一个椎间盘生物力学模型

椎间盘在脊柱运动中起着重要的作用,根据椎间盘的生物力学特点建立力学模型.采用复合材料力学中的弹性嵌入体解,建立了椎间盘的一个横观各向同性圆柱体力学模型.求出了腰椎间盘在直立位、弯曲及扭转作用下的应力应变和位移解.得出结论椎间盘在受复合载荷的作用下更易被破坏.     

考虑应变率效应的黏弹性减震材料本构模型

黏弹性减震材料的力学性能直接影响黏弹性装置的减震效果，其力学行为除了具有典型的超弹性特征外，亦会表现出显著的黏弹特性。为了准确描述黏弹性减震材料复杂的力学行为，在已有超弹性力学模型的基础上，构造多项式形式的黏度方程对材料的应变率效应进行表达，建立了相应的材料黏性应变能函数，同时引入流体动力学补强理论以考虑填料的影响，通过理论推导，建立能够考虑应变率效应的黏弹性减震材料本构模型，进而在不同加载应变率下对黏弹性减震材料的应力-应变关系进行了一系列试验研究，并利用试验数据对所建模型的准确性与适用性进行对比验证。结果表明：应变率对黏弹性减震材料的力学性能具有显著的影响，考虑应变率效应和填料补强效应后模型的预测鲁棒性得到了较大的提高，所建模型可在较广的应变范围(0~300%)内对不同应变率下黏弹性减震材料的应力-应变行为进行较为准确的预测。     

车辆移动荷载下黏弹性沥青路面的弹性等效方法

沥青路面设计规范中采用的力学模型是静载作用下弹性多层体系，而实际车辆作用为移动荷载，沥青层也表现为黏弹性。如何在路面设计中选取合适的弹性模量，从而近似表征移动荷载作用下黏弹性多层体系的力学行为是核心问题。首先，推导移动荷载作用下弹性/黏弹性多层体系力学响应解析解，获得各层力学响应与模量之间的理论关系。其次，基于理论关系，提出弹性模量的等效原则及流程，并以黏弹性三层体系为例，对比等效前后的力学响应分布和模量，验证弹性等效方法的有效性；最后，基于神经网络算法，以各沥青层黏弹参数、温度及车速为输入、等效弹性模量为输出，建立等效弹性模量预估模型。结果表明：等效弹性模量可在数值上反映黏弹性层的性质；各类力学响应分布在等效前后基本一致，证明此方法可有效地将移动荷载作用下黏弹性多层体系等效到静载作用下弹性多层体系；等效弹性模量预估模型可为沥青路面设计提供准确力学参数。     

聚合物改性水泥浆体黏弹性的频率响应(Ⅰ):动态力学分析EI北大核心CSCD

采用动态力学分析的频域方法研究了聚合物改性水泥浆体的黏弹性,通过对柔量的复平面分析,采用二级标准固体流变模型来描述聚合物改性水泥浆体的黏弹性行为,并求得了模型参数.对3种配比的乙烯/醋酸乙烯共聚物(EVA)乳胶粉改性水泥浆体试样在0.01~100.00 Hz频率下的试验结果进行拟合,结果表明:二级标准固体流变模型简单实用,能较好地解释聚合物改性混凝土的黏弹性行为,进一步验证了频域方法的实用性,以及二级标准固体流变模型的适用性;所得结果对聚合物改性混凝土黏弹性的研究有一定的参考意义,在实际应用中可以为满足干缩和徐变要求的混凝土配合比设计提供参考.     

