FFS

How a material's yielding behaviour changes the failure assessment line (FAL) in a BS 7910 fracture assessment. What yielding is, how continuous and discontinuous yielding (the Lüders plateau) differ, which materials fall into each group, how to make a safe assumption when you are not sure, and how Option 1 (swap the equations) and Option 2 (one equation, with a Lüders-strain step added to the reference strain) each handle the two cases. With original stress-strain and failure-assessment-line figures, the code equations, and a live online calculator.

A walkthrough of the three assessment options of the BS 7910:2019 Clause 7 Failure Assessment Diagram (FAD): Option 1 (yield/tensile strength only), Option 2 (true stress-true strain curve), and Option 3 (elastic-plastic J-integral). The code equations and their physical reading, how the three failure assessment lines step up in data need, accuracy and conservatism, when to choose which, and the low-strain-hardening exception — with an original comparison figure and a live online calculator.

A guide to BS 7910:2019 Annex P: it explains the physical meaning of the reference stress σ_ref and the reference-stress method, the equivalence of σ_ref and the limit load P_L, how it gives the FAD horizontal axis L_r, the general framework and net-section degradation, the plastic cut-off L_r,max and flow stress, and the calculation steps — with original diagrams and a live worked example.

A guide to BS 7910:2019 Annex M: starting from crack-tip stress singularity, it explains the physical meaning of the stress intensity factor K_I, the general Annex M framework and its correction factors, the semi-elliptical surface-crack solution and evaluation points, the weld-toe magnification factor Mk, and the full calculation steps — with original diagrams and a live worked example.

When two plates or shells to be welded together are 'not aligned' (axial misalignment or angular distortion), the load path of a tensile load is forced to bend, adding a layer of local bending stress σs at the weld. BS 7910:2019 Annex D is a look-up handbook: it gives a formula for each of 10 standardized misalignment configurations (7 butt-joint types + 3 cruciform types), letting you compute σs directly from the geometry, or convert it to a stress magnification factor km to feed into the Annex M stress intensity factor and the Clause 7 fracture assessment. This article gives the physics, then a figure and algorithm for each type.

FITNET's SSTP10 worked example — a welded stainless-steel wide plate with a through-thickness crack failing by ductile tearing. This post works out the assessment point in mechCalc's BS 7910 Clause 7 fracture assessment calculator (the calculator does not do a ductile tearing analysis, so K_mat is converted point by point and entered directly), shows where it lands on the Failure Assessment Diagram, and compares it point by point with FITNET: the horizontal coordinate L_r is close to the literature (0.511 vs 0.51), while the vertical coordinate K_r cannot be compared directly because the source includes an unquantified welding residual stress.

Across the four A533B welded-plate problems, the residual stress intensity factor K_I^S≈46 MPa·m^0.5 has always been entered directly into the FAD — but where does that number actually come from? This post uses the BS 7910 Annex M.4.2 calculator in mechCalc (finite-plate surface flaw, polynomial stress) to integrate the measured welding residual stress polynomial profile into the SIF at the deepest point of the crack, yielding 44.84 MPa·m^0.5 — only 2.5% off the 46 reported by FITNET.

Third of four problems on the welded A533B-1 plate: the HLAW specimen — as-welded, warmed to −30 ℃, with the load raised into the high load-ratio (large-plasticity) regime. We run it in mechCalc's BS 7910 Clause 7 fracture assessment calculator to see how the assessment calls plastic collapse once L_r=1.80 exceeds the cut-off value L_r,max, and why the relative weight of residual stress is diluted by plasticity at high L_r so that fracture toughness becomes the governing factor.

Second of four problems on the A533B-1 welded plate: same temperature as Problem 1 LLAW (−120 ℃), same region, same measured residual-stress profile — the only variable is that post-weld heat treatment (PWHT) was applied. Here we run LLHT in mechCalc's BS 7910 Clause 7 fracture-assessment calculator and watch a counter-intuitive result: its primary SIF is actually higher than LLAW, yet the assessment point lands lower, because the residual K_I^S drops from 46 to 5.

One of the four A533B-1 welded-plate problems: the LLAW specimen — as-welded, −120 ℃, low load ratio. It is the first of the four to fracture (1.27 MN). This post walks step by step through entering, computing, and reading the FAD in mechCalc's BS 7910 Clause 7 Fracture Assessment Calculator, to see exactly how the residual K_I^S of 46 MPa·m^0.5 pushes the deepest-point assessment point to K_r=2.59, far beyond the Failure Assessment Line.