The low-cycle fatigue (LCF) properties of multi-directional forging (MDF) and conventional extruded AZ31 magnesium alloy were evaluated by strain-controlled fatigue tests. The results show that MDF greatly improves the strength of AZ31 alloy, but slightly decreases the plasticity. Generally speaking, LCF life is closely related to plasticity. However, MDF samples still exhibit superior LCF properties even with reduced plasticity. The enhanced LCF life of MDF samples can be attributed to the decrease of tension-compression yield strength asymmetry caused by grain refinement and texture weakening. This makes MDF samples have low average stress and reduced hysteresis energy during cyclic loading. Simultaneously, MDF samples have a large fatigue crack stable propagation (FCSP) area, manifesting large critical crack size due to high toughness. These are helpful to alleviate fatigue damage and retard the nucleation and propagation of fatigue cracks.

Multi-direction forging (MDF) was used for the preparation of fine-grained AZ31 magnesium alloy. The uniaxial ratcheting behaviors were studied by conducting stress-controlled cyclic experiments under various loading conditions in ambient air. When elastic strain dominates ratcheting deformation, ratcheting strain keeps constant during cycling and is sensitive to mean stress. When dislocation slipping dominates, ratcheting deformation is similar to that of other metals. And MDF alloy shows high ratcheting strain than extruded counterpart due to significant dislocation activity at the same normalized loading conditions. When twinning involved, it can decrease the ratcheting strain, but aggravate fatigue lifetime due to increased accumulated cyclic damage and prior crack initiation sites. In addition, a modified energy-based model, which takes account for both the effects of tensile and compressive strain energy, was proposed to well predict the ratcheting lifetime of the AZ31 alloys.

Zhang, Lijun MD; Chen, Dong BS; Long, Yu MD; Li, Lingyi MD; Lyu, Yanlin MD; Meng, Meijun MD; Ma, Yuying MD; Wu, Yanjun MD; Leung, Felix W MD; Sha, Weihong MD; Chen, Hao PhD; Liu, Yufeng MD, PhD Author Information

This paper investigated the low cycle fatigue properties of ultrafine-grained Cu with equiaxed or lamellar grains. Although the lamellar grained structure shows higher cyclic softening than the equiaxed one, it exhibits a low-cyclic fatigue life improvement. This contradictory can be explained by the homogeneously distributed cyclic damage in the lamellar grained structure which presents a rotational dynamic recrystallization-led grain refinement and the significant intersecting shear bands during low cyclic fatigue. Simultaneously, plenty of secondary cracks in lamellar grained structure further retard the crack propagation by decreasing the stress concentration at the tip of main crack. The results manifest that the grain morphology is an important microstructural parameter controlling the low cyclic fatigue performance.

OBJECTIVE To develop a tri-light warning system for the early warning of novel coronavirus pneumonia (COVID-19) and stratification of patients. MATERIALS AND METHODS The system extracts radiomic features from CT images and integrates clinical record information to output a prediction probability and credibility of each prediction. It classifies patients in the general ward into red (high risk), yellow (uncertain risk), and green (low risk) labels. The system was tested using a multi-center cohort of 8,721 patients. RESULTS The system demonstrated reliability and performance validation under data distribution shifts, and was applicable to both the original strain and variant strains of COVID-19. DISCUSSION The tri-light warning system has the potential to improve patient stratification performance and identify epidemiological risks early, thus allowing for timely treatment and optimization of medical resource allocation. CONCLUSION The tri-light warning system based on conformal prediction is a reliable and effective method for the early warning and stratification of COVID-19 patients. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by the Young Scientists Fund of the National Natural Science Foundation of China (grant No. 82202150 to Xiao Li). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The protocol of this multi-center study was approved by the institutional review board of Jinling Hospital, Nanjing University School of Medicine (2020NZKY-005-02). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes The data that support the findings of this study are available on request from the corresponding author (G.M.L.). The data with participant privacy/consent are not publicly available due to hospital regulation restrictions.

