Rapid Loading Rates Research Articles

Mechanical Behavior of Polymer Braided Stent at Rapid Radial Loading

Stent implantation is the mainstream treatment for high-incidence vascular diseases. The stent is implanted into the blocked vessel with minimal trauma to restore blood flow. Polymer braided stents with superior biocompatibility and flexibility have broad application prospects in stent implantation. An ideal polymer stent should have suitable radial supporting capacity to withstand the cyclic radial load from vessels. Especially in the case of accelerated vasoconstriction caused by emotional excitement, drinking or fever, etc. However, there are currently limited studies on the mechanical properties of stent at rapid radial loading. In this work, the radial supporting capacity and fatigue properties of polymer stent at rapid loading rate were investigated by experiment and simulation. With the increase of radial loading rate, the stent has different deformation tendency and fatigue resistance. This study is helpful to study the structural changes of the polymer braided stent at different loading rates, and provide ideas for the evaluation and the optimization of the polymer braided stent.

A Review of Numerical Simulation and Modeling in High Strain Rate Deformation Processes

Numerical simulation and modeling play a crucial role in understanding and predicting the behavior of materials subjected to high strain rate deformation processes. These processes involve rapid deformation and loading rates, typically encountered in scenarios such as impact events, explosive detonations, metal forming, and crash simulations. By employing advanced computational techniques, researchers and engineers can gain insights into complex material behavior under extreme loading conditions. This paper provides an overview of numerical simulation and modeling approaches used in studying high-strain rate deformation processes. It discusses the challenges associated with capturing dynamic material response, the development of constitutive models, and the use of finite element analysis and computational fluid dynamics. The paper also highlights the importance of material characterization, model validation, and sensitivity analysis for accurate and reliable simulations. Additionally, it explores the application of numerical simulations in optimizing material properties, designing protective structures, and improving the performance of impact-resistant materials. Overall, this review paper emphasizes the significance of numerical simulation and modeling as powerful tools for advancing the understanding and design of high-strain rate deformation processes.

One‐dimensional consolidation of soil under multistage load based on continuous drainage boundary

SummaryIn engineering practice, a rapid loading rate can result in ground failure when the strength of soft soils is relatively low, and a multistage loading scheme is always utilized to deal with this situation. Firstly, under a multistage load and the continuous drainage boundary, an analytical solution of excess pore‐water pressure and consolidation degree is obtained by virtue of the superposition formula of excess pore‐water pressure, and a more general continuous drainage boundary under arbitrary time‐dependent load is developed. Then, a comparison with existing analytical solutions is conducted to verify the present solution. A preliminary attempt on applying the continuous drainage boundary into the finite element model is made, and the feasibility of the numerical model for the one‐dimensional consolidation under the continuous drainage boundary is verified by comparing the results calculated by FEM with that from present analytical solution. Finally, the consolidation behavior of soil is investigated in detail for different int erface parameters or loading scheme. The results show that, in land reclamation projects, a horizontal drain should be placed close to the boundary with a smaller interface parameter to improve the consolidation efficiency. The degree of consolidation is also related to the applied time‐dependent load and interface parameters.

Fasteners in Steel Fiber Reinforced Concrete Subjected to Increased Loading Rates

Increased loading rates on fasteners may be caused by high ground accelerations as a consequence of e.g., nuclear explosions, earthquakes or car collisions. It was concluded by Hoehler et al. (2006) that fasteners under rapid loading rates show an increased ultimate resistance in the concrete dominant failure modes or the ultimate resistance is at least as large as under quasi-static loading. Due to the increased demand on using fasteners in steel fiber reinforced concrete (SFRC), it is intended to show how the ultimate concrete cone capacity of fasteners changes under higher than quasi-static loading rate in normal plain concrete (PC) and in SFRC. This paper presents the results of an extensive experimental program carried out on single fasteners loaded in tension in normal plain concrete and in SFRC. The test series were conducted using a servo-hydraulic loading cylinder. The tests were performed in displacement control with a programmed ramp speed of 1, 100, 1000, and 3500 mm/min. This corresponded to calculated initial loading rates ranging between 0.4 and 1600 kN/s. The results of the tension tests clearly show that the rate-dependent behavior of fasteners in SFRC with 30 and 50 kg/m3 hooked-end-type fibers fits well to the previously reported rate-dependent concrete cone behavior in normal plain concrete. Additionally, a positive influence of the fibers on the concrete cone capacity is clearly visible.

