Dynamic Shear Response Research Articles

On the dynamic shear failure of Ti-6Al-4V in different test specimen geometries

In this paper, the dynamic shear response and failure of Ti-6Al-4V using four different test specimen geometries, viz. Hat-Shaped Specimen (HSS), Flat Hat-Shaped Specimen (FHSS), Chip Hat-Shaped Specimen (CHSS) and Double Shear Specimen (DSS), are critically examined and compared. Through a combination of experiments (using the standard Split-Hopkinson Pressure Bar system), finite-element simulations and metallographic examinations of their fracture morphology, the dynamic shear characteristics (strain hardening, strain rate strengthening effect and failure strain) of Ti-6Al-4V obtained using the different specimen geometries are critically examined, compared and analyzed. It will be shown that differences in the stress/strain uniformity, the plastic deformation zone, and the stress state induced by the different specimen geometries lead to discrepancies in the measured shear response and failure that were observed. The shear stress–strain curve obtained using the DSS will be shown to be more precise than the other specimen geometries.

A generalized Bouc–Wen model for simulating the quasi-static and dynamic shear responses of helical wire rope isolators

This research investigates the mechanical behavior of a helical wire rope isolator deforming along its shear direction. In particular, we present the results of an extensive experimental campaign including both quasi-static and dynamic tests. The former provide hysteresis loops characterizing the device quasi-static behavior; the latter, performed by using an electro-mechanical shaker, furnish frequency response curves describing the dynamic behavior of a rigid block supported by the tested device. To simulate such a complex behavior, we adopt a generalized Bouc–Wen model and identify its parameters on the basis of the quasi-static test results. Subsequently, such a model is employed to reproduce the frequency response curves of the isolated rigid block. Since the results of the dynamic tests suggest the presence of rate-dependent hysteresis phenomena in the isolated system, the generalized Bouc–Wen model is enhanced by introducing a linear viscous component. Finally, to substantiate the model validation, the experimental results obtained by applying a series of white noise signals are compared with those obtained numerically to demonstrate the model capability of reproducing the device behavior in non-stationary response conditions.

Passive elasticity properties of Octopus rubescens arms.

In this report, passive elasticity properties of Octopus rubescens arm tissue are investigated using a multidisciplinary approach encompassing biomechanical experiments, computational modeling, and analyses. Tensile tests are conducted to obtain stress-strain relationships of the arm under axial stretch. Rheological tests are also performed to probe the dynamic shear response of the arm tissue. Based on these tests, comparisons against three different viscoelasticity models are reported.

Dynamic Shear Responses of Combined Contaminated Soil Treated with Nano Zero-Valent Iron (nZVI) under Controlled Moisture

Nano zero-valent iron (nZVI) technologies have gained recognition for the remediation of heavily contaminated sites and reused as backfilling soil. The moisture environment at these sites not only impacts the reactions and reactivity of nZVI but also the dynamic responses of compacted backfilled soils. The research explored the effects of different nZVI dosages (0.2%, 0.5%, 1%, 2%, and 5%) on Lead-Zinc-Nickel ions contaminated soil under a controlled-moisture condition. Cyclic triaxial tests were performed to evaluate the dynamic responses of treated soil samples prepared using a consistent moisture compaction method. Particle size distribution and Atterberg limits tests assessed changes in particle size and plasticity. The study revealed a minor reduction in the particle size, liquid limit, plastic limit, and plasticity index of the contaminated soil. Notably, increasing nZVI dosages in treated soils led to growing Atterberg limits. An increase in the specific sand fraction of treated soils was observed with nZVI, suggesting nanoparticles–soil aggregations favoring existing larger particles. Stepwise loading cyclic triaxial tests indicated an optimal dynamic response of soil treated with 1% nZVI under the controlled-moisture condition, proven by notable enhancements in the maximum shear modulus, maximum shear stress, less shear strain, and higher damping ratio within the small strain range. It should be noted that moisture content in treated soils declined significantly with higher nZVI dosages during preparation, potentially impeding effective aggregation and the formation of a solid soil skeleton. These findings advance the importance of considering the balanced nZVI dosage and moisture content when employing the safety assessment of practical applications in both nano-remediation techniques and soil mechanics.

