深部煤岩界面超低摩擦时变模型及能量转化研究

深部煤岩超低摩擦型冲击地压实质是巨量煤岩体沿煤岩界面发生失稳滑动的时变过程,期间煤岩界面摩擦力和摩擦系数随时间变化,同时伴随煤岩界面摩擦力做功向煤岩冲击动能释放能量转化特征.为定量描述煤岩界面能量转化规律,引入量纲分析法,实验测定了煤岩弹性系数、阻尼系数和待定系数,给出了深部煤岩界面摩擦系数表达式.以沈阳红阳三矿为研究对象,通过实验研究和工程实际相结合,定义了冲击动能转化率新指标,验证了所建模型可靠性,定量描述了煤岩界面摩擦力做功向煤岩冲击动能转化规律.研究结果表明:深部煤岩界面摩擦系数随冲击载荷幅值增大而线性降低,随冲击载荷频率增大而线性增加.深部煤岩界面摩擦力的降幅和降低速率变化急剧,当冲击载荷幅值为5000 N、冲击载荷频率为500 Hz时,深部煤岩界面摩擦力降幅为97%、降低速率为38.9 kN/ms～41.38 kN/ms时发生超低摩擦效应.首次从摩擦力降低幅值和降低速率定量表征超低摩擦效应.结合实验和工程实际分析发现,能耗比实验结果均值为0.441,红阳三矿“11.11”冲击地压计算结果为0.488,两者较为接近,进一步证明所建模型合理性.     

关于脆性岩体岩爆成因的理论分析

大型工程开挖中,高地应力环境下高储能脆性岩体通常会通过脆性破裂快速释放应变能,产生岩爆。针对这类岩爆现象进行了一系列理论探讨,认为:(1)开挖条件下脆性岩体的岩爆破坏主要为张破裂或者张剪性破裂,破裂角一般较小,呈薄片状或刀口状。笔者认为开挖产生次生张应力和压剪应力条件下微裂纹裂尖出现张应力是可能的,因此采用格里菲斯强度理论研究开挖岩体破裂是有效的; (2)以格里菲斯强度理论为基础,分析了岩体在二维和三维情形下的岩爆破裂应力判据和破裂角,指出在有张应力的条件下,岩体的剪破裂角会减小,直至为零,这就解释了开挖面附近薄片状、刀口状破裂现象的原因; (3)分析了脆性岩体岩爆破裂的能量过程,指出张性破裂所耗能量较小,而张剪性和压剪性破裂耗能较高。认为岩爆破裂消耗的能量主要转化为新生裂纹的表面能和破裂碎片的动能,并指出表面能所占比例较动能为小。由此解释了脆性岩体岩爆破坏以动力效应为主的特征; (4)本文理论分析成果的工程应用价值在于:可以预示开挖脆性岩体破裂部位、破裂方式和破裂范围; 提出岩爆破裂的张性应力控制依据。     

作用在岩体裂隙网络中的渗透力分析

从岩体裂隙网络渗流的特点出发, 以单裂隙渗透力分析为基础, 分析了二维及三维情况下岩体裂隙网络渗流对岩体裂隙壁施加的两种作用力: 垂直于裂隙壁使裂隙产生扩容的法向渗透静水压力以及平行于裂隙壁和裂隙水流方向一致的切向动水压力, 推导出二维及三维情况下裂隙单元因这两种作用力而产生的等效结点力, 并应用算例定量分析了岩体裂隙网络渗透静水压力和动水压力共同作用对岩体应力的影响, 结果显示: (a)渗透力作用下裂隙上部岩体压应力减小, 而裂隙下部岩体压应力增大, 最大压应力增大 10 .5 3%; (b)渗透力作用下裂隙岩体拉应力增大, 最大拉应力增大 9.0 9%; (c)裂隙渗透力使岩体剪应力增大, 最大值达 2 3.75 %。     

