结构用橡胶集料混凝土受压全曲线试验及其本构模型

针对结构用橡胶集料混凝土（CRC）应保证与普通混凝土等强,而此类CRC单轴受压全曲线试验研究有限,尚无较成熟单轴受压本构模型的情况,分别进行了3组粒径为1~2 mm、掺量为0~100 kgm^-3的CRC立方体试块单轴受压试验及棱柱体试块受压应力-应变全曲线试验。结果表明：通过综合采用NaOH碱溶液处理橡胶颗粒及配合比优化设计的方法,可以精确控制CRC与普通混凝土等强,且峰值应变及极限应变明显增加,试块破坏过程温和缓慢,破坏时完整性较好。同时,现有的普通CRC单轴受压本构模型不适用于此类结构用CRC,而普通混凝土单轴受压Carreira-Chu本构模型虽与试验曲线吻合尚可,但其对CRC的适用条件有待考证。最后,通过曲线拟合试验数据,得到以过镇海模型为基础的结构用CRC本构模型参数的建议取值,以用于此类结构构件的分析与设计。     

高温后高强混凝土受压疲劳性能研究

利用电液伺服疲劳试验机,进行了C60高强混凝土的单轴受压疲劳试验,研究了其经100℃、400℃和700℃高温后表观特征、残余应变、疲劳寿命等的变化规律。试验结果表明：高温后高强混凝土的色泽变浅,部分400℃恒温0.5 h、1 h的试块呈铁锈红色,700℃时试块外表呈灰白色;在单轴受压疲劳荷载作用下,高温后高强混凝土的残余应变符合三阶段发展规律,较普通混凝土有更长的第二阶段。定义相对残余应变为损伤变量,建立了高温历程与受压疲劳损伤的关系模型,为经历重复荷载作用与不同加温历程等综合工况下高强混凝土疲劳试验研究及疲劳损伤评价奠定了基础。     

疲劳荷载对橡胶混凝土损伤和断裂性能的影响

虽然橡胶混凝土塑性和疲劳性能较好,但由于掺入橡胶,其在疲劳荷载下离散性增大,损伤过程及最终的断裂机制均不明确.为研究橡胶混凝土在疲劳荷载下的损伤和断裂性能,基于声发射开展了不同橡胶掺量的混凝土在疲劳荷载下的三点弯曲疲劳断裂试验.计算有效裂缝长度,分析疲劳荷载下不同橡胶掺量的混凝土裂缝长度a的变化规律,并利用裂缝长度a和...     

高温后高强混凝土单轴受压疲劳过程中细微观试验研究

利用超声、显微硬度检测、汞压力测孔等综合手段,对高温后高强混凝土单轴受压疲劳过程中的细微观结构进行了试验研究。通过测定声时和波幅、显微硬度、孔径分布、累积进汞量等参数,对比分析了高温后高强混凝土疲劳过程中细微观结构的变化规律;建立了高温后高强混凝土疲劳残余应变与声时、显微硬度之间的关系模型,并进一步揭示了高温作用与疲劳循环荷载综合工况下高强混凝土内部细微观结构的动态演化过程及损伤机理。研究表明:随着疲劳循环次数的增加,高温后高强混凝土的声时整体呈不断增大的趋势,而波幅与显微硬度呈减小的趋势;最可几孔径与总孔隙体积显著增大,孔径大于50 nm的有害孔和多害孔的数量明显增多,各参数的变化幅度整体呈快-慢-快的三阶段变化规律;在相同温度工况下,高强混凝土单轴受压疲劳过程中低应力水平在达到相同寿命比时造成的疲劳损伤要较高应力水平造成的损伤大;研究结果为遭受火灾或经其他高温历程的混凝土结构的无损检测、疲劳损伤分析及结构评估提供参考。     

混凝土双轴拉压、三轴拉压压变幅疲劳性能研究

利用大型多轴疲劳试验机,进行了拉压双轴和拉压压三轴荷载作用下混凝土两级、三级变幅疲劳试验研究,重点分析了残余应变的变化规律。试验结果表明：混凝土在拉压和拉压压加载工况下的残余应变主要与相对疲劳次数和侧压应力比有关,基本不受加载历程因素的影响。定义相对残余应变为损伤变量,建立了损伤演变方程,并进行了疲劳损伤分析和剩余疲劳寿命预测,为混凝土在多轴变幅疲劳试验研究及疲劳损伤评价提供参考。     

