Varying Strain Rates Research Articles

Impact mechanical properties of frozen soil after experiencing freeze–thaw cycles: Experimental and numerical study

When frozen soil serves as the foundation of engineering facilities in cold regions, it often suffers from the combined action of freeze–thaw cycles (FTC) and impact loading, which changes its stability and reliability. This study analyzed frozen soil by conducting FTC experiments with varying FTC numbers and impact loading experiments under varying strain rates. The experimental results revealed that frozen soil exhibited FTC and strain rate effects. The peak stress of frozen soil gradually weakened with a decrease in the strain rate and an increase in the FTC number. The expansion stress caused by the water–ice phase transition during an FTC was investigated, assuming that the expansion stress was comparable to the cyclic load, and the deterioration mechanism of frozen soil under the FTC action was discussed. An expression of FTC damage was derived using thermodynamic and continuous damage mechanical principles. A finite element model of frozen soil, derived from the cohesive zone model, was established by inserting cohesive elements into the common surfaces between solid soil elements. A traditional traction–separation (T–S) model for cohesive elements was improved by considering the influence of the strain rate using the overstress model. An elastic–plastic model was used to model the solid elements. The improved T–S model and elastic–plastic constitutive law were used to implement a numerical simulation via a user subroutine VUMAT integrated in ABAQUS/Explicit. When the FTC damage was considered, the microcrack evolution and impact mechanical behavior of frozen soil under impact loading after experiencing FTC action were observed. Having compared the numerical results with the experimental data, it is concluded that a good experimental–numerical correlation was obtained.

Viscoelastic and microwave resonant absorption studies of NixFe3−xO4 (0 ≤ x ≤ 0.7) mixed ferrite nanoparticle based magnetic fluid

We investigated the effect of Ni substitution on oleic acid coated Fe3O4 magnetic nanoparticles of 10–13 nm size dispersed in kerosene medium with enhanced colloidal stability. Study of molecular dynamics and coating of oleic acid to ferrite NixFe3−xO4 (0 ≤ x ≤ 0.7) nanoparticles was confirmed by Fourier transform infrared spectroscopy (FTIR) measurements. The increase of Zeta potential (ζ) up on Ni concentration confirms the stability of Ni substituted Fe3O4 magnetic nano fluid. Magnetization measurements (M-vs-H) reveals the substitution of Ni2+ suppresses the magnetic moment thereby decrease of saturation magnetization while increase in Ni concentration from x = 0–0.7 of Fe3O4 nano magnetic fluid. Moreover, field dependent elastic (G′) and viscous (G′′) modulus recorded at varying strain rate confirms a cross-over from viscoelastic-to-viscous behavior of Ni substituted Fe3O4 nanofluid. Further, the induced spin-disorder upon Ni concentration in corroboration with microwave resonant absorption (EPR) measurements through the increase of resonance field and narrowing of peak-to-peak linewidth indicating the suppression of magnetic dipole interactions and enhancement of super-exchange-interactions (Fe3+-O-Ni2+/Fe2+-O-Ni2+) . Moreover, the dominance of spin-spin interactions over the spin-lattice interactions was determined by EPR relaxation-time-scales: spin-spin relaxation (τ2) increases and spin-lattice relaxation (τ1) decreases, which is in conjunction with lande-g-factor while increasing Ni concentration. The present results are useful for knowing the effect of Ni concentration on magnetic and viscoelastic properties of NixFe3−xO4 (0 ≤ x ≤ 0.7) magnetic nanoparticles. Also, it offers a chance to create such types of stable nano magnetic fluids that may be actively controlled by outside magnetic fields, which results in heat sink damping materials in sealed devices and biomedical applications, etc.

