How do you calculate lap shear strength?

Divide the failure load by the measured overlap area. 5,000 N over a 25 x 12.5 mm overlap (312.5 mm²) is 16.0 MPa, 4.0 MPa above a 12 MPa requirement, the Apparent Lap Shear Strength calculator's own example. Use the overlap measured on each specimen, not the nominal dimensions.

Why is it called apparent shear strength?

The stress along a single-lap joint is not uniform: it peaks at the ends of the overlap. Load over area is an average that compares specimens of the same geometry and procedure, not the local peak stress and not an allowable for a different joint.

How does the workbook decide a batch result?

FAIL if any specimen or the batch mean is below the plan's required strength; Check if a specimen passes on strength but its failure mode is not one the plan accepts; In progress until the batch has the plan's minimum number of specimens; PASS otherwise.

Which failure modes are acceptable?

The ones your test plan accepts. The Failure modes list on Setup has a Yes or No for each; the example accepts cohesive, thin-layer cohesive and substrate failures and flags clean interface separations and mixed failures for review.

Does it apply statistics such as standard deviation or basis values?

No. It gives each specimen's strength and margin and each batch's mean. If your plan has a statistical acceptance rule, add it as a column alongside.

Does the workbook use macros?

No. It is a plain .xlsx with ordinary formulas, tables and native charts. The Verify sheet re-checks the formulas against fixed test specimens and shows Self-check: PASS.

Quality and Inspection

Lap Shear Test Log Excel Template

Apparent lap shear strength = failure load ÷ (measured overlap width × length). Log every specimen tested to failure and see its margin to the test plan's requirement, whether its failure mode is one the plan accepts, and a PASS, Check, FAIL or In progress result for every batch.

Free, and a plain .xlsx with no macros to enable. A CSV with live formulas and a printed how-to guide come with it.

Overview

This lap shear test log is a working Excel workbook for quality and test engineers, adhesive process engineers and lab technicians. Each specimen pulled to failure is one row with its failure load, measured overlap and failure mode; the workbook works out its apparent shear strength, looks up the requirement of the batch's test plan, and rolls the specimens up to a result per batch. It ships with 48 specimens from ten batches on two test plans of a fictional bonding line, so every tile and chart is filled in when you open it.

In the example, epoxy batch B-2612 averages 20.8 MPa against an 18 MPa requirement, but one specimen failed at the interface at 5,560 N over 25.4 x 12.7 mm, 17.2 MPa, so the batch fails. B-2613 passes on strength, every specimen above 19.7 MPa, but two of its five specimens separated cleanly at a surface, a failure mode the plan does not accept, so it needs a Check; it was the first batch after new abrasion pads on the prep station, and the batches after the pads were replaced pass. B-2620 has three of the five specimens its plan requires and shows In progress.

Apparent lap shear strength is a comparative specimen result, not the peak stress in the joint and not a design allowable. The download is a plain .xlsx with no macros. A CSV with live formulas is also included for other tools; the batch results, dashboard, charts, dropdowns and self-check are in the .xlsx.

What this template includes

Setup sheet with your test plans (required strength, description and minimum specimens), the failure modes each plan accepts, and the batches you test
Specimens table, one row per specimen: batch, test date, failure load, measured overlap width and length and failure mode, with a Check column
Per specimen: plan and required strength looked up through the batch, overlap area, apparent shear strength, margin and a PASS, Check or FAIL result
Per batch: specimens tested against the plan's minimum, mean strength, required strength, mean margin, the PASS, Check and FAIL counts and a batch result in words
Dashboard with four tiles (specimens tested, below requirement, failure modes to review, batches failing), mean strength against requirement, specimen results by batch, and the batch table
Method sheet with every formula, and a Verify sheet that re-checks the formulas against an independent reference and the Apparent Lap Shear Strength calculator (Self-check: PASS)
CSV with live formulas for the Specimens table; the batch results, dashboard, charts, dropdowns and self-check are in the .xlsx

Suggested use case

Use it to record lap shear tests for adhesive qualification, incoming lot checks or production batch release, and to see at a glance which batches pass, which fail and which need their failure modes reviewed.

How to use it

On Setup, list your test plans with their required strength and minimum specimens, mark which failure modes each accepts, and list the batches you test.
On Specimens, give each specimen a row: batch, specimen ID, test date, failure load, measured overlap width and length, and the failure mode.
Fix anything the Check column names.
Open the Dashboard: specimens below requirement, failure modes to review, and the result of every batch.

Frequently Asked Questions

How do you calculate lap shear strength?: Divide the failure load by the measured overlap area. 5,000 N over a 25 x 12.5 mm overlap (312.5 mm²) is 16.0 MPa, 4.0 MPa above a 12 MPa requirement, the Apparent Lap Shear Strength calculator's own example. Use the overlap measured on each specimen, not the nominal dimensions.
Why is it called apparent shear strength?: The stress along a single-lap joint is not uniform: it peaks at the ends of the overlap. Load over area is an average that compares specimens of the same geometry and procedure, not the local peak stress and not an allowable for a different joint.
How does the workbook decide a batch result?: FAIL if any specimen or the batch mean is below the plan's required strength; Check if a specimen passes on strength but its failure mode is not one the plan accepts; In progress until the batch has the plan's minimum number of specimens; PASS otherwise.
Which failure modes are acceptable?: The ones your test plan accepts. The Failure modes list on Setup has a Yes or No for each; the example accepts cohesive, thin-layer cohesive and substrate failures and flags clean interface separations and mixed failures for review.
Does it apply statistics such as standard deviation or basis values?: No. It gives each specimen's strength and margin and each batch's mean. If your plan has a statistical acceptance rule, add it as a column alongside.
Does the workbook use macros?: No. It is a plain .xlsx with ordinary formulas, tables and native charts. The Verify sheet re-checks the formulas against fixed test specimens and shows Self-check: PASS.