PdSi合金与金属Cr膜压痕蠕变研究

蠕变变形是薄膜和微机电系统应用中普遍存在的可靠性问题,因此有必要考察薄膜材料和小体积材料的蠕变行为。采用深度敏感纳米压痕方法对单晶PdSi合金和金属Ni基体上沉积Cr膜进行了室温压痕蠕变研究,分析蠕变应力指数和蠕变机制。结果表明:随硬度减小,蠕变深度增大,在不同应变率下计算得出应力指数PdSi合金在26.3~47.1之间;金属Cr膜在4.1~22.5之间。蠕变变形机制是位错的滑动和攀移,在高应变率下保载阶段瞬时影响更显著。     

圆轴的扭转

根据材料力学对线弹性材料圆轴扭转时应力计算的基本方法，计算一弹／粘塑性材料，塑性强化材料的扭转圆轴的应力与变形，分析了扭转时圆轴的蠕变。     

冻结粉土的动蠕变强度

根据不同振幅动荷载的三组蠕变试验结果,比较了冻结粉土在不同动荷载作用下的蠕变变形和动蠕变强度特征,发现,当动荷载振动幅值不同时,动蠕变曲线变化规律以及动蠕变强度特征变化规律都相似,但数值上有较大差别;在相同静荷载基础上叠加不同振幅动荷载时,在整个蠕变过程中,振幅越大,变形越大。而对于卸载到零的动荷载试验来说,初始蠕变阶段和稳定蠕变阶段的变形较小,但由于蠕变速率很大,变形迅速增加,很快进入渐进流阶段,随后变形变得很大;冻土的动蠕变强度随时间有规律地衰减;动荷载的振幅越大,破坏时间越短,土体越容易发生破坏。     

低应力水平下时间效应对岩石蠕变模型参数的影响

在岩石蠕变实验数据基础上,通过拟合分析,得到了蠕变模型的相关参数。通过对比理论计算数据与实验数据,结果发现:不考虑参数受时间尺度的影响将引起较大的误差,对于蠕变模型来说,其参数不是常数,而是随时间变化的量,时间尺度对模型参数影响较为明显;如考虑参数的时间相关性,建立非定常参数的蠕变模型方程,将比定常蠕变模型更能准确地反映岩石的蠕变变形特征。     

调质42CrMo钢的棘轮-疲劳交互作用研究

对调质42CrMo钢进行室温下各种应力循环和对称应变循环的低周疲劳实验,揭示材料的循环软化特性,棘轮变形和低周疲劳特性以及棘轮-疲劳交互作用。结果表明,调质42CrMo钢体现出明显的循环软化;在应力幅值或平均应力较高时,试样的棘轮变形较大,其破坏形式为延性破坏,而在应力水平较低时,材料的破坏由疲劳裂纹扩展所致的脆性断裂引起;材料在应力循环下的低周疲劳寿命由于有棘轮变形的产生而受到平均应力、应力幅值、最大应力和应变比等多种因素的影响。     

软弱岩石在滑坡事件中的危害及其防治

随着建设规模的扩大,滑坡事件由于其突发性和灾害性,越来越多地引起社会和专业工作者的重视,特别是软弱岩体的蠕变,更具隐蔽性、持续性,变形以常速率增长直至突发性的显性破坏,是一个有一定时段的发展过程,若在这个过程中及时发现并加以遏制,将会减少人民生命和财产损失。分析了岩石蠕变的影响因素,给出蠕变模型,提出了软弱岩石的蠕变预处理的一些措施。     

耐热钢蠕变损伤力学模型研究

在理论推证和试验的基础上,建立了一种崭新的蠕变损伤强度理论,引入了一个新的强度指标,即材料的极限有效损伤应力强度。实验证明它较之传统强度理论中的屈服极限或强度极限更具有合理性,实验测定结果的稳定性更好。因此,依据该强度理论,可对发生蠕变损伤的耐热钢构件或耐热钢结构的有效使用寿命,作出更加合理的估计。     

新型恒应力蠕变试验机装置研制及应用

基于原有蠕变试验机在实际测量过程中实验误差较大,不能实现恒应力加载,对其进行了改进,设计了一种新型恒应力蠕变试验机。对新型恒应力蠕变试验机加载力臂的结构进行了理论计算推导,分析了加载力臂设计的可靠性,并用该试验机测试了GH4169合金的蠕变曲线。结果表明,新型恒应力蠕变试验机可以保持蠕变试样始终受到恒定应力,能实现更精确地测量金属材料的蠕变性能的目的。     

称重传感器蠕变的模糊补偿方法研究

本文介绍了对传感器蠕变进行补偿的新方法 ,首次引入模糊识别的方法来确定载荷的变化情况 ,该方法可实现蠕变实时精确补偿 ,简便易行 ,避免了繁琐的传感器蠕变模型的建立和实现过程 .实验证明这种方法精度很好 .     

