The extensometer measures the deformation of the probe during the test with much greater accuracy than the displacement of the machine beam. The standard requires class 1 or better extensometers (according to ISO 9513) to determine the elastic limit by extension (Rp0,2).<\/span><\/p>

There are two main types:<\/span><\/p>

• Contact extensometers: they are mechanically attached to the test tube. They are precise and robust, but they must be removed before breaking them to avoid damaging them.<\/span><\/li>
• Video extensometers: measure by image analysis, without physical contact with the sample tube. They have the advantage of being able to remain active throughout the entire fracture and are ideal when the sample tube is thin or the material is fragile.<\/span><\/li><\/ul>

  At Servosis, we configure our testing systems according to each client's requirements: force capacity, extensometer type, clamps, and data acquisition software. Each installation is tailored to the material and standard that the laboratory needs to meet.<\/span><\/p>

  Step-by-step tensile test procedure<\/b><\/h2>

  The tensile test has a well-defined protocol. Here are the usual steps, as they are performed in a laboratory that works according to ISO 6892-1:<\/span><\/p>

  1. Reception and identification of the sample: record the origin of the material, the casting number, the state of supply (laminated, annealed, tempered\u2026) and the applicable product standard.<\/span><\/li>
  2. Machining of the sample: obtain the defined geometry from the original material. If the sample is already machined, verify dimensions with a caliper or micrometer.<\/span><\/li>
  3. Measurement of initial dimensions: measure the cross-section at three points along the calibrated length and take the minimum value as So. Mark Lo if post-rupture elongation is to be measured.<\/span><\/li>
  4. Placing in the machine: fix the probe in the clamps, aligning its longitudinal axis correctly with the load axis. A poor alignment introduces bending forces that distort the curve.<\/span><\/li>
  5. Positioning the extensometer: Fix the extensometer in the calibrated area. Verify the zero.<\/span><\/li>
  6. Definition of the test speed: according to the standard, Method A (control by specific deformation rate, more reproducible) or Method B (control by force rate). In many laboratories, Method A is used for the elastic zone and it is changed to Method B or free after the elastic limit.<\/span><\/li>
  7. Test execution: the machine applies the load continuously until the test tube breaks.<\/span><\/li>
  8. Extension rod removal: if it is contact type, remove it before the rupture occurs to avoid damage.<\/span><\/li>
  9. Post-rupture measurement: join the two halves of the broken probe and measure the length between the marks (Lu) and the minimum section at the point of rupture (Su) to calculate elongation (A) and strain (Z).<\/span><\/li>
  10. Generation of the report: the machine software automatically calculates Rp0.2, Rm, A and Z. The operator verifies that the test has been valid (breaking within the calibrated zone, without any abnormalities in the curve).<\/span><\/li><\/ol>

      A complete experiment \u2014from the preparation of the sample to the report\u2014 can take between 15 and 45 minutes depending on the material, the speed of the experiment and the parameters that need to be determined.<\/span><\/p>

      Dimensions that are obtained and how to interpret them<\/b><\/h2>

      The main result of the test is the stress-strain curve (\u03c3-\u03b5). Based on it, the software calculates the following magnitudes:<\/span><\/p>