Study of Strain-rate Effect in Two-dimensional Biaxial Test on Granular Material using Discrete Element Method

Numerical study to investigate the effect of various strain rates on global friction angle in the sand has been performed. Granular material behavior is influenced by several factors, among others: pack configuration, grain macro and micro roughness, confinement pressure, loading rate, etc. Sand is a granular material composed of discrete particles that the most refined microscopic techniques are needed to study its mechanical properties. In Indonesia, research related to the Discrete Element Method is still very limited. The two-dimensional discrete element method is capable to calculate the motion and interparticle contacts of large number of small particles, and each particle is modeled as a rigid circular element. The study started with the validation of the DEM model using YADE. Particles with a local friction angle of 35° are arranged in a closed rectangular box (frictionless wall). The number of particles used in this model validation simulation is 1000 sphere-type particles with monodisperse particle gradations. The simulation was done by a drained biaxial test with confinement stress of 100 kPa, thereafter varying strain rate are applied. Based on the deviatoric stress–axial strain curve from YADE, the result can be depicted on the Mohr circle to obtain the value of the global friction angle. It is found that the different value of strain rate affects its global friction angle. Increasing the value of the strain rate can increase the material global friction angle, which increases the strain rate from 1% to 5%, 10%, 25%, and 50% will increase its global friction angle by 5%, 5%, 14%, and 18%, respectively.

Microstructure Evolution in a β-γ TiAl Alloy during Hot Deformation under Variable Conditions

In contrast to practical hot compression processes, the testing of the hot workability of TiAl alloys is usually conducted under the conditions of constant strain rates and constant temperatures. This work aims at investigating the microstructural evolution of TiAl alloys on a Gleeble-3800 thermomechanical simulator under a variable strain rate (0.1, 0.01 and 0.001 s−1) at 1200 °C. The results show that, after a holding time of 30 s, the abrupt change in the strain rate at ε = 0.3 (engineering strain) has a remarkable influence on the flow stress and dynamic recrystallization (DRX) behavior of the β-γ Ti-44Al-6Nb-1Mo-0.3 (B, Y, La, Ce) (at.%) alloy. The flow stress demonstrates a rapid decrease with a sudden reduction in the strain rate. A duplex microstructure of γ + B2/β can be obtained under a high strain rate or continuous medium strain rate. During the two-step deformation, however, both γ→α phase transformation and DRX exist, and the content of the α phase demonstrates a significant increase when the strain rate becomes lower. Finally, a fine-grained structure of γ + B2/β + α2 phases with low residual stresses can be obtained via the two-step heat treatment processes. This provides a promising approach to significantly improve the hot workability of β-γ TiAl alloys.

Crustal Architecture Across Southern California and Its Implications on San Andreas Fault Development

AbstractIn this study, we perform a 2‐frequency sequential receiver function stacking investigation in Southern California. The resulting Moho depths exhibit similar patterns to previous studies while the crystalline crustal Vp/Vs values show more regional variations. Most Vp/Vs variations can be explained by compositional differences. We observe a dichotomy in Moho depth, Vp/Vs, and crustal strain rates between the Peninsular Ranges and Southern San Andreas Fault system. Comparisons between strain rates, Vp/Vs, and temperature suggest that crustal compositional variations may have played a more critical role in influencing the crustal strain rate variations in the Peninsular Ranges and Southern San Andreas than temperature. The structural and compositional variations provide a new insight into the causes of the migration of the Southern San Andreas Fault system and the formation of the “Big Bend.”

