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1.
非线性粘弹体的时间-温度-应力等效原理及其应用   总被引:10,自引:0,他引:10  
考虑粘弹性材料特征时间的应力相关性,认为应力水平与温度、压力、溶剂浓度、损伤及老化等材料特征时间的影响相似,有其等效性。依自由体积理论,推导了温度-应力移位因子的表达式,提出了时间-温度-应力等 效原理。应用此原理,可以将不同温度和应力水平下的儒变曲线移位成某一参考温度和参考应力水平下的主曲线,从而可以通过较高温度和应力水平下的短期蠕变行为来预测较低温度和应力水平下的较长期的蠕变行为。实例分析了高密度聚乙烯(HDPE)非线性蠕变行为的-应力等效性。  相似文献   

2.
胶凝原油蠕变的时间-温度-应力等效性   总被引:2,自引:0,他引:2  
黏弹性蠕变是胶凝原油重要的流变特性,要描述胶凝原油的黏弹性蠕变行为,必须同时考虑 应力、时间和温度等参数. 于是对胶凝原油进行了不同应力和不同温度下的蠕变实验,利用 时间-温度-应力等效原理分析了胶凝原油的非线性蠕变行为,得到了参考应力和参考温度下 的蠕变主曲线,并用黏弹性流变模型拟合得到了蠕变主曲线的表达式. 从而可以分别通过较 高温度和应力水平下的短期蠕变行为来预测较低温度和应力水平下的长期蠕变行为.  相似文献   

3.
对三种岩石在不同的应力下进行了蠕变实验,对蠕变实验曲线用粘弹模型进行了模型参数的反演,结果认为标准线性体、伯格斯和对数模型都是实验曲线的很好近似.为了进一步了解蠕变实验时间对模型参数的影响,研究了蠕变模型的预测功能.将实验蠕变曲线分成二部分,第一部分用于模型参数的反演,第二部分用于模型预测数据的检验.时间外延所得的模型的预测曲线都明显偏离了实测曲线,伯格斯和对数模型的预测曲线比实测曲线偏高,而标准线性体模型则偏低.根据不同时间的蠕变实验数据的比较和分析,认为实验时间对蠕变模型参数的反演有较为明显的影响,但只要对标准线性体模型作适当修正,引入与时间尺度有关的函数C(t),则该模型的预测能力就有较大的提高.  相似文献   

4.
为了克服传统元件组合模型不能描述岩石蠕变过程中非线性特征的缺陷,首先根据加速蠕变阶段的应变和应变率随蠕变时间急剧增大的特点,建立黏塑性应变与蠕变时间的指数函数关系并提出非线性黏塑性体.将该非线性黏塑性体与广义Burgers蠕变模型串联,建立可以描述岩石全蠕变过程的非线性黏弹塑性蠕变模型,根据叠加原理得到一维应力状态下的轴向蠕变方程.然后基于塑性力学理论指出岩石三维蠕变本构方程建立过程中的不足之处,并给出非线性黏弹塑性蠕变模型合理的三维蠕变方程.最后采用不同应力水平下砂岩轴向蠕变试验对模型合理性进行验证,结果表明:拟合曲线与试验曲线吻合度较高,所建蠕变模型能够很好地描述砂岩在不同应力水平下的蠕变变形规律,尤其对加速蠕变阶段的非线性特征描述效果很好,验证了模型的合理性.  相似文献   

5.
应力波动力扰动下脆性岩石的静力蠕变特性,对深部地下工程围岩变形的评价有重要的实践意义.动力载荷作用导致的局部细观裂纹损伤严重影响脆性岩石蠕变力学行为.基于细观裂纹扩展与应力关系模型、动力扰动损伤演化函数、静动力载荷演化路径函数与黏弹性本构模型,提出一种应力波动力扰动下脆性岩石蠕变断裂特性的宏细观力学模型.其中动力损伤通过控制岩石内部细观裂纹数量变化实现.模型描述了应力波动力扰动下岩石的应变时间演化曲线,解释了岩石动力扰动下蠕变失效特性.研究了不同应力波幅值及周期影响下的脆性岩石应变-时间关系曲线,并通过试验结果验证了模型的合理性.讨论了动力损伤变化形式,突变发生时刻,突变量的大小对岩石蠕变失效特性的影响.分析了应力波幅值、周期对岩石动态动力损伤效应以及蠕变失效特性的影响.主要研究结果:动力损伤的变化值越大,岩石蠕变失效发生时间越短.冲击载荷扰动期间,动力损伤发生的时刻及增加的形式,对动力扰动后的岩石应变及蠕变破坏时间影响很小.动力损伤变化量随应力波幅值增加、周期减小而加速增大.应力波幅值越大、周期越小,岩石发生蠕变失效时间越短.  相似文献   

