Deformation mechanism of fine structure and its quantitative relationship with quasi-static mechanical properties in near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr −2.9Zn alloy

The deformation mechanism of the fine structure composed of primary α phase (α_p) and acicular secondary α phase (α_s) on quasi-static mechanical properties is still not very clear. The main controversy is focused on the role of α_p in the mechanical behavior. In this paper, the microstructure of the heat-treated near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy after tensile tests was observed by transmission electron microscopy (TEM). And the results showed that in the slight deformation region the dislocations were accumulated at the intersection of α_p and β matrix separated by α_s, while only a few dislocations nucleated in β matrix. In the severe deformation region, a large quantity of dislocations in both α_p and β matrix were observed. It can be inferred that α_p deformed firstly and then activated the deformation of β matrix, that is, the thickness of α_p and the inter-particle spacing of α_s played a dominant role in the deformation process. The quantitative relationship between the yield strength and the microstructure parameters is consistent with this inference. By adjusting the solution treatment parameters and the subsequent aging treatment, three fine structures were obtained, and the corresponding mechanical properties were determined. Furthermore, the yield strength can be described by the mathematical model σ_y ​= ​756.4 ​+ ​135.6/h_p^1/2 +32.2/d_s^1/2, where h_p and d_s are the thickness of α_p and the inter-particle spacing of α_s, respectively.     

Hot deformation map and its application of GH4706 alloy

The hot deformation behaviors of GH4706 alloy were investigated using compression tests in a deformation temperature range from 900℃ to 1200℃ with a strain rate range of 0.001–1 s?1. Hot processing maps were developed on the basis of the dynamic material model and compression data. A three-dimensional distribution of power dissipation parameter (η) with strain rate and temperature reveals that η decreases in sensitivity with an increase in strain rate and a decrease in temperature. Microstructure studies show that the grain size of GH4706 alloy increases when η is larger than 0.32, and the microstructure exhibits local deformation when η is smaller than 0.23. The hot processing map at the strain of 0.7 exposes a domain peak at η=0.32 for the temperature between 940℃ and 970℃ with the strain rate from 0.015 s?1 to 0.003 s?1, and these are the optimum parameters for hot working.     

Ti-7333合金β锻动态再结晶行为

 利用Gleeble3800热模拟试验机研究了在温度870～970℃和应变速率0.001～10s^-1范围内,近β钛合金Ti-7333 β锻热变形的组织演化规律及动态再结晶行为.实验结果表明,Ti-7333钛合金在温度较高、应变速率较低的情况下变形时,表现出典型的动态再结晶行为,动态再结晶晶粒尺寸和再结晶体积分数均随变形温度升高和变形速率降低而增大,而应变速率对再结晶晶粒尺寸的影响较显著.在变形速率较高(>0.1s^-1)且变形温度较低(<870℃)时,晶粒严重变形拉长,但动态再结晶将很难发生.因子Z决定着动态再结晶晶粒尺寸,二者之间为幂指数关系.通过回归分析方法得出动态再结晶晶粒尺寸的数学表达式为：lnD_r=8.50949-0.31411lnZ.采用该表达式可以对一定变形条件的动态再结晶晶粒尺寸进行精确预测,从而为Ti-7333钛合金热变形条件下的组织控制提供可靠依据.不适当的热变形工艺会造成组织粗大或者不均匀,进而使材料性能恶化.因此,应该从材料组织均匀性和晶粒细化角度选择最佳的热变形参数.     

Investigation of the microcrack evolution in a Ti-based bulk metallic glass matrix composite

The initiation and evolution behavior of the shear-bands and microcracks in a Ti-based metallic-glass–matrix composite(MGMC) were investigated by using an in-situ tensile test under transmission electron microscopy(TEM). It was found that the plastic deformation of the Ti-based MGMC related with the generation of the plastic deformation zone in crystalline and shear deformation zone in glass phase near the crack tip. The dendrites can suppress the propagation of the shear band effectively. Before the rapid propagation of cracks, the extending of plastic deformation zone and shear deformation zone ahead of crack tip is the main pattern in the composite.     

