Large Shear Deformation Research Articles

Comparative analysis of stability of embankment on the basis of torsional ring shear test

Designing slopes and embankments is an important geotechnical stage in the framework of industrial, civil and transport construction. For analytical and numerical stability calculations for the first limiting state, soil strength parameters are required, obtained, as a rule, based on the results of field and laboratory studies. Currently, a significant number of methods and equipment for soil testing for shear have been developed. In this paper we focus on the method of testing of cohesive soils under torsional shear ring. It is believed that this type of shear tests most accurately repeats the mechanical process observed during the destruction of slopes and embankments with the formation of fixed cut surfaces and taking into account large shear deformations. This paper contains information on the design of an experimental instrument for a ring (cylindrical) shear of cohesive soil samples. The processing of the results of torsional shear with different speeds is presented, the parameters and methods for finding them. The main purpose of the tests - determination of residual strength parameters: the angle of internal friction and cohesion. Examples are given of using the parameters obtained during tests of a torsional shear for numerical simulation of embankment from cohesive soil.

Composite double network hydrogels with thermoresponsive colloidal nanoemulsions

AbstractWe report the formulation and mechanical characterization of double network (DN) composite hydrogels. The first network consists of covalently crosslinked poly(ethylene glycol diacrylate) (PEGDA), which forms a strong, brittle network that provides elasticity to the gel. The second network, sodium alginate, is ionically crosslinked with Ca2+ to allow increased dissipation of mechanical energy. The novelty of this system over existing DN hydrogels is the additional incorporation of a third mesoscale network, composed of thermoresponsive poly(dimethyl siloxane) (PDMS) nanoemulsions, which undergo colloidal gelation through the bridging of the PEGDA hydrophobic end groups into the PDMS droplets. The colloidally gelled microstructures are photopolymerized into a solid hydrogel by crosslinking the precursors with ultraviolet (UV) light. Tensile mechanical experiments performed on the crosslinked DN nanoemulsion hydrogels show that their rupture stress (0.17–0.34 MPa), fracture energy (144–421 J/m2), and Young's modulus (1–2.1 MPa) are comparable to similar systems in the literature. These mechanical measurements suggest that the gels may be suitable for manufacturing processes in which large shear rates and deformations are encountered.

Microstructure and crystallographic orientation evolutions below the superficial white layer of a used pearlitic rail

Although several studies have been conducted on the mechanism of the formation of white layer by cyclic large shear deformation, and its effect on rolling contact fatigue, limited research has been carried out to find a correlation between sub-superficial layer of running contact surface and the crystallographic orientation, microstructural changes, and distribution of shear deformation and dislocation density. In order to understand the microstructural evolution (i.e., microstructure and crystallographic orientation) a used pearlitic rail sample removed from the heavy-haul railroad was investigated in the current work. A very thin superficial white layer was observed, approximately 15 μm below the running contact surface. X-ray diffraction analysis confirmed the formation of a supersaturated ferrite phase with carbon content of approximately 3.78 C wt%. It could be attributed to the cementite dissolution due to severe shear and compressive stresses, during intense shear plastic deformation, from the rail-wheel interaction. The dominance of {110} ferrite grains parallel to the rail direction was characterised, in the transition layer between white layer and non-deformed pearlite structure, by X-ray diffraction and electron backscattered diffraction techniques. Formation of these grains, corresponding to the closed-pack plane of the ferrite matrix at the transition region, leads to great ductility and retarded crack formation.

Observations on fabric evolution to a common micromechanical state at the soil‐structure interface

SummaryThe fabric plays an important role in the mechanical behavior of granular material. The aim of this paper is to investigate the evolution of fabric in a soil‐structure interface (SSI) to a large shearing in an effort to clarify whether and how this form of fabric evolution can lead to a common microstructure. Using the discrete element method (DEM), two‐dimensional (2D) numerical interface shear tests were carried out, and certain macromechanical and micromechanical properties were exploited. All samples exhibited prominently localized strain in a zone covering the structure's surface (named the localized zone), and much lower density and higher soil fabric anisotropy levels were found inside this zone than outside it. Disregarding different initial void ratios, a common critical state microstructure was observed in large shear deformations of soil samples, with essentially the same fabric arrangement in terms of contact orientation and internal force transmission. Due to the systematic forming, buckling, and collapsing of force chains, an angular zone (called an α‐zone), in which contact density was sluggish to varying degrees, appeared and extended around the main direction of the distribution of contact orientation inside the localized zone. The gradual deterioration of the force chains' stability, as a result of an increasing void ratio, seemed to drive the α‐zone's extension and lead to the rare variation of microstructures in the critical state.

