Static fatigue experiments

The first experiments have been carried out by the LCPC putting the projector and the camera on a static fatigue device. The first applications showed interesting results, which validate the choice of measuring deflection basin with fringe projection. However, this technique needs to be improved in order to obtain an operational device. An ongoing project aims to mount the system on a heavy truck (Muzet et al. 2009). 

Static fatigue, or creep rupture, is the phenomenon of fracture which occurs some time after the application of a constant load. The applied stress is usually lower than that required to cause fracture under monotonic loading conditions but, as shown later, there is no clear distinction between static fatigue and monotonic loading since in the latter the stress is continuously applied and a finite time must elapse between application of the stress and fracture. Again such experiments have been conducted in the presence of a hostile environment, but these will be considered later in Section 8.3.5. 

Some important experiments have highlighted the role of voids in laminates under cyclic loading when in water. To validate the design of GRP hulls for durability and performance in the tropical waters of the Persian Gulf, the Procurement Executive of the UK Ministry of Defence commissioned creep and fatigue tests at loads equivalent to one-eighth of the static... 

A large number of experiments on fatigue were performed with completely reversed cycles (indicated in Fig. 7.2a), where the mean stress is zero (o max = o min)- Often in components exposed to fatigue, a pattern (as shown in Fig. 7.2b) is observed, resulting from the superposition of a static preload during the reversed cycle (see 7.2a) also note that the names of the cycle-patterns shown in Fig. 7.2 may have different nomenclature in the literature. This is also often stated differently, namely that the mean stress is ffm(= Cmean). represents a steady-state stress and the alternating stress is a variable stress. This stress cycle is asymmetrical, since the sum of Cmax and Cniin 0. Clearly, machine parts in service exposed to cyclic stresses may experience particular conditions in which min 0 or (7max 5 0-... 

---