Non-Stick Length of Polymer-Polymer Interfaces under Small-Amplitude Oscillatory Shear Measurement.

Interfaces in soft materials often exhibit deviation from non-slip/stick response and play a determining role in the rheological response of the overall system. We discuss detection techniques for the excess interface rheology using small-amplitude oscillatory shear (SAOS) measurements. A stacked bilayer of different polymers is sheared parallel to the interface and the dynamic shear response is measured. Deviation of the bilayer shear modulus from the superposition of the shear moduli of the component layers is analysed. Furthermore, we introduce a frequency-dependent non-stick length based on the bilayer SAOS response to characterize the excess interface rheology. We observe an approximate stick response in the interface in bilayers composed of the chemically same monomer as well as an apparent slip in the interface between immiscible polymers. The results suggest that the proposed non-stick length in SAOS is capable of detecting the apparent interfacial slip. The non-stick length in SAOS is readily applicable to other complex interfaces of different soft materials and offers a convenient tool to characterize the excess interface rheology.

Simulative and experimental study of metal/polymer interfacial dynamic shear response

Simulative and experimental study of metal/polymer interfacial dynamic shear response

Experimental study of shear behavior of rock–shotcrete interface under dynamic shearing: insights from interface roughness and strain rate

Rock–shotcrete structures are often suffered from dynamic shearing. However, the understanding of the dynamic shear response of rock–shotcrete structures is still at its infancy. To investigate the effects of strain rate and interface roughness on the dynamic shear response of rock–shotcrete structure, laboratory tests were carried out on the modified double notched sandstone–concrete specimen. Testing results show that the dynamic shear strength and dynamic peak strain of sandstone–concrete specimens are both far less than those of sandstone and concrete specimens. With increasing strain rate, the dynamic shear strength of sandstone–concrete specimen increases and the failure mode changes from interfacial shear failure to the mixed failure, i.e., the interfacial, concrete and sandstone shear failure. With the increase in interface roughness, the failure mode changes from sliding fracture to shear-off fracture, leading to an increase in dynamic shear strength and shear peak strain of sandstone–concrete specimens. In addition, it is the smallest sawtooth angle at the sandstone–concrete interface that dominates the dynamic shear strength of sandstone–concrete specimens. The findings in the present study could facilitate understanding the shear behavior and failure mechanism of the rock–shotcrete structure subjected to dynamic loading and be helpful in the efficient design, reinforcement and stability of rock–shotcrete engineering.

Rheological modeling and microstructural evaluation of oily sludge modified bitumen

The disposal of oily sludge (OS) and depletion of crude oil reservoirs has become a global problem for the petroleum industries. The rising cost of bituminous materials is also attributed to the depletion of crude oil reservoirs. Incorporating OS in the production of bitumen can reduce waste generation, thereby ensuring sustainability in petroleum industries. This study carried out a series of physicochemical, rheological and morphological tests to examine the suitability of OS as a bitumen modifier. OS and binders were subjected to Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) to characterize their morphological and chemical configuration. Using a dynamic shear rheometer (DSR) and response surface methodology (RSM), the performance characteristics of binders were analyzed and modeled. FTIR showed the identical functional groups responsible for the compatibility of OS and bitumen. Fit statistics and diagnostic graphs showed the significance and adequacy of the quadratic model for rutting and fatigue factors. Response surface plots showed that OS improved the fatigue resistance of bitumen. The OS up to 8 % addition improves fatigue resistance while keeping the performance grade (PG) identical to that of base bitumen.

Dynamic response of shear thickening fluid and protective properties of impregnated Kevlar fabrics under impact loading

Dynamic response of shear thickening fluid and protective properties of impregnated Kevlar fabrics under impact loading

Superior dynamic shear properties and deformation mechanisms in a high entropy alloy with dual heterogeneous structures

