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Wöhler Curve

To generate data useful for fatigue designs using the stress-life approach stress-loife fatiqu tests are usally carried out on several specimens at different fell reversed stress amplitudes ovar a range of fatigue lives for identically prepared specimens. The fatigue test data are often plotted on either semilog or log-log coordinates. The single curve that represents the data is called the S-N curve or Wöhler curve. When plotted on log-log scales, the curve becomes linear. The portion of the curve or the line with a negative slope is called the finite life region , and horizontal line is the infinite life region.

When generation log-log graphs of applied stress versus fatigue life from S-N fatigue tests , the y-coordinate is expressed in terms of the stress amplitude or the stress range , and the x-coordinate is expressed in terms of the number of reversals to failure or the number of cycles to failure.

(Fatigue testing and analysis: theory and practice ; Yung-Li Lee , pg , 105 ; 2005)

Endurance Limit

For most material , the logarithmic plot of S-N curve is approximated by a straight line . for some alloys , including the ferrous metal , the logarithmic plotting method will generate an additional straight linet o account fort he endurance limit the semilogarihmic method is the most widely used in engineering applications.

The endurance limit or fatigue limit is not a constant adn varies with the stress ratio , R. For a given material , the endurance limit can be influenced by the type of cycling loading. Experimental data obtained in the laboratory Show that the endurance limit of material tested in uniaxial loading is lower than the endurance limit tested in reverse bending , provided that the two loading cases are sujected to the same stress ratio R.

(Fatigue and fracture mechanics of high risk parts ; Bahram Farahmand, George Bockrath, James Glassco ; pg : 33-34 ; 1997)

Stereolithography

Stereolithography is one of the most important Additive Manufacturing Technologies currently available. This technology involves the curring or solidification of a liquid photosensitive polymer through the use of an irradiation light source , whicih supplies the energy that is needed to induce a chemical reaction bonding large numbers of small molecules , and forming a highly cross –linked polymer.

Stereolithograpihc processes transform a multifunctional prepolymer into a cross linked polymer through a chain reaction initiated by reactive species generated by light exposure.

(Stereolithography: Materials, Processes and Applications ; Paulo Bártolo , pg:7 , 2011)

Injection blow molding

Injection blow molding is the result of the marriage of two plastic processing systems. The basis for injection blow molding is injection molding , which is the most common of all systems used to mold solid plastic articles. The molded perform from which the container is blown is formed by injecting molten resin into the preform mold. The resin is plasticated by the reciprocating screw of the injection molder.In injection blow molding , the melt is channeled through a small opening called sprue bushing. The melt is then forced under high pressure through a gate and into a mold cavity that is machined to have the shape of desired parison. However in the case of injection blow molding , this parison is called a preform.

(Plastics processing technology ; Edward A. Muccio ;pg :124 ; 1994)