properties+-+hardness

=mechanical properties of materials=

=strength= A materials strength is its ability to withstand an applied stress (load/area) without failure Watch the following video of a tensile test of a thermoplastic HDPE (high-density polyethylene). Pause the video at the end to look at the important stress ( σ ), strain ( ε ) (extension/original length ) relationship (graphs) obtained for several test pieces. [] The following link shows the stress colour coded from blue (least) to red (most stress) [] The following link is an animation which shows the relationship between the graph and changes to the test piece [] Note; The straight line part of the curve is the elastic range of the material. If the load is removed here the material will return to its original length. The end of the straight line is the elastic limit beyond which the material deforms plastically if the material is ductile.  Ductility is a solid material's ability to deform under tensile stress while elasticity is its ability not to deform permanently.
 * Compressive strength is the capacity to withstand axially directed pushing forces
 * Tensile strength is the maximum stress while being stretched or pulled before necking
 * Shear strength is the ability to withstand shearing (the deformation of a material substance in which parallel internal surfaces slide past one another)
 * The **yield strength** or **yield point** of a material is defined as the stress at which a material begins to deform plastically.
 * Plasticity is the propensity of a material to undergo permanent deformation under load


 * [[image:220px-Cast_iron_tensile_test.JPG caption="This tensile test of a nodular cast iron demonstrates low ductility."]] || [[image:220px-Al_tensile_test.jpg width="242" height="302" caption="Tensile test of an Aluminium alloy. The local necking and the cup  and cone fracture surfaces are  typical for ductile metals"]] || [[image:157px-Ductility_svg.png width="187" height="181" caption="Schematic appearance of round metal bars after tensile testing. (a) Brittle fracture (b) Ductile fracture after local necking (c) Completely ductile fracture"]] ||

Example tensile test of steel[| http://youtu.be/ClLowisIpPQ]

Resulting test pieces

Shear strength test of concrete []

Compressive strength test of concrete []

Torsion tests []


 * Malleability **, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling.

=**toughness**= Toughness tests Tests can be done by using a pendulum and basic physics to measure how much energy it will hold when released from a particular height. By having a sample at the bottom of its swing, a measure of toughness can be found, as in the Charpy and Izod impact tests. Charpy impact test The apparatus consists of a pendulum axe swinging at a notched sample of material. The energy transferred to the material can be inferred by comparing the difference in the height of the hammer before and after a big fracture. The notch in the sample affects the results of the impact test. It is therefore necessary for the notch to be of regular dimensions and geometry. The size of the sample can also affect results, since the dimensions determine whether or not the material is in plane strain. This difference can greatly affect conclusions made The qualitative results of the impact test can be used to determine the ductility of a material. If the material breaks on a flat plane, the fracture was brittle, and if the material breaks with jagged edges or shear lips, then the fracture was ductile. Look at the Charpy impact test animation at [] Automated system []
 * Toughness** is the ability of a material to absorb energy and plastically deform without fracturing. Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing . It is also defined as the resistance to <span class="wiki_link_ext">fracture of a material when <span class="wiki_link_ext">stressed.

Izod impact test The Izod impact test differs from the <span class="wiki_link_ext">Charpy impact test in that the sample is held in a cantilevered beam configuration as opposed to a three-point bending configuration. Watch the following Izod test <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">[]

How much do you remember? Complete the following quiz =quiz - strength and toughness=

The next topic is =hardness=

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