Both heterogeneous grain structure and dual nanoprecipitates were designed in a Al0.5 Cr0.9FeNi2.5V0.2 high entropy alloy (HEA), and the dynamic shear responses were investigated by hat-shaped specimens in split Hopkinson pressure bar tests. The present HEA with heterogeneous structure displays an unprecedented synergy of dynamic shear strength and ductility, as compared to the literature data for other metals and alloys. The excellent dynamic shear properties in the unaged samples could be due to the dynamical grain refinement, the dislocations hardening, and the precipitation hardening. The aged samples with a higher volume fraction of coherent L12 nanoprecipitates display even better dynamic shear properties, as compared to the unaged samples, which can be attributed to the triggered planar dislocation slip, the stored higher density of dislocations, the formation of dislocation substructure and the more pronounced precipitation hardening for postponing the occurrence of the adiabatic shear band (ASB). The high strain rate, high strain/stress magnitude, high adiabatic temperature rise, and fast-cooling process within ASB were observed to induce the dynamic recrystallization and the phase transformation from FCC phase to B2 phase, and this newly observed phase transformation phenomenon was not observed before under quasi-static deformation conditions.

Dynamic shear response of ultra-high-performance fiber-reinforced concretes under impact loading

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is known as an advantageous material for enhancing the shear response capacity of structures subjected to extreme loads, such as in cases of missile strikes, terrorist attacks, or earthquakes. However, there is limited information on the shear response of UHPFRC, especially at high strain rates. In this study, the shear strength, shear strain capacity, and shear peak toughness of UHPFRCs with three fiber types, i.e., twisted fiber (LT), hooked fiber (LH), and smooth fiber (LS), were investigated at static and at high strain rates (up to 245 s−1). The results indicated all UHPFRCs exhibited shear strain hardening behavior accumulated to multiple microcracks at both static and high strain rates although their shear responses were found to be strongly dependent on the fiber type. Among the investigated fiber types, the LT fibers produced the highest shear resistance in terms of shear strength, shear strain capacity, and shear peak toughness at static rates, whereas LS fibers did at high strain rates. The LS fibers exhibited the highest strain rate sensitivity of shear resistance, followed by the LH and LT fibers. Unlike LS fibers, LH and LT fibers showed fiber breakage during the shear loading process at high strain rates. Based on the experimental results, empirical equations to predict the dynamic increase factor (DIF) of shear strength of UHPFRCs at high strain rates were also proposed.

Experimental analysis and predictive modelling of linear viscoelastic response of asphalt mixture under dynamic shear loading

The use of predictive models can facilitate the inclusion of shear parameters in asphalt mixture evaluation and design processes. Unlike more extensively studied tension–compression models, the currently existing shear model, the Hirsch model, has unrealistic constants, particularly for the prediction of phase angle. Aiming at an improved predictive model in shear, this study employs a simple shear apparatus to experimentally analyse the linear viscoelastic properties of asphalt mixtures for road paving. Master curves were constructed and compared between different asphalt mixtures. Additionally, the test results were also analysed in the Black space and the Cole-Cole space. The dynamic shear response of asphalt mixtures was thereafter modelled on the basis of the Hirsch model. As the original model for phase angle prediction was found to be unrealistic, a particular focus in this study was put on identifying realistic empirical relationships for predicting the phase angle of asphalt mixtures in shear. More reliable shear test results of asphalt mixtures were used to calibrate the model, and extra test data were utilized to validate the calibrated model. It is indicated that the predictive model after calibration could deliver results of greatly improved accuracy, especially at the high-frequency and low-frequency ends. The analysis and modelling also leads to realistic empirical relationships for predicting the phase angle of asphalt mixtures in shear. The experimental verification confirms the good prediction accuracy of the calibrated model and proposed empirical relationships.

Laboratory evaluation of dynamic shear response of sand – geomembrane interface

The seismic stability of geosynthetic structures incorporating soil-geomembrane interfaces depends largely on their response to dynamic loads caused by earthquakes or traffic. The present study investigates the dynamic shearing response of sand-smooth geomembrane interface through fixed block-type shake table tests. The influence of dynamic loading parameters, like sliding velocity, loading frequency, normal stress, displacement amplitude and the number of cycles, and relative density of sand on the shearing behavior of the sand-geomembrane interface, are examined. Results show that the peak cyclic shear stress is significantly influenced by normal stress, shear displacement amplitude, loading cycles, and relative density of sand. The dynamic coefficient of friction of the sand-geomembrane interface displays an increasing trend with an increase in loading frequency, shear displacement amplitude, and relative density of sand but decreases for the rest of the considered parameters. The shape of the hysteresis loops is dependent on the normal stress and displacement amplitude. The dynamic coefficients of friction are also compared with the corresponding values under static conditions. The results from the present study emphasize the importance of considering the design basis value of the dynamic coefficient of friction for each parameter during the design stage of geosynthetic structures involving sand and geomembrane.

