https://mechcalc.net/blog/en/ Recent content 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&#39;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 &#39;not aligned&#39; (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&#39;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&#39;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-hlht-fad-walkthrough/ Wed, 24 Jun 2026 13:00:00 +0800 https://mechcalc.net/blog/en/posts/bs7910-a533b-hlht-fad-walkthrough/ The finale of the four problems on the A533B-1 welded plate: same temperature and regime as Problem 3 (HLAW) — −30 ℃, high load ratio — but with post-weld heat treatment (PWHT). This article works through HLHT to show the double dividend of PWHT — it both relaxes the residual field (K_I^S 46→5) and restores toughness by an order of magnitude (K_mat 62→321) — and how this drives K_r down from 3.94 to 0.60; plus a thought-provoking twist: even with smaller residuals and higher toughness, HLHT fails at a slightly lower load than HLAW. 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&#39;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&#39;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&#39;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&#39;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-annex-m-ki-theory/ Mon, 25 May 2026 00:00:00 +0000 https://mechcalc.net/blog/en/posts/bs7910-annex-m-ki-theory/ A walkthrough of the analytical stress intensity factor solver in BS 7910:2019+A1:2020 Annex M — Newman-Raju semi-elliptical surface cracks in plates, the Folias bulging factor for thin shells, James &amp; Mills edge cracks in round bars, and weld-toe / weld-root magnification factors for cruciform joints — with whitebox formula substitution and a guide to the interactive calculator. 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. https://mechcalc.net/blog/en/posts/bs7910-annex-j-kmat-tutorial/ Sat, 16 May 2026 22:00:00 +0200 https://mechcalc.net/blog/en/posts/bs7910-annex-j-kmat-tutorial/ A walkthrough of the two K_mat estimation routes in BS 7910:2019 Annex J — the lower-shelf equation and the Master Curve — with full derivations, the T_K confidence margin explained, and three worked verification examples. https://mechcalc.net/blog/en/posts/vdi2230-10-eccentric-load-bending/ Mon, 20 Apr 2026 20:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-10-eccentric-load-bending/ The most complex part of VDI 2230: eccentric clamping and eccentric loading. This article explains the physical meaning of the eccentricity parameters ssym and a, the calculation of the corrected resiliences δP* and δP**, the substitutional moment of inertia IBers, and the key formulas of the opening check. https://mechcalc.net/blog/en/posts/vdi2230-09-worked-example-esv/ Mon, 20 Apr 2026 19:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-09-worked-example-esv/ A full VDI 2230 tapped-thread joint (ESV/TTJ) worked example. Compared with the previous DSV example, it highlights the key ESV differences in the resilience calculation, the nut-region elastic modulus, and the engagement-depth check. https://mechcalc.net/blog/en/posts/vdi2230-08-worked-example-dsv/ Mon, 20 Apr 2026 18:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-08-worked-example-dsv/ A full VDI 2230 through-bolt joint (DSV) worked example, going through R0–R13 in all 14 steps. It includes the specific input parameters, the intermediate result of each step and the final safety factors, tying the theory of the previous 7 articles into one executable calculation chain. https://mechcalc.net/blog/en/posts/vdi2230-07-strength-check-r7-r13/ Mon, 20 Apr 2026 17:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-07-strength-check-r7-r13/ The lower half of the VDI 2230 calculation chain — six strength checks (assembly stress, service stress, fatigue, bearing pressure, engagement depth, slip) plus the tightening torque R13. Each check&#39;s physical meaning, formula and safety factor explained one by one. https://mechcalc.net/blog/en/posts/vdi2230-06-preload-design-r1-r6/ Mon, 20 Apr 2026 16:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-06-preload-design-r1-r6/ The upper half of the VDI 2230 calculation chain R1–R6 explained: the tightening factor αA, the three sources of the minimum clamping force FKerf, the choice of force-ratio Φ formula, preload loss (embedding + thermal expansion), and the derivation of the minimum and maximum assembly preload. https://mechcalc.net/blog/en/posts/vdi2230-05-clamped-parts-resilience-cone/ Mon, 20 Apr 2026 15:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-05-clamped-parts-resilience-cone/ VDI 2230 uses an equivalent deformation cone (Ersatzverformungskegel) to model the compression zone of the clamped parts. This article explains the cone-angle formula, the cone-plus-sleeve combined model, multi-layer plate handling, and the key differences between DSV and ESV. https://mechcalc.net/blog/en/posts/vdi2230-04-bolt-elastic-resilience/ Mon, 20 Apr 2026 14:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-04-bolt-elastic-resilience/ VDI 2230 breaks a real bolt into a chain of series cylindrical segments to compute its total elastic resilience δS. This article walks through the substitutional lengths and resilience formulas of the head, shank, free thread, engaged thread and nut region one by one, and explains the difference between DSV and ESV. https://mechcalc.net/blog/en/posts/vdi2230-03-spring-model-force-distribution/ Mon, 20 Apr 2026 12:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-03-spring-model-force-distribution/ A detailed look at the core physical model of VDI 2230: the spring model (Federmodell), the elastic resiliences δS and δP, the joint diagram (Verspannungsschaubild), the physical meaning of the force ratio Φ, and the full derivation logic of the main equation Eq.16. https://mechcalc.net/blog/en/posts/vdi2230-02-scope-and-positioning/ Mon, 20 Apr 2026 11:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-02-scope-and-positioning/ The applicability conditions of VDI 2230 Blatt 1, the interface limiting dimension G, the family of standards it depends on, and the implicit premise about how force is transmitted. Making clear what the standard can and cannot compute, so you avoid applying it blindly in the wrong scenario. https://mechcalc.net/blog/en/posts/vdi2230-01-why-systematic-calculation/ Mon, 20 Apr 2026 10:00:00 +0200 https://mechcalc.net/blog/en/posts/vdi2230-01-why-systematic-calculation/ VDI 2230 is the globally recognized standard for the systematic calculation of high-strength bolted joints. This article explains the shortcomings of a simple strength check, the 14-step VDI 2230 calculation chain and the physical meaning of its main equation, to help engineers see why systematic bolt calculation is necessary. https://mechcalc.net/blog/en/posts/bolt-preselection-04-bearing-pressure/ Mon, 13 Apr 2026 21:15:00 +0200 https://mechcalc.net/blog/en/posts/bolt-preselection-04-bearing-pressure/ Why does a bolted joint fail as a whole when the surface is only crushed a tiny bit? This article uses the model of a &#39;stretched rubber band clamping a sponge&#39; to see through the mechanics of the bearing-pressure check: from microscopic peak crushing and macroscopic embedding (Setzen), to the elastic recoil that causes an irreversible loss of preload (clamping force), to the chain failure of loosening and fatigue fracture — and gives engineering measures such as controlling the limiting surface pressure and enlarging the bearing area. https://mechcalc.net/blog/en/posts/bolt-preselection-03-quick-table/ Mon, 13 Apr 2026 18:20:00 +0200 https://mechcalc.net/blog/en/posts/bolt-preselection-03-quick-table/ No calculation needed — one table for a preliminary estimate of bolt size! This article gives the minimal table-lookup method for bolt pre-selection: knowing only the maximum working load a single bolt carries — axial static load, axial dynamic load or transverse shear force — you can read the recommended nominal diameter (M4 and up) and the minimum property-class combination straight from the load-range table, a result in seconds, good for quick estimates on the shop floor and in technical discussion; for a precise calculation switch to the Kübler equation or the full VDI 2230 method. https://mechcalc.net/blog/en/posts/bolt-preselection-02-reduction-factors/ Mon, 13 Apr 2026 18:00:00 +0200 https://mechcalc.net/blog/en/posts/bolt-preselection-02-reduction-factors/ Where does the reduction factor κ in bolt pre-selection come from? Starting from the two-way stress state where axial tensile stress and torsional shear stress combine during tightening, this article uses the von Mises yield criterion to derive the definition, formula and engineering values of κ, explaining how thread friction acts like an &#39;invisible tax&#39; that cuts the bolt&#39;s axial load capacity, and why it appears in the denominator of the Kübler equation. https://mechcalc.net/blog/en/posts/bolt-preselection-01-load-to-size/ Thu, 26 Mar 2026 20:58:00 +0100 