Characterizing the Spheroidization Grade and Strength of 15CrMo Steel through Determining Fractal Dimension

The fractal dimension（FD） of surfaces has been widely used to characterize the properties of materials.However,most of the previous researches were concentrated on the correlation between the FD of surfaces and mechanical properties of materials,such as impact energy and fracture toughness,etc.The aim of this paper is to characterize the spheroidization grade and strength of 15CrMo steel through determination of FD of cementite phase on the basis of two-dimension microstructural image.Two methods,namely slit-island method（SIM） and box-counting method（BCM）,are used to determine the value of FD.It is found that the FD value evaluated by using BCM is generally higher than that evaluated by SIM.This phenomenon may be due to the difference in the principles used in different methods.Whether SIM or BCM is used,the spheroidization grade in 15CrMo steel linearly increases with decreasing the value of FD.The relationship between the FD value,D,and spheroidization grade,Sg,can be approximately expressed as D≌-0.11Sg＋A,where A is a constant value which is depended on the evaluation method.Both the ultimate strength and the yielding strength of 15CrMo steel increase with increasing FD of cementite phase.There may be a common relationship between the FD of cementite phase and strength of 15CrMo steel.When the FD of cementite phase in 15CrMo steel is determined,the strength of this steel can be evaluated.The present paper can provide a novel method to evaluate the strength and spheroidization grade of carbon steel through determination of fractal dimension（FD） of cementite phase.

Bonding strength of graded anti-corrosive coatings of fluoroethylenepropylene (FEP)/polyphenylene sulfide (PPS)

Fluororesin-based anti-corrosive coatings including graded FEP/PPS were prepared on carbon steel by melt powder coating, the bonding strength of all coating systems was determined by the pull-off test. It is found that the poor adhesion of fluororesin coatings to metallic substrates is improved obviously by the graded coating structure of FEP/PPS, and the bonding strength reaches up to 11.8 MPa for the five-layer system. Examination by electron probe microanalysis （EPMA） verifies that the distribution of main components is graded in the five-layer system, which is responsible for the enhancement of the interfacial bonding.

A Study on the Strength Surplus Coefficient of Cement

This study considers P.O42.5 cement from different sources and evaluates the related surplus coefficient(defined as the proportionality factor linking the measured compressive strength value of the cement after 28 days to the“standard”value of cement strength).The needed tests have been conducted using a mixer,a pressure testing machine,a flexural testing machine,a vibrating table a ramming rod,a feeder and a metal ruler.The average value of the measured cement strength surplus coefficient of cement produced by five distinct cement manufacturers has been found to be 1.16.These results can be used as the basis to reduce the production cost and improve the performance of commercial concrete.

Grade 91耐热钢的硬度与持久强度、许用应力和运行/剩余寿命的相关性研究

利用不同硬度Grade 91钢试件的持久强度数据研究该钢硬度与持久强度和最大许用应力的相关性。结果表明,采用系列硬度试件所做确定温度和外力下的持久实验同时存在性能高估和低估现象,将这些数据综合在一起预测/外推钢的持久强度与实际值差距较大,利用由此确定的105 h持久强度计算得到的最大许用应力对应用产生不完全符合实际的影响。同时研究得到Grade 91钢在确定温度下满足最大许用应力的硬度下限的确定方法:对于硬度在201(205)HBW及其以上的Grade 91钢部件,在575(600)℃及其以下温度运行时可满足ASME BPVC 2019版规范对Type 1和Type 2型材料最大许用应力的要求;硬度在204HBW及其以上的Grade 91钢部件在575℃及其以下温度运行时可满足ASME BPVC 2017版规范对壁厚大于75 mm部件最大许用应力的要求。因此,在已有硬度范围规定(ASME BPVC 2017-2019对Grade 91钢:190~250HBW)的情况下,下调最大许用应力的ASME BPVC 2019新规范给现有硬度范围下限的实施带来一定困难,即满足该硬度下限要求却不能满足最大许用应力要求。为解决这一问题未来有必要上调硬度下限值。此外,研究了Grade 91钢运行/剩余寿命评估算法中利用短时实验数据外延105 h持久强度的函数优化。结果表明,现用算法采用幂函数拟合存在性能高估现象,若采用对数函数将不同硬度试件的持久数据分开拟合则可明显提高与实验数据的吻合性;在此基础上研究所得已知运行条件下部件厚度-硬度-运行/剩余寿命的关系将安全性评估的技术参数融为一体,可体现该方法的适用性、可靠性和直观性。以上研究结果可供相关标准修订和工业实际应用参考。

