There is a need to derive a power spectral density (PSD) envelope for nonstationary acceleration time histories, including launch vehicle data, so that components can be designed and tested accordingly. Three methods are considered in the following paper using an actual flight accelerometer record. The… Read more
Prerequisite Reference Papers David O. Smallwood, An Improved Recursive Formula for Calculating Shock Response Spectra, Shock and Vibration Bulletin, No. 51, May 1981. DS_SRS1.pdf Rainflow Counting Tutorial Fatigue Damage Spectrum, Time Domain Fatigue Damage Spectrum Dirlik Method for PSDs Optimized PSD FDS Nonstationary * *… Read more
Options for including mean stress have been added to the Vibrationdata GUI package’s Fatigue Toolbox, for both stress time histories and PSDs. Four methods are available: Gerber Goodman Morrow Soderberg Matlab script: Vibrationdata Signal Analysis Package Here are some charts from Iowa State University: Fatigue… Read more
Fatigue is usually associated with tensile stresses. Engineering knowledge of compressive fatigue is very limited. Compression stresses do not cause cracks, but plastic compressive strain can cause tension stresses when the load is returned to zero and the resulting tension stress causes cracks. * *… Read more
The following scripts calculate the A, B, C, P coefficients to model a set of SN curves with varying R values: sin_curve_fit_R.zip sn_curve_fit_R.m is the main script. The remaining scripts are supporting functions. The equations are given in: sn_curvefit_equation.pdf * * * References: 1. MIL-HDBK-5J… Read more
PowerPoint Slides: webinar_35_fatigue_sine_random.pptx Audio/Visual File: NESC Academy Using Fatigue to Compare Sine and Random Environments – Recommend viewing in Firefox with Sliverlight Plugin * * * References: Steinberg’s Vibration Analysis for Electronic Equipment Sine and Random Vibration Equivalent Damage Rainflow Fatigue Posts * * * Matlab… Read more
NASA-STD-5019, Fracture Control Requirement for Spaceflight Hardware (excerpt) 4.1.1.12 Low-Risk Part This section addresses parts that can be classified non-fracture critical because of large structural margins and other considerations that make failure from a pre-existing flaw extremely unlikely. a. For a part to be classified… Read more
Rainflow fatigue cycles can be easily calculated for a single-degree-of-freedom subjected to a sine or sine sweep base input. The reason is that each pair of consecutive positive and negative response peaks forms a half-cycle. The relative fatigue damage can then be calculated from the… Read more
Here is a paper showing how fatigue damage can be calculated from a stress response PSD for a plate excited by an acoustic pressure field: acoustic_fatigue_plate.pdf The calculation method is given at: Fatigue Damage for a Stress Response PSD * * * The Matlab scripts… Read more
Here is a paper. Estimating Fatigue Damage from Stress Power Spectral Density Functions: estimate_fatigue_psd.pdf Note that the duration for the example in the paper was 600 sec. * * * This following Matlab program calculates the cumulative rainflow fatigue damage for an input stress PSD… Read more