Article révisé par les pairs
Résumé : Inasmuch as commercial fatigue machines do not have sufficient displacement amplitude for the study of high polymers (rubber, plastics ...), the authors had to design and build an original machine, having a displacement amplitude of up to 4 cm. The range of the test frequencies is between 1.2 and 3.150 c/mn and the maximum force that the machine can develop is 2 000 kg. The tress applied to the test piece is by imposed strain and is quasi-sinusoïdal. In order to study the flexural behaviour of the test pieces, the authors have designed and executed clamps by means of which the test piece can be strained by a constant bending moment, which is not the case with conventional devices. In addition, this system enables one readily to observe the test pieces during testing by means of a stroboscope having a release controlled by the machine and in particular allows the rates of propagation of the fracture to be studied. The examination of numerous fatigue-fractured test pieces shows that the fracture surfaaces in general reveal four very different areas that have developed successively: -the mirror, the fatigue fracture itself, then "the plastic furrow" and finally the brittle-fracture region. The authors have shown the influence of the frequency of stress on the dimensions of these different areas; thus, after a frequency threshold is reached, the "plastic furrow" no longer appears. They have been able to establish a low giving the length of the fatigue fracture itself in relation to the stress frequency. Finally, the authors have likewise proposed a law giving the length of the fatigue crack with reference to time, of the 1=K(t+to)1/2 type. © 1973 Secrétariat de Rédaction.