Publications

Abstract not provided.

Abstract not provided.

Thirteen segmented aluminum honeycomb samples (5 in. diameter and 1.5 in. height) have been crushed in an experimental configuration that uses a drop table impact machine. The 38.0 pcf bulk density samples are a unique segmented geometry that allows the samples to be crushed while maintaining a constant cross-sectional area. A crush weight of 175 lb was used to determine the rate sensitivity of the honeycomb's highest strength orientation, T-direction, in a dynamic environment of {approx}50 fps impact velocity. Experiments were conducted for two honeycomb manufacturers and at two temperatures, ambient and +165 F. Independent measurements of the crush force were made with a custom load cell and a force derived from acceleration measurements on the drop table using the Sum of Weighted Accelerations Technique with a Calibrated Force (SWAT-CAL). Normalized stress-strain curves for all thirteen experiments are included and have excellent repeatability. These data are strictly valid for material characteristics in the T orientation because the cross-sectional area of the honeycomb did not change during the crush. The dynamic crush data have a consistent increase in crush strength of {approximately}7--19% as compared to quasi-static data and suggest that dynamic performance may be inferred from static tests. An uncertainty analysis estimates the error in these data is {+-} 11%.

A mechanical isolator has been developed for a piezoresistive accelerometer. The purpose of the isolator is to mitigate high frequency shocks before they reach the accelerometer because the high frequency shocks may cause the accelerometer to resonate. Since the accelerometer is undamped, it often breaks when it resonates. The mechanical isolator was developed in response to impact test requirements for a variety of structures at Sandia National Laboratories (SNL). An Extended Technical Assistance Program (ETAP) with the accelerometer manufacturer has resulted in a commercial mechanically isolated accelerometer that is available to the general public, the ENDEVCO 7270AM6*, for three shock acceleration ranges of 6,000 g, 20,000 g, and 60,000 g. The in-axis response shown in this report has acceptable frequency domain performance from DC to 10 kHz and 10(XO)over a temperature range of {minus}65 F to +185 F. Comparisons with other isolated accelerometers show that the ENDEVCO 7270AM6 has ten times the bandwidth of any other commercial isolator. ENDEVCO 7270AM6 cross-axis response is shown in this report.

In order to determine the susceptibility of the MEMS (MicroElectroMechanical Systems) devices to shock, tests were performed using haversine shock pulses with widths of 1 to 0.2 ms in the range from 500g to 40,000g. The authors chose a surface-micromachined microengine because it has all the components needed for evaluation: springs that flex, gears that are anchored, and clamps and spring stops to maintain alignment. The microengines, which were unpowered for the tests, performed quite well at most shock levels with a majority functioning after the impact. Debris from the die edges moved at levels greater than 4,000g causing shorts in the actuators and posing reliability concerns. The coupling agent used to prevent stiction in the MEMS release weakened the die-attach bond, which produced failures at 10,000g and above. At 20,000g the authors began to observe structural damage in some of the thin flexures and 2.5-micron diameter pin joints. The authors observed electrical failures caused by the movement of debris. Additionally, they observed a new failure mode where stationary comb fingers contact the ground plane resulting in electrical shorts. These new failure were observed in the control group indicating that they were not shock related.