梯田式填筑-降雨时序作用下沟谷区高填方地基变形与边坡稳定性分析

山区城镇化建设力度逐步加大,削山填沟工程广泛分布,高填方地基沉降变形与边坡稳定性是安全建设最重要的问题之一。本文提出了梯田式填筑—降雨时序作用下沟谷区高填方地基变形与边坡稳定性分析方法,首先依托地质资料建立梯田式填筑数值仿真模型,然后通过试验确定填筑体的力学参数,分析梯田式填筑过程中边坡内部响应规律,最后在降雨时序作用下模拟高填方地基多场非完全耦合变形规律,并将此方法运用到湖北省十堰市郧西县扶贫产业园项目。研究表明：填筑体随含石量增加,粘聚力总体呈波动式下降趋势,内摩擦角相对变化不大,饱和作用下试样抗剪强度具有显著弱化作用;填筑时步过程中,填筑层对边坡变形影响具有一定的时空限制范围;降雨时序作用下,填方区降雨影响深度为距地表12 m范围附近,结合测斜长期监测数据,与模拟结果较为相似。研究成果能为削山填沟高填方边坡风险评估与地质灾害防治提供技术与实践经验。     

尾砂充填体力学参数混沌优化反分析研究

采场尾砂胶结充填体力学参数难以在实验室得到,有必要用反分析方法获取.采用有限元方法对不同充填体力学参数的变形结果进行计算,建立充填体力学参数与其变形结果的神经网络映射模型.用混沌优化与神经网络映射模型相结合,实现了充填体力学参数反演计算.对安庆铜矿高阶段充填体工程实例进行了分析,得出了不同配比尾砂胶结充填体力学参数.研究结果表明,混沌优化与神经网络相结合的反分析方法能实现全局寻优,具有较高的计算精度.图2,表3,参8.     

Influence of Cu content on the mechanical properties and corrosion resistance of Mg-Zn-Ca bulk metallic glasses

(Mg_66.2Zn_28.8Ca₅)_100?xCu_x (at%, x = 0, 1, 3, and 5) bulk metallic glasses (BMGs) of 2 mm in diameter were prepared by the conventional copper mold injection casting method. Besides, the influence of Cu content on the microstructure, thermal stability, mechanical properties, and corrosion behavior of Mg-Zn-Ca BMGs was investigated. It is found that the addition of Cu decreases the glass-forming ability of Mg-Zn-Ca BMGs. Crystalline phases are precipitated at a higher Cu content, larger than 3at%. The compressive fracture strength of Mg-Zn-Ca BMGs is enhanced by the addition of Cu. With the formation of in-situ composites, the compressive strength of the Mg-Zn-Ca alloy with 3at% Cu reaches 979 MPa, which is the highest strength among the Mg-Zn-Ca alloys. Furthermore, the addition of Cu also results in the increase of corrosion potential and the decrease of corrosion current density in Mg-Zn-Ca BMGs, thereby delaying their biodegradability.     

Compositional complexity dependence of dislocation density and mechanical properties in high entropy alloy systems

This study focuses on a quantitative analysis of dislocation accumulation after cold plastic deformation and mechanical properties of FeNiCoCrMn and TiNbHfTaZr high entropy alloys (HEAs) which are single phase fcc and bcc solid solutions, respectively. In order to study the role of compositional complexity from unary to quinary compositions on dislocation accumulation and mechanical properties after plastic deformation, the single solid solution phase forming sub-alloys of the two HEAs were investigated. All studied samples revealed a large plastic deformability under cold-rotary swaging process by 85–90% area reduction without intermediate annealing. The dislocation density of all studied samples, determined by Williamson-Hall method on synchrotron X-ray diffraction patterns, were between 10¹⁴ - 10¹⁵ m⁻² dependent on the alloy composition. The level of dislocation density after plastic deformation is not only affected by the number of constituent element but the lattice distortion and intrinsic properties in terms of stacking fault energy, modulus misfit, and melting point also impact the dislocation storage. The level of dislocation density determines the level of mechanical properties because of a resistance to dislocation motions. The hardness and yield compressive strength of the studied samples are proportional to the level of dislocation density.     

