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The mode of human immunodeficiency virus (HIV) transmission via injection drug use (IDU) still exists, and the recent shift in IDU-related transmission of HIV infection is largely unknown. The purpose of this study was to analyze the spatiotemporal sources and dynamics of HIV-1 transmission through IDU in Guangxi. We performed a molecular epidemiological investigation of infections across Guangxi from 2009 to 2019. Phylogenetic and Bayesian time-geographic analyses of HIV-1 sequences were performed to confirm the characteristics of transmission between IDUs in combination with epidemiological data. Among the 535 subjects, CRF08_BC (57.4%), CRF01_AE (28.4%), and CRF07_BC (10.7%) were the top 3 HIV strains; 72.6% of infections were linked to other provinces in the transmission network; 93.6% of sequence-transmitted strains were locally endemic, with the rest coming from other provinces, predominantly Guangdong and Yunnan; 92.1% of the HIV transmission among people who inject drugs tended to be transmitted between HIV-positive IDUs. HIV recombinants were high diversity, and circulating local strains were the transmission sources among IDUs in Guangxi. However, there were still cases of IDUs linked to other provinces. Coverage of traditional prevention strategies should be expanded, and inter-provincial collaboration between Guangxi, Yunnan, and Guangdong provinces should be strengthened. [ABSTRACT FROM AUTHOR]

Metals contain different kinds of spatial defects significantly reducing the fatigue performance. Accurate defect-based life prediction methods are required to improve structural integrity analysis and life design reliability. The present work developed a method to determine the equivalent crack length for defects based on continuum damage mechanics. The spatial effects of defects in the calculation of the equivalent crack were quantified and verified by fatigue tests. It is confirmed that the equivalent crack length of both slit and elliptic defects is affected not only by the defect geometry but also by the applied load. Based on the equivalent crack and combined with Paris' law, the predicted fatigue lives of various slit holes under different loading orientations are within the double scatter band and are much more accurate than the conventional projection method. • Developed a method to determine the equivalent crack length of an arbitrary defect for fatigue and fracture assessment. • Verified the developed method based on continuum damage mechanics computations and experiments. • Established a method to quantify the risk of a defect in structures. [ABSTRACT FROM AUTHOR]

In fretting fatigue, the local stress concept leads to a significant underestimation of fatigue life. Conventional fatigue models lack conservatism in dovetail structures due to mesh dependency and cumulative plastic deformations. The present study aims to develop a nonlocal life model for fretting fatigue of dovetail joints based on extensive experimental and computational analyses. Frictional work was analytically derived and utilized to describe fretting damage, combined with a multiaxial fatigue model. The developed model aligns well with experimental results under various loading conditions, with deviations falling within a double-error band. • Derived analytical expression for the frictional work to quantify the fretting damage. • Developed a nonlocal fretting fatigue model, incorporating the frictional work. • Confirmed strain localization in fretting contact simulation under cyclic plasticity. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites exhibit optimal high temperature property and complex nonlinear behaviors including irreversible deformations and stiffness degradation under different mechanical loading conditions. In the present work, the damage evolution of the material under multi-axial loads considering effects of loading-unloading cyclic was studied and a novel continuum damage constitutive model was proposed. The material degradation was decomposed into monotonic damages and cyclic damages. The anisotropic hardening behavior of the material was considered by taking orientation dependence into account. Compared to the experimental results, the constitutive model could accurately predict the stress-strain response and stiffness degradations of the oxide/oxide ceramic matrix composites for monotonic loading and cyclic loading. [ABSTRACT FROM AUTHOR]

Thermomechanical fatigue (TMF) is essential for ensuring the safety and efficiency of various thermal engineering systems, however, the underlying damage mechanisms remain unclear. In the present work, a damage evolution model is used to quantify damage mechanisms in nickel-based single-crystal superalloy DD6. The isothermal creep-fatigue model combining the fatigue and creep damages is developed to elucidate their interactions and validated by the tension-dwelling experiments. Finally, the experimentally measured TMF damage is quantitatively decomposed into fatigue, creep and extra TMF components. Significant TMF damage in the in-phase TMF is identified, especially in the [001] specimens, potentially attributed to the non-isothermal creep or oxidation, while damage in out-of-phase TMF aligns with the spiking oxidation mechanism. • Quantified effects of different damage mechanisms in thermomechanical fatigue. • Introduced continuum damage concept to describe thermomechanical fatigue damage processes. • Generated damage evolution models for isothermal fatigue, in-phase and out-of-phase thermomechanical fatigue. [ABSTRACT FROM AUTHOR]