岩石的动态压缩行为与超高速动能弹毁伤效应计算

目前正在研制的超高速动能武器对地打击速度达(5~15)马赫左右, 具有侵彻机理独特, 毁伤效应倍增的特点, 现有理论难以准确描述。本文系统总结了侵爆近区岩石介质的动态可压缩性行为, 发现(5~15)马赫超高速弹侵彻近区岩石介质介于流体和固体弹塑性之间的内摩擦侧限压力状态, 创新提出流体弹塑性内摩擦侵彻理论模型, 填补了低应力弹塑区到高应力流体区之间的应力状态表征空区, 首次获得随弹体侵速变化的弹靶相互作用全过程阻抗演变公式, 界定了钻地弹固体侵彻、拟流体侵彻和流体侵彻的最小动能阈值, 系统提出了超高速动能弹打击侵深、成坑及地冲击安全厚度的计算方法。通过弹体侵速1 100~4 200 m/s的(超)高速侵彻实验, 验证了理论计算公式的准确性。     

钨合金弹体对混凝土靶的超高速侵彻机理

为研究钨合金弹体超高速侵彻混凝土靶的相关机理,构建了适用于超高速撞击的金属强度模型、失效模型和混凝土的本构模型,对93钨合金弹体超高速撞击混凝土靶问题进行了数值模拟。开展了钨合金弹体超高速撞击混凝土靶实验,分析了靶板成坑特性,研究了侵彻总深度和残余弹体长度随撞击速度的变化规律,理论分析了长杆钨弹超高速撞击混凝土的侵彻模型和混凝土靶内的应力波传播。得到以下主要结论:（1）利用金属及混凝土的新本构模型获得的超高速撞击混凝土靶的破坏形貌数值模拟结果与实验结果一致;（2）超高速撞击条件下混凝土靶成坑为“弹坑＋弹洞”形,成坑体积与弹体动能近似成正比;（3）超高速撞击条件下,侵彻深度随弹速提高呈现先增大后减小的现象,高速段侵深降低是弹体经历销蚀侵彻后“刚体侵彻阶段”减少造成的;（4）建立的钨合金超高速撞击混凝土侵彻分析模型,可用来预估侵彻深度、残余弹长、蘑菇头直径等参数;（5）采用建立的超高速撞击混凝土靶内应力波传播理论模型得到的计算结果与实验结果吻合较好。     

弹体侵彻厚混凝土靶迎弹面成坑效应

为研究弹体侵彻厚混凝土靶的迎弹面成坑效应,总结了侵彻实验中的成坑现象,分析了经验公式对成坑深度、成坑直径和成坑角等成坑效应的预测效果;考虑了撞击速度、靶板强度、配筋以及弹体直径和质量等因素的影响,采用量纲分析方法建立了新型成坑效应计算公式及成坑阶段耗能计算公式;基于新型成坑效应计算公式,对成坑效应的影响因素和成坑耗能进行了参数化分析。结果表明:无量纲成坑深度受靶板强度、配筋率和弹体质量的影响较大;对于钢筋混凝土,成坑深度随撞击速度提升呈先增大后减小再增大的变化规律;在常见的侵彻速度和质量范围内,成坑角为15°～24°,质量对成坑角影响较小;迎弹面成坑耗能占弹体总动能的10%～25%,且配筋率和靶板强度对成坑耗能比例的影响较小;弹体质量越小,成坑阶段耗能占比越大。新型成坑效应计算公式对成坑深度、直径和角度的计算结果与实验数据吻合较好,可为侵彻弹体设计和工程防护提供参考。     

基于SPH方法粒子射流破岩数值模拟与实验研究

钻井液中加入体积分数为1%~3%的钢质粒子在钻头喷嘴处高速喷出冲击岩石,实现了粒子射流冲击和钻头机械联合破岩,有效提高了破岩效率。利用瞬态非线性动力学有限元模拟软件,基于光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法,考虑流体对粒子射流冲击的影响,建立了粒子射流冲击破岩的物理模型,获得了粒子射流参数对破岩体积的影响规律,进行了室内实验验证,验证了SPH方法的有效性。结果表明:粒子射流冲击岩石表面形成规则的V型冲击坑;同条件下粒子射流破岩体积是水射流破岩体积的2~4倍;随着粒子射流冲蚀时间的增加,粒子射流破岩体积不断增加,但破岩效率降低;粒子射流压力大于10 MPa后,粒子射流破岩效率迅速增大;喷射角度大于6°后,破岩效率迅速减小。     

