI controller combined with an inverse compensator and even to the discrete sliding mode controller connected with inverse compensator, confirming the effectiveness of the novel control method in alleviating hysteresis.

Multi-target active subspaces generated using a neural network for computationally efficient turbulent combustion kinetic uncertainty quantification in the flamelet regime

Propagating uncertainties in kinetic models through combustion simulations can provide important metrics on the reliability and accuracy of a model, but remains a challenging and numerically expensive problem especially for large kinetic models and expensive turbulent combustion simulations. Various surrogate model and dimension reduction techniques have previously been applied in order to reduce the cost of forward uncertainty propagation in combustion simulations, but these are often limited to low-dimensional, simple combustion cases with scalar solution targets. In the current work, we developed a neural network-accelerated framework for identifying a low-dimensional active kinetic subspace that applies to the entire temperature solution space of a flamelet table and can capture the mixture fraction and strain rate dependent effects of the kinetic uncertainty. We then demonstrated the computational savings enabled by this framework through a proof-of-concept, flamelet-based application in a Reynolds-averaged Sandia Flame D simulation using a chemical model for methane combustion with 217 reactions. By leveraging the large dimensional compression and low-cost scaling of the active subspace method, offloading the initial dimension reduction gradient sampling onto the laminar flamelet simulations, and accelerating the gradient sampling process with a specifically designed neural network, we were able to estimate the temperature uncertainty profiles across the solution space of the turbulent flame with strong accuracy of 70−85% using just seven perturbed solutions. Additionally, as it occurs entirely within the flamelet table, the cost of identifying the reduced subspace does not scale with the cost of the turbulent combustion model, which is a promising feature of this framework for future application to larger-scale and more complex turbulent combustion applications.

Combined rate-temperature effects in postnecking plasticity of A2-70 stainless steel

In this paper, a comprehensive study that integrates theoretical, experimental and FE analyses, elucidates the combined effect of strain, strain rate, and temperature on the mechanical response of A2-70 stainless steel. A wide series of tensile experiments on cylindrical specimens is presented, including low to high temperatures and quasi-static to dynamic rates. Opportune combinations of temperatures and strain rates are imposed in order to possibly separate and identify their respective effects on the flow curve of the material. The adopted experimental procedures based on neck-related measurements revealed the onset of secondary phenomena affecting dynamic tensile tests. Classical material models were found not suitable to correctly predict the complex elastoplastic deformation of this material. Thus, a new general material model is presented and used to account for the complex interplay between strain, temperature, and rate-dependent effects. Finite element simulations are conducted using both the proposed constitutive model and another classical model of dynamic hardening, to investigate and compare their predictive capability over the entire experimental campaign.

Numerically efficient and robust interior-point algorithm for finite strain rate-independent crystal plasticity

The challenges of classic rate-independent crystal plasticity models regarding the determination of active slip systems and computation of solutions due to linear dependent slip systems are still a field of active research. In that regard, interior-point methods are promising approaches because a logarithmic barrier term naturally avoids the combinatorial active set search, and these methods are applicable even when the gradient of inequality constraints is linearly dependent. In this paper, a new interior-point algorithm suitable for rate-independent crystal plasticity at finite strains is developed. For that purpose, the postulate of maximum dissipation is recast as a constrained optimization problem whose optimality conditions are derived by utilizing interior-point approaches. This optimization problem is discretized in time by means of an exponential time integration of the flow rule, and the time-discrete equations are solved by a Newton scheme. The focus of this paper is the efficiency and robustness of the implementation of this approach. In particular, the effect of different line search procedures, favorable residual forms, preconditioning methods, barrier parameter updates and the consistent algorithmic tangent modulus are discussed and further elaborated. In addition, aspects regarding uniqueness and well-posedness of the algorithm are analyzed in a geometrically linearized setting. Efficiency and robustness of the developed algorithm are shown by numerical examples of an FCC crystal including finite element simulations without stabilizing hardening or rate-dependent effects. Furthermore, the results are compared to the well-established augmented Lagrangian formulation.

Gradient-extended damage modelling for polymeric materials at finite strains: Rate-dependent damage evolution combined with viscoelasticity

While the strong rate-dependent effects of polymeric materials in the elastic regime are well studied, the time-dependent effects that arise in the inelastic damage regime are still difficult to model and are therefore the subject of investigation. In this work, we propose a simple but flexible formulation for the description of rate-dependent damage combined with viscoelasticity at finite strains. This model is based on a finite viscoelastic material formulation combined with a Perzyna-type approach to describe the damage evolution equation. With this formulation we are able to describe both damage due to creep and relaxation of the polymer matrix in both a qualitative and quantitative manner. Besides the main aspects of thermodynamic consistency, we describe the numerical implementation into finite elements and present numerical examples to demonstrate the capabilities of the proposed model. At last, we compare the model with experimental data and show the good predictive capabilities of this newly developed material model.

Finite element formulation and implementation of largely deformable soft viscoelastic brain tissue responses

The impact forces due to accidental head impacts make the brain tissue distorted, twisted, and cause Traumatic Brain Injury (TBI). One way to predict the injury level is through simulations with appropriate material modeling and a computational framework. This work focuses on the Finite Element (FE) formulation of white matter responses to improve TBI predictions. Rate-dependent effects of white matter deformation are captured through the numerical implementation of an experimentally verified constitutive equation and nonlinear evolution equations of internal state variables. An ABAQUS UMAT is developed. One-element FE simulations are compared with the analytical and experimental results. Motivated by real-life scenarios, a few 3D Boundary Value Problems (BVPs) are solved to investigate the white matter responses.

Effects of isolator modeling on the predicted responses of an HDR base-isolated building

This manuscript presents the assessment of numerical responses from a High Damping Rubber base-isolated building using six hysteretic models to capture the nonlinear behavior of the isolation system. The experimental data used to evaluate the numerical predictions includes responses from earthquake simulations of a full-scale base-isolated building. The analysis of experimental responses of the isolation system revealed that the onset of strain rate dependency effects increases the loading-path stiffness of the bearings, and a threshold of minimum strain rates to develop strain rate dependency effects in the reference isolation system was identified. The prediction of structural responses shows that the agreement with the experimental responses does not depend on the model’s ability to capture the nonlinear stiffening at large deformations. Instead, a better agreement of predictions with experimental shear forces and strains of the isolation system and peak inter-story accelerations are observed after implementing stiffer properties to indirectly incorporate the strain rate dependency effects. This study shows that implementing properties only from the softened state may lead to underestimating shear forces at the isolation level and inter-story structural responses. The assessment of numerical and experimental responses of the isolation system demonstrated the need to include the potential stiffness variation due to strain rate dependency in the isolators’ modeling.