https://mechcalc.net/blog/en/posts/bolt-preselection-01-load-to-size/ For a given working load, how large should the bolt be? This article covers the preliminary design and pre-selection of bolts: first read the nominal diameter and property class from a quick pre-selection table by load range, then use the Kübler equation to back out the thread stress cross-section from the axial working load and the required clamping force, combined with the tightening factor, reduction factor and simplified fatigue and bearing-pressure checks, to help engineers quickly size a bolt in the early design stage. https://mechcalc.net/blog/en/posts/bolt-basics-01-thread-geometry/ Sun, 22 Mar 2026 22:58:00 +0100 https://mechcalc.net/blog/en/posts/bolt-basics-01-thread-geometry/ The bolted joint is one of the most widely used connection methods in mechanical engineering. Starting from the inclined-plane nature of a thread, this article sets out thread geometry and classification: the lead angle, the pitch, the pitch diameter d2, the minor diameter d3 and other key geometry parameters; common thread profiles and technical standards such as metric ISO coarse/fine, pipe threads and trapezoidal threads; and the functional distinction between fastening bolts, motion screws and sealing/adjusting bolts — laying the geometric groundwork for the later bolt strength calculation and pre-selection. https://mechcalc.net/blog/en/posts/asme-xi-app-y-crack-growth/ Mon, 23 Feb 2026 00:00:00 +0000 https://mechcalc.net/blog/en/posts/asme-xi-app-y-crack-growth/ A walkthrough of the latest ASME BPVC Section XI Appendix Y models for fatigue crack growth and stress-corrosion cracking in austenitic, ferritic and nickel-base alloys, with a code-based online calculation guide. https://mechcalc.net/blog/en/posts/08-fatigue-crack-growth/ Sat, 21 Feb 2026 12:00:00 +0100 https://mechcalc.net/blog/en/posts/08-fatigue-crack-growth/ <blockquote> <p>🧮 <strong>Go straight to the calculator</strong>: to skip the derivation and use the online tool with a built-in verification flow, open the <a href="https://mechcalc.net/blog/calculators">fatigue crack growth calculator</a> from the large category cards on the calculators home page.</p> </blockquote> <h2 id="1-where-fatigue-crack-growth-sits-in-an-lbb-analysis">1. Where fatigue crack growth sits in an LBB analysis</h2> <p>At the core of a Leak-Before-Break (LBB) argument: you must show that, over the service life, the time for an initial non-penetrating surface flaw to grow by <strong>subcritical crack growth</strong> through the wall and cause a leak — and the time from leak to growth to the critical fracture size — is long enough for the monitoring system to detect it and act.</p> https://mechcalc.net/blog/en/posts/kta3206-lbb-analysis-guide/ Thu, 19 Feb 2026 09:00:00 +0100 https://mechcalc.net/blog/en/posts/kta3206-lbb-analysis-guide/ <p>This article explains how to use the <strong>seven-step method</strong> of the <strong>KTA 3206</strong> standard for a <strong>Leak-Before-Break (LBB)</strong> analysis of nuclear piping. It pairs with the <strong>KTA 3206 LBB Pipe Analysis</strong> module of the online calculator, taking you from theory to practice.</p> <blockquote> <p>🧮 <strong>Try the calculator now</strong>: open the <a href="https://mechcalc.net/blog/calculators">KTA 3206 LBB pipe analysis calculator</a> , choose &ldquo;Fracture Mechanics → KTA 3206 LBB Pipe Analysis&rdquo;, and enter the parameters to get results with a detailed formula derivation and visual charts.</p> https://mechcalc.net/blog/en/posts/lbb-leak-before-break-guide/ Mon, 02 Feb 2026 16:45:00 +0100 https://mechcalc.net/blog/en/posts/lbb-leak-before-break-guide/ <p>This is a detailed introductory guide to <strong>Leak-Before-Break (LBB)</strong>.</p> <p>LBB is a crucial safety concept in the structural integrity assessment of pressure vessels and piping. In short, it is an analysis that proves the equipment will <strong>produce a detectable leak first</strong>, before any catastrophic fracture — giving operators time to shut down and avoid a major accident.</p> <hr> <h3 id="1-what-is-leak-before-break-lbb">1. What is Leak-Before-Break (LBB)?</h3> <p><strong>Core definition:</strong> LBB is a property of a pressure-bearing system (pipe, vessel). It ensures that when a flaw (crack) is present, the crack will penetrate the wall to form a through-wall crack and produce a <strong>stable, detectable leak</strong> before it grows to the critical size that would cause overall structural instability (sudden fracture or plastic collapse).</p>