纳米改性再生骨料混凝土单轴受压疲劳性能

采用纳米二氧化硅对再生骨料混凝土(RAC)进行改性,开展了不同再生骨料取代率及纳米改性后的再生骨料混凝土单轴受压疲劳试验,研究其疲劳寿命、疲劳方程、疲劳变形规律及疲劳剩余强度,并利用纳米压痕试验从细观层面上分析探讨了纳米二氧化硅对再生骨料混凝土多重界面过渡区的影响。结果表明:再生骨料混凝土疲劳寿命均较好地服从两参数威布尔概率分布。50%保证率、0.75应力水平下,再生骨料混凝土的疲劳寿命比普通混凝土降低了25.8%,掺入纳米二氧化硅可显著提高再生骨料混凝土的疲劳寿命。对比应变演化曲线和剩余强度模型,纳米二氧化硅改性后的再生骨料混凝土,剩余强度衰减非线性规律明显。纳米二氧化硅的掺入提高了再生骨料混凝土多重界面过渡区的压痕模量,改善了再生骨料混凝土的疲劳性能。     

橡胶再生粗骨料混凝土的性能试验研究

为研究橡胶再生粗骨料混凝土的力学性能和疲劳性能,该文采用不同配合比橡胶再生粗骨料混凝土,进行了力学性能和疲劳性能试验。结果表明：1）再生粗骨料混凝土的抗压强度比普通混凝土提高了9.8%,但抗折强度比普通混凝土低,其弹性模量略有下降。2）再生粗骨料混凝土的基本力学性能随废弃橡胶颗粒的掺入有较显著的下降,折压比随之增加,峰值挠度、峰值应变和极限应变在一定范围内随橡胶颗粒含量的增加而增加。3）当橡胶颗粒掺量为20%时,橡胶再生粗骨料混凝土的极限应变是无橡胶再生粗骨料混凝土的3.46倍,同时显著增强了混凝土的疲劳寿命。     

循环荷载下混凝土疲劳损伤累积分析的颗粒流黏结退化模型

采用颗粒流程序对混凝土循环加载试验进行离散元模拟,模拟结果显示:局部摩擦耗能的分布反映出损伤发生的薄弱区域;累积摩擦耗能与循环加载次数呈线性关系;摩擦耗能的累积速率对循环荷载大小敏感。基于摩擦耗能与疲劳损伤之间的相关性,提出了基于摩擦耗能的黏结退化模型,分析了模型参数与疲劳寿命之间的关系。对疲劳试验的模拟结果表明:该文提出的模型能够模拟出循环荷载下混凝土的疲劳寿命,以及变形演变、刚度退化、裂纹发展等疲劳损伤累积行为,可用于分析复杂荷载工况下的疲劳损伤累积规律。     

混凝土三轴变幅拉-压疲劳性能试验研究

进行了最小应力水平为0.20fc,最大应力水平为0.20ft~0.55ft,定侧压为0.30fc的变截面混凝土试件三轴拉-压等幅和变幅疲劳试验,分析了混凝土三轴拉-压疲劳最大和最小纵向总应变的三阶段演变规律和级间相似性,给出了疲劳损伤演化规律。进一步验证了Miner线性损伤累积理论的不适用性,提出了非线性损伤累积模型,并进行了疲劳剩余寿命预测,通过与试验结果的比较表明该模型具有较高的精度和适用性。     

不同MgO掺量混凝土动态损伤特性的研究

对不同MgO掺量(0％、2％、4％、6％、9％、12％)的混凝土进行了应变速率(10-5s-1、10-4 s-1、10-3 s-1和10-2 s-1)下的单轴抗压试验研究,分析了不同MgO掺量混凝土的基本力学参数变化规律.结果表明:(1)相同应变速率下,随着MgO掺量的升高,混凝土的峰值应力和峰值应变整体上表现出升高的趋势,并且得到混凝土的峰值应力和峰值应变随MgO掺量变化的关系式;(2)相同MgO掺量下,混凝土单轴受压下的峰值应变随应变速率的变化离散性较大;(3)混凝土弹性模量随MgO掺量和应变速率的变化波动性较大;(4)基于Weibull统计理论分布的损伤本构模型,描述了不同MgO掺量的混凝土损伤破坏过程,混凝土材料的损伤发展主要有3个阶段:损伤起始阶段、损伤发展阶段和损伤破坏失稳阶段.     

Creep fatigue behaviour of Type 321 stainless steel at 650°C

Abstract

Type 321 austenitic stainless steel has been used in the UK’s advanced gas cooled reactors for a wide variety of thin section components which are within the concrete pressure vessel. These components operate at typically 650°C and experience very low primary stresses. However, temperature cycling can give rise to a creep fatigue loading and the life assessment of these cycles is calculated using the R5 procedure. In order to provide materials property models and to validate creep fatigue damage predictions, the available uniaxial creep, fatigue and creep fatigue data for Type 321 have been collated and analysed. The analyses of these data have provided evolutionary models for the cyclic stress strain and the stress relaxation behaviour of Type 321 at 650°C. In addition, different methods for predicting creep fatigue damage have been compared and it has been found that the stress modified ductility exhaustion approach for calculating creep damage gave the most reliable predictions of failure in the uniaxial creep fatigue tests. Following this, validation of the new R5 methods for calculating creep and fatigue damage in weldments has been provided using the results of reversed bend fatigue and creep fatigue tests on Type 321 welded plates at 650°C in conjunction with the materials properties that were determined from the uniaxial test data.     

