Fracture/Bending Tests

Learn about fracture/bending testing, when to use these test types and the typical probes and fixtures for use on your Texture Analyser.

What is a fracture/bending test?

This type of test can measure the fracture and break strength of hard and brittle products (or their flexibility) by bending the sample, usually until a break occurs. If a break does not occur whilst the sample is flexed then a measure of its flexibility can be performed instead – a degree of flexibility can be desirable or a characteristic to be avoided, depending upon the sample. Stable Micro Systems enables a wide range of tests in this field, using fixtures such as the Three Point Bend Rig which are adaptable to many types of sample, and also specialist attachments like the Crisp Fracture Support Rig or the Spaghetti Flexure Rig.

Bending is a combination of compression, tension and some shear. Bending tests are often used in materials testing, possible because they are easy to perform and it is not necessary to fix the specimen to an apparatus. Fracture mostly starts on the outside of the tensed part of the sample and therefore can be observed.

Basic cylinder probes may also be used for fracturability testing, for example, for assessing tablet fracturability in a Diametral Crushing Test. Fracture properties also can be studied by less well defined methods of deformation that may nevertheless yield real material characteristics. Examples are cutting of material, compression and biting between wedges.

When performing tests on samples that fracture or break quickly the duration of this type of test is very short (often less than 1 second). In this case it is recommended that a maximum data acquisition rate is selected, i.e., 2000 points per second, to collect as much detail in the short duration of time as possible.

Why perform a fracture/bending test?

Snapping and bending tests are usually applied to products that are in the shape of a bar or sheet. It is a versatile test (mostly commonly a 3 point bend test) and can be applied to many types of products that are available in, or can be cut or shaped into, elongated test beams. Usually the product is stressed until it breaks and the force required to do so is measured. The amount of deformation the sample will absorb before it fails may also be of interest. These breaking/bending characteristics can be very important measurement for materials where a high degree of strength may be required with a degree of flexibility so that a material does not shatter easily on small application of stress.

In the case of food normally testing involves large deformations. Fracture and/or yielding then become the salient features. Foods that exhibit fracturability are products that possess a high degree of hardness and low degree of adhesiveness. Snap, meaning to break suddenly upon the application of a force, is a desirable textural property in most crisp foods, e.g. fresh green beans and other high turgor vegetable, and potato chips and other snack items. The ability to snap is a measure of the temper of chocolate, the moisture content of crisp cookies, the turgor of fresh vegetables and the amounts of shortening in baked goods. The sharp cracking sound that usually accompanies snapping is the result of high energy sound waves generated when the stressed material fractures rapidly and the broken parts return to their former configuration. This test indicates product fracturability/brittleness/crispness and can be the major salient feature of a product

Examples of fracture/bend tests using various attachments and probes

Properties that can be measured with a fracture/bending test

Fracture/bending tests are typically chosen to measure:

Brittleness, snapping force, tip strength, flexibility, force to bend, bend modulus, Young’s Modulus of bend, fracture force, flexure modulus

To understand how these properties are measured visit the Textural Properties page.

Typical probes and fixtures used for fracture/bending tests

To understand how these fixtures are designed and manufactured visit the Texture Analysis Attachments page.

Other probes/fixtures and accessories are available to accommodate many specialist needs, or can be designed and manufactured to a specific customer brief.

Items with codes prefixed 'HDP/' must be used with the HDP/90 Heavy Duty Platform.

Items tagged * are Community Registered Designs.

You might also be interested in:

Article about Paper and cardboard testing using a Texture Analyser

Request an article about Tips and tricks for successful Fracturability Testing. Fracturability is the tendency of a material to fracture, crumble, crack, shatter or fail upon the application of a relatively small amount of force or impact.

The term encompasses crumbliness, crispiness, crunchiness and brittleness, and is usually displayed by a product of high degree of hardness and low degree of cohesiveness and is commonly the textural property possessed by baked goods, snacks and generally 'dry' products.

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