岩石损伤力学模型及其本构方程的探讨

１ 问题的提出 图１为典型的岩石应力－应变特性曲线［１］,其斜率随着应变的增大逐渐增大,至Ａ点后保持不变,到Ｂ点后又逐渐减小,在Ｃ点达到极大值,之后斜率为负,最终保持一定的残余强度（Ｄ点）,在应力不变条件下应变可无限增大。前人在研究岩石应力－应变曲线的基础上提出了许多岩石力学模型,以确定岩石的本构关系。如线弹性模型、理想弹塑性模型、双线性模型、多线性模型、双曲线模型、幂强化模型、应变软化模型等［１］。这些模型在一定范围内能反应岩石的应力－应变特性,有一定的工程应用范围。但是与岩石全应力－应变曲线相…     

论岩石的地质本质性及其岩石力学演绎

 简要论述岩石循环的地质作用,提出并讨论岩石地质本质性命题,侧重阐述岩石的物质性、结构性和赋存性,及其同地质演化的密切关系。作为岩石力学研究对象的岩石同其他工程建筑材料的不同之处就在于它的地质演化及所形成的地质本质性。通过对岩石本质性的认识,探讨岩石物理本属性,包括不均一性、不连续性的成因及其同地质本质性的关系。在此基础上讨论岩石力学本构性研究中对介质力学属性的考虑。试图通过岩石地质本质性、物理本属性到力学本构性的讨论建立起岩石力学与地质学相互认识和深入结合的知识通道。     

温度作用下脆性岩石的损伤分析

从花岗岩弹性模量随温度的变化规律入手,提出了热损伤的概念,在此基础上导出了热２演化方程和一维耦合弹脆性损伤本构方程,并讨论了损伤释放度随温度的演化规律。     

岩石力学损伤和流变本构模型研究

博士学位论文摘要 采用几何损伤理论和能量损伤理论对岩石的力学特性进行了研究和建模探索，并探讨了瞬时损伤对流变的影响。主要工作内容如下：     

考虑塑性变形的岩石损伤本构模型初步研究

利用细观力学的Eshelby等效夹杂方法建立了考虑损伤和无损岩石塑性变形的Helmholtz自由比能函数，并用连续损伤介质力学方法推导出了考虑损伤和无损岩石塑性变形耦合的岩石弹塑性损伤本构关系，给出了损伤演化方程和塑性应变发展方程，该模型还反映了岩石损伤部分不能承受拉应力等力学特性。     

具有统计损伤的岩石弹塑性本构模型研究

利用细观力学的Eshelby等效夹杂方法建立了岩石的弹塑性损伤统计本构模型，在该模型中采用了总体应变与各组成相间应变关系与总体应力与各组成相间应力关系不一样的假设，并用最优化方法确定该模型参数。建立的模型能够反映岩石破坏前应力．应变关系和轴向应变．横向应变关系，与试验结果比较表明该模型是合理的。     

岩石损伤流变理论模型研究

分析了岩石的多孔隙特性、强度实验的全应力-应变曲线、蠕变特性曲线和松弛特性曲线.提出两条基本假定在极慢速度加载过程中,损伤与外界所做的功成正比;损伤的速率和内平衡状态下的损伤与实际损伤之差成正比.推导了适合于任何应变不减小的加载和卸载过程的损伤演化统一微分方程.给出了几种情况下的计算特性曲线,不仅曲线形状与实测曲线相同,而且在定量关系上也与实际相符,这充分说明了假设的合理性和损伤演化方程的正确性.该损伤演化方程只有三个材料常数,而且这三个常数都可以很容易地根据实验数据确定.该方程对于认识岩石的力学性质有重要意义,对岩石力学的发展及各种岩石工程实际问题的解决都有重要的推动作用.     

冻融与荷载耦合作用下岩石损伤模型的研究

 针对寒区工程结构的冻融受荷岩石,提出冻融损伤、受荷损伤与总损伤的概念,拓展损伤变量的内涵;以岩石的初始损伤状态为基准状态,充分考虑岩石细观结构的非均匀性,运用损伤力学理论及推广后的应变等价原理,建立冻融受荷岩石损伤模型;通过损伤变量及本构方程来描述岩石材料细观结构的损伤演化及其宏观损伤行为,与岩石实际冻融破坏情况符合较好。研究结果表明：寒区工程结构的受荷岩石,其力学性能由冻融因子、荷载因子及其耦合效应所决定;冻融与荷载的共同作用使岩石总损伤加剧,并表现出明显的非线性特征,而其耦合效应使总损伤有所弱化;岩石的岩性和初始损伤状态确定各影响因素的权重,表现出不同的损伤扩展特性;相比而言,砂岩对冻融循环更敏感,而受荷损伤最终导致页岩破坏。     

