Damage modes

Figure 6-3 Damage Modes during Fatigue Life...

All of the information listed directly above is correlated to an all damages mode, individual subcategories of failure modes (internal leakage, for instance), and the influence parameters and their subdivisions. Realtime access is possible through a data base management system. 

Materials Degradation Effects. Virtually all of the effects of S02 on materials are associated with its dissolution in surface moisture as the primary mechanism of deposition (19). Thus an appropriate environmental index for materials damage should include not only the average ambient S02 concentration but also a measure of the portion of time that the material surfaces are wet and thus receptive to S02 deposition. Sulfur in the atmosphere has an additional adverse affect on some materials through acidification of precipitation however, for both "dry" deposition of S02 and impact by acid precipitation, the primary damage mode is attack by dilute acids. 

Chemicals with DNA-damaging modes of action are likely to cause cancers in children if the children themselves, or their mothers... 

Damage mode Visual 1-50 x fracture surface Metallography 50-1000 x (cross-section) Scanning electron microscopy, 20-10000 x (fracture surface)... 

Influence of Creep Rate Mismatch Ratio on Microstructural Damage Mode... 

Fig. 5.7 Macroscopic damage modes that occur during the tensile and flexural creep of fiber-reinforced ceramics. It is assumed that matrix or fiber damage is avoided during initial application of the creep load (see discussion of loading rate effects in the next section). Periodic fiber fracture can occur if the creep rate of the matrix exceeds that of the fibers. Periodic matrix fracture is common when the matrix has a higher creep resistance than the fibers. In this figure, it is assumed that initial microstructural damage is avoided during application of the creep load.

Fig. 5.9 Influence of initial loading rate on fiber and matrix stress and microstructural damage mode in materials where CMR< 1. Under rapid loading, the matrix stress may achieve a level sufficient to initiate matrix fracture.

In the general approach, the loads are applied incrementally until first-ply failure occurs. The type of failure, matrix or fiber, determines which properties of the failed plies must change to reflect the damage created. This is subjective and can cover a range of possibilities. The most conservative approach would completely discard affected properties for the failed plies. So for fiber failure, E would be set to zero. For matrix failure, E22 and G12 would be set to zero. Then, the loads would be incremented until another ply fails, and the procedure would be repeated to complete failure of the laminate. Less conservative approaches attempt to only partially discount stiffness values of the failed ply and even differentiate between tension and compression moduli. These methods can be reasonably accurate if they are accompanied by selected tests that help better define adjustment factors for the stiffness properties of failed plies. However, they are limited in applicability and accuracy because they are affected by the first-ply failure criterion used to trigger the failure sequence and because they do not correctly capture damage modes such as delamination and the interaction between them such as matrix cracks causing delaminations in adjacent ply interfaces. 

Three tests to failure on the C1 C1 C1 joint configuration were carried out in [41]. The study found that one joint failed in net-tension at hole 1 in the lower laminate at a joint load of 80 kN, while another failed by net-tension at hole 3 in the top laminate at 84 kN. The third joint tested failed by bolt failure at 76 kN. It should be noted that bearing damage was evident at holes where bolt failure occurred. However, as this damage mode is non-catastrophic, high loads are transferred through the bolt until... 

Figure 15.1 Lxjngitudinal tension of a 0/90 composite laminate. Highlight of several damage modes matrix cracking in transverse (T) lamina, splitting of longitudinal (L) laminae, and delamination between T and L laminae [6],...

When a composite panel is impacted, the projectile tends to exhibit through-the-thickness shear failure on layers near the impact face, forming a plug, while for back layers, the fibre damage mode resembles the tensile failure, as shown in Fig. 6.8. Similar phenomena were also found with dry fabric panels by Chen et al. The fact... 

Walter, T.R., Subhash, G., Sankar, B.V., and Yen, C.F. (2009) Damage modes in 3D glass fiber epoxy woven composites under high rate of impact loading. Composites Part B Engineering, 40, 584—589. 

---