二十辊森吉米尔轧机辊系稳定性的有限元分析

应用ABAQUS有限元软件建立了二十辊轧机有限元分析模型,研究了不同辊径配置及不同轧制力工况对二十辊森吉米尔轧机辊系稳定性的影响。结果表明:第1中间辊辊径差不小于2mm时,第1中间辊和第2中间辊被挤出;第2中间辊辊径差不小于4mm时,辊系失稳散落;第2中间随动辊比驱动辊小,会使第1中间辊辊间距变小,并使第2中间驱动辊与B、C支撑辊接触点的应力变小。随着轧制力的增大,第1中间辊的辊间距增大,第2中间驱动辊与B、C支撑辊接触点处的应力也增大。     

铸坯差温预压下处理工艺研究

由于对高性能钢的需求越来越广,进而对其连铸坯的质量要求不断提高,而铸坯中又以疏松缺陷最难消除。因此,对表面950℃、中心1 300℃以上的差温条件下的铸锭进行预压下试验,在铸锭大变形量部分,由于芯部处于高温奥氏体脆性区,塑性较差从而出现热裂;而小变形量部分,在差温作用下,铸锭内部优先变形,疏松和微观空洞被明显压合,又由于一定范围内的再结晶,减轻了铸锭内部的晶界偏析。试验结果表明,小变形量的差温预压下技术可以显著提高铸坯质量,具有进一步研究和在连铸坯生产中应用的重要价值。     

微米级银粉微观结构分析

通过使用XRD方法对热分解方法和碱体系还原得到的微米级银粉微观结构分析,结果表明微米级银粉都是纳米级的银晶体颗粒组成,且为面心立方结构;银粉晶粒表现为各向异性;制粉条件会影响银粉晶粒尺寸,升高热分解温度促使晶粒变小,机械整形和磨制促使晶粒变小;制备的银粉存在晶格畸变,均表现为晶格膨胀;制粉条件会影响晶面的布拉格衍射强度,且对不同晶面的影响程度存在差异。     

塑性变形与退火对Ag-Ti3AlC2复合材料性能的影响

研究了塑性变形和退火处理对热压烧结Ag-Ti3AlC2复合材料力学及电学性能的影响。结果表明,塑性变形+退火处理能显著提高复合材料的导电性,其中Ag-20%Ti3AlC2(体积分数)电阻率降幅达到15.02%;复合材料的抗拉强度随着变形量的增加而大幅提升,Ag-20%Ti3AlC2复合材料在Φ2 mm加工态时抗拉强度达到最高的462.42 MPa,经退火处理,其强度降低28.57%,延伸率提高435.11%,达到19.05%,综合力学性能显著提高。     

ABS塑料化学镀镍激光无钯活化工艺

化学镀是ABS塑料表面金属化最常用的方法之一,但在施镀前需要使用钯等贵金属对基体进行活化,使其具有催化活性。以NiSO_4与NaH_2PO_2混合配制活化液,涂覆于塑料基体表面,常温放置8~10min后,基体表面形成一层活化层;用激光均匀扫描基体表面,活化层在激光作用下反应生成活性Ni微粒使基体活化,再进行化学镀镍。采用正交试验优化激光活化各参数,通过扫描电镜对各阶段基体表面形貌进行表征,利用能谱和X衍射对活化及施镀后的基体表面成分进行分析,采用高低温冲击法检测镀层结合性。结果表明,当NiSO_4与NaH_2PO_2浓度分别为10g/L和40 g/L,光斑直径为1mm,扫描速率为5 mm/s,涂覆次数为2次时,镀覆效果最好;基体活化后,表面附着一层均匀的平均直径为30nm的活性Ni微粒催化核心;施镀后,镀层均匀致密,结合性较好。     

Effect of processing parameters on electropolishing of commercially pure Ti in an alcohol-based electrolyte

Commercially pure titanium (Cp-Ti) foils were electropolished by using a DC power source in an alcohol-based electrolyte. The influences of applied voltage, processing time, electrolyte temperature and agitation on surface morphology and surface oxygen content were investigated and are reported. Results showed that optimum surface finish in this electrolyte can be achieved at applied voltages in the range of 35–75?V with shorter times at higher applied voltage. Also, increasing electrolyte temperature efficiently accelerates the electropolishing process and gives better surface finishes with respect to that achieved with lower electrolyte temperature at short processing times. Oxygen content of the surface varies with processing parameters and directly affects the surface morphology. The smoothest surface finish was always accompanied by the lowest oxygen content on the surface.     

