Due to the way in which the atoms of solid materials are laid out, the way in which stress is applied will not only affect how they break but also at what point. Tension and compression is a perfect example of this, as a material may be exceptionally sturdy when stretched, and yet when compressed it may fail with relatively little effort. This is not always the case of course, but it is important to bear in mind that just because a material is impressive in one area, it should not assume that all other related ones are as formidable.
The tension, otherwise known as tensile stress, stretching or pulling strain, that needs to be applied to warp or deform a material is known as the materials ultimate tensile strength, which is often shortened simply to tensile strength. A very important part of engineering, when measuring the tensile strength of a material it is imperative that the details are clear and precise.
Tensile strength is not measured as simply as length or temperature are, as it needs to take into account several factors; including the materials size, where the load will be and the amount of time it will have to remain under stress. The unit used to measure, or rather depict, a materials tensile strength is called the 'pascal' and it is basically the simplified expression of one newton per metre squared.
Without going into too much detail, a newton is a measurement of force which is worked out using a formula that takes into consideration the material's weight and length; once this is worked out it is possible to attribute a portion of this strength to a particular cross section, which in this case 1m2. Once you know these things you would express the result in pascals; I.e. 1 pascal = 1 newton per m2, 10 pascals = 10 newtons per m2, and so on.
Discovering a material's tensile strength is important because if the applied stress or force exceeds it then, depending on the material, things could go a number of ways; all of which are bad. 'Elastic Deformation' is one possibility, and it is probably the best case scenario as it is reversible. Think about it as a spring in that you can pull it apart a little and when you release it will return to how it was; if too much force is applied however the spring will stretch, uncoil and not be able to return to its original shape. This is known as 'Plastic Deformation' and the point at which it occurs is known as the material's 'Yield Strength'.
Plastic deformation is not the worst thing that can happen however, in fact it is preferable as it shows the material is attempting to absorb the stress that is being put on it; where as some materials will simply break. This is what is known as 'Brittle Failure' and when it occurs the material fractures and splits into separate pieces, just like snapping a twig or breaking glass; this type of failure usually happens with little to no warning as generally speaking no elastic or plastic deformation occurs prior to it.
It would be inaccurate to say definitively that a metal, mild steel for example, has a tensile strength of –– because most metals are comprised of varying degrees of impurities and other elements; and as the ratios of these elements determine all the other properties of a material, it is safe to assume that it will have an effect on a material's tensile strength also.