金属材料干摩擦特性仿真方法与试验验证

通过设计的金属干摩擦特性试验装置,测量得到了金属材料试件在固定正压力下的干摩擦迟滞特性,并且在MSC/MARC中建立了与试验相一致的有限元模型来仿真预测干摩擦接触的粘-滑迟滞特性.通过与试验数据的比较,验证了仿真模型的正确性,发现有限元模型结果与试验结果以及理论计算结果吻合程度较好,从而有助于分析工程实际中材料干摩擦特性和阻尼特性,验证了有限元方法的可行性.     

浅谈特殊地区桥梁桩基础的设计

桩基础在桥梁设计中使用非常广泛,许多桩基础在特殊地质条件下的设计和施工过程中,都存在一些特殊的尚未解决好的技术问题,导致不安全因素或事故的发生.本文对特殊地区(软弱土层、黄土地区、多年冻土区)的桥梁桩基础设计中的部分值得注意的问题进行了简单阐述.     

Effects of vegetation type on soil resistance to erosion: Relationship between aggregate stability and shear strength

Soil water erosion and shallow landslides depend on aggregate stability and soil shear strength. We investigated the effect of vegetation on both soil aggregate stability and shear strength (through direct shear tests) in former croplands converted to vegetated erosion protection areas within the context of China's sloping land conversion programme. Four treatments were analysed in plots comprised of (i) 4 year old crop trees, Vernicia fordii, where understory vegetation was removed; (ii) V. fordii and the dominant understory species Artemisia codonocephala; (iii) only A. codonocephala and (iv) no vegetation. Soil samples were taken at depths of 0–5 cm and 45–50 cm. Root length density (RLD) in five diameter classes was measured, soil organic carbon (SOC), hot water extractable carbon (HWEC), texture and Fe and Al oxides were also measured. We found that mean weight diameter after slow wetting (MWD_SW) in the A-horizon, was significantly greater (0.94–1.01 mm) when A. codonocephala was present compared to plots without A. codonocephala (0.57–0.59 mm). SOC and RLD in the smallest diameter class (< 0.5 mm), were the variables which best explained variability in MWD_SW. A significant positive linear relationship existed between MWD_SW and soil cohesion but not with internal angle of friction. As herbaceous vegetation was more efficient than trees in improving aggregate stability, this result suggests that the mechanisms involved include modifications of the cohesive forces between soil particles adjacent to plant roots and located in the enriched in SOC rhizosphere, thus also affecting shear strength of the corresponding soil volume. Thus, vegetation stabilised soil under different hierarchical levels of aggregate organisation, i.e. intra- and inter-aggregate. Our results have implications for the efficacy of techniques used in land conversion programs dedicated to control of soil erosion and shallow landslides. We suggest that mixtures of different plant functional types would improve soil conservation on slopes, by reducing both surface water erosion and shallow substrate mass movement. Planting trees for cropping or logging, and removing understory vegetation is most likely detrimental to soil conservation.     

多节点加载预应力锚索格构梁室内模型试验研究

目前,计算格构梁的力学模型中,多采用弹性地基梁法进行计算,而对于边坡上的格构梁,受坡角和锚索倾角的影响,梁底面摩擦力的存在使得格构梁受力变得复杂。因此,在计算中采用合理的计算模型真实地反映格构梁的受力状态显得尤为重要。通过对多节点加载预应力锚索格构梁室内模型试验的研究,认为受边坡坡角和锚索倾角的影响,格构梁底面存在的摩擦力对格构梁的变形和受力状态有较大影响,并对实测结果与理论计算结果进行了对比分析,认为采用考虑摩擦的Winkler弹性地基梁模型能很好地反映格构梁的实际受力状态,更适合于工程应用。     

