Stress Strain Rate Research Articles

Hugoniot elastic limit of single-crystal tantalum at normal and elevated temperatures subjected to extreme strain rates

Large-scale nonequilibrium molecular dynamic simulations of impact-induced shock propagation in defect-free single-crystal Ta along the [001] direction is presented, paying particular attention to the formation of elastic-plastic two-wave structures. Plastic deformation and elastic limits of Ta single crystals for various crystal orientations were investigated in a recent paper [R. Ravelo et al., Phys. Rev. B 88, 134101 (2013)]. In the present paper, a comprehensive study on the Hugoniot elastic limit (HEL) and its dependence on associated physical parameters is reported. The observed attenuation of an elastic precursor in a stress-wave profile led to proposing wide-range scaling relations for HEL decay applicable for ultrahigh strain rates. The influence of a lateral dimension on the spatial profile of a stress wave and time profile of free surface velocity (FSV) in the distinct appearance of a spike-valley feature and its consequence on scaling relations is investigated. Further, it is shown that the commonly used method of calculating HEL from a FSV profile is inadequate for submicron-thick samples at high strain rates. The necessary modifications are incorporated that resulted in comparable HEL values by two complimentary approaches of stress and FSV profiles. Simulations carried out for increasing impact strength revealed a power law dependence of HEL with strain rate. A methodology based on extrapolation of stress decay law and strain rate scaling constructed by us is proposed here for prediction of HEL pertaining to larger length samples. Very good agreement between the predicted values and available experimental results makes the modeling robust and applicable for a wide range of strain rates and length scales. Finally, the study is extended for elevated sample temperatures up to melting. Interestingly, yield strength is shown to follow an increasing trend up to a certain temperature, beyond which it decreases. An empirical relation is proposed here for expressing temperature dependence of HEL that explains the observed yield strength anomaly. Results are justified through thermal analysis of shear stress and evolution of dislocation density.

Strain Rate and Stress Amplitude Effects on the Mechanical Behavior of Carbon Paste Used in the Hall-Héroult Process and Subjected to Cyclic Loadings.

Carbon products such as anodes and ramming paste must have well-defined physical, mechanical, chemical, and electrical properties to perform their functions effectively in the aluminum electrolysis cell. The physical and mechanical properties of these products are assigned during the shaping procedure in which compaction stresses are applied to the green carbon paste. The optimization of the shaping process is crucial to improving the properties of the carbon products and consequently to increasing the energy efficiency and decreasing the greenhouse gas emissions of the Hall–Héroult process. The objective of this study is to experimentally investigate the effect(s) of the strain rate, of the stress maximum amplitude, and of the unloading level on the behavior of a green carbon paste subjected to cyclic loading. To this end, experiments consisting of (1) cyclic compaction tests at different maximum stress amplitudes and strain rates, and (2) cyclic compaction tests with different unloading levels were carried out. The study obtained the following findings about the behavior of carbon paste subjected to cyclic loads. The strain rate in the studied range had no effect either on the evolution of the permanent strain as a function of the cycle number, nor on the shape of the stress–strain hysteresis during the cyclic loading. Moreover, samples of the same density that had been subjected to different maximum stress amplitudes in their loading history did not have the same shape of the stress–strain curve. On the other hand, despite having different densities, samples subjected to the same number of cycles produce the same stress–strain curve during loading even though they were subjected to different maximum stress amplitudes in their loading histories. Finally, the level of unloading during each cycle of a cyclic test proved significant; when the sample was unloaded to a lower level of stress during each cycle, the permanent strain as a function of the cycle number was higher.

Research on dynamic constitutive model and fracture criterion of 6082-T6 aluminium alloy

In this study, the mechanical properties of materials under different stress states, strain rates, and temperatures were tested, and a variety of material mechanical properties were obtained. The modified Johnson-Cook (JC) constitutive model and ASCE-MJC fracture criterion with Lode angle correction were calibrated. A 6082-T6 aluminium alloy projectile with a diameter of 5.95 mm was used in performing the Taylor impact test with an impact velocity ranging from 156.548 to −417.216 m/s. Mushrooming and shear cracking were observed during the test. A finite element model (FEM) corresponding to the test was established using the finite element software ABAQUS, and the model was used to predict the ductile fracture behaviour of the projectile. Through a comparison of experiments and parallel simulations, the ASCE-MJC fracture criterion was used to predict a very close fracture mode of the projectile. This proves the validity of the calibrated dynamic constitutive model and the fracture criterion. After comparing the finite element simulation results based on the classic JC fracture criterion prediction, it was found that the ASCE-MJC fracture criterion can better predict the ductility of 6082-T6 aluminium alloy, indicating that the fracture behaviour of the material has a significant Lode correlation. This improvement was verified. The validity of the modified JC constitutive model and ASCE-MJC fracture criterion in predicting the dynamic mechanical properties and fracture behaviour of the 6082-T6 aluminium alloy was also verified.

