Stress Intensity Factor

The first step of a fracture assessment is to compute the stress intensity factor $K_I$ at the crack tip. This guide explains what $K_I$ is and how BS 7910 Annex M computes it — from the general master formula and its correction factors to the common semi-elliptical surface-crack solution and the weld-toe correction. It feeds the vertical axis $K_r$ of the Failure Assessment Diagram (FAD), and together with Annex P (reference stress) for the horizontal axis $L_r$ completes the Clause 7 fracture assessment . ...

In the FAD assessment of the [[bs7910-a533b-residual-stress-fad|four A533B welded-plate problems]], the residual stress intensity factor for the as-welded case, $K_I^S \approx 46\ \mathrm{MPa\cdot m^{0.5}}$, has always been entered directly: FITNET obtained it by integrating the measured residual stress profile, and we simply fed that ready-made number into the vertical coordinate $K_r$. A natural follow-up question: how does that 46 actually emerge from a residual stress curve, and can mechCalc compute it on its own? ...

In the structural integrity assessment of pressure vessels, oil and gas pipelines, offshore steel structures and nuclear pressure-boundary components, the stress intensity factor (SIF, written $K_I$) is the central quantity of Linear Elastic Fracture Mechanics (LEFM). It measures precisely how strong the singular stress field is at the crack tip. The flaw assessment standard BS 7910:2019+A1:2020, published by The Welding Institute (TWI), sets out in its Annex M a classic, high-accuracy and self-consistent system of analytical SIF solutions for the eight common geometry groups met in engineering. This article explains its physical basis, the code calculation chain and its engineering use, and introduces an interactive online calculator built entirely in pure Python. ...

The fracture assessment of a cracked structure watches two competing failure modes. This guide uses a single Failure Assessment Diagram (FAD) to weave together the assessment principle, the calculation chain, and the BS 7910 assessment steps into one clear storyline. By the end you should be able to see how an assessment point is computed and how it is judged acceptable or not. Prologue: after a crack is found When an in-service pressure vessel, pipe, or welded structure is inspected, crack-like flaws are often found. The question the engineer must answer is not “can this crack be used” — a crack is not something you “use” — but rather: can the structure that contains this flaw still operate safely under the current loads? ...