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Hydrogels and organogels, as two crucial representatives of soft materials, have attracted immense interest. However, they develop independently along two parallel lines, and these gels with single networks have their inherent drawbacks. For example, hydrogels tend to freeze, and organogels are usually brittle. Herein, organogels were incorporated into a hydrogel matrix for the synthesis of organohydrogels GOHs through polymerization in Pickering emulsion. The rigid organogel domains contribute to enhancing the strength of organohydrogels. Besides this, the organogels derived from 12-HAS self-assembly behavior exhibit a gel-sol transition when the temperature reaches 70 °C, thus leading to a thermo-softening behavior in the GOHs. Due to the phase transition of organogel domains and the elastic hydrogel network, the resultant organohydrogels demonstrate high-strain shape-memory performance (over 1000%) which could help achieve full recovery in seconds. Consequently, GOHs are endowed with the potential of practical application in soft robots, wearable devices, and biological materials.

Grain refinement has been applied to enhance the materials strength for miniaturization and lightweight design of nuclear equipment. It is critically important to investigate the low-cycle fatigue (LCF) properties of grain refined 316LN austenitic stainless steels for structural design and safety assessment. In the present work, a series of fine-grained (FG) 316LN steels were produced by thermo-mechanical processes. The LCF properties were studied under a fully reversed strain-controlled mode at room temperature. Results show that FG 316LN steels demonstrate good balance of high strength and high ductility. However, a slight loss of ductility in FG 316LN steel induces a significant deterioration of LCF life. The rapid energy dissipation in FG 316LN steels leads to the reduction of their LCF life. Dislocations develop rapidly in the first stage of cycles, which induces the initial cyclic hardening. The dislocations rearrange to form dislocations cell structure resulting in cyclic softening in the subsequent cyclic deformation. Strain-induced martensite transformation appears in FG 316LN stainless steels at high strain amplitude (Δe/2 = 0.8%), which leads to the secondary cyclic hardening. Moreover, a modified LCF life prediction model for grain refined metals predicts the LCF life of FG 316LN steels well.

Filled vulcanizates exhibit the nonlinear Payne effect under dynamic deformations at high strain amplitudes, while the underlining mechanisms are still in dispute. Herein, polydimethylsiloxane (PDMS) networks are prepared via end-linking of α,ω-vinyl-terminated PDMS chains by the thiol-ene reaction, and the influences of silica on the dynamic rheological responses are investigated. The presence of silica tends to improve the crosslinking density alongside reinforcing the network, while silica itself does not contribute to the loss factor markedly. Furthermore, silica could promote the onset strain amplitude of the Payne effect and manifest the very weak overshoot of loss modulus near the onset amplitude. By creating master curves of the Payne effect of the filled vulcanizates referenced to the end-linking networks, it is evidenced that this effect and the accompanied weak overshoot are mainly rooted in the nonlinear Rouse dynamics of the network strands.

To understand the strengthening mechanism of precipitate against twin-mediated plasticity in magnesium–aluminum alloys, the measurements of the increase in the critical resolved shear stress due to impediment on twin thickening are accomplished based on atomistic simulation, specifically at a significantly low strain rate of 1.7 × 106 s−1. Results show conspicuous coupled effect of temperature and strain-rate on the precipitation strengthening. The strengthening effect vanishes if coherent twin boundary migration is purely stress-driven without thermal activations, due to the back-stress dominating over Orowan stress. At a finite temperature the strengthening effect becomes observable, and is distinctly amplified by high strain rates.

The goals of this study were to quantify and explain the effects of microstructure on the resistance of low-carbon steels to low-cycle fatigue and to extremely low-cycle fatigue (ELCF). Three different microstructures (ferrite–pearlite, ferrite–martensite, and ferrite–bainite–martensite) were tested, and their fatigue properties were analyzed using the strain-based Coffin–Manson model and an energy-based model. According to the Coffin–Manson model, ferrite–pearlite showed the best ELCF resistance, whereas in the energy-based model that considers the effect of tensile strength ferrite–bainite–martensite revealed the highest ELCF resistance. At similar tensile strength, ferrite–bainite–martensite had longer ELCF life than ferrite–martensite; the difference may be a result of the smaller strain incompatibility between bainite and ferrite than between ferrite and martensite. In all three microstructures, cracks initiated at the surface and propagated into the interior; this result indicates that fracture mode was not altered during cyclic loading at high strain amplitudes. Ferrite–martensite microstructure developed many sub-cracks surrounding a main crack; they could facilitate propagation of a main crack, and thereby degrade fatigue life at high strain amplitudes.

