Low Deformation Rates Research Articles

High-speed superplastic formability and deformation mechanisms of Ti6Al4V sheets

A low deformation rate is a significant disadvantage in the high-temperature superplastic forming (SPF) process, and grain boundary sliding (GBS) and creep mechanisms occur during deformation. The high-speed SPF method is being investigated to eliminate this disadvantage. Also, the high-speed SPF of Ti6Al4V (Ti64) sheet material and the effects of deformation mechanisms on formability were investigated experimentally. SPF and high-speed SPF treatments were carried out with hot tensile tests at specific temperatures, which in turn are 670, 770, 870, 890, and 910 °C at deformation rates of 10-2 to 10-3 s-1 and without a protective atmosphere. The deformation mechanisms in the microstructure of the samples were investigated by electron microscopy. In experimental studies, it has been observed that GBS deformation occurs at 870 °C and positively affects formability with 1489% elongation at 870 °C and 701% at 910 °C. While the effects of these deformation mechanisms were not observed clearly under 870 °C, it was observed that the superplastic formability had a decreasing trend at 890 °C and 910 °C with the effect of creep deformation.

Studying the high-rate deformation of soft materials via laser-induced membrane expansion.

Cavitation is a phenomenon that occurs when the internal pressure of a material exceeds the resistance to deformation provided by the surrounding medium. Several measurements, such as the blister test, bubble inflation, and cavitation rheology, take advantage of this phenomenon to measure the local mechanical properties of soft materials at relatively low deformation rates. Here, we introduce a new measurement called laser-induced membrane expansion (LIME) that measures the shear modulus of a thin membrane at high strain rates (≈106 s-1 to 108 s-1) by using laser ablation to rapidly expand a thin (tens of microns) elastomeric membrane. To demonstrate the capabilities of this measurement, we use LIME to study the mechanical properties of poly(dimethylsiloxane) (PDMS) membranes at several thicknesses (from 10 μm to 60 μm) and crosslink densities. We find that the shear modulus of the PDMS measured by LIME was weakly dependent on the crosslink density, but was strongly strain rate dependent with values ranging from 106 Pa to 108 Pa. This measurement platform presents a new approach to studying the mechanical properties of soft but thin materials over a range of deformation rates.

Deviation from roundness of cylindrical parts under pendulum surface plastic deformation

The dependence of the deviation from roundness (Δcr) of cylindrical parts on the main technological parameters of the pendulum RPM has been experimentally determined. It has been established that the pendulum SPD helps to reduce the deviation from roundness, and, consequently, to increase the accuracy of the diametrical dimensions of parts by 3—4 grades, while the minimum value of 6.2...6.4 μm is achieved under conditions of low deformation rate. In addition, using the statistica 10.1 software package, the measurement results were processed to determine the optimal modes that provide the smallest value.

Oceanic lobate ctenophores possess feeding mechanics similar to the impactful coastal species Mnemiopsis leidyi

AbstractLobate ctenophores are often numerically dominant members of oceanic epipelagic and midwater ecosystems. Despite this, little is known about their trophic ecology. Multiple, co‐occurring species are often found in these ecosystems and appear to feed similarly via feeding currents that entrain prey. We quantified the hydrodynamics, morphology, and behavior of four co‐occurring, cosmopolitan lobate species (Eurhamphaea vexilligera, Ocyropsis crystallina, Bolinopsis vitrea, and Leucothea multicornis) to evaluate whether their feeding mechanics lead to differential feeding rates and prey selection. We compared the feeding characteristics of these four oceanic species to the coastal lobate ctenophore, Mnemiopsis leidyi, which is known as a voracious zooplanktivore. We found that despite their morphological diversity, the five lobate species used the same mechanism to generate their feeding current—the hydrodynamics of their feeding currents were similarly laminar and with very low fluid deformation rates. Despite having similar feeding current traits, the species had different in situ swimming behaviors and feeding postures. We show that these different behaviors and postures lead to different prey encounter rates and that several of the oceanic species have the potential to feed at rates similar to or greater than M. leidyi. As such, the individual and combined trophic impact of oceanic lobate ctenophores is likely to be much greater than previously predicted.

Interlaminar Shear Characteristics of Typical Polyurethane Mixture Pavement.