Deformation behavior during hot torsion of an ultrahigh carbon steel containing 1.3 wt.% C

Abstract The torsion behavior of an ultrahigh carbon steel containing 1.3 wt.% C has been studied at high strain rates (2 – 26 s –1) and high temperatures (900 – 1200 °C). Adiabatic heating strongly affects the shape of the stress– strain curves. Grain size measurements at strains of ε = 2 and ε = 5 reveal that the austenite grain size does not change between these two strains and is finer than the initial austenite grain size. This is an indication that a recrystallization process took place in the interval of strains between ε peak and ε = 2 and that the deformation state associated to the strains of ε = 2 and ε = 5 can be considered as steady state. Stress–strain rate relations have been analysed for ε peak, ε = 2 and ε = 5. It has been found that data obtained at ε peak correlate well with a lattice diffusion-controlled dislocation creep process. On the other hand, analysis of the stress –strain rate relations found at the steady state indicated that the deformation occurs by the contribution of two independent mechanisms: grain boundary sliding controlled by pipe diffusion and slip creep controlled by lattice diffusion.

RETRACTED: Dynamic mechanical properties and modification of fracture criteria of 6061-T651 aluminum alloy

In order to investigate the effects of stress triaxiality, Lode angle, temperature and strain rate on the fracture characteristics of 6061-T651 aluminum alloy materials, the mechanical property tests of materials are carried under different stress states, temperature and strain rate using universal material testing machine. Firstly, the mechanical property test results show that the fracture strain of 6061-T651 aluminum alloy material decreases with the increase of stress triaxiality. And also, the fracture strain of material related to the Lode angle parameter, especially the effect of the Lode angle more significantly at the range of lower stress triaxiality. When the temperature less than 250 ℃, the temperature of material has significant influence on its flow stress, while the influence of temperature on its fracture strain can be ignored. While the temperature more than 250℃, the temperature of material has greatly influence on its flow stress and fracture strain. Moreover, the strain rate has no significant effect on the fracture strain of 6061-T651 aluminum alloy. Subsequently, basing on the test results of mechanical properties, the Modified Johnson-Cook(MJC) criterion is obtained by modifying Johnson-Cook(J-C) fracture criterion, and the parameters of MJC and Modified Mohr-Coulomb(MMC) fracture criterion are calibrated. Finally, the impact test of sphere projectile penetrating the 6061-T651 aluminum alloy target plate is conducted on a one-stage gas gun, and also the ballistic limit velocity and failure mode of target are obtained. In order to verify the validity of the model and parameters, and the corresponding 3D model of projectile impact target is established by using ABAQUS/Explicit finite element software. The results showed that the prediction results of Lode angle dependent MMC fracture criterion is closer to the test compared with the Lode angle independent MJC fracture criterion.

Dynamic Characteristics and Damage Constitutive Model of Mudstone under Impact Loading.

The mechanical response characteristics of mudstone from the ingate roadway of the west ventilation shaft in Yuandian No. 2 coal mine, Huaibei City, Anhui Province, China to dynamic loads were quantified in single- and cyclic-impact compression tests, using the split-Hopkinson pressure bar test device. The dynamic stress–strain relationships and the failure characteristics of mudstone samples under different impact loads were analyzed systematically. Considering the “rate effect” of the mudstone dynamic strength, the dynamic strength criterion of mudstone was proposed, and the dynamic damage constitutive model of mudstone was established, based on the statistical damage theory. In response to single-impact loads, with increasing impact pressure, the mudstone peak stress and strain gradually increased, and the peak stress and average strain rate increased nonlinearly. In response to cyclic-impact loads, with an increasing number of impacts, the mudstone peak stress first increased and then decreased, and the peak strain increased gradually. With increasing impact pressure, the number of impacts to the samples’ failure decreased gradually. By parameter identification and comparative analysis of the test results, the proposed dynamic damage constitutive model of mudstone was validated. The model can be used for stability analysis of roadway-surrounding rock under dynamic loads.

