用统一平面应就滑移线场理论求解厚壁圆筒的极限荷载

用统一平面应变滑移线场理论，得到了拉压性能不同材料的厚壁圆筒的极限荷载统一解，它也可以适用于拉压强度相等的材料，能充分发挥材料性能，减轻结构重量，取得多方面的经济效益。     

用统一强度理论求厚壁圆筒和厚壁球壳的极限解

采用俞茂宏统一强度理论分析了厚壁筒和厚壁球壳的极限荷载。得出了统一解形式。利用此解可以合理地得出不同材料的相应解,它既可以适用于拉压强度相等的材料,也可以适用于拉压强度不相等的材料,并且能充分发挥材料的性能,从而减轻结构重量,取得多方面的效益。     

线性荷载作用下外简支环板的极限荷载分析

对于线性荷载作用下外简支环板,引入统一强度理论,进行了极限荷载分析。并分别求出了两种特殊形式的线性荷载作用下的极限荷载统一解,得出参数b值及材料的拉压比α对极限荷载的影响曲线。统一强度理论中,选择不同的参数b,可以得到一系列不同的屈服准则,不同的b值可以对应不同的工程材料,其中b=0和b=1分别给出了下限解和上限解。工程实际中,α可根据实际材料的拉压强度直接确定。当α=1时,统一强度理论适用于拉压强度相同的材料,当a≠1时,适用于拉压强度不同的材料。因此文中所给出的解可以灵活应用于各种性能的材料,可以充分反映材料的SD效应及中间主应力效应。已有的Tresca准则,Mises准则,双剪应力屈服准则以及双剪统一屈服准则的解答均为本文解答的特例或线性逼近。     

不同拉压特性的厚壁球壳分析

为了研究内压作用下厚壁球壳的弹塑性性能,以双剪统一强度理论为基础,考虑材料拉压模量不同、拉压强度差异,建立了厚壁球壳的弹性、塑性及安定极限内压的统一解,分析了拉压模量、拉压强度、壁厚不同对各个统一解的影响。研究结果表明:材料的拉压模量不同、拉压强度差异对厚壁球壳的极限内压产生一定的影响;弹性、塑性及安定极限内压均随壁厚的增加而增大,随拉压比的增大而减小。安定极限内压随半径比的变化趋势,可为选择最优壁厚提供参考。该结论为厚壁球壳的设计及工程应用提供一定的参考。     

拉压强度不等材料的厚壁圆筒的统一极限解

采用俞茂鋐统一强度理论分析了厚壁圆筒的极限荷载,得出统一解形式,它既可以适用于拉压强度相等的材料,也可以适用于拉压强度不相等的材料．     

不同拉压特性的厚壁圆筒极限内压统一解

厚壁圆筒在实际工程领域中应用广泛,若能精确计算出极限内压,对预防事故发生,降低风险有重要意义.工程中存在许多材料,其拉压强度和拉压模量均存在差异,这些差异对极限内压的大小有显著影响.以往研究表明,仅考虑拉压强度与拉压模量的一个方面,计算结果与实际情况存在一定的误差.本文基于双剪统一强度理论,综合考虑中间主应力效应及材料拉压强度和拉压模量的不同,推导了内压作用下厚壁圆筒的弹、塑性状态的应力分布及弹性极限内压、塑性极限内压与安定极限内压的统一解,通过与其他文献对比分析验证了本文计算结果的正确性,分析了半径比、统一强度理论参数、拉压强度比与拉压模量系数对弹性极限内压、塑性极限内压及安定极限内压的影响.结果表明:统一解均随半径比和统一强度理论参数的增大而增大,随拉压强度比的增大而减小,弹性极限内压随材料拉压模量系数的增大而减小,当壁厚增加到一定值后,安定极限内压随材料拉压模量系数的增大而减小;材料的拉压模量不同、拉压强度差异对厚壁圆筒的安定性影响显著,考虑中间主应力效应可使材料的潜能得到更充分发挥,极限内压随半径比的变化规律可为选择合理壁厚提供参考,该结论可为厚壁圆筒的工程应用提供理论依据.     

拉压性能不同材料全量型本构关系及厚壁筒的应力分析

将经典全量理论作了推广，考虑了应力状态及塑性体积变形对拉压性能不同材料的塑性行为的影响。应用该本构模型分别计算了厚壁筒在内压和外压作用下的应力分布。给出了径向应力、环向应力和轴向应力沿壁厚的分布图。将本文的计算解与拉压性能相同(不考虑体积变形、强化曲线唯一)的幂函数强化材料的厚壁筒的理论解进行了比较。结果表明，材料的拉压性能不同对厚壁筒的环向应力和轴向应力影响较大。因此，对于拉压性能不同材料，考虑到其对应力状态及塑性体积变形敏感时，是不能将其简化成拉压性能相同、体积不可压缩、强化曲线唯一的理想材料。     

