节理岩体的随机本构关系

本文根据节理岩体变形等效的原则推导出多组节理岩体的等效连续模型的本构关系，在考虑岩体节理参数随机分布的基础上，依据Ｒｏｓｅｎｂｌｕｔｈ的概率理论求出能反映节理岩体随机特性平面问题弹性矩阵，该模型能更好反映节理岩体的工程特性。     

白垩系冻结砂岩动态统计损伤本构关系研究

为了研究饱和冻结砂岩的本构关系,依托白垩系地层煤矿立井建设中冻结凿井工程,开展室内SHPB冲击试验获取冻结砂岩在不同应变率下的动态应力应变曲线,在分析岩石动力学特性的基础上,建立了基于Weibull统计分布、Drucker-Prager破坏准则及等效应变原理的砂岩强度型动态统计损伤本构关系.结果表明:冻结砂岩动态应力应...     

强动载下岩石动态本构关系试验研究

高应变率下材料动态本构关系，目前主要通过Ｓ．Ｈ．Ｐ．Ｂ装置和轻气炮装置来获得。研究表明，平面波发生器加载更是一般爆破实验室适用的试验手段。Ｌａｇｒａｎｇｅ分析方法由于在材料动态性能实验分析中具有重要的指导和实用价值而越来越受到重视。本文主要评述它们在岩石介质材料中的应用和最新进展，对它们的历史和今后的发展趋势也作了简要说明。     

复合材料蠕变本构关系及实验测定Ⅰ.本构关系

蠕变是复合材料最重要的力学性能之一,实验表明:复合材料在蠕变条件下的变形可以分为弹性变形、粘弹性变形和粘塑性变形.应用不可逆过程的热力学和广义变量的概念可以分析材料的蠕变变形.本文首先回顾了热力学的基本方程;基于Schapery本构关系的假设和思路推导了蠕变本构关系的一般形式,其中包括弹性变形、粘弹性变形和粘塑性变形;考虑到广义力选取的不唯一性,本文提出了广义力选取的原则以使得到的本构关系尽可能地简单;由此本文给出了复合材料的一维蠕变,各向同性复合材料的二维蠕变和纤维增强复合材料平面内的蠕变的本构关系.     

应变控制加载下砼本构关系的试验研究

本文采用应变控制加载方式对砼的应力应变全过程曲线进行试验研究，完成了砼试块在单轴拉伸、单轴压缩、双轴压缩及双轴拉压状态下的全过程曲线测试，克服了荷载控制方式下不能测取其下降段的缺陷。     

自应力钢管轻砼中轻砼的本构关系及强度准则

本文采用理论分析与试验研究相结合的方法,通过对大量试验数据的计算,统计分析推导出自应力钢透轻砼中核心轻砼的本构关系及强度准则。为研究自应力钢筋轻砼基本构件的力学性能奠定了良好的基础。     

半固态金属成形的本构关系

将半固态金属成形的本构关系的描述分为低固相率的流变模型和高固相率的应力应变率关系,阐述了其发展过程中具有代表性的材料本构关系,为深入研究半固态金属成形工艺提供了参考。     

铁磁形状记忆合金本构关系的研究进展

主要分析了现有的关于铁磁形状记忆合金的本构关系,从它们所包含力学特点和基本理论出发进行了分类介绍,指出了存在的问题,最后对本构模型的进一步改进提出了修改意见。     

不同筋村的加筋土的本构关系研究

本文采用大三轴试验研究了不同结构筋村（条带式,双向垂直条带式和网）的加筋土的应力应就关系,分析了影响加筋土应力应变关系的因素,把三种加筋土的应力应就曲线与素土的进行了比较,探讨了筋材结构对其复合体应力变特性的影响,得出了三种加筋土的邓肯一张模型参数,其成果对加筋土结构的应力应变分析计算有一定参考价值。     

超低温环境下混凝土本构关系试验研究

针对超低温下混凝土本构关系进行试验研究,通过对试验数据整理分析,得出在20℃、0℃、?40℃、?80℃、?120℃、?160℃六个温度点下的应力-应变全曲线。该试验以抗压强度、弹性模量、峰值应变为主要测试指标。试验结果表明,试验温度越低,试件的破坏越迅速,测得的应力-应变全曲线下降段越短且越陡峭。随着温度降低,混凝土的峰值应变减小,脆性增大,强度与弹性模量均有所提高,且各自的提高程度与温度有关,全曲线的上升段与下降段可以用三次多项式与有理式分别拟合。     

A concise interface constitutive law for analysis of delamination and splitting in composite materials and its application to scaled notched tensile specimens

A concise constitutive law for cohesive interfaces is proposed in this paper. A new state variable is introduced to track the extent of damage accumulated at the interface. The constitutive equations not only account for mixed‐mode delamination propagation in composite materials, but also satisfactorily deal with mode ratio change during the debonding process. The interface model is implemented in the LS‐DYNA explicit finite element code. The model has been applied to scaled open hole tension tests on laminated composite material. Comparison between numerical results and experiments shows good correlation for failure modes and strengths for a range of different specimen sizes. Copyright © 2006 John Wiley & Sons, Ltd.     