Dynamic stability of biaxially strained thin sheets under high strain-rates: response to local perturbations

This work pertains to the stability of structures under rapid loading rates when inertia is taken into account. In contrast to the widely used approach in the relevant literature, which is based on the method of modal analysis to determine the structure’s fastest growing eigenmode—meaningful only for cases where the velocity of the perfect structure is significantly lower than the associated characteristic wave propagation speeds—the present study analyzes the time-dependent response to spatially localized perturbations of the transient (time-dependent) states of these structures, in order to understand the initiation of the corresponding failure mechanisms. We are motivated by the experimental studies of Zhang and Ravi-Chandar (Int J Fract 142:183-217, 2006), Int J Fract 163:41-65, (2010) on the high strain-rate expansion of thin rings and tubes, which show no evidence of a dominant wavelength in their failure mode and no influence of strain-rate sensitivity on the necking strains. Recently, Ravi-Chandar and Triantafyllidis (Int J Solids Struct 58:301-308, 2014) studied the dynamic stability of an incompressible, nonlinearly elastic bar at different strain-rates by following the evolution of localized small perturbations introduced at different times. The same approach is followed here for the biaxial stretching of thin plates, where we follow the time evolution of spatially localized perturbations and their interactions. The nonlinear time evolution of a such a perturbation is studied numerically and it is shown that these structures are stable until the time when the condition for the loss of ellipticity is reached. An analytical method, based on linearization, is used to define the size of the influence zone of a point-wise perturbation and we study its dependence on constitutive laws and loading conditions.

Determining the viscoelastic properties obtained by depth sensing microindentation of epoxy and polyester thermosets using a new phenomenological method

Epoxy and polyester thermosets are currently used as the polymer matrix material for many fiber-reinforced composite systems. The viscoelastic properties of these materials were investigated in this study by use of depth sensing microindentation. The microindentation tests performed had the load being applied at a rapid loading rate to a maximum load. This maximum load was held constant while the stylus continued to sink. It was then unloaded at a nominal rate. A new phenomenological model developed by Schwarzer in 2014 was used in this work to determine the viscoelastic properties. Two approaches or methods were used. The first method involved determining the three parameters by using hold time data combined with unloading data (this method is referred to in this work as ‘hold time method’). The second method used only the unloading data (this method is referred to in this work as ‘unloading method’). It was shown that the properties determined by the two methods are not the same but are dependent upon the strain rate behavior during the indentation test. Low load scratch tests were also performed. It was seen that as the sliding speed increased the depth of penetration decreased resulting in the coefficient of friction also decreasing. An understanding of the viscoelastic properties at the surface and how they affect friction are important in studying wear of these materials.

Simulating Ballast Shear Strength from Large-Scale Triaxial Tests

The railroad ballast layer consists of discrete aggregate particles, and the discrete element method (DEM) is the most widely adopted numerical method to simulate the particulate nature of ballast materials and their particle interactions. Large-scale triaxial tests performed in the laboratory under controlled monotonic and repeated loading conditions are commonly considered the best means to measure macroscopic mechanical properties of ballast materials, such as strength, modulus, and deformation characteristics, directly related to load-carrying and drainage functions of the ballast layer in the field. A DEM modeling approach is described for railroad ballast with realistic particle shapes developed from image analysis to simulate large-scale triaxial compression tests on a limestone ballast material. The ballast DEM model captures the strength behavior from both the traditional slow and the rapid shear loading rate types of monotonic triaxial compression tests. The results of the experimental study indicated that the shearing rate had insignificant influence on the results of the triaxial compression tests. The results also showed that the incremental displacement approach captured the measured shearing response, yet could save significant computational resources and time. This study shows that the DEM simulation approach combined with image analysis has the potential to be a quantitative tool to predict ballast performance.

