Effect of Temperature and Concentration of Ammonium Nitrate Solution on the Succeptibility of Mild Steel to Stress Corrosion Cracking

The effect of varying the temperature and the concentration of ammonium nitrate solution on the stress corrosion cracking (SCC) susceptibility of mild steel is studied. An increase in the temperature causes a decrease in the stress corrosion life. It appears that the susceptibility in the range 368 K to 380 K was greater than at other temperatures. Near the boiling point corrosion and stress corrosion occurs, at the boiling point, the cracking was associated with a high rate of general corrosion. Microscopic examination after stress corrosion testing in 10Wt%, 20Wt%, and 52Wt% NH4NO3 solution revealed that in all cases there was severe intergranular attack, especially at the high concentration.

Three-dimensional photoelasticity analysis of Nitinol Patellar Concentrator for treating patellar fractures

Objective: To analyze the biomechanical elements of Nitinol Patellar Concentrator (NT-PC) in heating commi nuted patellar fractures. Methods: The epoxy resin three dimensional photoelasticity pobal model was loaded with Nitinol Patellar Connector and frozen. After dividing layer, photographing and tracing, iterative method was used to calculate the stress value of every tuteed node. Rasults: Stress values of 1 262 nodes scattered in 12 layers were obtained The stress distribution indicated that an overall stress field was yield when the NT-PC fixated the patellar model, and there existed fixative stress in the facies articularis and distal pole of the patellar model. Conclusion: The NT-PC has evident therapeutic effect for the comminuted patellar fractures. The existing stress is helpful in maintaining anatomical reduction and enhancing fracture healing.

Three-Dimensional Stress Fields in Finite Thickness Plate with Hole Under Shear Load

The theoretical solutions are obtained for the three-dimensional(3-D)stress field in an infinite isotropic elastic plate with a through-the-thickness circular hole subjected to shear load at far field by using Kane and Mindlin′s assumption based on the stress function method.Based on the present solutions,the characteristics of 3-D stress field are analyzed and the emphasis is placed on the effects of the plate thickness and Poisson′s ratio on the deviation of the present 3-D in-plane stress from the related plane stress solutions,the stress concentration and the out-of-plane constraint.The present solutions show that the stress concentration factor reaches its peak value of about 8.9% which is higher than that of the plane stress solutions.As expected,the out-of-plane stress constraint factor can reach 1on the surface of the hole when the plate is a very thick one.

Effect of the Cavity-Cavity Interaction on the Stress Amplitude in Orthopedic Cement

The presence of porosities in bone cement (polymethylmethacrylate) in total hip prosthesis (THP) cemented is necessary for the diffusion of antibiotics, but it is a critical characteristic of weakening by the effect of stress concentration and the interconnecting pores. The aim of this study was to analyse by the finite element method (FEM), the size influence of micro-cavities in cement assuming the junction cup-bone, and the effect of cavity-cavity interaction on the stress level and distribution in cement according to the human stance defined by the implant position axis compared to that of the cup.

大跨连续梁拱组合体系桥拱脚结合段局部应力分析

大跨连续梁拱组合体系桥拱脚结合段的构造和受力复杂,需要对此处进行局部应力分析。结合工程实例,采用有限元法对拱脚结合段进行建模,提出了局部模型边界力的施加方法,并对其施加整体模型计算出的内力进行细部计算,分析局部应力状态。计算和分析结果表明,拱脚结合段的应力总体上满足设计规范要求,横隔板分别与顶板、底板和腹板相连接的倒角位置出现应力集中现象,建议对倒角设置平顺过渡段;在拱肋插入处的顶板和支座位置处的底板存在应力集中现象,建议对这些位置加强布置构造钢筋。

岩体变形及二次应力下矿体开采效应研究

为了解围岩在变形及二次应力下矿体开采效应的影响,本文选取-410 m中段采用现场试验与数值模拟相结合的方法对崩落法采矿进行矿体效应研究。结果表明:围岩应力发生震荡变化,在矿体上下盘围岩附近存在应力明显降低区域,下盘大于上盘,顶板最大主应力达0.44 MPa,局部呈现应力集中,且应力集中部位呈现类似水平零散分布的现象。同时开采边界呈现裂隙发育的状态。水平矿体有轻微下沉趋势,且在该中段的水平巷道边界和顶板裂隙附近易出现断层破碎带。竖直方向变形明显,且倾斜部位呈椭圆分布,最大下沉位移值达8.00 mm,最大上升方向变形值为3.03 mm,交界线附近易受到应力挤压现象。该研究对及时准确地掌握岩体变形规律和矿山安全信息使矿山安全有效合理地进行开采具有一定的指导意义。

