Brittle and Praline

For other uses of Brittle, see Brittle (disambiguation).

A material is brittle if it is subject to fracture when subjected to stress i.e. it has little tendency to deform (or strain) before fracture. This fracture absorbs relatively little energy, even in materials of high strength.

When used in materials science, it is generally applied to materials that fail in tension rather than shear, or when there is 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 material toughness is therefore a balancing act.

This principle generalizes to other classes of material. Naturally brittle materials, such as ceramics (most famously glass), are difficult to toughen effectively. Most such techniques involve one of two mechanisms: to deflect the tip of a propagating crack, for instance by introducing natural weaknesses of limited extent, or to create carefully controlled residual stresses so that cracks from certain predictable sources will be forced closed, as in the case of toughened glass and pre-stressed concrete. Both mechanisms tend to soften the material somewhat, although most ceramics are quite hard to begin with. The least-brittle structural ceramics are silicon carbide (mainly by virtue of its high strength) and transformation-toughened zirconia.

Supersonic fracture is crack motion faster than the speed of sound in a brittle material. This phenomenon was first discovered by scientists from the Max Planck Institute for Metals Research in Stuttgart (Markus J. Buehler and Huajian Gao) and IBM Almaden Research Center in San Jose, California (Farid F. Abraham).

Praline is a sweet food made from a mixture of nuts and boiled sugar, eaten as a confection or more commonly, as an ingredient in other confections. In Europe, the nuts are usually almonds, though sometimes hazelnuts. In Louisiana and Texas, USA, pecans are the nuts almost always used, and cream is often incorporated into mixture.

As originally invented in France, pralines were whole almonds coated in caramelized sugar, but in most other countries the word has since come to mean a smooth paste or powder made by grinding up such sugar-coated nuts. In The Netherlands, Germany and Belgium praline may refer to a filled chocolate of any sort. In Great Britain the term can refer either to praline (the filling for chocolates) or, less commonly, to the original whole-nut pralines.

Robert King Wilkerson one of the Angola Three makes pralines he calls Freelines. Wilkerson made pralines in prison while in solitary confinement. He burned paper in soda cans to cook the candies and gathered ingredients from other prisoners and guards.

Origin of the name

The praline (originally spelled prasline) is named after the French soldier and diplomat Marshal du Plessis-Praslin (1598-1675), whose cook invented it. It is said that this same cook, Clément Lassagne, after retiring from the marshal's service, founded the Maison de la Praline: the confectioner's shop which still exists in the town of Montargis some 110 km south of Paris.

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