Dynamic impact response of high Mn-steel at a strain rate of 3000 s−1 was investigated using the Split Hopkinson Pressure bar. The investigated steel depicted continuous yielding at high strain rat...

The mechanical behaviour of Mg–7Gd–5Y–1.2Nd–0.5Zr (wt. %) alloy with ultrafine grains was measured by split Hopkinson pressure bar method under the strain rates of 1000, 1500, and 2000 s−1 at room ...

The effects of grain boundaries (GBs) on the initiation of hydrogen-induced blisters in pure iron were investigated using synchrotron polychromatic X-ray Laue nano-diffraction. It was found that the random GBs were more susceptible to blistering than the coincidence site lattice grain boundaries. High strain levels and severe plastic deformation were observed around the random GBs after hydrogen charging, but not on the coincidence site lattice grain boundaries.

A model has been proposed to estimate the average number of fragments produced by ductile fracture of a rapidly expanding ring with arbitrary cross-section. The model uses a minimum number of constants characterizing the material properties of the ring. We assume that material of the ring is incompressible with the density ρ and its mechanical behavior obeys the ideal rigid-plastic model with yield stress Y. It is shown that the average number of fragments weakly depends on the cross-sectional shape, if characteristic size of the cross-section does not change. The results obtained by the model are compared with the experiments of Grady and Benson (Exp Mech 23:393–400, 1983) where the aluminum and copper rings were tested. The comparison shows good agreement with the experiments with the copper rings over the entire range of strain rates realized in these experiments. For the aluminum rings, such agreement is observed only for high strain rates.

To understand the high strain hardening capability of austenitic steels, dislocation density-based constitutive modelling has been actively employed. Despite the variation in their formulation, all...

The indentation test is often used to determine the mechanical properties of materials, and its results are typically compared with uniaxial test results. However, the relationship between the indentation and uniaxial tests is unclear. Previously, the limit at which the indentation and uniaxial tests can be related has been determined by finite element simulation and termed the critical strain of indentation. In the critical strain concept, the high strain of the stress–strain curve has a negligible effect on the indentation load–displacement curve. To date, the effect of critical strain has not been addressed in indentation experiments. In this study, the serration behavior of an Al-Zn-Mg alloy during natural aging was investigated using uniaxial tensile and indentation tests in order to clarify (i) the relationship between these tests and (ii) the critical strain of indentation. Similar to uniaxial tests, the serration behavior of indentation was affected by the strain rate effect. However, it was found that the serration behavior observed at high strain in the uniaxial test could not be observed in the indentation test, as indicated by the concept of critical strain. With aging, the serrations of the indentation disappeared; however, they were observed in the uniaxial tests. It was confirmed that the migration of Mg atoms affected the serration behavior of indentation. The critical strain was experimentally found by comparing uniaxial test and indentation test results.

Deformation response of DP1200 steel was studied under high strain rate. Ferrite cracking occurs when strain rate exceeds the critical range (500–700 s−1). Cracks in ferrite propagate to martensite/ferrite interface, weakening its inhibitory effect on adjacent martensite. Thus martensitic deformation becomes the main factor of total deformation earlier to enhance the total strength.

Through Ni-carbonyl CVD process, bulk Ni material (hereafter referred as CVD Ni) with bimodal grain structures, i.e. UF grains and large grains with UF/nano twins, can be produced. In tensile test, this material demonstrated a very good combination of strength and ductility as well as a special strain hardening behavior. Upon investigating the material's hardening behavior, a critical threshold strain, ec, of 0.02 was identified for the distinct change in the strain hardening behavior. Prior to this strain level, the strain hardening rate of the CVD Ni was found always higher than that of its counterpart coarse-grained (CG) Ni; but it dropped, after this strain, to the same level as the CG material. Furthermore, through the analysis of results from Tension Unloading Reloading-in-Tension (TURT) tests, this specific strain value was also found to be significant in the change of the hysteresis loop width as well as the back stress strain hardening responsible for the material's Bauschinger behavior. Microstructural evolution examination suggests that most of the twin boundaries (TBs) initially acted as obstacles to dislocation movement providing strong dislocation back stress and hence contributing to the strong hardening behavior. From the strain level of 0.02 and onwards, however, massive detwinning was detected which is responsible for the drop in the hardening rate. Finally, dislocation cell structures, that were typically evolved from entanglements of dislocation inside CG Ni, were also found inside the detwinned large grains of CVD Ni in the high strain regime, which yielded similar strain hardening behavior as in the CG Ni material.

