Suchergebnisse

In Switzerland and elsewhere, many psychological support hotlines were set up during the acute phase of the COVID-19 pandemic. Specialists in psychological first aid, in charge of developing and managing these hotlines, had to face an unknown situation, very different from the disasters for which they prepare themselves. Since the pandemic and the associated physical distancing were a potential threat to social cohesion, one could make the hypothesis that, by setting up hotlines, these professionals sought to reintroduce a form of proximity and to care for and cultivate the social connections among people. The pressure, feelings of emergency, anxious anticipation and expectation of the political authorities and the population may have favoured the development of these structures. Other factors certainly also played a role, such as the need to be useful and to exist as professional, or the need to act in order to reduce anxiety related to the pandemic. Altogether, these hotlines were little used, and their usefulness may be questioned. Similar phenomena have been observed - especially in the sanitary domain - with a multiplication of new offers, not always adjusted to specific identified needs, while health care services were on the same time under-used. Our observations plead against emergency responses in crisis situations and for reflecting on the measures to be put in place rather than to "act" them.

The Dassault Aviation Group designs and builds a wide range of aircraft models each year, for both private and military use. Some structural parts of the aircraft, in the form of reinforced stiffener panels machined directly into the bulk of Al2024T351 thick plates are studied. As part of the shaping process, these elements must be cold formed to give their final curvature. This process severely plastified some regions of the structure. In addition, these zones are likely to constitute sites of initiation and propagation of fatigue cracks.This study aims to analyze the interactions between the plastic phenomena induced by cold forming and the propagation of a fatigue crack during fatigue service loading. This thesis is conducted according to the following approach:An instrumented cold forming test has been performed on two self-stiffening technological specimens. From an experimental base of tensile tests, a model of anisotropic plastic behavior of the plate was proposed allowing the development of a cold forming structure simulation and an analysis of the residual state of the material following the process. Using all the results about residual plastic state, a compression and traction test on large test pieces has been performed (54 mm diameter slugs and flat tensile test pieces of 75x55 mm section) whose purpose is to produce a homogeneous volume of pre-deformed material in compression and traction (+/-10 % of plasticity) .A large campaign of fatigue tests has been realized on oligocyclic specimens and specimens of propagation (Compact Tension) extracted from the volumes of original and pre-deformed material allowing the characterization of the effects of the pre-deformation on the fatigue properties. A modified Forman propagation model has been identified from the velocity curves.Finally, self-stiffened structures formed have been subjected to a cyclic loading and the fatigue initiation and propagation behavior has been observed experimentally. A simulation of the fatigue loading of the structure after ...