Mechanics of zero degree peel test on a tape — effects of large deformation, material nonlinearity, and finite bond length

A common adhesive tape is a composite consisting of a stiff backing and a soft adhesive layer. A simple way to test how they respond to large shear deformation is the zero degree peel test. Because the backing is very stiff compared to the adhesive, the region where the adhesive layer is subjected to large shear can be hundreds of times its thickness. We use a large deformation hyperelastic model to study the stress and displacement fields in the adhesive layer in this test. Our analytical model is then compared with finite element (FE) results. Except for a small region near the peel front or the free edge, the predicted stress and deformation agree well with the FE model. We compare our result with linear theory and find that strain hardening and large deformation of adhesive can significantly affect the distribution of shear strain and stress state in the adhesive layer. For large deformation, our analysis shows that the lateral stress (parallel to the rigid substrate) is much larger than the shear stress in the adhesive layer. We obtain an exact expression for the energy release rate. Our result shows that the energy release rate determined by the nonlinear theory differs significantly from the linear theory in the regime of short bond lengths. We study the stress state near the peel front and the free edge using a FE model. The results in this work is not specific only to adhesive tapes, but also can be used to study the effect of shear in composites with similar geometry.

On the use of entangled wire materials in pre-tensioned rocking columns

This research explores potential application of entangled wire materials as intermediate layers between segments of pre-tensioned segmental bridge columns. An ensemble of free-decay vibration tests was conducted on small-scale columns with various configurations of intermediate layers. Wooden blocks were used for segments and the entire system was tightened together using a pre-tensioned steel tendon. Damping and frequency of the columns were determined and compared. It is demonstrated that entangled wire materials substantially increase total damping of the entire system in rocking. This result is very encouraging for future application of entangled wire materials in testing large-scale pre-tensioned segmental bridge columns. However, shear and axial stiffness of the layers require further improvement to reduce their large shear and axial deformations.

Nonlinear rheological behavior of gelatin gels: In situ gels and individual layers

The gelation procedure and the gelation time of gelatin gels may lead to apparently similar materials, however, with different rheological fingerprints under small and large oscillatory shear deformations. Here, in the first paper of this series, gelation of 3 and 5% w/w gelatin solutions at 5 °C was performed in situ on the rheometer plate and in custom-made casting modules to obtain individual gel layers. Large amplitude oscillatory shear (LAOS) tests were performed. The nonlinear deformation regime was qualitatively analyzed using normalized Lissajous-Bowditch curves. The MITlaos software was employed to decompose the total intracycle stress response and to calculate the Chebyshev coefficients ratios. The dynamic moduli of the fresh gels were measured directly after the in situ preparation and within a time frame until 1.5 h. In the strain sweeps, we observed intense stiffening followed by yielding above 200% strain. However, the individual gel layers aged for 24 and 48 h show different LAOS fingerprints. The extensive loops in the viscous Lissajous-Bowditch curves indicate an elastoplastic material response. Based on the overall nonlinear rheological response, we propose a structural formation that describes the behavior of the gels for the conditions studied here. In the second paper of this series, we give the impact of hard micro-fillers (glass beads) and we describe the nonlinear characteristics of the filled gels.

In Situ Study on Fracture Behavior of Z-Pinned Carbon Fiber-Reinforced Aluminum Matrix Composite via Scanning Electron Microscope (SEM).

Inside a scanning electron microscope (SEM) chamber, we performed an in situ interlaminar shear test on a z-pinned carbon fiber-reinforced aluminum matrix composite (Cf/Al) fabricated by the pressure the infiltration method to understand its failure mechanism. Experiments show that introducing a stainless-steel z-pin increases the interlaminar shear strength of Cf/Al composite by 148%. The increase in interlaminar shear strength is attributed to the high strength of the stainless-steel z-pin and the strong bonding between the z-pin and the matrix. When the z-pin/matrix interface failed, the z-pin can still experience large shear deformation, thereby enhancing delamination resistance. The failure mechanism of composite includes interfacial debonding, aluminum plough, z-pin shear deformation, frictional sliding, and fracture. These results in this study will help us understand the interlaminar strengthening mechanism of z-pins in the delamination of metal matrix composites.