Deformation failure behavior and fracture model of twin-roll casting AZ31 alloy under multiaxial stress state

The influence of temperature and strain rate on the deformation behavior of twin-roll casting AZ31 alloy has been examined as a function of stress state using notched and un-notched tensile specimens. Failure behavior during the physical tension was carried out using FEM simulations with different fracture criteria. Using a combined experimental-FEM investigation, the applicability of each fracture criterion was verified to serve the prediction for the crack initiation under multiaxial stress state. Results show that the critical fracture strain presents a clear exponential relationship with stress triaxiality and strain rate, and a linear relationship with temperature. Through the quantitative analysis of the relationship, a mathematical model can be well established. After comparison and verification, the fracture model can accurately predict the forming limit during the plastic deformation of twin-roll casted AZ31 magnesium alloy under complex stress state, and the classical Cockcroft & Latham criterion is the most suitable criterion for predicting the related crack initiation.

Counterexample-trained neural network model of rate and temperature dependent hardening with dynamic strain aging

Constitutive models dealing with the thermal and visco-plasticity of metals have seen wide applications in the automotive industry. A basic plasticity and fracture characterization of a 1.5 mm thick DP780 dual phase steel sheet based on uniaxial tensile (UT) experiments with seven distinct material orientations is complemented by low (∼0.001/s), intermediate (∼1/s) and high (∼150/s) strain rate experiments on notched tensile (NT) and shear (SH) specimens at temperatures ranging from 20 °C to 500 °C. At low strain rates, we observe a non-monotonic effect of the temperature on the force-displacement curves, with the highest curve obtained at 300 °C. Contrasting low speed tests, a monotonic effect of temperature is observed for intermediate and high strain rate experiments, with the highest curves obtained at 20 °C for both cases. Strain rate jump tests are performed proving the positive strain rate sensitivity of the steel. A machine-learning based plasticity model is developed to capture the observed complex strain rate- and temperature effect. The material is modeled as elasto-plastic, with a Hill’48 yield surface and a non-associated flow rule. The flow resistance is decoupled into a reference strain hardening term and a neural network term, which is a function of the plastic strain, strain rate, temperature, and an additional dynamic strain aging variable. The plasticity model is implemented into a material user subroutine and identified using a counterexample-guided hybrid experimental-numerical approach. The extracted loading paths reveal a complex rate and temperature effect on the ductility of DP780. A neural network based fracture initiation model is therefore adopted to describe the fracture onset across various stress states, strain rates and temperatures considered.

Failure Behavior of Laser Metal Deposited Additive Manufacturing Ti-6Al-4V: Effects of Stress State and Initial Defects.

To investigate the mechanical property and failure behavior of laser metal deposited additive manufacturing Ti-6Al-4V (LMD Ti64) in a wide range of stress states and strain rates, different types of specimens were tested at strain rates of 0.001-5000/s. Numerical simulations were conducted to collect the local fracture strain at the critical position where the failure happened for all specimens. By comparing with Ti64 alloy manufactured by different techniques, the failure behavior of LMD Ti64 alloy shows a stronger sensitivity to Lode angle parameter and strain rate. The role of initial defects in failure was discussed. It is found that high laser power and overlap ratio can improve the failure behavior by reducing the number of initial defects. The initial defects on the fracture surface at much higher strain rates were observed, indicating that the initial crack rather than initial void acts as the crack growth point leading to the final fracture at higher strain rates. The scanning electron microscope observation of the fracture surface shows that the failure mechanism of LMD Ti64 alloy varies from different stress states and strain rates. The failure mechanism is characterized by the shear fracture at the negative stress triaxiality, whereas the void growth fracture plays a dominant role in the failure mechanism of LMD Ti64 alloy at a high stress triaxiality on the quasi-static loading condition.