硫铝酸盐基高水材料强度与微观结构研究

研究了20℃和5℃时硫铝酸盐基高水填充材料的强度发展规律及微观结构,通过XRD、孔结构测试等方法研究了高水充填材料的微观结构与强度的关系,并重点研究了亚硝酸钠对高水充填材料水化产物微观结构及强度的影响.研究表明:高水充填材料的水化产物主要是以钙矾石为主的胶凝材料;亚硝酸钠具有促进硫铝酸盐水泥熟料水化和改善高水充填材料硬化体孔结构的双重作用,在5℃时这种作用更加明显.以硫铝酸盐基填充材料代替木材、钢材作为可泵性支护材料,具有凝结硬化速度快、施工方便、价廉等优点,但施工温度低于20℃时材料的性能研究报道甚少.     

水下爆破振动特征及衰减规律研究

针对传统质点峰值振动速度公式因没有考虑水体波动对爆破振动传播的影响导致预测结果精度较差的问题,以某核电站水下爆破实验为背景,分析了水下钻孔爆破时地面质点振动特征和水下爆破地震波的衰减规律。由现场实测爆破振动速度数据分析结果可知,水下爆破产生的地震波具有振幅小,衰减慢等特点,传统的质点峰值振动速度公式不适用于水下爆破振动传播的预测,鉴于此,对其进行修正。修正后的预测公式考虑水深比的影响,将拟合系数从0.45提高到0.92,由此可见,修正的预测公式能够更好地反映水下爆破振动衰减规律。由于爆破振动的频谱特征也是决定其灾害程度的重要因素,因此通过傅里叶变换,对比分析了水下爆破与露天爆破的频谱特征。结果表明,水下爆破具有明显的滤频效应,具有主频小,频带窄,能量小等特点。研究结果可为水下爆破灾害的有效控制提供依据。     

基于Weibull模型的C/C复合材料销钉剪切强度分布及本构关系

针对C/C复合材料销钉力学性能各向异性的特点,开展基于Weibull分布模型的C/C销钉剪切强度分布及本构关系研究,探讨不同剪切方向对C/C销钉剪切强度和剪切本构的影响规律。基于两参数Weibull分布模型,采用最小二乘法获得不同剪切方向上剪切强度的分布规律;根据C/C复合材料损伤失效机制,采用基于Weibull分布的弹性损伤模型表征材料的剪切本构关系,并通过试验数据获取损伤模型中的参数。结果表明:通过Kolmogorov-Smirnov拟合优度检验,两参数Weibull分布模型能较好地表征C/C销钉剪切强度的分布规律;沿45°方向剪切的C/C销钉,其剪切强度最高;随着剪切角度的增大销钉剪切刚度逐渐降低,从0°方向上的19.46 kN/mm下降到90°方向上的12.70 kN/mm。      

实时高温下与热处理后砂岩动态拉伸特性研究

为了开展实时高温下及加热冷却后岩石动态力学性质的对比研究,利用自行设计的加热装置结合SHPB系统对两种温度状态砂岩的动态拉伸特性进行试验研究,处理温度为常温(25℃)～600℃共7组。结果表明:砂岩的率效应在两种温度状态下都存在,热处理后的砂岩拉伸强度除100℃外都比常温状态小,且随着热处理温度的增大,拉伸强度减小,温度会影响试样的破坏形态。高温下砂岩的拉伸强度除600℃外都比常温状态大,且拉伸强度随着温度的升高先增大后减小,加载率对破坏模式起主导作用。高温下的热膨胀作用会抑制裂纹相互连接,使得岩石结构更加密实,导致砂岩在实时高温下的拉伸强度相比加热冷却后有很大的区别。     

Experimental and numerical investigation of the tension and compression strength of un-notched and notched quasi-isotropic laminates

Un-notched and notched (in the form of through-thickness open holes), quasi-isotropic AS4/3501-6 laminate coupons were tested in tension and compression. Basic lamina properties were also determined experimentally. Numerical analyses using linear elastic and progressive damage approaches were conducted. The linear elastic model either significantly underestimated (first-ply failure approach) or overestimated (last-ply failure approach) the strength of un-notched laminates. The progressive damage approach was able to predict accurately the un-notched strength, providing that the non-linear shear behaviour was accounted for and appropriate failure criteria used. It was also demonstrated that the progressive damage approach could be implemented, with satisfactory accuracy and efficiency, for open-hole strength prediction using basic material degradation laws, a shell element model and widely available commercial FEM software (ABAQUS). This is of practical use for industrial applications. In addition, for the purpose of comparison, a characteristic distance approach was also applied to the open-hole strength problem. It was found that using a linear analysis with a properly defined secant shear modulus this approach gave an accurate prediction, however at least one measured value of notched strength is still required for calibration using this approach.     