Material model calibration against axial-torsion-pressure experiments accounting for the non-uniform stress distribution

The need to calibrate material models towards complex multiaxial stress states has received much attention in the last decades. Such stress states are often obtained by axial, torsion and pressure experiments on tubular test bars. These experiments are typically simulated by considering the behavior in a single material point, using the thin-walled assumption of uniform stresses and strains. In this paper, a new simulation methodology that does not rely on the thin-walled assumption has been developed. The accuracy improvements are compared with experimental uncertainties for tubular test bars. Compared to using ABAQUS for equivalent simulations, a speed increase of 100–200 times was found. This simulation methodology has been implemented in an open source software material calibration software called matmodfit. The calibration of material parameters is first demonstrated for cyclic ratcheting axial-torsion experiments using thin-walled test bars. Thereafter, calibration of material parameters from experiments on solid test bars subjected to very large shear deformation under axial compression is performed. This demonstrates a key advantage with the proposed method: Thick-walled or even solid test bars can be modeled without loss of simulation accuracy at a low computational cost.

Startup steady shear flow from the Oldroyd 8-constant framework

One good way to explore fluid microstructure, experimentally, is to suddenly subject the fluid to a large steady shearing deformation and to then observe the evolving stress response. If the steady shear rate is high enough, the shear stress and also the normal stress differences can overshoot, and then they can even undershoot. We call such responses nonlinear and this experiment shear stress growth. This paper is devoted to providing exact analytical solutions for interpreting measured nonlinear shear stress growth responses. Specifically, we arrive at the exact solutions for the Oldroyd 8-constant constitutive framework. We test our exact solution against the measured behaviors of two wormlike micellar solutions. At high shear rates, these solutions overshoot in stress growth without subsequent undershoot. The micellar solutions present linear behavior at low shear rates; otherwise, their behavior is nonlinear. Our framework provides slightly early underpredictions of the overshoots at high shear rates. The effect of salt concentration on the nonlinear parameters is explored.

Temperature Dependency of the Deformation Behavior of Hybrid CFRP/Elastomer/Metal Laminates under 3-Point Bending Loads

Fibre-metal-elastomer laminates offer the possibility of using material combinations which often have to deal with premature delamination, for example due to different coefficients of thermal expansion or galvanic corrosion due to different electronegativities. The present study deals with laminates made of layers of CFRP and aluminum, each of which is bonded together by an elastomer layer. The shear-soft elastomer also allows the much stiffer aluminum and CFRP layers to be sheared off against each other under bending stress. This leads to complex deformation behavior. The shear of the elastomer also plays a crucial role in the damping behavior of the laminate. Due to large shear deformations in the elastomer layer, the combination of rigid layers and soft elastomer layers shows very good damping behavior according to the principle of constrained layer damping. Since bending vibrations that occur during normal use usually have only small amplitudes, the deformation behavior is of particular interest in the elastic range. Since this deformation behavior is strongly dependent on the shear modulus of the elastomer used and this in turn is strongly influenced by temperature, the deformation behavior is characterized at different temperatures. Within the scope of this investigation, quasi-static 3-point bending tests are carried out on different laminate lay-ups in the temperature range from -40 °C to +80 °C. The laminates are consolidated by compression molding and contain two different EPDM elastomers in varying layer thicknesses, unidirectional CFRP prepreg in biaxial layer lay-up and aluminum 2024 sheets. The deformation behavior is analyzed by digital image correlation. This is used to measure both the bending line of the overall composite and strains over the layer thickness. In particular, the shear in the elastomer layers is evaluated and set in relation to the bending lines. Finally, the ability of the laminate lay-up to damp bending vibrations is evaluated.

3D Pixel Mechanical Metamaterials.

Metamaterials have unprecedented properties that facilitate the development of advanced devices and machines. However, their interconnected building structures limit their applications, especially in the fields that require large deformation, rich programmability and efficient shape-reconfigurability. To break this limit and exploit more potentialities of metamaterials, an innovative material design strategy is proposed, named mechanical pixel (MP) array design. Similar to a screen that displays images by adjusting the colors of pixels, the metamaterials can form and reconfigure 3D morphologies by tuning the heights (lengths) of the MPs in the array. The strategy is demonstrated in a multistable metamaterial by experimental tests, theoretical analysis, and numerical simulations. Using this strategy, a large macroscopic shear deformation is obtained, and remarkable enhancements in the mechanical programmability, shape-reconfigurability and adaptability, and reusable shock-resistance are exhibited. Moreover, mechanical design and property prediction for the metamaterials are both greatly simplified due to the pixelated design. For a piece of the 3D pixel metamaterial with m n-unit MPs, the number of programmable displacement-force curves increases from n+1 to 2m∙n +1 , and the number of stable morphologies grows from n+1 to at least (n+1)m . This strategy can be used to enhance the merits and further excavate the potential of versatile metamaterials.

