Effect of austempering parameters on microstructure and mechanical properties of horizontal continuous casting ductile iron dense bars

In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.

Effect of heat treatment on microstructures and mechanical properties of extruded-rolled AZ31 Mg alloys

The deformation behaviors of extruded-rolled(ER)AZ31 Mg alloys with different rolling reduction and heat treatment were investigated.The results show that the accumulation of rolling reduction increases the density of twins,and refines the grain structures,which are in accordance with the enhanced strength and degraded plasticity.Tensile strength and plasticity of the alloy depend mainly on rolling reduction,while heat treatment temperature plays a more important role than heat treatment time at the same rolling reduction.With the increase of rolling reduction,the plasticity becomes more sensitive than strength on heat treatment. Recrystallization of extruded-rolled alloys will occur easily with deformation increasing,which is induced by addition of distortion energy.

Mechanical Test and Meso-Model Numerical Study of Composite Rubber Concrete under Salt-Freezing Cycle

A composite rubber concrete(CRC)was designed by combining waste tire rubber particles with particle sizes of 3~5 mm,1~3 mm and 20 mesh.Taking the rubber content of different particle sizes as the influencing factors,the range and variance analysis of the mechanical and impermeability properties of CRC was carried out by orthogonal test.Through analysis,it is concluded that the optimal proportion of 3~5 mm,1~3 mm,and 20 mesh particle size composite rubber is 1:2.5:5.5 kinds of CRC and 3 kinds of ordinary single-mixed rubber concrete(RC)with a total content of 10%~20%were designed under this ratio,and the salt-freezing cycle test was carried out with a concentration of 5%Na 2 SO4 solution.The physical and mechanical damage laws during 120 salt-freezing cycles are obtained,and the corresponding damage prediction model is established according to the experimental data.The results show that:on the one hand,the composite rubber in CRC produces a more uniform“graded”structure,forms a retractable particle group,and reduces the loss of mechanical properties of CRC.On the other hand,colloidal particles with different particle sizes are used as air entraining agent to improve the pore structure of concrete and introduce evenly dispersed bubbles,which fundamentally improves the durability of concrete.Under the experimental conditions,the CRC performance is the best when the overall content of composite rubber is 15%.

Fast determination of meso-level mechanical parameters of PFC models

To solve the problems of blindness and inefficiency existing in the determination of meso-level mechanical parameters of particle flow code (PFC) models, we firstly designed and numerically carried out orthogonal tests on rock samples to investigate the correlations between macro-and meso-level mechanical parameters of rock-like bonded granular materials. Then based on the artificial intelligent technology, the intelligent prediction systems for nine meso-level mechanical parameters of PFC models were obtained by creating, training and testing the prediction models with the set of data got from the orthogonal tests. Lastly the prediction systems were used to predict the meso-level mechanical parameters of one kind of sandy mudstone, and according to the predicted results the macroscopic properties of the rock were obtained by numerical tests. The maximum relative error between the numerical test results and real rock properties is 3.28% which satisfies the precision requirement in engineering. It shows that this paper provides a fast and accurate method for the determination of meso-level mechanical parameters of PFC models.

Construction of virtual mulch film model based on discrete element method and simulation of its physical mechanical properties

In China,especially in Xinjiang Region,mulch film remaining in the soil has severely jeopardized the safety of soil resources.To numerically simulate the residual film-soil-recovery implementation system,a virtual mulch film model with consistent physical and mechanical properties with real mulch film needs to be established.In this study,a flexible deformable virtual mulch film model was constructed using YADE software based on the Minkowski Sum principle and the ball-ball force-displacement constitutive rule,as well as the contact failure rule were established.The deformation behaviors of cylinders and PFacet elements,such as stretching,bending,and torsion,were described.By splicing the basic PFacet elements,a virtual mulch model was established.The mechanical model of a virtual mulch film under tension was established and the axial tensile stiffness coefficient kn was determined to be 43.30 N·m.To verify the physical and mechanical properties of this virtual mulch film,both real and virtual stretching and tearing tests were conducted.The experimental results showed that:in the process of stretching and tearing of real and virtual films,the properties of morphological features of both are basically identical;however,they clearly differ in force-displacement.The viscoelastic constitutive model between balls and yield judgment conditions requires further study.

