SafeLife Quick — Fracture Control & Fatigue Toolkit for Excel (v1.0)

SafeLife Quick is a seven-sheet Excel workbook that carries an aerospace fracture-control calculation from the initial NDE flaw to a documented life margin without leaving Excel. It was built for the situation every structural analyst eventually meets: a part has been declared fracture-critical, the program requires a damage-tolerance case to four service lives per NASA-STD-5019, and the full NASGRO or AFGROW run is either weeks away, unaffordable for a bracket, or needs an independent check. The workbook gives a traceable, cell-by-cell answer in minutes, and because every intermediate quantity is visible in a labeled cell rather than buried in code, a reviewer can follow the arithmetic line by line. There are no macros, no add-ins, and no external links; it opens and calculates in any current desktop Excel.

The calculation chain follows the standard. The NDE_Flaws sheet holds the standard minimum-detectable crack sizes by inspection method (eddy current, penetrant, magnetic particle, ultrasonic, radiography) and crack type (part-through surface, through, corner, embedded), in the NASA-STD-5009 convention of depth a and half-length c at both the a/c = 0.2 and a/c = 1.0 aspect ratios, plus a row for a program-demonstrated special-NDE flaw. Each row's key is explained in a hover note so a new user knows what ET-PTC-0.2 means and where it came from. Selecting a key on the CrackGrowth sheet automatically pulls the initial flaw, resolving the through-crack and radiography rules (a = t, a = 0.7t) without user intervention.

The CrackGrowth sheet is the tool's core. From the initial flaw, it integrates da/dN = C·(K_max(1−R)^m)^n over 300 logarithmically spaced increments of crack depth, evaluating the geometry factor at every step from the Newman-Raju semi-elliptical surface-crack solution (depth point, finite-width and finite-thickness corrections, aspect ratio held constant), the Feddersen secant solution for a center through crack, the Tada polynomial for an edge crack, or a free-surface-corrected corner-crack approximation, selected from a dropdown. Growth stops at the threshold ΔK_th, and failure is declared when K_max reaches the selected toughness (K_IC for thick sections or K_c/K_app for thin sheet) or the crack reaches the far surface. Results are reported as cycles to failure, critical crack depth, fracture margin at the initial flaw, life margin against service life times the life factor (4 by default, editable for program requirements), a PASS/FAIL verdict, and a leak-before-burst indicator that tells you whether the crack breaks through before it fractures. The full integration table is exposed so you can see where the life is consumed, and the Walker conversion from the R at which the material data were fitted to the R of your load cycle is done for you in a labeled cell.

The K_Solutions sheet is the single-point companion: enter one crack, one stress, thickness and width, and it lays out every Newman-Raju term (Q, M1, M2, M3, g, f_φ, f_w) for both the depth and surface points, alongside the through-crack, edge-crack and corner-crack values, with fracture margins against the chosen toughness, a validity check on the solution limits, and a net-section yield check so you know when LEFM has stopped being the right question. The Fatigue_SN sheet handles conventional fatigue for non-fracture-critical parts and as a sanity check on fracture-critical ones. It uses the MIL-HDBK-5 / MMPDS equivalent-stress form log N_f = A − B·log(S_eq − C) with both the S_max(1−R)^p and S_a + k·S_m variants exactly as printed under the handbook figures, applies a fatigue notch factor, sums Miner damage over a twelve-block spectrum at the factored life, flags blocks outside the curve's validity, and tabulates the curve at any R for plotting. Classical Goodman, Gerber and Soderberg corrections are available as overrides for comparison.

The Materials library ships with six alloys covering the common aerospace families: 2024-T3 and 7075-T6 aluminum sheet, Ti-6Al-4V annealed sheet, 300M steel at 280 ksi, A-286 bar and Inconel 718 sheet. Static allowables (A- or S-basis F_tu, F_ty, E), plane-strain toughness, thin-sheet apparent toughness and the S-N equation constants are transcribed from MIL-HDBK-5J with the table or figure number cited in the adjacent cell; the Paris constants for 7075-T6, Ti-6Al-4V, 300M and Inconel 718 are fitted from the handbook's crack-propagation figures and say so, with the digitized points and the stress ratio of the fit recorded so you can judge them. Values the handbook does not provide are marked in orange as placeholders that must be replaced with program data before deliverable use, which is exactly how a fracture-control board expects to see them. Twenty rows are provided so you can add your own alloys, product forms and grain directions from MMPDS, a NASGRO material file or test, and every dropdown in the workbook picks them up immediately.

The Classification sheet turns the NASA-STD-5019 decision flow into eleven yes/no questions and returns the part's category (exempt, contained, low-risk, fail-safe, leak-before-burst pressure vessel, or fracture-critical safe-life), the required analysis approach, and a flag for stress-corrosion or hydrogen-embrittlement follow-up, so the fatigue tab and the crack-growth tab are each used where the standard actually requires them. A Summary sheet links every margin and verdict onto one page for the stress report.

Two things make the workbook practical for someone who did not build it. A How_To_Use sheet walks through each tab in the order you would use them, with a worked example using the shipped inputs (a penetrant-inspected 7075-T6 bracket at 30 ksi that passes S-N fatigue comfortably and fails the damage-tolerance case by a factor of forty, which is the whole reason 5019 requires the crack-growth analysis) and a troubleshooting section. The same content is supplied as a Word user guide. Input cells are blue on yellow, formulas are black, cross-sheet links are green, and the key inputs carry hover notes explaining what to enter and why.

Assumptions and limits are stated on the sheets rather than hidden. The crack-growth integration is constant-amplitude with a Walker R correction, no load-interaction retardation, no environmental term, and a fixed a/c during growth; the corner-crack solution is an approximation; the Newman-Raju solution is implemented for a/c ≤ 1. Spectrum loading, two-degree-of-freedom growth and environmental cracking still belong in NASGRO or AFGROW, and this workbook is the independent check beside them, not a replacement. The NDE flaw table should be verified against the current revision of NASA-STD-5009 and edited if your program's NDE plan differs. Units are US customary throughout (ksi, inches, ksi√in, in/cycle). The crack-growth integration has been verified against an independent fine-step numerical integration to within 0.1 percent, and every formula recalculates without error.