固化粉煤灰三轴压缩试验研究

通过固化粉煤灰三轴压缩试验,分析固化剂的掺入比、固化粉煤灰混合料的密度、龄期对剪切强度的影响及固化粉煤灰的应力变化规律,确定满足高等级公路材料的要求.     

含能材料受限三轴压缩实验的数值模拟

从含能材料三轴压缩实验的基本公式出发,推导了考虑摩擦力之后各力学参数的计算公式。提出一种将实测数据与受限三轴压缩的试件——钢筒库伦接触摩擦有限元模型相结合的方法,利用动力有限元程序分析,考虑了摩擦力的影响。通过对ＴＮＴ炸药的受限三轴动态压缩实验的计算机模拟,估算了摩擦系数ｆ,并给出了材料的屈服强度值的修正公式。     

基于三轴压缩试验的水泥土力学特性研究

处于不同环境和条件下的水泥土力学特性直接影响水泥土工程的安全性和耐久性.因此,通过室内三轴试验,设计了不同的水泥掺入比,不同围压,对分别在海水和清水环境下养护的试件进行了水泥土的三轴压缩试验,研究了海水环境、水泥掺量、围压对水泥土的力学特性的影响规律.试验结果表明,水泥土三轴压缩的应力-应变曲线总体呈现软化型,水泥掺量愈大,其水泥土的脆性特征越显著;随着围压的增加,试件破坏时的延性特征越明显;随着水泥掺量的增加,水泥土的极限应力差值逐步增大,而极限应力差值所对应的应变逐步变小;随着围压的增大,水泥土的极限应力差值逐步增大,而水泥土破坏时峰值所对应的应变越大;水泥土的黏聚力和内摩擦角随着水泥掺量的增加均逐步增大;与清水环境相比较,海水环境下水泥土的抗剪强度、黏聚力和内摩擦角均有降低.其研究成果为水泥土工程的安全性和耐久性设计提供技术参数,具有一定的工程意义和参考价值.     

ECC三轴压缩特性试验研究

为探究纤维增强水泥基复合材料(ECC)在复杂应力状态下的受压特性,通过常规三轴压缩试验得到了不同围压下的ECC应力-应变曲线,分析了ECC的强度特性、变形规律以及破坏模式.试验结果表明:PVA纤维的掺入、施加围压能够有效约束ECC的径向变形并提高其韧性,且ECC的轴向峰值抗压强度和峰值应变随围压的提高而增大.ECC的三轴受压变形过程表现为弹性变形-应变硬化-应变软化三阶段,且围压越大,应力-应变曲线的软化段变化越缓和.在三轴受压状态下,ECC的主压应力、轴向峰值应变与围压有较好的线性相关性.     

纤维布加固混凝土的轴压力学性能研究

为了提升混凝土柱的轴压力学性能,共设计了5组纤维布加固混凝土柱,分别对5组混凝土柱进行了轴压性能测试。结果表明,JFRP和NFRP试件相较未采用纤维布加固的混凝土柱的承载力分别提升了34%和43%,最大压应变分别提升了196%和178%,纵向钢筋的最大应变分别提升652%和552%;相较于CFRP试件,JFRP和NFRP试件的最大承载力也提升了约85%左右,表明组合方式更加有利于提升纤维布加固混凝土的承载力和延性。相较于CFRP试件的脆性破坏,JFRP和NFRP试件的破坏形式则呈现出弹塑性破坏形态。     

南京地区粉土的不排水三轴压缩试验

通过全自动三轴仪进行了南京地区粉土的三轴不排水的试验,研究了围压和干密度对应力-应变曲线、孔隙水压力曲线和有效主应力比曲线的影响.试验表明:高围压状态下粉土试样呈现出弱应变软化型,而低围压状态下呈现出应变稳定型;低围压下试样在加载初期产生正孔隙水压力,随后产生负孔隙水压力,其后基本保持稳定;干密度越大,主应力差峰值越大,表现出较大的剪胀性,孔隙水压力易出现负孔隙水压力;干密度值较高时,土样处于密实状态,表现出剪胀特性,有效主应力比-应变曲线近于应变软化型;围压较低、干密度较大时,试样易表现出软化特征,试样出现剪切带破坏,强度明显下降.     