ANKLE LIGAMENT REPAIR FOR RESTORATION OF FUNCTION: EXPLORING THE APPLICATION OF DECELLULARIZED GRAFTS

Ligament integrity is directly associated with ankle stability. Nearly 40% of ankle sprains result in chronic ankle instability, affecting biomechanics and potentially causing osteoarthritis. Ligament replacement could restore stability and avoid this degenerative pathway, but a greater understanding of ankle ligament behaviour is required. Additionally, autograft or allograft use is limited by donor-site morbidity and inflammatory responses respectively. Decellularised porcine grafts could address this, by removing cellular material to prevent acute immune responses, while preserving mechanical properties.This project will characterise commonly injured ankle ligaments and damage mechanisms, identify ligament reconstruction requirements, and investigate the potential of decellularised porcine grafts as a replacement material.Several porcine tendons were evaluated to identify suitable candidates for decellularisation. The viscoelastic properties of native tissues were assessed using dynamic mechanical analysis (DMA), followed by ramp to ‘sub-rupture’ at 1% strain/s, and further DMA. Multiple samples (n=5) were taken along the graft to assess variation along the tendon.When identifying suitable porcine tendons, a lack of literature on human ankle ligaments was identified. Inconsistencies in measurement methods and properties reported makes comparison between studies difficult.Preliminary testing on porcine tendons suggested there is little variation in viscoelastic properties along the length of tendon. Testing also suggested strain rates of 1%/s sub-rupture was not large enough to affect viscoelastic properties (no changes in storage or loss moduli or tanẟ). Further testing is underway to improve upon low initial sample numbers and confirm these results, with varying strain rates to identify suitable sub-rupture sprain conditions.This work highlights need for new data on human ankle ligaments to address knowledge gaps and identify suitable replacement materials. Future work will generate this data and decellularise porcine tendons of similar dimensions. Collagen damage will be investigated using histology and lightsheet microscopy, and viscoelastic changes through DMA.

Integrated Johnson–Cook and Zerilli–Armstrong constitutive model for flow-stress prediction of AZ31B alloy

ABSTRACT An appropriate constitutive model is essential for trustworthy numerical simulations and the analysis of material deformation behaviour during the metal-forming process. In the present work, the quasi-static warm tensile response of AZ31B alloy ranging from 200°C to 350°C with an incremental difference of 50°C and the strain rates from 10−1 to 10−3 s−1 is investigated experimentally and predicted using the Johnson–Cook and Zerilli–Armstrong (JC-ZA) constitutive model. The temperature and strain rate variation has a substantial impact on flow-stress behaviour. The model prediction efficacy is analysed based on the correlation coefficient (R), average absolute error (Δ), and their standard deviation (s). It is evident that the integrated JC–ZA model has better accuracy, with a correlation coefficient of 94.5%, average absolute error (Δ) of 3.97%, and a standard deviation of 5.67%.

Biofidelic gallbladder tissue surrogates

ABSTRACT The gallbladder tissue is one important functional tissue of the human abdomen, but the biomechanics of the gallbladder tissue has not been much explored due to biosafety and ethical concerns with cadaveric sample testing. This study aimed to develop tissue surrogates by conducting an experimental study to mimic the mechanical properties of human gallbladder tissue. To meet the objectives, 15 candidate test coupons were fabricated with varying compositions and uniaxially tested at varying strain rates to configure the stress versus strain responses. The results of the tested coupons were compared with the literature on human cadaveric gallbladder tissue to determine the test coupons (i.e. surrogates) mimicking the mechanical properties. The hyperelastic curve fit model (Mooney–Rivlin) was used to quantify the non-linear behaviour of the developed gallbladder tissue surrogates. The biofidelic gallbladder surrogates with realistic mechanical properties have been developed for the first time in the literature. Such surrogates would be helpful to better understand injury biomechanics, trauma research, and making different medical models for educational purposes.

Estimation of crustal strain in Kashmir Himalayan region of north India using continuous GPS measurements

Global positioning system (GPS) measurements of crustal deformation provide insight into the crustal plate velocity and strain rate variation in the actively deforming Earth's crust. GPS measurements in the Kashmir Himalaya indicate that most of the crustal motion between the Indian Plate and southern China is accommodated along the Himalayan arc, resulting in the accumulation of crustal strain and locking of the Main Himalayan Thrust (MHT). Here, we present geodetically estimated spatial and temporal crustal strain rates in the Kashmir Himalaya from GPS measurements to understand the nature of crustal deformation. We processed and analysed GPS data from 21 sites across Kashmir Himalaya along with several IGS sites. We find that the average deformation rate of the GPS sites in Kashmir Himalaya with reference to the Indian Plate range between 2.8 and 15.5 ± 1 mm/year. The GPS results illustrate that the strain rate field is dominated by a compression component with its rate as 7.2 × 10−8 strain/year and the maximum shear strain, γmax, of 1.9 × 10−7 strain/year. The earthquake focal mechanisms suggest that earthquake activity in the Kashmir Himalaya is predominantly manifested in the form of thrust motion. The maximum principal shear strain value reflects that the Kashmir Himalaya is under NE–SW compressional regime. The spatial distribution of crustal strain indicates that the region north‐east of Kashmir Valley is accumulating maximum strain, resulting in the stress build‐up and could be the region of a future large earthquake.