Thermal shock resistance behavior of a functionally graded ceramic: Effects of finite cooling rate

This work presents a semi-analytical model to explore the effects of cooling rate on the thermal shock resistance behavior of a functionally graded ceramic （FGC） plate with a periodic array of edge cracks. The FGC is assumed to be a thermally heterogeneous material with constant elastic modulus and Poisson＇s ratio. The cooling rate applied at the FGC surface is modeled using a linear ramp function. An integral equation method and a closed form asymptotic temperature solution are employed to compute the thermal stress intensity factor （TSIF）. The thermal shock residual strength and critical thermal shock of the FGC plate are obtained using the SIF criterion. Thermal shock simulations for an Al2O/Si3N4 FGC indicate that a finite cooling rate leads to a significantly higher critical thermal shock than that under the sudden cooling condition. The residual strength, however, is relatively insensitive to the cooling rate.

Importance of Sand Grading on the Compressive Strength and Stiffness of Lime Mortar in Small Scale Model Studies

Mortars provide the continuity required for the stability and exclusion of weather elements in masonry assemblies. But because of the heterogeneity of the mortar, its mechanism of behaviour under different load effects is dependent on the properties of the constituents of the mortar. The aim of paper is to determine the effect sand grading for various cement-sand-lime mortar designations (BS) and strength classes (EC) on the compressive strength and stiffness of mortar. Two silica sands;HST 95 and HST60 were used to make mortars in three strength classes: M2, M4 and M6, corresponding to mortar designations iv, iii and ii respectively. The results show that mortar made with the HST60 sand (coarser grading) usually resulted in mortar with a higher compressive strength and stiffness. The One Way ANOVA analysis of both compressive strength and stiffness at a significance level of 5% on the effect of sand grading on the two parameters also shows that they are both significant. There is also strong evidence of a linear correlation between the stiffness and compressive strength. The results indicate that in order to replicate full scale behaviour of masonry at model scales, the grading of fine aggregate in the models should be similar so as to properly model full scale behavior.

Preparation and Properties of a New Mediumdensity and High-strength Ceramic Proppant

Based on the needs of the market,a new 52 MPa medium-density and high-strength ceramic proppant was prepared by adopting third grade bauxite and clay as raw materials and using the solid phase sintering method,and the effect of the firing temperature on the microstructure,phase composition and mechanical properties of the ceramic proppant was studied. The broken resistance mechanism of this ceramic proppant was also discussed. The results show that the main phases of the prepared ceramic proppant are mullite and corundum; the broken rates are 3. 92% and 7. 21% under 52 MPa and69 MPa,respectively.

基于截面配筋率的钢筋混凝土统一本构关系研究

为避免数值化分析中直接处理钢筋与混凝土之间的复杂关系,推导出钢筋混凝土构件轴心受压统一理论公式,做了不同配筋率与不同混凝土强度等级下的钢混棱柱体轴心受压试验,利用试验量测的荷载位移数据,结合Matlab曲线拟合工具的线性回归与拟合功能,建立了一种基于截面配筋率的能够描述钢筋混凝土材料力学性能的统一本构关系。对试验梁进行数值化分析表明,所建立的数值化模型应力应变特征与试验结果吻合较好,证明了该模型在钢筋混凝土实际运用过程中的可行性与适用性。

980MPa级先进高强钢的发展

选用轻量化汽车材料时应综合考虑材料的性能、质量和成本。目前,先进高强钢被广泛用于汽车工业。先进高强钢有双相钢、相变诱导塑性钢、马氏体钢、复相钢、淬火-配分钢、DH钢等。综述了980 MPa及以上高强钢的分类和主要钢种,汽车用高强钢的化学成分、显微组织、力学性能和使用性能,并结合实际零件的制造过程对这些高强钢的焊接和成形性能作了较深入的探讨,简述了其发展现状和研究进展。