Modification Effect of P+Sr+Ce Compound on Microstructure and Properties of Cast High Silicon Heat-Resist Aluminum Alloy

The P ＋ Sr ＋ Ce compound modification technologies of as-cast Al-21Si-1.5Cu-1.5Ni- 2.5Fe- 0.5Mg alloy were investigated by means of orthogonal test. Orthogonal test results show that 3% （CaH2PO4 ＋ 2CASO4）＋ 0.2%Sr ＋ 0.2%Ce is the optimum additive of modification treatment which can fine eutectic and primary silicon also can change the form of rich-iron phase at same time. The needle form of rich-iron phase is Al9FeSi3, which is prored by X-ray diffraction analysis and X-ray energy spectrum analysis. After compound modification treatment, the needle form of rich-iron phase disappeared and the fish bone form of rich-iron and rich-Ce phase that is AlsCeFe emerged. Both at room temperature and at 300℃, the tensile strength of the alloy after the modification treatment with the optimum additive is 30% lager than that of the alloy unmodified. Observed by SEM, the brittle intercrystalline tensile fracture changed into a blended one in which has many dimples.

A Palladium Based Alloy for Prosthetic Dentistry: Structure and Properties

Using the results of physical and chemical researches and mechanical tests of the Pd-Au-Cu-Sn system alloys, a new palladium-based alloy has been chosen and studied in detail. It has a higher plasticity and a lower hardness than the Palladent alloy, widely used in prosthetic dentistry: its hardness is lower than 300 MPa, and its specific elongation is 10%~14 %. At the same time, such important practical characteristics of the alloys as the strength of adhesion to ceramics and thermal expansion coefficient are almost similar.

改性水玻璃固化模拟月壤抗压性能试验与分析

为探究改性水玻璃模数、质量分数、固化温度、固化时间及养护龄期等因素影响下模拟月壤抗压强度的变化规律,基于正交试验分析了上述因素对固化模拟月壤抗压强度的敏感度,并通过X射线衍射(X-ray diffraction,XRD)和扫描电子显微镜(scanning electron microscope,SEM)扫描试验探讨了改性水玻璃对模拟月壤的固化机理。正交试验结果表明:合适的影响因素水平能提高模拟月壤的抗压强度,养护龄期为28 d、激发剂模数为1.8、质量分数为50%、固化温度为65℃、固化时间为9 h时,抗压强度达到极值。微观试验结果表明:在激发剂模数为1.8、质量分数为50%条件下,改性水玻璃能提高水化硅铝酸钙凝胶产量,充填试样内部孔隙,使结构更加紧密,故模拟月壤抗压强度得到提高。

选区激光熔化AlSi10Mg蜂窝夹层管制备及其力学性能研究

目的研究SLM工艺参数对蜂窝夹层管残余应力、变形以及力学性能的影响。方法采用正交试验法研究了不同工艺参数对选区激光熔化成形零件残余应力和变形的影响。通过有限元模拟的方法,仿真AlSi10Mg蜂窝夹层管的3D打印过程,得到成形管件的残余应力分布及变形程度。制备蜂窝夹层管3D打印试样,将实心管作为对照组,对比测试管件在轴向压缩、径向压缩及三点弯曲条件下的力学性能。结果激光功率对残余应力和变形的影响最大。采用最优参数组合打印的管件微观形貌中不同熔池之间呈现出相互交错的结构,致密度达99.78%。轴向压缩中实心管的承载极限为497 MPa,蜂窝夹层管的最大承载极限为390 MPa。在径向压缩条件下,蜂窝夹层管承载能力是实心管的86.62%。在三点弯曲试验中蜂窝夹层管出现2次波峰,承载极限为52 MPa,与实心管的承载极限非常接近。结论确定最优参数组合为:激光功率200 W、扫描速度1200 mm/s、扫描间距100μm,蜂窝隔板厚度0.6 mm、蜂窝孔对边距离5 mm。相同尺寸的蜂窝夹层管相较于实心管质量可以降低22.68%,其力学性能降低并不明显。

