effect of strain rate on brittle facture.

hello It is my the first time that I use google groups,therefor if I don't know sth about that please don't blame me.
MY question is about the mecanizem of effect of strain rate on brittle fracture. thanks for your guide.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
mahmood shaikhattar wrote:

Plastic Strain is the result of dislocation movement and/or twinning. Brittle fracture occours instead of deformation. Now think: Would you think that the stress necessary for plastic deformation increases or decreases with increasing strain rate? What will happen, when the strain rate increases more and more?
Michael Dahms
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

thanks for your attaention I know that by increasing strain rate the movement of dislocation should be increased,but they themselves prevent their movement because of their transverse of stress field,.. thus by these difficulties slip and deformation should be decreased,so the yield point of metal should be increaed,but my question is why this cuase brittle fracture and how does it explain by formulas, because I have a ceminerate about it that it should be takes 45 minutes and this is not enough. thanks again.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
mahmood shaikhattar wrote:

If the stress for dislocation movement is greater than the cleavage stress, brittle fracture will occur.
Michael Dahms
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I saw some women on some of the roller coasters at Busch Gardens (I live about 2 km from the park) that had some serious cleavage stress.
http://www.coastergallery.com/2000T/BGT.html
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.com (mahmood shaikhattar) wrote in message

In cases where there is no plastic, viscous, or creep flow it is often the case that increasing strain rate increases fracture stress because of stress corrosion effects.
This is because slow strain rates give lots of time for corrosive chemicals (like water vapor) to attack a stressed flaw tip.
There are also a few counterexamples where chemical corrosion tends to broaden rather than sharpen crack tips in which case slow strain rate gives higher fracture stress.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@newarts.com (dave martin) wrote in message

ok thank u, I find sth in this book" mechanical behavior of metals at extremely high strain rates" by j.buchar,z.bilek,f.dusek. It's about high velocity deformation of metals,but I don't know that in high strain rate what's happen to metal that it causes fracture because fracture need cracks and in this book talking about shock wave in high strain rate,but I still don't know how cracks initiate that high strain rate causes brittle fracture. thank u very much.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
mahmood shaikhattar wrote:

Google 'brittle crack initiation' >5000 hits.
HTH
Michael Dahms
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.