Critical patients and intensive care unit (ICU) patients are the main population of COVID-19 deaths. Therefore, establishing a reliable method is necessary for COVID-19 patients to distinguish patients who may have critical symptoms from other patients. In this retrospective study, we firstly evaluated the effects of 54 laboratory indicators on critical illness and death in 3044 COVID-19 patients from the Huoshenshan hospital in Wuhan, China. Secondly, we identify the eight most important prognostic indicators (neutrophil percentage, procalcitonin, neutrophil absolute value, C-reactive protein, albumin, interleukin-6, lymphocyte absolute value and myoglobin) by using the random forest algorithm, and find that dynamic changes of the eight prognostic indicators present significantly distinct within differently clinical severities. Thirdly, our study reveals that a model containing age and these eight prognostic indicators can accurately predict which patients may develop serious illness or death. Fourthly, our results demonstrate that different genders have different critical illness rates compared with different ages, in particular the mortality is more likely to be attributed to some key genes (e.g. ACE2, TMPRSS2 and FURIN) by combining the analysis of public lung single cells and bulk transcriptome data. Taken together, we urge that the prognostic model and first-hand clinical trial data generated in this study have important clinical practical significance for predicting and exploring the disease progression of COVID-19 patients.

The characteristics of COVID-19 patients with autoimmune rheumatic diseases (AIRD) have rarely been reported. Patients with AIRD have suppressed immune defense function, which may increase their susceptibility to COVID-19. However, the immunosuppressive agents AIRD patients routinely used may be beneficial for protecting the cytokine storm caused by SARS-CoV-2. In this retrospective study, we included all confirmed cases in Huoshenshan Hospital from February 4 to April 9. Data were extracted from electronic medical records and were analyzed for clinical and laboratory features using SPSS (version 25.0). Of 3059 patients, 21 had the comorbidities with systematic lupus erythematosus (SLE) and/or rheumatoid arthritis (RA), including 5 with SLE, 15 with RA, and 1 with Rhupus. The proportion was 57.1% for severe cases, 61.9% for either severe or critical cases, and 4.8% for critical cases. The main manifestations, ARDS and ICU admission rate, as well as the mortality and length of hospital stay of COVID-19 in AIRD patients were similar to COVID-19 patients in the general population. Our preliminary experience shows that patients with AIRD tend to have a higher risk of SARS-CoV-2 infection, and may be at risk for a severe but less likely critical disease course. Further investigation is needed to understand the immunological features of these diseases.

Uniaxial ratcheting behavior of an extruded Mg-10Gd-3Y rare-earth magnesium alloy was studied by performing stress-controlled cyclic tension experiments in ambient air. The effects of mean stress and stress amplitude on the ratcheting response and the ratcheting lifetime were explored. As the mean stress or the stress amplitude was increased, the ratcheting strain multiplied, whereas the ratcheting lifetime was shortened. Compared to the conventional Mg alloys, the addition of rare-earth elements suppressed the twinning/de-twinning events and restricted the development of ratcheting strain. In addition, dynamic precipitations were developed during the ratcheting deformation of the Mg-10Gd-3Y alloy at room temperature. This cyclic stress-induced dynamic precipitation is thought to play a critical role in the strong cyclic hardening exhibited during the ratcheting deformation of the Mg-10Gd-3Y alloy. A modified fatigue parameter, which takes account for both the effects of mean stress and stress amplitude, was proposed to well predict the ratcheting lifetime of the Mg-10Gd-3Y alloy.

AZ31 magnesium alloy sheet was produced through variable-plane rolling (VPRing) under different temperatures, and a conventional rolled AZ31 alloy was investigated for comparison. A basal texture was formed during these two processes. The texture intensity was closely related to dynamic recrystallization and deformation mechanism. Four types of twins appeared, namely {10-12} extension twins, {10-13} and {10-11} contraction twins and {10-11}-{10-12} double twins. High rolling temperature and rolling plane alteration were beneficial for activating {10-11}-{10-12} double twins. The tensile strengths revealed a declining trend with elevated rolling temperatures. The AZ31 alloy rolled at 573 K showed advantageous combination with a high yield strength of 286 MPa and compromised elongation of 5%. The mechanical anisotropy of VPRed AZ31 sheet decreased with nearly similar yield strengths along the roll direction (RD), transverse direction and 45° away from the RD. The VPRing process improved the rollability and strength of Mg alloy and reduced its mechanical anisotropy.