工程爆破问题数值模拟研究

工程爆破方法在开矿、筑坝、修路和凿洞中得到了广泛使用,经验和分析表明,当炸药埋深超过40米时,重力对爆破抛掷现象有明显影响,但目前缺乏系境研究。本文提出了一个用于爆破作用下的岩体本构数学模型,并用二维轴对称数值计算方法对有重力影响的工程爆破问题初始阶段进行了详细研究,计算结果包括爆炸应力波的传播规律,岩体的加速与破坏过程,空腔与地表面的运动规律,抛掷区的形成与划定,能量分配关系等,结果表明:重力对爆炸波的传播基本无影响,重力仅影响抛掷区的大小和抛掷区动能占总爆炸能的比例。     

Effect of the impulse of a meteorite on the dimensions of the impact crater

Formulas for the diameter and depth of an explosion crater are obtained which take into account the energy and impulse of the explosion products, rock strength, burial depth of the explosive charge, and gravity. Using the explosive-shock analogy, the obtained relations are extended to the case of meteorite (impactor) impact on the planet’s crust (target). It is shown that in the gravity cratering regime, the influence of the impulse of the impactor is significant and increases with increasing its size. In the strength cratering regime, the impulse has little effect on crater dimensions. It is established that crater dimensions are determined mainly by the kinetic energy of the impactor and, to a lesser degree, by its impulse.     

Dynamic damage constitutive relation of mesoscopic heterogenous brittle rock under rotation of principal stress axes

A micro-mechanics-based model is developed to investigate microcrack damage mechanism of four stages of brittle rock under rotation of the principal stress axes. They consist of linear elastic, non-linear hardening, rapid stress drop and strain softening. The frictional sliding crack model is applied to analyze microcracks nucleation, propagation and coalescence. The strain energy density factor approach is applied to determine the critical condition of microcrack nucleation, propagation and coalescence. The inelastic strain increments are formulated within the framework of thermodynamics with internal variables. Rotation of principal stress axes affect the dynamic damage constitutive relationship and the failure strength of brittle rock.     

冲击速度和轴向静载对红砂岩破碎及能耗的影响

地下岩体工程爆破开挖中,距爆源不同距离处岩体承受的地应力和动载荷大小不同,从动载荷的角度表征岩石动态破坏结果与工程实际更吻合。为研究动载荷和地应力大小对岩体破碎和能量耗散特性的影响,利用动静组合加载试验装置,分别设置7个冲击速度和轴向静应力等级,对红砂岩试件进行冲击试验。根据试件的破碎状况,分析不同静应力工况下冲击速度对岩石破坏模式和机理的影响。计算不同工况下的应力波能量值,研究冲击速度和轴向静应力对岩石能耗特性的影响。对破坏试件进行筛分试验,研究岩石破碎分形维数随冲击速度和轴向静应力的变化关系。结果表明,随着冲击速度的增大,试件的破坏程度逐渐加大。无轴压时岩石试件破坏后整体仍是一个圆柱体,属于张拉破坏;有轴压时岩石试件宏观破坏后呈沙漏状,属于拉剪破坏。岩石耗散能随冲击速度的升高呈二次函数关系递增;轴向静应力越高,递增幅度越小。随着冲击速度的升高,岩石分形维数由零逐渐增加;随着轴向静应力的升高,分形维数由零转为大于零的临界冲击速度先升高后降低。     

动能火箭弹定深技术

根据某火箭破障弹的性能特点,设计了动能侵彻战斗部和机械定深发火机构,使其可根据目标的强度和厚度控制战斗部在最佳深度处爆炸,以发挥战斗部的爆破威力。理论和试验证明所设计的动能火箭弹结构合理可行。     