作物-内生微生物响应CO_(2)浓度升高与干旱胁迫的作用机制研究进展

全球变暖、二氧化碳(CO_(2))浓度升高和局部地区干旱加剧等环境变化对作物生长发育及产量造成的影响日趋明显。内生微生物是一类与宿主植物形成互利共生机制的微生物,由于其长期生活在植物体的特殊环境中,对作物的生长发育和抗逆性具有重要作用,两者的共生关系会直接影响作物对环境变化的响应。本文主要综述作物-内生微生物共生系统及其在CO_(2)和干旱胁迫下对作物生理过程的调控,探讨了作物内生微生物群落的多样性以及促生效果、抑菌作用、抗逆能力,并重点关注了作物-内生微生物系统如何提高环境的耐受特性。具体而言,内生微生物可以通过提高宿主的气孔调节能力、增加根系吸收水分和养分的能力等方式,帮助作物适应CO_(2)浓度升高和干旱胁迫,从而减小环境变化对作物生长的负面影响,提高作物产量。此外,内生微生物还可以激活宿主的防御系统,提高其对病原体的抵抗能力,从而减轻病害对作物的影响。未来的研究应关注作物-内生微生物共生系统在不断升高的CO_(2)浓度和干旱复合胁迫下的响应机制,以提高作物对极端环境变化的抗性,为作物抗逆性育种提供新的思路和策略。

盐度胁迫下亚硝酸盐型同步脱氮除硫性能急性响应及功能菌群分析

针对生物处理高盐含氮废水过程中亚硝酸盐积累问题,因亚硝酸盐同步脱氮除硫工艺具有高基质耐受性和高基质去除性能,为探究该工艺对盐度(氯化钠的质量分数)胁迫的急性耐受性能,分别考察了盐度梯度和基质质量浓度对亚硝酸盐型同步脱氮除硫工艺性能的单一急性影响。升高基质质量浓度显著提高了基质去除速率(显著性值p<0.05),硫化物和亚硝酸盐中S和N的去除速率最高可达(88.7±0.57) mg·L^(-1)·h^(-1)和(5.51±0.21) mg·L^(-1)·h^(-1);而升高盐度则明显抑制了基质去除速率(p<0.01),硫化物和亚硝酸盐中S和N的去除速率降至(23.33±1.10) mg·L^(-1)·h^(-1)和(1.98±0.09) mg·L^(-1)·h^(-1)。并探究了不同盐度梯度和基质质量浓度联合作用下该工艺性能应激响应。当NaCl质量分数<2.4%时,适当升高基质质量浓度有助于提高硫化物去除速率,NaCl对硫化物去除速率的促进率分别为0.28(180 mg·L^(-1))和0.27(240 mg·L^(-1));而不论基质质量浓度如何,升高盐度皆使亚硝酸盐去除速率显著下降(p<0.01),且抑制率随基质质量浓度升高而增大。经高通量测序技术分析,该工艺优势功能菌属为sulfurovum、rhodobacteraceae、sulfurimonas和microbacterium,其相对丰度分别在28.55%~11.25%。

含缺陷油气管道在土壤环境下应力腐蚀数值模拟

基于有限元数值模拟的方法,分析研究高强度管线钢在应力作用下,不同土壤离子(Cl^(-)、HCO_(3)^(-)、SO_(4)^(2-))浓度和不同温度时的电化学腐蚀特征。结果表明:随着离子浓度和温度的增加,缺陷处的腐蚀电流密度均呈现增加的趋势;在塑性应变阶段,由于缺陷中心应力集中,机械-电化学效应显著,缺陷中心位置相较于两端腐蚀更加严重,中心位置的腐蚀电流密度显著增加。

掘进巷道过断层破碎区联合支护技术

基于长春兴煤矿602运输顺槽掘进揭露F4断层时受应力叠加影响,巷道围岩变形严重,提出了“桁架锚索+让压锚索+梯形钢棚”联合支护技术,根据实际应用效果来看,采取联合支护技术后应力区巷道围岩变形、收敛现象得到了有效控制,加快了巷道掘进速度,提高了巷道成型率,取得了显著应用成效。

基于热点应力设计弧形焊环栓钉研究

目前随着钢混结构的普遍应用,栓钉作为连接件,其疲劳性能问题也备受关注,尤其是焊趾处的应力集中效应。文中将基于热点应力法对一种新型弧形焊环进行尺寸设计,通过ABAQUS并采用线性外推方式对4种不同直径栓钉的焊环高度、宽度、倒角进行参数分析。研究结果表明,栓钉焊趾处的热点应力随焊环高(宽)度的增加、倒角的减小而减小。说明增加焊环的高(宽)度、减小焊环的倒角能够减小焊趾的应力集中效应。