叶蜡石物理性能的研究

文章介绍了研究叶蜡石物理性能的方法,在分析了焙烧工艺对叶蜡石物理性能影响的基础上,研究了焙烧温度与叶蜡石失水百分数、叶蜡石块的抗压强度及剪切强度之间的联系.实验发现叶蜡石失水百分数与焙烧相同温度下叶蜡石抗压强度具有线性关系,并探索了判断叶蜡石软硬程度的依据.     

基于三轴压缩试验的软岩遇水强度软化规律研究

针对软岩遇水软化导致强度降低的现象,对云南省富源县的典型软岩试样进行了三轴压缩试验,讨论了软岩遇水软化的强度变化规律。试验首先获取了该软岩的矿物成分、扫描电镜图片和浸水前后的结构状态变化;然后分别对天然状态和饱水状态的两种试样开展了常规三轴压缩试验,测定不同围压(1、3、5 MPa)下的应力-应变关系曲线。试验结果表明:软岩在浸水12h后,其岩体结构出现明显的崩解现象,表明软岩的水敏性较强;分析软岩的三轴应力-应变曲线可以看出该试样主要经历初始压密、线弹性变形、塑性变形和破坏后软化4个阶段;通过对比两种状态试样的峰值强度发现该软岩试样的软化程度随围压的增加有一定程度的减弱。研究结果对于围岩支护工程中软岩的长期稳定性分析具有一定的参考价值。     

基于Druck-Prager和MISO模型的混凝土 三轴压缩行为有限元模拟

本文采用有限元分析软件ANSYS模拟了不同围压(0,25.5,51.2 MPa)条件下素混凝土圆柱试样压缩响应特征。首先,综合对比分析了Druck-Prager模型及多线性强化(MISO)模型的模拟效果。此外,进一步基于MISO模型分析了混凝土试件端部约束条件对模拟结果的影响。最终得到的主要结论包括:(1)单轴压缩条件下,有限元模拟结果与试验结果一致性较好,且Druck-Prager模型更适宜模拟混凝土体应变特征;(2)施加围压时,MISO模型所得抗压强度较保守,而Druck-Prager模型高估了混凝土抗压强度;(3)就MISO模型而言,端部摩擦约束对混凝土应力—应变曲线无显著影响,但会加剧混凝土体积膨胀(剪胀)。     

GFRP板加固混凝土方柱的轴压力学性能研究

通过试验对比素混凝土方柱与包裹GFRP板的方柱的力学和变形性能，得出在轴压情况下GFRP板加固混凝土方柱能显著提高柱的承载力和应变的结论，给出在轴压作用下混凝土柱条带和全包GFRP板进行加固的计算公式。     

Effect of pyrophyllite incorporation in porcelain composition on mechanical properties and microstructure

China clay (Kaolin) and quartz in the ratio of 1:2 was progressively replaced by pyrophyllite in a conventional porcelain mix. Addition of 15% pyrophyllite as a replacement of a combination of china clay and quartz decreased the linear shrinkage by 5.03% while fired strength was improved by about 31.5% compared to that of the conventional body fired at 1300 °C. Incorporation of pyrophyllite beyond 15% resulted in early vitrification of porcelain composition, although in lower proportion the effect is not so significant. Percentage of mullite was found to increase in the fired specimens even when kaolinite was progressively replaced by pyrophyllite. However, beyond 22.5% pyrophyllite addition, there occurred large volume of glass formation. Presence of large volume of glassy phase as well as formation of large pores of various shapes resulted in deterioration in ceramic properties. The size and shape of mullite crystals is to a large extent controlled by the fluidity of the liquid matrix from which they grow and this is again a function of temperature and composition.     