In this study, the logarithmic-power model has been used to predict hot deformation behavior of alloy 800H at high temperatures. This is for the first time that the logarithmic-power model is examined to model the flow stress curves with negligible flow softening at high strain rates. To this end, flow stress curves of alloy 800H obtained at deformation temperatures from 850°C to 1050°C and at strain rates of 5 and 10 S−1 were employed. The Johnson–Cook model and Shafiei constitutive equation were also used to prove the accuracy of the logarithmic-power model in prediction of flow stress curves of alloy 800H. Evaluation of mean error of flow stress at different deformation conditions showed that the logarithmic-power model can give a more precise estimation of flow stress curves than Johnson–Cook model. Furthermore, it was found out that the accuracy of the Logarithmic-power model and Shafiei constitutive equation was roughly the same in terms of maximum errors obtained in prediction of flow stress curves. Accordingly, it can be concluded that the logarithmic-power model can be employed as a comprehensive model for a wide range of deformation conditions.

Electrochemical actuators based on electronic conducting polymers can convert electrical energy into mechanical work. The amplitude of the electromechanical response is related on volumetric charge density of conducting polymer electrodes and strain-to-charge ratio, an empiric electromechanical coupling parameter. In this work we describe the elaboration of high performance trilayer bending actuators by the electro-interpenetration of a conducting polymer, i.e. poly(3,4-ethylenedioxythiophene) (PEDOT), within a host membrane. The host membrane is first elaborated as an interpenetrating polymer networks combining nitrile butadiene rubber network and poly(ethylene oxide) network. An oxidative chemical prepolymerization of EDOT allows turning the host membrane into conductive substrate suitable for subsequent electropolymerization. The electropolymerization of EDOT from the chemically polymerized layer allows controlled interpenetration of PEDOT underneath the surface. A significant increase of local concentration of PEDOT in the electrodes, compared to those obtained from oxidative polymerization lead to a significant increase of the charge density. The polymerization conditions do not have significant impact on sign and absolute value of strain-to-charge ratio, but it can be improved by the nature of the electrolyte. The combination of these two effects leads to an actuator with up to 15% of strain difference.

Skin-mountable physical sensors that can individually detect mechanical deformations with high strain sensitivity within a broad working strain range and temperature variations with accurate temperature resolution are a sought-after technology. Herein, a stretchable temperature and strain dual-parameter sensor that can precisely detect and distinguish strain from temperature stimuli without crosstalk is developed, based on a printable titanium carbide (MXene)-silver nanowire (AgNW)-PEDOT:PSS-tellurium nanowire (TeNW) nanocomposite. With this dual-parameter sensor, strain and temperature are effectively transduced into electrically isolated signals through the electrically conductive MXene-AgNW and thermoelectric PEDOT:PSS-TeNW components, respectively. In addition, the synergistic effect between the MXene nanosheets and PEDOT:PSS also greatly enhances the stretchability and sensitivity of the sensing devices. These properties enable the nanocomposite to decouple responses between temperature and strain stimuli with an accurate temperature resolution of 0.2 °C and a gauge factor of up to 1933.3 in a working strain range broader than 60%.

Thermomechanical processing determines the practical applications of metal–matrix composites (MMCs) by contributing to the interrelationship between their microstructure and properties. In this study, we investigate the changes in Al-3.0Cu-1.2Mg/SiCp (40 vol%) caused by the tension applied at high temperatures and strain rates. The study shows the microstructural changes and mechanical characteristics resulting from the cold/warm and hot rolling of the extruded material. It is observed that hot rolling has a favorable effect on the restoration of the defects formed in parts of the extruded bar. The microstructural characteristics of the composite related to the deformation-induced redistribution of the secondary inclusions in the matrix and fracture of the reinforcement particles are shown. High-temperature uniaxial tensile testing of the studied composite conducted under high strain rates (10−1 and 10−2 s−1) indicates an increase in the ductility. The decrease in the stress of the tested samples is attributed to the refined grains in the matrix after the thermomechanical processing. The testing of the given material provides the stress–strain relationships, which indirectly assist in ranking the relative formabilities of the differently processed sheets of the MMCs with a high-volume fraction of the reinforcement particles. The proposed approach may be considered for the near net-shaped manufacturing of MMCs with high wear resistance and low thermal expansion coefficients.