6.
将沥青混合料看作是由沥青砂和粗骨料组成的两相复合材料,提出了应用自洽方法预测沥青混合料粘弹性性能的一般思路.采用四参量流变模型描述沥青砂的粘弹性能,通过 Laplace 变换将时间域的粘弹性问题转化为变换域的线弹性问题,然后经 Laplace 逆变换将变换域的解转化到时间域.利用不同温度、不同应力水平下沥青砂的单轴压缩蠕变实验,拟合四参量流变模型参数,预测了沥青混合料在不同温度和不同应力水平下的蠕变曲线,并与实验结果进行了比较,发现蠕变的早期阶段预测值与实验值基本符合.最后进一步分析了温度、应力水平对沥青混合料蠕变行为的影响.  相似文献   

7.
为揭示岩石峰后蠕变失稳特性,利用MTS815电液伺服岩石力学试验系统,对红砂岩进行了峰后蠕变试验,采用线性回归的方法估算了蠕变失稳时间,探讨了损伤、初始围压以及围压增量对峰后蠕变特性的影响规律。结果表明:随着损伤的加大,蠕变变形速率增大,蠕变失稳时间缩短。同一围压下,各级应力水平下蠕变量随应力水平的增大而增大,且服从指数函数关系。增大初始围压,各级应力水平下的蠕变变形速率均有一定程度的降低,且对等速蠕变阶段蠕变速率的影响较加速蠕变阶段蠕变速率大,蠕变失稳时间延长。施加围压增量,大大减小了蠕变变形速率,促使了加速蠕变阶段向等速蠕变阶段转化,明显延长了蠕变失稳时间,减小了蠕变形变量。研究结果为工程围岩的长期稳定性分析提供了参考依据。  相似文献   

8.
为合理描述人工冻结法施工的矿井土层力学特性,对某矿井土样的重塑土进行单轴抗压强度实验和单轴压缩蠕变实验,得到重塑冻结黏土在不同温度及载荷加载等级下的应力-应变曲线和蠕变曲线。实验结果表明:冻结温度越低,土样的单轴强度越大;相同冻结温度下,土样的蠕变变形随着应力水平的升高而增大。单轴压缩蠕变的等时应力-应变曲线随时间发展向应变轴靠拢;土样经历初始蠕变和等速蠕变两个阶段,在较高应力水平下有进入加速蠕变的趋势;对S--M模型中各参数的意义进行修正并考虑温度的影响,得到人工冻结黏土改进S--M蠕变显式模型,然后采用粒子群算法对人工冻结黏土S--M蠕变模型参数进行优化。改进S--M蠕变显式模型理论计算值与实验值吻合良好,表明改进S--M蠕变显式模型能较好模拟人工冻结黏土的蠕变特性。改进S--M蠕变显式模型为人工冻土蠕变计算提供一种新方法。  相似文献   

9.
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。  相似文献   

10.
通过实验测定了有机玻璃(PMMA)在不同初始应变率和初始应变下的应力松弛曲线。分析了三种应变率(0.001s~(-1)、0.01s~(-1)和0.1s~(-1))下不同初始应变(5%、7%、10%和15%)的实验结果。结果表明:初始加载应变率会影响有机玻璃高分子链段的运动速度,进而对应力松弛行为产生影响;不同初始应变对应力松弛的影响,则体现为不同变形程度对PMMA高分子链运动速度的影响。将PMMA的应力松弛视为两个阶段即应力快速松弛段和应力缓慢松弛段,基于对这两个阶段的分析,提出了一个非线性应力松弛本构模型。对实验得到的应力松弛曲线采用上面提出的本构模型进行数值拟合,吻合结果良好。此外,还对模型中参数的影响因素进行了分析讨论。结果表明该本构模型可以用于描述PMMA的非线性应力松弛行为。  相似文献   

11.
In order to predict the mechanical performance of the polyvinyl chloride(PVC) at a high operating temperature,a series of short-term tensile creep tests(onetenth of the physical aging time) of the PVC are carried out at 63 C with a small constant stress by a dynamic mechanical analyzer(DMA).The Struik-Kohlrausch(SK) formula and Struik shifting methods are used to describe these creep data for various physical aging time.A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters(the initial creep compliance,the characteristic retardation time,and the shape factor) determined by the aging time.It is shown that the momentary creep compliance curve of the PVC at 63 C can be very well fitted by the SK formula for each aging time.However,the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures,and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinates have shown a nonlinear phenomenon.Moreover,the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case.Finally,the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.  相似文献   