Temperature effects of shape memory alloys (SMAs) in damage control design of steel portal frames

The objective of the present study is to analytically investigate temperature effects of an axial-type seismic damper made of shape memory alloys (SMAs) equipped in steel frames. Based on a modified multilinear one dimensional constitutive model of SMAs, two types of SMAs are employed, which have different stress plateau and different stress growth rate with temperature increase. Temperature effects of SMA dampers on seismic performance upgrading are discussed in three aspects: different environment temperatures; rapid loading rate induced heat generation and different SMA fractions. The analysis indicates that the effect of environment temperature should be considered for the SMA damper in steel frames. However, the rapid loading rate induced heat generation has little adverse effect.

Linking zircon U–Pb and garnet Sm–Nd ages to date loading and metamorphism in the lower crust of a Cretaceous magmatic arc, Swakane Gneiss, WA, USA

Synorogenic basin development and subsequent collapse and loading provide important constraints on the Late Cretaceous crustal structure of the North America Cordillera. High grade metasedimentary rocks of the Swakane Gneiss in the North Cascades have been interpreted to include ca. 73Ma detrital zircon that requires a protolith age considerably younger than metamorphic ages of adjacent terranes. This detrital interpretation requires rapid loading rates of 7–8mm/yr, heating to 750°C in <5myr, and partial exhumation prior to ca. 68Ma. We present new U–Pb zircon and Sm–Nd garnet dates for the Swakane Gneiss that directly date metamorphism and provide a basis for evaluating this model of Late Cretaceous deposition, loading, and crustal structure.Garnet preserves compositional evidence for growth during high pressure amphibolite-facies metamorphism and little subsequent modification. New garnet–rock Sm–Nd isochrons of 73.5±1.2, 71.3±2.8, and 65.8±0.7Ma, tightly constrain the timing of garnet growth. Swakane Gneiss zircons preserve complex magmatic, detrital, and metamorphic histories. Most zircons have distinct cores and homogeneous overgrowths. Detrital zircon cores include significant Proterozoic and Mesozoic components with low U/Th ratios. Homogeneous metamorphic zircon rims have high U/Th (>5) and define an array of concordant U–Pb dates from 75 to 63Ma. The new zircon U–Pb and garnet Sm–Nd ages establish that the youngest regional metamorphism was diachronous and occurred between 75 and 63Ma. Our dataset precludes post 73Ma deposition and instead suggests that sedimentation occurred after ca. 91Ma and ended before ca. 75Ma. Using these age constraints for deposition and metamorphism, we propose new loading rates of 1–3mm/yr and conclude that the Swakane Gneiss protolith was likely deposited in a small, short-lived, intra-arc basin that subsided, filled in, and collapsed quickly due to overthrusting of arc crust.

Limitation of Finite Element Analysis of Poroelastic Behavior of Biological Tissues Undergoing Rapid Loading

