Simulation of the Long Term Behaviour of Plastics Components

Summary: This paper presents a method to model the mechanical behavior of polymers over a wide time- and load-range by means of finite element analyses. The method includes a material model as well as the determination of material parameters to calibrate the material model. As a special feature of this method the model is calibrated only by using creep data that are commonly available in material data bases. So the procedure improves the simulation of the long time behavior of plastic-components without an additional experimental effort. In combination with time-temperature-superposition principle, the temperature dependency of the long term behavior is represented, too. The simulation results are validated by creep experiments on an example part.     

高强混凝土徐变力学实验研究

为掌握苏通大桥连续刚构桥所用C60高强混凝土的徐变性能,开展了自然环境下配筋高强混凝土的徐变力学试验.为获得徐变试验所需75t的加载力,设计并制造出95t的徐变加载装置,解决了混凝土徐变试验大吨位加载的问题.针对应变测试过程中温度变化对应变测试的影响作了深入的探讨,提出了应变计温度影响的修正方法.通过试验结果与现行桥规JTG D62-2004的比较得出:配筋高强混凝土徐变系数远小于规范取值,且在170天后徐变系数有收敛的特征.试验结果说明,实桥所用C60高强混凝土的徐变可以满足桥梁对混凝土耐久性的要求.     

分级加卸载硬岩短时蠕变特性实验研究

由单向抗压强度实验及8级加卸载短时蠕变实验,得到蠕变下限为27MPa的细砂岩试样典型的坚硬岩石脆性断裂特征.应力-应变等时曲线线性回归函数的相关系数均高于0.92,长期强度与瞬时强度之比达94.39%,证明细砂岩试样的整体蠕变特性不强.应力-轴向应变等时曲线线性回归函数的平均相关系数高出应力-径向应变等时曲线线性回归函数的平均相关系数3.92%,因此其轴向非线性蠕变特性相对于径向非线性蠕变特性更弱.随着时间延续,细砂岩试样的非线性蠕变特性总体服从负Gauss分布规律,具有明显的时间效应.随加载应力水平的提高,应力-轴向应变等时曲线和应力-径向应变等时曲线线性拟合函数的平均相关系数下降幅度分别为0.97%和0.67%,线性相关性普遍降低.所以细砂岩试样的非线性蠕变程度随加载应力水平的提高而提高,载荷效应明显.     

Nonlinear creep and ductile creep rupture of perfectly elastoplastic rods under tension

The paper is concerned with the problem of predicting nonlinear creep strains and time to ductile rupture of prismatic rods under constant tension. The material of the rod is assumed isotropic, homogeneous, and perfectly plastic. The problem is solved using models that take into account the change in the geometry of the rod during creep, the finiteness of the creep strains, and the effect of the initial and actual elastic strains. The conditions whereby the characteristic dimension of the rod tends to infinity and the accumulated and real strains in the viscous flow are limited are used as a failure criterion. The calculated results are compared with experimental data for a number of steels and alloys to formulate the conditions for the ductile rupture and embrittlement of metallic materials under uniaxial creep __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 4, pp. 120–133, April 2008.     

深部灰岩三轴蠕变特性实验研究

采用MTS815岩石材料力学试验机,在温度28℃条件下,对重庆市万盛区某煤矿深部掘进巷道灰岩进行了三轴蠕变试验,对不同偏应力水平下该巷道灰岩的蠕变特性进行了分析。结果表明,蠕变试验的曲线显示该灰岩蠕变具有非线性特征,其蠕变特性随着围压的增加而更加明显。对深部灰岩的蠕变模型进行初步探讨,回归得出深部灰岩在不同应力水平下蠕变应变随时间变化的Burgers蠕变方程。分析表明,Burgers模型能较好地反映该深部灰岩的蠕变规律。该模型所确定的本构关系可以作为该深部灰岩蠕变本构模型来预测其蠕变发展。     

深水油气田控制井眼缩径的钻井液密度研究

深水地层上覆岩层压力低,钻井安全泥浆密度窗口窄,发生井下事故的风险更大,需要确定水平井眼的变形规律,减少或避免因疏松砂岩储层蠕变缩径造成的井下复杂情况和事故。荔湾3—1气田是我国第一个即将投入开发的深水油气田,利用分级加载的方式测试了荔湾3—1气田疏松砂岩储层的蠕变变形规律。应用拉格朗日元法进行数值模拟计算,得出了荔湾3—1气田疏松砂岩储层水平井井眼缩径变形随时间的的变化规律和控制井眼缩径率的钻井液密度图版,分析了水深对水平井井眼变形的影响。结果表明,在相同条件下,深水油气田因疏松砂岩储层蠕变缩径而影响水平井安全钻进的风险比陆地和浅水油气田更小。研究结果对确定深水水平井安全钻井周期和开展水平井极限延伸长度的研究具有指导意义。     

蠕变损伤的随机模糊分析

在考虑材质劣化和空洞损伤的蠕变损伤模型基础上 ,建立蠕变损伤的失效概率模型。通过进一步对蠕变损伤模糊性的讨论 ,提出了蠕变损伤的模糊失效概率模型。算例表明 ,考虑模糊因素是必要的。最后讨论了随机变量的分布情况 ,得到了一些有益的结论     

锁口叶片销钉强度分析

阐述了锁口叶片销钉强度计算的方法、步骤、准则等 ,分析了神头第一发电厂 6号机K- 2 0 0 - 1 65- P型机组 2 a级锁口叶片销钉的断裂原因 ,并对锁口叶片销钉剪切蠕变强度的校核进行了探索。     

Mathematical model of creep for a microinhomogeneous nonlinearly elastic material

A mathematical model is proposed to describe the experimentally observed creep effect on the instantaneous elastic deformation of physically nonlinear elastic microinhomogeneous materials. Using a structural model of the medium, it is shown that, during unloading of a sample after creep at constant stress, the elastic strain can be both larger and smaller than the elastic strain during loading. It is shown that calculation results for a biocomposite material are in good agreement with experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 157–163, May–June, 2008.     

含裂纹结构时间相关的疲劳断裂理论与剩余寿命评价技术

高温结构的疲劳失效是与时间相关的, 建立这一失效机制下的断裂理论和寿命评价技术, 进而控制结构失效是人们多年来努力的目标. 从裂纹扩展控制参量、裂纹扩展规律和寿命评价技术、材料老化与环境因素影响和结构完整性评定工程方法等几个方面, 对近年来这一领域的研究进展进行了总结, 并对今后该领域的发展方向进行了预测.