不同性能水平下600 MPa级高强钢筋混凝土柱位移角限值研究

基于性能抗震设计思想的600 MPa级高强钢筋混凝土柱位移角限值研究,对于推广高强钢筋混凝土柱的应用至关重要。通过17根HTRB630高强钢筋混凝土柱试件和3根HRB400钢筋混凝土柱试件的拟静力试验研究了其抗震性能。与HRB400钢筋混凝土柱相比,HTRB630高强钢筋混凝土柱的滞回曲线的形状没有发生明显改变,试件具有较好的承载能力和延性。将基于Kunnath损伤模型计算的损伤指数与试验中测量的损伤指数范围进行了比较,结果表明,Kunnath损伤模型可以准确计算HTRB630高强钢筋混凝土柱的损伤指标。根据HTRB630高强钢筋混凝土柱的破坏特点,以屈服点、峰值点和极限点作为高强钢筋混凝土柱的性能水平控制点。基于性能抗震设计的思想,将600 MPa级高强钢筋混凝土柱的性能水平划分为5个性能水平,即正常使用、暂时使用、修复后使用、生命安全和接近倒塌性能水平。结合参考文献中600 MPa级高强钢筋混凝土柱的试验数据,对65个600 MPa级高强钢筋混凝土柱各特征点的位移角进行了相对频率统计分析,得到了600 MPa级高强钢筋混凝土柱在暂时使用、修复后使用和接近倒塌3个性能水平下具有超过90%安全保证率的位移角限值分别为1/150、1/80和1/60。

卸荷损伤砂岩的分级加载三轴蠕变力学特性试验研究

为探究含初始卸荷损伤砂岩的三轴蠕变力学特性,借助MTS816岩石力学试验系统通过控制卸荷量制备了不同初始卸荷损伤程度的砂岩试样,开展了卸荷损伤砂岩分级加载三轴蠕变力学试验,分析了初始卸荷损伤程度对砂岩应变特征、蠕变速率、变形模量、长期强度及破坏模式的影响规律。研究结果表明:(1)分级蠕变条件下,不同初始卸荷损伤程度砂岩的轴向和环向应变均呈阶梯式增长,轴向瞬时应变随载荷水平的增加呈近线性增长趋势,而环向瞬时应变呈非线性增长趋势,且随初始卸荷损伤程度的加剧,增加单位荷载引起的轴向瞬时应变增量不断增加;(2)卸荷损伤砂岩在非破坏阶段经历了瞬时变形、减速蠕变和稳态蠕变3个阶段,稳态蠕变速率随初始卸荷损伤程度的增加呈指数增长趋势;砂岩在破坏阶段经历了瞬时变形、减速蠕变、稳态蠕变和加速蠕变4个阶段,其中加速蠕变阶段用时极短,却能产生较大的扩容变形,导致岩样发生失稳破坏;(3)砂岩蠕变总时长、平均变形模量和长期强度均随初始卸荷损伤程度的增加呈非线性减小趋势,当初始卸荷损伤程度超过70%后,砂岩蠕变总时长、平均变形模量和长期强度降幅急剧增加,最高可达24.77%、33.28%和21.79%;(4)随着初始卸荷损伤程度的增加,砂岩蠕变破坏模式由单一的剪切破坏逐渐向复杂的张拉-剪切混合式破坏转变。

工业副产石膏制备高强石膏的方法及其应用技术

本文论述了高强石膏的制备方法,从高强石膏传统的制备工艺入手,分析了蒸压法(饱和蒸汽法)、常压盐/酸溶液法和加压盐/酸溶液法的优点及缺点,阐释了在高强石膏的制备过程中转晶剂的应用以及优化颗粒级配对提高α-半水石膏性能的重要性,论述了高强石膏的技术要求。在建材、模具铸造、航空航天、医疗以及美术制品等领域,高强石膏有非常广泛的应用,介绍了其出众的性能,最后讨论了水膏比对高强石膏硬化浆体强度的影响,以及高强石膏制品耐水性差的原因和解决方法。

