Xiao Chuan You

Atomistic simulations of tension properties for bi-crystal copper with twist grain boundary

Molecular dynamics simulation using an EAM potential to explore the tension response for a nanowire with a twist grain boundary (GB) is presented in this paper. The relationship between the GB strength and the interface dislocation structure is discussed. For a low angle twist GB, partial dislocations nucleate from the screw dislocation at the GB before yielding and the interface yields at the point when the dislocation networks lose their stability. For a high angle twist GB, the interface yields at the point when the whole interface structure is disturbed and partial dislocations propagate into the grain after the yielding point. In addition, the study provides an insight into the understanding of the atomic mechanism for tension localization at the GB, which is obvious for the high angle twist GB, but indistinct for the low angle twist GB. The results presented may have obvious implications for the nanowire test.

Development of Multi-Scale Computation Framework to Investigate the Failure Behavior of the Materials

With the development of material science, especially as MEMS/NEMS are playing a more and more important role in modern engineering, some mechanical behaviors of materials, e.g., fracture, shear instability, need to be investigated from multidisciplinary perspective. The molecular dynamics (MD) simulations are performed on single-crystal copper block under simple shear to investigate the size and strain rate effects on the mechanical responses of face-centered cubic (fcc) metals. It is shown that the yield stress decreases with the specimen size and increases with the strain rate. Based on the theory of dislocation nucleation, a modified power law is proposed to predict the scaling behavior of fcc metals. In the MD simulations with different strain rates, a critical strain rate exists for each single-crystal copper block of given size, below which the yield stress is nearly insensitive to the strain rate. A hyper-surface is therefore formulated to describe the combined size and strain rate effects on the plastic yield stress of fcc metals.

Fracture Analysis for Damaged Aircraft Fuselage Using Substructure Method

This paper primarily describes the development and application of substructure computational analysis techniques to determine stress intensity factors for the damaged panels subjected to fatigue internal pressure. A program based on substructure analysis technique has been developed for the fracture analysis of curved aircraft panels containing cracks. This program may create whole model which consists of substructure superelements and obtain fracture parameter of the crack by expanding results in superelement automatically. For instance, a typical test curved panel model consists of 7 frames and 8 stringers is calculated. This numerical approach has been validated through comparison between the calculation SIF results and available experimental data of a typical test panel with a longitudinal crack. The technique that has been established here is also applied to the other analysis of a test series of cracked panel with 7 frames and 10 stringers. SIFs of four cracks in it with different crack lengths are obtained efficiently.

Numerical Solution of Elas-Plastic Impact Load of Tube Column

The explicit numerical method is used to trace the impact procedure of the tube columns impacted by a rigid body. The bar and rectangle tube models are both used to simulate the tube column. The elastic and elas-plastic impact load with different mass ratio and impact speed are obtained. The calculation results show that: for elastic models, the bigger the mass ratio and the higher the rigid body speed, the bigger the peak value of elastic impact load; at the same time, the more obvious the reduction effect of local buckling of rectangle tube on the peak value of impact load and the longer the contact time of tube model; so the peak value of impact load of the rectangle tube is not proportional to the rigid body speed. The stress wave in the tube causes a little difference between the load curves of tube model and bar model. For elas-plastic models, the higher the rigid body speed and the smaller the mass ratio, the bigger the peak value of impact load and the longer the contact time. The higher the rigid body speed, the bigger the difference between elastic and elas-plastic impact load peak value due to the expanding of plasticity. Because of the effect of local buckling, the peak value of elas-plastic impact load of rectangle tube is always lower than that of bar.

Analysis of the Load-Carrying Capability of the Casing Plug Joint of Steel Tube Structures Considering the Contact Effect

Nonlinear finite element model analysis of the casing plug joints of steel tubular has been realized by ANSYS software. The law of load-carrying capability and stiffness of joint are separately gained by changing the ratio of length and diameter (R/L) and the ratio of the casing length and the main tube length (l/L). The influence of the casing thickness on the load-carrying capability and stiffness are also discussed. The results indicated that the load-carrying capability and stiffness of the joints both increase with the ratio(R/L) increment and the ratio of the casing length and main tube length (l/L). When the main tube thickness is equal to casing thickness, the load-carrying capacity of joints achieves the most.

Contact and Friction at Nanoscale

Molecular Dynamics (MD) simulations of indentation and scratch over crystal nickel (100) were carried out to investigate the microstructure evolution at nanoscale. The dislocation nucleation and propagation during process were observed preferably between close-packed planes. Dislocation loops are formed under both indentation and scratch process, and indentation and friction energy were transferred to the substrate in the form of phonon of disordered atoms, then part of the energy dissipated and rest is remain in the form of permanent plastic deformation.

One Method of Fluid-Solid Coupled Interaction Simulation

In this article we presented a method of Fluid-Solid coupled simulation via FLUNET and ABAQUS in problems such as Aero/Hydro-Elasticity problems. UDF (user define function) script file in the Fluent software was utilized as the ‘Connecting File’ between FLUENT and ABAQUS for Aero-Elastic computations. Firstly, the fluid field was computed by Navier-Stokes Equation and the structure movement was directly integrated by the dynamics Equation, respectively. Then, the ‘Connecting File’ exchanged the computed data through the fluid and structure’s interface. The next analysis step continued. Analysis of the computed results showed that this coupling method designed for aero-elastic system was feasible and can be also used for other Fluid-Structure Coupling problems.

A Numerical Implementation of a 3D Crystal Plasticity Model for Directionally Solidified Ni-Based Superalloy

Directionally solidified (DS) Ni-based superalloys are extensively used in applications such as turbine blades that require a material with high strength, good creep, and fatigue and corrosion resistance, even at elevated temperature. In this paper, a 3D continuum crystal plasticity model is used to simulate the DS Ni-based superalloy, with application to uniaxial loading in the longitudinal and transverse orientations. Under the Arso (1983) crystal plasticity framework, the constitutive model invokes the kinematic hardening rule, and the yield criterion and flow rule are built on individual slip systems. Compared with the experiment date, we found that this model was able to accurately describe the stress-strain response undergo uniaxial loading, and could also capture the the Bauschinger effect of the cyclic plastic deformation of the DS Ni-base superalloy.