Polyurethane (PU) can be used as a road material binder, and its mechanical properties, durability, temperature stability, and other road performance metrics are good. However, the interlayer bonding between PU mixtures and asphalt mixtures is poor. The influence of the pavement structure, interlayer treatment scheme, load, and environmental factors on the interlayer shear characteristics of PU mixture composite pavement is analysed. Further, dynamic modulus, Hamburg rutting, accelerated loading, and inclined shear tests were conducted, and the typical PU mixture pavement shear stress was calculated. The interlaminar shear stress of double layer PU mixture pavement, polyurethane–asphalt composite pavement, and typical asphalt pavement were calculated. The results showed that the PU mixture has a low rutting deformation rate, stable mechanical properties, and strong resistance to the coupled action of temperature, water, and loading. The double-layer PU mixture structure has good water-temperature stability and fatigue resistance; however, freeze–thaw and accelerated loading cause great damage to the double-layer PU mixture structure. The residual shear strength ratio after freeze–thaw cycles and accelerated loading is only 50.3% and 35.6%, respectively, while the influence on the double-layer asphalt mixture structure is less. The theoretical calculation results of different pavement structures show that when the temperature increases from 10 °C to 50 °C, the interlaminar shear stress of polyurethane–asphalt composite pavement increases by about 20%. Additionally, the shear stress of pavement PU mixture pavement and typical asphalt pavement is mainly affected by load, and the temperature changes have an obvious effect on the interlayer shear stress of polyurethane–asphalt composite pavement. The calculated maximum shear stress of the three pavement structures with different working conditions is less than the interlaminar shear strength measured by the inclined shear test, indicating that the interlaminar treatment scheme of composite specimens can meet the shear resistance requirements of the three typical pavement structure types.

Volume-shear coupling in a mesoscopic model of amorphous materials.

We present a two-dimensional mesoscopic model of a yield stress material that includes the possibility of local volume fluctuations coupled to shear in such a way that the shear strength of the material decreases as the local density decreases. The model reproduces a number of effects well known in the phenomenology of this kind of material. In particular, we find that the volume of the sample increases as the deformation rate increases; shear bands are no longer oriented at 45^{∘} with respect to the principal axis of the applied stress (as in the absence of volume-shear coupling); and homogeneous deformation becomes unstable at low enough deformation rates if volume-shear coupling is strong enough. We also discuss the effect of this coupling on some out-of-equilibrium configurations, which can be relevant to the study of the shear bands observed in metallic glasses.

Frictional constitutive behavior of chlorite at low shearing rates and hydrothermal conditions

Chlorite is a common, but understudied phyllosilicate mineral along continental and subduction zone faults. To understand the potential role of chlorite in different modes of fault slip, we measure the constitutive frictional properties of chlorite at low rates of deformation and shallow hydrothermal conditions by shearing powdered samples of water-saturated chlorite in the triaxial saw-cut configuration. Experiments were conducted at 25 to 130 °C, 130 MPa confining pressure, pore pressures from 10 MPa to 120 MPa, slip rates from 0.001 to 10 μm/s, and shear displacements up to 7.5 mm. The frictional strength of chlorite increases with increasing temperature from 25 to 130 °C (μ = 0.4 to 0.46), accompanied by an increased abundance of Riedel shears. Chlorite also transitions from rate-strengthening behavior at fast slip rates (0.1 to 10 μm/s) to rate-weakening or rate-neutral behavior at lower slip rates (0.001 to 0.01 μm/s), consistent with one hypothesis for the cause of slow slip. This transition in frictional behavior reflects different microphysical processes controlling the direct and evolution effects of friction. At low deformation rates, the magnitude and temperature sensitivity of the direct effect (a) are consistent with subcritical fracture. In contrast, the evolution effect (b) is insensitive to temperature and increases systematically with decreasing strain rate. We propose the increase in b and resulting rate-weakening behavior of chlorite with decreasing slip rate is controlled by time-dependent properties of adsorbed water to mineral surfaces.

