n-value vs r-value compares two different sheet-metal test properties. The n-value is the tensile strain-hardening exponent. The r-value is the plastic strain ratio, associated with plastic anisotropy and resistance to thickness change under in-plane loading.
For an aluminum sheet purchase, give each result its own column. Preserve the test method, specimen direction and stated measurement basis. Neither number alone approves a forming tool or a finished component.
On this page
n-value vs r-value: what does each describe?
ASTM E646-16(2024)’s public overview identifies n as a strain-hardening exponent determined through tension testing of metallic sheet. It describes the parameter in relation to strengthening during plastic deformation and relative stretch formability in similar metallic systems.
ASTM E517-24’s public overview identifies r as a plastic strain ratio for sheet-metal deep-drawing applications. It describes resistance to thinning or thickening under tensile or compressive forces in the sheet plane and connects the parameter with plastic anisotropy.
These summaries identify the properties. They do not provide a forming recipe or prescribe an aluminum-grade acceptance value. Use the applicable material requirement and the responsible laboratory’s complete report for a real order.
| Report property | Keep with the result |
|---|---|
| n: strain-hardening exponent | Method, reported strain interval and test conditions |
| r: plastic strain ratio | Method, specimen orientation and stated strain basis |
| Tensile or yield strength | Separate stress heading and units |
| Elongation | Separate percentage and specimen basis |
Keep the stress and elongation columns distinct as well. Our tensile versus yield strength guide explains those stress headings; it does not convert them into either of these sheet-forming parameters.
Check 1: preserve the exact property heading
Start with the name printed on the supplier’s document. Retain the symbol and any suffix or subscript. Ask for the legend when a spreadsheet abbreviates the property.
A comparison headed simply “forming value” cannot show which result was supplied. Request the original laboratory heading before moving the number into a controlled purchasing record.
Ask whether the entry is a reported result, a specified requirement or a typical reference. Those are different kinds of evidence. Label the category next to the value instead of allowing a catalog entry to look like a lot-specific test.
If both properties are required, use two lines in the inquiry. Record any missing entry as pending clarification. Avoid filling a blank cell with a neighboring value merely to make the comparison complete.
Check 2: retain specimen direction
The E517 overview explains that r can differ with specimen orientation relative to rolling direction. Its example uses a subscript to identify that direction. Keep the reported designation rather than removing it for a shorter column label.
Ask the laboratory to define the reference direction and explain how each specimen is identified. A note such as “longitudinal” needs a clear relationship to the supplied product and its rolling reference.
When several directions appear, keep them on separate rows with their labels. If a report includes an average, request its stated definition and the underlying entries used. Do not construct an average from an incomplete collection of results.
Carry the agreed orientation requirement into sample identification. If pieces are cut for laboratory preparation, ask the laboratory to specify the required markings and starting-piece arrangement. Use that instruction for the actual handover.
Check 3: read the stated strain basis and conditions
E646’s overview allows n to be determined for specified portions of the plastic stress-strain curve. It also notes that the result can depend on test rate and temperature. Retain the reported interval and conditions rather than treating every n entry as the same calculation.
E517 explains that r can depend on strain level for some materials and that the report can identify the strain at measurement. Preserve that information wherever it is stated.
Ask the laboratory whether the proposed comparison uses a consistent basis. If one report omits an interval or a necessary condition, request clarification. The buyer should not invent a test setting to resolve a missing field.
Keep the method designation and revision on the record. If a supplier proposes a different method, ask the responsible material authority to assess it. A familiar symbol does not establish equivalence between different reporting arrangements.
For another pair of deformation results, see elongation versus reduction of area. Each property needs its own definition and measurement basis.
Check 4: connect the result to the offered sheet
Identify the alloy, material condition, sheet product and applicable thickness description. Retain the report’s sample identity and its documented connection to the offered material.
If the material has several delivery stages, identify the condition represented by the report. A record for an earlier state should not silently become the evidence for a later supplied state.
Keep the original document with its issuer and reference. Where stock comes through an intermediary, request the documented link between the delivery identifier and the source record.
Our material certificate review covers that identity connection. The two forming-related fields discussed here are additional result headings; they do not replace the rest of the required material evidence.
Have the authorized reviewer assess the actual acceptance requirement. This guide supplies no universal minimum n or r value and no approved substitution between aluminum grades.
A fictional comparison reveals two different gaps
Imagine sheet inquiry NR8 asks for both properties under an agreed laboratory requirement. Offer A supplies an r entry but leaves n blank. Offer B supplies an n entry with a stated interval but gives no material-lot connection.
For A, request the missing n information. The existing r entry is useful under its own heading, but it does not answer the other property request.
For B, preserve the n entry and request the material identity link. The right heading and an interval still need the evidence that connects the result to the offered sheet.
This invented example contains no numerical material limits or actual supplier findings. It shows why completeness and traceability require separate checks. The appropriate reviewer must decide whether the completed evidence satisfies the order.
Prepare the cutting handover after material review
Once the material and required documents are approved, send the released sheet identity, piece drawing, quantity and delivery-stage requirements to the processing supplier.
If pieces are reserved for test preparation, identify that quantity separately from production blanks. Obtain the laboratory’s starting-piece dimensions and marking instruction before cutting them.
Keep stock identity and any required direction markings connected through handling and packing. Record which pieces went to the agreed laboratory preparation stage.
Send JiurunCut the defined cutting-stage inquiry when the material form and part scope are relevant. Keep sheet-forming feasibility and laboratory acceptance with the responsible technical teams.
Buyer questions about n-value vs r-value
Does a larger r entry prove a missing n requirement is met?
No. Retain the separate property headings and obtain the requested evidence.
Can I compare results without their conditions?
Ask the laboratory to confirm the reporting bases before using the numbers for acceptance.
Does either property approve the finished part?
Use the actual geometry, material and forming assessment together with the agreed final-part requirements.