高效率、高精度耦合算法及对材料冲击响应特性应用的研究

发布时间：2018-01-23 17:42

本文关键词： 光滑粒子法 FE-SPH耦合算法应力波钢纤维混凝土应变率效应损伤软化效应侵彻　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：作为一种粒子类方法,光滑粒子法在冲击动力学问题的计算中具有其特定的优势,比如它很适合进行大变形、断裂和破碎的处理,并且可以很方便的追踪物质界面等。本文在介绍光滑粒子法一般理论的基础上,研究了核函数和光滑长度在应力波的光滑粒子法模拟中的作用,并采用光滑粒子法完成了对材料层裂的数值模拟。相对素混凝土,钢纤维混凝土具有更高的强度和韧性,适用于军事防护工程和民事建筑,本文对钢纤维混凝土的动态力学性能进行了深入研究,重点在于应变率、损伤和钢纤维含量对混凝土的强度和韧性的影响及其耦合作用,并给出了相应的本构模型。FE-SPH耦合方法结合了光滑粒子法和有限元法的优势,同时具有较高的效率和精度,非常适用于侵彻等冲击动力学问题的模拟,本文深入研究了 FE-SPH耦合算法,重点在于单元-粒子接触算法,并采用二维轴对称FE-SPH耦合程序对钢纤维混凝土侵彻问题进行了数值模拟,验证了耦合算法的可靠性,并研究了钢纤维混凝土的抗侵彻机理。本文的研究内容和创新成果主要包括:本文第2章阐述了光滑粒子法的基本思想,介绍了光滑粒子法中核近似和粒子近似的基本概念。将连续介质力学守恒方程在直角笛卡尔坐标系下进行了光滑粒子离散,研究了利用光滑粒子方法进行连续介质动力学问题计算需要考虑的一些基本问题,包括CFL条件、核函数、可变光滑长度、粒子搜索方法和本构嵌入等。最后引入改进的光滑粒子方法(CSPM),说明了其优越性。在第3章中将通量修正输运法引入光滑粒子法以进行间断面的处理,并对通量修正输运法与人工粘性法的处理效果进行了对比。研究了核函数和光滑长度对光滑粒子法模拟应力波的影响,给出了适用于应力波模拟的核函数和相应光滑长度,并给出了一个代表模拟精度的参数。采用CSPM方法对45#钢的层裂进行了模拟,以实验结果为依据,对比了 FDM和CSPM给出的自由面速度时程曲线,证明CSPM方法可以更好的模拟固体中的应力波传播和层裂问题。第4章首先对钢纤维混凝土的霍普金森杆实验技术进行了研究,重点研究了整形器的原理:减少入射波高频部分,更好的维持恒应变率加载和应力均匀状态。利用霍普金森杆研究了六种不同钢纤维体积比混凝土的动态力学行为,分析了应变率和钢纤维体积比对混凝土强度、峰值应变和能量耗散的影响,探讨了应变率效应和钢纤维增强效应的机理。在分析总结了前人有关混凝土应变率效应方面成果的基础上,提出了一个新的动态增强因子公式,并对动态增强因子公式嵌入本构的方式进行了修正。基于上述实验和理论分析结果,提出了一个新的混凝土粘塑性损伤软化本构模型,此模型在物理上更加严谨,在处理方法上更加简洁明了,并且能够很好的反映混凝土材料的应变率效应、应变率突跃效应、卸载非线性回滞效应和损伤软化效应等各种力学行为;在对新本构模型进行拟合的过程中,发展了一种逐步积分最小二乘法,并采用这种方法拟合出本构关系和损伤演化方程的全部参数,方法简洁有效,适用于一切含损伤的材料本构关系参数的确定。最后,第5章对有限元-光滑粒子耦合算法(FE-SPH)进行了研究和改进,重点是有限元单元-光滑粒子的转化算法、有限元单元间的接触算法、光滑粒子间的接触算法和有限元单元-光滑粒子间的接触算法。基于本文对钢纤维混凝土动态力学性能的研究成果,在二维轴对称FE-SPH耦合程序中引入钢纤维混凝土的本构模型,对45#钢弹体侵彻钢纤维混凝土的过程进行了数值模拟;对比了实验和数值计算得到的剩余速度,验证了程序的有效性;给出了不同时刻的侵彻图形,分析了钢纤维混凝土的抗侵彻机理,认为加入钢纤维增强了混凝土的抗压强度、抗拉强度和韧性,并可有效阻止材料损伤裂纹的扩展,这些因素都提高了钢纤维混凝土的抗侵彻能力。
[Abstract]:As a kind of particle method, SPH method has its particular advantages in the calculation of impact dynamics problems, such as it is suitable for large deformation, fracture and fragmentation, and can easily track the material interface. Based on the general introduction of SPH theory, study the role of nuclear function and the smooth length in smoothed particle method to simulate the stress wave in, and by SPH method to complete the numerical simulation of spallation. Compared to plain concrete, steel fiber reinforced concrete has higher strength and toughness, suitable for military protection engineering and civil construction, the dynamic mechanical properties of steel fiber reinforced concrete conducted in-depth research, focuses on the influence of strain rate, and damage of steel fiber content on the strength and toughness of concrete and its coupling effect, and gives the corresponding constitutive model of.FE-SPH coupling method A combination of SPH method and finite element method, the efficiency and it has a high precision. The simulation is very suitable for dynamic problems of penetration impact, this paper studies the FE-SPH coupling algorithm, focuses on the unit - particle contact algorithm, and the two-dimensional axisymmetric FE-SPH coupling procedure to simulate the steel fiber reinforced concrete the penetration problem, verify the reliability of the coupling algorithm, the anti penetration mechanism of steel fiber reinforced concrete and research. In this paper, the research contents and innovations include: the second chapter elaborates the thought of SPH method, introduces the basic concepts of SPH method in approximation and continuum mechanics. The conservation equations in Cartesian coordinates of Descartes smooth particle discrete, studied the continuum dynamics calculation needs to consider the use of SPH method Some basic problems, including CFL, kernel function, smoothing length, particle search method and constitutive