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A fundamental prerequisite for obtaining realistic finite element simulation of machining processes, which has become a key machinability assessment for metals and alloys, is the establishment of a reliable material model. To obtain the constitutive model for wire–arc additive-manufactured ATI 718Plus, Hopkinson pressure bar is used to characterise the flow stress of the alloy over a wide range of temperatures and strain rates. Experiment results show that the deformation behaviours of as-deposited ATI 718Plus superalloy are influenced by the applied strain rate, test temperature and strain. Post-deformation microstructures show localised deformation within the deposit, which is attributable to the heterogeneous distribution of the strengthening precipitates in as-deposited ATI 718Plus. Furthermore, cracks are observed to be preferentially initiated at the brittle eutectic solidification constituents within the localised band. Constitutive models, based on the strain-compensated Arrhenius-type model and the modified Johnson–Cook model, are developed for the deposit based on experimental data. Standard statistical parameters, correlation coefficient ( R ), root-mean-square error ( RMSE ) and average absolute relative error ( AARE ) are used to assess the reliability of the models. The results show that the modified Johnson–Cook model has better reliability in predicting the dynamic flow stress of wire–arc-deposited ATI 718Plus superalloy.

The mechanical behavior of titanium alloys has been mostly studied in quasi-static conditions when the strain rate does not exceed 10 s−1, while the studies performed in dynamic settings specifically for Ti-based composites are limited. Such data are critical to prevent the “strength margin” approach, which is used to assure the part performance under dynamic conditions in the absence of relevant data. The purpose of this study was to obtain data on the mechanical behavior of Ti-based composites under dynamic condition. The Metal Matrix Composites (MMC) on the base of the alloy Ti-6Al-4V (wt.%) were made using Blended Elemental Powder Metallurgy with different amounts of reinforcing particles: 5, 10, and 20% of TiC or 5, 10% (vol.) of TiB. Composites were studied at high strain rate compression ~1–3 × 103·s−1 using the split Hopkinson pressure bar. Mechanical behavior was analyzed considering strain rate, phase composition, microstructure, and strain energy (SE). It is shown that for the strain rates up to 1920 s−1, the strength and SE of MMC with 5% TiC are substantially higher compared to particles free alloy. The particles TiC localize the plastic deformation at the micro level, and fracturing occurs mainly by crushing particles and their aggregates. TiB MMCs have a finer grain structure and different mechanical behavior. MMC with 5 and 10% TiB do not break down at strain rates up to almost 3000 s−1; and 10% MMC surpasses other materials in the SE at strain rates exceeding 2200 s−1. The deformation mechanism of MMCs was evaluated.

The deformation behaviors of Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 eutectic high-entropy alloy (EHEA) under high strain rates have been investigated at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). The current Co0.96Cr0.76Fe0.85Ni1.01Hf0.40 EHEA exhibits a high yield strength of 740 MPa along with a high fracture strain of 35% under quasi-static loading. A remarkable positive strain rate effect can be observed, and its yield strength increased to 1060 MPa when the strain rate increased to 3000/s. Decreasing temperature will further enhance the yield strength significantly. The yield strength of this alloy at a strain rate of 3000/s increases to 1240 MPa under the LNT condition. Moreover, the current EHEA exhibits a notable increased strain-hardening ability with either an increasing strain rate or a decreasing temperature. Transmission electron microscopy (TEM) characterization uncovered that the dynamic plastic deformation of this EHEA at RT is dominated by dislocation slip. However, under severe conditions of high strain rate in conjunction with LNT, dislocation dissociation is promoted, resulting in a higher density of nanoscale deformation twins, stacking faults (SFs) as well as immobile Lomer–Cottrell (L-C) dislocation locks. These deformation twins, SFs and immobile dislocation locks function effectively as dislocation barriers, contributing notably to the elevated strain-hardening rate observed during dynamic deformation at LNT.

The impact mechanics of micrometre-scale metal particles with flat metal surfaces is investigated for high-velocity impacts ranging from 50 m s−1 to more than 1 km s−1, where impact causes predominantly plastic deformation. A material model that includes high strain rate and temperature effects on the yield stress, heat generation due to plasticity, material damage due to excessive plastic strain and heat transfer is used in the numerical analysis. The coefficient of restitution e is predicted by the classical work using elastic–plastic deformation analysis with quasi-static impact mechanics to be proportional to Vi−1/4 and Vi−1/2 for the low and moderate impact velocities that span the ranges of 0–10 and 10–100 m s−1, respectively. In the elastic–plastic and fully plastic deformation regimes the particle rebound is attributed to the elastic spring-back that initiates at the particle–substrate interface. At higher impact velocities (0.1–1 km s−1) e is shown to be proportional to approximately Vi−1. In this deeply plastic deformation regime various deformation modes that depend on plastic flow of the material including the time lag between the rebound instances of the top and bottom points of particle and the lateral spreading of the particle are identified. In this deformation regime, the elastic spring-back initiates subsurface, in the substrate.

Adiabatic shear bands (ASBs) are known to be the dominant damage mechanisms in structural materials under high strain rate loading such as magnesium (Mg) alloys. Therefore, to tailor the mechanical performance of Mg alloys for structural applications, there is a need to understand their susceptibility to strain localization and formation of ASBs, including the mechanism of crack initiation and propagation. In this study, as-fabricated (extruded) and heat-treated (annealed at 400 °C) AZ31B Mg alloys were subjected to high strain rate loading using the direct impact Hopkinson pressure bar (DIHPB) under different strain rates (834–2435 s−1) at room temperature. The impact specimens failed through the occurrence of strain localization, formation of diffused ASBs, and initiation/propagation of micro-cracks along the path of evolved ASBs. Thus, strain localization results in crack initiation and propagation despite the inherent brittle nature of the Mg alloys. Furthermore, in regions with evolved shear bands, there was a low occurrence of twin/micro-twins. This observation suggests that shear band formation dominates over the micro-twinning effect in Mg alloys. Also, the presence of fractured second-phase particles dispersed within voids and along shear band path suggests particle fragmentation and refinement due to the strain localization. Second-phase particle fragmentation also played a role in void nucleation, growth, and coalescence during the deformation. In addition, there seems to be a threshold strain rate (~>2225 s−1) beyond which the specimen fractures regardless of the initial microstructure of the Mg alloys.

