https://mechcalc.net/blog/en/tags/ffs/ Recent content in FFS on MechCalc how-to Guide https://mechcalc.net/blog/og-default.png https://mechcalc.net/blog/og-default.png Hugo en Sat, 04 Jul 2026 10:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-yielding-behaviour-fad/ Sat, 04 Jul 2026 10:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-yielding-behaviour-fad/ 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. https://mechcalc.net/blog/en/posts/bs7910-clause7-fad-options/ Fri, 03 Jul 2026 21:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-clause7-fad-options/ 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. https://mechcalc.net/blog/en/posts/bs7910-annex-p-ref-stress-tutorial/ Thu, 02 Jul 2026 10:30:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-annex-p-ref-stress-tutorial/ 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. https://mechcalc.net/blog/en/posts/bs7910-annex-m-ki-tutorial/ Thu, 02 Jul 2026 10:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-annex-m-ki-tutorial/ 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. https://mechcalc.net/blog/en/posts/bs7910-annex-d-misalignment/ Fri, 26 Jun 2026 10:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-annex-d-misalignment/ 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. https://mechcalc.net/blog/en/posts/bs7910-sstp10-fad-walkthrough/ Thu, 25 Jun 2026 14:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-sstp10-fad-walkthrough/ FITNET's second FAD worked example, SSTP10 — a welded stainless-steel wide plate with a through-thickness crack failing by ductile tearing. This post runs it in mechCalc's BS 7910 Clause 7 fracture assessment calculator, watches where the assessment point lands on the Failure Assessment Diagram, and cross-checks point by point against FITNET: the horizontal coordinate L_r matches almost digit-for-digit (0.511 vs 0.51), while the vertical coordinate K_r is cross-method (the source includes unquantified welding residual stress), so only L_r can be compared. https://mechcalc.net/blog/en/posts/bs7910-a533b-residual-kis-annexm/ Thu, 25 Jun 2026 10:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-residual-kis-annexm/ 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 — and shows how mechCalc reproduces this key intermediate quantity on its own. https://mechcalc.net/blog/en/posts/bs7910-a533b-hlaw-fad-walkthrough/ Wed, 24 Jun 2026 12:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-hlaw-fad-walkthrough/ 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. https://mechcalc.net/blog/en/posts/bs7910-a533b-llht-fad-walkthrough/ Wed, 24 Jun 2026 11:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-llht-fad-walkthrough/ 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. https://mechcalc.net/blog/en/posts/bs7910-a533b-llaw-fad-walkthrough/ Wed, 24 Jun 2026 10:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-llaw-fad-walkthrough/ 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 assessment point to K_r=2.59, far beyond the Failure Assessment Line. https://mechcalc.net/blog/en/posts/fitnet-ffs-overview/ Wed, 24 Jun 2026 00:00:00 +0800 https://mechcalc.net/blog/en/posts/fitnet-ffs-overview/ In the fracture-mechanics and fitness-for-service (FFS) literature, FITNET is a name you cannot avoid. This article traces the origins of the FITNET EU project from public sources: how it descends from SINTAP, who led and funded it, its scale, what the four modules of the FITNET FFS Procedure each cover, and why its fracture module is highly comparable to BS 7910. https://mechcalc.net/blog/en/posts/bs7910-a533b-residual-stress-fad/ Tue, 23 Jun 2026 00:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-residual-stress-fad/ A set of large welded A533B-1 steel plates tested in four-point bending to fracture, built to answer a question engineers keep asking: where exactly does welding residual stress push the assessment point on the Failure Assessment Diagram (FAD)? We first lay out the background and the shared method, then break the four specimens (LLAW / LLHT / HLAW / HLHT) into four problems, give the FAD inputs and results for each, and re-run everything independently with mechCalc's BS 7910 Clause 7 fracture assessment, cross-checking point by point against the original literature. https://mechcalc.net/blog/en/posts/ffs-intro/ Fri, 19 Jun 2026 12:00:00 +0800 https://mechcalc.net/blog/en/posts/ffs-intro/ FFS in one minute: can a structure with a flaw keep running? What methods do engineers use to decide? https://mechcalc.net/blog/en/posts/bs7910-fracture-assessment-tutorial/ Sat, 16 May 2026 22:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-fracture-assessment-tutorial/ A guide to BS 7910:2019 Clause 7 fracture assessment: starting from the two failure modes, it uses a single Failure Assessment Diagram (FAD) to tie together the fracture-mechanics principle, the K_I / σ_ref / K_r / L_r calculation chain, and the standard assessment steps — with original diagrams and a live worked example.