The finite element method is used in biomechanics to provide numerical solutions to simulations of structures having complex geometry and spatially differing material properties. Time-varying load deformation behaviors can result from solid viscoelasticity as well as viscous fluid flow through porous materials. Finite element poroelastic analysis of rapidly loaded slow-draining materials may be ill-conditioned, but this problem is not widely known in the biomechanics field. It appears as instabilities in the calculation of interstitial fluid pressures, especially near boundaries and between different materials. Accurate solutions can require impractical compromises between mesh size and time steps. This article investigates the constraints imposed by this problem on tissues representative of the intervertebral disc, subjected to moderate physiological rates of deformation. Two test cylindrical structures were found to require over 10(4) linear displacement-constant pressure elements to avoid serious oscillations in calculated fluid pressure. Fewer Taylor-Hood (quadratic displacement-linear pressure elements) were required, but with complementary increases in computational costs. The Vermeer-Verruijt criterion for 1D mesh size provided guidelines for 3D mesh sizes for given time steps. Pressure instabilities may impose limitations on the use of the finite element method for simulating fluid transport behaviors of biological soft tissues at moderately rapid physiological loading rates.

Critical assessment of anaerobic processes for continuous biohydrogen production from organic wastewater

Production of biohydrogen using dark fermentation has received much attention owing to the fact that hydrogen can be generated from renewable organics including waste materials. The key to successful application of anaerobic fermentation is to uncouple the liquid retention time and the biomass retention time in the reactor system. Various reactor designs based on biomass retention within the reactor system have been developed. This paper presents our research work on bioreactor designs and operation for biohydrogen production. Comparisons between immobilized-cell systems and suspended-cell systems based on biomass growth in the forms of granule, biofilm and flocs were made. Reactor configurations including column- and tank-based reactors were also assessed. Experimental results indicated that formation of granules or biofilms substantially enhanced biomass retention which was found to be proportional to the hydrogen production rate. Rapid hydrogen-producing culture growth and high organic loading rate might limit the application of biofilm biohydrogen production, since excessive growth of fermentative biomass would result in washout of support carrier. It follows that column-based granular sludge process is a preferred choice of process for continuous biohydrogen production from organic wastewater, indicating maximum hydrogen yield of 1.7 mol-H 2/mol-glucose and hydrogen production rate of 6.8 L-H 2/L-reactor h.

The steady state abrasion of rubber: Why are the weakest rubber compounds so good in abrasion?

This paper examines the blade abrasion of four different rubber materials, unfilled natural rubber (NR), unfilled styrene butadiene rubber (SBR), unfilled butadiene rubber (BR) and carbon black filled styrene butadiene rubber. Each is abraded until the steady state abrasion pattern is developed on the surface of moulded rubber wheels. The steady state conditions are measured using the weight loss per revolution of the wheel. The abraded surface is cut to examine the typical asperity profile. Each profile is modelled using finite element analysis to calculate the stored energy release rate for each combination of material and test condition. The stored energy release rate when combined with an independent measure of the rate of crack growth measured using a fatigue crack growth test gives a reasonable prediction of the abrasion rate for both SBR materials as well as the BR. However, the NR materials appear to be about 30 times worse in abrasion than would be expected from the cyclic fatigue crack growth measurements. This is most likely to result from the strain induced crystallisation being suppressed by the very rapid loading rates that are encountered during blade abrasion. It is apparent that the low strength of the BR material results in much smaller asperities being formed under steady state abrasion. When these asperities are modelled they create very low values of strain energy release rate which results in a much slower abrasion rate. Conversely the strongest material NR has the longest tongue on the asperity and this in turn generates much larger values for the tearing energy at the tip of the asperity and this contributes to its poor abrasion resistance.

Rate-dependent phase transformations in nanoindented germanium

There is considerable controversy over the deformation behavior of germanium (Ge) under nanoindentation using a sharp diamond tip, with a diverse range of observations that suggest competing mechanisms. Here we show the deformation mechanism of Ge can be controlled by the rate of applied load. Loading rate is varied over three orders of magnitude using depth-sensing nanoindentation. At slow loading rates, shear-induced plasticity is observed. At rapid loading rates (&amp;gt;100 mN s−1), pressure-induced phase transformations are detected by ex situ micro-Raman spectroscopy and transmission electron microscopy. This switch in the deformation mechanism is due to the differing rate sensitivities of the respective deformation modes, shear-induced plasticity or pressure-induced phase transformation.