To study the dynamic mechanical properties and damage evolution mechanism of Beishan deep granite under medium and high strain rates, dynamic mechanical tests for the deep granite specimens with different strain rates were conducted using the split Hopkinson pressure bar (SHPB) device. The improved Zhu–Wang–ang (ZWT) dynamic constitutive model was established, and the relationship between strain rate and strain energy was investigated. The test results show that the strain rate in the dynamic load test is closer to the strain rate in the rock blasting state when the uniaxial SHPB test is applied to the granite specimens in a low ground stress state. Peak stress has a linear correlation with strain rate, and the dynamic deformation modulus of the Beishan granite is 152.58 GPa. The dissipation energy per unit volume and the energy ratio increase along with the strain rate, whereas the dissipation energy per unit volume increases exponentially along with the strain rate. There is a consistent relationship between the damage degree of granite specimens and the dissipation energy per unit volume, which correspond to one another, but there is no one-to-one correspondence between the damage degree of granite specimens and the strain rate. To consider the damage and obtain the damage discount factor for the principal structure model, the principal structure of the element combination model was improved and simplified using the ZWT dynamic constitutive model. The change of damage parameters with strain rate and strain was obtained, and the dynamic damage evolution equation of Beishan granite was established by considering the damage threshold.

The effect of strain rates (έ) on the microstructure, texture, and mechanical properties of the Mg–5Zn–0.6Mn alloys during high strain rate rolling at 300 °C are studied. Increasing έ promotes dynamic recrystallization (DRX). The DRX grain grows from 1.0 to 3.4 μm, and the DRX volume fraction increases from 76 to 93% with έ rising from 10 to 25 s –1 . The maximum intensity values of basal texture decrease from 2.74 to 2.09 with increasing έ. The texture weakening is mainly attributed to the increase in DRX volume fraction and the number of tensile twins. The alloy sheets rolled at 10 s –1 possess optimal comprehensive mechanical properties (the tensile strength of 321 MPa, yield strength of 240 MPa, and elongation of 24.9%), attributing to the smallest DRX grain size, and the largest geometrically necessary dislocations density and precipitation density. Graphical abstract

The present study focuses on the mechanical behaviour and formability of the aluminium alloy 2024-T3 in sheet form with a thickness of 0.8 mm. For this purpose, tensile tests at quasi-static and intermediate strain rates were performed using a universal testing machine, and high strain rate experiments were performed using a split Hopkinson tension bar (SHTB) facility. The material’s anisotropy was investigated by considering seven different specimen orientations relative to the rolling direction. Digital image correlation (DIC) was used to measure specimen deformation. Based on the true stress–strain curves, the alloy exhibited negative strain rate sensitivity (NSRS). Dynamic strain aging (DSA) was investigated as a possible cause. However, neither the strain distribution nor the stress–strain curves gave further indications of the occurrence of DSA. A higher deformation capacity was observed in the high strain rate experiments. The alloy displayed anisotropic mechanical properties. Values of the Lankford coefficient lower than 1, more specifically, varying between 0.45 and 0.87 depending on specimen orientations and strain rate, were found. The hardening exponent was not significantly dependent on specimen orientation and only moderately affected by strain rate. An average value of 0.183 was observed for specimens tested at a quasi-static strain rate. Scanning electron microscopy (SEM) revealed a typical ductile fracture morphology with fine dimples. Dimple sizes were hardly affected by specimen orientation and strain rate.

A dislocation density-based model for alloy 718 in the annealed state is proposed in order to accurately describe the deformation behavior of this alloy for a wide range of thermo-mechanical loadings. The model accounts for numerous microstructural mechanisms, including strain hardening, grain size effect, dynamic strain aging (DSA), solid solution strengthening, as well as phonon and electron drag which affects dislocation movements at high strain rates. Two types of recovery mechanisms are also included: recovery due to dislocation glide and recovery associated with cross-slip of screw dislocations. The model is calibrated using experimentally determined stress–strain curves for both low and high strain rates in the order of 10–3 to 103 s−1, and for temperatures in the range 20 °C to 800 °C. The stress–strain data computed with the model are in good agreement with the experimental data. The inclusion of DSA is found to be effective in the combination of temperatures and strain rates corresponding to experimental observations. The solid solution strengthening contribution increases with decreasing temperature and increasing strain rate. The drag effect in the model proves to be significant only for deformation at high strain rate (~ 103 s−1).

The effect of strain rate on the microstructure and deformation mechanism of a Mg–Y–Nd–Zr alloy was studied. The microstructure and texture were examined by optical microscopy and electron backscatter diffraction, and the dislocation structures were observed by transmission electron microscopy. The results showed that the Mg–Y–Nd–Zr alloy exhibited positive strain rate sensitivity under high-strain-rate compression. At a strain rate of 830 s −1 , many grains were re-oriented owing to the formation of a large number of tensile twins in the specimen. With increasing strain rate, the number of extension twins decreased, but those of contraction twins, double twins, and < c + a > dislocations increased. The dominant deformation mechanism of the material changed from extension twin-dominated deformation to extension twin- and < c + a > slip-dominated deformation.