# Calculation of the axial stress in UCS test simulation

**URL:** <https://forum.itascainternational.com/t/calculation-of-the-axial-stress-in-ucs-test-simulation/673>\
**Category:** PFC\
**Tags:** fish, suggestions\
**Created:** [July 21, 2022, 10:55pm UTC](https://forum.itascainternational.com/t/calculation-of-the-axial-stress-in-ucs-test-simulation/673 "2022-07-21T22:55:14Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![xiongyu](https://avatars.discourse-cdn.com/v4/letter/x/da6949/32.png) [@xiongyu](https://forum.itascainternational.com/u/xiongyu)\
**Post date:** [July 21, 2022, 10:55pm UTC](https://forum.itascainternational.com/t/calculation-of-the-axial-stress-in-ucs-test-simulation/673/1 "2022-07-21T22:55:14Z")

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Hello  
I am using PFC to simulate UCS test. I used three methods to monitor the axial stress (see attached): (1) based on the stress on the loading wall; (2) measurement circles that cover the whole specimen; (3) measurement circles that cover the center area of the specimen.  
I obtained three significant different results of UCS (see attached). I wondering which one should be chosen for UCS? What is the best way to monitor the axial stress in UCS test in PFC? Thanks.

 ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/1X/1fed01bcac3422b5102ac1abc28b924ed753ed35.jpeg)  
 ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/1X/6bdf0a66802979a7b6e6c581926a696f9b574f99.png)

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**Author:** ![dpotyondy](https://yyz1.discourse-cdn.com/flex031/user_avatar/forum.itascainternational.com/dpotyondy/32/1399_2.png) [@dpotyondy](https://forum.itascainternational.com/u/dpotyondy)\
**Post date:** [July 22, 2022, 2:36pm UTC](https://forum.itascainternational.com/t/calculation-of-the-axial-stress-in-ucs-test-simulation/673/2 "2022-07-22T14:36:22Z")

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I suggest using the wall-based stress measurements, because these can be compared directly with what is measured in a real physical test. Note that all three measurement schemes are giving the same axial stress during the portion of the test where the specimen is not experiencing any damage — i.e., during the portion in which the specimen is behaving elastically. As the peak load is approached in a UCS test, the damage begins to localize, with some regions unloading, and it is this localization that may be causing the difference in peak values.  
Cheers,  
David Potyondy

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**Author:** ![xiongyu](https://avatars.discourse-cdn.com/v4/letter/x/da6949/32.png) [@xiongyu](https://forum.itascainternational.com/u/xiongyu)\
**Post date:** [July 29, 2022, 3:52pm UTC](https://forum.itascainternational.com/t/calculation-of-the-axial-stress-in-ucs-test-simulation/673/3 "2022-07-29T15:52:08Z")

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Hello Dr. Potyondy  
Thank you for your kind help.  
Cheers

Xiongyu