不同加载速率和围压作用下沥青混凝土三轴压缩力学特性数值模拟研究

为研究加载机制下路面沥青混凝土的力学特性,利用颗粒流数值模拟软件PFC3D建立满足实际沥青混凝土粒径级配的数值模型,并对其进行三轴压缩试验,分析不同围压及加载速率下沥青混凝土的力学特性.结果表明:同一围压下,随着加载速率的逐渐增大,试样的峰值应力、峰值应变和弹性模量均呈逐渐递增的趋势,以围压0.5 MPa为例,加载速率...     

高层建筑深基础周围岩体在不同加载速率的细观特性研究

为研究高层建筑深基础周围岩体在加载机制下的细观力学特性,文章以辽宁某在建房建项目为工程背景,采用颗粒流数值模拟方法对该深基础围岩(砂岩)在不同加载速率下进行单轴压缩试验研究。结果表明:随着加载速率的逐渐增大,砂岩的单轴抗压强度、弹性模量、峰值径向应变和轴向应变均呈逐渐增大的趋势;相同加载速率下,试样表现出显著的拉伸破坏模式。随着加载速率的逐渐增大,砂岩破坏时随产生的裂隙数呈逐渐减小变化趋势,加载速率由0.5 mm/s增大至2.5 mm/s,拉伸裂隙减幅为9.65%,剪切裂隙减幅为17.05%,表明加载速率对剪切裂隙的影响更加显著。     

田坪特大桥桩基础混凝土力学特性的数值模拟研究

桥梁桩基础混凝土的承载能力是桥梁安全运营的关键。文章以田坪特大桥为工程背景,利用颗粒流数值模拟方法对该桥的桩基混凝土进行双轴压缩数值模拟研究,并通过裂隙体积应变法计算了不同加载速率下混凝土力学特性。结果表明:加载速率对混凝土的力学特性影响显著。随着加载速率的逐渐增大,混凝土的峰值强度、弹性模量均呈逐渐增大趋势,而泊松比则随加载速率逐渐减小,且加载速率对混凝土峰值强度影响更为显著;随着加载速率的逐渐增大,混凝土的起裂应力和扩容应力均呈逐渐递增趋势,起裂水平和扩容水平同样逐渐递增,但二者变化幅度较小,加载速率对混凝土起裂水平的影响更为明显。研究结论可为类似工程提供可靠的技术依据。     

冻融循环作用下隧道围岩单轴力学特性试验研究

针对冻融循环对隧道围岩力学特性的损伤问题,文章以中国沈阳在建地铁隧道砂岩为研究对象,采用MTS815.02多功能岩石力学试验分析系统对该隧道砂岩分别进行了不同冻融循环次数下的连续单轴压缩试验和连续单轴蠕变试验,分析了砂岩的各关键物理参数随冻融循环次数变化的规律。实验结果表明：冻融循环对砂岩产生了较为明显的劣化效应,随着冻融循环次数的逐渐增加,砂岩峰值强度、弹性模量均逐渐减小,峰值应变、泊松比逐渐增大。采用Origin软件对实验数据进行拟合发现,各参数与循环次数值之间均满足指数函数关系,即在相同冻融次数下,荷载水平越高,砂岩蠕变特性越显著,在第六级荷载水平下,冻融循环次数越多,砂岩破坏时的荷载水平越小,蠕变速率越小,破坏模式逐渐由脆性过渡到延性。     

热处理砂岩在干燥和饱水条件下的动态拉伸强度与破坏机理（英文）

为了研究不同加载速率下具有水热耦合损伤岩石的拉伸强度和破坏机理,在干燥和饱水条件下,对热处理砂岩进行一系列静态和动态劈裂试验。实验结果表明,高温有效地削弱砂岩试件的抗拉强度,P波速度随温度的升高而降低。总体而言,岩石热损伤随温度的升高而逐渐增大,但在100°C时出现明显的负损伤。饱水砂岩试样的间接抗拉强度低于干燥砂岩的,说明水-岩相互作用导致热处理岩石产生二次损伤。砂岩在干燥和饱水条件下的动态拉伸强度均随应变率的增大而增大。饱水砂岩比干燥砂岩表现出较强的加载率依赖性,但岩石的加载速率敏感性随热处理温度的升高而降低。利用扫描电子显微镜技术,对极端温度引起的岩石热破裂进行分析,进一步探讨热处理后砂岩在不同加载速率条件下的水物理机制。     

诱导卸荷对岩石力学性质弱化的影响(英文)