The present paper computationally investigated and characterized thermo-mechanical crack-tip fields under elastoplastic fatigue crack growth. The Δ J -integral is generally path-dependent and its far-field value is introduced to describe the singular crack tip field under considering thermo-mechanical loading influence. The influence of crack closure in fatigue crack growth is studied and quantified for thermo-mechanical fatigue crack growth. It confirms that the incorporation of temperature cycling does not affect the solution form of the crack-tip field dominated by Δ J eff , in analogy to an isothermal fatigue crack. However, the singular crack stress and the far-field effective Δ J eff for TMF are affected by the phase angle of the thermo-mechanical loads. • The crack-tip field in the closing process can be uniquely characterized by Δ J eff,far . • The TMF Δ J -integral is an increasing function of the path size in the plastic zone. • Δ J variations imply a higher driving force under IP TMF than that under OP TMF. [ABSTRACT FROM AUTHOR]

• Established a quantified relation between thermal shock damage and porosity increment in the CMC. • Illustrated evolutions of nano-porosity and micro-porosity under cyclic thermal shock conditions. • Proposed a representation model of thermomechanical degradation of oxide/oxide ceramic matrix composites. • Clarified chemical reactions during cyclic thermal shock processes in tap water for the CMC material. The oxide/oxide ceramic matrix composites display complex mechanical behavior under thermo-mechanical loading conditions. The present work focuses on micro-structural evolution and resultant macroscopic properties during cyclic thermal shocks. Micro-structural investigation reveals that variations of nano-, micro- and macro-pores in the matrix characterize collective behavior of micro-structural evolution in the material. Material damage development is characterized by micro-cracking in the matrix and can be described by the matrix porosity increment. The present investigation confirms the unique correlation between the porosity and the micro-structural degradation evolution of the material under different loading conditions. [ABSTRACT FROM AUTHOR]

Highlights • ST-RC column is an innovative type of composite structure. • The secondary confining force was determined. • A modified superposition method was developed. • The predictions of the proposed formula fitted well with the test results. Abstract The steel tube-reinforced concrete (ST-RC) column is an innovative composite structure that has been increasingly applied in high-rise buildings and bridge piers in China. This study aims to investigate the axial capacity of the ST-RC stub column by means of a modified superposition method. Primarily, the sectional confining force equilibrium was elaborated to explain the confinement mechanism of the ST-RC column under concentric compression, which involves the confining stress induced from the inner steel tube and secondary confining stress induced from the peripheral steel hoops. Thereafter, a modified method for predicting the axial capacity of the ST-RC column, considering the secondary confinement, was developed according to a stress and strain analysis. Thirdly, 41 published specimens were collected to verify the accuracy of the proposed method. It was demonstrated that the current method fitted strongly with the tests results and exhibited satisfactory adaptability. Finally, four other methods according to ACI 318, AIJ, EC 4, and CECS 188-2005 were verified in the same scenario. It was found that the current method exhibited superior correlation with the experimental results compared with conventional approaches. It will be favorable to obtain the viable axial capacity of the ST-RC column by using the presented solution. [ABSTRACT FROM AUTHOR]

Highlights • Established a quantified relation between thermal shock and damage in the CMC. • Introduced a damage evolution model for cyclic thermal shock for the CMC material. • Illustrated correlations between energy dissipation and material damage under cyclic thermal shock conditions. • Proposed a continuum damage model for thermomechanical fatigue of the CMC material. Abstract Thermal shock is a typical loading case for high temperature components in turbines. The ceramic matrix composites become attractive for their high temperature behavior. However, their low heat conductivity makes thermal shock damage a typical damage mechanism for the turbine application. In the present paper, microstructural evolutions of the oxide/oxide ceramic matrix composite under thermal shock are studied experimentally. The mechanical behavior is related to the thermal shock temperature and cycles. The thermomechanical damage is characterized by degradation of the macroscopic elastic modulus. A thermal shock damage model is introduced based on the continuum damage mechanics principle, which can describe monotonic as well as cyclic thermal shock damage processes. [ABSTRACT FROM AUTHOR]

