Dear all,
I am new in the forum, very interesting place I have found
I am learning how to do a DBA using ASME BVPC Sect.VIII code. I created my own vessel to work with, and after a few analyses I have a couple of questions:
1. I realised that at least 4 failure modes are identified by the code. Based on screening criteria, my vessel dimensions and characteristics excluded it for a fatigue calculation. In any case, ratchening is mandatory. So I carried out a static analysis in ANSYS Mechanical, with a load-unload condition (t=1-Pressure=0, t=2-Pressure=Pmax, t=3-Pressure=0, t=4-Pressure=Pmax....and so on). I have very low plastic strain (so I guess this criteria is not fulfiled according with that is said in the code). A chart of max.stress, max.deformation, volume....exhibits a constant trend after a couple of cycles(I mean, for example, t=2-max.stress=1e+08, t=4-max.stress=1,001e+08....t=10-max.stress=1,01e+08...). Is this enough to guarantee the bessel is safe against ratchening? If not, what criteria should I follow for determine properties are not varying with cycles? Sorry if I am not explaining this well.
2. I used a static structural analysis as a pre-stress condition for Eigenvalue Buckling, in order to determinate the load multipliers. I found all of them with negative values. I think I undersatnd the physical meaning, but, how is this translatred to the norm criteria? Should I choose absolute values? Or should I deactivate the "Include negative multiplier" option in Anaysis Settings? I choose 4 modes to find, is this enough? Is there any rule of thumb to guess this number of modes? I guess the deformation contour plot has no physical meaning, is that correct?
Many thanks in advance and I apologise if my english is not good enough...I am glad to become a aparto of this interesting community!
Kind regards,
Charas
I am new in the forum, very interesting place I have found
I am learning how to do a DBA using ASME BVPC Sect.VIII code. I created my own vessel to work with, and after a few analyses I have a couple of questions:
1. I realised that at least 4 failure modes are identified by the code. Based on screening criteria, my vessel dimensions and characteristics excluded it for a fatigue calculation. In any case, ratchening is mandatory. So I carried out a static analysis in ANSYS Mechanical, with a load-unload condition (t=1-Pressure=0, t=2-Pressure=Pmax, t=3-Pressure=0, t=4-Pressure=Pmax....and so on). I have very low plastic strain (so I guess this criteria is not fulfiled according with that is said in the code). A chart of max.stress, max.deformation, volume....exhibits a constant trend after a couple of cycles(I mean, for example, t=2-max.stress=1e+08, t=4-max.stress=1,001e+08....t=10-max.stress=1,01e+08...). Is this enough to guarantee the bessel is safe against ratchening? If not, what criteria should I follow for determine properties are not varying with cycles? Sorry if I am not explaining this well.
2. I used a static structural analysis as a pre-stress condition for Eigenvalue Buckling, in order to determinate the load multipliers. I found all of them with negative values. I think I undersatnd the physical meaning, but, how is this translatred to the norm criteria? Should I choose absolute values? Or should I deactivate the "Include negative multiplier" option in Anaysis Settings? I choose 4 modes to find, is this enough? Is there any rule of thumb to guess this number of modes? I guess the deformation contour plot has no physical meaning, is that correct?
Many thanks in advance and I apologise if my english is not good enough...I am glad to become a aparto of this interesting community!
Kind regards,
Charas
