基于Design-Expert的碱激发粉煤灰建筑外墙腻子配合比优化试验研究

为了拓展工业固体废弃物粉煤灰的回收利用途径,减少对环境造成的污染,增加其在筑材料中回收利用率。在建筑外墙腻子中加入碱性激发剂(Ca(OH)_(2)、Na_(2)SiO_(3))、粉煤灰,研究碱性激发剂的激发效果。同时通过Design-Expert设计试验,分析主要组分对腻子漆膜粘结强度、吸水量的影响。结果表明:加入碱性激发剂5%,粉煤灰32.5%时,吸水量减少14%,粘结强度增加43%。乳胶粉对吸水量、粘结强度的影响非常显著(P<0.0001),其次是粉煤灰的加入量。通过加入碱性激发剂、提高乳胶粉占比,粉煤灰掺量能达到32%~65%,原配比中水泥的掺量相对减少0%~16%。

On the Loads for Strength Design of Cutterhead of Full Face Rock Tunnel Boring Machine

Cutterhead loads are the key mechanical parameters for the strength design of the full face hard rock tunnel boring machine(TBM).Due to the brittle rock-breaking mechanism,the excavation loads acting on cutters fluctuate strongly and show some randomness.The conventional method that using combinations of some special static loads to perform the strength design of TBM cutterhead may lead to strength failure during working practice.In this paper,a three-dimensional finite element model for coupled Cutterhead–Rock is developed to determine the cutterhead loads.Then the distribution characteristics and the influence factors of cutterhead loads are analyzed based on the numerical results.It is found that,as time changes,the normal and tangential forces acting on cutters and the total torque acting on the cutterhead approximately distribute log normally,while the total thrusts acting on the cutterhead approximately show a normal distribution.Furthermore,the statistical average values of cutterhead loads are proportional to the uniaxial compressive strength(UCS)of cutting rocks.The values also change with the penetration and the diameter of cutterhead following a power function.Based on these findings,we propose a three-parameter model for the mean of cutterhead loads and a method of generating the random cutter forces.Then the strength properties of a typical cutterhead are analyzed in detail using loads generated by the new method.The optimized cutterhead has been successfully applied in engineering.The method in this paper may provide a useful reference for the strength design of TBM cutterhead.

Limitations and potential design risks when applying empirically derived coal pillar strength equations to real-life mine stability problems

The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.

Strength Design Method for Tubing Hanger of Subsea Christmas Tree Against Big Temperature Difference

The tubing hanger is an important component of the subsea Christmas tree, experiencing big temperature difference which will lead to very high thermal stresses. On the basis of API 17D/ISO 13628-4 and ASME VIII-1, and by comprehensively considering the erosion of oil and the gravity load of the tubing, a calculation model is established by regarding design pressure and thermal stress, and the method for designing the tubing hanger of the horizontal Christmas tree under big temperature difference condition is developed from the fourth strength theory. The proposed theory for strength design of the tubing hanger in big temperature difference is verified by numerical results from ABAQUS.

Engineering Structure and Strength Design of Reducer Bend under Internal Pressure

Standard reducer bends have structural functions of both bend and reducer pipe at the same time. However, there is a lack of strength design method in the current codes. In order to develop the strength design method of the reducer bends subjected to internal pressure, analytical formulas are re-examined. Finite element analysis and stress measurements of the reducer bend are carried out. It is found that it is not appropriate to analyze the reducer bends by using thin membrane theory. The formula derived directly from circumferential stress formula of reducer bends under internal pressure is conservative, which is further verified by the finite element analysis results and it can thus be applied to piping design.

Design of a low-alloy high-strength and high-toughness martensitic steel

To develop a high strength low alloy （HSLA） steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstructure and mechanical properties of the designed steel were investigated by optical microscopy, scanning electron microscopy, tensile testing and Charpy impact test. The results show that cementite exists between 500℃ and 700℃, M7C3 exits below 720℃, and they are much lower than the austenitizing temperature of the designed steel. Furthermore, the Ti（C,N） precipitate exists until 1280℃, which refines the microstructure and increases the strength and toughness. The optimal alloying components are 0.19% C, 1.19% Si, 2.83% Mn, 1.24% Ni, and 0.049% Ti; the tensile strength and the V notch impact toughness of the designed steel are more than 1500 MPa and 100 J, respectively.

