Experimental study on the time-dependent dynamic mechanical behaviour of C60 concrete under

To study the dynamic mechanical behavior of C60 concrete at high temperatures, impact tests under different steady-state temperature fields (100, 200, 300, 400 and 500.℃) were conducted under a variety of durations at the corresponding constant high temperature, namely 0, 30, 60, 90 and 120.min, employing split Hopkinson pressure bar (SHPB) system. In addition, the impact tests were also conducted on the specimens cooled from the high temperature to the room temperature and the specimen under room temperature. From the analysis, it is found that C60 concrete has a time-dependent behavior under high-temperature environment. Under 100, 200, 300, 400 and 500.℃ steady-state temperature fields respectively, as the duration at the corresponding constant high temperature increases, the dynamic compressive strength and the elastic modulus decrease but the peak strain generally ascends. After cooling to the room temperature, the dynamic compressive strength and the elastic modulus descend as well, but the peak strain increases first and then decreases slightly, when the duration increases. For specimens under and cooled from the high-temperature, as the temperature increases, the dynamic compressive strength and the peak strain raise first and then reduce gradually,and the dynamic compressive strength of specimen under high temperature is higher than that of the specimen cooled from the same high temperature.     

混凝土压缩试验的改善及动态损伤

为了探求混凝土动态压缩试验入射波形的改善方法,从而进一步研究冲击荷载作用下混凝土动态损伤及力学性能,采用常规的大直径分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)进行混凝土的动态压缩试验。然而入射脉冲的弥散效应和严重的高频震荡现象会对试验结果会产生较大的误差,所以试件在破坏前应力均匀分布要求且保持恒应变率加载是保证试验有效性及试验结果可靠性的关键。通过黄铜整形器改善入射波形以减小试验误差,然后利用理论公式与试验相结合的方式,通过控制变量,进一步研究气压、冲击次数等对混凝土动态损伤的影响。研究结果表明:较薄的小直径实心铜片整形器可以提高试验准确度;随着重复冲击次数的增加,混凝土损伤度逐渐提高,动态弹性模量减小,抵抗冲击的能力减弱。     

Numerical investigation on the tensile fracturing behavior of rock-shotcrete interface based on discrete element method

Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young's modulus of shotcrete were considered. Six different undulations of rock-shotcrete interface were set up. The influences of multiple parameters on the bearing characteristics of the rock-shotcrete interface were studied. The results showed that a better support performance can be obtained by increasing the Young's modulus of shotcrete rather than the tensile strength of shotcrete. For different tensile strength and Young's modulus, the increase of sawtooth height has different effects on the support performance. The failure mechanism of the rock-shotcrete interfaces was analysed in detail. The stress shielding effect and stress concentration effect caused by the shape characteristics of rock-shotcrete interface were observed. The influence of these parameters on the overall support performance should be fully considered in a reasonable support design.     

Experimental investigation on dilatancy behavior of water-saturated sandstone

It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the water-saturated red sandstone, analyzed the influences of confining pressure and pore pressure on dilatancy property of water-saturated rock, and discussed the reasonable basis of the stress of dilatancy onset as a strength design parameter of rock engineering, finally established the prediction model of the stress of dilatancy onset under the impacts of confining pressure and pore pressure. The results show that the strength parameters(the stress of dilatancy onset and peak strength) and deformation parameters(axial strain and circumferential strain) of water-saturated sandstone increase with the confining pressure, and the relations can be fitted with a positive linear function. The cohesion and internal friction angle obtained from the stress of dilatancy onset decrease by 11.57% and 7.33%, respectively, when compared with those obtained from the peak strength. The strength parameters and deformation parameters of water-saturated sandstone decrease basically with the increase of pore pressure, in which the relations between strength parameters or axial strain and pore pressure can be fitted with a negative linear function. However, the relation between the peak circumferential strain and the pore pressure should be characterized by a negative exponential function, and the circumferential strain at dilatancy onset isn't affected by the pore pressure.     

基于损伤的PHC桩单轴受拉动态本构模型研究

通过引入应变率强化因子、损伤弱化因子和预应力强化因子,并分析它们对预应力混凝土强度的影响,建立了一个单轴受拉动态本构模型用于描述PHC桩在冲击载荷作用下的冲击特性.对比了试验结果与该模型的数值模拟结果,结果表明:模型预示结果在变形趋势上符合很好,在数值精度上与试验结果符合良好.本成果可为振动沉桩过程中控制振动锤参数提供依据,能有效防止因拉应力过大而导致PHC桩被拉断的事故.     

混凝土动力损伤本构关系的基研理论及应用

概括了建立混凝土动力损伤本构模型的基础理论,简述了应用这些基本理论在建立混凝土动损伤本构方面的应用,对相关研究的特点和不足做了分析,为进一步建立科学合理实用的混凝土动损伤本构提供较全面的理论总结和前瞻性启发,对相关理论的发展趋势做了展望,为这方面的工作提供指导.     

