Mecanica

Facultad de Ingeniería

Resistencia de Materiales


One of those materials
¿What are the properties of materials? The properties of material are characteristics of it, describes how it work in different situations. For example a bar of steel has different properties one of these is stiffness, therefore we can use it to support structures and other things.
Let us note the materialproperties that are of primary interest to an engineer designing some structure or machine. In spite of materials have a lot of properties we focus on five properties: Brittleness, Ductility, Stiffness, Resilience and Strength. For the course these are the more important characteristics.

Strength
The ability of a material to stand up to forces being applied without it bending, breaking, shattering ordeforming in any way
There are different strength values of interest.
1. The yield strength is the highest stress that the material can withstand without undergoing significant yielding. The yield-point stress or the offset yield stress, whichever is appropriate for the particular material, is taken as the yield strength.

2. The fracture stress if different from the ultimate stress maybe of interest. It is the value of stress at fracture.

3. The Tensile strength or ultimate tensile strength is a limit state of tensile stress that leads to tensile failure in the manner of ductile failure (yield as the first stage of that failure, some hardening in the second stage and breakage after a possible "neck" formation) or brittle failure (sudden breaking in two or more pieces ata low stress state). Tensile strength can be quoted as either true stress or engineering stress.

4. The Impact strength is the capability of the material to withstand a suddenly applied load and is expressed in terms of energy. Often measured with the Izod impact strength test or Charpy impact test, both of which measure the impact energy required to fracture a sample. Volume, modulusof elasticity, distribution of forces, and yield strength effect the impact strength of a material. In order for a material or object to have higher impact strength the stresses must be distributed evenly throughout the object. It also must have a large volume with a low modulus of elasticity and a high material yield strength
Uniaxial stress is expressed by

Where
F is the force [N] acting onan area A [m2] the area can be the undeformed area or the deformed area, depending on whether engineering stress or true stress is of interest.

Stiffness
The stiffness of material is basically the ratio of stress to strain. Stiffness is the interest primarily in the linearly elastic region; therefore, Young’s Modulus, E, is the value used to represent the stiffness of a material.
Thestiffness, k, is a measure of the resistance offered by an elastic body to deformation. For an elastic body with a single Degree of Freedom (for example, stretching or compression of a rod), the stiffness is defined as

Where:
F is the force applied on the body
δ is the displacement produced by the force along the same degree of freedom (for instance, the change in length of a stretched spring)
Inthe International System of Units, stiffness is typically measured in newton per meter. In English Units, stiffness is typically measured in pounds (lbs.) per inch.
The stiffness of a structure is of principal importance in many engineering applications, so the modulus of elasticity is often one of the primary properties considered when selecting a material. A high modulus of elasticity is soughtwhen deflection is undesirable, while a low modulus of elasticity is required when flexibility is needed.

Ductility
Material that can undergo large strain before fracture are classified as ductile materials; those than fail at small values of strain are classified as brittle materials. Strictly speaking, the terms ductile and brittle refer to modes of fracture, and a material like structural...