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ATA Shock Test Machine

An Executive Summary of the Project is Here

Overview:

ATA Engineering, Inc. is an engineering consulting firm that emphasizes in analysis and test-driven design solutions. ATA needs a method to provide high gravitational accelerations (g) to test samples. The company has a solenoid shaker as their current system, but this is limited to high amplitude only for frequencies within a certain band. Therefore, they have asked students to develop and build a machine to transmit controlled, transient shock pulses to test articles for environmental shock testing. To ensure that the machine can achieve shock pulses that their current shaker system cannot achieve, they have asked that the machine be tunable to adjust the pulse length and the acceleration level of the induced shock.

A typical shock test has the following objectives:

1. Measure transmissibility across isolation systems

2. Measure force, strain, displacement, or acceleration on the test article

3. Perform a direct assessment of damage using visual inspection or a functionality check

Objectives:

ATA needs a machine that generates the following shock profiles of specific amplitude and pulse length:

Table 1: Acceptance Test Pulse Shapes

The requirements for the machine are:

• It can test samples up to 61 cm x 61 cm x 61 cm (2' x 2' x 2') samples, up to 34 kg (75 lbs).

• It can achieve the given pulse profiles in Table 1 with a measurable repeatability to within 10% of the specified amplitude and 10% of the specified pulse width.

• Shock impulse shape must be approximately be a half-sine wave

  • This means that all major motion is in one direction (NO negative acceleration)

  • Any ringing that occurs after the approximate half-sine wave has been achieved can be ignored

Final Design:

An impactor swinging on the large steel frame seen below was created in order to produce the energy required to create the above pulse profiles. The impactor is a series of steel plates bolted together. The plates can be added or removed to adjust mass of the impactor. A winch on the back end of the frame allows for easy lifting of the impactor and the drop height can be adjusted to control impact velocity. The maximum drop height is 2 meters. A threaded impact tip is fastened to the front face of the impactor and is manufactured to have a specific stiffness. This stiffness can be adjusted by machining different impact tips and controls the duration of the impact pulse.

The test article of interest is bolted to the aluminum fixture plate. The fixture plate receives the pulse provided by the impactor and transmits the pulse into the test article through the fixture bolts. The fixture plate sits on top of a foam stack. The foam has a low natural frequency and is intended to act as a free boundary so that the pulse into the excitation plate is uncorrupted by outside fixtures for longer than the duration of the impact pulse. The excitation plate and foam stack sit on a waxed wood slider so that the excitation plate can achieve displacements required by certain pulse profiles without the foam experiencing too much deformation.

Figure 2: Photo of Entire During Testing

Summary of Performance Results:

The predictability and repeatability of the machine are illustrated by the following plots containing accelerometer data from a first test iteration.

The above plot illustrates a well predicted acceleration pulse before tuning. Tuning of the drop height would likely correct the pulse amplitude.

The plots below illustrate the repeatability of the machine.

The following data outline the pulse characteristics:

1st Trial: 9.70 g, 16.6 milliseconds

2nd Trial: 10.25 g, 16.5 milliseconds

3rd Trial: 10.32 g,16.5 milliseconds