限制性剪切蠕变的渐进式破坏发育模式与本构方程分析

以标准红砂岩方形试样为研究对象,运用自行研制开发的软弱煤岩剪切蠕变试验设备和煤岩细观力学特性测控软件、超声波检测设备,对红砂岩限制性剪切、限制性剪切蠕变过程的破坏过程、破坏模式、渐变特性进行了分析。结果表明：红砂岩试样在限制性剪切、限制性剪切蠕变条件下表现出明显的渐变破坏特性;大部分试验过程中试样内部的超声波速减小幅度较小,仅在临近破坏处有明显减小;红砂岩限制性剪切蠕变破坏发育过程表现为先形成主控破裂面,又在其附近区域形成丰富微裂隙,并发育、相互贯通,最后克服剪切面摩擦力并发生突发式破坏,且伴有较大断裂声;其破坏模式发育过程呈渐进式,破坏模式呈突发式;建立了一种可以表征红砂岩剪切蠕变渐进式破坏发育过程的本构模型。     

Testing and modeling studies on creep characters of supports for tunnel using nonlinear constitutive model

Creep characters of tunnel supports structure is analyzed according to triaxial creep test of concrete specimen of deep tunnel supports structure adopting MTS815 hydraulic servo system. The creep parameters of nonlinear creep model are presented based oncreep curve. The finite element numerical model has been established considering tunnel construction process, creep characters of surrounding rock and support structure. The displacement characteristics, the effective stress and the maximum shear stress in different position in primary support and second lining are obtained through creep characters analysis of surrounding rock and supports structure. The features of displacement and stress dependent time of tunnel supports has visible difference comparing with discard creep effect and calculation displacement and practical monitoring results is basic concordance. The creep characters of surrounding rock and tunnel supports should be considered for deep tunnel.     

Characteristics of triaxial creep and constitutive relationship of outburst coal

The creep characteristics of coal and rock under confining pressure in Songzao, P.R. China were studied. The experimental data were analyzed and discussed in detail. The characteristics of creep could be described by the generalized K B model after the experimental data were fitted. The parameters of the model were obtained. The results show that when the creep load was σ≥σs, the curve of coal and rock under confining pressure displayed three typical phases. In the first and second phases, the fitted curve was consistent with the test curve. Thus, the generalized K B model can describe the whole process of coal creep under confining pressure.     

Triaxial creep model and its stability analysis of gas containing coal 

Investigation on the creep property of coal containing gas is an effective means for understanding the mechanism of delay outburst of coal and gas in a coal mine. This paper conducts triaxial creep tests on the specimens of gas containing coal using a self made creep experimental apparatus to determine the creep law for coal containing gas. An improved triaxial creep model is developed for containing gas by coupling a Nishihara model with another visco elasto plastic body which can describe the deformation property of non Newtonian fluids. The parameter fittings are conducted based on the experimental dada.The present model is examined in terms to the results of triaxial creep tests in various stress level cases. The result shows that the proposed model for gas containing coal can properly represent the creep deformation at different creep stages, especially at the accelerating stage. The instability condition of the model for coal containing gas is also discussed according to stability theories of differential equation solution.     

Experimental Study Creep Characteristics on Creep and Cyclic of Saturated Soft Clay

Several long term creep and cyclic creep tests of Shanghai soft clay are performed in the laboratory. Test results have been obtained under various combinations of confining stresses, deviation static stress ratios and deviation cyclic stress ratios. The results reveal that the axial creep strain increases with the increase of deviation static stress ratio under a constant confining stress, while it also increases with the increase of confining stress under a constant deviation stress ratio. Such a phenomenon is similar to that from the cyclic creep tests, but the following creep strain increase will be significantly reduced after a period of cyclic loading. The results will benefit the expressway, railroad and underground constructions.     

疲劳／蠕变交互作用下塑木地板的断裂机理

对塑木地板进行抗弯性能测试,分别选取25％和75％两种应力水平进行疲劳／蠕变试验。研究了塑木地板在疲劳／蠕变复合作用下的断裂机理。结果表明：随着应力水平的增加,蠕变应变也随之增加,75％应力水平时产生的应变为25％应力水平时的3倍;其疲劳／蠕变曲线与纯蠕变曲线十分相似;在25％的应力水平作用后,材料的剩余抗弯强度为原来的94％～97％。     