天然蚕丝/氨纶包覆参数对包覆纱力学性能的影响

研究包覆纱纺纱参数与力学性能间的关系是精确调控压力衣的服装压的基础。设计L_(9)(3^(4))正交试验,研究纺纱参数(捻度比、内捻度、牵伸倍数)对力学指标(应力松弛率、弹性回复率、断裂强度)的影响并评选最优组合。采用二次通用旋转组合设计分析纺纱参数与纱线模量的关系,并建立数学预测模型。结果表明:影响应力松弛率和断裂强度的因素依次为捻度比>内捻度>牵伸倍数;影响弹性回复率的因素依次为牵伸倍数>内捻度>捻度比。排队评分法得出,牵伸倍数2.8、内捻度1600捻/m、捻度比70%时纱线的综合性能最优。初始模量随捻度和牵伸倍数的增大而先减小后增大,随捻度比的增大而增大;拉伸模量随牵伸倍数的增大而先减小后增大,随内捻度和捻度比的增大而增大。

固废基盾构惰性同步注浆材料力学性能及抗水分散性研究

以典型固废矿渣微粉、粉煤灰、硅灰为原料制备固废基盾构惰性同步注浆材料,采用六因素五水平正交试验,开展了注浆材料力学性能及抗水分散性的试验研究。结果发现:增大碱激发剂模数,减小其掺量,则浆液抗压强度下降;水胶比、膨水比对浆液抗动水冲刷能力的影响较大;碱激发剂掺量和水胶比是影响浆液水陆强度比的主要因素。根据正交试验极差分析和综合性能平衡,确定了注浆材料的优选配合比:水胶比1.00,胶砂比0.45,膨水比0.35,减水剂掺量1.5%(质量分数),碱激发剂模数1.6,碱激发剂掺量20%(质量分数),此时注浆材料28 d抗压强度为13.02 MPa,水陆强度比为80.83%,3 h动水冲刷质量损失率为5.62%;并开展了稠度、凝结时间、泌水率和结石率等性能试验,测试指标均达到了活性浆液的要求。以上研究为工业固废在盾构注浆技术领域的应用提供了一定的研究基础和实验依据。

基于正交试验的地聚合物胶凝材料性能研究

以粉煤灰和矿渣作为原材料,基于正交、优化试验确定地聚合物胶凝材料的最优配合比,即粉煤灰与矿渣粉质量比为1∶2,碱激发剂掺量为12%,水玻璃模数为1.2。开展微观试验,以探讨地聚合物反应机理。研究结果表明,地聚合物胶凝体系中含有C-S-H,C-A-S-H和N-A-S-H,其相互交织构成了密实的微观结构,水泥基胶凝材料反应产物主要为Ca(OH)_(2)、钙矾石、SiO_(2)等,且在水泥基胶凝材料界面可看到明显层状叠加的Ca(OH)_(2)、针棒状的钙矾石等物质形成的结构层;水泥基胶凝材料具有较多孔隙,导致水泥基胶凝材料性能弱于地聚合物胶凝材料。

Si、Cu、Ti对亚共晶铝硅合金组织与性能的影响

使用正交试验的方法研究了Si、Cu、Ti三种合金元素对铸造亚共晶铝硅合金组织及性能的影响。结果表明,铸态合金中主要由α(Al)、共晶Si、θ-Al_(2)Cu、Q-Al_(5)Cu_(2)Mg_(8)Si_(6)和Π-Al_(8)Mg_3FeSi_(6)相组成,热处理后θ-Al_(2)Cu相更均匀的析出,而Π相转变为β-Al_(5)FeSi(Cu)相。经过元素调控和T6热处理后的铸造铝硅合金通过力学性能测试发现,当Si含量为9%、Cu含量为1.5%、Ti含量为0.1%时,T6(固溶520℃保温5 h+时效180℃保温4 h)处理的铝合金强塑性匹配达到最佳。合金的室温抗拉强度和伸长率分别为422 MPa和6.2%,250℃保温1 h的高温抗拉强度和伸长率分别为215 MPa和9.6%,为缸盖材料的应用和发展提供了一定的理论指导。