Normalization of global longitudinal strain after 20 squats in elite athletes

Abstract Funding Acknowledgements Type of funding sources: None. Background/Introduction: Transthoracic echocardiography (TTE) is often the first diagnostic imaging modality of choice in athlete care to differentiate between physiological adaptation to sports and pathology. Left ventricular (LV) global longitudinal strain (GLS) has been suggested as a tool to detect early signs of myocardial diseases in athletes. However, low rates of myocardial deformation can also be associated with cardiac adaptation to sports. We hypothesized that observing decreased cardiac deformation in elite athletes may be a sign of an outspoken relaxed cardiac state, rather than pathology. Therefore, we investigated whether a short exercise bout can normalize strain values in elite athletes with abnormal resting GLS. Methods We prospectively enrolled elite athletes who participated in the ELITE (Evaluation of Lifetime Participation in Intensive Top-level Sports and Exercise) cohort. In short, ELITE is a prospective athlete cohort, which collects medical history, ECG, TTE and cardiac magnetic resonance (CMR) data in elite athletes (Olympic/Paralympic level or comparable). For this analysis, we analysed TTEs of asymptomatic athletes without cardiovascular disease and with a structurally normal heart on CMR. TTE (Vivid, GE) was performed in each athlete according to guidelines at rest. After a short exercise bout, consisting of 20 squats, additional GLS, LV ejection fraction (EF), and LV stroke volume (SV) measurements were assessed when heart-rate (HR) was comparable to HR during pre-exercise measurements. TTE data was assessed using EchoPAC (GE). GLS delta (pre- to post-exercise) for each athlete was calculated were plotted, using R. GLS ≥ -16% was considered decreased and -16% ≥ GLS > -18% borderline. Results Our population comprised 73 athletes (26% women), mean age (±SD) of 25.6 ± 6.5 years, BSA of 2 ± 0.2m2, and athletic disciplines road cycling (n = 28), soccer (n = 12), hockey (n = 8), swimming (n = 5), tennis (n = 5) and 8 miscellaneous sports (n = 15). Mean pre- and post-exercise GLS were -18.2 ± 2.1% vs -20.5 ± 2.0% (P < 0.001; Figure 1), EF 57 ± 4% vs 59 ± 6% (P = 0.006; Figure 1), SV 89 ± 20ml vs 99 ± 24ml (P = 0.008), and HR 56 ± 12bpm vs 56 ± 13bpm (P = 0.875). We observed an increase of myocardial deformation after a short bout of exercise: mean GLS delta of -2.3 ± 1.9%. Finally, we found a decreased strain in 14 athletes (19%), in which pre- and post-exercise GLS were -15.1 ± 0.8% and -18.6 ± 2.3%, P= <0.001, Figure 1). Only 1 athlete (1%, no other signs of cardiac pathology: MRI, biomarkers, complaints) had post-exercise decreased GLS. We found 9 athletes with a deteriorated cardiac deformation (delta GLS ≤ 0%), pre- and post-exercise GLS were -20.4 ± 1.4% and -19.9 ± 1.5% (maximal GLS post-exercise was -17.7%, Figure 1). Conclusion GLS normalizes in 99% of healthy (elite) athletes. In athletes with decreased GLS at rest, performing a short exercise bout is a pragmatic method to separate decreased GLS due to pathology from sport adaptation Abstract figure 1

High Strain Rate Behavior of Harmonic Structure Designed Pure Nickel: Mechanical Characterization, Microstructure Analysis and Modelisation

