考虑裂隙变形参数的岩体单轴压缩损伤模型

为了更准确地预测裂隙对岩体压缩力学特性(如强度和刚度)的影响,需要建立更为合理的裂隙岩体压缩损伤模型。为此,基于相关试验数据和裂隙岩体单轴压缩力学行为,采用损伤及断裂理论对目前断续裂隙岩体压缩损伤模型中存在的不足进行了深入分析,并对其进行了3方面的改进,即:不再将裂隙变形参数视为定值、考虑了裂隙面上法向正应力产生的负第一应力强度因子(K_(I))、考虑了裂隙面上有效剪应力产生的K_(I),由此最终提出了考虑裂隙变形参数的岩体单轴压缩损伤本构模型。最后采用试验数据对该模型的合理性进行了验证,发现与现有模型相比,该模型明显提高了岩体单轴压缩弹性模量和损伤值的预测精度,尤其是当裂隙倾角为0°时,该模型计算得到的弹性模量为4.306 MPa,与实测弹性模量4.310 MPa几乎相同。因此,该模型能够很好地刻画岩体单轴压缩力学行为,这也说明考虑裂隙变形参数对岩体单轴压缩力学特性的影响是十分必要的。该研究可为准确预测裂隙岩体的单轴压缩力学行为提供参考。

考虑冻融作用的混凝土单轴压缩损伤本构模型

为研究冻融循环作用后混凝土的应力-应变行为及其在冻融作用后的持荷性能,对比研究同为C40强度等级的普通混凝土(NC)与自密实混凝土(SCC)经受冻融作用后的单轴压缩应力-应变关系,并进一步基于应变等价性假说和统计损伤理论建立冻融循环作用后混凝土单轴压缩损伤本构模型,探讨相应损伤变量随冻融循环作用次数和单轴压缩应变发展的演变特性。研究结果表明:所建立的损伤本构模型可较好地描述冻融循环作用后NC和SCC在单轴压缩荷载下的应力-应变关系;在单轴压缩过程中,冻融循环产生的微裂纹闭合导致损伤变量增长速率下降;NC与SCC的冻融损伤变量随冻融次数变化的规律均可用指数函数进行预测;掺入膨胀剂和黏度改性材料可以有效降低SCC的冻融损伤速率。

A whole process damage constitutive model for layered sandstone under uniaxial compression based on Logistic function

Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.

Static compressive properties and damage constitutive model of rubber cement mortar with dry-and wet-curing conditions

To investigate the static compressive properties and mechanical damage evolution of rubber cement-based materials(RCBMs) with dry-and wet-curing conditions, uniaxial compression and cyclic loading-unloading tests were carried out on rubber cement mortar(RCM). The mechanical properties of the uniaxial compression specimens cured at 95%(wet-curing) and 50%(dry-curing) relative humidities and cyclic loading-unloading specimens cured at wet-curing were analyzed. Under uniaxial compression, the peak stress loss ratio is higher for dry-curing than for wet-curing. The peak strain decreases with the increase of rubber content, and the peak strain increases with the decrease of curing humidity. Under cyclic loading-unloading, the variation trends of residual strain differences of the normal cement mortar and RCM at each cyclic level with the number of cycles are basically the same, but the failure modes are different. The analysis of the internal mesostructure by a scanning electron microscope(SEM) shows that initial damage is further enhanced by reducing curing humidity and adding rubber aggregate. The damage constitutive model based on strain equivalence principle and statistical theories was used to describe the uniaxial compression characteristics of RCM, and the law of mechanical damage evolution was predicted.