DCB Mode-I calculations

Crack Calibration to a_eff & da/dN

Sample Information

Enter specimen name and geometry (defaults provided).

Sample Name

Variable Name

B (mm) – Width

2h (mm) – Total thickness

l1 (mm) – Load to near support

l2 (mm) – Support span

a₀ (mm) – Precrack length

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 a_eff 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.

CSV file

Please upload a CSV file to begin.

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 = d_max/P_max, 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”.

Final Table – N, Pmax, dmax, C, a_eff

This table lists the filtered points used to build a_eff, 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.