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 Some of the best structural engineering field trips are unplanned. While passing through St Pancras International station in London, I photographed three artifacts that together tell a 159-year story of structural engineering: the great Barlow train shed roof, a foundry plate cast in 1867,… 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
Introduction In the predawn hours of June 29, 2026, a severe thunderstorm complex swept across central South Dakota. The South Dakota Mesonet station at Highmore, in Hyde County, recorded a straight-line wind gust of 131 mph (58.6 m/s) at about 6:15–6:25 a.m. local time. The… 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
The image shows a MIL-S-901D Barge Test. A reader recently wrote in with two requests: (1) blog posts on surface ship shock and shock response spectra derived from acceleration data, and (2) coverage of underwater explosion (UNDEX) shock effects on submerged components such as batteries.… Read more