滤布力学性能的试验研究

通过4种合成纤维滤布的强力拉伸试验,测得了滤布在干、湿两种状态下的力学性能指标,得出了不同拉伸速度对滤布断裂强度和断裂伸长率的影响,同时指出当滤布的应力超过屈服点时,会出现应力松驰现象。     

A computational and experimental investigation of the mechanical properties of single ZnTe nanowires

One-dimensional nanostructures such as ZnTe, CdTe, Bi(2)Te(3) and others have attracted much attention in recent years for their potential in thermoelectric devices among other applications. A better understanding of their mechanical properties is important for the design of devices. A combined experimental and computational approach has been used here to investigate the size effects on the Young's modulus of ZnTe nanowires (NWs). The mechanical properties of individual ZnTe nanowires in a wide diameter range (50-230 nm) were experimentally measured inside a high resolution transmission electron microscope using an atomic force microscope probe with the ability to record in situ continuous force-displacement curves. The in situ observations showed that ZnTe NWs are flexible nanostructures with the ability to withstand relatively high buckling forces without becoming fractured. The Young's modulus is found to be independent of nanowire diameter in the investigated range, in contrast to reported results for ZnO NWs and carbon nanotubes where the modulus increases with a decrease in diameter. Molecular dynamics simulations performed for nanowires with diameters less than 20 nm show limited size dependence for diameters smaller than 5 nm. The surface atoms present lower Young's modulus according to the simulations and the limited size dependency of the cylindrical ZnTe NWs is attributed to the short range covalent interactions.     

An experimental research on the fluidity and mechanical properties of high-strength lightweight self-compacting concrete

This paper evaluates the high-strength lightweight self-compacting concrete (HLSCC) manufactured by Nan-Su, of which the main factor PF of its design mixing method has been modified and improved.The study analyzes HLSCC performance at its fresh condition as well as its mechanical properties at the hardened condition.The evaluation of HLSCC fluidity has been conducted per the standard of second class rating of JSCE, by three categories of flowability, segregation resistance ability and filling ability of fresh concrete.For the mechanical properties of HLSCC, the study has been conducted as follows: compressive strength with elapsed age, splitting tensile strength, elastic moduli and density, all at its cured after 28 days.As a result, HLSCC at its fresh condition has been rated as less than LC 75% and LF 50% for the mix ratio of lightweight aggregate, thus satisfying the second class standard of JSCE.The compressive strength of HLSCC at 28 days has come out to more than 40 MPa in all mix except the case with LC 100%, while the structural efficiency in relation to its density tended to increase proportionally as the mixing ratio of LF increases. The relationship between the splitting tensile and compressive strength has been calculated as f_s=0.076f_ck+0.5582. The range of elastic moduli has come out as 24-33 GPa, comparably lower than the control concrete.Compressive strength and structural efficiency of HLSCC at 28 days from the multiple regression analysis resulted as f_c=−0.07619LC_A+0.08648LF_B+46.714 and f_se=−0.00436LC_A+0.0627LF_B+20.257, respectively.     

Computational investigation of the mechanical properties of nanomaterials

The mechanical responses of carbon nanotubes are examined using classical molecular dynamics simulations. Several different types of nanotubes are considered, including pristine single-walled tubes that are empty, filled with fullerenes to form peapods, filled with other nanotubes to form multi-walled tubes, or chemically functionalized. In addition, the responses of single-walled nanotubes with wall vacancies are considered. The results show how the bending force of filled nanotubes increases relative to the bending force of empty nanotubes and indicates how these increases come about. In addition, the simulations reveal the way in which the magnitude of these increases depend on the type of filling material and, in the case of multi-walled tubes, the number of inner tubes. These simulations further illustrate the way in which the inner nanotubes support higher external loads than the fullerenes in cases when the outer nanotubes are identical. The results also indicate that both the bending and buckling forces depend on temperature and the reasons for this dependence are discussed. Lastly, the simulations demonstrate the way in which the introduction of vacancy defects and covalently bound functional groups to the nanotube walls degrades the nanotubes' mechanical properties.     

