Graduate Thesis Or Dissertation
 

Development of a method to determine the penetration velocity of a powder actuated fastener

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  • The purpose of this work was to design a system for measuring the velocity of a powder actuated fastener or drivepin during penetration. This system would provide a tool for further investigation into drivepin penetration characteristics. The main characteristic of interest is the instantaneous acceleration from which the forces on the drivepin can be determined. This acceleration was determined by designing a transducer whose output is drivepin position versus time and calculating the instantaneous velocity and acceleration, graphically and numerically, from these data. A powder actuated drivepin is a special nail-like pin which is driven into hard materials by the force of a charge of gunpowder. The powder actuated tool is similar to a pistol except the projectile is the drivepin and the charge is in a separate brass jacket. The penetration velocity previously referred to is the velocity spectrum during the total time the drivepin is in motion. Some of the transducers that were considered are listed with comments which affected their evaluation. Among these transducers, the linear resistance potentiometer was selected for this measuring system. It has the following characteristics: a. Simplicity b. High frequency response c. Good linearity d. Marginal mechanical strength e. Low, but sufficient output With this potentiometric transducer, an oscilloscope and camera were added to provide a time base and a permanent record. The test results or data are recorded as photographs of the oscilloscope trace. Various techniques for differentiating these data are discussed. These techniques include graphical, approximating polynomials by the method of finite differences, and best fitting curve by the method of least squares. Additional mathematical presentations are included to show the measuring system's linearity and frequency response and the equations of motion of the powder actuated tool and piston. The final configuration of the measuring system is a battery energized slide wire mounted inside a barrel and a collector mounted opposite the slide wire. The head of the drivepin contacts the slide wire during penetration and transfers this voltage to the collector. The collector voltage is fed into an oscilloscope for display as a function of time. The external trigger signal for starting the display is obtained from the first motion of drivepin as it passes through a metal foil on the surface of the material to be penetrated. This potentiometric measuring system was found to be adequate for the purpose intended. However, some mechanical modifications are recommended.
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