高强预填集料混凝土灌浆料制备与灌注效果评价

预填集料混凝土是在模板内预铺粗集料,然后注入灌浆料填充集料间隙而形成的一种新型混凝土。作为预填集料混凝土的重要组成部分,灌浆料的性能与灌注质量直接影响预填集料混凝土的整体性能,但现有灌浆料因流动度或强度不足,难以满足高强预填集料混凝土的灌注要求。设计正交试验,探究了水胶比、胶砂比和胶凝材料体系对灌浆料工作性能与力学性能的影响规律,提出高强大流态灌浆料的制备方法,并采用重力灌注和泵送灌注进行了预填集料混凝土模拟灌注试验,从试件外观质量、灌注密实度和抗压强度等方面验证了灌浆料的灌注效果。结果表明:水胶比是影响灌浆料综合性能的主要因素,胶砂比主要影响灌浆料的流动性,双掺粉煤灰和硅灰可以协同提升灌浆料的工作性能与力学性能。高强预填集料混凝土采用泵送灌注效果优于重力灌注,相同条件下泵送灌注可达到更高密实度,但利用净浆或流动度较高的砂浆作为灌浆料时,重力灌注法也能达到较好密实灌注效果。采用0.3水胶比、双掺15%的粉煤灰和4%的硅灰,制备出流动度值为35 s的净浆,其28 d抗压强度为70.9 MPa,密实灌注的预填集料混凝土28 d抗压强度可达96.8 MPa。

喷射沙漠砂混凝土工作和力学性能正交试验研究

为了制备喷射沙漠砂混凝土,采用正交试验研究水胶比、砂率、粉煤灰替换率、沙漠砂替换率及单位用水量对喷射沙漠砂混凝土工作性能和力学性能影响的规律,得出其最优配合比,并构建了强度预测模型。结果表明:影响工作性能显著性的因素顺序为水胶比>沙漠砂替换率>单位用水量>砂率>粉煤灰替换率,影响28 d抗压强度显著性的因素顺序为水胶比>沙漠砂替换率>粉煤灰替换率>单位用水量>砂率,影响28 d劈裂抗拉强度显著性的因素顺序为水胶比>粉煤灰替换率>沙漠砂替换率>单位用水量>砂率。喷射沙漠砂混凝土的最优配合比为水胶比为0.43、沙漠砂替换率为30%、粉煤灰替换率为20%、砂率为50%、减水剂用量为2%、单位体积用水量为180 kg·m^(-3)。提出的喷射沙漠砂混凝土立方体抗压强度和劈裂抗拉强度预测模型精度较高。本研究可为喷射沙漠砂混凝土的应用提供参考。

经验知识监督的RC墩柱力学性能神经网络分析方法

基于试验或数值模拟的单一墩柱力学性能分析方法难以兼顾计算精度和效率,纯数据驱动的分析方法存在可解释性差和对数据依赖性强等问题。为此,本文通过研究钢筋混凝土(RC)墩柱力学性能试验数据、经验知识和机器学习的融合机制,提出了经验知识监督的RC墩柱力学性能神经网络(knowledge-guided neural network,KGNN)分析方法。首先,建立了包含761组RC墩柱拟静力试验样本的数据库;随后,基于经验知识分析了RC墩柱主要特征对其力学性能的影响规律,构建了相应的数学表征方法;最后,将RC墩柱试验数据及经验知识融入人工神经网络架构和训练过程,建立了高精度、可解释、可通用且不依赖大量训练数据的RC墩柱力学性能KGNN分析模型。本文提出的KGNN分析方法与纯数据驱动神经网络(BPNN)的结果对比表明:BPNN在测试集上表现更好,在分析墩柱承载力时均方根误差(E)和拟合系数(R^(2))分别为0.070和0.978,KGNN模型的E和R^(2)分别为0.108和0.942;但由于BPNN所预测的墩柱特征对承载力的影响规律与经验知识并不吻合,即未能准确反映墩柱特征与其力学性能间的关系,BPNN模型发生了过拟合;而KGNN方法不仅可以快速准确获得RC墩柱力学性能,且预测规律与经验知识吻合较好,具有更高的可靠性和实用性。因此,融合试验数据与经验知识的神经网络有望成为一种新的RC结构力学性能分析方法。

