KNOW-HOW Simulation g…/… Mastering simulation methods and tools for composite design hole or slot is assumed to be the lower bound. Thus any damage to the laminate would lie between the open hole (circle or slot) and the intact laminate. It appears that the use of maximum stress or strain criteria leads to either over-conservative or unsafe laminate design, depending on the load combination. Life prediction of damaged laminates Constituent-based micromechanics of failure (MMF) can be used to predict not only strength but also life. Thus, the computed effect of damage in a laminate includes residual strength and life, as shown in Figure 3. The same approach can be applied to random fatigue. The result for a wind turbine blade is shown in Figure 4. A similar approach can be implemented for an aircraft wing. The results presented were obtained using Super Mic-Mac+, an Excel-based MMF tool for strength and life prediction. Compression after impact (CAI) Compression after impact (CAI) is a standard test in the aircraft industry. However, the test programme can be very expensive due to its complexity and generate limited data. The proposed approach to study compression after impact is based on the flow chart shown in Figure 2, where naturally-induced damage and multiple delaminations are used to determine the damaged specimen’s residual strength. The residual strength prediction based on naturally-induced impact damage (as measured by NDE and GOM techniques) can be validated by uni- and multiaxial tests. Fig. 4: 42-year life prediction for a wind turbine blade under random fatigue Repair assessment Repairs are required to maximize the service life of many operating structures. A damage tolerance tool incorporating repair assessment functions is proposed here. An example of a scarf patch is shown in Figure 5. Fig. 2: Global-local impact damage model Fig. 5: Scarf repair analysis of a damaged composite plate Fig. 3: Comparison of predicted and measured S-N curves for laminates subjected to multiaxial loads MMF was used along with the element failure method (EFM) to determine its effectiveness, as shown in Figure 6. The results were validated against available test data as shown in Figure 7. 90 jec composites magazine / No56 April 2010