embedding. Finally the introduction of improved SPH method (CSPM), shows its superiority. The third chapter will be in flux corrected transport method is introduced into the SPH method for processing discontinuity, comparison and the treatment effect of the flux corrected transport method and artificial viscosity method. The kernel function and the smoothing length simulated the stress wave effect of SPH method, are given for the kernel function of stress wave simulation and the corresponding smooth length parameter is given a representative simulation accuracy by the method of CSPM. 45# steel layer crack was simulated on the basis of experimental results, comparing the free surface velocity of FDM and CSPM given time curve, simulation of solid proved that CSPM method can better the stress wave propagation and spall problems. The fourth chapter firstly Hopkinson test technology of steel fiber reinforced concrete is studied, focusing on the principle of pulse shaper: reduce the incident wave frequency components, to better maintain the constant strain rate loading and uniform stress state. Using the Hopkinson bar on six different steel fiber volume ratio of the dynamic mechanical behavior of concrete, strain rate and analysis the steel fiber volume ratio and concrete strength, peak strain and the effect of energy dissipation, discusses the mechanism of enhancement effect and strain rate effect of steel fiber are summarized. Based on the analysis of previous studies on the strain rate effect of concrete achievements, put forward a new dynamic enhancement factor formula, and the dynamic enhancement factor formula embedded constitutive the method is modified. The experimental and theoretical analysis based on the results, proposed a new concrete viscoplastic damage softening constitutive model, this model is physically more In the processing method is more rigorous, concise, and can well reflect the strain rate effect, strain rate effect, unloading nonlinear hysteresis effect and damage softening effect of various mechanical behavior; in the process of the new constitutive model were fitted in the development of an integral least square method. By fitting a constitutive relation and damage evolution equation of all parameters of this method, method is simple and effective, suitable for all materials with damage to determine the constitutive relation parameters. Finally, the fifth chapter of the finite element smoothed particle coupling algorithm (FE-SPH) is studied and improved, the focus is on finite element - transformation algorithm smooth particle contact algorithm, finite element contact between the smooth algorithm between particles and finite element - smooth inter particle contact algorithm. In this paper, the dynamic mechanical properties of steel fiber concrete based on The research results, the constitutive model of steel fiber reinforced concrete is introduced in the two-dimensional axisymmetric FE-SPH coupling in the program, the process of 45# steel projectile penetrating steel fiber concrete was simulated; the residual velocity is calculated by experimental and numerical comparison, verify the effectiveness of the program; given penetration graphics at different times. Analysis of the anti penetration mechanism of steel fiber reinforced concrete, adding that the steel fiber reinforced concrete compressive strength, tensile strength and toughness, and can effectively prevent the damage of crack propagation materials, these factors have increased the steel fiber concrete anti penetration ability.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB12

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