The development of new architecture metallic alloys with controlled microstructures is one of the strategic ways for designing materials with high innovation potential and, particularly with improved mechanical properties as required for structural materials [1]. Indeed, unlike conventional counterparts, metallic materials having so-called harmonic structure displays strength and ductility synergy. The latter occurs due to a unique microstructure design: a coarse grain structure surrounded by a 3D continuous network of ultra-fine grain known as “core” and “shell”, respectively. In the present study, pure harmonic-structured (HS) Nickel samples were processed via controlled mechanical milling and followed by spark plasma sintering (SPS), detailed in previous work [2]. In previous studies, the mechanical behavior under quasi-static loading at room temperature has been evaluated and showed the superior mechanical properties of HS pure Ni over the homogeneous conventional counterpart [3]. The present work aims at characterizing the mechanical properties of HS pure Ni under room temperature dynamic loading, through a Split Hopkinson Pressure Bar (SHPB) test, and the underlying microstructure evolution. A stopper ring was used to maintain the strain at a fixed value of about 20% (Fig. 1). Five samples (named B1 to B5) were impacted using different striker bar velocity (V0) from 14 m/s to 28 m/s, yielding strain rate in the range 4000-7000 s-1. Results were considered until a 10% deformation value, which is the deformation threshold for the constant strain rate assumption [4]. Figure 1: SHPB test mounting with a stopper ring The evolution flow stress with the strain rate for harmonic and conventional structure (CS) (using data from quasi-static and high rate experiments) makes it possible to identify two domains with a transition around 3000 s-1. First domain operating at low deformation rates is conventionally associated with the thermal activated movement of dislocation, whereas the second domain at high strain rates is associated with viscous drag. The non-deformed (INIT), and post-SHPB microstructure (B1 to B5), were investigated by EBSD (Fig. 2) and show that while strain rate increase, grains size within the core decrease. An in-depth analysis of grains and grain boundaries were made to highlight the thermal (such as dynamic recrystallization) or mechanical (such as grains fragmentation by dislocation) contribution within the “core” and “shell”. Figure 2: Cross section EBSD map of the initial sample from post-SPS process (INIT) One of the most widely used methods for determining dynamic behavior of materials is the SHPB technique developed by Kolsky [6]. A 3D simulation of SHPB test was created through ABAQUS in dynamic explicit. This 3D simulation allow taking into account all modes of vibration. An inverse approach was used to identify the material parameters from the equation of Johnson-Cook (JC) by minimizing the difference between the numerical and experimental data. The JC’s parameters were identified using B1 and B5 samples configuration. Predictively, identified parameters of JC’s equation shows good result for the others sample configuration (Fig. 3) (a)(b) Figure 3: 3D simulation assembly of SHPB test from ABAQUS (a) and output data of SHPB test from experiment and numerical test for the sample B4 (b) Furthermore, mean rise of temperature within the harmonic Nickel sample can be obtained through ABAQUS and show an elevation of about 35°C for all fives sample. At this temperature, thermal mechanism cannot be activated. Therefore, grains fragmentation within the core is mainly due to mechanical phenomena for a fixed final strain of 20%

Late Quaternary Tectonics along the Peri-Adriatic Sector of the Apenninic Chain (Central-Southern Italy): Inspecting Active Shortening through Topographic Relief and Fluvial Network Analyses

Abstract Active compressional tectonics along the outer front of the Apenninic-Maghrebian chain (Italy) is well documented along the northern and central segments and in Sicily. On the other hand, the Southern Apenninic Outer Front (SAOF) orogenic activity is well established only until the Lower-Middle Pleistocene. We address the hypothesis of its subsequent late Quaternary activity in central-southern Italy (Abruzzo and Molise regions). We integrated topographic and fluvial network analyses along with morphotectonic investigation of fluvial terraces to identify evidence of differential rock uplift. We compared the results with the main geolithological units, known structural elements, and long-term deformation history from seismic line interpretation. We found variable evidence suggesting localized rock uplift in the Abruzzo region along the SAOF (Abruzzo Citeriore Basal Thrust segment) and inward structures on its hanging wall (Casoli-Bomba high), as well as along part of the Struttura Costiera thrust. Middle-to-Late Pleistocene deformation is constrained by terrace tilting and disruption along the Pescara river. Localized shortening along segments of the Apenninic Outer Front could explain the observed pattern of anomalies which is difficult to explain with long-wavelength regional uplift alone. Our reconstruction is consistent with the long-term deformation of the area and agrees with its seismotectonic setting. Despite the low deformation rate context and the peculiar geological setting which challenges the interpretation of the topographic and geomorphic signals, this study compels reconsideration, in terms of seismic hazard assessment, of the existence of late Quaternary active thrusting in central-southern Italy.

High Temperature Deformation Behavior and Microstructure Evolution of Low-Density Steel Fe30Mn11Al1C Micro-Alloyed with Nb and V.

The thermal processing parameters is very important to the hot rolling and forging process for producing grain refinement in lightweight high-manganese and aluminum steels. In this work, the high temperature deformation behaviors of a low-density steel of Fe30Mn11Al1C alloyed with 0.1Nb and 0.1V were studied by isothermal hot compression tests at temperatures of 850–1150 °C and strain rates between 0.01 s−1 and 10 s−1. It was found that the flow stress constitutive model could be effectively established by the Arrhenius based hyperbolic sine equation with an activation energy of about 389.1 kJ/mol. The thermal processing maps were developed based on the dynamic material model at different strains. It’s shown that the safe region for high temperatures in a very broad range of both deformation temperature and deformation strain and only a small unstable high deformation region, located at low temperatures lower than 950 °C. The deformation microstructures were found to be fully recrystallized microstructure in the safe deformation region and the grain size decreases along with decreasing temperature and increasing strain rate. Whereas the deformation microstructures is composed by grain refinement-recrystallized grains and a small fraction of non-recrystallized microstructure in the unstable deformation region, indicating that the deformation behaviors controlled by continuous dynamic recrystallization. The Hall Petch relationship between microhardness and the grain size of the high temperature deformed materials indicates that high strength low-density steel could be developed by a relative low temperature deformation and high strain rate.