研究在诱导卸荷作用下如钻孔、爆破、切缝和注水软化岩石的力学性能弱化规律。设计常规三轴加载、峰前和峰后卸载三种试验方案。试验结果表明:加载条件下的岩石破坏主要是由压缩变形所致,而卸荷条件下沿卸荷方向的岩石破坏为强烈的扩容所致。只要存在卸荷作用,岩石在较小的轴向应力下便可以发生破坏,甚至是强烈的脆性破坏。同时,卸荷过程中岩石泊松比随围压的降低逐渐增大。弹性模量随围压的减小先缓慢增加,在达到屈服强度后迅速降低。试验证明卸荷作用下岩石的强度弱化速率更快。     

应变速率对TiNi形状记忆合金压缩力学行为的影响

考察了中温时效处理后的Ti-50.9%Ni(摩尔分数)合金在实验温度为20℃,不同应变速率下的轴向压缩应力-应变力学行为.实验结果表明:随着应变速率的增加,合金的应力诱发马氏体相变临界应力逐渐增加,相变平台逐步消失,卸载后的残余应变减小,加载-卸载变形曲线的应力(应变)滞后也减小;在较高加载速率下,合金表现出类线性超弹性变形行为,可获得高达4.5%的类线性超弹性.     

不同围压和轴压下花岗类岩石的动力特性分析

岩石的动态力学性能是研究岩石介质中应力波传播规律和岩石动载破坏机理的关键,是评价围岩在爆炸、地震等动荷载作用下稳定性的关键参数,同时也是开展岩石材料和结构动荷载作用下的数值计算以及抗震抗爆结构工程设计的基础,本文以某预选厂址的花岗类岩石为研究对象,在Φ50 mm杆径SHPB试验系统上进行冲击压缩试验研究,针对不同围压、不同轴压和不同冲击荷载的作用下,研究花岗类岩石在冲击荷载作用下的动态力学响应,获得其在不同应变率加载时的动态力学参数(动态破坏强度、动弹性模量、动粘聚力和动内摩擦角等)和变化规律,为各类防护工程岩石的抗爆性能研究提供依据。     

围压、温度及损伤程度对隧道围岩渗透率的影响

针对围压、温度及损伤状态下隧道围岩的渗透性问题,文章结合辽宁某在建隧道的工程实际,通过室内三轴试验和气体渗透试验对该隧道砂岩进行了研究,分析了围压、温度及损伤程度对砂岩渗透率的影响.结果表明:随着围压的逐渐增大,砂岩的渗透率呈逐渐递减趋势,渗透率与围压之间表现为负相关关系;随着温度的逐渐升高,砂岩的渗透率呈逐渐递减趋势...     

不同加载速率下氧化铝纳米线弯曲力学行为的分子动力学研究（英文）

采用LAMMPS软件建立弯曲加载下α-Al₂O₃纳米线的分子动力学(MD)模型,计算并分析不同加载速率下α-Al₂O₃纳米线的原子应力和应变,揭示加载速率对其弯曲力学行为的影响规律。研究结果表明：α-Al₂O₃纳米线在不同加载速率下的最大表面应力-转角曲线均可分为弹性变形、塑性变形和破坏3个阶段,弹性极限点可通过加、卸载循环下的曲线对称性来确定;加载速率对α-Al₂O₃纳米线的塑性变形影响很大,但对弹性模量影响较小;当加载速率增加时,塑性变形阶段缩短,材料更易发生脆性断裂,且弹性极限和强度极限(由直接和间接MD法确定)更加接近。MD模拟结果与改进的弯曲环路试验结果吻合良好,从而验证分子动力学建模和计算方法的有效性。直接MD法是确定在任意加载速率下(无论发生脆性还是韧性断裂)纳米晶须弹性极限和强度极限的有效方法。     

寒区隧道围岩冻融损伤试验研究

针对寒区隧道围岩冻融损伤问题,文章以辽宁某在建隧道为工程背景,采用核磁共振和声波检测技术对不同冻融循环次数后的隧道围岩(砂岩)进行检测试验,同时对检测后的试样还进行了单轴加载试验,分析了冻融作用对隧道围岩加载前后的损伤劣化机制.结果表明:随着冻融循环次数的逐渐增加,试样的T2谱总面积逐渐增大,核磁共振T2谱信号逐渐增强...     

