Frequently Asked Questions
Common questions about using MatTest and interpreting results.
Is my data uploaded to a server?
No. MatTest runs entirely in your browser. Your file is read locally using JavaScript File APIs, and no data is sent to any server. You can even use MatTest offline after the page has loaded.
What file formats are supported?
CSV (.csv), tab-separated (.txt, .tsv), and Excel (.xlsx, .xls). The file must have a header row and numeric data. Excel files: only the first sheet is read.
My elastic modulus looks wrong. What should I do?
In Advanced Mode, you can manually specify the E-fit strain range. Select a range where the curve looks clearly linear (avoid the toe region at the start and the yielding region at the end). A good R² is typically above 0.998. Also check your unit selections — using kN instead of N or mm² instead of m² will shift the modulus by orders of magnitude.
The yield strength does not match what I expect. Why?
MatTest uses the offset proof stress method (default: 0.2% offset). If your material has a distinct upper/lower yield point (e.g., low-carbon steel), the 0.2% offset method may intersect the stress-strain curve differently than the lower yield plateau. For these materials, consider reading the yield stress directly from the chart. You can also change the offset percentage in the settings.
Why is true stress/strain shown only up to UTS?
The formulas ε_true = ln(1+ε_eng) and σ_true = σ_eng×(1+ε_eng) assume uniform deformation and volume conservation. After the UTS, necking causes non-uniform deformation: the local strain in the neck is much higher than the nominal strain, and the actual stress in the neck is much higher than the calculated value. Post-necking true values are approximate and shown dashed for informational purposes only.
What is the Considere criterion?
The Considere criterion (also called Hart's stability condition) states that necking initiates when the rate of strain hardening can no longer compensate for the load-bearing area reduction: dσ_true/dε_true = σ_true. Graphically, this is where the hardening rate curve crosses the true stress curve from above. This condition gives the true strain at the onset of necking, which corresponds to the UTS in terms of engineering stress.
What is the Hollomon equation and when is it valid?
The Hollomon (power law) equation σ_true = K×ε_p^n describes the relationship between true stress and plastic true strain for many metallic materials in the mid-strain range. n is the strain hardening exponent (higher n = more uniform deformation) and K is the strength coefficient. It is typically valid between the yield point and the UTS. Very low strains (near yield) and very high strains (near fracture) often deviate from the power law.
My n-value R² is low. Is this a problem?
A low Hollomon R² (e.g., below 0.95) indicates the material does not follow a simple power law over the analyzed range. This is common for dual-phase steels, TRIP steels, aluminum alloys with serrated flow, and other materials with complex hardening behavior. Try adjusting the Hollomon range in Advanced Mode to focus on the most linear region of the log-log plot. Consider that some materials require two-stage Hollomon fits.
How is fracture strain estimated?
MatTest now estimates fracture strain from the post-UTS engineering stress response, not simply from the last recorded point. It first looks for the earliest stress-collapse point where the smoothed post-UTS stress falls to 10% of UTS or less and stays broadly below 15% across the next few points. If no such collapse is found, it falls back to the largest post-UTS stress drop; if that is also unclear, it uses the final recorded point with low confidence. Machine break-detection timing can still shift the estimate slightly from the exact physical separation point.
Can I export results to CSV or Excel?
MatTest supports PDF export and Excel (.xlsx) export from the results screen. CSV export is not available in the current version.
Can I analyze multiple specimens at once?
Not in the current version. You analyze one specimen at a time. Reload the page for a fresh analysis. Multi-specimen overlay comparison is on the roadmap.
My file has extra header rows or comment lines. Will this work?
For CSV files, MatTest uses PapaParse which is fairly robust, but unusual headers may cause issues. For Excel files, MatTest searches the first 5 rows for a valid header row. If your file has many comment rows, try removing them in a text editor before uploading.
Is MatTest free to use?
Yes. MatTest is free for research and educational use. See the Terms of Use for details.