Highlights • Experiments confirm significant effects of multiaxial thermomechanical effects to fatigue damage. • Conventional fatigue life models cannot predict thermomechanical fatigue. • Mean stress relaxations and TMF failure mechanisms are related to varying temperature and multiaxial fatigue. • A new TMF life model has been introduced and verified by the multiaxial TMF tests. Abstract Recent investigations revealed significant differences of thermomechanical fatigue from isothermal fatigue. Quantifying effects of thermomechanical loads in fatigue life assessment is still an open issue. In the present work, extensive experiments are performed for a popular nickel-based superalloy under both isothermal and thermomechanical loading conditions to quantify the influence of varying temperature and multiaxial mechanical loads. Various multiaxial fatigue life models show significant deviations and cannot describe the thermomechanical fatigue life. Based on the experiments and failure analysis a new thermomechanical fatigue model is introduced to assess non-proportional thermomechanical loads and can calibrate thermomechanical multiaxial fatigue reasonably. [ABSTRACT FROM AUTHOR]

Highlights • Introduced and verified a multiaxial damage evolution model for porous sintered metals with varying porosity. • Established and identified a power-law relation between mechanical property and material porosity. • Proposed a prediction model for the fracture strain as function of stress triaxiality and porosity. • Illustrated damage mechanisms of the sintered metals depending on the porosity and confirmed the normal fracture as the dominant mechanism for the material failure. Abstract Micro-structure of sintered powder metals is characterized by the high porosity. Experiments confirm that the major mechanical property can be expressed in a power-law function of the porosity. In the present work the interdependence between the porosity and the elastic-plastic mechanical property as well as the damage evolution in sintered metals with varying porosity is investigated experimentally and analytically. A damage characterization is introduced based on the stiffness degradation to predict the inelastic behavior of the sintered material and the damage process. The proposed damage evolution model is further verified under multi-axial loading conditions. [ABSTRACT FROM AUTHOR]

Highlights • Introduced a new constitutive model for thermo-mechanical cyclic plasticity. • Describing the complex hardening behavior by kinematic and isotropic hardening. • Using Tanaka factor to describe non-proportional hardening under multiaxial loading. • Representing thermo-mechanical behavior by parameters from isothermal tests. Abstract High temperature components work mainly under thermo-mechanical loading conditions. Recent investigations reveal significant effects of the thermo-mechanical coupling on material behavior. In the present work, extensive experiments are performed for nickel-based superalloy Inconel 718 under both isothermal and thermo-mechanical loading conditions. Within the framework of the Ohno-Wang cyclic plasticity, a modified constitutive model is suggested to describe cyclic hardening/softening, non-proportional hardening, non-masing effects observed in the experiments. The implicit integration algorithm is developed and implemented into a commercial finite element code. Comparison between experiments and computations confirms that the suggested model can predict the cyclic plastic behavior under most different varying temperatures and multi-axial loading paths reasonably. [ABSTRACT FROM AUTHOR]

Nickel-based single-crystal alloys undergo microstructural degradation induced by thermal exposure. The directional rafting of microstructures significantly affects the mechanical properties and makes the material anisotropic. For structural design, establishing a quantitative description of microstructural effects in a constitutive model becomes essential and is still a tough research topic in multi-scale materials modeling. In the present work, the fabric tensor was correlated with the anisotropic cyclic crystal plasticity of nickel-based single-crystal alloys with the help of neural networks. The microstructural representative volume elements with various single-crystal morphologies were generated by the phase-field method and the deformation behaviors were studied under different crystal orientations and loading configurations. The neural network analysis confirmed that the fabric tensor can present anisotropic single-crystallographic microstructural features and describe mechanical behavior under both monotonic and cyclic multi-axial loading conditions. The history-dependent anisotropic cyclic hardening or softening behavior of the material can be captured by the introduced microstructural state variable. A principal component analysis (PCA) aided gradient-based attribution method was proposed to evaluate the importance of input variables. The characterization of different material components and their contribution to the stress–strain relationships are investigated and validated. The fabric tensor was verified to be an effective microstructural indicator for the continuum plasticity of single-crystal alloys. • Rafting microstructures of single-crystal alloys are represented by fabric tensors. • Anisotropic crystal behaviors are correlated with fabric tensors by neural networks. • The cosine components represent asymmetric crystallographic properties of alloys. • The PCA attribution reveals correlations of fabric tensors in constitutive modeling. [ABSTRACT FROM AUTHOR]