The fatigue life of a Fe–15Mn–10Cr–8Ni–4Si seismic damping alloy, undergoing cyclic deformation-induced martensitic transformation from face-centered-cubic austenite to hexagonal-close-packed martensite, is investigated at extremely high strain amplitudes at which common steels exhibit extremely low cycle fatigue (ELCF) with a fatigue life (Nf) less than 102 cycles. Hourglass-shaped specimens were subjected to diametral strain-controlled cyclic tension–compression loading at room temperature with axial strain amplitudes ranging from 4 × 10−2 to 1 × 10−1. The alloy exhibits superior Nf, for example, 112 cycles at the axial strain amplitude of 8 × 10−2, at which a carbon steel is reported to fail at less than 10 cycles. To the best of our knowledge, the Nf of the alloy is the highest ever among ferrous alloys and steels at extremely high strain amplitudes.

The electronic band structure of Germanium has been studied under high strain ( > 1 % ) using a combination of Keating’s model and Tight-Binding formalism. The study has been performed for different kinds of strains (uniaxial and biaxial) and considering the three main crystallographic directions of Germanium: 〈 0 0 1 〉 , 〈 1 1 0 〉 and 〈 1 1 1 〉 . Our results have been compared with the predictions of Deformation Potential Theory, observing an important disagreement for deformations higher than 1 % and showing a non-linear dependency on the strain applied. These results are corroborated experimentally, proving the accuracy of the approach.

The dynamic recrystallization mechanism and microstructure evolution in an extruded AZ31 rod during hot torsion deformation at 150 °C were investigated. It indicated that several dynamic recrystallization mechanisms were initiated during hot torsion deformation, including discontinuous DRX (DDRX), continuous DRX (CDRX) and twinning induced DRX (TDRX). With increasing strain, CDRX became the dominant DRX mechanism and contributed to a remarkable refinement of grains. A gradient distribution of dynamic recrystallization grains on the cross section of samples generated due to the gradient shear strain in twisted samples. Hot torsion can also arouse the c-axis of grains to rotate towards the extrusion direction. From low strain to high strain, the recrystallized grains exhibited a similar texture development with the deformed grains. The relevant mechanisms were revealed.

This paper presents an implementation of the Cohesive Crack Model using the Strong Discontinuity Approach technique to simulate the fracture of the concrete and other quasi-brittle materials at different strain rates. Since one of the principal applications of this model is to simulate the fracture at high strain rates, it has been programmed as a user subroutine in the commercial explicit finite element solver LS-DYNA. For the validation of the model, in addition to studying the sensitivity to element size, it has been compared with a collection of experimental results, both in quasi-static and dynamic regimes. The results prove the ability of the model to accurately reproduce different parameters, such as load-displacement curves, crack trajectories or fracture mechanisms.

By the method of cold rolling, appropriate intermediate annealing and final annealing treatments, the multi-scale lamellar structure of ultrafine grains distributed in ribbons with coarse grains was produced in an Al-1.2Mn alloy, which displayed excellent combination of high strength and good ductility compared to coarse-grained and ultrafine-grained alloys. The high strength of the alloy with multi-scale lamellar structure is attributed to back stress strengthening associated with the formation of geometrically necessary dislocations and the good ductility results from the high strain hardening rate during plastic deformation. Loading-unloading-reloading tests were carried out to measure the back stresses of the alloys. The results show that the back stress of the specimen with multi-scale lamellar structure is much higher than that of the coarse-grained specimen.

The dynamic compressive behaviour of sandwich panels with shear thickening fluid (STF) filled pyramidal lattice truss cores at high strain rates is studied and compared with that of pure STF as well as the sandwich panels with empty and water filled pyramidal lattice truss cores by modified split Hopkinson pressure bar (SHPB) apparatus. The dynamic compressive strengths of the sandwich panels while filled with STF increase significantly when compared to the strengths of the sandwich panels with empty pyramidal lattice truss cores. It is interesting to note that the sandwich panel with the STF filled pyramidal lattice truss core shows “1 + 1 >> 2” dynamic energy absorption behaviour. The excellent energy absorption behaviour of the sandwich panel with STF filled truss core is interpreted by the transformation of deformation modes of core beams from non-symmetry to symmetry after filled with the STF through strong interaction between the buckling behaviour of pyramidal lattice truss core and the shear thickening behaviour of the filled STF material.

