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
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
Fuse Pins: The Structural Fuse That Holds the Engine On Jet engine pylons contain deliberately weakened pins designed to shed the engine under extreme overload — and two Boeing 747 freighter accidents showed what happens when the fuse itself fails from fatigue. An electrical fuse… Read more
Pointed Gothic arches framing the choir, Notre-Dame de Paris. Smooth and Pointed Arches: Loads, Stress, Fracture, and Fatigue Introduction The accompanying photograph shows the interior of Notre-Dame de Paris, where every opening is spanned by a pointed arch. Stand in a Roman basilica instead and… Read more
Introduction Uniaxial fatigue methods, whether stress-life, strain-life, or spectral, presume that a single stress or strain component tells the whole damage story. Real hardware disagrees. Shafts carry bending plus torsion, pressure vessel nozzles see biaxial membrane stress plus thermal bending, and vibrating structures respond in… Read more
Image credit: Nikhil Patil Introduction Most vibration-induced fatigue problems in aerospace and industrial structures live comfortably in the high cycle fatigue (HCF) regime, where nominal stresses remain below yield and the stress-life (S-N) method with rainflow cycle counting serves well. But some of the most… Read more
Image https://empowering-technologies.com/metal-improvement/ultrasonic-impact-treatment/process/: Introduction Welded joints are the fatigue-critical details in most steel structures. The weld toe combines a sharp geometric stress concentration, tensile residual stresses approaching yield, and microscopic slag intrusions that act as pre-existing cracks. As a result, the fatigue strength of an as-welded… Read more
Following the recent post on the Dang Van criterion, this companion post covers its two closest relatives: the Crossland criterion (1956) and the Sines criterion (1959). A quick note on nomenclature: the Crossland criterion is sometimes misremembered as “Crossfield” — the correct attribution is to… Read more
Most of the fatigue methods featured on this blog — rainflow counting, Dirlik and my Meta-Dirlik spectral correction, dwell-corrected rainflow — answer the question: how much damage does a stress history accumulate? The Dang Van criterion answers a different and complementary question: will a complex… Read more