Normalization of global longitudinal strain after a 30-seconds exercise bout in elite athletes

Abstract Background/Introduction Transthoracic echocardiography (TTE) is often the first diagnostic imaging modality of choice in athlete care to differentiate between physiological adaptation to sports and pathology. Mechanical strain as outcome measure, i.e. left ventricular (LV) global longitudinal strain (GLS), has been suggested as a tool to detect early signs of myocardial diseases in athletes. However, low or very low rates of myocardial deformation can also be associated with cardiac adaptation to sports. We hypothesize that observing decreased cardiac deformation in elite athletes may be a sign of an outspoken relaxed cardiac state, rather than pathology. Therefore, we investigated whether a short exercise bout can normalize strain values in elite athletes with abnormal resting GLS. Methods We prospectively enrolled elite athletes who participated in the ELITE (Evaluation of Lifetime Participation in Intensive Top-level Sports and Exercise) cohort. In short, ELITE is a prospective athlete cohort, which collects medical history, ECG, TTE and cardiac magnetic resonance (CMR) data in elite athletes (Olympic/Paralympic level or comparable). For this analysis, we analysed TTEs of asymptomatic athletes without cardiovascular disease and with a structurally normal heart on CMR. TTE (Vivid, GE) was performed in each athlete according to guidelines at rest. After a short exercise bout, consisting of 20 squats, additional measurements were performed when heart-rate (HR) was comparable to HR during pre-exercise measurements. TTE data was assessed using EchoPAC (GE). Paired t-tests were calculated for functional parameters; boxplots for pre- and post-exercise measurements; and GLS delta (pre- to post-exercise) for each athlete was calculated were plotted; using R. GLS ≥−16% was considered decreased and −16% ≥ GLS >−18% borderline. Results Our population comprised 51 athletes (35% women), with a mean age (±SD) of 26.4±5.2 years, and mean BSA of 2±0.3m2. Athletic disciplines consisted of road cycling (n=25), hockey (n=7), swimming (n=5), and 7 miscellaneous sports (n=14). We observed an increase of myocardial deformation after a short bout of exercise: mean GLS delta of 2.6±2% (pre- vs post-exercise GLS: −18.2±2.1% vs −20.8±1.9%; P≤0.001; Figure, A). Furthermore, mean LV stroke volumes were 94±19ml vs 103±23ml (P=0.020), ejection fractions (EF) 57±4% vs 60±4% (P≤0.001), and HR 55±10bpm vs 54±13bpm (P=0.8). Finally, we found a decreased strain in 8 athletes (16%), in 7 of which increased to normal values. Mean delta GLS was 4.5±2.2 (pre- vs post-exercise GLS: −14.9±1.1% vs −19.4±2.7%, P=0.002, Figure, B). The athlete who did not show an increase to normal GLS levels had a decreased LV EF (42%), but showed no other signs of cardiac pathology (MRI, biomarkers, complaints). Conclusion In athletes with abnormal GLS at rest, performing a short exercise bout may provide a pragmatic method to separate decreased GLS due to true pathology from sports adaptation. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Amsterdam Movement Sciences

Screening MXenes for novel anode material of lithium-ion batteries with high capacity and stability: A DFT calculation

As an advanced battery technology, lithium-ion batteries have attracted extensive attention, especially in electric vehicles. However, low capacity and poor stability are two factors hindering more extensive application of lithium-ion batteries. Herein, we performed a screening study on MXenes including M2C, MC2, M2N, MN2 (M = Sc, Ti, V, Cr), in the search for promising lithium-ion battery anode materials by using density functional theory (DFT) calculations and ab initio molecular dynamic (AIMD) simulations. The theoretical capacities of Ti2N and V2N are 975 mAh/g and 924 mAh/g, respectively. Based on low deformation rate, and small energy variation, Ti2N and V2N have higher stability than that of graphite electrodes. The lower diffusion barrier accelerates the charging and discharging process of the battery. Considering their low diffusion barrier, excellent conductivity, high theoretical capacity, low deformation rate and high thermal stability, Ti2N and V2N are proposed as promising anode materials for lithium-ion batteries. The adsorption of lithium-ion belongs in the category of weak adsorption where the d-band center is negative. However, it is strong adsorption when the d-band center is positive. A linear relationship between the lithium-ion concentration and adsorption energy is developed for strong adsorption, which can be used to guide the design of high-capacity electrode materials.