Dynamic characteristics of high stressed red sandstone subjected to unloading and impact loads

In the process of deep projects excavation,deep rock often experiences a full stress process from high stress to unloading and then to impact disturbance failure.To study the dynamic characteristics of three-dimensional high stressed red sandstone subjected to unloading and impact loads,impact compression tests were conducted on red sandstone under confining pressure unloading conditions using a modified split Hopkinson pressure bar.Impact disturbance tests of uniaxial pre-stressed rock were also conducted(without considering confining pressure unloading effect).The results demonstrate that the impact compression strength of red sandstone shows an obvious strain rate effect.With an approximately equal strain rate,the dynamic strength of red sandstone under confining unloading conditions is less than that in the uniaxial pre-stressed impact compression test.Confining pressure unloading produces a strength-weakening effect,and the dynamic strength weakening factor(DSWF)is also defined.The results also indicate that the strain rate of the rock and the incident energy change in a logarithmic relation.With similar incident energies,unloading results in a higher strain rate in pre-stressed rock.According to the experimental analysis,unloading does not affect the failure mode,but reduces the dynamic strength of pre-stressed rock.The influence of confining pressure unloading on the shear strength parameters(cohesion and friction angle)is discussed.Under the same external energy impact compression,prestressed rock subjected to unloading is more likely to be destroyed.Thus,the effect of unloading on the rock mechanical characteristics should be considered in deep rock project excavation design.

Surface Effects on the Scatter of SH-Wave by a Shallow Buried the Elliptical Hole

The methods of complex function, multi-polar coordinate system, and conformal mapping are used to solve dynamic stress concentration factor. The surface elasticity theory is applied to obtain the stress boundary conditions on the surface. The effects of frequency and the ration of the major and minor axis of the ellipse on the dynamic stress concentration factor around the elliptical nano-hole are discussed in detail. When the size of elliptical hole shrinks to nanometers, the numerical results show that the surface effect has a significant effect on the scattering of SH-wave.

Surface Effects on the Diffraction of P Wave by an Arbitrary Shaped Cavity

This paper presents the effects of surface effects in the cavity of variable curvature. The wave function expansion method and the conformal mapping method are used in the solution of dynamic stress concentration factor around an irregularly shaped cavity at nano-scale. The stress boundary conditions on the surface are obtained by using the generalized Young-Laplace equation. The results show that the degree of stress concentration becomes more obvious with curvature increasing. Taking the elliptical cavity as an example, the influence of the ration of the major and minor axis of the ellipse, the numbers of the incident wave and the surface effects on the dynamic stress concentration factor are analyzed. The ration of the major and minor axis, the incident wave frequency and the surface effects show the pronounced effects on the dynamic stress concentration distributions.

基于孔边应力集中的页岩渗透率模型及应力敏感性评价

页岩储层油气主要储集于基质孔隙,考虑不同应力状态下孔隙周边的应力集中,采用复变函数与保角变换计算孔隙变形,建立基于孔边应力集中的渗透率模型,基于实验结果验证渗透率模型可靠性,分析页岩渗透率的应力敏感性。结果表明:基于孔边应力集中的渗透率模型可合理表征有效应力和孔隙压力对页岩渗透率的影响,孔隙压力增大能减弱页岩渗透率对有效应力变化的敏感性;不同方向的有效应力对页岩渗透率的影响具有显著差异,椭圆孔隙短轴方向应力对渗透率的影响较椭圆孔隙长轴方向应力高30%;常规模型(CB模型)未考虑椭圆孔隙的孔边应力集中,显著低估孔隙压力和水平有效应力变化对页岩渗透率的影响;在单轴应变的条件下,常规模型显著高估椭圆孔隙短轴方向应力和上覆岩层应力对页岩渗透率的影响,低估页岩渗透率达32%。该结果为分析压裂应力方向变化较大的储层渗透率提供依据。

空孔对爆生裂纹扩展的力学行为研究

为了探究空孔对爆生裂纹扩展的影响,结合ANSYS/LS-DYNA有限元软件建立了空孔爆破损伤模型,理论上推导了空孔附近的岩体质点应力分布方程,分析了空孔效应对于破碎机理与裂纹扩展的影响。结果表明:空孔自由面效应会在空孔附近引起冲击压力骤增和震速变化,出现迎爆面处岩石“片落”现象;空孔背爆面处的震速明显小于迎爆面的震速,说明空孔具有很好的泄压降震效果;通过对冲击压力和裂隙区半径的解析解计算与数值计算结果对比,冲击压力的误差11.81%,而裂隙区半径的误差9.49%,两者结果较为接近。

