Engineering Case

Irradiation raises yield strength and lowers fracture toughness, so the assessment point of a cracked plate drifts toward the failure assessment line year by year. This post assesses the FITNET training example 'Plate under neutronic irradiation' with the BS 7910 Clause 7 fracture assessment calculator: 12 assessment points are compared one by one with the source, and the most critical point (year 20, 350 MPa) has a reserve factor on load of 1.19 against about 1.2 read from the source chart. All inputs, calculation steps and comparison tables are included.

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.

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.

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.

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 compare each result with the original literature, to see what residual stress and post-weld heat treatment each contribute.