In order to investigate the dynamic splitting tensile strength of reactive powder concrete (RPC) under high strain rates, split Hopkinson pressure bar experiments are conducted on hybrid-fiber-reinforced (2% steel fiber and 0·2% polypropylene fiber) RPC. The results show that the dynamic splitting tensile strength of RPC increases with an increase in nominal strain rate from 100 to 350 s−1. The splitting tensile strength dynamic increasing factor (SDIF) of RPC is lower than that of ordinary concrete with the same compressive strength. This is mainly because the compactness of RPC is higher than that of normal concrete. Further, considering that it is not safe to apply the calculation method of SDIF to RPC in the European code Comité Européen du Béton, empirical relations of SDIF and strain rate for RPC with hybrid fibers are proposed. The proposed SDIF–strain rate relations for RPC can be used to computer programs for evaluating the dynamic response of RPC structures.

Recrystallization and subsequent twin formation in > 99.99% pure copper is investigated by in situ annealing in a scanning electron microscope. Distinct microstructural evolution mechanisms are observed for specimens deformed using 5% and 25% cold-rolled reductions. Upon annealing the former, growth and twinning of existing grains via strain-induced boundary migration is observed while the latter exhibits nucleation and growth. Serial sectioning indicates that recrystallization in the low strain condition is surface dominant while nucleation occurs through thickness in the high strain condition. Geometrically necessary dislocation densities are calculated and mapped to identify the localized driving pressures for each recrystallization mechanism.

High strain isothermal compression tests at temperatures of 700–1200°C and strain rates of 0.1–50 s−1 were performed in a Gleeble-3800 thermal simulator to investigate the hot deformation behaviour...

In this study, twins were introduced into pure Mg by pre-deformation, the strain amplitude dependent damping in pre-strained pure magnesium was investigated using cyclic vibration. The strain amplitude dependent damping curve exhibited a hysteretic loop as the strain amplitude was cycled. The damping value was greater during the high strain amplitude regime when the strain amplitude increased than when strain amplitude decreased. For the low strain amplitude regime, the opposite trend was observed. The results point to the damping behavior transitions between the two regimes occurring at a specific strain amplitude, increasing commensurately with increased pre-strain. This hysteretic loop phenomenon is attributed to the difference in mechanical energy consumed by the motion of the twin boundaries during cyclic vibration. The hysteretic loop indicates that twin dampening already exists. Therefore, the strain amplitude value of the intersection may be used as a reference parameter to detect twin damping.

To enable shape-memory polymer networks to achieve recoverable high deformability with a simultaneous high shape-fixity ratio and shape-recovery ratio, novel semi-crystalline slide-ring shape-memory polycaprolactone-based polyurethane (SR-SMPCLU) with movable net-points constructed by a topologically interlocked slide-ring structure was designed and fabricated. The SR-SMPCLU not only exhibited good shape fixity, almost complete shape recovery, and a fast shape-recovery speed, it also showed an outstanding recoverable high-strain capacity with 95.83% Rr under a deformation strain of 1410% due to the pulley effect of the topological slide-ring structure. Furthermore, the SR-SMPCLU system maintained excellent shape-memory performance with increasing the training cycle numbers at 45% and even 280% deformation strain. The effects of the slide-ring cross-linker content, deformation strain, and successive shape-memory cycles on the shape-memory performance were investigated. A possible mechanism for the shape-memory effect of the SR-SMPCLU system is proposed.

Energy absorption of steel with Transformation-induced Plasticity (TRIP) under bending deformation needs to be carefully examined at very high strain rates for its new applications in the automotive industries. Energy absorption members made of the steel can suppress severe damages by traffic accidents. However, it is difficult to apply three-point bending test based on the split Hopkinson pressure bar (SHPB) method because a use of a thick pre-cracked specimen is required for such materials with high toughness. In contrast, if the impact small punch test, which dominant deformation mode of a relatively-small specimen is bending, is established, its experimental arrangement might become simpler and the SHPB technique is applicable. In this study, a novel and reliable impact small punch testing method based on SHPB technique with high accuracy is developed for an investigation on impact energy absorption of the steel with TRIP. Besides, its design, feasibility and validity are confirmed by finite element simulation for austenitic stainless steel SUS304, a representative of steel with TRIP. The obtained experimental as well as computational results show that the developed testing apparatus for impact small punch test based on SHPB technique is reliable and reasonable for the investigation on impact energy absorption of the high toughness material including steel with TRIP.

