Three Point Bend Rig

Breaking strength/stress of rigid samples can be determined by performing a three point bend test. A test specimen of either rectangular or circular cross-section is supported as a beam between two supports that are a known distance apart. A compressive deflection is applied at a constant rate to the centre of the sample (which is also central to the supports) until either a predetermined force value is reached or the specimen breaks.

This large Three Point Bend Rig provides a base with graduated variable support length up to 240mm and accommodates samples up to 90 mm wide. A flexure unit is attached to the Load Cell. Rollers are provided on both supports and the flexure unit, to minimise friction during the test.  Typical applications include measuring the break strength of biscuits, chocolate bars and packaging. A test may, for example, be used to assess the effect of different ingredients/processes used, or to examine typical finished product problems such as moisture uptake.

Measurements include flexural stress, flexural stress at break, flexural strength, conventional deflection, flexural stress, flexural strain, flexural strain at break, flexural strain at flexural strength, flexural strain at maximum flexural stress, flexural modulus.

The breaking strength (force per unit width) or breaking stress (force per unit area) of the sample is taken as the maximum strength or stress value of the curve. Other textural characteristics that may be of interest are the distance to break and the gradient of the slope during application of force. The distance to break gives an indication of the brittleness of the sample as this shows how far a sample can be deformed before fracture. The gradient of the slope indicates sample toughness; the higher the gradient, the tougher the sample.

A self-supporting material with maximum width of 90mm.

• Rollers reduce friction.
• Enables wider and longer samples to be tested with greater support distance.
• Not ideal for the testing of small samples.