- Brittleness
, and usually makes a snapping sound.
When used in
materials science , it is generally applied to materials that fail in tension rather than shear, or when there is little or no evidence of plastic deformation before failure.When a material has reached the limit of its strength, it usually has the option of either deformation or fracture. A naturally
malleable metal can be made stronger by impeding the mechanisms of plastic deformation (reducing grain size,dispersion strengthening ,work hardening , etc.), but if this is taken to an extreme, fracture becomes the more likely outcome, and the material can become brittle. Improving materialtoughness is therefore a balancing act.Toughening
This principle generalizes to other classes of material. Naturally brittle materials, such as
glass , are not difficult to toughen effectively. Most such techniques involve one of two mechanisms: to deflect or absorb the tip of a propagating crack, or to create carefully-controlled residual stresses so that cracks from certain predictable sources will be forced closed. The first principle is used inlaminated glass where two sheets of glass are separated by an interlayer ofpolyvinyl butyral , which as aviscoelastic polymer absorbs the growing crack. The second method is used intoughened glass andpre-stressed concrete . A demonstration of glass toughening is provided byPrince Rupert's Drop . Brittlepolymers can be toughened by using rubber particles to initiate crazes when a sample is stressed, a good example beinghigh impact polystyrene or HIPS. The least-brittle structural ceramics aresilicon carbide (mainly by virtue of its high strength) and transformation-toughenedzirconia .Effect of pressure
Generally, the "
brittle strength " of a material can be increased bypressure . This happens as an example in thebrittle-ductile transition zone at an approximate depth of 10 km in the Earth's crust, at which rock becomes less likely to fracture, and more likely to deform ductilely.Crack growth
Supersonic fracture is crack motion faster than the speed of sound in a brittle material. This phenomenon was first discovered by scientists from theMax Planck Institute for Metals Research inStuttgart (Markus J. Buehler andHuajian Gao ) andIBM Almaden Research Center in San Jose, California (Farid F. Abraham ).ee also
*
Izod impact strength test
*Charpy impact test
*Fractography
*Fracture
*Forensic engineering References
* Lewis, Peter Rhys, Reynolds, K, and Gagg, C, "Forensic Materials Engineering: Case studies", CRC Press (2004).
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