In-situ Mg77Cu12Zn5Y6 bulk metallic glass matrix composite with extraordinary plasticity

Mg base BMG alloys have attracted a great deal of attention for its low density and relative low cost. To date, BMG alloys with millimeter scale have been fab- ricated by using conventional copper cast and die cast method in Mg-Ni-Ce[1], Mg-Ni-La[2], Mg-C…     

煤矿区域构造应力场的实测与模拟

以某煤矿为工程背景 ,在分析原位多点实测应力分布特征的基础上 ,通过建立适合工程特点的数值分析模型 ,采用 DDM( Displacement Discontinuity Method)模拟了该工程区域的复杂断裂构造应力场 .分析探讨了复杂断层构造对煤矿区域应力状态的影响 .研究结果表明 ,煤矿区域原岩应力分布状态主要受断层构造的支配 ,断层的叠加扰动使原岩应力场重新分布 ,造成煤矿区域原岩应力状态的极端各向异性特征     

Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical (USC) rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s-1. The softening mechanism was dynamic recovery (DRV) at 950°C and the strain rate of 1 s-1, whereas it was dynamic recrystallization (DRX) under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ·mol-1. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate (θ)–flow stress (σ) and -?θ/?σ–σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s-1, with a power dissipation efficiency η greater than 31%.     

In-situ observation on the deformation behaviors of Fe-Mn-C TWIP steel

The microstructure and crack behaviour of twinning induced plasticity (TWIP) steel during tensile deformation was investigated with in-situ scanning electron microscopy (SEM). The results show that there are two modes of plastic deformation during tensile test in the Fe-Mn-C TWIP steel: dislocation gliding and deformation twins. During the process of tensile deformation, secondary deformed twins are found. Inclusions have played a role in the course of ductile fracture, and microcracks initiate from inclusions and twin-twin intersections.     

模拟夹层的大变形有限元等厚节理单元模型

利用大变形有限元基本理论,提出了模拟夹层的大变形有限元等厚节理单元模型,并推导了其相关的大变形有限元计算公式,解决了夹层的大变形有限元模拟计算问题.     

Kinetic analysis and strain-compensated constitutive models of Ti-42.9Al-4.6Nb–2Cr during isothermal compression

The hot deformation behavior of Ti-42.9Al-4.6Nb–2Cr (at. %) was investigated by isothermal compression tests at the deformation temperature range of 1373–1573 K, strain rate range of 0.001–1.0 s⁻¹, up to the strain of 0.69. The flow stress test results of Ti-42.9Al-4.6Nb–2Cr showed negative temperature and positive strain rate sensitivity. Besides, strain had a great effect on the hot deformation behavior of Ti-42.9Al-4.6Nb–2Cr. Kinetic analysis was adopted to assess the hot workability of Ti-42.9Al-4.6Nb–2Cr via apparent activation energy (Q) of hot deformation, strain-rate sensitivity index (m) and strain hardening index (n). The Q value varied from 607.1 ± 0.7 kJ·mol⁻¹ to 512.6 ± 10.8 kJ mol⁻¹ with the increasing of strain from 0.1 to 0.6. The effect of strain on the Q value at the deformation temperatures below 1473 K was mainly related to dynamic recrystallization of γ phase and kinking of γ lamellae, while the Q value at the deformation temperature above 1473 K might be linked to γ→α phase transformation and DRV of α phase. Based on the kinetic analysis, strain-compensated Arrhenius model and Hensel-Spittel model were successfully established to predict the hot workability (flow stress). Average absolute relative errors of established strain-compensated Arrhenius model and Hensel-Spittel model were 7.52% and 11.95%, respectively. Moreover, both established constitutive models can be extrapolated for predicting the flow stress of Ti-42.9Al-4.6Nb–2Cr to larger strain levels.     