Stress corrosion of copper in sulfide solutions: Variations in pH‐buffer, strain rate, and temperature

AbstractCopper is the intended canister material for the disposal of spent nuclear fuel in Sweden. At repository depth the groundwater may contain dissolved sulfide. The main goal for this work is to study the tendency for stress corrosion of copper in sulfide solutions and examine the influence of various experimental parameters on stress corrosion. Slow strain rate testing was performed on copper test rods in solutions with 1.0 mM sulfide. The pH was kept near neutral with phosphate or borate buffer. The test matrix included variations in temperature, strain rate, and duration of the tests as well as salt and buffer concentrations. Cross‐sections of the specimens after testing were investigated using scanning electron microscope/energy dispersive X‐ray spectroscopy detector. Stress–strain curves do not reveal any signs of stress corrosion. However, intergranular corrosion in the shape of crack and pit‐like features developed in all tests with 1.0 mM sulfide. The length of the deepest features in all these tests was of the same order of magnitude (10–20 µm). The suggested mechanism proposes that crack‐like features originate at the surface of the copper metal from the oxidation of grain boundaries that behave as slightly less noble.

Curvature Ductility Factor of Reinforced Concrete Beams with Confinement under Different Strain Rates of Loading

The purpose of this work is to investigate the influence of confinement on the curvature ductility factor of reinforced concrete beams at low and high strain rates of loading. The curvature ductility of beams is affected by the tension reinforcement ratio, the compression-reinforced ratio, the compression strength of concrete <img src=image/14828877_01.gif>, and the yield strength of steel <img src=image/14828877_02.gif>. The degree of transverse reinforcement is another component that determines beam flexural behavior. A model of steel and restricted concrete under varying strain rates of loading was utilized to compute the curvature ductility factor. The reinforced concrete section is studied in this research to determine the confinement of the beam and the different strain rates of loading. The ratio of the volume of rectangular steel hoops to the volume of the concrete core, <img src=image/14828877_03.gif>, represents the confinement. Six values of <img src=image/14828877_03.gif> are investigated to ensure an acceptable degree of ductility capacity. It is concluded that the ACI-Code balanced reinforcement ratio is impacted by confinement, and that it is lower than the ratio achieved when confinement is present. In this work, specific values of the curvature ductility factor for beam sections constructed with the ACI code were reported for <img src=image/14828877_02.gif>=60 ksi (414 MPa), <img src=image/14828877_01.gif>=4 ksi (27.6 MPa). Furthermore, the maximum quantity of tension reinforcement max influences the curvature ductility factor.

The role of the Ebro Block on the deformation experienced within the Pyrenean realm: Insights from deformable plate tectonic models

Plate kinematic models of the Pyrenees have been extensively debated due to discrepancies between plate kinematic constraints for the Iberian plate and Atlantic/Tethyan related plate motions. Recently, the morphology of the Iberian plate and its partitioning into several continental blocks has been proposed as a solution towards reconciling discrepancies between previously published reconstructions that treat Iberia as a single, rigid, tectonic plate. Herein, the first deformable plate tectonic modeling study of the Pyrenean realm is presented using previously published and newly presented reconstructions of Iberia. Special emphasis is given to the kinematics of the Ebro Block, a continental block situated between the Pyrenees and Iberian Ranges, whose kinematics are considered to play a key role in the extensional deformation experienced within the Pyrenean realm. Temporal variations in strain rate and crustal thickness calculated by deformable plate models provide insights regarding the pre-orogenic template of the Pyrenees and the variability in regional stress directions along the Iberia-Eurasia plate boundary from the Triassic to Cenomanian. Models that propose transtensional rift phases within the Pyrenean realm induced by the Landes High and Ebro Block kinematics since the Triassic are successful in deriving crustal thicknesses indicative of a pre-orogenic hyperextended rifted margin within the Pyrenean realm. The results of this study demonstrate the importance of continental block kinematics during rift-related deformation and their impact on the evolution and partitioning of rift domains. Furthermore, this study also highlights potential avenues to consider for improving future plate kinematic models of Iberia, and regions elsewhere.

