Experiments and modeling of double-peak precipitation hardening and strengthening mechanisms in Al-Zn-Mg alloy

The aim of the present work is to develop a model for simulating double-peak precipitation hardening kinetics in Al-Zn-Mg alloy with the simultaneous formation of different types of precipitates at elevated temperatures based on the modified Langer-Schwartz approach. The double aging peaks are present in the long time age-hardening curves of Al-Zn-Mg alloys. The physically-based model, while taking explicitly into account nucleation, growth, coarsening of the new phase precipitations and two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing）, was used for the analysis of precipitates evolution and precipitation hardening during aging of Al-Zn-Mg alloy. Model predictions were compared with the measurements of Al-Zn-Mg alloy. The systematic and quantitative results show that the predicted hardness profiles of double peaks via adding a shape dependent parameter in the growth equation for growth and coarsening generally agree well with the measured ones. Two strengthening mechanisms associated with particle-dislocation interaction （shearing and bypassing） were considered operating simultaneously in view of the particle size-distribution. The transition from shearing to bypassing strengthening mechanism was found to occur at rather early stage of the particle growth. The bypassing was found to be the prevailing strengthening mechanism in the investigated alloys.

Modeling of whole process of ageing precipitation and strengthening in Al-Cu-Mg-Ag alloys with high Cu-to-Mg mass ratio

A physically based numerical model to predict the microstructure evolution and yield strength of high Cu-to-Mg mass ratio Al-Cu-Mg-Ag alloys during the whole ageing process was developed.A thermodynamically-based precipitation model,employing the classical nucleation and growth theories,was adapted to deal with the precipitation kinetics (evolution of radius and volume fraction of precipitates for Ω phase) of aged Al-Cu-Mg-Ag alloys.The model gives an estimation of the precipitation kinetics (evolution of radius and density of precipitates for both θ' and Ω phases) of the alloy.The strengthening model based on Orowan mechanism was deduced.The microstructural development and strength predictions of the model are generally in good agreement with the experimental data.

Quantifying Solid Solution Strengthening in Nickel-Based Superalloys via High-Throughput Experiment and Machine Learning

Solid solution strengthening(SSS)is one of the main contributions to the desired tensile properties of nickel-based superalloys for turbine blades and disks.The value of SSS can be calculated by using Fleischer’s and Labusch’s theories,while the model parameters are incorporated without fitting to experimental data of complex alloys.In thiswork,four diffusionmultiples consisting of multicomponent alloys and pure Niare prepared and characterized.The composition and microhardness of singleγphase regions in samples are used to quantify the SSS.Then,Fleischer’s and Labusch’s theories are examined based on high-throughput experiments,respectively.The fitted solid solution coefficients are obtained based on Labusch’s theory and experimental data,indicating higher accuracy.Furthermore,six machine learning algorithms are established,providing a more accurate prediction compared with traditional physical models and fitted physical models.The results show that the coupling of highthroughput experiments and machine learning has great potential in the field of performance prediction and alloy design.

Strengthening mechanisms based on reinforcement distribution uniformity for particle reinforced aluminum matrix composites

A modified mixed strengthening model was proposed for describing the yield strength of particle reinforced aluminum matrix composites.The strengthening mechanisms of the composites were analyzed based on the microstructures and compression mechanical properties.The distribution uniformity of reinforcements and cooperation relationship among dislocation mechanisms were considered in the modified mixed strengthening model by introducing a distribution uniformity factor u and a cooperation coefficient fc,respectively.The results show that the modified mixed strengthening model can accurately describe the yield strengths of Al3Ti/2024Al composites with a relative deviation less than1.2%,which is much more accurate than other strengthening models.The modified mixed model can also be used to predict the yield strength of Al3Ti/2024Al composites with different fractions of reinforcements.

