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GENOA Failure Criteria (Table 8) - takes into account the failure contributions such as: 1) Longitudinal Tensile, 2) Longitudinal Compressive, 3), Transverse Tensile, 4) Transverse Compressive, 5) Normal Tensile, 6) Normal Compressive, 7) In Plane Shear, 8) Transverse Normal Shear, 9) Longitudinal Normal Shear, 10) Modified Distortion Energy, and 11 relative rotation criterion. In addition to failure mechanism the software correlates the critical failure events such as damage initiation, damage propagation, fracture initiation, fracture propagation, and final residual strength.

Damage Evolution Metrics – In addition to the failure criteria discussed in Table 8, eight damage related functions are calculated (Figure 9) such as follows: 1) Strain Energy, 2) Percent Damage Volume (DAMAG) versus Load – representing margin of safety. Computed from the ratio of the total damage volume of the defect to the total volume of the composite structure, multiplied by 100. Is an overall indicator of structural degradation, 3) Damage Energy Release Rate (DERR) - for acoustic emission, inspection, nondestructive evaluation. It is the ratio of the incremental work done by external forces to the incremental volume of damage created during a load increment that causes damage, 4) Total Damage Energy Release Rate (TDERR) – for global failure evaluation. It displays the ratio of total energy expended to the total damage produced, 5) Damage Energy or cumulative damage energy is computed based on the strain energies exhausted by damage mechanisms. It is an overall index of degradation similar to the percent damage, 6) Strain Energy Damage Rate (SEDR) is the ratio of incremental strain energy to incremental damage volume and is computed as the incremental work done by external forces minus the damage energy exhausted during the same load increment. Very low levels of SEDR indicate critical loading levels where most of the external energy exhausted, 7) Stress Intensity Factor (Kcr) corresponds to mode I from fracture mechanics where Kcr is the average material stress multiplied by the square root of pi times the simulated crack length, 8) Crack growth length for both crack opening and through-the-thickness accumulation.

Figure 9. Damage Evolution Metrics as Derivatives
of Energy Release Rate

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