A numerical simulation study on mechanical behaviour of coal with bedding planes under coupled static and dynamic load

To investigate the bedding influence on coal mechanical behaviour in underground environments such as coal or rock burst, simulations of dynamic SHPB tests of pre-stressed coal specimens with different bedding angles were carried out using a particle flow code 2-dimensional(PFC2D). Three impact velocities of 4, 8 and 12 m/s were selected to study dynamic behaviours of coal containing bedding planes under different dynamic loads. The simulation results showed that the existence of bedding planes leads to the degradation of the mechanical properties and their weakening effect significantly depends on the angle h between the bedding planes and load direction. With h increaseing from 0° to 90°, the strength first decreased and subsequently increased and specimens became most vulnerable when h was 30° or 45°.Five failure modes were observed in the specimens in the context of macro-cracks. Furthermore, energy characteristics combined with ultimate failure patterns revealed that maximum accumulated energy and failure intensity have a positive relation with the strength of specimen. When bedding planes were parallel or perpendicular to loading direction, specimens absorbed more energy and experienced more violent failure with increased number of cracks. In contrast, bedding planes with h of 30° or 45° reduced the specimens' ability of storing strain energy to the lowest with fewer cracks observed after failure.     

冻融环境下混凝土力学性能试验及损伤演化

在我国西部寒区,冻融作用往往是导致混凝土破坏的主要因素之一。通过对饱水状态下的多组混凝土试样进行冻融循环试验,并对试验后的试样进行了单轴压缩试验,从损伤和能量耗散的角度对试样进行了力学性能的分析;运用CT细观试验的方法初步对经历不同冻融循环次数下的试样进行了细观结构分析。通过试验研究,得到了饱水状态下混凝土材料的冻融破坏特征,以及不同冻融循环次数下试样质量、单轴应力-应变全过程曲线、抗压强度、能量耗散和细观结构的变化特征,系统研究了冻融循环下混凝土主要物理力学性能及损伤演化规律,为寒区重大工程冻融灾变预测提供较可靠的基础依据。     

大直径SHPB弥散效应实验研究

实验分别采用铝片作为波形整形器和橡胶胶片作为软性介质,通过SHPB冲击实验研究了2种方法对改善加载波波形的效果影响.实验表明这2种方法都可以有效改善加载波的波形,减小和消除应力波的弥散效应.从加载波波形上来看,铝片的效果要优于橡胶胶片.     

预制装配式多键群剪力键力学行为试验研究

为研究预制装配式群钉连接件键群数量对剪力键受力特性的影响,开展了单键群及双键群装配式群钉剪力键推出加载试验,对比研究单键群和双键群试件的荷载滑移曲线、破坏形态及抗剪承载力,并结合三键群及四键群试件数值模拟,研究多键群下的装配式剪力键承载力折减效应.研究表明:单键群和双键群剪力键的破坏模式均为栓钉剪断,单键群试件的裂缝数...     

C75混凝土动态劈裂行为试验与数值模拟分析

为研究C75混凝土动态抗拉强度特性和应变率效应,采用大直径霍普金森压杆,对其开展动态劈裂试验,并对试样中应力平衡进行检验,同时,基于ANSYS/LS-DYNA软件数值模拟混凝土的动态劈裂破坏过程.采用MATLAB将劈裂强度公式中的圆盘内部应力等值线进行可视化,基于修正的Griffith准则对巴西圆盘中心起裂现象进行理论分析.结果表明:在10⁰~10¹/s应变率范围内,混凝土劈裂强度与应变率对数基本呈现线性增长关系;在较低弹速下试件表现为沿径向对称破裂,随着弹速的增加,试样两端出现明显的三角形破碎区域,且靠近入射端破碎较严重;二维受力状态下,巴西圆盘试样的最大与最小主应力之比(σ₁/σ₃)等值线近似呈封闭的菱形,其比值在圆盘的中心处达到最大值-3.0;考虑应变率效应的Cowper-Symonds黏塑性本构能够较好地表征C75混凝土的动力学行为,其模拟的试样破坏过程与采用高速摄影技术观测到的结果吻合度较高;C75混凝土的抗拉特性明显优于同样水灰比下的C35混凝土,但其应变率敏感性要比C30土工聚合物混凝土低.     

