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Power Cycling Life Prediction of 96.5Sn3Ag0.5Cu solder
Posted Oct 12, 2014, 7:13 a.m. EDT Studies & Solvers, Structural Mechanics Version 4.4 1 Reply
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Hi to all,
I'm trying to set up a FEM method in order to evaluate the number of cycles to failure for thermal fatigue in a power electronic device, composed by IGBTs and diodes.
The steps that I implemented are the following:
1- Input parameters: P_IGBT; P_diode; V_IGBT; V_diode.
2- Heat transfer in solids: Heat source 1: P_IGBT/V_IGBT; Heat source 2: P_diode/V_diode; T=25°C in baseplate of device;
3- Structural mechanics: Thermal expansion in all domains, with input temperature (ht) from the result of Heat transfer in solids; fixed constraint in baseplate;
4- Fatigue: based on strain; Selection of fatigue model: Smith-Watson-Topper criterion, elastic solution with intake restriction; field of solution: solid mechanics; fatigue parameters: sigma'f=276[MPa], b=-0.05; esp'f=0.325; c=-0.57; Young's modulus and Poisson's ratio from material; K'=304 [MPa]; n'= 0.086.
After the computation, I correcty visualize the maximum distribution temperature and von Mises stress, but I can't calculate the number of cycles to failure, in fact the expression ftg.ctf (or log10(ftg.ctf) returns to me the value 0.
Can you help me?
Best regards
Mario Nisi
I'm trying to set up a FEM method in order to evaluate the number of cycles to failure for thermal fatigue in a power electronic device, composed by IGBTs and diodes.
The steps that I implemented are the following:
1- Input parameters: P_IGBT; P_diode; V_IGBT; V_diode.
2- Heat transfer in solids: Heat source 1: P_IGBT/V_IGBT; Heat source 2: P_diode/V_diode; T=25°C in baseplate of device;
3- Structural mechanics: Thermal expansion in all domains, with input temperature (ht) from the result of Heat transfer in solids; fixed constraint in baseplate;
4- Fatigue: based on strain; Selection of fatigue model: Smith-Watson-Topper criterion, elastic solution with intake restriction; field of solution: solid mechanics; fatigue parameters: sigma'f=276[MPa], b=-0.05; esp'f=0.325; c=-0.57; Young's modulus and Poisson's ratio from material; K'=304 [MPa]; n'= 0.086.
After the computation, I correcty visualize the maximum distribution temperature and von Mises stress, but I can't calculate the number of cycles to failure, in fact the expression ftg.ctf (or log10(ftg.ctf) returns to me the value 0.
Can you help me?
Best regards
Mario Nisi
1 Reply Last Post Oct 17, 2014, 2:25 a.m. EDT
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Posted:
1 decade ago
Hi Mario
A fatigue response giving log10(ftg.fus)=0 indicates that the left hand side (Sigma_n,max*delta(Epsilon_1)/2) in the SWT equation is high. Observe that both a stain and a stress contributes to this term. High stresses and strains can be found at sharp corners and interfaces between elastic and viscoplastic or creep materials.
In case you have proportional loading you could also compare the principal strain range multiplied with a reasonable value of the stress and see how it relates to the right hand side of the SWT relation assuming one cycle.
Regards
Mateusz
A fatigue response giving log10(ftg.fus)=0 indicates that the left hand side (Sigma_n,max*delta(Epsilon_1)/2) in the SWT equation is high. Observe that both a stain and a stress contributes to this term. High stresses and strains can be found at sharp corners and interfaces between elastic and viscoplastic or creep materials.
In case you have proportional loading you could also compare the principal strain range multiplied with a reasonable value of the stress and see how it relates to the right hand side of the SWT relation assuming one cycle.
Regards
Mateusz