How to Measure Fracturability and Brittleness
FRACTURABILITY/BRITTLENESS 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. It is usually displayed by a product of high degree of hardness and low degree of cohesiveness and is the textural property commonly possessed by baked goods, snacks and generally 'dry' products.
Fracturability encompasses crumbliness, crispiness, crunchiness and brittleness. A material is brittle if it is liable to fracture when subjected to stress. That is, it has little tendency to deform (or strain) before fracture and usually makes a snapping sound.
The usage, including eating, of foods normally involves large deformations. Fracture and/or yielding then become the salient features. During deformation of a more or less solid material, local stresses and strains are always highest near inhomogeneities; fracture starts near or at such places. During fracture these defects grow, new surfaces are formed and the material ultimately falls into pieces.
Fracture starts if the local stress is higher than the adhesive or cohesive forces in the material at that place. It propagates spontaneously if the deformation energy that is released when the material fractures is at least equal to the energy needed to create new surfaces. Both processes, fracture initiation and propagation, depend on the presence of defects; larger defects cause fracture to occur at lower overall stresses and strains.
The Acoustic Envelope Detector can be employed for any material which produces an audible noise when tested as it captures another dimension (i.e. sound) during the test which can also be analysed and used as a measured product feature. This is usually for brittle materials and the acoustic signal is as a result of a crack, break, snap or failure of some type.
Typical properties that can be obtained from a texture analyser graph:
Rupture Point, Crispness, Fracturability, Crunchiness, Brittleness, Fracture Strength, Fracture Distance, Work of Failure, Breaking Strength
Typical Texture Analyser graph with annotated properties of gel and tablet rupture tests
In most materials, peak force is usually the start of fracture. The force then falls either to zero if fracture is complete, or falls partially if fracture is incomplete. Fracture does not always start at the highest point on the curve but usually the start of fracture is recorded as a peak on the curve. During a test it is important to visually monitor the start of fracture.
Fracturability (single break) is usually represented by a characteristic sharp curve (usually a thin triangle shape). In a curve such as that shown above, the following are often recorded:
• Distance at break = ‘fracturability'/’brittleness' (mm)
• ‘Force at break' = ‘hardness' (g/kg)
• Gradient of slope = ‘toughness'/'stiffness' (g/mm)
Typical Probe/Fixture used for Measurement:
Cylinder, Needle, Cone and Spherical Probes >>
Three Point Bend Rig >>
Crisp Fracture Support Rig >>
Knife Blades >>
Lipstick Cantilever Rig >>
Spaghetti Flexure Rig >>
The above are only typical examples of fracturability/brittleness measurement. We can, of course, design and manufacture probes or fixtures that are bespoke to your sample and its specific measurement.
Once your measurement is performed, our expertise in its graphical interpretation is unparalleled – no-one understands texture analysis like we do. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.
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