Transients and Evolution in NiTi

Many of the applications that seek to utilize shape memory alloys for their unique set of properties inevitably must deal, on some level, with the dimensional instability that is inherent to these materials under cyclic thermomechanical loading conditions. As a result, a better understanding of the transient and evolutionary behavior of a shape memory alloy is critical to both the successful design of useful actuation systems and development of accurate material models that can adequately capture the types of dimensional instability that can arise during component design. To this end, a set of experiments were conducted wherein the temperature cycling excursion was held fixed while the applied stress was varied. The results indicated that the extent of strain evolution produced under the initially applied stress has a significant impact on both the amount of transient that is observed as well as the rate of evolution observed under subsequent stress levels. In particular, lowering the applied stress to 50 MPa after cycling under an initial stress of 75 MPa did not stabilize the strain. However, lowering the applied stress to 50 MPa after cycling under an initial stress of 150 MPa produced a nearly saturated strain/temperature response. The thermomechanical observations are discussed in terms of the nature of strain evolution and its connection to the concept of a local/global minimization of the energy of the system, however, the exact mechanisms associated with these strain evolutions were not determined.     

Green water impact pressure on a three-dimensional model structure

Green water impact pressure due to plunging breaking waves impinging on a simplified, three-dimensional model structure was investigated in the laboratory. Two breaking wave conditions were tested: one with waves impinging on the vertical wall of the model at the still water level and the other with waves impinging on the horizontal deck surface. Pressure measurements were taken at locations in two vertical planes on the deck surface with one at centerline of deck and the other between the centerline and an edge. Impact pressure was found to be quite different between the two wave conditions even though the incoming waves are essentially identical. Two types of pressure variations were observed??impulsive type and non-impulsive type. Much higher pressure was observed for the deck impingement wave condition, even though the flow velocities were quite close. Void fraction was also measured at selected points. Impact pressure was correlated with the mean kinetic energy calculated based on the measured mean velocities and void fraction. Impact coefficient, defined as the ratio between the maximum pressure at a given point and the corresponding mean kinetic energy, was obtained. For the wall impingement wave condition, the relationship between impact pressure and mean kinetic energy is linear with the impact coefficient close to 1.3. For the deck impingement wave condition, the above relationship does not show good correlation; the impact coefficient was between 0.6 and 7. The impact coefficient was found to be a function of the rate of pressure rise.     

ANALYSIS OF ACCUMULATION CHARACTERISTICS OF ELASTIC DEFORMATION ENERGY OF SURROUNDING ROCK IN RECTANGULAR ROADWAY1)

煤矿冲击地压主要发生在巷道中,其主要原因之一是巷道围岩积聚了大量的弹性能。为得出矩形巷道围岩弹性变形能积聚特征,降低巷道支护成本,推导了巷道冲击破坏失稳能量准则,并建立了矩形巷道围岩能量积聚计算模型,理论分析了采深、巷道断面尺寸和煤层厚度对矩形巷道围岩能量积聚影响规律,得出：矩形巷道积聚的弹性能随采深的增加而增大,采深越深,巷道积聚的弹性能增长速率越快。巷道围岩积聚能量随巷道断面尺寸增加而增大。当煤层厚度小于巷道影响范围时,巷道积聚能量随煤层厚度增加而增大。在实际工程中,尽可能减小巷道断面尺寸,尽可能沿顶、底板布置巷道。研究结果为冲击地压巷道布置和降低巷道支护成本提供了理论依据。     

基于岩石蠕变及D-P准则的深部巷道围岩弹塑性分析

为深入分析岩石蠕变及中间主应力对深部高应力软岩巷道围岩稳定性及分区变形特性的影响机理, 通过剖析长期荷载作用下深部巷道围岩的变形特征, 揭示了基于围岩蠕变特性的深部巷道围岩四分区变形机理, 并依据Druck-Prager准则及关联性流动法则考虑了中间主应力、岩体扩容及应变软化的影响, 推导出巷道围岩各分区应力、变形和半径解析解. 结合工程算例, 通过对现场监测数据以及不同力学模型的计算结果进行对比分析, 论证了本文理论的科学性, 并揭示了不同强度准则和围岩参数对深部巷道围岩各分区形态的影响规律. 结果表明, 忽视深部巷道围岩的蠕变特性将导致初始黏聚力的取值大于实际值, 从而造成围岩的理论承载能力大于实际承载能力; 在[0, 0.7]区间内提高中间主应力系数可有效控制围岩塑性区及破碎区范围的扩展; 当初始黏聚力及内摩擦角减小时, 中间主应力系数对围岩塑性区、破碎区范围及巷道变形的影响力显著提高. 研究成果可为地下工程支护设计及围岩稳定性评估提供理论参考.      