拉压性能不同材料的几种结构的极限分析

给出了拉压性能不同材料（简称具有Ｓ－Ｄ效应的材料）的几种结构的极限载荷公式。揭示出材料的拉压性能不同对几种结构承载能力的影响规律。所给出的极限载荷公式可供工程设计人员参考。     

线性强化材料厚壁圆筒的统一极限分析

运用统一强度理论对承受内压的拉压屈服强度不同的线性强化材料的厚壁圆筒进行了极限载荷分析，得到了适用于多种材料的厚壁圆筒极限载荷的统一解析式．     

不同拉压特性的双层厚壁圆筒极限承载力解答

采用统一强度理论并考虑材料拉伸与压缩弹性模量的差异性,建立均匀内压作用下双层厚壁圆筒的应力表达式,获得了其内压相应的弹性极限解答、塑性极限解答,并分析拉压强度比、拉压模量系数、统一强度理论参数、半径比及分层半径对弹性、塑性极限内压的影响规律．研究结果表明：弹性、塑性极限内压随拉压强度比的增加而减小,但随统一强度理论参数、半径比的增加而增大;弹性极限内压随分层半径的增加呈现先增大后减小变化,随拉压模量系数的增加而一直减小;塑性极限内压与拉压模量系数、分层半径无关．应用于实际工程时,可根据所得结果选择合理的壁厚及分层半径,再根据材料特性确定其他参数,以便更加准确地计算结构的受力状况．     

材料破坏过程可视化实验教学方法研究1)

基于数字图像相关技术,提出材料破坏过程可视化的实验教学方法,并以混凝土材料为例,介绍该方法在劈拉与单轴压缩实验中的应用及其效果。通过监测混凝土劈拉与压缩破坏过程,分析了该材料破坏模式,揭示了混凝土材料劈拉与压缩破坏机理。应用数字图像相关方法获得试件表面应变场分布,验证了材料破坏机理,并提出适用的破坏强度理论。     

爆炸加载时光弹性材料动态性能参数的测定

文章从工程应用的角度出发介绍了测定爆炸加载时光弹性材料动态性能参数的方法。给出了环氧树脂、聚碳酸脂的动态测定结果,还给出了环氧树脂的(i～K)关系及静态抗拉、抗压强度。     

Predicting the Dynamic Compressive Strength of Carbonate Rocks from Quasi-Static Properties

In this study, the split Hopkinson pressure bar testing method was used to quantify the dynamic strength characteristics of rocks with short cylindrical specimens. Seventy dynamic compression tests were conducted on 10 different carbonate rocks with the split Hopkinson pressure bar apparatus. Experimental procedure for testing dynamic compressive strength and elastic behaviour of rock material at high strain rate loading is presented in the paper. Pulse-shaper technique was adopted to obtain dynamic stress equilibrium at the ends of the sample and to provide nearly a constant strain rate during the dynamic loading. In addition to dynamic tests, the physical properties covering bulk density, effective porosity, P-wave velocity and Schmidt hardness of rocks, and mechanical properties such as quasi-static compressive strength and tensile strength were determined through standard testing methods. Multiple linear regression analyses were carried out to investigate the variation of dynamic compressive strength depending on physical and mechanical properties of rocks and loading rate. A three parameter model was found to be simple and provided the best surface fit to data. It was found that dynamic compressive strength of rocks increases with increase in loading rate and/or increase in rock property values except porosity. Statistical tests of regression results showed that quasi-static compressive strength and Schmidt hardness are most significant rock properties to adequately predict the dynamic compressive strength value among the other properties. However, P-wave velocity, quasi-static tensile strength of rocks could also be used to estimate the dynamic compressive strength value of rocks, as well, except the bulk density and effective porosity.     

Experimental Study on the Complete Tensile Stress-Deformation Curve of Fully Graded Concrete

Experimental Techniques - Concrete is a type of quasi-brittle material with high compressive strength and low tensile strength. To obtain the complete tensile stress-deformation curve of massive...     

类岩石材料力学特性的试验及数值模拟研究

在进行多组不同配比类岩石材料单轴压缩试验和巴西试验的基础上,详细分析了石膏水泥比和石英砂含量对类岩石材料的单轴抗压强度、抗拉强度及弹性模量等力学参数的影响规律,力图找到适合模拟现场砂质泥岩的类岩石材料及配合比。利用颗粒流程序(PFC)模拟,进一步研究了高径比和围压对类岩石材料力学特性的影响。结果表明:随着石膏水泥比的增大,抗压强度和弹性模量均逐渐减小,而抗拉强度逐渐增大;随着石英粉含量的增大,抗压强度和弹性模量均先增大后减小,而抗拉强度则为先减小后增大。结合单轴压缩过程的声发射特征,揭示了裂纹扩展与声发射有密切的关系。PFC2D模拟获得的力学参数与室内试验相近,破裂模式也与实际情况相似。通过尺寸效应的研究可知试样的高径比在2.0~2.5较合理。随着围压的增大,试样的峰值强度、残余强度、峰值应变及弹性模量等力学参数均增大,且围压会改变试样的破裂模式。     

