NTB SpecPro

Adhesive joint strength estimate

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Free tool · Adhesive bonding

Adhesive joint strength estimate

Enter the overlap width and length, the shear strength from the adhesive data sheet and a safety factor; bond area, approximate failure load and allowable load are calculated instantly. Everything runs in your browser.

Also available in: Türkçe · العربية

Bond area– mm²
Approximate failure load– kN
Allowable load– kN

Area = b × l · Failure load ≈ area × τ / 1000 (kN) · Allowable load = failure load / safety factor

The shear strength on the data sheet is the average measured on a standard single-lap specimen (ISO 4587 / ASTM D1002 type); in a real joint the stress concentrates at the overlap ends, the average strength falls as the overlap grows, and temperature, humidity and ageing reduce it. That is why safety factors of 3–5 are common. This is an approximation; validate the design by testing your own specimens.

For information only; the adhesive data sheet, the specification and test results govern. The final assessment rests with the responsible design/process engineer.

Let the app keep your bonding recordsThe Adhesive bonding module offers surface preparation, cure records, failure surface assessment and PDF reports.
Try the Adhesive bonding module

Curious?

Why can the average shear strength mislead?In a single-lap joint the load is eccentric; peel and stress concentration occur at the ends while the middle carries little. The data-sheet value is measured on a short, thin specimen; with a long overlap and a thick bond line the average strength drops noticeably.
Does a longer overlap raise the strength proportionally?No. Beyond a certain length the extra area carries almost no load; the bond line is stressed at the ends. Increasing the width, geometry that reduces peel (double lap, tapering) and a more flexible adhesive are more effective than more length.
How much does surface preparation matter?A lot. Poor cleaning or the wrong surface treatment leads to adhesive (interfacial) failure and strength far below the data sheet. Assessing the failure surface is the simplest check of bond quality.
How do I keep bonding records?Surface preparation steps, adhesive lot and expiry date, cure temperature–time record and the test coupon result are kept together. The Adhesive bonding module of the app keeps them in one record, assesses the failure surface from a photo and produces the PDF report.

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