Effects of welding angle on microstructure and mechanical properties of longitudinal weld in 6063 aluminum alloy extrusion profiles

In order to explore the effects of welding angle on microstructure and mechanical properties of longitudinal weld, a porthole die with different welding angles was designed and manufactured, by using which various extrusion experiments were carried out. The microstructure and mechanical properties of longitudinal weld were characterized, and the extrusion process was simulated. The results show that as welding angle increases, the longitudinal weld gradually transforms from a linear shape to a cross shape. A larger welding angle will not only reduce stress triaxiality and strain rate in the main welding zone, but also increase area of the dead metal zone, thus leading to poor welding quality. The crystal orientations of <100> and <111>//ED can be found in the welding zones of the profiles extruded by using the dies with different welding angles, and the texture components exhibit significant differences. There are a certain number of dislocations, a small amount of Mg2Si precipitates and insoluble iron-containing intermetallic compounds in the welding zones. By comprehensively considering the influence of welding angle on welding quality, extrusion load, effective stress and strain of the porthole die, the welding angle ranges under different welding quality requirements were determined. It is found that the welding quality is higher when the range of welding angle is 38–46°, the welding quality is lower when the range of welding angle is 54–68°. If taking in account both of welding quality and porthole die strength requirement, the preferred welding angle is recommended to be in the range of 46–54°.

Analysis of operational window in Freeman Technology uniaxial powder tester

The operational window of the recently developed Freeman Technology Uniaxial Powder Tester (UPT) in terms of specimen aspect ratio (H/D), consolidation stress, and consolidation and failure strain rates is investigated for a range of bulk solid materials. The results show that the measured uniaxial unconfined yield stress (uUYS) decreases as aspect ratio increases but this sensitivity of uUYS to H/D reduces significantly for aspect ratios of greater than 1.5. The sensitivity of uUYS to aspect ratio is attributed to the intersection of slip planes with the top and bottom platens. The critical aspect ratio (defined as a ratio beyond which uUYS becomes independent of aspect ratio) is found to be a material-specific property, but it is increased with increasing consolidation stress. A correlation between the internal angle of friction and the critical aspect ratio is found, but it does not follow previously reported work. This discrepancy could be attributed to the differences in the packing fraction of the samples in uniaxial compression and the shear cell tests which were used to measure the internal angle of friction. uUYS is found to be independent of consolidation strain rate for the range investigated here (0.005 to 0.05 s−1). A very high level of repeatability is observed for the measurement of compressibility response of bulk solids with no sensitivity to consolidation strain rate uniaxial compression; powder flow; flowability; unconfined yield stress; aspect ratio; strain rate; compressibility.

Multiscale Approaches Including ANN and M5P-Tree with SI and OBJ Assessment Tools to Predict the Shear Thinning of Bentonite Drilling Muds Modified with Clay Nanosize at Various Elevated Temperatures

Improving the flowability behavior of the water-based drilling mud (WBM) using bentonite under high-temperature conditions is significant in the drilling borehole operations. In this study, the influence of bentonite and clay nanoparticle (CNP) contents on the non-Newtonian fluid (rheology) properties such as initial shear stress and fluid’s resistance to flow (viscosity) under high-temperature conditions were tested and quantified. The shear stress and shear strain rate relationships of WBM were simulated using two new rheological models of the vapor pressure and modified Hoerl models, and the modeling outcomes were validated with the Herschel–Bulkley (HB) model. This study also analyzed and formulated more than 268 data sets, including observational data and data obtained from previously published studies ranging with bentonite in the drilling muds from 2% to 8% (%wt. of water), 0% to 1% of CNP (%wt. of bentonite), and heating temperatures were ranging from 25°C to 100°C. The HB rheological model predicted initial shear stress better than the other two rheological models depending on several statistical assessments. The initial shear stress of drilling muds can be predicted well based on bentonite, CNP contents, and temperature using various simulation techniques. According to several statistical tests, the nonlinear regression and artificial neural network (ANN) performed stronger than other model techniques to predict the yield stress of WBM as a function of bentonite, CNP contents, and temperature.

Multi-physics FE-analysis and measurements for thermo-mechanical fatigue crack growth rate testing applications

The presented methodology in this study is addressed to in-phase (IP) and out-of-phase (OOP) loading cycles in stationary and transient thermo-mechanical fields. The subject of the numerical and experimental study is a single edge notch tension (SENT) specimen produced from a high-temperature nickel-based alloy ХН73М. In order to determination a local thermo-mechanical stress-strain rate and displacement fields a new algorithm for the multi-physics numerical calculations developed and implemented incorporates Maxwell 3D, Fluent and Transient Structural modules of ANSYS 2021R1. The employment of proposed algorithm to represent the cyclic history associated with the TMF conditions in the experiments, multi-physics finite element (FE) modelling of the stress, strain and displacement fields in the SENT specimen was performed. Additionally, time dependent non-uniform temperature fields were determined with the same cyclic variations and magnitudes as in the experimental OOP and IP cycling. As a complement to the FEM computations, the infra-red thermography temperature distribution measurements was implemented for the TMF state in the experiments in the SENT specimen. The comparison multi-physics FE-analysis and direct measurements shown in the present study is intended to contribute to a better understanding of the different mechanisms driving TMF crack growth and the address the outstanding questions associated with basic methodology.

