Analysis of Dynamic Failure of Plastic Spherical Shells Under Local Impact

Aim To study the dynamic failure of the plastic spherical shell impacted by a missile. Methods The deformation mode of spherical shells was given by introducing isometric transformation. The governing equation of motion of the rigid plastic spherical shell was given by energy balance. This equation was solved by using Runge Kutta method. Results The relationships between the impact force, dimple radius, central point deflection and time were obtained. The response time initial velocity, the maximal impact force permanent initial velocity, the central point deflection initial velocity and the dimple radius initial velocity characteristics were respectively plotted. Conclusion A comparison made between the theoretical results and the experimental ones indicates that the two groups of results are in conformity with each other.

Contribution to the Study and Analysis of the Lightning Aggression on the Wind Turbine

Generally, lightning damage has mainly been to home appliances and telephones, towers and power transmission and generation equipment mal functions and damage due to strikes on power lines. With the adoption of wind power generation equipment, however, lightning damage is also increasing in this area. Through his dimensional characteristics, the wind power system is more exposed in the nature compared to all others systems. Lightning damage is the single largest cause of unplanned downtime in wind turbines, and that downtime is responsible for the loss of countless megawatts of power generation. The wind turbines are important structures, since they can easily attract the wrath of storms hits heights close, they can also capture the most distant. The rotation of the blades may also trigger lightning and result in considerable increase in the number of strikes to a wind turbine unit. Since wind turbines are tall structures, the lightning currents that are injected by return strokes into the turbines will be affected by reflections at the top, at the bottom, and at the junction of the blades with the static base of the turbine. We present our contribution in this paper to study lightning strokes and their effects on the wind turbines with the aim to enrich the work and to suggest more effective means of protection against lightning.

Continuum damage mechanics based modeling progressive failure of woven-fabric composite laminate under low velocity impact

A continuum damage mechanics (CDM) meso-model was derived for both intraply and interply progressive failure behaviors of a 2D woven-fabric composite laminate under a transversely low velocity impact.An in-plane anisotropic damage constitutive model of a 2D woven composite ply was derived based on CDM within a thermodynamic framework,an elastic constitutive model with damage for the fibre directions and an elastic-plastic constitutive model with damage for the shear direction.The progressive failure behavior of a 2D woven composite ply is determined by the damage internal variables in different directions with appropriate damage evolution equations.The interface between two adjacent 2D woven composite plies with different ply orientations was modeled by a traction-separation law based interface element.An isotropic damage constitutive law with CDM properties was used for the interface element,and a damage surface which combines stress and fracture mechanics failure criteria was employed to derive the damage initiation and evolution for the mixed-mode delamination of the interface elements.Numerical analysis and experiments were both carried out on a 2D woven glass fibre/epoxy laminate.The simulation results are in agreement with the experimental counterparts,verifying the progressive failure model of a woven composite laminate.The proposed model will enhance the understanding of dynamic deformation and progressive failure behavior of composite laminate structures in the low velocity impact process.