岩石损伤力学理论研究进展

首先回顾了岩石损伤理论的发展历史,并简单介绍了岩石损伤力学的研究内容。详细讨论了如何从宏观及微观角度定义损伤变量以及各自的优缺点,接着介绍了一些损伤演化方程的确立,最后介绍了近年来在损伤本构方程方面的研究。     

热力耦合作用下岩石流变模型的本构研究

 高放废物深埋处置和深部采矿中,岩石在温度和应力长时间作用下表现出流变特性。对3种常用的流变元件：弹性元件、黏性元件和塑性元件进行讨论,对其在温度和应力作用的变形特性做了相应的假设,然后基于西原流变模型,得出热力耦合作用下西原模型的蠕变方程、卸载方程和松弛方程,当把温度影响因素去除,方程可退化为只受到载荷作用下西原模型的本构方程。通过这些本构关系可大致预测特定温度变化条件下岩石的流变破坏时间,并得出温度的变化会缩短岩石的流变破坏时间,温度变化率越大,岩石的破坏时间越短,分析认为其量级是相当的,即温度升高变化率每增加一个数量级,破坏时间就缩短一个数量级。这对研究深部岩石流变变形特性具有重要的指导意义。     

温度对岩石动态断裂韧度的影响研究

根据Central Cracked Circular Disk-Split Hopkinson Pressure Bar(CCCD-SHPB)测试原理,采用平台巴西圆盘开展温度对岩石类材料动态断裂性能影响的实验研究。实验中控制加载速率基本一致,仅改变试件测试的温度,实现了岩石材料在同一加载速率、不同温度下的动态断裂实验,进而开展岩石材料动态断裂韧度的温度相关性研究。实验结果表明,当温度处于8～100℃时,动态断裂韧度随着温度的升高而逐步下降,近似呈线性关系。     

高温下预应力混凝土力学性能的研究

预应力混凝土与普通混凝土相比具有不可替代的应用优势,广泛使用于各类工程建筑之中。然而在高温状况下,预应力混凝土的材料性能会随温度变化而产生一系列不利的变化。对该变化产生的动态机理进行阐述,以期在工程建筑中能够对预应力混凝土技术的推广和应用起到一定的积极促进作用。     

Mechanical performances and stress states of rock bolts under varying loading conditions

A comprehensive study including laboratory tests and numerical modeling was performed to investigate factors of rock bolt fracture. Experimental tests were performed to evaluate the mechanical performances of bolt ends including the thread and adjacent. The effects of installation angle, pretension and accessories (plate, washer and nut) were evaluated. It is found that a bolt installed with an oblique angle to roadway surface suffers a complex stress combination of tensioning, bending and twisting on the bolt. This complex stress is much greater than the tensile stress, leading to cracking and growth at the location of bending causing the thread to fail even though the tensile stress is less than the yield strength. Bolt thread is more vulnerable to fracture than rebar.     

循环荷载作用下岩石疲劳变形及特性试验研究

通过开展恒定加卸载速率,不同偏应力条件下的循环加卸载试验,研究了轴向应变、径向应变以及体积应该随循环次数的演化过程,得到了在不同偏应力条件下岩石的平均变形模量随循环次数与偏应力的变化关系,进而分析了循环荷载作用下岩石疲劳变形及特性。研究结果表明：（1）偏应力在50MPa之前,轴向应变、径向应变、体积应变以及变形模量随着循环次数的变化基本稳定,反之,表现出发散的趋势;（2）偏应力在80MPa作用下的平均变形模量较1IOMPa作用下的大,这是岩石内部裂隙增加和扩张的结果;（3）在不同偏应力条件下,平均变形模量随着偏应力的增大逐渐增大且趋于收敛。     

A review of experimental and theoretical research on the deformation and failure behavior of rocks subjected to cyclic loading

Rock engineering is highly susceptible to cyclic loads resulting from earthquakes, quarrying or rockbursts. Acquiring the fatigue properties and failure mechanism of rocks is pivotal for long-term stability assessment of rock engineering structures. So far, significant progress has been gained on the mechanical characteristics of rocks subjected to cyclic loading. For providing a global insight of typical results and main features of rocks under cyclic loading conditions, this study comprehensively reviews the state-of-the-art of deformation and failure mechanism and fatigue constitutive relationship of rocks subjected to cyclic loading in the past 60 years. Firstly, cyclic tests on rocks are classified into different types based on loading paths, loading parameters, loading types and environment conditions. Secondly, representative results are summarized and highlighted in terms of the fatigue response of rocks, including the deformation degradation, energy dissipation, damage evolution and failure characteristics; both laboratory testing and numerical results are presented, and various measurement techniques such as X-ray micro-computed tomography (micro-CT) and digital image correlation (DIC) are considered. Thirdly, the influences of cyclic loads on the mechanical characteristics of rocks are discussed, including the cyclic stress, frequency, amplitude and waveform. Subsequently, constitutive relationships for rocks subjected to cyclic loading are outlined, in which typical fatigue constitutive models are compared and analyzed, regarding the elastoplastic model, the internal variable model, the energy-based damage model and the discrete element-based model. Finally, some ambiguous questions and prospective research are interpreted and discussed.     

