Applied Mechanics and Materials Vols. 117-119

Abstract: The Green quasifunction method(GQM) is employed to solve the bending problem of clamped orthotropic thin plates with trapezoidal boundary shape. Firstly the governing differential equation of the problem is reduced to the boundary value problem of the biharmonic operator, and then it is reduced to the Fredholm integral equation of the second kind by Green’s formula. A Green quasifunction is established by using the fundamental solution and the boundary equation of the problem. This function satisfies the homogeneous boundary condition of the problem. The irregularity of the kernel of the integral equation is overcome by choosing a suitable form of the normalized boundary equation. A numerical example demonstrates the feasibility and efficiency of the proposed method, and it is a novel mathematical method.

Abstract: One of tasks of fracture mechanics analysis is to get J resistance curves and fracture toughness of ductile materials. Based on the dimensionless theory, a modified Spb method from the load separation method was proposed. In order to apply load separation method to analysis the fracture toughness of a material from its test data, the testing application J-LSS (J resistance curve-Load Separation Software) has been developed by using visual basic (VB) language and was applied to obtain the fracture toughness values of Cr2Ni2MoV rotor steel and 316L stainless steel. Additionally, the differences between the traditional normalization method and the modified S^pb method in analyzing fracture toughness through J-LSS were discussed. The modified S^pb method presented in the paper is more available and can be recommended to renew the current material fracture toughness standard test.

Abstract: Nowadays concrete-filled steel tube is widely used as a building structure. For concrete added with expanding agent, certain stresses will be produced during the solidification process. This is due to the fact that concrete solidification can not be conducted freely by the constraints of the steel tube. An algorithm of computational procedure for concrete chemical solidification stresses has been proposed, and an incremental calculation formula is derived in this paper. In addition, a testing facility has been designed and conducted to measure the circumferential strain during the solidification process. The calculation results are in good agreement with experimental data. The results show that the chemical solidification stress of concrete filled steel tube is not only related to the geometrical size of the structure and expanding rate of the concrete, but also related to the time history of expansion process. It is found that the stresses will become larger if the concrete expansion occurs later under the condition of identical expansion rates of the concretes.

Abstract: This paper presents a three-dimensional viscoelastic model to study the interactions of a penny-shaped interfacial crack and a center of dilatation in the infinite viscoelastic bimaterial, which can model the rock fracture subjected to stress and thermal dilatation during some engineering process. A distinct issue associated with the present work is the incorporation of viscoelastic behavior of bimaterial. The proposed problem is first transformed into the Laplace space, and the solution in the transform space is obtained by decomposing the original problem into two auxiliary problems: (I) a center of dilatation near a bimaterial interface (no crack); and (II) a penny-shaped interfacial crack subject to internal tractions that cancel out those induced in auxiliary problem (I). The mode I, II and III stress intensity factors (SIFs) in the time domain are obtained with the inverse Laplace transform.

Abstract: Brittle media, such as rock mass, usually contain a great number of joints or cracks, which lead to varying mechanical properties and failure behaviors of different rock masses. In this paper, the DDARF method is adopted to simulate the crack initiation, propagation, coalescence and failure process in rock masses prefabricated with the different crack number and spacing under loading. The corresponding stress-strain curves and strength envelope are obtained. The parameters are applied in a case study. The differences in the failure behaviors of the intact and jointed rock masses after cavern excavation are analyzed and compared.

Abstract: In this work, a nondimensional load separation conforming to similarity principle was proposed. Based on this new principle, similarity simulation of the physical phenomenon between the prototype sample and the dimension-changed model sample can be implemented. Then, a modified separation parameter S_pb method was developed, which can absolutely eliminate the effect of referencing blunt cracked specimen on the instantaneous crack length estimation of the sharp cracked specimen, and the forced blunt-corrected initial crack length and the final crack length are recommended as the calibration points for J-resistance curve estimation. Finally, the modified S_pb method is successfully applied in the J-resistance curve estimation of two steels with CT and SEB specimens, respectively.

Abstract: A Finite-element parallel computing frame—PANDA and its implementation processes are introduced. To validate the parallel performance of the PANDA frame, a series of tests were carried out to obtain the computing scale and the speedup ratios. First, three different large-scale freedom degree models (i.e. 1.83 million, 7 million and 10 million) of a typical engineering clamp were created in MSC.Patran and were translated into geometric-grid files that can be identified in PANDA frame. Second, Linear static parallel computations of the three cases were successfully carried out on large parallel computers with preconditioned conjugate gradient methods in PANDA frame. The speedup ratios of the three cases were obtained with a maximum process number of 64. The results show that the PANDA frame is competent for carrying out large-scale parallel computing of 10 million freedom degrees. In each scale，the parallel computing is nearly linearly accelerated along with the increase of process numbers, moreover, a super-linear speedup appears in some cases. The speedup curves show that the linear degree increases when the computing scale enlarges. The influence of different communication bandwidths on computing efficiency was also discussed. All the testing results indicate that the PANDA frame has excellent parallel performance and favorable computing scalability.

Abstract: Following the modified Gurson model in meso-mechanics, the models with spherical holes are established by the assumption which the matrix meets the two-parameter elliptic yield condition. The macroscopic stress expression which contains micro structure parameters and the material equation of yield surface are given by the upper bound theorem of plastic limit analysis. The parameters of the matrix material and damage(porosity) which impact on macroscopic yield surface equation are discussed. These works provide theory foundations for material damage and design.

Abstract: A development system on gear parametric design and check based on Pro/E4.0 and Visual C++ was built in the paper. The system included three modules: the standard spur gear, helical gear and bevel gear. According to the human-machine interface, the 3D parameterization model and 2D engineering drawing of the gear were achieved. And according to the actual situation of the load, the gear was automatically calculated, checked and output results. The system was adjusted successfully

Abstract: Based on micro structure of Ni-based single crystal superalloy, a γ/γ’ two-phase unit cell finite element model was established, and its cyclic stress-strain was simulated under tension/torsion cyclic loading. A low cycle fatigue (LCF) life prediction model of single crystal superalloy was proposed by using cyclic plasticity strain energy as a parameter based on energy dissipation theory. Calculation results of macro finite element model and γ/γ’ two-phase unit cell micro finite element model, and multiaxial LCF test data of CMSX-2 Ni-based single crystal superalloy along [001] orientation were applied to fit the LCF life model by multiple linear regression. The results show that the unit cell model not only reflects the microstructure characteristics of single crystal Ni-based superalloy, but also is better than the macro model in accuracy of analysis, and greatly improve the accuracy of fatigue life prediction. Almost test data fall into the factor of 2.0 scatter band.