The present work focuses on the quantification of creep and oxidation effects in the prediction of both isothermal and thermomechanical fatigue life for a nickel-based superalloy. The creep damage was evaluated using the time-fraction method and the ductility-exhaustion method. A diffusion-dominated environmental damage parameter was proposed based on the mechanism of oxygen-assisted intergranular cracking and applied to thermomechanical fatigue life assessment. The results revealed that creep damage appears to be negligible and environmental damage seems more dominant in the current study. The proposed model provides a unified description for both isothermal and thermomechanical fatigue. • Confirmed the linear accumulation model for creep-fatigue damage in the vacuum but not in the air. • Quantified the significant influences of the oxygen environment on TMF damage process. • Established a mechanism-based unified life prediction model for IF, C-F and TMF. [ABSTRACT FROM AUTHOR]

The crack-tip fields of elastoplastic fatigue crack growth with crack closure are studied and correlated to the Δ J -integral. Computational results confirmed that the singularity of the effective stress ranges of the opening process reduces with increasing crack closure, whereas the effective stress ranges from the closing process possess the known HRR solution form. The far-field Δ J eff -integral can be used to characterize the crack-tip field stress in the closing process, which is not affected by the loading ratio and by the path dependence of the Δ J -integral. Based on extensive FEM computations, an estimation formula for the effective Δ J eff -integral was proposed for various loading ratios and plastic hardening materials. The in-plane constraint effects in fatigue crack growth can be quantified based on the J − Q concept of elastoplastic fracture mechanics, within the frame of Δ J eff - Q characterization. The relationship between Q and the transverse stress defined in the closing processes was established for a quantitative description of the crack tip constraint. • The crack-tip field in the closing phase can be uniquely characterized by the effective far-field Δ J-integral. • The crack closure affects the stress singularity and the Δ J-characterization in the opening-phase stress field. • The constraint effect on fatigue crack growth can be controlled by the effective far-field Δ J-integral together with the Q factor. [ABSTRACT FROM AUTHOR]

Highlights • Low-cycle fatigue behavior of corroded RC beams are studied experimentally. • The fatigue cycles decreased with the increase of mass loss. • The fatigue design curve of CEB-FIP 2010 is safe for corroded RC beams. Abstract The study performs experimental investigation of the behavior of reinforced concrete (RC) beams with corroded steel reinforcement under low-speed and low-cycle fatigue loads. A total of 14 specimens were tested. The results indicated that the fatigue life cycles decreased by 88.7% when the mass loss increased from 1.56% to 12.56%. The fatigue lives from the present tests were compared with those from other experimental studies and predictions from the CEB-FIP 2010 code and indicated that the fatigue life of concrete estimated by the code is safe for a corroded beam under low-cycle fatigue loading. [ABSTRACT FROM AUTHOR]

Highlights • Highlighted several models for cracks with severe constraint effects. • Critical reviewed cohesive zone models for three-dimensional cracks. • Discussed fatigue damage accumulation as well as constraint effects in three-dimensional fatigue crack modeling. Abstract Damage tolerance assessment is a keen topic in modern industrial product design. Under certain loading conditions fatigue crack growth is elastoplastic and the Paris' law becomes not applicable. In the past decades numerous cohesive zone models were proposed and investigated for predicting elastoplastic fatigue crack growth. However, three-dimensional cracks were not considered properly. The constraint effects to cohesive zone modeling were not explicitly studied so that the three-dimensional crack cannot be analyzed reasonably. Different cyclic cohesive zone models were introduced but lacking in experimental verifications. In the present paper cohesive zone models for three-dimensional crack growth under both monotonic and cyclic loading conditions are critically reviewed and commented. Suggestions are given with respect to engineering applications. [ABSTRACT FROM AUTHOR]