Cavitation dynamics in a vitrimer

Vitrimer is a polymer network with dynamic covalent bonds, which can be dynamically broken and reformed. Thanks to the dynamic covalent bonds, vitrimer behaves like an elastomer at high deformation rate or low temperature but a viscous fluid at low deformation rate or high temperature. In this article, we study the cavitation dynamics in a vitrimer, which is known to be an important damaging mechanism in it. In the formulation, a nonlinear three-dimensional rate-dependent constitutive model for the vitrimer is adopted, in which both of the strain stiffening and the kinetics of dynamic exchanging reactions are considered. The theory predicts strong dependence of the cavitation dynamics on the loading rate. The computational results may help to reveal some critical insights into the rate-dependent fracture in vitrimer.

A discrete element framework for modeling the mechanical behaviour of snow Part II: model validation

A micro-scale modelling approach of snow based on the extension of the classical discrete element method has been presented in the first part of this study. This modelling approach is employed to predict the mechanical response of snow under compression dependent on strain rate, initial density and temperature. Results obtained under a variety of conditions are validated with experimental data for both micro- and macro-scale, in particular the broad range between ductile i.e. low deformation rates and brittle i.e. high deformation rates regimes are investigated. For this purpose snow is assumed to be composed of ice grains that are inter-connected by a network of bonds between neighbouring grains. This arrangement represents the micro-scale of which the interaction is described by inter-granular collision and bonding. Hence, the response on a macro-scale is largely determined by inter-granular collisions and deformation and failure of bonds during a loading cycle. Consequently, validation was first carried out on micro-scale deformations at different loading rates and temperatures. Hereafter, macro-scale simulations of confined and unconfined, deformation-controlled compression tests have been predicted and were successfully compared to experimental data reported in literature.

Study of monotonic and cyclic mechanical behavior and microstructural evolution at a high temperature of ASTM A297 HP steel modified with niobium

The present work studies the effects of niobium on the mechanical properties and the elastoplastic/viscoelastic behavior at 927 °C of ASTM A297 grade, HP cast stainless steel in the as-cast material, to simulate the actual work condition. Tensile tests were carried out at different temperatures, differential scanning calorimetry (DSC), relaxation tests, the fatigue of continuous cycles under the triangular waveform, and fatigue with a trapezoidal waveform of the type “Dwell” with dwell times of 120 and 300 s as specified in the E2714-13 standard and hot torsion tests, to analyze the variations in the mechanical properties. The results of the mechanical tests and studies of the microstructural evolution, as well as of its later analyzes, provided data, not only in the form of data sheet's for the application of the values obtained in projects but concurrently after comparing property and microstructure, to deepen the phenomenology of mechanical stress behavior versus monotonic and cyclic deformation, high-temperature deformation mechanisms, dynamic recovery, of the type of microstructure resulting after the tests and also of the fracture mechanisms associated with the types of mechanical stresses imposed on the material, obtained by through the mechanical tests mentioned above. The high-temperature fatigue tests showed expected stress versus strain behavior, where cycles without dwell times showed lower hysteresis area values, from where the energy consumed in a strain cycle is calculated. The increase in the consumed energy values is due to the insertion of the dwell times, but it is important to note that for the tests that contain dwell times of 120 s and 300 s they did not show significant differences between the consumed energy, showing a saturation effect of tension that does not promote more significant inelastic strains. The cyclic mechanical fatigue stresses with dwell times and the low deformation rate led to intense precipitation of secondary carbides Cr23C6 chromium alloys added to the intrinsic properties of stainless steel dislocation slip were factors that resulted in the dynamic recovery phenomenon. Fractographic analyzes performed on monotonically fractured specimens and specimens after fatigue tests revealed that the material is prone to fracture in intergranular regions.

