Physical Property Measurement: Fracture Testing in Tension

Many foods and pharmaceuticals are not normally subject to tensile forces in their manufacture and consumption. There are, however, exceptions, e.g. dough, gels, spaghetti and adhesives. 

These tests can also be performed on materials from which elongated test specimens can be cut and gripped within the clamps of the Texture Analyser to be stretched. This could include fruit, vegetables and meat. In any case this type of test yields reliable results for tensile modulus, yield stress and strain, strength and strain to fracture, and, if the crack area can be measured, the fracture toughness of the material.

The simplest method of tensile testing is when the specimen comes in an elongated shape (either rectangular or circular in cross-section) or from which reproducible test beams can be cut. 

The specimen is gripped at either end and stretched until it breaks. Clamping the ends of the specimen may present difficulties but these can often be overcome. 

Stable Micro Systems supply a variety of rigs and clamps that allow tensile tests to be carried out on most products.

Typical force/deformation plots and measurable fracture properties
Examples include noodles and spaghetti. All products that can be pulled out, extruded or cut into elongated test specimens, such as pastes, dough, snacks, sausages, chocolate bars show a similar force/deformation profile. In some foods and many materials the increase in force reading is linear up to the point of sample yield or the beginning of plasticity or flow of the material.

Interpretation of results:
In tensile tests the most important fracture property is indicated by the peak in the profile, i.e. the point of breaking. Strong materials give higher fracture stress whereas more deformable materials give a higher fracture strain. The tougher the material the higher the energy. It is worth noting that materials that deform a long way before breaking tend to be tougher (larger area under the curve) than those that go to a higher fracture strain but break quickly. A high peak force should not be confused with greater fracture toughness.

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We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

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