Extraction of zinc and copper–zinc mixtures from ammoniacal solutions into emulsion liquid membranes using LIX 84I®

Abstract Emulsion liquid membranes with LIX 84I as extractant were used to extract zinc and copper–zinc mixtures from ammoniacal media. The effects of various emulsion parameters and process parameters on zinc extraction were investigated. The optimal pH was 8.1. The stripping rates were found to be slower than the loading rates in ELMs. The extraction and stripping data using LIX 84I were obtained for Zn and Cu–Zn mixtures to discern the influence of individual steps on ELM extraction. A synergistic effect was observed for loading and stripping zinc in the presence of copper. Zinc stripped faster than copper when the zinc concentration was higher or comparable with copper. Separation factors for Cu/Zn were found to be in the range of 1.1–1.4. When Cu–Zn mixtures were extracted in ELMs, it was observed that the whole extraction process was governed by the loading of copper and zinc in the membrane phase and other considerations such as stripping, diffusion etc. were completely masked by the rapid loading rates of copper in the ELMs. The separation factor βCu/Zn was found to be a maximum of 3.5 indicating the possibility of selective separation of copper from Cu–Zn mixtures using ELMs.

Two-dimensional strain fields on the cross-section of the bovine humeral head under contact loading

The objective of this study was to provide a detailed experimental assessment of the two-dimensional cartilage strain distribution on the cross-section of immature and mature bovine humeral heads subjected to contact loading at a relatively rapid physiological loading rate. Six immature and six mature humeral head specimens were loaded against glass and strains were measured at the end of a 5 s loading ramp on the textured articular cross-section using digital image correlation analysis. The primary findings indicate that elevated tensile and compressive strains occur near the articular surface, around the center of the contact region. Few qualitative or quantitative differences were observed between mature and immature joints. Under an average contact stress of ∼1.7 MPa, the peak compressive strains averaged −0.131±0.048, which was significantly less than the relative change in cartilage thickness, −0.104±0.032 ( p<0.05). The peak tensile strains were significantly smaller in magnitude, at 0.0325±0.013. These experimental findings differ from a previous finite element analysis of articular contact, which predicted peak strains at the cartilage–bone interface even when accounting for the porous-hydrated nature of the tissue, its depth-dependent inhomogeneity, and the disparity between its tensile and compressive properties. These experimental results yield new insights into the local mechanical environment of the tissue and cells, and suggest that further refinements are needed in the modeling of contacting articular layers.

Finite Element Modeling for Strain Rate Dependency of Fracture Resistance in Compact Bone

Crack growths in compact bones driven by various strain rate levels were studied using finite element modeling. The energy resistance curves in bovine femur cortical bones were characterized, whereas the orthotropic viscoelasticity in bone materials was accounted for to assess the effect of strain rate on the energy resistance curve. The models were also used to justify the anticipated plane strain response as a result of rather thick specimens used in experiments. Similarities were found between the experimental and model results when crack resistance ability exhibited in bones with slow loading rates, while unstable crack growth existed in bones with rapid loading rates. The critical energy release rates slightly decreased with the increase in strain rates. The hybrid experimental and computational method introduced in this study could be beneficial for application in fracture study in which standard experiments cannot be validly performed.

Forced Detachment of the CD2-CD58 Complex

The force-induced detachment of the adhesion protein complex CD2-CD58 was studied by steered molecular dynamics simulations. The forced detachment of CD2 and CD58 shows that the system can respond to an external force by two mechanisms, which depend on the loading rate. At the rapid loading rates of 70 and 35 pN/ps (pulling speeds of 1 and 0.5 Å/ps) the two proteins unfold before they separate, whereas at slower loading rates of 7 and 3.5 pN/ps (pulling speeds of 0.1 and 0.05 Å/ps), the proteins separate before the domains can unfold. When subjected to a constant force of 400 pN, the two proteins separated without significant structural distortion. These findings suggest that protein unfolding is not coupled to the adhesive function of CD2 and CD58. The simulations further confirm that salt bridges primarily determine the tensile strength of the protein-to-protein bond, and that the order of salt bridge rupture depends mainly on the position of the bond, relative to the line of action of the applied force. Salt bridges close to this line break first. The importance of each of the salt bridges for adhesion, determined from the simulations, correlates closely with their role in cell-to-cell adhesion and equilibrium binding determined by site-directed mutagenesis experiments.