Impact Failure of Polycrystalline Diamond Cutters

Polycrystalline Diamond (PCD) Cutters are ultra-hard tools used for oil and gas drilling. These tools can fail in the form of spalling due to impact. In this paper, direct impact and quasi-static loading are used to investigate the failure force for leached PCD cutters when loaded at an angle on the edge of their chamfer with a PCD striker or platen. Impact experiments were performed using an impedance match system which ensures the sample is only loaded once; this allows subsequent analysis of the failure surfaces. The failure force at high deformation rate is around 8 kN and at low deformation rate 6.3−+2.3 kN. The failure force required for spalling increases with increasing deformation rate. High speed imaging is also used to explore the failure history of the cutters.

The two-level elastic-viscoplastic model: analysis of the influence of crystallite orientation distribution in the reference configuration and the complexity of loading on the behavior of polycrystalline materials

Components and structural elements used in modern technology are often exposed to significant loads in wide ranges of high and low temperature and deformation rates, high stresses and loading rates.. All these factors, as well as complex loading schemes that must be considered when designing structures of different sizes - from miniature to large-scale -, put forward increased requirements for the properties of materials. A significant part of the structures used in various industries are made of polycrystalline metals and alloys. The physical and mechanical properties of polycrystalline aggregates in finished products depend on their phase and component composition, meso- and microstructure, including the orientation of crystallites (grains, subgrains), symmetry properties of subgrains, and on the initial (residual) stresses that occur during their manufacturing. Experimenting with full-scale structures requires considerable material and time expenditures, therefore mathematical modeling approaches are applied, especially for designing structures and their manufacturing processes. Mathematical modelling provides an opportunity to describe processes in any materials with this or that degree of accuracy. Constitutive relations (or constitutive models) are the most important element of the mathematical models developed for solving these problems. Currently, the most promising among these models are multilevel models based on the introduction of internal variables and crystal plasticity. When analyzing the elastic-plastic deformation of various products, the isotropic constitutive relations are often used to simplify the analysis of the elastic component of deformations. The present work is devoted to the study of errors arising when the anisotropic elastic properties of crystallites are replaced by the corresponding isotropic properties of the materials with BCC, FCC and HCP lattices for different laws of orientation distribution of crystallites in a polycrystalline aggregate in the reference configuration. Using the two-level model based on the elastic-viscoplastic crystal plasticity, a series of numerical experiments on simple shear loading, sequences of two simple loads and cyclic deformation were performed to analyze the evolution of the stress-strain state and to estimate the residual stresses in crystallites.

Material flow behavior and microstructural evolution during refill friction stir spot welding of alclad 2A12-T4 aluminum alloy

In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of al-clad 2A12-T4 aluminum alloy during refill friction stir spot welding. There are two material flow components, i.e., the inward- or outward-directed spiral flow on the horizontal plane and the upward- or downward-directed flow on the vertical plane. In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer. In the refill stage, this is process reversed. As such, there is no obvious vertical plasticized metal flow between adjacent layers. Welding leads to the coarsening of S (Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone. Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.

A solid state bonding technology for metal plate by shear-extrusion and the analysis of microstructure and bonding strength

Abstract A shear-extrusion bonding (SEB) technology is developed for the bonding of metal plates with the background of endless hot rolling of strip steel. Two key process parameters, deformation ratio and deformation rate, are analyzed by experiments using Q345 steel from the perspective of microstructure and bonding strength. The main findings are: (i) With increasing deformation ratio, the width of bonding interface gradually decreased and the refined grains on both sides of the bonding interface are found. When the deformation ratio is below 75 %, the deformation rate has a significant influence on the closure of holes. The width of bonding interface is smaller at a low deformation rate. However, no obvious difference is found in terms of grain refinement degree. Nevertheless, when the deformation ratio reached 100 %, the grains on both sides of the bonding interface are finer at low deformation rate. When the deformation ratio increased to 150 %, an excellent bonding can be obtained. (ii) In terms of bonding strength, as deformation ratio increases, the plasticity of specimens tends to increase whether at low or high deformation rate. Interestingly, the plasticity property of processed specimens can precede the raw material when the deformation ratio reaches 125 % at low deformation rate. When the deformation ratio reaches 125 % at low deformation rate or 100 % at high deformation rate, the bonding strength can reach the tensile strength of the raw material.