滞后型岩爆孕育过程的围岩时效变形

以隧洞围岩的时效变形诱发滞后型岩爆为核心,围绕隧洞围岩的时效变形特性进行声发射辅助岩石三轴蠕变实验和现场微破裂监测实践。研究隧洞围岩在蠕变过程中的微破裂前兆及其时空演化规律,根据卸荷蠕变变形损伤演化规律及蠕变率随时间的发展阶段特征,构建高应力作用下岩体蠕变损伤模型。建立微震活动信息与物理、力学参数变化之间的联系,应用大规模数值分析方法进行不同偏应力作用下隧洞围岩的流变失稳研究。结果表明:深埋岩体隧洞中,岩爆的时间、空间、强度等分布存在较明显的规律性,岩爆发生之前普遍存在一个孕育过程,并伴随着大量微破裂的产生和微震能量的释放(微震前兆),微震活动对岩爆事件普遍具有时间优先性和空间一致性,可利用其指导安全施工,从而为滞后型岩爆预测和安全施工提供新的研究思路。     

施工过程中混凝土徐变对结构竖向变形影响的有限元模拟

通过有限元模拟及算例验证,分析了高层建筑考虑施工过程中混凝土材料徐变对结构竖向变形的影响。分析表明,混凝土的徐变变形作用对柱的轴力影响不大,但对柱端弯矩影响较大;考虑徐变变形的柱端弯矩计算结果较没有考虑徐变变形的情况有显著减小。在考虑徐变影响的情况下,各层位移均有所增加,且两者的最大差值相差较大,很可能会影响结构的正常使用,在设计过程中不应忽视。该研究结果可为考虑高层建筑结构在施工过程中材料的徐变性能对结构内力的影响提供理论依据及分析方法。     

蠕变条件下完整岩石的起裂和扩展准则

The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers,And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers.The characteristics of crack initation and propagation of rocks under creep condition.however,are very improtant for rock engineering and still not paid enough attention by researchers,In this paper,the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain,the Sichuan Province of China.Cuboid specimens under three point bending were used in this investigation.All specimens were classified into four sorts and used for Mode-I fracutre of creep frcture tests.The experimental result shows that due to creep deformation.rock crack will inevitably initialt and propagate under a load of KI,which is less than fracture toughness KIC but not less than a constant(marked as KIC2),KIC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture tough ness KIC.defined as creep fracture toughness in this paper,KIC2 should be considered as an importnat parameter on design and computation of rock engineering.The microstructureal mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect,and the validity of test result was explained.The test result was also verified in rheological theory.When KI is more than KIC2 but less than KIC,rock crack will initiate and propagate after a time interval of sustained loading under creep condition.In order to find the relation between duration of sustained lading.which can lead to crack initiation and propagation,and the initial stress intensity factor KI,an unequal0interval time sequence forecasting and predicting model was introduced,and the relation was obtained for homogeneous and isotropic fine-grained red sandstone.Finally a modified fracture toughness formula was given,in which the influence of fracture process zone(FPZ) was fully considered.     

基于参数敏感性的自密实混凝土徐变模型

由于配合比的特殊性,自密实混凝土的徐变性能与普通混凝土存在差异。文章对自密实混凝土多参数进行徐变试验,分析胶骨比、水胶比、砂率和粉煤灰掺量4 个参数的敏感性,建立自密实混凝土双曲线徐变模型,应用于自密实混凝土长期变形的预测。     

In-plane creep buckling of concrete-filled steel tubular arches

The creep-induced deformation of the arch rib of concrete-filled steel tubular （CFST） arches under a sustained load can increase the bending moment, which may lead to earlier stability failure called creep buckling. To investigate the influences of concrete creep on the buckling strength of arches, a theoretical analysis for the creep buckling of CFST circular arches under distributed radial load is performed. The simplified Arutyunyan-Maslov （AM） creep law is used to model the creep behavior of concrete core, and the creep integral operator is introduced. The analytical solutions of the time-dependent buckling strength under the sustained load are achieved and compared with the existing formula based on the age-adjusted effective modulus method （AEMM）. Then the solutions are used to determine the influences of the steel ratio and the first loading age on the creep buckling of CFST arches. The results show that the analytical solutions are of good accuracy and applicability. For CFST arches, the steel ratio and the first loading age have significant influences on creep buckling. An approximate log-linear relationship between the decreased degrees of the creep buckling strength and the first loading age is found. For the commonly used parameters, the maximum loss of the buckling strength induced bv concrete creen is close to 40%     

Adjustment of B3 model for drying concrete with additives based on experimental data

All currently avalable concrete creep predicting models cannot describe well the creep of a concrete structure because they all leave the effects of additives out of consideration. The purpose of this work was to modify model B3 for overcoming this deficiency. We tested thirteen specimens of C40 and C50 concrete with additives, out of which nine were for creep and four for shrinkage tests over a 700 d period under controlled temperature. We compared the experimental results for creep and shrinkage with those obtained by using model B3, and derived modification terms through regression analysis. Based on the experimental results of identical specimens under varied stress levels, we also derived a function considering the effect of stress level on creep. It is suggested that the creep prediction models without adjustment should not be used for modem concrete with a variety of additives.     

成都裂隙性黏土流变特性试验

以成都裂隙性黏土为对象,进行一系列室内试验,探讨了成都裂隙性黏土的流变特性。通过三轴固结不排水蠕变试验,得到不同围压下各级偏应力水平的全过程蠕变曲线和应力—应变等时曲线,对试验结果做了讨论,并建立了蠕变方程。其中应变—时间关系采用伯格斯模型,应力—应变关系采用指数函数的蠕变方程,拟和曲线与试验曲线很好的吻合,较好地表达了土体的应力—应变—时间关系。