Plastic Deformation Mechanism of High Strength and Toughness ZK61 Magnesium Alloy Plate by Multipass Horizontal Continuous Rolling.

ZK61 magnesium-alloy plate with high tensile strength and elongation is obtained by combined multipass symmetric hot rolling and asymmetric warm rolling. Deformation history considering varying strain rate obtained from the macro-finite element analysis of the selected passes are introduced into the viscoplastic self-consistent model (VPSC) as initial boundary conditions for macro- multiscale and micro-multiscale coupling analysis. VPSC simulation results show that in the initial stage of rolling deformation, the basal <a> slip is the dominated deformation mode, supplemented by prismatic <a> slip and pyramidal <c+a> slip. With increased rolling strain, the pyramidal <c+a> slip presents competitive relationship with basal <a> slip, and the activation amount of {101-1} compression twins is limited. During asymmetric rolling, the basal <a> slip is dominant, followed by the pyramidal <c+a> slip. Experimental results show that the basal texture is gradually strengthened after symmetric rolling, and grain size is refined due to the activation and recrystallization of twins. Asymmetric rolling makes the basal texture deflect 10° to the rolling direction and further refine the grain size. With the ongoing of symmetric rolling, the mechanical anisotropy of the plate weakens, and the yield strength, tensile strength, and plasticity of the material improves. In particular, after asymmetric rolling, the tensile strength in the RD and TD directions of the plate reaches 391.2 MPa and 398.9 MPa, whereas the elongation reaches 19.8% and 25.5%.

Effect of strain rate on fractography texture descriptor of AA6063/(Si3N4)x/(Cu(NO3)2)y (x=12%, y = 2–6%)composite after multiple ECAP passes: second order statistical texture analysis conjunction with regression analysis

The tensile strength of the ECAP processed composite of AA6063/(Si3N4)x/(Cu(NO3)2)y (x=12%, y=2-6%) at various strain rates from 0.0001 to 1s-1 with an increment of 10 was examined in relation to the seven-fracture image texture descriptor through void features such as void size and distribution. In order to measure the matrices of voids on the fracture surface created through the coalescence of void results to enhance the material hardening as strain rate increases, the second order statistical texture analysis has been used. With respect to the rising strain rate, it was observed that the composite fracture image feature parameter correlation, homogeneity improved by 6 %, and 20.74% for AA6063/12%Si3N4/6%Cu(NO3)2 after I passes as compared to AA6063/12% Si3N4 after III pass. The contrast was reduced by around 58.643% when reinforcement went from a single reinforcement of 12% Si3N4 with I Pass to a composite of two reinforcements (Si3N4, Cu(NO3)2) that had 6% Cu(NO3)2 with I Pass. After three passes on AA6063/12%Si3N4/2%Cu(NO3)2, the maximum entropy was seen due to the material's increased plastic deformation, which led to an uneven particle distribution. As strain rate and copper nitrate percentage grew from 0 to 6 percent, the tensile strength of the composite improved by 34.69%. To assess the importance of fracture image features in relation to tensile strength with respect to strain rate, a regression model was developed. In order to get information about the fracture studies from fractography, the contrast with varying strain rate was nevertheless the aspect, which had the greatest influence.