AZ31 magnesium alloy was produced via variable-plane rolling (VPR) under different temperatures. The effects of rolling temperature on the microstructure, texture and mechanical properties were investigated. A double-peak basal texture was formed during VPR treatment. Dynamic recrystallization (DRX) was observed during the VPR treatment, and it can reduce the texture intensity owing to the coalescence of sub-grains. Four types of twins were observed in the VPR treatment: {10-12} extension twins, {10-13}, {10-11} contraction twins and {10-11}-{10-12} double twins. The suitable temperature of AZ31 magnesium alloy for VPR treatment is determined as 623 K through experiments with tensile yield strength of 240 MPa, compressive yield strength of 162 MPa and elongation of 13%. Owing to the important impact of temperature on mechanical properties, the alloy was further VPRed with a decrease in temperature pass-by-pass. The high temperature of 623 K at the initial passes randomized the texture, which led to notably high ductility.

The uniaxial ratcheting behavior of ultrafine-grained pure Cu processed by equal-channel angular pressing (ECAP) was investigated through uniaxial asymmetric cyclic stress-controlled experiments at room temperature. The effects of the mean stress and stress amplitude on the uniaxial ratcheting response and ratcheting life of the ECAP Cu were analyzed. With increasing mean stress or stress amplitude, the ratcheting strain and its rate increased, but the ratcheting life decreased. An approach based on Basquin's method was used to describe the fatigue lifetime of the ECAP pure Cu. Additionally, a power law relationship was adopted to describe the cyclic steady creep rate. Finally, the microscopic and macroscopic fracture features were examined. It was found that at high peak stresses, cyclic creep governs the overall failure process; otherwise, cyclic creep-fatigue interaction is the dominant failure mode.

An attempt is made to rationalize the effect of pre-strain history on fatigue behaviors of AZ31 magnesium alloy. Axial fatigue tests were conducted in the extruded and pre-compressioned AZ31 alloy under low cycle total strain control fatigue conditions. The pre-strain process influences the plastic deformation mechanism activated during fatigue deformation, especially during tensile loading, by enhancing the activity of detwinning mechanism. The low-cycle fatigue lifetime of extruded AZ31 alloy can be enhanced by the pre-compression process. And the hysteresis energy was successfully used to predict the low-cycle fatigue lifetime.

The microstructural evolution and mechanical properties of AZ31 magnesium alloy produced by variable-plane rolling (VPR) were investigated. Two types of weak textures were formed: basal texture in odd pass and double-peak basal texture in even pass. Dynamic recrystallization (DRX) was observed during the VPR treatment, and the nucleation of grains during DRX was dependent on the coalescence of subgrains. Three types of twins were observed in the VPR treatment: {10-12} extension twins, {10-13} contraction twins and {10-11}-{10-12} double twins. The {10-11}-{10-12} double twinning is the underlying mechanism in the formation of the double-peak texture. Tensile testing revealed improved strength without loss of ductility. The Hall–Petch relationship can be used to describe the strengths in any even pass with the same texture. The significant strengthening is ascribed to the refined grain, twin boundaries, texture hardening, and high dislocation density.

The fatigue properties of variable-plane-rolled (VPRed) and conventional extruded AZ31 magnesium alloy were investigated using total strain-controlled fatigue tests with various applied strain amplitudes. The results indicated that both the strength and elongation of the VPRed samples were higher than those of the conventional extruded samples because of their refined grain size and weak texture. Consequently, the fatigue lives of the VPRed samples were longer than those of the conventional extruded samples under strain-controlled cyclic loadings. The Manson–Coffin and Basquin approaches were used to describe the fatigue lifetime of this wrought AZ31 alloy. Finally, the microscopic and macroscopic fracture features were examined. The conventional extruded sample contained more extensive and well-developed twins than the VPRed sample in the stable propagation area of the cracks. The appearance of residual twins in the fracture surface resulted from the competition between the reverse plastic zone size ahead of the crack tip and the cyclic hardening–softening characteristic.