Experimental Investigation on GCr15 Steel for Marine Vessels Treated by Ultrasonic Assisted Equal Channel Angular Extrusion

Wang, X. and Yu, Y., 2018. Experimental investigation on GCr15 Steel for marine vessels treated by ultrasonic assisted equal channel angular extrusion. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 548–551. Coconut Creek (Florida), ISSN 0749-0208.ECAE deformation refines grain via large shear deformation. Ultrasonic assisted plastic deformation can reduce flow stress of the material and reduce the friction coefficient, etc. In this paper, ultrasonic is applied to the ECAE deformation process, and impact of ultrasonic assisted ECAE forming process on microstructure and mechanical properties of GCr15 steel for marine vessels is studied. The results show that: With ultrasonic assisted ECAE process, ultrafine-grained material can be obtained, compared with the case without ultrasonic vibration extrusion, for GCr15 steel for marine vessels microstructure, average grain size of cementite is 10μm; the sample underwent ECAE one-pass extrusion, with extrusion force at 11098 N, one-pass extrusion force of UV-ECAE was 10090 N, with extrusion force reduced by 9% compared to before; microhardness without ECAE was 365 HV, but significantly increased to 580 HV after ECAE and significantly increased to 620 HV after ultrasonic assisted ECAE, up by 70% compared with that before extrusion.

Nonlinear viscoelastic properties of native male human skin and in vitro 3D reconstructed skin models under LAOS stress

This work discusses the first set of rheometric measurements carried out on commercially accessible juvenile and aged skin models under large amplitude oscillatory shear deformations. The results were compared with those of native male whole human and dermis-only foreskin specimens, catering to a few ages from 0.5 to 68 years, including specimens from a 23-year-old male abdomen. At large strains, strain thinning was more pronounced for the dermis of the young skins and for their whole skin counterparts. An inverse qualitative tendency was observed for the adult skins and the skin models. This can be explained by the high dermal collagen compactness associated with an incomplete epidermal proliferation. The qualitative Lissajous plots as well as the quantitative dimensionless indices analyzed using the MITlaos software indicated predominant nonlinear intracycle elastic strain stiffening and viscous shear thinning for all the native specimens at the maximum deformation. For the full thickness models, we have evidence of structure collapse and yielding under similar conditions. The whole skin specimen from the 68-year-old male showed smaller age-dependent nonlinear elastic contributions than the dermis, which we relate to the epidermal degeneration taking place during aging. Regardless of the age group, the models manifested more pronounced intercycle and intracycle elastic nonlinearities, and their magnitudes were significantly larger. The nonlinear elastic trends will serve as advanced standards for understanding and delineating the mechanical limits of destructive and non-destructive deformations of such unique biomaterials.

Contraction of Entangled Polymers After Large Step Shear Deformations in Slip-Link Simulations.

Although the tube framework has achieved remarkable success to describe entangled polymer dynamics, the chain motion assumed in tube theories is still a matter of discussion. Recently, Xu et al. [ACS Macro Lett. 2018, 7, 190–195] performed a molecular dynamics simulation for entangled bead-spring chains under a step uniaxial deformation and reported that the relaxation of gyration radii cannot be reproduced by the elaborated single-chain tube model called GLaMM. On the basis of this result, they criticized the tube framework, in which it is assumed that the chain contraction occurs after the deformation before the orientational relaxation. In the present study, as a test of their argument, two different slip-link simulations developed by Doi and Takimoto and by Masubuchi et al. were performed and compared to the results of Xu et al. In spite of the modeling being based on the tube framework, the slip-link simulations excellently reproduced the bead-spring simulation result. Besides, the chain contraction was observed in the simulations as with the tube picture. The obtained results imply that the bead-spring results are within the scope of the tube framework whereas the failure of the GLaMM model is possibly due to the homogeneous assumption along the chain for the fluctuations induced by convective constraint release.

