User:Benatar.1/WE7407 Article 3
Need some help from peer review,
1) Should I expand on testing methods? 2) Should I add more on powdered metallurgy? 3) Should I discuss what UTS means in more detail?
I have more information, just not sure on how to properly expand.
Green Strength
[edit]Green strength, or handling strength, can be defined as the strength of a material before processing to form it's final ultimate tensile strength. This strength is usually considerably lower than the final ultimate of a material. The term green strength is usually referenced when discussing non-metallic materials such as adhesives and elastomers (such as rubber). It also has recently been referenced in metallurgy applications such as powdered metallurgy.
Green Strength of Adhesives
[edit]A joint made by the use of an adhesive can be referred to as an adhesive joint or bond.
The green strength of adhesives is the early development of bond strength of an adhesive. This value is usually significantly lower than the final curing strength. Most adhesives typically have a initial green strength and a final ultimate tensile strength listed for their application. For household adhesives, this data is usually reflected on the packaging.
The best example of this is in typical epoxies from a local hardware stores. During initial curing, the epoxy will travel into an initial curing phase, also called "green phase", when it begins to gel. At this time, the epoxy is no long workable and will move from being tacky to a firm rubber-like feel. While the epoxy is only partially cured at this point, it has formed a lower green strength. Normally, this takes roughly 30 min to 1 hour. It typically takes up to 24 hours for a standard epoxy to cure to its final full strength.[1][2]
Temperature plays a key factor in the time it takes for an adhesive to form the green strength. While this can vary from adhesive to adhesive, in general heat can speed up the process to form the green strength and the overall curing time.
Mechanical testing can be used to verify the green strength of a material. This will allow the user the understand the amount of load that can be applied in the green phase before final cure.
Tensile loading can be tested by various tensile test. Multiple ASTM specifications exist for the tensile testing of adhesives that are fairly easy to follow. These test include attaching the adhesive to two adherents (typically wood or steel) then testing the joint with a pull-type test.
Shear loading can also be tested in respect to green strength. Most adhesive bonds used in actual design requires the bond to typically be in a state of shear, not tensile. Because of this, it is very important to understand the shear loading of a joint in respect to it's green strength and final strength. Just like in tensile loading, ASTM provides very specific testing methods for a joint in shear loading. Other testing such as cleavage loading and peel test can be used to establish both green strength and final strength of a material. These are typically not reflected on the data sheet for standard adhesives, but can be used for testing of adhesives based on their applications in residential and commercial environments.[3]
Green Strength of Elastomers
[edit]
Green strength is a term in the elastomer industry to describe the strength of an elastomer in unvulcanized and uncured state. The most popular type of elastomer this is referenced for is rubber. For rubber composites, the green strength is key during forming of the rubber in manufacturing such as radial tires, tank tracks, etc. These rubbers must be stretched from one mill to another during processing to form the final vulcanized product. The green strength allows this to happen without tearing or wrinkling of the material before final curing is complete.
To improve the green strength of elastomers to prevent issues during forming, various additives and compounds are typically added to the composite. Also, fabrication and forming techniques have been modified to reduce the amount of stress on the material before it it vulcanized. This is a major issues in the tire making industry as it requires lots of forming, stretching, and bending during fabrication before the final curing is complete. [4]
Green Strength of Metals
[edit]Green strength of metals is typically referenced in the field of powder metallurgy. Powder metallurgy refers to the fabrication of materials or components from powdered metallurgy.[5]
- Need to add more details on this**
References
[edit]- ^ "Important Characteristics of Several Common Adhesive Tests". https://www.adhesivesmag.com/articles/86462-important-characteristics-of-several-common-adhesive-tests.
{{cite web}}: External link in|website=|url=(help) - ^ "Epoxy Chemistry".
- ^ Pocius, Alphonsus (2012). Adhesion and Adhesives Technology: An Introduction (3rd ed.). Hanser. ISBN 978-1-56990-511-1.
- ^ Ma, Liquing. "Method to improve green strength in elastomers". Google Patents.
- ^ Luk, Sydney (1996). "Enhanced Green Strength Material System for Ferrous and Stainless P/M Processing" (PDF). PM2TEC '96 World Congress.