高轴压和围压共同作用下受频繁冲击时含铜蛇纹岩能量演化规律

探讨高轴压和围压共同作用下频繁冲击扰动试验过程中伴随主要能量的种类,并推演冲击扰动前后弹性能、塑性能等能量的计算公式;采用预加载围压、高轴压、0.5 MPa冲击气压模拟深部岩体承受的水平应力、垂直高应力及爆破开挖扰动的影响开展动力学试验,并基于试验结果分析含铜蛇纹岩的动力学特征及能量演化规律。研究结果表明:含铜蛇纹岩能承受的扰动冲击次数随轴压增大而减小,随围压增大而增大,且动态峰值应力随扰动冲击次数增加而减小;随扰动冲击次数的增加,岩样伴随的弹性能先增大后趋于减小,伴随的塑性能呈增大的趋势发展,反射能和入射能的比值与透射能和入射能比值的变化规律相反,前者呈增大趋势,后者呈减小趋势;单位体积吸(释)能随扰动冲击次数的增加呈下凸曲线趋势变化,其均值随围压增大先减小后增大,随轴压增大而减小。     

隧洞式内衬储气库极限储存压力解析解

隧洞式内衬储气库是一种新型能源储存方法,有助于平衡供需,推动国家由化石能源向绿色能源的持续过渡,有利于国家“碳中和、碳达峰”目标的实现.本文采用极限平衡方法和弹塑性分析方法推导隧洞式内衬储气库极限储存压力的解析解.在极限平衡方法中,考虑上覆围岩自重、破裂面受力和极限储存压力,选用刚性锥模型,推导了上限压力表达式;在弹塑性分析方法中,根据围岩中应力分布规律和剪切、抗拉强度,推导获得了弹塑性条件下上限与下限压力表达式.最终综合考虑两方法求得的结果,确定极限储存压力解析解.结果表明:极限平衡方法求得上限压力与埋深呈二次函数关系,且随着侧压力系数的增大而增大;弹塑性分析方法确定的上限压力和下限压力与埋深呈线性关系,下限压力随着侧压力系数的增大而减小,且Ⅰ级围岩条件下的内衬储气库不用考虑下限压力.在侧压力系数λ=1.2时上限压力最大,因此应尽量在侧压力系数为1.2的围岩条件下修建隧洞式储气库.最后根据典型工况下上限和下限压力曲线给出内衬洞室推荐压力范围.     

On dynamic buckling phenomena in axially loaded elastic-plastic cylindrical shells

Some characteristic features of the dynamic inelastic buckling behaviour of cylindrical shells subjected to axial impact loads are discussed. It is shown that the material properties and their approximations in the plastic range influence the initial instability pattern and the final buckling shape of a shell having a given geometry. The phenomena of dynamic plastic buckling (when the entire length of a cylindrical shell wrinkles before the development of large radial displacements) and dynamic progressive buckling (when the folds in a cylindrical shell form sequentially) are analysed from the viewpoint of stress wave propagation resulting from an axial impact. It is shown that a high velocity impact causes an instantaneously applied load, with a maximum value at t=0 and whether or not this load causes an inelastic collapse depends on the magnitude of the initial kinetic energy.     

孔隙流体耦合效应对射流冲击应力分布的影响分析

运用全解耦流固耦合理论,建立了水射流冲击岩石介质流固耦合数值分析模型,给出了数值算法,计算分析了考虑和不考虑孔隙流体耦合效应对射流冲击岩石时应力分布的影响规律。结果表明,在射流冲击作用下,如不考虑孔隙流体耦合作用,最大拉应力位于冲击面,离冲击中心径向距离与喷距成正比,最大剪切应力位于岩石冲击中心下部约0.5倍喷嘴直径位置;如考虑孔隙流体耦合作用,最大拉应力位于岩石冲击中心下部约0.4倍喷嘴直径位置。数值分析结果可为水射流破岩机理研究中岩石破坏准则的选择提供依据。