天然软黏土的弹黏塑性本构模型：进展及 发展

天然软黏土由于土结构的存在表现出比较复杂的力学特性：应力应变关系的时效特征;固有各向异性和诱发各向异性;土颗粒间的胶结和大孔隙结构在变形过程中的破坏。基于上述某些试验现象,学者们提出了很多一维和三维的弹黏塑性本构模型。为了弥补现有模型对软黏土力学特征的描述考虑不足,作者在弹黏塑性力学理论的框架下,由浅入深地建立了一系列的天然软黏土的本构模型： ① 在 非结构性 土的一维压缩试验基础上建立一维弹黏塑性本构模型; ② 在 非结构性 土 的 三轴试验基础上扩展一维模型到三维弹黏塑性本构模型; ③ 在 结构性 土 的 一维压缩试验基础上扩展一维非结构性土模型到一维结构性土模型; ④ 结合前面的模型和结构性土的三轴试验现象提出三维结构性软黏土的弹黏塑性本构模型。 所有模型均得以验证。 三维 结构性 土 模型需要的试验成本同修正剑桥模型,且所有参数的确定都非常直接。     

剪切双曲线型等效时间流变模型

为了预测变剪应力荷载下的流变变形,运用热力学内变量连续介质力学和Yin-Graham等效时间法来推导剪切流变模型。首先把Mesri双曲线型蠕变公式推广到耗散空间,在耗散空间绘制黏塑性剪应变与剪应力等效时间线。其次利用Yin-Graham等效时间法建立了黏塑性剪应变速率与等效时间关系方程,获得黏塑性剪应变速率与应力水平和黏塑性剪应变之间的函数表达式。最后利用耗散剪应力等于真实剪应力这个力学关系式,把黏塑性剪应变速率表达式和线弹性本构方程相结合,建立了一维弹黏塑性剪切流变方程,研究了流变方程分别采用绝对等效时间和相对等效时间表示的表达式。基于这个流变方程,获得了三轴固结排水剪切蠕变试验中单级加载和多级加载的剪切流变解。实例表明,剪切流变模型能够较好地模拟软土三轴固结排水剪切蠕变试验成果。     

高层建筑深基础沉降计算的黏弹性分析

研究假定土体为线性黏弹性介质,其在内部力作用下的应力球张量和应变球张量间符合弹性关系,而应力偏张量和应变偏张量间符合三参数固体黏弹性应力应变关系。基于半空间体内部受竖向集中力的Mindlin弹性解,根据弹性-弹黏性相应原理,推导了竖向集中力作用在半无限体内部时的竖向位移黏弹性解。通过对位移解进行Laplace逆变换,给出了竖向位移的时域解。作为解答的应用,推导了三参量固体黏弹性半无限体内部矩形面积上作用有三角形分布、均匀分布荷载时的黏弹性沉降计算式。将深基础视为一等代实体墩基础,建立了置于非均匀地基中的桩基础黏弹性沉降计算方法。为了便于计算与工程应用,根据黏弹性理论解编制了计算程序。结果验证与实例分析表明,文中理论解是正确的,研究结果为工程实际应用提供了理论依据。     

扇形铅黏弹性阻尼器的等效力学模型

为使扇形铅黏弹性阻尼器便于在有限元软件分析及工程应用中选用,根据该阻尼器的构造、材料特性构建扇形铅黏弹性阻尼器在有限元软件中的等效力学模型,并通过该模型在大型有限元分析软件SAP2000的模拟分析与试验、精细化模型进行验证。结果表明:扇形铅黏弹性阻尼器的等效力学模型的建立是可行的,能很好地对阻尼器在有限元软件中进行模拟分析。     