A flawless bulk AZ31 magnesium alloy with extensive mechanical twins was produced by variable-plane rolling, in which the sample was rotated 900 around its longitudinal axis between passes. The unique orientation relationship between the parent grains and the twin grains favours twinning during variable-plane rolling, which leads to the formation of extensive twins. Tensile testing revealed an excellent balance of mechanical properties, with a yield strength of 280 MPa and 15.5% elongation to failure. The significant strengthening originates from the effective blockage of glide dislocations by numerous conventional grain boundaries and twin boundaries. A weak double-peak (slightly off-basal) texture is formed during variable-plane rolling, which helps in achieving the desired level of ductility. (C) 2014 Elsevier Ltd. All rights reserved.

The low-cycle fatigue properties of extruded Mg-10Gd-2Y-0.5Zr (GW102k) magnesium alloy have been studied and compared to those of conventional extruded AZ31 magnesium alloy. Typical post-fatigue microstructure and surface morphology features are presented for both the GW102k and AZ31 alloy. It is found that GW102k alloy contains a large amount of precipitated particles and possesses a relatively weak basal texture, which gives rise to near symmetric yield asymmetry. Different from AZ31 alloy, the GW102k alloy shows near-symmetric stress-strain hysteresis loops and marginal cyclic hardening. This symmetry significantly reduces tensile mean stress during low-cycle fatigue process. Due to the small reversible plastic zone size, the GW102k alloy shows rough faceted fracture surfaces in the fatigue crack propagation zone. Accordingly, the low-cycle fatigue life of GW102k alloy is found to be longer than that of AZ31 alloy. (C) 2013 Elsevier Ltd. All rights reserved.

Deformation twinning is widely observed in face-centered cubic (fcc) metals. The stress for activating twinning is an important issue to be solved. We presented an expression linking to twinning stress based on the total energy change associated with the formation of a twinning nucleus according to the classical nucleation theory. We assume there exist no energy fluctuations to overcome the nucleation barrier. The expression can predict the twinning stress for fcc metals, which is in excellent agreement with experimental results with simple form. Finally, we introduce a measure twinability to quantify the propensity of fcc metals to twin as opposed to cross-slip.

通过恒应变控制疲劳实验,比较了常规挤压与等径角变形AZ31镁合金的疲劳寿命、表面变形形貌和疲劳断口.结果表明,等径角变形AZ31镁合金在疲劳过程中表现出明显的循环软化,且应变幅越大,软化越显著;晶粒在循环过程中发生再结晶行为,其长轴沿着等径角变形的剪切方向;等径角变形工艺可以显著延长镁合金的低周疲劳寿命,归因于疲劳延性系数的增加;由于裂纹尖端的疲劳塑性区尺寸较小,等径角变形合金断口表面较为平坦.

Magnesium alloy Mg-3%Al-1%Zn (AZ31) billets prepared from equal channel angular pressing (ECAP) were utilized in low-cycle fatigue tests in order to investigate their fatigue life. Fully reversed strain-controlled tension-compression fatigue tests were conducted at the frequency of 1 Hz in ambient air. The microstructures were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The hysteresis loops of the ECAP processed and conventionally extruded samples display obviously different shapes in the total strain amplitude range from 0.2% to 0.6%. Accordingly, the low cycle fatigue lives of ECAP processed samples are found to be longer than those of extruded samples, which can be attributed to the different in the hysteresis energy incorporating tensile strain energy.

The lowq-cycle fatigue properties of Mgq-8Alq-0.5Zn (AZ80) magnesium alloy have been studied as a function of precipitation state. It has been shown that the presence of precipitates significantly reduces tensionq-compression yield asymmetry, compared with solution treated material. This decreased asymmetry significantly reduces tensile mean stress during lowq-cycle fatigue process. As the cyclic deformation progressed, an abrupt increase in the plastic strain amplitude prior to failure is observed, representing the onset of fatigue crack initiation. This increase disappears in the aged sample, which leads to the significantly decreased area of crack propagation zone, and shorter lifetime. Due to the enlarged reverse plastic zone size, the aged sample showed microscopically rough faceted fracture surfaces in the fatigue crack propagation zone. (C) 2012 Elsevier Ltd. All rights reserved.