When stresses and strains have been calculated in plies (or some of the plies), the failure indices can be estimated too. One presents below the different failure theories that are proposed in FeResPost, and how these failure theories can be used to estimate laminate reserve factors.
In this section, one conventionally uses integer subscripts to denote that tensor components are given in ply axes and Roman subscripts to indicate principal components. Often, only in-plane components of ply stress or strain tensors are used to estimate criteria. Then, the principal components are estimated as follows:
In the rest of this section all the allowables used in failure criteria have positive values. Even the compressive allowables are .
Table II.1.2 summarizes the criteria available in FeResPost. For each criterion, the Table provides:
Criterion | Material | Section | Derived | ||
Name | Type | Number | Stress | F.I. | R.F. and S. R. |
“Tresca2D” | metallic | II.1.10.1 | yes | yes | yes |
“VonMises2D” | metallic | II.1.10.2 | yes | yes | yes |
“VonMises3D” | metallic | II.1.10.3 | yes | yes | yes |
“MaxStress” | tape or fabric | II.1.10.4 | no | yes | yes |
“MaxStress3D” | tape or fabric | II.1.10.5 | no | yes | yes |
“MaxStrain” | tape or fabric | II.1.10.6 | no | yes | yes |
“MaxStrain3D” | tape or fabric | II.1.10.7 | no | yes | yes |
“CombStrain2D” | tape or fabric | II.1.10.8 | no | yes | yes |
“MaxTotalStrain” | tape or fabric | II.1.10.6 | no | yes | yes |
“MaxTotalStrain3D” | tape or fabric | II.1.10.7 | no | yes | yes |
“CombTotalStrain2D” | tape or fabric | II.1.10.8 | no | yes | yes |
“TsaiHill” | fabric | II.1.10.9 | no | yes | yes |
“TsaiHill_b” | fabric | II.1.10.10 | no | yes | yes |
“TsaiHill_c” | fabric | II.1.10.11 | no | yes | yes |
“TsaiHill3D” | fabric | II.1.10.12 | no | yes | yes |
“TsaiHill3D_b” | fabric | II.1.10.13 | no | yes | yes |
“TsaiWu” | fabric | II.1.10.14 | no | yes | yes |
“TsaiWu3D” | fabric | II.1.10.15 | no | yes | yes |
“Hoffman” | fabric | II.1.10.16 | no | yes | yes |
“Puck” | tape | II.1.10.17 | no | yes | yes |
“Puck_b” | tape | II.1.10.18 | no | yes | yes |
“Puck_c” | tape | II.1.10.19 | no | yes | yes |
“Hashin” | tape | II.1.10.20 | no | yes | yes |
“Hashin_b” | tape | II.1.10.20 | no | yes | yes |
“Hashin_c” | tape | II.1.10.20 | no | yes | yes |
“Hashin3D” | tape | II.1.10.21 | no | yes | yes |
“Hashin3D_b” | tape | II.1.10.21 | no | yes | yes |
“Hashin3D_c” | tape | II.1.10.21 | no | yes | yes |
“YamadaSun” | tape | II.1.10.22 | no | yes | yes |
“YamadaSun_b” | fabric | II.1.10.23 | no | yes | yes |
“Honey3D” | honeycomb | II.1.10.24 | no | yes | yes |
“HoneyShear” | honeycomb | II.1.10.25 | no | yes | yes |
“HoneyShear_b” | honeycomb | II.1.10.26 | yes | yes | yes |
“Ilss” | all | II.1.10.27 | yes | yes | yes |
“Ilss_b” | all | II.1.10.27 | yes | yes | yes |
Note that many of the criteria presented here are particular cases of a general quadratic criterion that requires first the calculation of a failure index:
then a test is done on the calculated value:
This means that no failure occurs if (ply or laminate passes the failure test) and one has failure if .
Several failure theories discussed below are obtained by expressing the coefficients in the expressions above by expressions depending on the material allowables. Also for the Tsai-Wu criteria discussed in section II.1.10.14 and II.1.10.15, the parameters are directly characterized for the material.
Note that the 2D criteria defined in this section often correspond to the failure criteria defined in ESAComp.
ESAComp failure criterion | CLA criterion ID | section |
“Maximum Shear Stress (Tresca)” | “Tresca2D” | II.1.10.1 |
“Von Mises” | “VonMises2D” | II.1.10.2 |
“Maximum Strain” (in ply axes) | “MaxStrain” | II.1.10.6 |
“Maximum Stress” (in ply axes) | “MaxStress” | II.1.10.4 |
“Tsai-Wu” | “TsaiWu” | II.1.10.14 |
“Tsai-Hill” | “TsaiHill” | II.1.10.9 |
“Hoffman” | “Hoffman” | II.1.10.16 |
“Simple Puck” | “Puck” | II.1.10.17 |
“Modified Puck” | “Puck_b” | II.1.10.17 |
“Hashin” | “Hashin” | II.1.10.20 |