温度对胎面材料压缩力学性能影响规律研究

环境温度对轮胎胎面材料力学性能有重要影响,它直接影响接地性能。为获取不同温度下胎面橡胶材料的压缩力学性能,进行了准静态单轴压缩实验。基于此,获取不同温度、不同速度下的应力-应变关系,揭示温度及应变率对其压缩力学性能的影响规律。采用Mooney-Rivlin本构模型来表征胎面橡胶压缩荷载下的力学行为。结果表明,在低应变率时应变率的影响不明显;在20-90℃温度范围内,随着温度的升高,橡胶压缩模量减小。Mooney-Rivlin本构模型拟合与实验结果相符,它为不同温度下胎面橡胶压缩性能分析奠定理论基础。     

改性叶蜡石/SBR复合材料的性能研究

采用几种偶联剂分别对叶蜡石进行湿法和干法改性,研究改性叶蜡石/SBR复合材料的性能.试验结果表明,与未改性叶蜡石/SBR复合材料相比,改性叶蜡石/SBR复合材料的ML和MH增大,t90-t10缩短,综合物理性能提高,其中采用1.5份钛酸酯偶联剂NDZ-101湿法改性叶蜡石的补强效果最好;扫描电镜分析表明,叶蜡石经偶联剂改性后可提高其在SBR中的分散性,增强其与SBR的结合能力.     

An investigation on the bound rubber and dynamic mechanical properties of polystyrene particles‐filled elastomer

Polymeric nanoparticles have many advantages as the reinforcing filler of rubber. To investigate the mechanism of the reinforcement, nanocomposites of poly(styrene‐butadiene) rubber (SBR) filled with polystyrene (PS) particles as the reinforcing agents was prepared. Morphology and dynamical mechanical properties of PS particles‐filled SBR were investigated. It was found that the polymer chains of the elastomer could be absorbed onto the PS particles, in reminiscent to the concept of bound rubber in inorganic filler‐filled elastomeric system. The adsorbed polymer layer can form up glassy bridges between neighboring filler particles, leading to the agglomeration of the filler particles and the reinforcement of the elastomer. With higher filler content or smaller filler size, the numbers of the glassy bridges increase, and the modulus of the elastomer increases. With higher strain or higher temperature, the filler–filler interaction is disrupted and the material is softened. The study discovered the existence of bound rubber in PS particles‐filled elastomer and illustrated its influence on the dynamic mechanical properties, which could be helpful to design the polymeric nanoparticles for rubber reinforcement. POLYM. COMPOS., 38:1112–1117, 2017. © 2015 Society of Plastics Engineers     

An investigation of the interfacial adhesion between reclaimed newspaper and recycled polypropylene composites through the investigation of their mechanical properties

The effects of different parameters (e.g. method of defibration of newspaper; size of the fiber; type and concentrations of coupling agents, impact modifiers, and fire retardants) on the mechanical properties of old newspaper fiber-filled recycled polypropylene (PP) have been evaluated. Statistical methods were applied to determine the effects of variables on the tensile strength, Young's modulus, tensile toughness, and impact strength. Statistical analysis revealed that the composites based on newspaper fiber prepared by mechanical defibration showed a better tensile strength compared with those prepared by the steam explosion process, while the latter type of fiber outperformed the former as far as the other mechanical properties are concerned. In the presence of maleic anhydride grafted PP (MPP) and the initiator dicumyl peroxide (DCPO), the tensile strength of the composites increased with increasing fiber loading and fiber size. Moreover, both the tensile strength and the modulus increased with an increase in the concentrations of MPP and DCPO, even in the presence of an impact modifier and fire retardants for surface-modified newspaper-filled composites. Since the tensile strength of short fiber reinforced composites is strongly dependent of the degree of adhesion between the fiber and matrix, the experimental results suggest that either one of these (MPP and DCPO) or both act as the interfacial bonding agent to develop a strong interphase between old newspaper fiber and recycled PP.