Dynamic thermomechanical behavior of fine-grained Mg alloy AMX602

This paper details the dynamic mechanical behavior of a fine-grained Mg alloy, AMX602 (Mg-6%Al-0.5%Mn-2%Ca), produced via the Spinning Water Atomization Process (SWAP), followed by compaction and extrusion, to obtain a fully dense plate. The rapid cooling from melt of SWAP results in a coarse powder with a fine-grained microstructure, and the consolidation of this powder followed by extrusion produces a relatively weak rolling texture. The mechanical behavior of the plate was measured in dynamic compression at different temperatures, quasi-static and dynamic tension at room temperature, and under dynamic shear at room temperature. In each case the behavior was probed in the different loading directions corresponding to the processing directions–extrusion, transverse, and normal. AMX602 has relatively high strength and modest ductility. Increasing the temperature increases the compressive strain-to-failure only a small amount, while reducing the flow stresses. In tension, however, the ductility in the normal direction is essentially zero, but modest in the other two directions. The large anisotropy and tension/compression asymmetry of typical rolled Mg alloys is significantly reduced in this material, and the anisotropy reduces further as the temperature increases. The dynamic shear response was measured for different shear planes but there was large specimen-to-specimen variation, however the resistance to shear localization is relatively poor. Despite the high strength of AMX602, the limited ductility hinders its performance in ballistic scenarios and restricts usage.

Dynamic Shear Deformation of a Precipitation Hardened Al0.7CoCrFeNi Eutectic High-Entropy Alloy Using Hat-Shaped Specimen Geometry.

Lamellar eutectic structure in Al0.7CoCrFeNi high-entropy alloy (HEA) is emerging as a promising candidate for structural applications because of its high strength-ductility combination. The alloy consists of a fine-scale lamellar fcc + B2 microstructure with high flow stresses > 1300 MPa under quasi-static tensile deformation and >10% ductility. The response to shear loading was not investigated so far. This is the first report on the shear deformation of a eutectic structured HEA and effect of precipitation on shear deformation. A split-Hopkinson pressure bar (SHPB) was used to compress the hat-shaped specimens to study the local dynamic shear response of the alloy. The change in the width of shear bands with respect to precipitation and deformation rates was studied. The precipitation of L12 phase did not delay the formation of adiabatic shear bands (ASB) or affect the ASB width significantly, however, the deformed region around ASB, consisting of high density of twins in fcc phase, was reduced from 80 µm to 20 µm in the stronger precipitation strengthened condition. We observe dynamic recrystallization of grains within ASBs and local mechanical response of individual eutectic lamellae before and after shear deformation and within the shear bands was examined using nano-indentation.

Experimental Study of the Dynamic Shear Response of Rocks Using a Modified Punch Shear Method

Cohesion and internal friction angle are the two material parameters used in the Coulomb model to predict rock failure in many rock engineering applications. Although these two parameters have been extensively quantified under static conditions using the direct shear or the triaxial compression methods, the effect of dynamic loading on these parameters is not yet clear. A dynamic punch shear method was proposed by Huang et al. (Rev Sci Instrum 82:053901. https://doi.org/10.1063/1.3585983 , 2011) to measure the dynamic cohesion of rocks, and the dependence of cohesion on the loading rate has been revealed. To further investigate the effect of dynamic loading on the internal friction angle and thus the complete dynamic shear response of rocks, this method is extended in this study to include the normal stress by applying lateral confinement to a disc specimen. The confinement is realized by enclosing the specimen assembly in a 1.5 inch diameter Hoek cell. The dynamic load is applied by a split Hopkinson pressure bar system, which is modified to ensure that the specimen assembly remains intact in the Hoek cell during pressurization by applying a static axial pre-stress. Three groups of green sandstone specimens under confinements of 0, 10 and 20 MPa are tested with different loading rates. The results show that the dynamic shear strength exhibits significant rate dependency and it thus increases with the loading rate and the normal stress. The dynamic cohesion increases with the loading rate, while the internal friction angle remains constant.

