Enter specimen name and geometry (defaults provided).
Geometry legend (asymmetric DCB setup): • l1 = distance from loading pin to the nearer support • l2 = distance between the two supports (support span) • a₀ = initial precrack length (measured from load line to crack tip)
Important: L1 and L2 define the asymmetric three-point bending configuration used in this test. Changing these values will directly affect the calculated compliance, energy release rate, and mode-mixity results.
Crack Calibration to a_eff & da/dN Calculator
This tool helps you process fatigue test data from a Double Cantilever Beam (DCB) Mode-I test.
You upload the raw load–displacement CSV, use a few visual crack length measurements to calibrate
compliance, and then obtain effective crack length aeff and crack growth rate da/dN.
Step 1 – Upload fatigue test CSV
Upload the raw load–displacement history from your DCB Mode-I fatigue test.
Each row should contain the cycle count N, maximum/minimum load
Pmax, Pmin, and corresponding opening displacements dmax, dmin.
Please upload a CSV file to begin.
Detected columns
N (cycles)
Pmax [N]
dmax [mm]
Pmin [N]
dmin [mm]
Format reminder Required columns: N, Pmax, dmax, Pmin, dmin. Delimiter can be comma (,) or semicolon (;). In a DCB Mode-I test, the opening displacement at the load line is used to estimate compliance at each cycle block.
Step 2 – Enter N and visual crack length a (mm)
Here you link a few visually measured crack lengths a (from photos or microscope)
to the corresponding fatigue cycles N. The tool finds the closest CSV row in N,
computes the compliance C = dmax/Pmax, and fits a calibration between
a and C. Some example values are pre-filled; you can edit or delete them.
Quick DCB Mode-I explanation (simple view) In a Double Cantilever Beam (DCB) specimen loaded in Mode-I, the beam arms open under tensile loading, a crack grows from the starter notch, and the opening displacement increases for the same load as the crack length increases. The ratio C = d/P is the compliance and is strongly linked to the crack length.
#
N (cycles)
a (mm)
Pmax [N]
dmax [mm]
Pmin [N]
dmin [mm]
C [mm/N]
Use the example N and a values or enter your own. You need at least 2 valid points, then click “Fit m & D”.
Step 3 – Calibration result (log₁₀(C) vs log₁₀(a))
The calibration assumes a power-law compliance relation
C = D · am, or in log form:
log₁₀(C) = m · log₁₀(a) + log₁₀(D).
This step shows the fitted parameters and how well the points lie on this line.
Slope m
–
log₁₀D
–
D
–
R² (fit quality)
–
Final Table – N, Pmax, dmax, C, a_eff
This table lists the filtered points used to build aeff,
keeping only rows where the effective crack length increases by at least 0.1 mm.
Upload and fit to see results.
N
Pmax [N]
dmax [mm]
C [mm/N]
a_eff [mm]
log₁₀(C) vs log₁₀(a_eff)
This plot lets you visually check the calibration in log–log space. A good calibration
should appear approximately linear.
da/dN (7-point & Secant) – a_eff increment ≥ 0.1 mm
For each eligible point, the crack growth rate da/dN is estimated using a 7-point
linear regression and a secant method, then the percentage difference is reported.
No data yet.
a_eff [mm]
N
da/dN 7-pt
da/dN sec
Error [%]
Export a compact PDF report including calibration parameters, tables and plots.