STUDY ON THE METHOD OF FATIGUE STRENGTH DESIGN FOR DYNAMICALLY LOADED JOURNAL BEARING

In this paper, a novel design method, which is different from the traditional and empirical one (i. e., taking p and pv as the basic checking parameters) is presented for the fatigue strength design of dynamically loaded journal bearings. The method makes it possible that dynamically loaded bearings can be desed as same as other machine elements by stress-strength criterion. The practical design results show that the method has high accuracy and reliability, and may open a new visa in bearing fatigue designs.

Factorial Experimental Design to Study the Effects of Layers and Fiber Content on Concrete Flexural Behavior

Experimentation has come a long in helping researchers achieve breakthroughs in their different scientific areas and engineering happens to be one of those areas with the most impact from experimental advancement. The need for valid experimental results free from biases and confounding conclusions has prompted the development of new experimental techniques that takes consideration of all applicable factor and combinations in providing answers on a research topic, and the Factorial Experimental design credited to Sir Ronald Fisher is one technique yielding highly valid results. This paper uses the factorial design of experiments to research the flexural impact of polyvinyl acetate fiber and layered concrete in construction. The experiment considered two levels of fiber contents and two levels of layers, and prepared samples with all combinations of the variable factors. The samples were tested after 7 days from casting for flexural strength and an advance statistical analysis was performed on the flexural responses of the samples using R-program. The results from the analyses revealed the significance of the variables to the flexural strength of the samples, as well as their interactions. The experiment concluded that based on the number of layers and fiber content used for the experiment, casting concrete in layers does have a significant negative effect on the flexural strength of concrete, and the failure pattern of concrete members under flexural load in evidently influenced by the material composition of the concrete, and that it can be evidently influenced by casting the concrete in layers.

Optimization of tensile strength for new type acetone-urea-formaldehyde furan resin using uniform design

In this study,the 24 h tensile strength of new type acetone-urea-formaldehyde furan resin (nitrogen content 3%) was investigated by uniform design optimization.Four independent variables such as acetone:formaldehyde molar ratio (mol/mol),solution pH value,reaction temperature (℃) and reaction time (min) were considered in the experiments.U13(134) uniform design was employed and the equation of 24 h tensile strength model was obtained after 13 experimentations.The 24 h tensile strength was optimized by applying single factor experiments and stepwise non-linear regression analysis.Minitab (Minitab 15 trial version) and MATLAB (R2010a trial version) were used for data analysis.The t-value and p-value indicate that the major impact factors include the interaction effect of solution pH value and reaction temperature (X2X3),the linear terms of acetone:formaldehyde molar ratio (X1),reaction time (X4) followed by the square effects of acetone/formaldehyde molar ratio (X1X1).The optimized results were achieved with the acetone:formaldehyde molar ratio (mol/mol) at 3:1,solution pH value at 6.0,reaction temperature at 70℃,and reaction time at 140 min,respectively.This method can not only significantly reduce the number and cost of the tests,but also provide a good experimental design strategy for the development of furan resin.The investigation shows that the predicted results of 24 h tensile strength are consistent well with the experimental ones.

基于响应面法的血管支架拉伸、扭转性能优化及考虑加工精度影响的强度可靠性分析

为分析设计变量对血管支架拉伸性能、扭转性能的精准影响,进行血管支架拉伸性能、扭转性能优化,考虑加工精度的影响,进行血管支架的强度可靠性分析。方法:取血管支架支撑筋宽度、支撑筋长度、连接筋宽度和支架厚度为设计变量,应用斯皮尔曼等级相关系数法分析设计变量对血管支架拉伸刚度、扭转刚度等响应变量的精准影响;采用响应面方法进行以拉伸刚度、扭转刚度为目标进行血管支架的优化设计;对优化后的血管支架,考虑加工精度所致设计变量的随机性,利用六西格玛工具分析应力的概率分布。结果:对于血管支架拉伸刚度,支撑筋宽度和连接筋宽度灵敏度系数大,且均为正值;对于血管支架扭转刚度,支撑筋宽度灵敏度系数较大,且为负值;优化后的血管支架相比原始血管支架,拉伸刚度降低了11.5%;扭转刚度减小了50.6%;考虑加工精度所致设计变量的随机性进行可靠性分析,在可靠度为99.8%时,虽然血管支架的拉伸刚度和扭转刚度最大值高于优化值,但血管支架的最大应力满足强度条件。结论:支撑筋宽度对血管支架的拉伸性能影响最大,连接筋宽度次之,支撑筋长度和支架厚度影响较小;支撑筋宽度对血管支架的扭转性能影响最大,连接筋宽度、支撑筋长度和支架厚度影响较小;随机因素加工精度对血管支架优化目标有一定的影响,但优化结果仍是可靠的。本文提供了一种血管支架优化的思路:首先是进行基于目标的优化,然后考虑随机因素的影响进行基于概率的强度可靠性分析。