Effect of Filler Morphology on Viscoelastic Properties of PDMS-Based Magnetorheological Elastomers

ABSTRACTThe viscoelastic properties of magnetorheological elastomers (MREs) are tunable with an external magnetic field, which provides them with greater functionality than conventional reinforced polymers. Despite the abundant amount of literature studying the complex micromechanics of MREs, the effect of filler morphology (including particle size, shape and superficial texture) is an aspect that has been recurrently overlooked. This paper presents a multiscale experimental investigation of the microscopic mechanisms governing the macroscopic viscoelastic behavior of PDMS-silicone-based MREs, with an emphasis on the effect of filler morphology on both the microstructure and the overall dynamic shear response of MREs. Sixteen different MREs were produced using four different iron powders of varying average particle size, shape and texture. The morphology of iron particles and the microstructure of the fabricated materials were analyzed via X-ray computed nanotomography and scanning electron microscopy. In addition, the shear moduli of the specimens were monitored under coupled magneto-mechanical loading via dynamic mechanical analysis. This study shows that the particle size affects the strength of the magnetic interparticle interactions, which produce a confining effect on the rubber matrix, while the particle shape and texture have a great influence on the rubber-filler mechanical adhesion.

Effects of different heat treatments on the dynamic shear response and shear localization in Inconel 718 alloy

The effects of different heat treatments on the dynamic shear response and the adiabatic shear localization characteristic of Inconel 718 alloy (Inconel 718) are studied by the flat hat-shaped sample subjected to the Split Hopkinson Pressure Bar (SHPB) loading. The microstructures of the concentrated shear zone are examined by optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and Vickers micro-hardness tests, respectively. The results indicate that the aged Inconel 718 with higher yield strength and lower strain hardening rate is easier to form an adiabatic shear band (ASB) than that of the solution treated Inconel 718 under dynamic shear loadings. Meanwhile, it has been found that the δ phase plays an important role in inhibiting the shear localization of the solution treated Inconel 718. Little plastic deformation occurs in the region adjacent to the ASB in the aged Inconel 718, whereas significant plastic deformation occurs in a certain width area around the ASB in the solution treated Inconel 718.

A modal approach to determine direct shear of beams subjected to impulse

Protecting important structures against blast loading is vital. Most engineering practitioners use either a Single Degree of Freedom (SDOF) approximation of the dynamic response to blast loading or a computationally expensive numerical model. In this paper, a modal approach is proposed that provides a more accurate and less conservative estimate of direct shear, the transient dynamic shear response developed within a few milliseconds of pressure wave arrival, than the estimate based on SDOF. By way of example and via the proposed approach, simple analytical expressions to estimate the direct shear are developed for simply-supported beams. The estimates are compared with the results of a series of dynamic analyses of a refined finite element model of the beam, performed using LS-DYNA. Very close agreement between the results of numerical modeling and analytical estimates are observed. In addition, the estimated direct shear is significantly lower than the value obtained from the SDOF method. The proposed approach, thus provides an efficient and accurate estimate of the direct shear to be used in structural design.

Dynamic response of shear thickening fluid reinforced with SiC nanowires under high strain rates

In this letter, SiC nanowires were adopted to reinforce the nanoparticle-based shear thickening fluid (STF) to improve its rheological properties. The reinforced STF showed a significant increase in viscosity. A Split-Hopkinson pressure bar was implemented to evaluate the dynamic response of STF at strain rates in the range of 3 × 103–1.2 × 104/s. For the pure STF, the flow stress reaches a saturation value with increasing strain rates and shows almost no strain rate sensitivity, whereas the flow stress of the reinforced STF increases with strain rates, and the strain rate sensitivity to flow stress is obvious owing to the resistance of nanowires. The essence of this study is to reveal that there is a limiting value of the flow stress of traditional nanoparticle-based STF at high strain rates due to the lubrication force among particles. SiC nanowires can be used to break this limitation of the nanoparticle-based STF.