A high-sensitivity, low-cost, ultrathin microbubble structure based on an Unsymmetrical air-microbubble Fabry-Perot interferometer (UAFPI) is proposed. The UAFPI, which has an ultrathin wall of ~6 μm, is constructed by splicing chemically-etched erbium-doped fiber (EDF) to form an air microbubble and applying a taper to one side of the air microbubble. Compared with the air-microbubble Fabry-Perot interferometer (AFPI), the UAFPI has a high strain sensitivity of 10.15 pm/μe, which is approximately three times higher than that of the AFPI, and a low-temperature sensitivity of 2.4 pm/°C in the range of 25–80 °C. The proposed sensor has several benefits, including high strain sensitivity, low-temperature sensitivity, a simple fabrication process, and low cost. Therefore, such a UAFPI-based strain sensor has broad prospects for mass production and practical applications.

Fatigue damage has special relevance on the life span of mechanical components and structures, as it takes responsibility for a large majority of the registered structural failures in service. The continuous need for the weight reduction and improved design optimization of components and a growing need for greater lifespans of equipment, forced the understanding of the fatigue behavior of materials either under multiaxial loading cycles or under increased number of loading cycles. Fatigue tests were always performed under uniaxial fatigue loads. However, it is generally recognized that multiaxial stresses occur in many full-scale structures, being rare the occurrence of pure uniaxial stress states. In the following, a wide range of multiaxial fatigue failure criteria have been developed that may be applied to different metallic materials. These failure criteria may be classified as strain based for high strain loading conditions or stress based for higher lifespans in the elastic loading regime. These criteria are nowadays used in design optimization also contributing to the weight reduction and improved lifespans of modern equipment. Present manuscript is a review of the main specimens and equipment where research can be carried out for performing multiaxial fatigue tests under bi-axial stress states. Being a personal view, it will be based on the author experience on the performance of multiaxial fatigue tests under axial/torsion loading using mechanical actuated or servo-hydraulic fatigue testing machines or biaxial fatigue tests using electromagnetic actuators in cruciform specimens. Further research is needed and is being carried out concerning multiaxial very high cycle fatigue in order to achieve better improvements in weight reduction of components and structures and also in complex variable amplitude loading with adequate damage accumulation models.

To evaluate the dynamic mechanical properties of 25CrMo4 steel, the stress-strain curve of 25CrMo4 steel have been obtained by performing quasi-static and impact compression experiments at strain rates ranging from 0.001 s − 1 to 4163 s − 1 . The 25CrMo4 steel displays an obvious strain rate effect and its hardening rate changes with the strain and strain rate. It even shows softening effect at high strain rates. Further, the grains of 25CrMo4 steel show features of both body-centered cubic (BCC) and face-centered cubic (FCC) structures and are severely stretched and fragmented during impact loading, as evidenced by microscopic observations. Based on these two points, the Zerilli-Armstrong (ZA) constitutive equations have been improved reasonably. These can provide the mechanical properties of 25CrMo4 steel during impact compression loading, which can in turn be used as reference values for practical engineering analysis.

Lightweight steels containing a considerable content of Al show high specific strength and ductility, but there are some drawbacks such as low yield strength and stringer-type bands formed along the rolling direction. Here we design new duplex lightweight steel in order to complement the drawbacks, and achieve ultra-high yield strength (865 MPa), good ductility (41%). Submicron ferrite mainly affects high yield-to-tensile ratio, and high strain hardening is attributed to Lomer-Cottrell lock and planar slip, and cell structure by further deformation in austenite. These results are expected to provide a desirable possibility for applications to reinforcement components requiring high yield-to-tensile ratio.

Previous HotQC studies of Cu nanovoids undergoing volumetric expansion conducted by the authors have uncovered a quasistatic-to-dynamic transition at a critical strain rate of the order of 10^8 s^(-1). At low strain rates nanovoid expansion takes place under essentially isothermal conditions, whereas at high strain rates it happens under essential adiabatic conditions. In this paper, we present a comparative study concerned with two different scenarios, each representing a variation on the reference case presented in [1]: (i) aluminium (Al) nanovoids undergoing volumetric expansion; and (ii) copper (Cu) nanovoids undergoing uniaxial deformation. Scenario (i) addresses material specificity by replacing Cu by Al in the reference case, whereas scenario (ii) addresses the effect of triaxiality by replacing volumetric expansion by uniaxial expansion in the reference case. We find a distinct quasistatic-to-dynamic transition in both scenarios, which suggests that the transition is indeed universal, i.e. material and strain-triaxiality independent. By contrast, the fine structure of the dislocation mechanisms that mediate void growth are strongly material and loading specific.