轻木夹芯/碳纤维复合材料结构后推构型无人机机身设计与分析

设计了一款后推构型轻木夹芯/碳纤维复合材料结构无人机机身,完成了机身气动外形设计、流场分析和内部结构设计。建立了机身结构有限元模型,完成了结构刚度校核。编写子程序,将3D Hashin失效准则嵌入计算模型,基于三类失效模式构建极限状态函数g(x),对机身结构进行了强度及稳定性校核。采用等步长施加超设计载荷,预测了结构的初始损伤位置及模式。对机身蒙皮铺层方案进行了优化设计,采用g(x)函数对更改铺层方案后的结构性能进行了评估。研究结果表明:着陆工况和最大飞行速度工况的机身蒙皮表面压强最大值均在机头整流罩区域。两种工况的极限状态函数g(x)均大于0,最大位移分别为3.076 mm和2.92 mm,机身结构满足刚度、强度和稳定性要求。对着陆工况施加1.17倍设计载荷时,油料舱下壁板轻木芯材发生压缩分层初始损伤。机身结构失稳发生于侧面蒙皮,提高45°铺层占比可提高蒙皮的稳定性。玻纤蒙皮铺层优化后,在质量不变的条件下,结构稳定性裕度提高了7.2%。

Optimal Design for Thin-Walled Box Beam Based on Material Strength Reliability

According to the reliability of material strength,the optimal design for the cross sectional size of thin walled box beam was studied.Firstly the cross sectional size as design random variable was determined,then its stochastic nature was researched,with which the objective function is to seek the maximum reliability of the beam under given constraint conditions.This way is not the same as the conventional optimal design for the minimum weight of the material.With establishing the optimal objective,the reliability of the material under conditions of static and fatigue was considered.The corresponding calculated expressions are given.Normally the cross section sizes are fitted to the normal distribution,for the simplification of the design variable,the variation of the section size is assumed as a dependent variable proportional to the mean of the size.The way is different not only with the conventional optimal design but also with the common reliability design.The maximum reliability of material is obtained,meanwhile the area of the cross section is reduced,i.e.,the weight of the material is decreased.

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。

基于遗传算法的大型矩形压力容器刚强度优化设计

为了解决矩形压力容器承压能力较差、应力状态较复杂、结构优化设计难度高的难题,利用遗传算法可自适应调整搜索方向这一特性,开展了某矩形特征水洞试验段的刚强度优化设计。厘清了该工程问题的约束条件,开展了结构初步设计,采用手动迭代开展了结构优化设计;并在完成参数化建模与仿真、构建代理模型、建立优化设计流程的基础上,基于遗传算法开展了该水洞试验段的结构优化设计。该方法与初步设计结果相比,减重34.98%;与手动迭代优化设计结果相比,减重10.49%。

戈壁集料混凝土物理性能及抗压强度研究

为资源化利用西北地区工程建设开挖的弃方材料——戈壁集料,基于西北某机场扩建工程的戈壁集料,首先对戈壁集料基本物理性能及矿物成分进行分析,随后以水灰比、戈壁砂率、戈壁细集料种类及水泥浆量为变化参数,先后对戈壁集料混凝土的工作性能、破坏形态以及抗压强度进行研究。试验结果表明:戈壁集料含泥量高,其黏土矿物含量约20%且以吸水能力强的蒙皂石和伊利石为主;随水灰比减小,戈壁粗集料混凝土的坍落度减少,而抗压强度近似线性增大,与普通混凝土规律一致;同配合比下,全戈壁集料混凝土抗压强度高于戈壁粗集料混凝土,但前者的拌合物表现更黏稠;筛除粒径小于0.15 mm的戈壁细集料虽可小幅提高全戈壁集料混凝土的坍落度,但对抗压强度不利;随砂率增加,戈壁集料混凝土的坍落度增大,其抗压强度先增后减。最后,通过回归分析为戈壁集料混凝土配合比提供参考。

10 MW级海上风电新型浮式基础结构强度分析

针对应用于50 m水深海域的10 MW海上风力机,设计由三浮筒及三立柱组成的新型浮式基础,建立带有骨材结构的有限元分析模型。对于有关此新型浮式基础的设计波参数,一般选用随机性设计波的方法来确定,对波浪载荷工况下的整体结构。重点研究浮筒的骨材尺寸以及骨材间距对新型浮式基础强度的影响规律,并得到纵横骨材尺寸组合对新型浮式基础整体强度的影响规律。研究表明,新型浮式基础结构高应力区域位于3个浮筒连接处,浮筒板单元应力水平受骨材尺寸和骨材间距的共同影响,采用合适的尺寸间距组合可在应力水平相当的情况下显著降低用钢量。

