Ultra High-Speed Impact simulated with FEM


Problems of Space Debris and
Ultra High-Speed Metal Cutting Processes, etc.



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Damage of impacted surface strongly depends on an impact speed when an object collides with other object at a high speed (ultra high-speed). Stress increment generated at an impacted surface depends on a mass density of the object, a velocity of stress wave in the object and a change of a particle velocity of the object. An impact stress does not depend on the volume of the object. Of course, the forces acting on the impacted surface depend on the area of the impacted surface. By considering a relationship between the stress wave and the impact stress, we can easily image that a catastrophic damage must occur when a space debri collides with a space station, though the volume of a space debris are too small to capture by a radar. Because the impact speed is so fast. It is thought that the speed reaches about from 8 to 16 km/s.

If you will go to astrospace, you have to watch out a space debris not to recieve it.

A speed of an elastic wave is faster than that of plastic wave. The speed of an elastic wave (sonic wave) for a general structual metal is about 5000 m/s. It depends of Young's modulus and a mass density. While, the plastic wave speeds, which depends on the slope of the stress-strain curve of the material (flow stress characteristic), are about from 1/10 to 1/100 of the elastic wave speed, if the sploe of the stress-strain curve is convcave down.

When a collision speed is faster than a plastic wave speed or elastic wave speed, the shock wave will be generated. Since it is quite difficult to conduct a crash test at ultra high-speed, numerical simulation technique is useful to predict the phenomena on the collision. It is worth to note that it is indispensable to introduce the detail material properties to predict the phenomena in detail.

The example of the results simulated by using of a FEA (Finite Element Analysis) are shown below. The simulation were performed with a dynamic thermo elastic plastic FEA (RdynFem) that I have developed. A projectile collides with a target at an ultra high-speed.

result1

This animation is shown the stress distribution simulated.

resylut2

This animation is shown the temperature distribution simulated.

In theses case, the boundary conditions of upper, bottom and right hand side surfaces are fixed contitions in the right hand side body. The particle velocity on the surface is zero.

result3 result4

Left hand side figures are shown the stress distribution, while right hand side figures are shown the temperature distribution simulated.

In theses case, the boundary conditions of upper, bottom and right hand side surfaces are free contitions in the right hand side body. The stress perpendicular to the surface is zero.

These results were simulated with the FEM software "RDynFem" that has been developed by Dr.Jun Shinozuka.


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