岩石弹黏塑性流变试验和非线性流变模型研究

采用分级增量循环加卸载和单级加载方式,对金川有色金属公司 III 矿区二辉橄榄岩试样进行弹黏塑性流变试验,在对流变试验数据进行深入分析基础上,详细研究该类岩石各蠕变阶段非线性黏弹塑性变形特性,将衰减蠕变曲线分离为黏弹性分量与黏塑性分量,研究各衰减蠕变变形分量的非线性特征,建立定常流动速率及加速蠕变率的应力、时间的拟合函数.根据不同应力水平下的加、卸载蠕变试验曲线,提出由瞬弹性Hooke体、黏弹塑性村山体、黏塑性改进Bingham体串联而成的新的岩石非线性弹黏塑性流变模型,对模型参数辩识,提出非线性元件参数的确定方法.该流变模型具有两个屈服极限且流变元件参数是关于应力和时间的拟合函数,考虑了衰减蠕变阶段和加速蠕变阶段的非线性特征,能反映不同应力水平下岩石流变规律,尤其能较合理地模拟岩石加速蠕变,从理论上给出非线性弹黏塑性流变模型的松驰方程和三维蠕变方程.利用不同应力水平下岩石蠕变全程试验曲线,对提出的非线性弹黏塑性流变模型进行充分验证.试验曲线与非线性流变模型理论曲线较吻合,显示所建非线性弹黏塑性流变模型的正确性与合理性.     

统一流变力学模型参数的确定方法

统一流变力学模型同时包含黏弹性、黏塑性、黏性、黏弹塑性4种基本流变力学性态,根据岩石在不同应力水平下的加卸载蠕变试验曲线特性,可以全面地对统一流变力学模型及其14个特殊情况下的模型进行辨识.以采用统一流变力学模型对流变模型进行辨识的方法为基础,对流变力学模型参数的确定方法进行研究.先介绍黏弹性、黏塑性、黏性、黏弹塑性这4个基本流变力学模型模型参数的确定方法.然后,将蠕变试验数据中的蠕变应变量分离成衰减蠕变应变分量(其蠕变曲线函数可表示为指数函数)和定常蠕变应变分量(其蠕变曲线形函数可表示为与时间成比例的线性函数)2部分.并分别介绍衰减蠕变应变分量中同时含有黏弹性和黏弹塑性2种应变,以及定常蠕变应变分量中同时含有黏性和黏塑性2种应变这2种情况的流变力学模型参数确定方法.最后,通过锡矿山页岩和东乡铜矿红砂岩2种岩石在不同应力水平下加卸载蠕变试验结果,给出2个流变模型参数确定的实例.     

显微镜辅助下微创椎间盘髓核摘除术治疗腰椎间盘突出症

目的探讨显微镜辅助下微创椎间盘髓核摘除术治疗腰椎间盘突出症的临床疗效。方法对46例腰椎间盘突出症患者采用显微镜辅助下微创椎间盘髓核摘除术治疗。观察46例患者手术时间、术中出血量、手术前后JOA评分及临床疗效等情况。结果单节段手术时间60~90 min,平均55 min;术中出血量50~120 mL,平均85 mL。双节段手术时间80~180 min,平均75 min;术中出血量60~150 mL,平均100 mL。46例患者术后均获随访,随访时间6~24个月,平均8.6个月。应用改良JOA评分法评价疗效,优33例,良11例,可2例;优良率为95.7%。JOA总分：术前为（4.13±0.79）分,术后为（13.06±2.54）分;术后JOA总分明显高于术前,差异有统计学意义（t=19.67,P〈0.01）。结论显微镜辅助下微创椎间盘髓核摘除术具有创伤小、出血少、术后恢复快及疗效满意等优点,是治疗腰椎间盘突出症一种较好的手术方法。     

A fuzzy logic model to predict specific energy requirement for TBM performance prediction

Prediction of tunnel boring machine performance is a critical key for successful tunnel excavations. Specific energy requirement of disc cutters, which is defined as the amount of energy required to excavate a unit volume of rock, is one of the important parameters used for performance prediction of these machines. Much research has been conducted to predict cutting parameters of disc cutters using analytical, empirical and numerical approaches. In recent years alternative methods, such as fuzzy logic, have been extensively used to deal with subjects having ambiguities and uncertainties. In this study, a model was established to predict specific energy requirement of constant cross-section disc cutters in the rock cutting process by using fuzzy logic method. This model is based on experience and the database which consists of linear cutting test results that were generated over for many years at the Earth Mechanics Institute of the Colorado School of Mines. The model predicts specific energy requirements of disc cutters using uniaxial compressive and tensile strength of rocks, disc diameter and tip width, penetration and spacing of cuts.     