Improved mechanical properties and strengthening mechanism with the altered precipitate orientation in magnesium alloys

Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-MgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 Mg alloy.The experimental results showed that the compressive yield strength(CYS)of the sample containing prismatic plates increased 40 MPa and the compression ratio raised by 22%compared to that containing basal plates.The underlying strengthening mechanism was analyzed via a yield strengthen(YS)model with a function of grain size,precipitate characters(size,oritention,fraction)and Schmid factor(SF).It revealed that the improvement of CYS was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning deformation.Particularly,the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and SF.Besides,the decreased CRSS ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in Mg alloy might be enhanced.More activated slip systems provided more mobile dislocations,contributing to the large compression ratio of the Mg rolled sheet with prismatic plates.

A three-dimensional solution of hydraulic fracture width for wellbore strengthening applications

Determining the width of an induced hydraulic fracture is the first step for applying wellbore strengthening and hydraulic fracturing techniques. However, current 2-D analytical solutions obtained from the plane strain assumption may have large uncertainties when the fracture height is small. To solve this problem, a 3-D finite element method(FEM) is used to model wellbore strengthening and calculate the fracture width. Comparisons show that the 2-D plane strain solution is the asymptote of the 3-D FEM solution. Therefore, the 2-D solution may overestimate the fracture width. This indicates that the2-D solution may not be applicable in 3-D conditions. Based on the FEM modeling, a new 3-D semi-analytical solution for determining the fracture width is proposed, which accounts for the e ects of 3-D fracture dimensions, stress anisotropy and borehole inclination. Compared to the 2-D solution, this new 3-D semi-analytical solution predicts a smaller fracture width.This implies that the 2-D-based old design for wellbore strengthening may overestimate the fracture width, which can be reduced using the proposed 3-D solution. It also allows an easy way to calculate the fracture width in complex geometrical and geological conditions. This solution has been verified against 3-D finite element calculations for field applications.

Solid solution strengthening and damping capacity of Mg-Ga binary alloys

The mechanical behaviors and damping capacities of the binary Mg−Ga alloys with the Ga content ranging from 1 to 5 wt.%were investigated by means of optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),hardness test,tensile test and dynamic mechanical analyzer(DMA).The hardness(HV_(0.5))increases with the increase of Ga content,which can be described as HV_(0.5)=41.61+10.35c,and the solid solution strengthening effect∆σ_(s)of the alloy has a linear relationship with c^(n),where c is the molar fraction of solute atoms and n=1/2 or 2/3.Ga exhibits a stronger solid solution strengthening effect than Al,Zn or Sn due to the large atomic radius difference and the modulus mismatch between Ga and Mg atoms.The addition of Ga makes the Mg−Ga alloys have better damping capacity,and this phenomenon can be explained by the Granato−Lücke dislocation model.The lattice distortion and the modulus mismatch generated because of the addition of Ga increase the resistance to motion of the dislocation in the process of swinging or moving,and thus the better damping capacity is acquired.

超高强Ti-15Mo-2.7Nb-3Al-0.2Si钛合金的强化行为及模型

基于XRD、OM、SEM和TEM分析,研究超高强Ti-15Mo-2.7Nb-3Al-0.2Si钛合金的组织演变及强化行为。结果表明,位错强化和析出强化效应对该合金的屈服强度影响较大。冷轧+再结晶+冷轧+双时效组合工艺可获得1518 MPa的最高屈服强度,这主要归因于显微组织中的高密度残存位错及密集而细小的次生α相。建立复合强化模型,其预测误差在16.6%以内。此外,研究发现次生α相体积分数的增加可以不断强化晶内区域,这使得沿晶断裂开始出现并逐渐占据整个断裂面。