In this study, the approximate estimates of elastic-plastic J and COD for thin-walled pipes with axial through-wall cracks (TWCs) and high strain hardening exponents under internal pressure are developed based on the GE/EPRI and enhanced reference stress (ERS) methods. For the estimations based on the GE/EPRI method, the proposed tabulated plastic influence functions for fully plastic J and COD are derived from three-dimensional finite element (FE) analyses. On the basis of these plastic influence functions, an optimized reference load (which plays an important role in the ERS method) is newly suggested. Finally, the present elastic-plastic J and COD estimations are verified by comparing the predicted results with the FE results using actual tensile behavior of SA312 type 304 SAW stainless steel. The estimations based on both GE/EPRI and ERS methods provide better approximations for thin-walled pipes with axial TWC and high strain hardening exponent, than do the existing estimations. The importance of the elastic-plastic fracture mechanics assessment, using the present solutions for thin-walled pipe with axial TWC and high strain hardening exponent, are also discussed.

High-strain-rate deformation in ultrasonic additive manufacturing was analyzed by performing microstructural characterization via electron microscopy. The micro-asperities on the top tape surface, which were formed by contact with the sonotrode surface, underwent cyclic deformation in the shear direction at high strain rates during welding with an additional tape. This caused plastic flow and crushing of the micro-asperities, and a flattened interface was formed between the upper and lower tapes. Further, surface oxide films were fractured and dispersed by ultrasonic vibration, and metallurgical welding was achieved.

Columnar-grained Cu-Al-Mn shape memory alloy (SMA) exhibits excellent superelastic fatigue properties at high strain amplitude, and its functional fatigue life reaches above 103 cycles at tensile strain of 4%–10%. As the increase of loading-unloading cycle number, the transformation stress and superelastic recovery rate decrease. The decay coefficient of recovery rate is about 1.4. Fatigue cycles for Cu-Al-Mn SMAs can be divided into four stages according to the significant changes of superelasticity: plateaus stage, rapid attenuation earlier stage, rapid attenuation later stage, functional incapacitation stage. The columnar-grained Cu-Al-Mn SMA shows larger range of stable superelasticity than other polycrystalline counterparts.

This assessment considers recent work on friction stir processing (FSP), which has been demonstrated to be an effective method for grain refinement and synthesis of new alloys and composites. The grain refinement is attributed to high strain rates leading to recrystallisation, while external cooling suppresses grain growth during cooling. The technique is capable of producing nanocrystalline alloys, and also able to disperse nanoparticles into alloys. The mechanical properties of processed materials agree with a combination of existing models for grain refinement, and precipitate reinforcement theory. Further improvements in the technique may help deal with severe tool wear during the FSP of composites, and reduce the complexity of composite fabrication using novel processing methods and tooling.

Commercially available yarns are promising precursor for artificial muscles for smart fabric-based textile wearables. Electrochemically driven conductive polymer (CP) coated yarns have already shown their potential to be used in smart fabrics. Unfortunately, the practical application of these yarns is still hindered due to their slow ion exchange properties and low strain. Here, a method is demonstrated to morph poly-3,4-ethylenedioxythiophene:poly-styrenesulfonate (PEDOT:PSS) coated multifilament textile yarns in highly twisted and coiled structures, providing >1% linear actuation in 1.62% strain. Compared to the untwisted, regular yarns, the twisted and coiled yarns produce >9x and >20x higher strain, respectively. The strain and speed are significantly higher than the maximum reported results from other electrochemically operated CP yarns. The yarns actuation is explained by reversible oxidation/reduction reactions occurring at CPs. However, the helical opening/closing of the twisted or coiled yarns due to the torsional yarn untwisting/retwisting assists the rapid and large linear actuation. These PEDOT:PSS coated yarn actuators are of great interest to drive smart textile exoskeletons. Funding Agencies|Promobilia Foundation [F17603]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO Mat LiU) [2009-00971]; Swedish Research CouncilSwedish Research Council [2014-3079]; Carl Trygger Foundation [CTS:17-215]; European UnionEuropean Union (EU) [825232]; University of Wollongongs Visiting International Scholar Award