古建用落叶松木材物理力学性能预测及其影响因素

为实现对木结构古建筑的预防性保护,有必要对木构件的材质性能进行及时有效的预测和评价。采取小试样-缩尺-足尺递进的方式,将微钻阻抗仪和应力波检测等无损检测方法与实验室物理力学性能测试相结合,构建并检验了落叶松木材物理力学性能与微钻阻抗值和波阻模量关系预测模型,进而提出了古建用落叶松木材物理力学性能的现场无损检测分析方法。研究结果表明:落叶松小试件密度与微钻阻抗值呈现明显的线性正相关关系,木材密度与微钻阻抗值线性方程相关系数为0.91;落叶松小试样顺纹抗压强度、抗弯强度及抗弯弹性模量与波阻模量呈现较明显的线性正相关关系,木材顺纹抗压强度、抗弯强度、抗弯弹性模量与波阻模量线性方程相关系数分别为0.86,0.74,0.74;通过微钻阻抗仪和应力波检测可推算落叶松木材物理力学性能。利用小试件测试数据所建立的预测方程进行落叶松大试件物理力学性能推算存在一定的误差,其缩尺试件密度和顺纹抗压强度预测值与实际值平均偏差分别为12%和16%,足尺试件密度和顺纹抗压强度预测值与实际值平均偏差分别为16%和17%。现场预测应同时考虑测试路径因素,自心材至边材区域,落叶松木材密度、顺纹抗压强度、微钻阻抗值沿径向表现为增大趋势,外层微钻阻抗值比整体平均微钻阻抗值大4%~16%。在古建筑木构件强度检测评估中,应进行木构件的整体微钻检测;若条件所限无法进行整体检测时,应针对不同树种的径向变化规律进行微钻阻抗值的修正。

某心墙坝土料分散性判别与石灰改性土的性能规律分析

分散性土作黏土心墙会影响大坝的防渗安全,通过针孔试验、碎块试验对新疆某心墙土料的分散性进行了判别,分别采用天然河水与石灰进行改性试验,研究不同石灰掺量和陈化时间对改性土物理、力学性能的影响规律。结果表明,黏粒含量为12%是土料产生物理性、化学性分散的界限;采用天然河水进行改性,效果不佳,当石灰掺量为3%时,可完全消除分散性;土样掺入1%的石灰后,界限含水率变化明显,最大干密度由1.79 g/cm3降至1.69 g/cm3、压缩模量由13.4 MPa增至19.4 MPa、黏聚力由25.1 kPa升至43.3 kPa;随石灰掺量的增加,最大干密度提高、内摩擦角减小,黏聚力增大;随着陈化时间的延长,液限呈增长趋势,最大干密度在24 h内较稳定,之后开始降低,240 h后趋于稳定,压缩性在72 h内变化不明显,而后开始增强。由于石灰中含有大量的钙离子,因此使分散性土的性能发生变化。

高填充油茶果壳基木塑复合材料的制备及力学性能

以油茶果壳和不同塑料即聚丙烯、高密度聚乙烯(PE-HD)、低密度聚乙烯、线性低密度聚乙烯为原料,采用模压成型的方法制备了高填充油茶果壳基木塑复合材料,利用电子万能试验机和悬臂梁冲击试验机测试其力学性能。通过单因素试验分析塑料种类对复合材料力学性能的影响,确定较优塑料种类后进一步优化制备参数。以壳粉含量、增容剂马来酸酐接枝聚乙烯(MAPE)含量、热压温度、热压时间为设计因素,以弯曲强度、弯曲弹性模量、拉伸强度、冲击强度为力学性能优化目标,设计L_(9)(3^(4))正交试验,研究了高填充油茶果壳基木塑复合材料的制备工艺,利用极差分析和方差分析得到了较优配方和工艺参数组合。研究表明:当添加塑料为PE-HD时,复合材料的弯曲强度最大为34.40 MPa,拉伸强度最大为18.20 MPa,力学性能较优;壳粉含量为65%时,添加7%MAPE的复合材料强度较好,弯曲强度最大为33.66 MPa;优化制备参数组合为壳粉含量55%,MAPE含量5%,热压温度160℃,热压时间10 min。

室温碱激发粉煤灰基胶凝材料制备及其性能研究

以不同细度粉煤灰为原料,加入适量矿渣和水泥熟料,并以钠水玻璃为碱激发剂,在常温下制备出了碱激发粉煤灰基胶凝材料。采用正交试验的方法,分析了原状粉煤灰与磨细粉煤灰质量比、碱激发剂中NaOH含量、矿渣用量和碱激发剂掺量对碱激发粉煤灰基胶凝材料抗压强度的影响,结合XRD和SEM对试样进行表征。结果表明:当原状粉煤灰和磨细粉煤灰质量比为1∶3、碱激发剂中NaOH含量为15%、矿渣用量为固废的20%、碱激发剂掺量为液体总量的13%时,胶凝材料3、28、60d抗压强度分别为19.6、29.0、35.5MPa。粉煤灰与矿渣中的Al—O键和Si—O键断裂,发生重组生成硅铝酸盐C-A-S-H凝胶和C-S-H凝胶。