CFRP及EWSS复合加固震损双层高架桥框架式桥墩恢复力模型研究

为研究碳纤维布(Carbon Fiber Reinforced Polymer,CFRP)及外包型钢(Externally Wrapped Steel Section,EWSS)复合加固震损双层高架桥框架式桥墩的恢复力模型,对1榀原型对比试件、1榀无预损加固试件和2榀遭受不同地震损伤加固试件进行了低周往复加载破坏试验,获取了滞回曲线并提取骨架曲线,分析其滞回特性,提出一种弹性段和强化段为双折线、下降段为指数函数且考虑初始损伤的骨架曲线模型;采用试验数据回归拟合方法,定量描述了试件滞回曲线卸载刚度的退化规律,考虑了同级加载承载力退化和定点指向特征,建立了恢复力模型。研究结果表明:复合加固试件滞回曲线捏缩现象明显,呈倒S型,各滞回环分别相交于骨架曲线上正向、负向荷载为屈服荷载0.25倍的点,峰值荷载后EWSS产生包辛格效应;所提出的骨架曲线模型对中度震损和重度震损加固试件下降段指数函数的参数k建议取值分别为3.6和3.4;所建立的骨架曲线模型和恢复力模型计算结果与试验实测结果吻合较好,可为该类结构弹塑性地震反应分析提供依据。

预应变对S30408不锈钢力学性能和马氏体相变的影响

为了探究不同预应变量下S30408不锈钢力学性能的变化规律,课题组在室温下对S30408不锈钢开展不同预应变量下的单轴拉伸试验,分析了预应变对其力学性能及马氏体相变的影响规律,在此基础上建立了考虑预应变影响的修正Ludwigson模型,并结合基于Johnson-Cook的脆化模型合理预测预应变后材料力学性能。结果表明:随着预应变量的增加,S30408不锈钢的屈服强度明显增加,抗拉强度缓慢增加,断后延伸率降低;利用金相和X射线衍射试验获取不同预应变量下微观组织和析出相成分,发现在预应变量大于9%后,S30408不锈钢开始逐渐出现形变诱导的马氏体相变。课题组的研究实现了不同预应变量下的S30408不锈钢应力-应变关系的合理评价。

C型钢缀板柱的有限元模拟方法研究

缀板柱以其制造简便、稳定性高且价格低廉的优势,在工程钢结构中得到了广泛应用,如何准确模拟缀板与立柱之间的连接情况,是工程结构有限元模拟时的重要问题。文章采用有限元软件ANSYS,研究C型钢缀板柱中缀板与立柱之间连接情况的有限元模拟问题,通过对比单元整体建模与节点耦合建模的模拟结果,分析了节点耦合连接方法的模拟原理并提出了使用时的注意事项。计算分析表明:整体建模模拟效果较好但不便于模型修改和精细化模拟,节点耦合便于修改但需要考虑耦合方法和连接面积。文章提出的简化统一耦合方法模拟效果好,适应性强,对于工程实践中的有限元模拟工作具有一定指导意义。

基于7075铝合金时效强化机理分析的工艺优化

为了获得最佳的时效工艺和有效提升实验效率,以JMatPro仿真方法为基础,研究了7xxx系铝合金的时效强化机理,获得了铝合金的最佳时效工艺参数。通过JMatPro仿真得到时效过程中析出相的体积分数,获得了经典的JMAK动力学方程,再通过析出相长大模型得到时效过程中析出相的尺寸。然后,分别使用时效强化模型和JMatPro仿真方法计算时效后合金的强度,与时效强化模型相比,使用JMatPro仿真方法可以将合金强度峰值预测精度提高了0.72%;峰值时间预测精度提高了18.28%。最后,通过拟合JMatPro的仿真结果,获得了强度峰值、峰值时间与时效温度的关系表达式,为制定最佳的时效工艺参数提供指导。

基于CB-Attention的JavaScript恶意混淆代码检测方法

当今JavaScript代码混淆方法日益多样,现有检测方法在对混淆代检测时会出现漏报和误报的情况,为解决该问题,提出一种基于CB-Attention的JavaScript恶意代码检测方法。由SDPCNN模型和BiLSTM+Attention模型构成,SDPCNN对短距离间的语义特征信息进行提取,BiLSTM+Attention获取JavaScript代码中长距离间的语义信息特征。为验证所提方法的有效性,将该方法与其它方法进行对比,对比结果表明,该方法具有较好的检测效果,F1-Score可达98.78%。