12.
13.
Stress-dependence of the intrinsic time of viscoelastic materials is investigated. The influence of stress level on the intrinsic time is considered to be similar to that of temperature, pressure, solvent concentration, damage and physical aging. The time-temperature-stress equivalence principle is proposed, by employing which, the creep curves at different temperatures and stress levels can be shifted into a master curve at reference temperature and stress level. Thus the long-term creep behavior of viscoelastic materials at a lower temperature and stress can be predicted from the short-term one at a higher temperature and stress. As an example, the nonlinear creep behavior of high-density polyethylene (HDPE) at room temperature is studied using the time-temperature-stress equivalence principle presented. Project supported by the National Natural Science Foundation of China (No. 19632030, 50003005) and by the Education committee of Human Province (No. 99C122).  相似文献   

14.
We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite demonstrates aging behaviour wherein it undergoes time-dependent enhancement of its elastic modulus as well as its characteristic relaxation time. However, under application of the normal stress, the rate of aging decreases and in the limit of high stress, the aging stops with the suspension now undergoing a plastic deformation. Overall, it is observed that the aging that occurs over short creep times at small normal stresses is the same as the aging that occurs over long creep times at large normal stresses. This observation allows us to suggest an aging time–process time–normal stress superposition principle, which can predict rheological behaviour at longer times by carrying out short time tests.  相似文献   

15.
Two experimental techniques are described for the determination of the change of specific volume of polymers with temperature and aging time, which allow measurements between – 160 °C and + 200 °C. Four technical amorphous polymers, PS, PVC, PMMA and PC have been investigated. Volume-temperature curves under constant rate of cooling are presented and interpreted with respect to relaxation processes known from other physical investigations. The rate dependence of dilatometric glass transition temperatures is compared with the time dependence of rheometric glass transition temperatures from shear creep data. Volume relaxation data at constant aging temperature are presented. Aging is found to proceed until very low temperatures in the glassy state for e.g. PMMA.For polystyrene, a comparison is made between the predictions of a very simple theory of volume relaxation due to Kovacs with experimental data, using additional information from volume temperature curves and the time temperature shift of the shear creep transition. The theory predicts a rate of volume relaxation which is much lower than that found by experiment.  相似文献   

16.
Creep behavior of the Zr-1.5Nb-0.4Sn-0.1Fe-0.1Cu alloy sheet is investigated from 300℃ to 400℃ in the stress range from 50 MPa to 180 MPa along the rolling direction. The measured strain rates range from 8.8 × 10^-10 s^-1 to 4.7 × 10^-7 s^-1. The activation energies are estimated to assess the creep deformation mechanisms in this alloy. The strain rate is slightly different at low stress, while it shows a distinct difference at high stresses. Stress exponents of this alloy increase with increasing applied stress at all testing temperatures. It is concluded that the creep deformation of the Zr-1.5Nb-0.4Sn-0.1Fe-0. 1 Cu alloy is controlled by the diffusion creep at low stress region and by the climbing of dislocations at high stress region.  相似文献   

17.
岩石蠕变特性试验研究   总被引:2,自引:0,他引:2  
胡波  王宗林  梁冰  李刚  王俊光  陈宫 《实验力学》2015,30(4):438-446
针对大安山煤矿+550水平西二石门围岩蠕变变形严重的问题,采用室内蠕变试验与理论分析相结合的方法研究岩石蠕变特性。选取泥质粉砂岩作为软岩试样,通过自制三轴蠕变仪对所取岩样进行恒围压分级增轴压的三轴压缩蠕变试验,结果表明:随应力水平的提高,起始蠕变速率增大,进入稳态蠕变阶段用时延长,稳态蠕变速率从0h-1增大到3.12e-4·h-1,瞬时应变以线性关系增加,围压9MPa条件下的起始蠕变应力阈值为6MPa,当应力水平超过岩石长期强度时出现加速蠕变。基于蠕变试验规律,考虑起始蠕变应力阈值,将一种可用阶跃函数表示的开关元件与广义K体并联,并引入损伤元件对CVISC蠕变模型进行改进。采用1st-Opt中的Levenberg-Marquardt+通用全局优化法计算蠕变参数并进行反演。反演结果表明理论曲线与试验曲线的吻合效果较好,证明了所建模型的合理性。上述研究成果可为岩石工程的长期稳定性分析提供试验和理论依据。  相似文献   

18.
Physical aging typical of semi-crystalline polymers was evidenced in green (never dried) wood from three tropical hardwood species. The assumption of uniform aging rate was verified by the construction of master curves from series of tensile creep tests in the fibre direction, performed at increasing time elapsed after a quench following heating above the glassy transition. The rheological response during periods of creep small enough to neglect the progress of aging was described by a model made of a spring in series with a parabolic dash-pot where only the characteristic time depends on the aging time. The model was able to describe results obtained by a previous author on softwood loaded transversally to the fibres. The possible role of a transient adsorption process consecutive to the quench is discussed.
Jana DlouháEmail: Email:
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