Dynamic tensile strength and failure mechanisms of thermally treated sandstone under dry and water-saturated conditions

To study the tensile strength and failure mechanisms of rock with hydro-thermal coupling damage under different loading rates, a series of static and dynamic splitting tests were conducted on thermally treated sandstone under dry and water-saturated conditions. Experimental results showed that high temperatures effectively weakened the tensile strength of sandstone specimens, and the P-wave velocity declined with increasing temperature. Overall, thermal damage of rock increased gradually with increasing temperature, but obvious negative damage appeared at the temperature of 100 °C. The water-saturated sandstone specimens had lower indirect tensile strength than the dry ones, which indicated that water−rock interaction led to secondary damage in heat-treated rock. Under both dry and water-saturated conditions, the dynamic tensile strength of sandstone increased with the increase of strain rate. The water-saturated rock specimens showed stronger rate dependence than the dry ones, but the loading rate sensitivity of thermally treated rock decreased with increasing treatment temperature. With the help of scanning electron microscopy technology, the thermal fractures of rock, caused by extreme temperature, were analyzed. Hydro-physical mechanisms of sandstone under different loading rate conditions after heat treatment were further discussed.     

基于PFC3D的路基土细观特征数值模拟研究

为研究围压作用对路基土细观特征的影响,本文以辽宁某在建高速公路为工程背景,采用颗粒流软件PFC^3D对该公路路基土进行不同围压下的三轴压缩数值模拟试验,分析试样内部裂隙及颗粒间接触力随围压的分布规律。结果表明:在宏观上,随着围压的增大,峰后曲线逐渐由应变软化向应变硬化过渡;在细观上,随着围压的逐渐增大,试样内部裂隙逐渐增多,且拉伸裂隙明显多于剪切裂隙;颗粒间法向接触力和切向接触力均随围压逐渐增大,土样的各向异性在围压的作用下逐渐增强。     

Analyses and predictions of rock cuttabilities under different confining stresses and rock properties based on rock indentation tests by conical pick

The rock indentation tests by a conical pick were conducted to investigate the rock cuttability correlated to confining stress conditions and rock strength. Based on the test results, the regression analyses, support vector machine (SVM) and generalized regression neural network (GRNN) were used to find the relationship among rock cuttability, uniaxial confining stress applied to rock, uniaxial compressive strength (UCS) and tensile strength of rock material. It was found that the regression and SVM-based models can accurately reflect the variation law of rock cuttability, which presented decreases followed by increases with the increase in uniaxial confining stress and the negative correlation to UCS and tensile strength of rock material. Based on prediction models for revealing the optimal stress condition and determining the cutting parameters, the axial boom roadheader with many conical picks mounted was satisfactorily utilized to perform rock cutting in hard phosphate rock around pillar.     

Failure behavior of horseshoe-shaped tunnel in hard rock under high stress: Phenomenon and mechanisms

A particle flow code (PFC) was first applied to examining the mechanical response of a horseshoe-shaped opening in prismatic rock models under biaxial compression. Next, an improved complex variable method was proposed to derive the stress distribution around the opening. Lastly, a case study of tunnel failure caused by rock burst in Jinping II Hydropower Station was further analyzed and discussed. The results manifest that a total of four types of cracks occur around the opening under low lateral confining stress, namely, the primary-tensile cracks on the roof-floor, sidewall cracks on the sidewalls, secondary-tensile cracks on the corners and shear cracks along the diagonals. As the confining stress increases, the tensile cracks gradually disappear whilst the spalling failure becomes severe. Overall, the failure phenomenon of the modelled tunnel agrees well with that of the practical headrace tunnel, and the crack initiation mechanisms can be clearly clarified by the analytical stress distribution.     

Bonding strength of Invar/Cu clad strips fabricated by twin-roll casting process

Based on traditional twin-roll casting process, Invar/Cu clad strips were successfully fabricated by using solid Invar alloy strip and molten Cu under conditions of high temperature, high pressure and plastic deformation. A series of tests including tensile test, bending test, T-type peeling test and scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) measurements were carried out to analyze the mechanical properties of Invar/Cu clad strips and the micro-morphology of tensile fracture surfaces and bonding interfaces. The results indicate that no delamination phenomenon occurs during the compatible deformation of Invar/Cu in bending test and only one stress platform exists in the tensile stress?strain curve when the bonding strength is large. On the contrary, different mechanical properties of Invar and Cu lead to delamination phenomenon during the uniaxial tensile test, which determines that two stress platforms occur on the stress?strain curve of Invar/Cu clad strips when two elements experience necking. The average peeling strength can be increased from 13.85 to 42.31 N/mm after heat treatment at 800 °C for 1 h, and the observation of the Cu side at peeling interface shows that more Fe is adhered on the Cu side after the heat treatment. All above illustrate that heat treatment can improve the strength of the bonding interface of Invar/Cu clad strips.