Image courtesy of: https://incastt.com/inclusion-defects-in-investment-casting/ Non-metallic inclusions are unavoidable by-products of steelmaking, casting, and welding. They range in size from sub-micron oxide clusters to hundred-micron sulfide stringers, but their fatigue consequence is disproportionate to their size. This post catalogs the common inclusion species by alloy family,… Read more
Tom Irvine | VibrationData.com | Structural Dynamics, Shock, Vibration & Acoustics Abstract. The Dirlik method estimates spectral fatigue damage from a stress power spectral density (PSD) assuming Gaussian amplitude statistics. When a measured stress time history is stationary yet exhibits kurtosis κ > 3 (leptokurtic),… Read more
Hardness is cheap and fast to measure — but how far can it really predict fatigue behavior? Introduction Hardness is one of the cheapest and fastest mechanical properties to measure — a Rockwell or Brinell indenter, a few seconds, and a single number. Because hardness… Read more
Nearly every published S/N curve was measured under steady, repeatable loading. Real structures never see that. Introduction The S/N curve — stress amplitude versus cycles to failure — is the foundation of classical fatigue analysis. It is intuitive, experimentally well-established, and embedded in virtually every… Read more
Introduction A previous VibrationData post examined cold dwell fatigue in titanium — the phenomenon in which simply holding a moderate stress for one to two minutes causes far more damage per cycle than the same stress applied and immediately removed. The mechanism is driven by… Read more
Introduction Most engineers have an intuitive feel for fatigue: apply a stress repeatedly, and eventually the material cracks — even if each individual load is well below the static yield strength. Dwell fatigue adds a further, less intuitive twist. Dwell fatigue occurs when a sustained… Read more
Introduction Shock and vibration environments are almost always characterized in terms of velocity. The shock response spectrum (SRS) is fundamentally a pseudo-velocity construct. Random vibration specifications are integrated to give RMS velocity as a check on response severity. Field data from accelerometers is routinely converted… Read more
Introduction Flow stress is one of those quantities that shows up everywhere in structural metals engineering, yet it rarely gets the dedicated treatment that stress intensity factor, S-N curves, or fatigue strength coefficients receive. It appears quietly in cyclic plasticity models, in fracture toughness test… Read more
Introduction A question that comes up regularly in fatigue testing and vibration qualification programs is whether the frequency of cyclic loading — or the associated strain rate — influences the fatigue life of a component. The honest answer is: it depends very much on the… Read more
Strain Rate Effects: Why Metals Get Stronger but Less Ductile Under Dynamic Loading Introduction A common observation in shock, impact, and ballistic engineering is that metals behave differently under dynamic loading than they do under slow, quasi-static loading. A structural steel or aluminum alloy that… Read more