      Magnitude<\/b><\/p><\/th>	Symbol<\/b><\/p><\/th>	Unit<\/b><\/p><\/th>	What it measures<\/b><\/p><\/th><\/tr><\/thead>
      L\u00edmite el\u00e1stico<\/span><\/p><\/td>	Rp0.2<\/span><\/p><\/td>	MPa<\/span><\/p><\/td>	Tension to which the material undergoes a plastic deformation of 0.2 %<\/span><\/p><\/td><\/tr>
      Resistance to traction<\/span><\/p><\/td>	Rm<\/span><\/p><\/td>	MPa<\/span><\/p><\/td>	Maximum tension sustained before rupture<\/span><\/p><\/td><\/tr>
      Extension after rupture<\/span><\/p><\/td>	A<\/span><\/p><\/td>	%<\/span><\/p><\/td>	Permanent plastic deformation in the fracture zone<\/span><\/p><\/td><\/tr>
      Strictness<\/span><\/p><\/td>	Z<\/span><\/p><\/td>	%<\/span><\/p><\/td>	Reduction of cross-section at the breaking point<\/span><\/p><\/td><\/tr>
      Young Module<\/span><\/p><\/td>	E<\/span><\/p><\/td>	GPa<\/span><\/p><\/td>	Susceptible to the elastic zone; stiffness of the material<\/span><\/p><\/td><\/tr><\/tbody><\/table> Table 2. Main measurements obtained in the tensile test according to ISO 6892-1.<\/span><\/p> In addition to these magnitudes, many laboratories also determine the Rm\/Rp0.2 ratio (hardening ratio), which provides information about the material\u2019s ability to redistribute stresses before fracture \u2014 a relevant data point in seismic design and forming applications.<\/span><\/p> Expected results according to the type of steel<\/b><\/h2> The values obtained in the test must always be interpreted in relation to the requirements of the corresponding product standard. But as a guideline, here are the typical ranges for the most common steels:<\/span><\/p> Structural steel S235 (EN 10025): Rp0.2 \u2265 235 MPa, Rm between 360 and 510 MPa, A \u2265 26 %.<\/span><\/li> Structural steel S355: Rp0.2 \u2265 355 MPa, Rm between 470 and 630 MPa, A \u2265 22 %.<\/span><\/li> Austenitic stainless steel 304 (EN 10088): Rp0.2 \u2265 210 MPa, Rm \u2265 520 MPa, A \u2265 45 %.<\/span><\/li> High-strength steel (AHSS, DP or TRIP type for automotive applications): Rm between 600 and 1500 MPa with different Rp0.2 levels depending on the grade.<\/span><\/li> Tool steel (tempered and quenched): Rm > 1200 MPa, Reduced (2\u20138 %).<\/span><\/li><\/ul> If the result falls below the minimum value required by the product standard, the material is rejected. If there is excessive dispersion between samples from the same batch, the laboratory has to investigate whether there is variability in the material, in the preparation of the samples, or in the test itself.<\/span><\/p> Common errors that invalidate the test<\/b><\/h2> Over the years, at Servosis we have seen some patterns that repeat themselves when the results of a tensile test are questionable:<\/span><\/p> Poor alignment of the probe in the jaws: this generates bending forces that artificially raise the apparent elastic limit.<\/span><\/li> Test speed too high: In the elastic zone, excessive load rates increase the measured Rp0.2, especially in steels with a yield point.<\/span><\/li> Extensor with incorrect zero or out-of-date calibration: the Young modulus and Rp0.2 calculated values may deviate significantly.<\/span><\/li> Poor machining of the probe: tool marks or abrupt changes in section in the calibrated area cause premature or non-representative breakage.<\/span><\/li> Uncontrolled temperature: in materials sensitive to temperature (such as certain high-strength steels or austenitic stainless steels), testing outside the \u00b15 \u00b0C range compared to 23 \u00b0C may alter the results.<\/span><\/li> Break outside the calibrated length: The measured elongation is not representative. Invalid result according to the standard.<\/span><\/li><\/ul> Many of these errors can be avoided with well-maintained and calibrated equipment. If your laboratory is evaluating whether its current equipment meets the requirements of ISO 6892-1, at Servosis we can help you <\/span>analyze the status of your testing machine<\/span><\/a> and propose the necessary improvements.<\/span><\/p> Frequently asked questions about the tensile test on steel<\/b><\/h2> The questions we receive most often from laboratories, PhD students, and process engineers who work with this test:<\/span><\/p> Question<\/b><\/p><\/th> Response<\/b><\/p><\/th><\/tr><\/thead> What test speed does ISO 6892-1 require?<\/b><\/p><\/td> The standard defines two methods: Method A (control by deformation rate) and Method B (control by force rate). Method A is the most accurate and recommended when full traceability of the results is required.