This paper reviews current design code models such as AISI, Australian Standards, Eurocode 3, GB 50018, and some empirical models proposed by researchers for calculating corner yield strength and average yield strength of the full section. The experimental database of 102 carbon steel tensile coupon tests in the literature is utilized to evaluate applicability and reliability of these models. The cross-section types, strength of steel and thickness of section are considered in the database. After comparison and investigation, three new suggested empirical methods for predicting the corner yield strength are suggested. It is demonstrated that the new suggested models fit well with the experimental data and exhibit satisfactory adaptability, which can be easily used for engineering designs. Finally, the limiting values of the strength of the steel and the ratio of inner corner radius to thickness are suggested. • The methods of the yield strength of corner considered cold formed effect are collected and analyzed • 102 experimental test data are collected, including various section shapes • Suggested empirical formulas are presented • Verification and limitations of the models are given [ABSTRACT FROM AUTHOR]

Inflammation plays a significant role in the development of obesity-related complications, but the molecular events that initiate and propagate such inflammation remain unclear. Here, we report that mice fed a high-fat diet (HFD) for as little as 1-3 days show increased differentiation of myeloid progenitors into neutrophils and monocytes but reduced B lymphocyte production in the bone marrow. Levels of neutrophil elastase (NE) and the nuclear factors CCAAT/enhancer-binding protein α (C/EBPα) and growth factor-independent 1 (GFI-1) are elevated in hematopoietic stem and progenitor cells from HFD-fed mice, but mice lacking either NE or C/EBPα are resistant to HFDinduced myelopoiesis. NE deletion increases expression of the inhibitory isoform of p30 C/EBPα, impairs the transcriptional activity of p42 C/EBPα, and reduces expression of the C/EBPα target gene GFI-1 in hematopoietic stem and progenitor cells, suggesting a mechanism by which NE regulates myelopoiesis. Furthermore, NE deletion prevents HFD-induced vascular leakage. Thus, HFD feeding rapidly activates bone marrow myelopoiesis through the NE-dependent C/EBPα-GFI-1 pathway preceding vascular damage and systemic inflammation. [ABSTRACT FROM AUTHOR]

The martensitic phase transformation of the metastable austenitic steel increases yield strength and ultimate stress, but decreases ductility. Evolution of the martensite depends on both plastic strain and stress triaxiality. Experiments at room temperature reveal that the martensitic phase transformation in the austenitic stainless steel 06Cr19Ni10 becomes obvious only for large strains, e.g. > 30 % . Increasing the material temperature may diminish the phase transformation significantly. By testing specially fabricated specimens, the cold hardening of the material was decomposed into a plastic strain related part and a martensitic phase part. Comparison with experiments confirms that the mechanical behavior of the austenitic-martensitic material can be described by J 2 plasticity, combining with the Santacreu model for the phase transformation. Furthermore, the stress-controlled fatigue experiments on the distorted stainless steel display that in the high cycle fatigue regime the plastic strain improves the material's fatigue resistance, while the martensitic phase transformation increases the fatigue property in the finite life regime. However, in the ε - N diagram the benefits from the martensitic phase transformation decrease with loading amplitude and the plastic deformation may reduce fatigue performance. In the LCF region the distorted material shows generally worse fatigue property than the base material. [ABSTRACT FROM AUTHOR]

Experimental investigations reveal very different damage mechanisms in porous sintered metals from those of conventional dense materials. Interactions between the inherent porosity and heterogeneous matrix result in complicated deformation behavior and fatigue damage processes. In the present work, the damage evolution in the sintered metal under multi-axial cyclic loading conditions is studied experimentally and computationally. The total damage is divided into the stress-related elastic damage, the plastic damage induced by the plastic deformations and the fatigue damage driven by cyclic loading. To predict the cyclic deformation behavior as well as the fatigue damage evolution, a nonlinear fatigue damage model coupled with the critical plane concept is proposed, embedded into the Ohno–Wang cyclic plasticity and implemented into the FEM software ABAQUS based on an implicit integration algorithm. The proposed damage model is computationally and experimentally verified under multi-axial cyclic loading paths with different strain amplitudes. A good agreement between experimental and computational results shows that the present model is able to describe cyclic mechanical behavior and fatigue damage of porous metals. [ABSTRACT FROM AUTHOR]