共查询到19条相似文献,搜索用时 125 毫秒
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应用岩石损伤破裂过程渗流-应力耦合分析系统F-RFPA^2D,模拟分析了含单孔岩石试样的水压致裂过程。通过对水力压裂过程中裂纹的萌生、扩展、渗透率演化规律及渗流——应力耦合机制的模拟分析,初步揭示了岩石水压致裂过程的失稳力学行为。进一步对比分析不同围压作用下的岩石裂纹的渐进扩展和破裂过程,数值模拟结果和实验结果具有较好的一致性。 相似文献
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本文详细阐述和讨论了岩石裂纹分别在拉应力、剪应力作用以及拉剪应力共同作用下的扩展、闭合以及裂纹面上应力的传递问题。利用Barenblatt内聚力模型分析了裂纹顶端内聚力和裂纹面间摩擦力对裂纹扩展的阻尼作用, 讨论了在裂纹扩展过程中裂纹面间的接触条件、接触状态对裂纹扩展的影响。 相似文献
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本文详细阐述和讨论了岩石裂纹分别在拉应力、剪应力作用以及拉剪应力共同作用下的扩展、闭合以及裂纹面上应力的传递问题。利用Barenblatt内聚力模型分析了裂纹顶端内聚力和裂纹面间摩擦力对裂纹扩展的阻尼作用。讨论了在裂纹扩展过程中裂纹面间的接触条件、接触状态对裂纹扩展的影响。 相似文献
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压坯断裂性能参数的准确测定对压坯裂纹损伤预测分析至关重要.本文采用圆弧型加载方式的巴西圆盘实验对两种金属粉末(H(o)gan(a)s ASC 100.29和H(o)gan(a)s Distaloy AE)压坯的断裂性能参数进行研究.利用高清摄像机对实验过程进行拍摄,将金属粉末压坯从变形到完全断裂破坏的全过程进行详细地分析描述.结合相关理论研究及数值分析计算,提出压坯断裂性能参数包括断裂韧度Kk和断裂能量Gc的确定方法.将不同相对密度的压坯试样用于试验分析计算,得出金属粉末压坯断裂性能参数Kk和Gc与相对密度的函数方程. 相似文献
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粉末注射成形坯冷凝过程产生应力开裂的计算机预测 总被引:1,自引:0,他引:1
用有限差分法模拟了粉末注射成形简单坯件冷却凝固过程内应力的生成,以预测坯件内是否产生裂纹,并将计算结果与文献实验结果作了比较;同时,作者还简要探讨了模型中引入误差的主要原因。 相似文献
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针对环形薄壁类粉末冶金零件压坯的残余应力进行分析,采用修正的Drucker-Prager Cap弹塑性本构模型对金属粉末压坯压制、卸载和脱模过程进行数值模拟,同时考虑不同零件压坯几何参数(高径比和厚径比)以及压制工艺条件(摩擦条件和脱模角度)对压坯内残余应力的影响.研究结果表明,压坯脱模后的残余应力分布规律是压坯侧表面出现明显的压应力层,内部为拉应力区域,且越靠近压坯中心值越小.随着高径比和厚径比的增加,其残余应力逐渐减小;随着摩擦系数的增加,压坯表面的轴向残余压应力不断增大且压坯内部的拉应力也不断加大;适当增加脱模角度有利于压坯内应力释放而减小残余应力.通过正交模拟试验及方差分析可知,厚径比和脱模角度对金属粉末成形脱模后压坯残余应力影响更为显著. 相似文献
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奥钢联林茨公司为了生产厚355 mm、宽1 600 mm的特厚板坯,升级改造了第3炼钢厂的5号连铸机。该弧形连铸机最初设计生产的板坯最大厚度为285 mm,弧形半径为10 m,配置了直结晶器,对带液芯的铸坯进行弯曲和矫直。在这种类型的连铸机上生产厚度为355 mm铸坯的主要问题是板坯的几何形状。由于弯曲时铸坯角部变形,铸坯可能出现小的皮下热裂纹。为了模拟在浇注过程中结晶器液面到弧形段开始位置的连铸板坯变形,使用ABAQUS软件开发了有限元3D模型。该热力学模型结合材料的粘弹性定律计算浇注过程凝固坯壳的张应力和压应力。据观测,模拟计算出的浇注过程凝固坯壳的张应力和压应力的分布与小热裂纹的外形大致相符。还将抽样测量的板坯几何形状与有限元计算结果进行了比较。采用热机建模计算结果,通过优化结晶器锥度和强化出结晶器后铸坯窄面的冷却,改进了板坯的几何形状。 相似文献
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Simulation of Crack Propagation in Asphalt Concrete Using an Intrinsic Cohesive Zone Model 总被引:1,自引:0,他引:1
Seong Hyeok Song Glaucio H. Paulino William G. Buttlar 《Canadian Metallurgical Quarterly》2006,132(11):1215-1223
This is a practical paper which consists of investigating fracture behavior in asphalt concrete using an intrinsic cohesive zone model (CZM). The separation and traction response along the cohesive zone ahead of a crack tip is governed by an exponential cohesive law specifically tailored to describe cracking in asphalt pavement materials by means of softening associated with the cohesive law. Finite-element implementation of the CZM is accomplished by means of a user subroutine using the user element capability of the ABAQUS software, which is verified by simulation of the double cantilever beam test and by comparison to closed-form solutions. The cohesive parameters of finite material strength and cohesive fracture energy are calibrated in conjunction with the single-edge notched beam [SE(B)] test. The CZM is then extended to simulate mixed-mode crack propagation in the SE(B) test. Cohesive elements are inserted over an area to allow cracks to propagate in any direction. It is shown that the simulated crack trajectory compares favorably with that of experimental results. 相似文献
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AbstractPowder die compaction is modelled using the finite element method and a phenomenological material model. The Drucker–Prager cap model is modified with the goal to describe the formation of cracks during powder transfer, compaction, unloading, and ejection of the parts from the die. This is achieved by considering the cohesive strength and the cohesion slope, which characterise the current strength of the powder compact in the Drucker–Prager model, as state dependent variables. Evolution equations are formulated for these variables, so that the strength increases by densification and decreases by forced shear deformation. Some of the parameters appearing in the evolution equations are determined from measured green strength values. An iron based powder (Distaloy AE) is used for the experiments. Examples are shown to demonstrate that the density distribution can be calculated accurately as compared with an experiment, that cracking can be modelled at least qualitatively correctly, and that the compaction of complex 3D parts can be simulated. 相似文献