Effects of microstructure on uniaxial strength asymmetry of open-cell foams

Based on the elongated Kelvin model, the effect of microstructure on the uniaxial strength asymmetry of open-cell foams is investigated. The results indicate that this asymmetry depends on the relative density, the solid material, the cell morphology, and the strut geometry of open-cell foams. Even though the solid material has the same tensile and compressive strength, the tensile and compressive strength of open-cell foams with asymmetrical sectional struts are still different. In addition, with the increasing degree of anisotropy, the uniaxial strength as well as the strength asymmetry increases in the rise direction but reduces in the transverse direction. Moreover, the plastic collapse ratio between two directions is verified to depend mainly on the cell morphology. The predicted results are compared with Gibson and Ashby''s theoretical results as well as the experimental data reported in the literature, which validates that the elongated Kelvin model is accurate in explaining the strength asymmetry presented in realistic open-cell foams.     

Constitutive modeling of ice in the high strain rate regime

The objective of the present work is to propose a constitutive model for ice by considering the influence of important parameters such as strain rate dependence and pressure sensitivity on the response of the material. In this regard, the constitutive model proposed by Carney et al. (2006) is considered as a starting basis and subsequently modified to incorporate the effect of brittle cracking within a continuum damage mechanics framework. The damage is taken to occur in the form of distributed cracking within the material during impact which is consistent with experimental observations. At the point of failure, the material is assumed to be fluid-like with deviatoric stress almost dropping down to zero. The constitutive model is implemented in a general purpose finite element code using an explicit formulation. Several single element tests under uniaxial tension and compression, as well as biaxial loading are conducted in order to understand the performance of the model. Few large size simulations are also performed to understand the capability of the model to predict brittle damage evolution in un-notched and notched three point bend specimens. The proposed model predicts lower strength under tensile loading as compared to compressive loading which is in tune with experimental observations. Further the model also asserts the strain rate dependency of the strength behavior under both compressive as well as tensile loading, which also corroborates well with experimental results.     

Numerical study of strength properties for a composite material with short reinforcing fibers

A numerical approach to the determination of strength properties for concrete with short reinforcing fibers on the basis of the finite element method is proposed. The mathematical model takes into account various processes of nonlinear deformation of the concrete matrix under compressive and tensile loads, the possibility of developing the inelastic strains in the concrete matrix and reinforcing fibers and the nonlinear interaction between them. The effect of fiber concentration, various loading surfaces for the material matrix, and the bonding type on the deformation of a composite material is analyzed. Numerical examples of strength analysis are given.     

内埋炸药下超高韧性水泥基复合材料的抗爆性能

为研究超高韧性水泥基复合材料(ultra-high toughness cementitious composites, UHTCC)在内埋炸药爆炸下的抗爆性能和损伤破坏规律,对不同炸药埋深下的UHTCC和高强混凝土(high-strength concrete, HSC)进行了内埋炸药抗爆实验。得到了两种材料靶体的破坏状态,并利用接触爆炸的实验结果计算出了两种材料的抗爆性能参数。结果表明,在相同条件下,UHTCC抗爆性能优于高强混凝土。为了进一步探究UHTCC的抗压强度、抗拉强度以及拉伸韧性对靶体在内埋炸药下抗爆性能的影响,首先,采用改进的K&C模型对炸药埋深为40 mm的超高韧性水泥基复合材料靶体进行数值模拟,模拟结果与实验结果基本吻合,并根据数值模拟的结果得到了爆炸冲击波沿靶体径向衰减速度大于轴向衰减速度这一规律,验证了数值模型的有效性;然后,通过调整改进K&C模型中与抗压强度、抗拉强度以及拉伸韧性相关的参数,数值预测了不同抗压强度、抗拉强度以及拉伸韧性下UHTCC靶体的破坏状态,发现增强UHTCC的韧性可以有效防止靶体发生整体性破坏,增大UHTCC的抗拉强度可以减小靶体迎爆面的开坑直径,增大UHTCC的抗压强度对减小开坑直径效果不明显。     

钢纤维掺量对活性粉末混凝土力学性能的影响

通过实验研究了活性粉末混凝土的基本力学性能(抗压强度、劈拉强度和抗折强度),分析了钢纤维掺量对活性粉末混凝土力学性能的影响,拟合得到了抗折强度与劈拉强度之间的关系表达式。在实验分析的基础上,建立了不同钢纤维体积含量活性粉末混凝土受压应力-应变全曲线的数学表达式。研究结果表明：钢纤维体积含量在1.0%～3.5% 之间时,活性粉末混凝土的抗压强度、劈拉强度和抗折强度均随着钢纤维掺量的增加而增大;当钢纤维体积含量超过3.5% 后,活性粉末混凝土抗压强度下降,劈拉强度略有提高,而抗折强度仍有明显的提高。