<\/span><\/p><\/td><\/tr> How many samples are needed for a valid test?<\/b><\/p><\/td> It depends on the product and the applicable product standard. The usual practice is to test between 2 and 5 samples per batch. ISO 6892-1 specifies the geometry of the sample, but the number of replicates is defined by the product standard or the laboratory protocol.<\/span><\/p><\/td><\/tr> What is the difference between Rp0.2 and Re?<\/b><\/p><\/td> Re is the conventional elastic limit (in materials with a marked yield point). Rp0.2 is the elastic limit due to extension of 0.2 %, which is used when there is no defined yield point. In structural steels, Re usually appears; in stainless steels, Rp0.2.<\/span><\/p><\/td><\/tr> Can the test be done without an extensometer?<\/b><\/p><\/td> Technically yes, but the results are very limited: only the maximum load and the breaking strength are obtained. Without an extensometer it is not possible to determine the modulus of elasticity, the elastic limit by extension, or the elongation with precision. The ISO 6892-1 standard requires an extensometer for valid results.<\/span><\/p><\/td><\/tr> What happens if the test tube breaks outside the calibrated area?<\/b><\/p><\/td> If the break occurs outside the calibrated length (Lo), the result of the elongation is not valid according to the standard. In that case, the test must be repeated with a new sample. This is one of the most common causes of rejection of results in laboratories.<\/span><\/p><\/td><\/tr> Does the same machine work for steel and for polymers?<\/b><\/p><\/td> It depends on the configuration. A well-equipped universal machine can test both materials, but they require different tools (pliers, extensometers) and very different force ranges. For polymers, the reference standard is ISO 527 or ASTM D638, not ISO 6892-1.<\/span><\/p><\/td><\/tr><\/tbody><\/table> In short<\/b><\/h2> The tensile test on steel is a relatively simple test in appearance, but it requires rigor at every step: a well-machined test specimen, calibrated equipment, the correct test speed, an appropriate extensometer, and an operator who knows how to interpret the resulting curve.<\/span><\/p> ISO 6892-1 exists precisely to ensure that this rigor is reproducible: no matter where the test is conducted, the results must be comparable. That is what gives value to the Rp0.2 or Rm data that appears on a material certificate.<\/span><\/p> If your laboratory is sizing or upgrading its traction equipment, at Servosis we have been manufacturing and upgrading for decades. <\/span>universal testing machines<\/span><\/a> adapted to the real needs of each client. There is no standard solution that works the same for everyone.<\/span><\/p> Do you want to know if your traction equipment complies with ISO 6892-1?\u00a0<\/b><\/p> Tell us about your case and we will study it without obligation.<\/span><\/a><\/p> Contact us at<\/span><\/a><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t \n\t\t\t\t\t\t \n\t\t\t\t\t \n\t\t\t \n\t\t\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":" El ensayo de tracci\u00f3n en acero es uno de los ensayos mec\u00e1nicos m\u00e1s habituales en laboratorios industriales y de investigaci\u00f3n. Su objetivo es simple: tirar de una probeta hasta que rompe, midiendo en cada momento la fuerza aplicada y la deformaci\u00f3n sufrida. A partir de esa curva de carga-deformaci\u00f3n se extraen las propiedades mec\u00e1nicas que […]<\/p>\n","protected":false},"author":4,"featured_media":16613,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"om_disable_all_campaigns":false,"inline_featured_image":false,"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[18],"tags":[],"class_list":["post-16603","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-noticias"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/posts\/16603","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/comments?post=16603"}],"version-history":[{"count":11,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/posts\/16603\/revisions"}],"predecessor-version":[{"id":16618,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/posts\/16603\/revisions\/16618"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/media\/16613"}],"wp:attachment":[{"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/media?parent=16603"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/categories?post=16603"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.servosis.com\/en\/wp-json\/wp\/v2\/tags?post=16603"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}