Application Note | Yield Strength Testing
Yield and Tensile Strength of Steel and Aluminum by Indentation
Measuring YS and UTS with a Flat Diamond Punch Instead of Machined Tensile Coupons
Research & Experimental Testing
Duanjie Li, Jonathan Thomas & Pierre Leroux
Visual Design & Editorial
Andrew Shore
Introduction
Yield strength (YS) is the stress at which a material begins deforming plastically and will not return to its original shape when an applied stress is removed. Ultimate tensile strength (UTS) is the maximum stress a material can withstand before breaking. These two properties indicate the upper limit loads that can be applied to mechanical parts and structures. Yield strength and Ultimate tensile strength play vital roles in material production in annealing, forging, rolling, and pressing processes.
Why Measure Yield and Tensile Strength by Indentation
Traditionally Yield Strength and Ultimate Tensile Strength have been tested using a large tensile testing machine requiring enormous strength to pull apart test specimens. It is costly and time-consuming to properly machine many test coupons for a material where each sample can only be tested once. Small defects in the sample create a noticeable variance in test results. Different configurations and alignments of the tensile testers in the market often result in substantial variations in testing mechanics and outcomes.
NANOVEA’s innovative indentation method directly provides Yield Strength and Ultimate Tensile Strength values comparable to values measured by conventional tensile tests. This measurement opens a new realm of testing possibilities for all industries. The simple experimental setup significantly cuts sample preparation time and cost compared to the complex coupon shape required for tensile tests. Multiple measurements on a single sample are possible with a small indentation size. It prevents the influence of defects seen in tensile test coupons created during sample machining. YS and UTS measurements on small samples in localized area allow for mapping and local defect detection in pipelines or auto structures.
ℹ️ Learn more about indentation lab services for yield and tensile strength.
Measurement Objective
In this application, the NANOVEA Mechanical Tester measures the Yield Strength and Ultimate Tensile Strength of stainless steel SS304 and aluminum Al6061 metal alloy samples. The samples were chosen for their commonly recognized Yield Strength and Ultimate Tensile Strength values showing the reliability of NANOVEA’s indentation methods.
NANOVEA PB1000 Large Platform
Mechanical Tester
Test Procedure
The Yield Strength and Ultimate Tensile Strength tests were performed on the NANOVEA Mechanical Tester in the Microindentation mode. A cylindrical flat diamond tip of 200 µm diameter was used for this application. SS304 and Al6061 alloys were selected for their extensive industrial application and commonly recognized Yield Strength and Ultimate Tensile Strength values, in order to show the great potential and reliability of the indentation method. Samples were mechanically polished to a mirror-like finish before testing to avoid surface roughness or defect influence on test results. Test conditions are listed in Table 1. More than ten tests were performed on each sample to ensure the repeatability of the test values.
| Material | SS304 | Al6061 |
|---|---|---|
| Applied force (N) | 40 | 30 |
| Loading rate (N/min) | 80 | 60 |
| Unloading rate (N/min) | 80 | 60 |
Table 1: Test conditions of YS and UTS for SS304 and Al6061.
Results and Discussion
Load-displacement curves of the SS304 and Al6061 alloy samples are shown in Fig. 2 with the flat indenter imprints on the test samples inset. Analysis of the “S” shaped loading curve using special algorithms developed by NANOVEA calculates Yield Strength and Ultimate Tensile Strength. Values are automatically calculated by the software as summarized in Table 2. Yield Strength and Ultimate Tensile Strength values obtained by conventional tensile tests are listed for comparison.
| Material | Yield strength (MPa) | Ultimate tensile strength (MPa) | ||
|---|---|---|---|---|
| Indentation | Tensile test | Indentation | Tensile test | |
| SS304 | 277 ± 21 | 275 | 609 ± 16 | 620 |
| Al6061 | 231 ± 18 | 241 | 301 ± 9 | 300 |
Table 2: YS and UTS of SS304 and Al6061 measured using indentation and tensile tests.
The results show good agreement in YS and UTS measurements of the SS304 and Al6061 alloys between indentation and tensile techniques. YS and UTS tested by indentation with NANOVEA’s Mechanical Tester exhibit superior precision and repeatability. The indentation technique for YS and UTS evaluation is substantially more time- and cost-effective than conventional tensile testing procedures. Indentation does not require expensive and complicated sample machining, enabling fast quantitative mapping of YS and UTS values on small samples while detecting localized mechanical defects of mechanical parts in service.
Conclusion
In this study, we showcased the capacity of NANOVEA Mechanical Tester in evaluating Yield Strength & Ultimate Tensile Strength of stainless steel and aluminum alloy sheet samples. The simple experimental setup significantly cuts the time and cost for sample preparation required for tensile tests. The small indentation size makes it possible to perform multiple measurements on one single sample. This method allows YS/UTS measurements on small samples and localized areas, providing a solution for YS/UTS mapping and local defect detection of pipelines or auto structure.
The Nano, Micro or Macro modules of the NANOVEA Mechanical Tester all include ISO and ASTM compliant indentation, scratch and wear tester modes, providing the widest and most user friendly range of testing available in a single system. NANOVEA’s unmatched range is an ideal solution for determining the full range of mechanical properties of thin or thick, soft or hard coatings, films and substrates, including hardness, Young’s modulus, fracture toughness, adhesion, wear resistance and many others. In addition, optional 3D non-contact profiler and AFM Module are available for high resolution 3D imaging of indentation, scratch and wear track in addition to other surface measurements such as roughness.
Frequently Asked Questions About Yield and Tensile Strength by Indentation
What are yield strength and ultimate tensile strength?
Yield strength (YS) is the stress at which a material begins deforming plastically and will not return to its original shape when the stress is removed. Ultimate tensile strength (UTS) is the maximum stress a material can withstand before breaking. Together they indicate the upper limit loads for mechanical parts and structures.
Why measure yield strength by indentation instead of tensile testing?
Tensile testing needs machined coupons that can each be tested only once, and small defects and differences between tensile testers cause variance. Indentation cuts sample preparation time and cost, allows multiple measurements on one sample, and avoids defects introduced when machining coupons.
How does the indentation method work?
A cylindrical flat diamond tip of 200 µm diameter is pressed into the polished sample in microindentation mode, and special NANOVEA algorithms analyze the “S” shaped loading curve to calculate YS and UTS automatically.
How do indentation results compare with tensile tests?
They agree well. SS304 gave a YS of 277 ± 21 MPa and UTS of 609 ± 16 MPa by indentation, against 275 and 620 MPa by tensile test; Al6061 gave 231 ± 18 and 301 ± 9 MPa, against 241 and 300 MPa.
Where is indentation-based yield strength useful?
On small samples and localized areas, enabling YS and UTS mapping and local defect detection, for example in pipelines or automotive structures and in mechanical parts in service.
Which NANOVEA instrument measures yield strength by indentation?
The NANOVEA Mechanical Tester in microindentation mode. Its Nano, Micro and Macro modules include ISO and ASTM compliant indentation, scratch and wear modes.