Description of fatigue damage in carbon black filled natural rubber

The present paper describes macroscopic fatigue damage in carbon black‐filled natural rubber (CB‐NR) under uniaxial loading conditions. Uniaxial tension‐compression, fully relaxing uniaxial tension and non‐relaxing uniaxial tension loading conditions were applied until sample failure. Results, summarized in a Haigh‐like diagram, show that only one type of fatigue damage is observed for uniaxial tension‐compression and fully relaxing uniaxial tension loading conditions, and that several different types of fatigue damage take place in non‐relaxing uniaxial tension loading conditions. The different damage types observed under non‐relaxing uniaxial tension, loading conditions are closely related to the improvement of rubber fatigue life. Therefore, as fatigue life improvement is classically supposed to be due to strain‐induced crystallization (SIC), a similar conclusion can be drawn for the occurrence of different types of fatigue damage.     

A method for modelling of fatigue life for rubbers and rubber isolators

A method for modelling fatigue life of rubbers and rubber isolators is presented in this paper. Firstly, a fatigue experiment is carried out for a rubber dumbbell cylindrical specimen and a rubber isolator. Based on the finite element analysis, the damage parameters including the strain energy density, the maximum principal Green–Lagrange strain and the effective stress are calculated and discussed. Secondly, three fatigue life prediction models are established by using the three damage parameters and using the relation between the measured fatigue life of a dumbbell cylindrical specimen and the computed value of the damage parameters. Thirdly, three proposed prediction models are used to investigate which one can be best used to predicting fatigue life of rubber isolators, taking a typical powertrain rubber isolator as studying example. The fatigue lives of the rubber isolator predicted by the three models are compared with the experimental life. The results demonstrate that the predicted fatigue lives of the rubber isolator using the three fatigue models agree well with the experimental fatigue life within a factor of four, and the model using the effective stress as the damage parameter can predict the fatigue life within a factor of two, which has the best accuracy among the three models.     

混凝土的P-D-ε曲线及其累积损伤特性分析

本文在大量试验的基础上建立了描述混凝土在疲劳载荷作用下损伤与应变的概率关系的 曲线。使用该曲线可以十分方便地研究在不同存活率下混凝土的损伤阈值应变、破坏极限应变与损伤量的关系，判断混凝土结构在任意应变状态下所处的损伤状态或剩余强度。提供了一种依据实测应变量及应变变化评估混凝土结构可靠度和寿命的有效途径。     

单向聚酯帘线增强橡胶材料疲劳特性研究

利用自行建立的试验系统, 首次对单向聚酯帘线增强橡胶材料进行了疲劳测试, 研究了应变、频率和温度对疲劳损伤累积的影响, 并给出了疲劳寿命预报方程, 为评价轮胎的疲劳特性、预报轮胎的疲劳寿命提供了有效的手段。      

Concurrent ratcheting–fatigue damage analysis of uniaxially loaded A‐516 Gr.70 and 42CrMo Steels

This study intends to investigate the concurrent interaction of fatigue damage and ratcheting strain in two commonly used steel alloys of (American Society for Testing and Materials) ASTM A‐516 Gr.70 and 42CrMo, respectively for pressure vessels and high grade machinery parts over uniaxial stress cycles. Ratcheting extension and fatigue damage progress were both characterized cycle‐by‐cycle over life cycles of tested materials. The interaction of ratcheting and fatigue damage was defined based on mechanistic parameters involving the effects of mean stress, stress amplitude and cyclic softening/hardening response of materials. The extent of ratcheting effect was defined by product of average ratcheting strain per cycle, and maximum stress value during a cycle, while fatigue damage was analysed based on earlier developed energy‐based models of Xia–Ellyin, and Smith–Watson–Topper. Overall damage due to ratcheting and fatigue was calibrated through a weighting factor at various mean/ cyclic amplitude stresses. An algorithm was developed to evaluate overall damage due to ratcheting and fatigue stress cycles of materials subjected to various mean and amplitude stresses. The estimated lives at different mean stresses and stress amplitudes for ASTM A‐516 Gr.70 and 42CrMo samples showed good agreements as compared with those of reported experimental data.