Propagation response, fatigue crack

Fatigue Crack Propagation Response. Typical FCF responses are summarized In Table II and In Figs. 5-9. As may be seen by comparison of the data with those reported In reference 9 the behavior of the control specimens agrees well with the behavior found with the earlier series. Although the curves exhibit some curvature not previously observed, the positions of the curves fit well with those of the previous ones, and the values of da/dN at AK = 0.6 MPav fall closely on the curve as a function of M (see Fig. 2, reference 9). 

Figure 6. Fatigue crack propagation response of systems based on ERL 4221 epoxy , 0/100 dark star, 25/75, crambe white star, 25/75, lunaria , 25/75, linseed ...

The fatigue crack propagation for the 3003-0 alloy is compared in Fig. 8 with the behavior of aluminum alloys 2024-T3, 7075-T6, 6061-T6, and 5083-0 The data fall within the response of the other alloys. 

Fig. 7 Development of fatigue cracks in an epoxy/glass contact under gross slip condition (1Hz, displacement amplitude 60 xm) (from [97]). White arrows indicate the occurrence of crack initiation and propagation at the edge of the contact under the action of tensile stresses. The lateral contact stiffness, K, is essentially a measurement of the elastic response of the epoxy substrate within the contact zone. Brittle crack propagation is associated to a drop in stiffness due to the additional accommodation of the imposed displacement provided by crack opening mechanisms...

In the case of structural joints, cohesive failure of the adhesive is often observed. Indeed, in many instances, the requirement will be to engineer failure within the bulk of the adhesive layer. Modelling of the adhesive response as a function of water uptake with temperature is carried out to represent the influence of environmental exposure. With fatigued structural joints, by combining the use of fracture mechanics and appropriate modelling tools, the resultant crack propagation rates and consequently durability levels can be predicted as a function of various environmental and mechanical test parameters, such as frequency. Fatigue threshold values can be determined, which are used to predict durability performance. " ... 

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