考虑岩石脆—塑性过渡特性的地下洞室受力分析

本文讨论了岩石脆—塑性过渡特性。采用川本眺万的岩石应力—应变关系曲线的理想化假设,建立了新的强度准则。在适当的假设条件下,导出了考虑该特性的圆型洞室应力状态计算公式,计算分析表明:围岩有软—弹、残—软—弹、残—塑—弹三种应力状态。     

Mechanical behaviour of scaled-down unsupported tunnel walls in hard rock under high stress

A large number of scaled-down tunnel experiments were undertaken to investigate the response of unsupported walls to an increased stress field. The experiments were undertaken in 200 mm diameter tunnels that were drilled into intact rock blocks of sandstone and granite ranging in strength from moderately strong to very strong. The tunnels were loaded by a servo-controlled, 450 tonne capacity INSTRON compression testing machine. As the ratio of intact rock strength to induced stress decreased, the unsupported tunnel walls became increasingly unstable. Critical ratios of compressive strength to induced stress were determined for critical instability stages such as tunnel spalling and also pillar crushing adjacent to the tunnels. The physical models have been simulated using three-dimensional finite element modelling. The values of the critical ratios correlate well with underground observations of full scale tunnels with similar Uniaxial Compressive Strength materials. Dynamic ejection velocities similar to those calculated from back analysis of actual failures have been determined. In addition, the seismic responses prior and during key failure stages have been established as a function of the increased loadings.     

GFRP夹芯板力学性能的试验和定量评估

对广泛应用在海洋建筑中的夹芯结构的力学性能进行了分析,夹芯结构由玻璃纤维表皮包裹PVC泡沫材料或聚酯核所构成。系统的试验研究和定量评估显示,夹芯结构强度的理论预测和实际破坏机理能被有效位误差所影响,特别是存在剪力荷载的情况下。此外,由于抗剪刚度低及弹性恒定与外壳和核心材料失谐,破坏模式和强度受垂直于夹芯板中部的最终应力的影响。尤其是带有PVC泡沫核的夹芯结构,应力的交互作用导致了外壳与核心的分离破坏,而带有聚酯核的结构致使核剪力粘结破坏。借助精确的非线性模拟,对目前复杂荷载下用于设计阶段的精确的破坏标准也进行了拓展。     

Effect of Temperature Exposure on the Flexural Mechanical Behavior of Two Pultruded Composites

The use of non-metallic composites at floor gratings in offshore platforms is driven by the need for increased component life in corrosive environments. As a result, these floor gratings contribute to a lower demand for maintenance and greater operational continuity. However, these composite materials have limitations when are exposed to high temperatures. The application of these floor gratings, on ships and floating offshore platforms have the requirement to retain a significant level of mechanical integrity during and after exposure to a fire. In this work, the mechanical behavior of two composites materials after being subject to a temperature rise was evaluated. One composite has an isophthalic polyester resin as matrix and the other used a phenolic resin. Before the mechanical characterization, thermogravimetric analysis was performed to determine the temperatures of beginning of the thermal degradation, and the microstructure of the composites was evaluated by digital image analysis. From the results of the thermal analysis a temperature of 250°C was chosen as the maximum one to be used, in order to evaluate the behavior of these composites in regions close to fire but not directly exposed to fire. Flexural properties of the two composites were performed by three-point bending test with 25 specimens of each composite. For the phenolic resin composite, the test specimens were manufactured with the average dimensions of 90.5 mm long, 19.5 mm large and 4.2 mm thick. The average dimensions of isophthalic composite specimens were 135.0 mm long, 25.0 mm large and 6.9 mm thick. The results show that the isophthalic resin matrix composite lost its mechanical integrity with the time of exposure to temperature, while the phenolic matrix composite maintained their properties. For example, regarding the maximum flexural stress a decrease of almost 50% was measured for the isophthalic matrix composite in comparison to only 3% for the phenolic matrix composite. However, the mechanical behavior of this composite was impaired by the presence of a high content of voids (5.7%) and of touching fibers arising from the manufacturing process.     

轻钢-混凝土组合梁抗火计算方法

应用ANSYS软件计算了轻钢-混凝土组合梁截面在标准升温模式下的温度场，并分析了各参数对截面温度场的影响；然后利用其后处理功能将温度场计算结果导入轻钢-混凝土组合梁抗火计算程序，对其抗火全过程曲线和抗力折减系数进行了分析。结果表明：由于混凝土的热作用，钢梁的温度明显低于无混凝土时的裸钢构件；影响全过程曲线和抗力的折减系数的主要参数是梁高和钢梁厚度，而其它参数影响较小；抗力折减系数的变化在后期比前期剧烈一些。