Hybrid effect of stress state and strain rate on the deformation and ductile fracture behaviour of TRIP800 steel sheet

The plastic deformation and ductile fracture (DF) bebaviour of a Transformation Induced Plasticity (TRIP) steel TRIP800 was investigated under different stress states and strain rates. Five specimens with different geometries were employed to obtain different stress states and deformation mechanisms. The results showed that both the stress state and strain rate have a significant effect on the mechanical properties and fracture mechanism of this alloy. It was found that the TRIP800 exhibits almost no strain-rate sensitivity below ∼0.15 plastic strain for the medium strain rates from 1 s−1 to 100 s−1. Furthermore, scanning electron microscopy (SEM) fractography studies showed that when the specimen failed under pure shear state it exhibited a shear fracture mode, while samples deformed under the uniaxial tensile and plane strain states exhibited a dominant dimple fracture mode. With an increase in the loading strain rate, the dimple fracture was restricted under lower stress triaxiality and enhanced at higher stress triaxiality, whereas the shear fracture was enhanced at a lower Lode angle.

Study of SCC of X70 Steel Immersed in Simulated Soil Solution at Different pH by EIS.

An electrochemical study of stress corrosion cracking (SCC) of API X70 steel in a simulated soil solution at different pH values (3, 8 and 10) was carried out. The stress conditions were implemented by slow strain rate stress test (SSRT) and the SCC process was simultaneously monitored by electrochemical impedance spectroscopy (EIS). Fracture surface analysis and corrosion product analysis were performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the susceptibility to SCC was higher as the pH decreases. In the acid solution, hydrogen evolution can occur by H+ and H2CO3 reduction, and more atomic hydrogen can diffuse into the steel, producing embrittlement. EIS results indicated that the anodic dissolution contributed to SCC process by reducing the charge transfer resistances during the SSRT test. While SEM micrographs shown a general corrosion morphology on the longitudinal surface of samples. At higher pH (pH 8 and pH 10), the SCC susceptibility was lower, which it is attributed to the presence of corrosion products film, which could have limited the process. Using the angle phase (φ) value it was determined that the cracking process started at a point close to the yield strength (YS).

Effect of Strain Rate on Mechanical Behavior and Microstructure Evolution of Ti-Based T110 Alloy

Recently developed thermally hardenable medium-level alloyed titanium alloy T110 was studied from the viewpoint of microstructure influence on the mechanical behavior under quasi-static and high-strain rate deformation. The globular microstructures of two types differing in aspect ratio of α-globules were formed under thermomechanical processing conditions with different reductions (εtotal = 2, and 3) and final annealing at 850 °C, 3 h. The thermally hardened state was formed by conventional solid-solution treatment at a temperature of two-phase α+β field (880 °C, 45 min), water quenching, and final aging (550 °C, 5 h). Stress–strain dependencies were estimated on tension with strain rates varied from 8·10−4 to 4·10−2 s−1, as well as compression with a strain rate of 10−3 s−1 (quasi-static) and under high-strain rates varied from 870 s−1 to 3520 s−1; the deformation with high-strain rates has been achieved using split Hopkinson pressure bar (SHPB) technique. The tested material was also assessed using strain energy (SE) parameter. A parallel study of the microstructure and crystallographic texture formed during testing allowed to propose a reliable deformation and fracture mechanisms, depending on the stress state (tension, compression) and strain rate. A special role of the initial microstructure is noted, which determines the plasticity of the tested alloy, the sites of pore nucleation, features of crack growth, as well as the localization of deformation, which is determined by the mode and rate of loading. It is established and explained why the best balance of strength and ductility, and thus, the highest SE values in the all tests carried out were ensured by the alloy in the state with a more uniform microstructure of globular morphology (after the rolling with reduction εtotal =3), which, in turn, provided general superiority over the widely used Ti-6Al-4V alloy.