Li^(+)浓度对化学增强锂铝硅玻璃性能的影响

采用一步法化学增强工艺,研究了熔盐中Li^(+)的富集对不同厚度锂铝硅玻璃表面压应力、应力层深度、弯曲强度、硬度等性能的影响,选择Na_(3)PO_(4)作为熔盐除杂剂并对净化效果进行了评定。研究表明:熔盐中Li^(+)浓度增加至4800×10^(-6),3 mm化学增强锂铝硅玻璃的表面压应力、弯曲强度、硬度下降16.8%、16.8%、10.6%;8 mm化学增强锂铝硅玻璃的表面压应力、弯曲强度、硬度下降17.6%、14.7%、9.8%。熔盐中Li^(+)浓度的变化未对化学增强锂铝硅玻璃应力层深度产生明显影响。Na_(3)PO_(4)具有较好的除杂效果,化学增强锂铝硅玻璃的表面压应力、弯曲强度、硬度得到了明显的恢复,为保证化学增强锂铝硅玻璃在可见光波段具有较高的透光率,除杂剂Na_(3)PO_(4)的掺量不宜超过1%(质量分数)。

健脾消肿颗粒治疗PHN大鼠的疗效观察及作用机制的初探

目的:观察健脾消肿颗粒治疗PHN大鼠的疗效以及其作用机制。方法:选取健康雄性SPF级Wistar大鼠,适应性喂养后随机抽取正常对照组后,进行造模,正常对照组腹腔一次性注射生理盐水,1 ml/100 g,造模组腹腔一次性注射等量羊抗Fx1A抗血清。造模成功后分组,随机分为模型组、健脾消肿颗粒组。灌胃8周,分别于0周、2周、4周、8周后留取24 h尿,测定各组大鼠24 h尿蛋白定量。8周后处死大鼠取材,留取血清及组织样本。行光镜HE、PASM染色,免疫荧光等检测,观察各组大鼠肾脏一般病理形态学的改变情况。RT-PCR,免疫组化检测肾组织Podocin、Nephrin的蛋白表达量以及mRNA的表达量。结果:(1)给药2周、4周、6周、8周后,健脾消肿颗粒组24 h尿蛋白定量较模型组明显下降,差异有统计意义(P<0.05);(2)在白蛋白水平,模型组较正常对照组明显下降,差异有统计学意义(P<0.05)。(3)免疫组化:模型组、健脾消肿颗粒组WT1的表达较正常对照组均有所下降,差异有统计学意义(P<0.05);与模型组比较,健脾消肿颗粒组WT1的表达明显升高,差异有统计学意义(P<0.05)。模型组podocin的表达异常较正常对照组显著升高,差异有统计学意义(P<0.05),健脾消肿组与正常对照组差异无统计学意义(P>0.05)。(4)RT-PCR:与正常对照组比较,健脾消肿颗粒组nephrin、podocin、podoplanin各指标的表达与正常对照组差异无统计学意义(P>0.05),模型组podocin表达异常,较正常对照组显著升高,差异有统计学意义(P<0.05),其余两指标升高较正常对照组差异无统计学意义,但有显著升高趋势。结论:(1)健脾消肿颗粒疗效确切,可以降低PHN大鼠模型24 h尿蛋白,升高血浆白蛋白;(2)健脾消肿颗粒可以改善PHN大鼠病理损伤,保护足细胞并促进其修复;(3)足细胞相关蛋白nephrin、podocin等蛋白出现过表达可能仍提示足细胞损伤,蛋白表达上调或下调可能与足细胞损伤严重程度以及病情严重程度相关。PHN模型中是否存在基因突变,nephrin、podocin等足细胞蛋白的表达与氧化应激水平关系仍待进一步的验证。