Layered composite entangled wire materials blocks as pre-tensioned vertebral rocking columns

This work focuses on entangled wire materials as an option for use between segments of a novel self-centring bridge pier inspired from the human spine mechanism to increase energy dissipation capability of the pier in rocking. A comprehensive set of free-decay vibration tests was conducted on small-scale columns with and without entangled wire materials. Wooden blocks are used as vertebrae with entangled wire materials as intervertebral disks. The whole system is tied together using a pre-tensioned tendon. Dynamic properties of columns (i.e. frequency and damping ratio) were then identified and compared. It is found that the use of entangled wire materials significantly increases the energy dissipation capacity of the system during rocking. This finding is very encouraging for future use of entangled wire materials composite systems in large-scale testing of the proposed rocking column, while their shear and axial stiffness needs be improved to reduce large shear and axial deformations.

Insight into the weak strain overshoot of carbon black filled natural rubber

Weak strain overshoot (WSO) of loss modulus accompanying with strain softening under large amplitude oscillatory shear deformation is a common phenomenon that occurs in many systems but is still far from being clarified. Study about WSO has a strong practical significance, for it is directly related to sharp increase of energy dissipation of elastomer nanocomposites experiencing dynamic deformation of large strain amplitudes. Herein a systematical investigation was performed on WSO of uncured natural rubber (NR) and its low-loading carbon black compounds and a frequency-temperature-volume fraction diagram for the onset of WSO is firstly proposed to shed light on the mechanisms. A comparison of rheology behaviors of uncured polyisoprene rubber and NR and cured polyisoprene rubber suggests that WSO in NR originates from the non-isoprene fraction. Fourier-transform infrared spectroscopy measurement suggests the dissociation of hydrogen bonding at high temperatures, which accelerates the stress relaxation.

Effect of Hot Shear Deformation on Microstructure Formation

A new physical simulation method for evaluating the effect of shear deformation on the evolution of a microstructure is proposed using niobium-bearing steel. The effects of the processing conditions, such as pre-heat treatment, strain rate, and cooling rate, on the formation of ultrafine grains were experimentally examined by the shearing method named the “interrupt shearing test”. This method utilizes a high-speed compression testing machine and is capable of simulating the formation of fine grained steel in the phase transformation procedure. Large shear deformation has been reproduced by the proposed method, and a grain size of approximately 1μm has been obtained by controlled mist cooling.

Delayed fracture in cold blanking of ultra-high strength steel sheets

Hydrogen-induced delayed fracture at cold-blanked edges of 1–1.5 GPa ultra-high strength steel sheets was investigated. The blanked edges undergo large shear deformation and tensile residual stress, and thus the risk of delayed fracture is high, especially for the 1.5 GPa sheet. The effects of residual stress, surface quality and hardness of the sheared edge on the occurrence of delayed cracking were examined. Delayed cracking was caused by press blanking, whereas no cracking occurred for laser blanking because of compressive residual stress. For the 1.5 GPa sheet, delayed cracking was prevented by heating above 250 °C and a stain above 0.005.

Phase-field modeling of stacking structure formation and transition of δ-hydride precipitates in zirconium

δ-hydride structures in Zr nuclear fuel-rod cladding significantly affect mechanical properties. A micromechanical phase-field model is developed to investigate the effect of interfacial energy anisotropy and elastic interaction on the nucleation, stacking structure formation, and stacking structure transition of δ-hydrides. It is found that the nucleation probability and growth of δ-hydride near pre-existing hydrides are strongly spatially dependent. Results show that (1) the δ-hydride has a platelet-like shape. The large shear deformation associated with lattice mismatches and a small interfacial energy of its broad interface cause the orientation of the δ-hydride off the basal plane approximately 14.7°. (2) Stress-induced nucleation of δ-hydrides near a pre-existing hydride results in the unique stacking structure formation. (3) The morphology and alignment of stacking structures, called as macroscopic hydrides which consist of microscopic hydrides with certain stacking sequences, change under stresses. The alignment of macroscopic hydrides changes from along the circumferential direction to along the radial direction under tensile hoop stress while the orientation of microscopic hydrides remains parallel to the basal plane. These results are in agreement with experimental observations. The simulations reveal that stress-induced heterogeneous nucleation and growth is the mechanism for the formation and transition of unique macro-hydride stacking structures.