海陆交互相软土固结抗剪强度指标变化规律研究

以珠三角地区海陆交互相淤泥质软土为研究对象,通过室内直剪试验探究不同固结压力和固结度下抗剪强度及抗剪强度指标的变化规律,提出抗剪强度及对应指标-固结度-固结压力三维Logistic数学模型。研究结果表明,当固结压力P≥200 kPa、固结度U≥40%时,软土黏聚力(c)和内摩擦角(φ)增长较为明显;当U=100%时,各级固结压力作用下的软土抗剪强度(τ)相较于初始状态分别提高了7.89、12.73、13.50、18.20、22.38 kPa;所给出的三维数学模型可直接计算出某一固结压力和固结度下的抗剪强度指标c、φ、τ。研究成果能够更为准确地评价该地区软土地基逐级加载过程中的整体稳定性。

密实度对格栅-再生混凝土骨料界面剪切特性的影响

为探究相对密实度、颗粒级配及法向应力等因素对格栅-再生混凝土骨料界面剪切特性的影响,通过大型直剪仪对不同相对密实度的再生混凝土骨料进行单调直剪试验。结果表明:在不同相对密实度、颗粒级配、法向应力影响因素下,界面均呈现出峰值后剪切软化现象;相对密实度对界面剪切特性有显著影响,随着相对密实度的增大,界面抗剪强度、剪切模量、似黏聚力、内摩擦角及整体剪胀量均呈现增大趋势;随着不均匀系数的增大,界面峰值抗剪强度与残余抗剪强度均增大,剪胀现象明显;界面峰值抗剪强度随法向应力的增加近似线性增长,增加幅值、剪胀量随法向应力的增大呈现减小趋势。

下肢康复训练机器人联合等速肌力训练对老年脑卒中偏瘫患者神经功能、步行能力、Lovett肌力分级及平衡能力的影响

目的分析下肢康复训练机器人联合等速肌力训练对老年脑卒中偏瘫患者神经功能、步行能力、Lovett肌力分级及平衡能力的影响。方法回顾性分析2022年1月至12月于中国中医科学院西苑医院康复医学科接受康复治疗至少8周的86例老年脑卒中偏瘫患者的临床资料,依据训练方法不同分为联合组(n=43)和对照组(n=43)。对照组行常规康复训练联合等速肌力训练,联合组在对照组基础上行下肢康复训练机器人训练。观察分析两组训练前及训练8周后神经功能、步行能力、Lovett肌力分级、平衡能力、不良反应。结果训练后,两组NIHSS评分、Rankin评分均较训练前降低,且联合组NIHSS评分、Rankin评分分别为(10.96±1.32)、(2.12±0.24)分,均低于对照组[(15.93±1.79)、(2.65±0.29)分],差异均有统计学意义(P<0.05)。训练后,两组FAC高分级均较训练前增加,且联合组FAC及Lovett肌力高分级比例均大于对照组,差异均有统计学意义(P<0.05)。训练后,两组BBS评分均较训练前升高,且联合组BBS评分(45.19±4.83)分,高于对照组[(38.76±4.18)分],差异均有统计学意义(P<0.05)。两组均无显著不良反应。结论下肢康复训练机器人联合等速肌力训练可改善老年脑卒中偏瘫患者神经功能,提高其步行能力、Lovett肌力分级及平衡能力,安全性高。

亚热带海洋全浸泡环境下钢筋混凝土劣化规律研究

针对亚热带海洋环境混凝土中钢筋锈蚀问题,通过模拟亚热带海洋环境,对不同强度等级和阻锈剂掺量的钢筋混凝土试件进行全浸泡侵蚀试验,利用电化学无损检测、氯离子含量测试,结合微观检测分析了钢筋混凝土的腐蚀劣化规律。研究结果表明:混凝土强度等级的提高和阻锈剂掺量的增加均能明显提升钢筋混凝土的耐腐蚀性能。其中,C30混凝土抗锈蚀性能最差,120 d时,腐蚀电流密度为0.118μA/cm^(2),极化电阻为220 kΩ·cm^(2),混凝土电阻为87.3 kΩ·cm^(2),钢筋-混凝土界面区转移电阻为77.3 kΩ·cm^(2),达到脱钝状态;混凝土强度等级提高至C50时,腐蚀电流密度减小了58.47%,极化电阻增加了3.82倍,混凝土电阻增加了44.56%;阻锈剂掺量为6 kg/m3时,腐蚀电流密度减小了47.45%,极化电阻增加了2.81倍,钢筋-混凝土界面区转移电阻增加了72.43%。