Computational and Experimental Method for Assessing the Thermal Strength of High-Loaded Diesel Engines

The article discusses the reasons of fatigue failure of pistons of high-loaded diesel engines. A deformation-kinetic criterion is proposed, generalized to non-isothermal loading, which allows more correct calculation of the number of thermal loading cycles before the appearance of fatigue damage. For a specific implementation of the proposed criterion, a calculated assessment of the piston stress-strain rate was carried out using the FEM. The boundary conditions for the calculation were obtained by thermometry of the piston head on a non-motorized thermal stand (TS). Comparison of the calculated and experimental values of the number of thermal cycles before the appearance of cracks on the edge of the combustion chamber (CC) of pistons made by casting and isothermal stamping is given.

Role of stress relaxation in stress-induced polymer crystallization

Stress relaxation is a common process that reduces the deformation of polymer coils against the strain-induced crystallization during the processing of polymeric materials for fibers, thinfilms and molding plastics. By introducing Maxwell model of stress relaxation into each polymer in dynamic Monte Carlo simulations, we compared stress-induced to strain-induced polymer crystallization under parallel conditions of various strain rates and temperatures. The results demonstrated the scenario of competitions among the factors of stress relaxation, strain rates and temperatures in the crystallization process. We found that, owing to fast stretching, the limited extent of stress relaxation plays the dominantly kinetic role rather than the expected thermodynamic role in the retardation of crystallization, similar to the factor of high strain rate. In addition, we observed the enhanced stress relaxation during the post-growth process of polymer crystallization, which influences the finally achieved crystallinity and crystal morphology. Our results facilitate a better understanding of polymer crystallization during the fast stretching processing.

Diffusion-Driven Exfoliation of Magneto-Optical Garnet Nanosheets: Implications for Low Thermal Budget Integration in Si Photonics

Rare-earth iron garnets are instrumental in the development of integrated nonreciprocal passive devices such as isolators and circulators in silicon photonics. Unfortunately, monolithic integration of garnet on-chip requires annealing temperatures much higher than the thermal budget of a semiconductor foundry. Here, we report the mechanical exfoliation of large area (0.2 mm × 0.2 mm) nanosheets of a high-gyrotropy cerium-doped terbium iron garnet (CeTbIG) enabled by a strain-enhanced vacancy diffusion process that follows the Nabarro–Herring (lattice diffusion) model. Diffusivities calculated from the strain rate–stress data (1.13 × 10–18 m2s–1) identify iron and rare-earth cations as the rate-determining lattice diffusants. Cross-section scanning transmission electron microscopy reveals an exfoliation gap located ∼30 nm into the film, comparable to the cation diffusion length, which appears to verify the model. With a saturation magnetization of 18 emu cc–1 and a Faraday rotation of −2900°cm–1 at 1550 nm, the magnetic and optical properties of the nanosheets are comparable to their thin-film values. Diffusion-driven exfoliation will open foundry-acceptable pathways for heterogeneous integration of garnets on photonic waveguides and protect devices from the high-temperature processes used in crystallizing garnet films.

Strain rate dependent plasticity and fracture of DP1000 steel under proportional and non-proportional loading

To assess the effect of stress state and strain rate on damage and fracture of a commercial DP1000 steel with a very fine microstructure, an extensive series of tests were performed. Using finite element simulations, eight different sample geometries, including a dogbone, a central hole, a shear and several notched samples, were designed to achieve both proportional and non-proportional stress states using conventional test benches. Tested at quasi-static, intermediate and, dynamic deformation rates, in total 175 tests were performed. Local strain fields were obtained by digital image correlation. A correction procedure was worked out to eliminate the influence of thermal softening. After testing, scanning electron microscopy was employed to analyse the fracture surfaces. Tests and fractography allowed to draw systematic conclusions on the response of the DP1000 steel. A two-stage strain rate sensitivity of strength is found with a gradually increasing slope at low strain rates and a much steeper rise at high strain rates, which is further amplified at higher triaxiality stress states. The experimentally derived fracture loci revealed a dominant, detrimental impact of the stress triaxiality that is most pronounced at intermediate strain rates. A remarkable, non-monotonic evolution of the fracture strain with strain rate is observed: the highest values were obtained at intermediate rates. Scanning electron microscopy images of the fracture surfaces indicate a void-assisted ductile fracture, though with the occurrence of brittle features triggered at dynamic strain rates. Fracture morphology and dimple features are heavily dependent on stress state, strain rate and loading path.