fracture toughness evaluation from impact testing

[vinston]

Hi,
I have conducted impact testing on my NbSi alloy at RT which is very brittle. What could be the relevant formula to evaluate the fracture toughness (stress intensity factor) of the material? I have few relations to calculate stress intensity factors but it's not clearly explained it can be used for brittle material as well. What other properties can be evaluated from the available data from the impact testing.
thank you
Vinston

 

[Zogzog]

Vinston,

try cross posting to the nuclear engineering fourm, nukes are BF gurus. I used to know those equations but they have long been flushed from my memory.

Scott Peterson
Training Manager
Power Plus Engineering

http://www.epowerplus.com

 

[metengr]

vinston;
There are no direct correlations between impact energy values and fracture toughness (KIc) for metals. There have been conversion formulas that are used for the upper shelf impact energy conversion of CVN to KIc for certain steels but again these are only used as approximate conversions and must be used with caution.

 

[vinston]

thanks for the input metengr, ZOgzog I posted it in the Nuclear forum..

 

[TVP]

Vinston,

Impact testing will only provide some useful information if it is instrumented to collect force vs. displacement data. A typical Charpy impact test that only provides the final energy absorbed will not provide any information on the fracture toughness, especially for a brittle intermetallic like NbSi. You need to perform real fracture toughness testing according to a standard like ASTM E 1820.

 

[Zogzog]

Charpy V-notch test? You are bring back brain cells I though died years ago. I used to love materials testing but havent used it in 20 years. You get a star!

 

[vinston]

TVP,
yes the test was conducted to get force vs Displacement data.I have the max force (load) before fracture and diplacement values. I remember for plastic material we can evalutae the energy absorbed by the specimen before fracture by integrating the area under the curve but how about the energy in case for brittle material where you get a single peak? I am gonna do 3pt Bending test as well to determine the fracture toughness but I want to compare the both values.
thanks
vinston