不同强度等级铁矿废石骨料混凝土抗氯离子渗透性能

在固废资源化发展背景下,利用铁矿废石骨料生产混凝土可以有效缓解天然砂石资源面临枯竭的困境。为研究不同强度等级铁矿废石骨料混凝土的抗氯离子渗透性能,设计了水胶比分别为0.59、0.35和0.23的混凝土,进行了立方体抗压强度试验,并采用电通量法分别测试了养护28 d和56 d混凝土的抗氯离子渗透性能。试验结果表明:养护28 d后,3种混凝土立方体抗压强度分别为25.3 MPa、54.6 MPa和79.9 MPa,渗透性评价依次为低、很低和极低;养护56 d后,3种混凝土的抗压强度分别增长16.9%、9.4%和7.4%,且电通量明显降低,说明养护龄期对渗透性的影响显著;混凝土的电通量与抗压强度具有极强相关性,呈线性递减关系。

Functionally graded Al_2O_3-ZrO_2 composite prepared by centrifugal slip casting and its mechanical properties

Compositionally graded composite of alumina-20%zirconia (volume fraction) was fabricated by using centrifugal casting incorporated with relatively thin slip. An EPMA analysis exhibited a nearly linear variation of the alumina/zirconia ratio along the centrifugal direction; zirconia tended to accumulate in the bottom section, while alumina in the top section. Such a graded structure exhibited a considerably higher flexural strength when the alumina rich surface was subjected to a tensile stress than compositionally uniform composite of the same average composition. Fracture toughness measurement across the specimen thickness by indentation method revealed that the crack lengths along the vertical and horizontal directions were different. The anisotropy of the fracture toughness was accounted for by the variation of the residual stress across the specimen thickness.

125ksi超级马氏体油管成分-组织-性能-工艺综合控制技术

125ksi钢级15Cr超级马氏体不锈钢具有优良的高强度、高韧性匹配与耐CO_(2)腐蚀性能,是深度>7000 m深井油井管的候选材料。从成分设计、生产工艺、组织调控等方面,论述了15Cr超级马氏体不锈钢油管的高强高韧综合控制技术。成分控制方面,采用无δ铁素体成分设计,w[Cr]取15%,w[Ni]取6.5%~7%,w[C]取0.01%~0.03%,w[Cu]取1.25%~1.5%,Cr、Ni元素合理匹配是降低δ铁素体含量的主要因素,C、Cu含量的合理匹配是获得高强高韧力学性能的关键因素。冶炼工艺方面,研究了电弧炉钢杂质元素的影响,结果表明,V、N、Al杂质元素会增加15Cr钢的硬度,将回火温度提高至550~575℃,能够降低硬度保证韧性。热加工成型方面,通过热变形试验,获得了15Cr钢的动态再结晶规律,制定了无缝管热穿孔成型变形温度1100~1150℃,能够获得细小的再结晶晶粒。组织性能调控方面,通过热处理工艺研究,确定了正火温度采用950~980℃,即能保证晶粒尺寸不明显长大,又能获得高强度与高韧性的匹配。

1961—2023年新疆区域冷空气过程强度特征

利用1961—2023年新疆105站日平均气温和日最低气温,24、48、72 h日最低气温降温幅度以及NCEP/NCAR再分析日资料,分析新疆区域不同强度冷空气过程的变化特征,探究影响新疆区域冷空气过程的关键环流因子。结果表明:1961—2023年新疆区域冷空气过程共计发生746次,其中中等强度冷空气过程149次,强冷空气过程136次,寒潮过程461次。新疆区域冷空气过程整体呈减少趋势,21世纪后新疆区域寒潮过程在冷空气过程中所占比率逐渐增加,但寒潮过程年平均强度波动不显著。新疆区域发生强寒潮过程的关键因子是乌拉尔山阻塞高压和欧亚冷高压,乌拉尔山阻塞高压和欧亚冷高压强盛时,有利于高纬度冷空气南下,新疆区域易暴发寒潮。