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Ductility was determined in experimental four‐point bending tests of smooth specimens of tool steel. The tool steels had different contents of carbides and carbide sizes and with a hardness of approximately 60HRc. Two of the materials tested were produced powder metallurgically, one was spray formed and one was conventionally uphill ingot cast. Carbide size distribution analysis was performed on planar polished sections of each material. Correlation between carbide microstructure and ductility performance was obtained. The fracture mechanisms were investigated with fractography. A 3D FE‐model was used to simulate the four‐point bending tests and thereby analyse the matrix flow curve. Also the strain at failure was analysed for each material when simulations were performed based on experimental data. SEM‐images of the materials carbide microstructure were used to create 2D FE‐models. The models simulated crack initiation and propagation by removing elements in the steel matrix as the plastic strain reached a critical level. With three variants, simulations of crack initiation and propagation at carbides were investigated. That was carbides with no cohesion to matrix, carbides fixed to the matrix and carbides with internal cracks. Comparison of strains at failure for the 2D and the 3D FE‐models showed good correlation. 相似文献
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X. J. Xin P. Jayaraman G. Jiang R. H. Wagoner G. S. Daehn 《Metallurgical and Materials Transactions A》2002,33(8):2649-2658
The explicit finite element method (FEM) has been used to simulate the compaction of monolithic and composite powder compacts.
It is concluded that with the proper FEM model and appropriate loading speed, explicit FEM can be used to simulate powder
compaction with satisfactory accuracy. The simulated pressure-density curves for four periodic powders are in reasonable agreement
with experiments using model powders consisting of rods. The effects of the friction coefficient, Poisson’s ratio, and hardening
exponent on densification are investigated. Powder compacts consisting of particles with larger Poisson’s ratio, larger interparticle
friction, and larger hardening exponent are more diffcult to consolidate in monotonic compaction. Compaction of multiparticle
arrays is also simulated to assess the effects of packing randomness and particle rearrangement. The results reveal that local
packing details affect the compaction behavior and, in general, the more heterogeneous the powder mixture is, the more difficult
it is to consolidate the powder compact. Networking of hard particles significantly increases the densification resistance. 相似文献
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An isotropic model for creep damage of concrete under uniaxial compression is proposed, where the combined effect of nonlinear viscous strain evolution and crack nucleation and propagation at high stress levels is considered. Strain splitting assumption is used for creep and damage contributions. Creep is modeled by a modified version of solidification theory. As usual in the modeling of damage of concrete, a damage index based on positive strains is introduced. As particular cases, the proposed model reduces to linear viscoelasticity for long time low stress levels whereas, for very high stresses, tertiary creep causing failure at a finite time can be described. The effect of strength variation with time is also included. The model is numerically implemented to perform time integration of nonlinear equations by means of a modified version of exponential algorithm. The model is validated through comparison with experimental results. Some numerical examples are also presented, where the roles of concrete ageing and strength variation with time are investigated. 相似文献
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F. Bradley A. C. D. Chaklader A. Mitchell 《Metallurgical and Materials Transactions B》1987,18(2):371-380
The fracture behavior of refractory components heated from one end is simulated using a twodimensional constant heating rate
thermoelastic model and the maximum principal tensile stress fracture criterion. Dimensionless graphical relationships that
can be used to predict location of fracture and orientation of cracking are presented. Dimensional analysis and the finite
element numerical method are used to develop a general solution for the total strain energy. Based on the premise that extent
of crack propagation is directly related to available strain energy at fracture and inversely related to the surface energy
per unit area, the solution for total strain energy is used to derive a damage resistance parameter useful for the design
and selection of refractory components that accounts for material properties, geometry, and heating and cooling rate. Model
predictions of location of fracture, orientation of cracking, and extent of crack propagation are in general agreement with
experimental results previously reported in the literature. Limitations of the two-dimensional thermoelastic model are discussed. 相似文献
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将爆破损伤视为爆破应力波和爆生气体压力共同作用的结果,分别考虑不同的地应力条件(侧压力系数0.5、1和2,竖直方向地应力5 MPa和10 MPa)和节理角度(30°、45°、60°和90°),开展含节理岩体双孔爆破过程的数值模拟,研究爆生裂纹萌生—扩展—贯通过程的演化规律.无节理时,初始应力场对爆生裂纹的扩展具有一定的导向作用,裂纹扩展主方向趋于最大地应力方向.节理对裂纹的扩展方向具有一定的影响,节理角度为30°时,爆生裂纹与节理面连通,形成典型的‘之’字形断裂.节理对裂纹萌生和扩展具有明显的促进作用,有利于孔壁上下侧裂纹沿竖直方向的扩展. 相似文献