船用907A钢的动态力学性能和本构关系

为了得到船用907A钢的动态力学性能及本构关系,运用静态试验机及分离式Hopkinson压杆加载装置,在应变率为0.000 33~2 680 s-1范围内得到了准静态拉伸及动态压缩条件下的应力应变曲线,对比了Cowper-Symonds模型和Johnson-Cook模型,并基于CS模型对应变硬化效应进行了修正。结果表明,船用907A钢具有明显的应变率强化效应和非线性应变硬化效应;CS模型比JC模型更能准确描述其应变率强化效应。     

氮化硅陶瓷动态损伤性能研究

利用零普金森杆加载系统对氮化硅陶瓷的动态冲击应力－应变特性作了实验研究，并与氮化硅陶瓷的静态压缩应力－应变特性作了比较，结果表明，氮化硅陶瓷在动态冲击应力作用下，应力－应变关系呈现非线性行为，而在静态压缩应力条件下，应力－应变关系主要表现为准线性行为。     

板锥网壳结构的受力性能分析

采用组合结构有限元法详尽分析了板锥网壳结构的受力特性,并与普通双层网壳结构进行了比较,分析结果表明,板锥网壳结构受力性能合理,比双层网壳结构具有更大的优越性。     

PBT纤维的热行为及力学性能

本文研究了不同拉伸温度、不同拉伸比ＰＢＴ纤维的热行为和力学性能．ＤＳＣ结果表明：ＰＢＴ纤维的Ｔｇ在恒定温度下，随拉伸比的坤加而升高．当拉伸比低于４、０时，随拉伸温度的升高，ＰＢＴ纤维的Ｔｇ降低，当拉伸比大于３．０时，ＰＢＴ纤维的Ｔｇ随拉伸温度升高而升高，拉伸温度对ＰＢＴ纤维的初始模量及抗很强度的影响呈现出与上述相似的规律性．     

涤沦纤维的动态力学分析

对涤沦纤维的未拉伸丝、全拉伸丝、ＰＯＹ、ＤＴＹ分别进行动态力学——温度谱测试的论述，发现经历各种生产过程后的涤沦纤维动态力学性能截然不同，分析了涤纶纤维的结构与性能的变化。     

Experimental study on the mechanical properties of rocks at high temperature

The mechanical properties of marble, limestone, and sandstone as well as the stress-strain curve, the varying characteristics of the peak strength, the peak strain and elastic modulus were studied by using the MTS810 Rock Mechanics Servo-controlled Testing System under the action of temperatures rang- ing from room temperature to 800℃ . Results show that (1) the peak strength and elastic modulus of marble fluctuate at the temperature from normal to 400 ℃ ; and they decrease gradually over 400℃ . (2) With th...     

Experimental and numerical investigations on dynamic and acoustic responses of a thermal post-buckled plate

Experiments were carried out for a clamped rectangular aluminum plate to study the dynamic and acoustic behaviors in both pre-and post-buckling ranges under thermal loads.Plate temperature was elevated from ambient value to the level above the theoretical critical buckling temperature of the plate.In the whole test temperature range,the measured frequencies decreased to the minimum values in sequence,and then turned to increase as temperature rose.The softening effect of thermal stresses played the leading role in the decreasing stage and the stiffening effect of thermal buckling deflection became the major influence factor in the increasing stage.The later one could drive the temperature equilibrium point of the heated plate to move towards lower temperature range.All the frequencies would not drop to zero due to the inherent initial deflection which provides additional stiffness to the plate.Dynamic responses state two variation trends in different temperature ranges,shifting toward the lower frequency range and closing up in the mid-frequency range.The characters of spectrum responses changed gradually as the temperature was elevated.Numerical simulations gave predictions with same variation trend as the test results.     

水泥土动力特性室内试验及复合地基抗震特性分析

通过在ＨＸ－１００多功能三轴仪上的动三轴试验及在Ｄｒｎｅｖｉｃｈ Ｌｏｎｇ－Ｔｏｒ型共振柱仪上的竖向激振试验,研究了水泥土的动本构关系,指出水泥土的动应力应变骨干曲线可以用双曲线模型来描述,并且对水泥土的阻尼特性进行了探讨。其次,探讨了水泥土材料的初始动弹性模量和水泥掺合比、围压的相互关系。最后,利用Ｌｏｍａ地震记录,结合一维剪切梁模型,对水泥搅拌桩加固软土地基前后场地放大效应进行对比分析,得到的     

内置钢箱-混凝土连续组合梁受力性能试验

为研究超静定内置钢箱-混凝土组合梁的塑性设计方法,进行了4根两跨内置钢箱-混凝土连续组合梁试验,获得了试验梁裂缝分布与开展、变形发展、破坏特征及塑性内力重分布等方面的试验结果.通过分析,给出了内置钢箱-混凝土连续组合梁等效塑性铰区长度计算公式,提出了以支座控制截面弯矩弹性计算值与组合梁正截面破坏时钢箱所承担弯矩之差为调幅对象、以相对塑性转角为自变量的弯矩调幅设计方法.