Nearly every random vibration fatigue course teaches that the response of a single-degree-of-freedom system to broadband base excitation has Rayleigh-distributed peaks. The claim is repeated so often that it has hardened into doctrine. It is a good approximation for the largest peaks, which is why… Read more
A random vibration analysis in a finite element code will happily report an RMS von Mises stress, or an RMS resultant shear force in a bolt, and the analyst will happily multiply it by three and compare it against an allowable. Both quantities are useful.… Read more
A question that comes up whenever a laboratory is planning its first large electrodynamic shaker installation: the specification and the quotations keep referring to a seismic mass, or a reaction mass, or an inertia block. Is that a real, physically heavy object that has to… Read more
A question that comes up whenever a laboratory is planning its first large electrodynamic shaker installation: the specification and the quotations keep referring to a seismic mass, or a reaction mass, or an inertia block. Is that a real, physically heavy object that has to… Read more
The Problem Here is a problem that comes up more often than the standards would suggest. An engineer is deriving a random vibration maximum predicted environment (MPE) for launch vehicle components mounted very close to the engines. Accelerometer data from engine test stand and stack… Read more
Does Compression Grow Cracks? — Vibrationdata Vibrationdata Fracture & Fatigue Stress intensity conventions At a stress ratio of R = −1, the choice between full-range and clipped ΔK is worth a factor of 2n in life. It is usually the largest single lever in a… Read more
A recurring question in Central and Eastern North America (CENA) seismic qualification goes something like this: the site-specific ground motion exceeds the IEEE 693 required response spectrum above 10 Hz, sometimes by a factor of two to four. Does that mean the equipment is unqualified?… Read more
Composite Materials in Turbofan Jet Engines | Structural Dynamics & Mechanics Vibrationdata · Structural Dynamics & Material Physics Composite Materials in Turbofan Jet Engines Aeromechanics, Centrifugal Mechanics, Impact Damage Tolerance, and Aeroelastic Tuning Introduction The modern high-bypass turbofan represents one of the most demanding optimization… Read more
A Shell station on a Huntsville, Alabama arterial. Four slender columns, a flat deck roughly 60 feet by 30 feet, fifteen feet of clearance, and a fascia band carrying the brand colors. It is one of the most repeated structural forms in North America, and… Read more
A change to a single equation in ASME B31.3 has meaningful consequences for how piping displacement stress is evaluated in high-cycle service. The change is small in appearance and large in effect, and it is worth understanding both the arithmetic and the seventy years of… Read more