The use of acoustic emission to determine characteristic dynamic strength and toughness properties of steel

The dynamic J integral at crack initiation ( J id) and dynamic yield stress ( σ yd) are useful parameters to characterize elastic-plastic material behaviour under rapid loading rates. The critical step for evaluating J id and σ yd under the condition of the three point impact bending test is the detection of the crack initiation and of the yield point in the impact load–deflection curve, respectively. This paper presents an acoustic emission (AE) based method to determine the ductile crack initiation and additionally the beginning of yield. The experimental techniques used to evaluate σ yd and J id include both instrumented pendulum impact tests with the AE transducer within the striker (tup) and medium rate three point bend (TPB) tests with additional AE transducers on the specimen surface. Results obtained from the tests indicate that the AE method is capable of detecting general yielding and the onset of ductile crack growth (initiation). Different types of pulse shaped AE signals can be observed. They were connected with characteristic features during the loading process.

Gearing Up With Plastic

This article explains the engineering design concepts behind injection-molded gears that make drives lighter, quieter, and less costly. As the experience base with plastic gears has grown, computer-aided-design (CAD) tools have advanced. The most powerful advantages of plastic gears may be the design opportunities they afford. Gear geometries overlooked by designers used to metal are often easy to mold in plastic, and they can reduce drive size, weight, and cost. The operating speed of plastic gears obviously impacts operating temperature. However, rapid-loading rates can also affect material properties. For some materials, the faster a tooth is loaded, the higher the effective modulus and strength. It is highlighted that designers of plastic gears should also pay special attention to shaft attachment. Bore tolerances naturally impact true center distances, sometimes resulting in loss of proper gear action. Problems with prototypes can also tempt gear designers to change resins—a costly mistake given the different shrinkage characteristics of various plastics. It is better to rework the tooth profile than switch the material, unless it is clear that the wrong material was chosen.

The effect of hydrogen on the fracture toughness of alloy X-750

The effect of hydrogen on the fracture toughness behavior of a nickel-base superalloy, Alloy X-750, in the solutionized and aged condition was investigated. Notched bend specimens were tested to determine if the fracture process was stress or strain controlled. The fracture was observed to initiate at a distance between the location of maximum stress and maximum strain, suggesting that fracture required both a critical stress and strain. The effect of hydrogen was further investigated and modeled using fracture toughness testing and fractographic examination. The fracture toughness of the non-charged specimen was 147 \(MPa\sqrt m \). Charging with hydrogen decreased the fracture toughness, Klc, to 52 \(MPa\sqrt m \) at a rapid loading rate and further decreased the toughness to 42 \(MPa\sqrt m \) for a slow loading rate. This is consistent with the rate-limiting step forthe embrittlement process being hydrogen diffusion. The fracture morphology for the hydrogen-charged specimens was intergranular ductile dimple, while the fracture morphology of noncharged specimens was a mixture of large transgranular dimples and fine intergranular dimples. The intergranular failure mechanism in Alloy X-750 was a microvoid initiation process at grain boundary carbides followed by void growth and coalescence. One role of hydrogen was to reduce the void initiation strain for the fine intergranular carbides. Hydrogen may have also increased the rate of void growth. The conditions ahead of a crack satisfy the critical stress criterion at a much lower applied stress intensity factor than for the critical fracture strain criterion. A model based on a critical fracture strain criterion is shown to predict the fracture behavior.