Mechanics and stress propagation in non-equilibrium cytoskeleton composites

The cytoskeleton is able to access a wide range of material properties to facilitate cellular processes in a controlled and precise manner via active restructuring and reconfiguration of its constituents by ATP-consuming motor proteins. In vitro cytoskeleton composites have been shown to exhibit tunable mechanical properties, and the addition of force-generating motors to these composites induces non-equilibrium dynamics and restructuring. We characterize the effects of non-equilibrium activity on the mechanical properties of actin-microtubule composites driven by variable concentrations of kinesin motor clusters by performing optical tweezers microrheology experiments. We measure the nonlinear force response of the composites subject to cyclical strain at varied strain rates. Additionally, we measure stress propagation through the composites due to locally imposed strain using differential dynamic microscopy (DDM). We uncover a transition from dissipative to stiffening force response of the composites at mesoscopic lengthscales, with a non-monotonic dependence on kinesin concentration. Our work sheds light on how active restructuring by motor proteins tunes the material response of the cytoskeleton to local stresses, enabling diverse processes such as shape change, motility, and repair.

Hybrid effects of carbon nanotubes and steel fiber on dynamic mechanical properties of ultra-high performance concrete

This study aims to investigate the hybrid effects of carbon nanotubes (CNTs) and steel fiber (SF) on dynamic mechanical behavior of ultra-high performance concrete (UHPC) under the high-speed dynamic loading effects. The functionalized CNTs content varied from 0.0% to 0.20%, and SF volume content was added from 0.5% to 2.0%. The UHPC specimens were tested at strain rates ranging from about 60 s−1 to 240 s−1 using the split Hopkinson pressure bar. The dynamic behavior of specimens was evaluated in terms of stress–strain relationships, energy absorption capacity and failure patterns. Test results show that dynamic compressive properties of UHPC are strongly sensitive to strain rates. The individual addition of CNTs obviously improves the dynamic performance of plain UHPC, and there exists an optimal CNTs content of about 0.10% to achieve better improvement effects. The dynamic increase factor (DIF) is almost unrelated to CNTs content but closely correlated to strain rate variations, which can be well described by a modified empirical formula. Furthermore, it is found that the hybrid CNTs and SF display more significant reinforcing effects on dynamic properties of UHPC, as the UHPC specimen with 0.10% CNTs and 2.0% SF exhibits the highest dynamic compressive strength and toughness. Meanwhile, UHPC reinforced by hybrid fibers is less sensitive to high strain rates compared to plain UHPC. From microscopic observations, it is reasonably believed CNTs and SF exert synergistic reinforcing effects on UHPC matrix in view of their respective characteristics, which are more significant in improving the interfacial transition zone (ITZ) structure between SF and the surrounding matrix. This work promotes a fundamental understanding for the reinforcing effects of CNTs on UHPC, and provides an effective strategy to reinforce UHPC from multiscale perspectives.

Isomorphs in sheared binary Lennard-Jones glass: Transient response.

We have studied shear deformation of binary Lennard-Jones glasses to investigate the extent to which the transient part of the stress strain curves is invariant when the thermodynamic state point is varied along an isomorph. Shear deformations were carried out on glass samples of varying stability, determined by cooling rate, and at varying strain rates, at state points deep in the glass. Density changes up to and exceeding a factor of two were made. We investigated several different methods for generating isomorphs but none of the previously developed methods could generate sufficiently precise isomorphs given the large density changes and nonequilibrium situation. Instead, the temperatures for these higher densities were chosen to give state points isomorphic to the starting state point by requiring the steady-state flow stress for isomorphic state points to be invariant in reduced units. In contrast to the steady-state flow stress, we find that the peak stress on the stress strain curve is not invariant. The peak stress decreases by a few percent for each ten percent increase in density, although the differences decrease with increasing density. Analysis of strain profiles and nonaffine motion during the transient phase suggests that the root of the changes in peak stress is a varying tendency to form shear bands, with the largest tendency occurring at the lowest densities. We suggest that this reflects the effective steepness of the potential; a higher effective steepness gives a greater tendency to form shear bands.