圆盘厚径比对岩石劈裂抗拉强度影响的试验研究

 由于巴西圆盘抗拉强度公式是基于弹性力学平面问题的解析解,计算结果与直接拉伸试验得到的抗拉强度有较大的差异。基于此,对100余个不同厚径比的砂岩圆盘试样进行劈裂抗拉试验,试验结果表明,随着试样厚径比的减小,抗拉强度逐渐增大,当厚径比约小于0.3时,其抗拉强度逐渐增大并趋于一个相对稳定值,其变化曲线可用三次函数较好的拟合。为了更加完整地把握厚径比对抗拉强度的影响,特建立不同厚径比的三维有限元模型,对圆盘中心轴线上等效应力的分布规律进行详细的研究。研究结果表明,试样中轴线上的最大拉应力出现在试样端面的中心,而且试样的厚径比越大,圆盘的端面中点处拉应力相对越大,圆盘最先起裂的位置发生在端面中心点,而不是内部中心点,有限元计算的结果很好地解释了试验数据的分布规律;通过对有限元结果进行多元拟合,给出考虑厚径比的巴西圆盘抗拉强度修正公式,经验证修正公式具有较好的适用性。研究成果为岩石抗拉强度的正确测定提供有益的依据。     

基于等摩擦耗能的滚刀多目标优化布局

基于接触力学理论建立了滚刀摩擦耗能数学模型,对影响摩擦耗能的主要参数进行了显著性分析。以滚刀摩擦耗能差异最小为原则,通过遗传算法对原刀盘极径、极角以及滚刀半径选型建立优化模型。以TB880E刀盘为实例,研究表明:优化边缘滚刀刀间倾角后,摩擦耗能标准差降低88.78%;优化中心滚刀刀间距后,摩擦耗能标准差降低4.15%;重选边缘滚刀半径后摩擦耗能标准差降低16.4%;极角优化后径向不平衡力降低28.22%;倾覆力矩降为10.33 N·m。该研究可用于刀盘的布置设计及滚刀半径选型,对减少滚刀磨损量差异和提高掘进效率具有重大意义。     

盘形滚刀与岩石相互作用理论研究现状及分析（一）

全断面岩石掘进机盘形滚刀破岩理论是全断面岩石掘进机研制及其施工工程工期预测等的理论基础。通过对国内外学者对盘形滚刀破岩理论研究成果的分析,总结建立这些成果所依据的模型特点和分析方法,据此将这些模型分为经验模型、一维模型、二维模型和三维模型进行论述,国内外学者对一维模型的研究较深入,成果也较多;对二维模型的研究次之,但也产生了相对成熟和实用的结论;对三维模型的研究则较少,尚未建立成熟和实用的结论。     

Prediction of thrust and torque requirements of TBMs with fuzzy logic models

For successful tunnel excavations, selection of proper tunnel boring machine (TBM), optimization of design parameters and prediction of their performance are critical. Normal and rolling forces of disc cutters are used for determination of thrust, torque and power requirement of TBMs as well as prediction of their performance. Much research has been conducted to predict these parameters of disc cutters using analytical, empirical and numerical approaches. In recent years alternative methods, such as fuzzy logic, have been extensively used to deal with subjects having ambiguities and uncertainties. A model was established to predict normal forces of constant cross section (CCS) disc cutters in the rock cutting process by using fuzzy logic method. The other model which predicts specific energy requirement of disc cutter can also be used for predicting the rolling forces of these cutters. These models are based on experience and verified the database which consists of linear cutting test results generated at the Earth Mechanics Institute of the Colorado School of Mines. The models predict forces of disc cutters using uniaxial compressive and tensile strength of rocks, disc diameter and tip width, penetration and spacing of cuts.     