螺栓与被连接件间轴向相对刚度的修正计算

螺栓连接结构的载荷分配比例和螺栓与被连接件间的轴向相对刚度密切相关。为了更准确地求解螺栓连接结构中螺栓与被连接件间的轴向相对刚度，基于被连接件垂直于螺栓轴的各受压层压应力均匀分布与非均匀分布形式下的轴向压缩变形量解析式，结合有限元仿真结果，提出了被连接件压缩变形体起始直径的修正公式及轴向压缩变形量的修正解析式。通过提取仿真应力值，对压应力理论修正方程、压应力仿真拟合方程进行积分计算。对比计算结果发现：用仿真拟合方程计算得到的被连接件压缩变形体轴向压缩变形量与用理论修正方程计算得到的变形量的误差小于2.5%，这说明用仿真拟合方程求解被连接件压缩变形体的轴向压缩变形量具有较高的精度。研究结果表明：修正起始直径与夹紧长度、螺栓头与螺母支承面直径呈线性关系。压应力非均匀分布下，用被连接件压缩变形体轴向压缩变形量的修正解析式求解螺栓与被连接件间轴向相对刚度时，误差小于2%，表明该修正解析式能够较为准确地计算螺栓与被连接件间的轴向相对刚度。在修正起始直径的基础上，基于被连接件各受压层压应力非均匀分布的轴向相对刚度计算结果比基于均匀分布的更准确。研究结果为理论研究和实际工程中准确分析螺栓的受力情况提供了一定参考。     

木粉疏水改性对HDPE基木塑复合材料性能的影响

采用一种操作简便且易于工业推广的方法对木粉进行疏水改性，具体过程为：将3种可热聚合的单体，即甲基丙烯酸甲酯（MMA）、甲基丙烯酸丁酯（BMA）和苯乙烯（St）均匀喷洒在木粉上，经过预热处理后，与配方中其他组分，如高密度聚乙烯（HDPE）和马来酸酐接枝聚乙烯（MAPE）等通过高速混合机混合均匀，采用双螺杆挤出机造粒后，注射制备木塑复合材料（WPC）样条，测试其力学性能。另外，考察了疏水改性对WPC接触角、维卡软化温度、洛氏硬度、吸水性能、热性能的影响规律。结果表明：疏水改性后WPC的接触角增大，木粉和HDPE的界面相容性改善，力学性能得到明显提高。其中，当MMA、BMA和St的添加量为3%时，WPC的力学性能最好，与疏水改性前相比，弯曲强度分别提高了17.3%、26.3%和27.5%，弯曲模量分别提高了24.4%、24.4%和26.0%，冲击强度分别提高了54.7%、57.7%和60.5%。 此外，疏水改性后WPC的维卡软化温度、洛氏硬度、耐水性和耐热性也得到改善。     

Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints

A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer (CFRP) sheets was proposed and evaluated. The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses. Five T-joints were physically tested: one bare joint to obtain the peak load and corresponding displacement (D_1m), two reinforced joints to provide a reference, and two pre-damaged then retrofitted joints to serve as the primary research objects. The ratio of the pre-loaded specimen chord displacement to the value of D_1m was considered to be the degree of damage of the two retrofitted joints, and was set to 0.80 and 1.20. The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06% over the corresponding unreinforced specimens. However, the capacity of the retrofitted specimen was 2.51%–22.77% lesser compared with that of the directly reinforced specimens. Next, 111 numerical analysis models (0.63≤b≤0.76, 9.70≤g≤16.92) were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage. The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping, and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters. Finally, reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results. The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.     

厚松散层薄基岩坚硬顶板工作面覆岩破坏电法监测

掌握导水裂缝带发育高度对于厚松散层薄基岩煤矿工作面安全开采具有重要的意义。在煤层采动影响前,在工作面巷道向煤层工作面顶板施工1个仰孔,布置孔中电极电缆,形成钻孔电法监测系统。在巷道中连接并行电法仪器和钻孔电缆,数据采集方式称为AM法。随采煤工作面位置逐渐接近并进入钻孔控制范围,监测电极电流值和视电阻率值发生变化。结果表明:对潘北煤矿厚松散层薄基岩坚硬顶板工作面电法监测显示,弯曲下沉带电极电流值和视电阻率值较为稳定,受采动影响程度较小;导水裂缝带内,电极电流值明显下降,视电阻率值明显升高;顶板高度0~40 m采动超前影响范围可达410 m左右;工作面坚硬顶板砂岩地层为控制覆岩破坏的关键层,采空区上方坚硬顶板岩层垮落滞后工作面9~16 m;工作面导水裂缝带高度为37 m,导水裂缝带未发育到基岩面,风化砂质泥岩裂隙在采动应力作用下存在闭合现象。