Plastic deformation and ductile fracture of L907A ship steel at increasing strain rate and temperature

A combined theoretical, numerical, and experimental approach is adopted to systematically characterize the plastic deformation and ductile fracture behaviors of L907A low-alloy ship steel widely used in ship construction, with the effects of strain rate and thermal softening duly accounted for. A mixed Swift-Voce hardening model coupled with strain rate and temperature-dependent terms is proposed, while the Hosford-Coulomb model of ductile fracture is modified by introducing temperature-dependent term to account for the effect of thermal softening. To calibrate the parameters appearing in the constitutive models, dynamic uniaxial tensile tests at varying strain rates (0.001 ∼ 5200 s−1) and quasi-static uniaxial tensile tests at varying temperatures (20 ∼ 800 °C) are separately performed, with the coupling between strain rate and temperature effects ignored. The calibrated plasticity and ductile fracture models are numerically implemented with the method of finite elements (FE), and their applicability to practical applications is validated against experimental results of ballistic impacts. Normal and oblique impacts on L907A target plates with conical, hemispherical, and blunt projectiles are considered. Good agreement between FE simulation results of plastic deformation and ductile fracture modes and those measured experimentally is achieved, thus demonstrating the viability of the established plasticity and fracture models of L907A steel for applications in complex ballistic impact scenarios.

Additive friction stir deposition of SS316: Effect of process parameters on microstructure evolution

Solid state nature of additive friction stir deposition (AFSD) additive manufacturing process is very advantageous in terms of defect formation and microstructural refinement in the material. Current study presents the process optimization, microstructural evolution and kinetics of recrystallization for AFSD deposited low stacking fault energy material - SS316. As deposited microstructure shows equiaxed ultra fine grains with an average grain size of ~5.0 ± 0.5 μm. Shear deformation at high temperature during processing leads to the operation of restoration mechanisms. Observation of necklace type microstructure in the as deposited SS316 is attributed to discontinuous dynamic recrystallization during processing. Recrystallization kinetics of the AFSD SS316 is characterized using Johnson-Mehl-Avarami-Kolmogorov (JMAK) model. Deformation – thermal cycling during AFSD process resulted in inconsistent recrystallization kinetics. Variation in strain, strain rate and temperature during processing with processing parameters result in varying microstructure and tool wear. High strength-ductility combination and sustained work hardening in as deposited SS316 appear to arise from transformation and twinning during deformation, leading to the formation of hierarchical twins and martensitic phase after deformation. • A high strength and work hardening alloy – SS316 is additively manufactured using a novel additive friction stir deposition. • Porosity free builds with fine equiaxed grain structure is formed in as deposited material as a result of discontinues dynamic recrystallization during processing. • Microstructure of the deposited material and the tool wear during processing varied with variation in the process parameters. • Activation of twining and transformation during deformation resulted in excellent tensile properties with yield strength of 415 ± 10 MPa and ductility 75 ± 5% in as deposited material.

Experimental Investigation of the Size Effect of Rock under Impact Load

When measuring the compressive strength of rock, size and strain rate are the two main influencing factors. To study the rock strength size effect, rock specimens with length-to-diameter ratios of 0.5, 0.6, 0.7, 0.8, 0.9 and 1 were subjected to static loading tests using the RMT rock mechanics test system and dynamic loading with the split Hopkinson pressure bar, respectively. Based on the Weibull size-effect formula, the experimental results were compared with the improved formula obtained. The results show that rock strength is influenced by size and strain rate. Both the dynamic increase factor and rock strength are proportional to strain rate. The different failure modes of rock with size variation and strain rate variation are described according to the failure process of the specimens. The same length-to-diameter ratio specimens produced more fragments with a strain rate increase. Under the same strain rate of impact, the larger the rock specimen, the finer the broken fragments. Considering the factor of strain rate in the Weibull size-effect formula, the calculated result is accurate. The improved size-effect formula could be used to better elaborate the potential mechanisms of dynamic rock strength. In the unified theoretical formula containing static and dynamic loads, the relationship of rock strength, size and strain rate is well described.