冻融作用对植被混凝土抗剪强度的影响

为探讨冻融作用对植被混凝土生态基材抗剪强度的影响,选取冷端温度、含水率和融化温度为影响因素,采用快剪试验监测原始样与冻融样的黏聚力和内摩擦角.结果表明：1）经历冻胀与融沉过程后,植被混凝土的黏聚力降低,内摩擦角在多数情况下表现为增大,二者的耦合作用显示抗剪强度有所降低;2）随着冷端温度的降低,植被混凝土冻融后的黏聚力逐渐减小,而内摩擦角却逐渐增大;3）含水率对植被混凝土黏聚力与内摩擦角的影响具有双重效应,随着含水率的增大,植被混凝土冻融后的黏聚力先快速减小而后缓慢减小至稳定值,而内摩擦角却逐渐减小;4）融化温度的改变不会造成黏聚力和内摩擦角的变化,仅影响冻结植被混凝土的融沉历时.     

重庆缙云山典型植被原状土抗剪强度的灰色关联度分析与评价

采用SDJ-1型三速电动直剪仪对重庆缙云山5种典型植被的原状土抗剪强度进行室内测定，得出其抗剪强度变化规律，通过运用灰色关联法对其影响因子和对5种典型植被进行分析，结果表明：所选取的影响因子对黏聚力C的影响大小依次为：干密度〉小于0．001mm黏粒含量〉不均匀系数Cu〉根密度〉天然含水率〉有机质含量；影响因子对内摩擦角ψ的影响大小依次为：不均匀系数Cu〉小于0．001mm黏粒含量〉天然含水率〉干密度〉有机质含量〉根密度；5种典型植被对土壤抗剪强度影响最大为楠竹林，平权灰色关联度为0．851，最小为灌木林，平权灰色关联度为0．711，说明楠竹林土壤在自然条件下具有较大的抗剪强度。     

基于分形理论的结合面静摩擦因数改进模型

从理论上提出了一种基于分形理论的结合面静摩擦因数改进模型,表示出结合面静摩擦因数与无量纲法向总载荷之间非线性隐函数关系。仿真结果表明,静摩擦因数f随着法向总载荷P*和材料特性参数φ的增加而增加,随分形特征尺度参数G*的增加而减小,静摩擦因数f与法向总载荷P*呈微凸弧非线性关系;分形维数D在1.1～1.4范围内,静摩擦因数f随着D的增加而增加,在1.5～1.9范围内,静摩擦因数f随着D的增加而减小;研究表明该模型可以用于进行结合面静摩擦因数的预测。     

考虑粘滑摩擦的时变振动系统模态参数辨识

将摩擦因素引入时变振动系统的模态辨识中.采用时变多变量Prony法,对振动系统的多输出响应信号建立时变多变量Prony模型,并利用递推最小二乘法估计模型参数,提取出振动系统的模态特征信息.数值仿真中,对含复合频率信号的频率进行了辨识,辨识值与理论值较好的吻合性验证了该方法的有效性.应用实例中,对平面两杆操作臂中的滑动质量块建立了考虑LuGre摩擦的运动方程,利用时变多变量Prony法辨识出含粘滑摩擦的操作臂的固有频率,结果令人满意,验证了该方法的可行性.     

气动夯管锤和滑轮组在定向钻回拖中的应用

针对管道回拖过程中容易出现卡钻的问题,提出3种解决方法:夯管锤振击解卡、滑轮组解卡以及夯管锤和滑轮组配合解卡.以林头村抚河穿越工程为例,在夯管锤振击解卡和滑轮组解卡均失败的情况下,采用夯管锤和滑轮组配合解卡的现场操作工艺.结果表明:经过4d解卡施工,管道完全从孔洞中拖回地面,管道和防腐层完好无损,仅焊口处的防腐带略有剥裂.由于滑轮组行程存在一定弊端以及缺乏钢丝绳防护措施,夯管锤和滑轮组配合解卡的方法尚需进一步改进.(图5,参4)     

丁苯橡胶磨损特性及其硬度分析

通过不同的配比,研究了石墨与丁苯橡胶体系摩擦磨损特性的变化以及对体系硬度的影响。探讨了应用石墨填充了苯橡胶改变其摩擦磨损特性的可行性。