Effect of further water curing on compressive strength and microstructure of CO2-cured concrete

This study aims to investigate the effects of further water curing on the compressive strength and microstructure of CO₂-cured concrete. The results showed that concrete with a residual w/c ratio of 0.25 showed the most rapid strength development rate upon further water curing due to hydration of uncarbonated cement particles. Thermogravimetric, IR-spectrophotometric and scanning electron microscope examinations indicated that further hydration of the cement particles could form C-S-H gel and ettringite crystals. The results showed that the calcite formed during the initial CO₂ curing was consumed during the further hydration of C₃A, and produced calcium monocarbonaluminate hydrate. Also, Ca(OH)₂ was not detected due to its reaction with the formed silica gel. Mercury intrusion porosimetry test results indicated that the porosity and pore size of the CO₂ cured mortar decreased further after water curing.     

The effects of multiple overloads and absorbed hydrogen on the fatigue strength of notched steel specimens

It is well known that earthquakes can damage structures and machinery. After an earthquake, those components, which have been obviously damaged are scrapped and replaced, and most of the components which have not been obviously damaged will continue to be used even after earthquakes. However, as will be shown, the earthquake may have severely impaired the fatigue strength of such components by introducing unfavourable residual stresses and short cracks at stress raisers. In addition, if such components should contain hydrogen, an increasingly possible scenario for the hydrogen economy in the future, then it is shown that the loss of fatigue strength can be even greater. This paper explores the extent of fatigue degradation due to overloads and to absorbed hydrogen. It was shown that generation of small crack and tensile residual stress imposed by overloads caused substantial decrease of residual fatigue strength compared with that in the initial state. It was also shown that hydrogen enhanced more reduction. Hydrogen enhanced reduction in two ways. The crack generated by overloads grew deeper in hydrogen charged material. In addition to this, the reduction of ΔK_th also occurred in hydrogen charged material. These two factors worked together to reduce the residual fatigue strength after multiple overloads.     

中美致密砂岩气成藏分布异同点比较研究与意义

致密砂岩气已成为全球非常规天然气勘探的重点领域。中国致密砂岩气分布范围广,目前已在鄂尔多斯、四川等盆地实现了规模开发;美国落基山地区是致密砂岩气十分发育和勘探相对成熟的地区。对比研究中美致密砂岩气的形成条件和成藏特征是加快中国致密气开发利用与开拓勘探思路的有效途径。中国与美国致密气藏对比研究表明,中美致密砂岩气具有以煤系地层为主要烃源岩、储层致密、存在异常地层压力、源储紧邻与气藏大面积分布等共性特征;差异性主要体现在致密气源岩沉积环境与热演化程度,储层非均质性及其致密化因素,气藏纵向和平面分布特征等方面;控制中美致密砂岩气成藏条件和特征差异性的主要因素是沉积盆地性质、沉积环境和后期构造作用。针对中国致密砂岩气的特殊性,加强储层非均质性、优质储层预测、气藏的分布规律的研究以及加强工程技术攻关提高单井累计产量是致密砂岩气勘探开发工作的重点。     

A study of the workability of natural hydraulic lime mortars and its influence on strength

Lime mortars are currently used for both repairs to historic buildings and new construction. An important mortar property is workability. Lime mortars are often described as highly workable, however, due to the many variables contributing to workability, this is difficult to quantify. Workability largely depends on water content, and this will greatly affect compressive and flexural strengths, which in turn will determine the overall quality and durability of a mortar. The objective of this paper is to examine the relationship between workability and strength of naturally hydraulic lime (NHL) mortars in order to optimize their properties for a more efficient use in building. To this aim, mortars of several hydraulic strengths were mixed with different water contents in order to vary flow diameters and characterize workability. Compressive and flexural strength were then tested to measure the effect of the initial flow on the strength of the hardened mortar. This paper demonstrates that NHL 3.5 and 5 mortars require a flow value close to that of 185 mm prescribed by the European standards whereas NHL 2 mixes require a significantly lower value. This paper concludes that one universal flow value is inadequate when trying to optimize strength of NHL mortars and that, in order to optimize strength, mortars should be mixed to attain a different flow diameter for each hydraulic strength. However, other properties such as bond strength and water retention need to be considered before unique flow diameters are prescribed to lime mortars of different hydraulic strengths.