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。     

循环荷载下硅藻土应变和孔压特性

针对嵊州硅藻土的高结构性及地基应力场的复杂多变，应用GDS 动三轴仪进行不同围压和不同循环应力比下的不排水循环加载试验，分析应力-应变滞回曲线演化、应变累积特性、回弹特性及孔压特性．研究表明：循环应力比及围压对原状硅藻土应变和孔压的发展规律影响明显，随着循环应力比的增加，滞回曲线由线性状态转变为非线性状态，且逐渐向x 轴倾斜，累计应变和回弹应变都随着循环应力比的增加而略微增加，但总应变基本小于2 %；残余孔压比随循环应力比增大而增大，范围为0.1~0.5．并且存在一个临界循环应力比，其值随有效围压的增大而减小，范围为0.8~2.2，当循环应力比大于该值时，试样内部产生一个破裂面迅速发生破坏．在相同循环应力比下，试样的应变随着有效围压的增大而增大．     

应变率历史对应力应变曲线的影响

利用普通SHPB实验系统、双试件SHPB实验系统，对一特种钢材进行了不同应变率历史的动态压缩实验，获得了不同应变率历史所对应的应力应变曲线。通过量化平均应变率相同的情况下不同应变率历史所对应的应力应变曲线的差别，以及量化应变率历史的恒定程度，初步分析了应变率历史对应力应变曲线的影响。研究结果表明:特别是在较高平均应变率下，应变率历史对试件材料的应力应变曲线有明显的影响，在材料动态本构关系研究中应当考虑应变率历史的影响。     

Constitutive relationship of brittle rock subjected to dynamic uniaxial tensile loads with microcrack interaction effects

A micromechanical model is proposed to describe both stable and unstable damage evolution in microcrack-weakened brittle rock material subjected to dynamic uniaxial tensile loads. The basic idea of the present model is to classify the constitution relationship of rock material subjected to dynamic uniaxial tensile loads into four stages including some of the stages of linear elasticity, pre-peak nonlinear hardening, rapid stress drop, and strain softening, and to investigate their corresponding micromechanical damage mechanisms individually. Special attention is paid to the transition from structure rearrangements on microscale to the macroscopic inelastic strain, to the transition from distribution damage to localization of damage and the transition from homogeneous deformation to localization of deformation. The influence of all microcracks with different sizes and orientations are introduced into the constitutive relation by using the statistical average method. Effects of microcrack interaction on the complete stress-strain relation as well as the localization of damage for microcrack-weakened brittle rock material are analyzed by using effective medium method. Each microcrack is assumed to be embedded in an approximate effective medium that is weakened by uniformly distributed microcracks of the statistically-averaged length depending on the actual damage state. The elastic moduli of the approximate effective medium can be determined by using the dilute distribution method. Micromechanical kinetic equations for stable and unstable growth characterizing the ‘process domains’ of active microcracks are taken into account. These ‘process domains’ together with ‘open microcrack domains’ completely determine the integration domains of ensemble averaged constitutive equations relating macro-strain and macro-stress. Theoretical predictions have shown to consistent with the experimental results.     

A stabilized complementarity formulation for nonlinear analysis of 3D bimodular materials

Bi-modulus materials with different mechanical responses in tension and compression are often found in civil, composite, and biological engineering. Numerical analysis of bimodular materials is strongly nonlinear and convergence is usually a problem for traditional iterative schemes. This paper aims to develop a stabilized computational method for nonlinear analysis of 3D bimodular materials. Based on the parametric variational principle, a unified constitutive equa-tion of 3D bimodular materials is proposed, which allows the eight principal stress states to be indicated by three para-metric variables introduced in the principal stress directions. The original problem is transformed into a standard linear complementarity problem (LCP) by the parametric virtual work principle and a quadratic programming algorithm is developed by solving the LCP with the classic Lemke’s algo-rithm. Update of elasticity and stiffness matrices is avoided and, thus, the proposed algorithm shows an excellent conver-gence behavior compared with traditional iterative schemes. Numerical examples show that the proposed method is valid and can accurately analyze mechanical responses of 3D bimodular materials. Also, stability of the algorithm is greatly improved.     

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.     

基于能量耗散的岩石脆性评价方法

脆性评价是页岩气钻井以及压裂工艺设计的重要环节.然而,现今对于脆性的定义十分模糊,且脆性评价的方法没有成熟的理论作为支撑.本文以岩石应力应变关系为基础,采用能量法来进行储层岩石脆性评价.根据断裂力学裂纹尖端的非线性场理论,以前端区作为尖端特殊的屏蔽构型,来描述储层岩石在断裂过程中能量的耗散. 通过计算本征内聚力与前端区稳态阻力比值来表征储层岩石的脆性指数. 研究表明,能量耗散相对越大,岩石的脆性指数越低,其塑性特征表现得越明显. 基于能量耗散的储层岩石脆性评价是分析岩石力学特性的重要内容,也为压裂选层提供了重要依据.      

Solution of contact problems on the basis of a refined theory of plates and shells

Solutions of contact mixed boundary-value problems for a plate and for a cylindrical shell are given. These solutions are obtained with the use of equations for shells constructed by expanding solutions of elasticity theory equations with respect to the Legendre polynomials. Results of numerical simulations of the stress state in the vicinity of points with changing conditions on the frontal faces of the shell are presented. The results obtained are compared with analytical solutions of elasticity theory problems and with solutions obtained on the basis of the classical equations of the shell theory. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 169–176, September–October, 2008.     

橡胶粒子改性水泥混凝土的变形性能及其受力分析

研究橡胶粒子改性水泥混凝土的变形性能和受力情况,并对橡胶粒子的影响机理作了初步探讨。结果表明,掺加橡胶粒子可明显改善混凝土的干缩变形性能、韧性及极限变形能力,同时会降低混凝土的抗折、抗压强度。橡胶粒子对混凝土早期(3 d)抗折、抗压强度影响较小,但对混凝土28 d抗折     

On two approaches to determining the axisymmetric elastoplastic stress-strain state of laminated shells made of isotropic and transversely isotropic bimodulus materials

The paper compares two approaches to determining the axisymmetric elastoplastic stress-strain state of laminated shells made of isotropic and transversely isotropic materials with different elastic moduli in tension and compression. The approaches use different nonlinear constitutive equations describing the elastic deformation of the transversally isotropic bimodulus materials. Both approaches employ the theory of deformation along paths of small curvature and the Kirchhoff-Love hypothesis for the whole laminate to describe the deformation of the isotropic materials. The problem is solved by the method of successive approximations. The solutions of specific problems obtained by the two approaches are analyzed __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 6, pp. 59–69, June 2008.