The authors of this paper have recently shown that deformation in layered solids is not mediated by basal dislocations, as conventional wisdom would have it, but rather by a new mechanism labeled ripplocations. The latter are defects that form in layered materials as a consequence of confined buckling. Here, using shock wave compression---at extremely high strain rates---of Ti${}_{3}$SiC${}_{2}$, a member of the nanolayered MAX-phase family, the authors show that in some ways Ti${}_{3}$SiC${}_{2}$ behaves like a ductile metal but, in others, it behaves more like a hard, brittle ceramic. In other words, the unique dual-nature behavior of Ti${}_{3}$SiC${}_{2}$ is like nothing seen before. The authors attribute this behavior to its nanolayered structure and believe it reflects how ripplocations respond to very high strain rates. This work not only provides new results on the dynamic mechanical properties of Ti${}_{3}$SiC${}_{2}$, but is a critical first step towards understanding the response of ripplocations in layered solids to high strain rates.

International audience; A mechanobiological model of bone remodeling is developed involving mineralization in a moving diffuse interface separating the marrow containing the bone cells responsible for the remodeling from the newly formed bone. A scalar phase field quantifies the degree of mineralization within the interface at the level of the bone microstructure, varying continuously between the nil lower value (no mineral) and unity for the fully mineralized phase corresponding to new bone. The field equations for the mechanical, chemical, and interfacial phenomena are written under the umbrella of thermodynamics of irreversible processes. A strain gradient model is developed to account for the impact of the underlying hierarchical microstructure on the effective response of bone. Second gradient terms are motivated by the high strain and stress concentrations close to defects, both at mesoscopic and microscopic scales. The combination of the balance equations for the microforce associated to the phase field and the kinetic equations lead to the Ginzburg–Landau equation for by the phase field with a source term accounting for the dissipative microforce.

Strain distribution and void formation sites were investigated in fine multi-layered steel sheets subjected to tensile deformation. The sheets comprised of alternating layers of ferrite and martensite wherein the layer thickness was varied but remained sufficiently thin to suppress their early fracture. Additionally, the influence of layer thickness on the deformation and fracture behavior was discussed. The elongation was not significantly enhanced with decreasing layer thickness. Furthermore, strain was inhomogeneously introduced in the sheets and continuously distributed regardless of the layers. The high strain regions were distributed more finely as the layer thickness decreased. Cracks were generated at the highly strained martensite layer, which grew to large voids. The fracture surface on the martensite layer comprised of fine dimples, while that on the ferrite layer consisted of large and shallow dimples or a cleave-like fracture surface. Therefore, the coalescence of large voids developed in the martensite layer, accompanied by the secondary voids or quasi-cleavage fracture in the ferrite layer, results in the fracture of the multi-layered steel sheets. Based on the calculation with Scheyvaerts's criterion, the critical stress of void coalescence was approximately equal in the steel sheets with 17, and 97 layers, which was why the layer thickness hardly affected the elongation of the steel sheets.

In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural relaxation at high strain rates, which leads to a larger free volume concentration within shear bands and makes the BMG softer. It is concluded that the activation volume increases with temperature in the inhomogeneous deformation region, whilst its value at high temperatures, where the deformation regime is homogeneous, decreases with temperature rise.

We perform molecular dynamics simulations to simulate the c-axis compression of single crystal Ti at high strain rates under uniaxial strain conditions. Since it is well known that molecular dynamics simulations heavily rely upon the type of potential used, a comprehensive study is presented in which four different commonly utilized potentials for Ti (Ackland, Mishin, Kim and Hennig) are evaluated against their abilities to demonstrate different variants of compression twins, dislocation structures and structural phase transformation. We find that { 1 0 1 ¯ 1 } and { 1 1 2 ¯ 2 } twins activate for Ackland and Mishin potentials, while only { 1 0 1 ¯ 1 } twins activate for Kim potential. No compression twin systems activate for Hennig potential. The c-vector analysis of unknown structure generated with Ackland, Mishin and Kim potentials shows that the unknown structure has { 1 0 1 ¯ 1 } twin-like orientations and the structure factor analysis gives a signature of pressure-induced ω phase for the twin-like oriented unknown structure. No signature of twin-like oriented unknown structure and ω phase is observed for Hennig potential. The large amount of dislocation density is observed for Ackland potential followed by Mishin, Kim and Hennig potentials. The presence of compression twins and high dislocation density for Ackland, Mishin and Kim potentials suggest that the c-axis deformation is accommodated by twins and slip together, while only slip accommodates the c-axis deformation for Hennig potential. Based on these observations and as well as on the formulation of the above mentioned potentials, Kim potential is being recommended for use under c-axis uniaxial compressive strain loading situations.