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Foundation ::
Engineering Applications ::
GISS
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GISS
Generalized Impact Stress Software
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SOURCE CODE AVAILABLE
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Determining the elastic impact stresses generated within a struck body is of great concern. However, due to the complex mathematics involved, exact solutions are not feasible for most engineers. The Generalized Impact Stress Software (GISS) was designed to assist engineers in predicting impact stress caused by a variety of impact scenarios.
Benefits and applications of GISS
GISS is straightforward, simple to implement on PC's, user friendly, and can handle a variety of boundary conditions applied to the struck body being analyzed. The program has been verified by confirming results of several textbook cases and known solutions to simple problems. The concept has wide-spread applications including the modeling of motion and transient stress of a spacecraft. Other uses include analysis of the slamming of a piston, fast valve shutoffs, and the play of a rotating bearing assembly. GISS provides a fast and inexpensive analytic tool for stress analysis, and should reduce dependency on expensive impact tests for answers.
How GISS works
The program determines the impact stresses within a one-dimensional body by tracking the acoustic waves generated by the impact, and their reflections and transmissions as a function of position and time. The impact could take place at one end or both ends of the body. The method was originally conceived to solve impact stress of the Liftoff Seal of the High Pressure Fuel Pump of the Space Shuttle Main Engine. The method has been generalized to solve a range of problems and can be applied to any product which could potentially have a high impact load.
The program treats the collision as purely elastic, allowing analyses to be performed for many cases in which permanent deformations are not expected. The results of a simulation could also be used to determine whether the yield stress of the material is exceeded.
Prior to running the program, the struck body to be analyzed must be approximated as a series of one-dimensional elements. Non-rigid body motion of elements is taken into account; thus, compressions and tensile forces at element boundaries after impact are modelled as a function of time. Boundary conditions and loads applied must be specified by the user, along with the pressure reflection coefficients for waves encountering the external boundaries of the system from the interior of the system, and transmission coefficients for waves propagating into the system from the outside environment.
After determining the stresses and particle velocities at each boundary within the system, GISS prints the maximum and minimum stress calculated, with the locations and times where they occur. The output can be presented by printing stress velocity values, and by plotting spatial or temporal stress.
GISS carries the NASA case number MFS-29628. It was originally released as part of the COSMIC collection.
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