渔用超高分子量聚乙烯/石墨烯纳米复合纤维的结构与蠕变性能

采用熔融纺丝法制备渔用超高分子量聚乙烯(UHMWPE)/石墨烯(GR)纳米复合纤维,研究了GR含量对UHMWPE纤维结构、热性能、力学性能与蠕变性能的影响。结果显示,GR在UHMWPE纤维基体中的分散情况以纳米级厚度为主,当GR含量为1‰和3‰时,GR在UHMWPE纤维基体中分散均匀,当GR含量为5‰时,GR在UHMWPE纤维基体中出现大的团聚体。与纯UHMWPE纤维相比,UHMWPE/GR纳米复合纤维的断裂强度和结节断裂强度均有显著提高,表明一定含量的GR可有效增强UHMWPE的抗蠕变性能且降低其蠕变速率。当GR含量为3‰时,断裂强力提高了31.9%,蠕变率降低了27.3%。当UHMWPE经GR改性后,纳米粒子与聚乙烯链段相互作用力增强,晶区附近受限的非晶区链段增多,α转变峰逐渐增强增宽。研究表明,通过纳米改性技术,可以显著提高超高分子量聚乙烯纤维的力学性能和抗蠕变性能,为实现渔用材料的高性能化提供理论依据。     

木材静曲蠕变成套测试系统的研发

为解决木材变湿蠕变测试普遍存在的环境参数(温湿度和风速)控制方式和控制精度不足、蠕变变形量测试灵敏度和精度不足、数据智能采集和处理以及系统安全防护不足等问题,在集成现有技术的基础上研发出一套木材蠕变测试系统。该系统包括环境气候箱、蠕变测试机架、木材蠕变变形量及干缩湿胀测试单元、荷载同时装卸单元、数据采集和处理单元、系统保障和防护单元6个部分。该系统可在温度为0~70℃、相对湿度为10%~98%、风速为0.3~5.6 m/s时对木材或木基材料的普通蠕变和机械吸附蠕变进行长时间稳定的测试、记录,蠕变变形量及木材厚度方向的干缩湿胀检测精度为±0.01 mm,数据采样间隔在1 s~24 h范围内可调。与现有木材蠕变测试系统相比,本系统在多参数自动同步获取、数据采样精度、运行稳定性、安全性和环境风速可调性等方面有独特优势。通过前期对木材112 d循环变湿蠕变量、干缩湿胀量及环境温湿度参数的观测和测试结果分析,证实该套检测系统可对木材的蠕变挠度、干缩湿胀量、环境温湿度等参数进行长期连续稳定的检测、记录和显示,所有测试指标均能达到设计预期。同时,由于该系统具有多参数协同检测和精度较高等特性,使得实测木材变湿蠕变比采用喷蒸变湿处理试件所获蠕变测试结果在局部地方存在明显差异,如吸湿过程中的木材静曲挠度并不都是反向减小,而是取决于吸湿速率和外荷载的竞争关系,从而为木材静曲变湿蠕变机理的揭示提供了有力证据。该系统的研制为精确可控变温变湿环境下木材蠕变机理的研究提供了新的平台。     

Development and Application of Nonlinear elasto-viscoplastic constitutive model

A complex nonlinear rheological mechanical behavior of rocks is discussed。Based on Peirc’s Scale factor, a nonlinear elasto-viscoplastic constitutive model is proposed; meanwhile stress return algorithm and consistent tangent modulus are derived. According to the UMAT interface requirement of ABAQUS, the corresponding UMAT codes are programmed. The numerical test results show that the establishment of nonlinear elasto-viscoplastic rheological model can uniformly describe creep process under different stress states,which demonstrate the extensive adaptability of the model. Using the nonlinear elasto-viscoplastic constitutive model,the rheological numerical analysis is applied to rock tunnel, the variation with time of the tunnel crown settlement and contact pressure are obtained. These results indicate that the developed model is correct and reliable,and will have good application prospects.     

Numerical Study on the Thermal-Mechanical Stability ofQinghai-Tibet Railway Embankment in Permafrost Regions

According to some basic theories of physics of frozen soil, heat transfer, frozen soil mechanics and frozen soil rheology, a mathematical model for moisture, heat and stress analysis of frozen embankment is established, in which the moisture and heat field are interacted with each other, the mechanical properties of frozen soil is decided by soil temperature and a in-situ test creep equation of frozen soil is also introduced. Meanwhile, its finite element program is written. Then, an experimental section of Qinghai-Tibet is taken as example, and the thermal-mechanical stability of the embankment is studied in detail. Through comparing with observational data, it is found that, the proposed analytical model is correct and reasonable, and it can well describe and predict the long-term stability of the embankment of Qinghai-Tibet railway.