Application of scaled boundary finite element method in static and dynamic fracture problems

The scaled boundary finite element method （SBFEM） is a recently developed numerical method combining advantages of both finite element methods （FEM） and boundary element methods （BEM） and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors （SIFs） directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled. The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.

SEMI-ELLIPTIC SURFACE CRACK IN AN ELASTIC SOLID WITH FINITE SIZE UNDER IMPACT LOADING

In this paper a semi-elliptic surface crack problem in an elastic solid of finite size under impact loading is investigated. An analysis is performed by means of fracture dynamics and the finite element method, and a three-dimensional finite element program is developed to compute the dynamic stress intensity factor. The results reveal that the effects of the solid＇s boundary surface, crack surface, material inertia and stress wave interactions play significant roles in dynamic fracture.

A unifying approach in simulating the shot peening process using a 3D random representative volume finite element model

Using a modified 3D random representative volume（RV）finite element model,the effects of model dimensions（impact region and interval between impact and representative regions）,model shapes（rectangular,square,and circular）,and peening-induced thermal softening on resultant critical quantities（residual stress,Almen intensity,coverage,and arc height）after shot peening are systematically examined.A new quantity,i.e.,the interval between impact and representative regions,is introduced and its optimal value is first determined to eliminate any boundary effect on shot peening results.Then,model dimensions are respectively assessed for all model shapes to reflect the actual shot peening process,based on which shape-independent critical shot peening quantities are obtained.Further,it is found that thermal softening of the target material due to shot peening leads to variances of the surface residual stress and arc height,demonstrating the necessity of considering the thermal effect in a constitutive material model of shot peeing.Our study clarifies some of the finite element modeling aspects and lays the ground for accurate modeling of the SP process.

Circulation intensity and axial dispersion of non-cohesive solid particles in a V-blender via DEM simulation

In this study, discrete element method （DEM） was employed to simulate the movement of non-cohesive mono-dispersed particles in a V-blender along with particle-particle and particle-boundary interactions. To validate the model, DEM results were successfully compared to positron emission particle tracking （PEPT） data reported in literature. The validated model was then utilized to explore the effects of rotational speed and fill level on circulation intensity and axial dispersion coefficient of non-cohesive particles in the V-blender. The results showed that the circulation intensity increased with an increase in the rotational speed from 15 to 60 rpm. As the fill level increased from 20% to 46%, the circulation intensity decreased, reached its minimum value at a fill level of 34% for all rotational speeds, and did not change significantly at fill levels greater than 34%. The DEM results also revealed that the axial dispersion coefficient of particles in the V-blender was a linear function of the rotational speed. These trends were in good agreement with the experimentallv determined values reported bv previous researchers.

Enhancement of structure stability and luminescence intensity of LiYF_4:Ln^(3+)nanocrystals

LiYF_4 nanocrystals with tetragonal structure were adopted as the host materials for the phosphors and scintillators owing to the low phonon energy and high optical transparency. LiYF_4：Ln^（3＋）（Ce^（3＋）,Eu^（3＋）） nanocrystals were fabricated by solvothermal method. Under UV excitation, they could emit visible light. In order to improve the luminescence intensity, the method of co-doping LiYF_4 nanocrystals with Sc was adopted. Sc^（3＋） ions could reduce the lattice expansion caused by the doping of Ce^（3＋） or Eu^（3＋） whose ionic radius was larger than Y^（3＋）. Crystal structure of Li（Y,Sc）F_4：Ln^（3＋） kept much more stable and the luminescence intensity could be significantly enhanced when the concentration of Sc was a moderate value. Thermoluminescence was employed to analyze the electron traps in Li（Y,Sc）F_4：Ce^（3＋）. Results suggested that the suppression of the generation of electron traps with the co-doping of Sc contributed to the enhancement of luminescence intensity of LiYF_4：Ce^（3＋）.

Analysis of urban metabolic processes based on input-output method： model development and a case study for Beijing

Discovering ways in which to increase the sustainability of the metabolic processes involved in urbanization has become an urgent task for urban design and management in China. As cities are analogous to living organisms, the disorders of their metabolic processes can be regarded as the cause of ＂urban disease＂. Therefore, identification of these causes through metabolic process analysis and ecological element distribution through the urban ecosystem＇s compartments will be helpful. By using Beijing as an example, we have compiled monetary input- output tables from 1997, 2000, 2002, 2005, and 2007 and calculated the intensities of the embodied ecological elements to compile the corresponding implied physical input-output tables. We then divided Beijing＇s economy into 32 compartments and analyzed the direct and indirect ecological intensities embodied in the flows of ecological elements through urban metabolic processes. Based on the combination of input-output tables and ecological network analysis, the description of multiple ecological elements transferred among Beijing＇s industrial compartments and their distribution has been refined. This hybrid approach can provide a more scientific basis for management of urban resource flows. In addition, the data obtained from distribution characteristics of ecological elements may provide a basic data platform for exploring the metabolic mechanism of Beijing.