Publications

Abstract not provided.

Several programs at Sandia National Laboratories have adopted energy spectra as a metric to relate the severity of mechanical insults to structural capacity. The purpose being to gain insight into the system's capability, reliability, and to quantify the ultimate margin between the normal operating envelope and the likely system failure point -- a system margin assessment. The fundamental concern with the use of energy metrics was that the applicability domain and implementation details were not completely defined for many problems of interest. The goal of this WSEAT project was to examine that domain of applicability and work out the necessary implementation details. The goal of this project was to provide experimental validation for the energy spectra based methods in the context of margin assessment as they relate to shock environments. The extensive test results concluded that failure predictions using energy methods did not agree with failure predictions using S-N data. As a result, a modification to the energy methods was developed following the form of Basquin's equation to incorporate the power law exponent for fatigue damage. This update to the energy-based framework brings the energy based metrics into agreement with experimental data and historical S-N data.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Materials subject to cyclic loading have been studied extensively and experimentally determined comparisons of stress to number of cycles are used to estimate fatigue life under various loading scenarios. Fatigue data are traditionally presented in the form of S-N curves. Normally, S-N data are derived from cyclic loading but the S-N results are also applicable to random vibration loading and, to some extent, shock. This paper presents an alternate presentation of fatigue data in terms of input energy and number of cycles to failure. In conjunction with this study, a series of shock tests was conducted on 3D printed cantilever beams using a 6-DOF shaker table. All of the beams were tested to failure at shock levels in the low-cycle fatigue regime. From these data, a nominal fatigue curve in terms of input energy and number of shocks to failure was generated and compared with the theoretical developments.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

The relationship between the damage potential of a series of relatively low level shocks and a single high level shock that causes severe damage is complex and depends on many factors. Shock Response Spectra are the standard for describing mechanical shock events for aerospace vehicles, but are only applicable to single shocks. Energy response spectra are applicable to multiple shock events. This paper describes the results of an initial study that sought to gain insight into how energy response spectra of low amplitude shocks relate to energy response spectra of a high amplitude shock in which the component of interest fails. The study showed that maximum energy spectra of low level shocks cannot simply be summed to estimate the energy response spectra of a high level, failure causing single shock. A power law relationship between the energy spectra of a low amplitude shock and the energy spectra of the high amplitude shock was postulated. A range of values of the exponent was empirically determined from test data and found to be consistent with the values typically used in high-cycle fatigue S-N curves.