三种固废改性生土材料配方设计及力学性能研究

为改善生土材料的力学性能,本研究以铁尾矿、煤矸石、电石渣、油泥与水泥等材料作为掺和料对生土进行改性。基于单形格子法设计配方,对3种配方、180个改性生土试件进行抗压强度试验,研究不同因素对试件破坏形态、抗压强度和试验数据离散性的影响;利用频数分析法,研究了固废改性生土材料的最优配方;通过CT扫描,从细观层面分析受荷后材料内部的分形和孔隙。结果表明:改性生土试件抗压破坏形态基本相同,极限位移受掺料影响显著。以煤矸石与电石渣、铁尾矿与水泥、油泥与水泥作为掺和料均可大幅提高改性生土试件的力学性能,掺和料种类、掺量对改性生土试件强度及数据离散性影响显著。经过频数寻优,3种配方的理想强度掺和料配比分别为1)铁尾矿12.1%~19.5%(质量分数,下同)、水泥13.9%~19.1%、生土65.5%~69.9%;2)电石渣6.7%~14.1%、煤矸石8.9%~11.8%、生土76.7%~81.8%;3)油泥11.4%~14.4%、水泥17.4%~19.4%、生土67.1%~70.5%。材料内部的分形和孔隙特征稳定,表现出较小的波动性和良好的密实性。

CFRP-PE-不锈钢筋混凝土短柱的设计方法研究

进行了17个CFRP-PE-不锈钢筋混凝土短柱和8个对比试件的轴压试验,探究不锈钢种类、箍筋间距、CFRP厚度、PE厚度对该类组合柱的破坏模态、荷载-应变曲线、极限应变、极限承载力、延性的影响规律.试验结果表明:在CFRP和混凝土间设置PE垫层能提高该类组合短柱的延性和变形能力,并降低其承载力;增大CFRP厚度可提高其承载力和极限应变,但试件表现出增大的脆性;减小箍筋间距或增大钢筋强度可显著提高其承载力、峰值应变和延性.建立了有限元模型,有限元分析表明:增大PE厚径比会显著提高该类组合短柱的变形能力和延性,并降低CFRP对其承载力的影响;增大配箍率、不锈钢强度、CFRP抗拉强度、CFRP厚度可提升该类组合短柱的极限应变与承载力;提高混凝土强度会提高该类组合短柱的峰值承载力,但降低其极限应变.最终建议了该类组合短柱的延性设计方法、承载力模型和极限应变模型.

大型耙吸挖泥船结构设计要点

为实现大型耙吸挖泥船结构设计安全、合理、可靠,以某大型耙吸挖泥船为例,分析大型耙吸挖泥船结构设计特点,从结构设计、强度评估、疲劳评估和振动评估等角度论证其设计要点,通过对泥舱结构设计分析,给出泥舱设计的关键节点,对关键节点进行强度分析和疲劳分析,结果表明,该船局部关键区域应力水平较高,低周疲劳在关键区域的疲劳中占据主要地位,建立三维有限元模型计算挖泥船固有频率,对比该大型耙吸挖泥船激励频率与固有频率,结果表明,船体总振动固有频率通常可以避开激励频率,生活楼固有频率与激励频率较为接近。

低强度再生混凝土微观形态与力学性能的相关性研究

建筑垃圾来源复杂,为提高再生混凝土的资源利用,并满足基本工程应用要求,在仅考虑再生骨料密度、吸水和含水率、压碎指标的条件下,采用再生粗骨料混凝土配合比设计法配置低强度再生混凝土,结合切片法和SEM扫描电镜对再生混凝土的孔隙结构变化与微观形貌进行观察,分析水胶比、减水剂、粉煤灰对低强度再生混凝土内部结构的影响,发现当水胶比降低时,再生混凝土内部结构的密实度提升,絮状C-S-H之间更为密实,多害孔的比例降低,抗压和劈裂强度提高;当减水剂掺量提升时,钙钒石(AFt)的含量增加,内部结构更为致密;粉煤灰对再生混凝土的抗压和劈裂强度呈负面影响,降低C-S-H与再生骨料之间的粘结性,内部孔隙率变大,坍落度升高,可降低经济成本。