大直径中空孔直眼掏槽爆破的空孔应力集中效应研究

为了探明大直径中空孔直眼掏槽爆破的力学机理,采用理论分析和数值模拟方法研究了大直径中空孔直眼掏槽爆破的空孔应力集中效应。建立了空孔应力集中效应的力学模型,基于弹性力学和波动力学理论阐明了空孔应力集中效应的力学机理;开展了典型工况下大直径中空孔直眼掏槽爆破的数值模拟,并基于应力波传播、岩体损伤和岩体第一主应力峰值等结果分析了空孔的应力集中效应。研究结果表明:空孔应力集中效应主要源自孔洞应力集中效应和应力波叠加效应;大直径中空孔直眼掏槽爆破过程中,应力波在空孔壁处发生反射并与入射波产生叠加,叠加多位于空孔邻近区域以及掏槽孔间区域;岩体损伤程度较高的区域主要为掏槽孔周边、空孔周边以及相邻掏槽孔与空孔形成的三角区域,掏槽孔周边以外的损伤区域与应力波叠加区域基本对应;空孔附近存在显著的应力集中效应,且距空孔壁越近的位置应力集中效应越明显。研究成果拟为隧道工程大直径中空孔直眼掏槽爆破设计提供理论基础。

Formulization of Three-Dimensional Stress and Strain Fields at Elliptical Holes in Finite Thickness Plates

Stress raisers such as holes are inevitable in structures at which stress concentration occurs and the static as well as fatigue strength of the structures can be significantly weakened. Therefore, to accurately evaluate the stress concentration factor and stress fields at holes is of essential importance for structure design and service life prediction. Although stress and strain concentration and fields at holes in finite thickness plates strongly change with and along the thickness, manuals of stress concentration for engineering design are mainly based on twodimensional theory and no explicit formula is available even for circular holes in finite thickness plates. Here we obtain for the first time a complete set of explicit formulae for stress and strain concentration factors and the out-of-plane constraint factor at circular as well as elliptical holes in finite thickness plates by integrating comprehensive three-dimensional finite element analyses and available theoretical solutions. The three-dimensional stress distributions ahead of holes can also be predicted by the obtained formulae. With their accuracy and the corresponding applicable range being analyzed and outlined in detail, the formulae can serve as an important fundamental solution for three-dimensional engineering structure design and guideline for developing threedimensional analytical methods.

Finite element analysis of stress concentrations and failure criteria in composite plates with circular holes

In this study, the （SCF） in cross-and-angle-ply stress concentration factors laminated composite plates as well as in isotropic plates with single circular holes subjected to uniaxial loading is studied. A quadrilateral finite element of four-node with 32 degrees of freedom at each node, previously developed for the bending and mechanical buckling of laminated composite plates, is used to evaluate the stress distribution in laminated composite plates with central circular holes. Based up on the classical plate theory, the present finite element is a combination of a linear isoparametric membrane element and a high precision rectangular Hermitian element. The numerical results obtained by the present element compare favorably with those obtained by the analytic approaches published in literature. It is observed that the obtained results are very close to the reference results, which demonstrates the accuracy of the present element. Additionally, to determine the first ply failure （FPF） of laminated plate, several failure criterions are employed. Finally, to show the effect of E1/E2 ratio on the failure of plates, a number of figures are given for different fiber orientation angles.

On three-dimensional stress analysis of periodic notched plates under tension

By using the finite element method,three-dimensional models of a number of periodic blunt and sharp notches subjected to tension loading are investigated.The aim of this research is to investigate the thickness effect on the location of maximum stress and notch stress intensity factor(NSIF)of corresponding blunt and sharp periodic notches respectively.With this aim,different number of periodic notches as well as different notch opening angles are examined.While for two-dimensional plates weakened by periodic notches some results are available in the literature,this paper first faces the problem of three-dimensional cases.A total of about 100 geometrical configurations are investigated.It is found that,the effect of plate thickness of periodic notched components can be characterized by the relative value with respect to the depth of the notch(H/t).For the blunt periodic notches with relatively higher values of H/t ratio,the value of the maximum tensile stress is located near the free surface.On the contrary for lower values of H/t,it is placed at the middle plane.The same behaviour is observed for sharp periodic notches in terms of notch stress intensity factors.