基于分段回归模型的变形监测数据分析

通过对回归模型在变形监测的应用研究,结合工程实例,对某高铁隧道的拱顶沉降值运用分段回归模型进行分析预测,建立时间和位移变形量的回归分析模型,并从统计检验、曲线线型、拟合度三个层面进行评价,得出分段回归模型可以较好的预测隧道断面的变形趋势,从而验证了该方法的工程实用价值。     

Insights into plastic deformation mechanisms of austenitic steels by coupling generalized stacking fault energy and semi-discrete variational Peierls-Nabarro model

The generalized stacking fault energy (GSFE) is a key parameter to determine the plastic deformation mechanisms of austenitic steels. However, the underlying physics why the GSFE can affect the plastic deformation behaviors remains unclear. In this paper, the plastic deformation mechanisms of austenitic steels with different carbon (C) additions were investigated by coupling the GSFE with the semi-discrete variational Peierls-Nabarro (P–N) model. The internal mechanisms behind the P–N stress and plastic deformation were explained at atomic scale. It is found that the positions and contents of C atoms affect the GSFE of austenite, and thus regulate plastic deformation behaviors of austenitic steels by influencing dislocation core structure. As exemplified that with 4 ​at.%C in austenite, the intrinsic stacking fault energy increases from −433 to −264 mJ/m², and the stacking fault width increases to 6.62b from 4.72b of FCC-Fe with b being the Burgers vector. This corresponds to the plastic deformation mechanism dominated by the ε martensitic transformation with the lattice changing from FCC to HCP. With increasing C contents to 8 ​at.%, the intrinsic stacking fault energy of austenite increases to −9.01 mJ/m², while the stacking fault width decreases to 6.03b. The plastic deformation tends to proceed via the mechanical twinning mode. The present investigation establishes a solid foundation for clarifying the plastic deformation mechanisms of austenitic steels from the perspective of the dislocation core structure.     

Thermal behavior of zirconia-dop ed mullite gel fibers

The zirconia-doped mullite gel fibers were prepared via a sol-gel method.The thermal behaviors of the gel fibers during pyrolysis were investigated by means of thermal gravitydifferential scanning calo...     

机械故障稀疏特征相似性度量优化研究

针对当前机械故障诊断研究忽略了对其参数的选取与优化,导致准确性较差等问题,提出基于量子遗传 算法优化的机械故障稀疏特征相似性度量方法。基于先进行信号非线性混合,再进行去混合。将峭度作为目 标函数,利用量子遗传算法,对盲源分离过程的分离矩阵参数与非线性去混合参数进行优化,实现机械故障盲 源分离。基于故障信号处理,利用量子遗传算法与最小二乘支持向量机(LSSVM: Least Squares Support Vector Machine)相结合实现机械故障稀疏特征相似性度量。当LSSVM在机械故障诊断时对模型参数选取,利用量子遗 传算法针对 LSSVM 模型参数进行优化。将 LSSVM 参数选取问题转换为优化问题,利用优化后的 LSSVM 分类 模型实现机械故障稀疏特征相似模式分类。实验结果表明,该方法可以实现高效盲源分离,机械故障诊断准确 率高,运行性能良好。     

基于孔隙介质理论的路基压实度确定方法

为克服以往路基压实度快速检测法中需要繁琐的标定试验及忽视初始地应力对变形参数影响的缺陷,建立了路基压实度快速检测新方法.首先,基于孔隙介质理论,研究了孔隙率、变形模量及密度随路基材料变形而变化的规律;其次,引入分层总和法和分级加载思想,考虑初始地应力和路基变形均影响路基力学参数变化的特征,建立静力贯入条件下贯入荷载-沉降解析关系;然后,在路基静力贯入试验测得荷载-沉降试验曲线的基础上,利用自适应遗传退火算法反演得路基贯入荷载-沉降解析关系中的各参数,从而建立基于孔隙介质理论的路基压实度确定方法;最后,通过工程实例对比可知,本文方法精确度满足工程要求,检测过程中无需繁琐的灌水法标定试验,能快速准确地检测路基压实度,表明了本文方法的合理性和可行性.     

高应力下脆性岩石卸荷力学特性及数值模拟

高地应力下脆性岩体工程开挖变形机理、稳定性评价及灾害控制技术研究一直是岩石力学和工程地质研究的难点问题。基于高应力下脆性岩石卸荷力学试验分析,明确了卸荷过程中的岩石力学参数及变形破坏演化规律,发现高应力下脆性岩石的破坏具有较明显的应变强度特征。分析了高应力下脆性岩石卸荷破坏采用张拉屈服的Griffith应变强度准则的合理性,建立了考虑卸荷屈服引起岩体力学参数变化的弹脆塑性数值计算方法,并在实际工程中得以验证。