复合地层中盾构滚刀磨损实用预测方法及应用

盾构机在复合地层掘进过程中常因刀具磨损量过大而产生掘进工效降低和刀具失效等问题。依托深圳地铁13号线白应区间复合地层段滚刀磨损数据,根据Rabinowicz磨粒磨损计算模型提出了一种滚刀磨损量实用预测方法。该方法结合滑移率计算公式和刀盘扭矩、刀盘推力得到滚刀滑动距离,通过科罗拉多矿业学院模型(CSM模型)、岩石强度参数和滚刀贯入深度确定接触面法向荷载,根据滚刀设计参数确定其材料强度。通过确定影响滚刀磨损量的三个主要因素(滑动距离、接触面法向荷载和材料强度),推导出了考虑盾构滚刀磨损体积计算公式,并采用深圳地铁13号线白应区间复合地层段滚刀实测磨损量与磨损量预测值进行对比验证。结果表明:实测磨损量与预测较为吻合,验证了所提出的滚刀磨损量预测方法的合理性,研究成果可为复合地层中盾构滚刀磨损量预测和换刀时机的确定提供理论依据。     

Effect of replacing disc cutters with chisel tools on performance of a TBM in difficult ground conditions

A summary of a research program covering a period of two years on the performance of a TBM in a very complex and difficult geology is presented in this study. The formations in the study area varied from alluvium, sludge, mudstone, shale and limestone to quartzite with strengths from soft to very hard. The dykes frequently intruded the sedimentary rocks resulting in different degrees of weathering and fracturing in the country rock causing tremendous delays in progress rate of the TBM. The disc cutters started cutting inefficiently in clayey medium strength ground with extreme water income, at where also excessive disc consumptions started due to insufficient friction between the disc cutters and very soft (sludgy) formation, and it was decided to replace all disc cutters with chisel tools (ripper, scraper). Before making this important decision that could affect totally the excavation efficiency and production rate, some theoretical estimations were performed using the Evans’ cutting theory after some modifications based on the previous experimental studies for relieved cutting mode and wear flat, front ridge and vee-bottom angles found in complex shapes of chisel tools to estimate deterministically the torque and thrust requirements of the TBM.Field measurements of the torque and thrust requirements of the TBM equipped with the chisel tools validated the theoretical considerations and the deterministic model used for predicting the performance. Statistical analysis indicated that the model could be used reliably for performance prediction. This study also gave a unique opportunity to compare the performance of disc cutters and chisel tools used on the same TBM at variety of grounds and to analyze the effect of replacing disc cutters with chisel tools on the performance of the TBM. The field measurements indicated that the chisel tools were superior to the disc cutters in especially soft to medium strength rocks.     

Analysis on the damage behavior of mixed ground during TBM cutting process

Accurate prediction of rock cutting forces of disc cutters is especially significant for the design and construction of tunnel boring machine (TBM). Through the analysis of motion trajectory of TBM disc cutters, a three-dimensional model of rock breaking process of disc cutters is established. In terms of the rock strain which is resulted from the interaction between disc cutters and rock during the process of rock breaking, a three-dimensional cutting forces model is proposed with disc cutters set at certain parameters and in certain sizes. Subsequently, the equation of contacting forces between rock and disc cutter is derived. Moreover, a new method has been presented for the study of the rock breaking theory of the disc cutter and it also provides guidance for the design and application of TBM in tunnel excavation. The three-dimensional model for the rock breaking mechanism is used for predicting the cutting force for the situation of mixed ground.The damage field and the rock failure zone induced by disc cutter for mixed ground are also discussed in this study. In detail, the rock damage zones are divided into two parts, one is the left damage field which located in the outside of disc cutter. The other is the right damage field which located in the outside of disc cutter. The influence of the rock ground dip on the rock failure zone was also studied by parameter analysis.