螺栓头下圆角强化参数的理论计算模型研究

螺栓头下圆角强化是依靠滚压形成塑性形变使表面产生残余压应力实现强化效果,强化效果的关键是滚压参数的确定。参数确定常以正交试验法或仿真加试验验证的方法进行参数摸索验证,存在参数验证周期长、试验成本高及效率低下的问题。针对此问题,该文通过构建圆角理论模型并进行接触力学分析,给出强化参数的计算方法,再通过试验验证,提高强化参数确定的效率。

新农科背景下涉农高职院校耕读育人模式建设探索与实践

在新农科建设背景下,为培养知农爱农新型人才,迫切需要打造人才培养新模式。耕读教育是落实立德树人的关键环节,对提升涉农高职院校学生学农、知农、爱农的素养和专业实践能力具有重要意义。分析了耕读育人模式建设的重要性,讨论现阶段耕读教育存在的问题,从涉农高职院校耕读育人模式视角,以杨凌职业技术学院为例,提出了“五融入五强化”耕读育人模式,以期提升新型人才培养质量,为涉农高职院校耕读育人模式建设提供借鉴与参考。

基于统一强度理论的自紧身管残余应力分析

基于统一强度理论,考虑材料拉压异性和鲍辛格效应的影响,采用双线性强化材料模型对身管进行自紧分析,推导了身管加载应力、卸载应力、残余应力及工作应力的解析解,得到了弹塑性交界面半径、反向屈服半径的计算公式,提出了最佳自紧度和自紧压力的计算方法,通过与实验数据进行对比,验证了本文理论解的正确性,分析了材料拉压强度比、中间应力系数等参数对身管残余应力、弹塑性交界面半径、反向屈服半径和最佳自紧压力的影响。结果表明,反向屈服半径、弹塑性交界面半径、弹塑性交界面处残余应力与材料拉压强度比成正比,与中间应力系数成反比;最佳自紧压力与材料拉压强度比成反比,与中间应力系数成正比。

电场实时加载下煤层气解吸-扩散特性实验研究

为探究电场实时加载下煤层气解吸-扩散特性,揭示电场强化煤层气高效抽采的机理影响特征,设计并研发了可控电场强度下煤层气解吸-扩散实验系统;实验探究了电场加载下煤体的CH4和CO_(2)解吸-扩散变化特征,并通过幂函数扩散模型计算各场强作用下的CH4扩散系数。结果表明:不同吸附质在电场实时加载下煤层气解吸量均得到一定程度提升,但电场对CO_(2)解吸量影响特征更加明显,同时电场能够强化煤体瓦斯的初始解吸速度;与未加电场相比,特征场强为30、60、90 kV/m时CH4初始解吸速率提升了6.9%、15.3%、14.6%,而CO_(2)依次提升了3.4%、6.7%、9.2%;电场加载下煤体CH4幂函数扩散模型能够高度的与实验值相吻合,扩散系数具有随着加载场强的增大而逐渐增大变化特征,电场有利于煤中甲烷的解吸、扩散。

不同波长激光冲击强化力学效应数学模型构建

为实现更好的强化效果,克服强化后表面形貌不够均匀等问题,设计不同波长激光冲击强化的力学效应数学模型。使用Johnson-Cook模型构建金属构件的材料本构模型,对基础材料模型加载激光冲击波压力,以激光冲击强化原理为依据,构建不同波长下的构件激光冲击强化有限元模型。基于构建的有限元模型,探究材料的动态屈服强度与构件材料的雨贡纽弹性极限之间的关系,构建应变与冲击波峰值压力之间的理论模型,根据该模型表示激光冲击强化产生的残余压应力,完成不同波长激光冲击强化力学效应数学模型的构建。测试结果表明,基于该模型强化后,实验构件表面形貌整体比较均匀,凹坑深度较小,过光斑中心直线上构件材料表面位移变化区间在[-0.4,0.5]之间,说明设计模型性能较好,具有实用性。