50^th Anniversary Article: Multiaxial Fatigue Testing of Composites: From the Pioneers to Future Directions

Abstract

This paper presents an overview on the experimental investigation of the response of composite materials under multiaxial cyclic loading, starting from the pioneering works in the early 1970s to arrive to the research activities run in these days by the scientific community and concluding with the areas still open. The experimental techniques and sample geometries are compared, illustrating advantages and drawbacks of each solution, also with reference to the outcomes of the research. The influence of the main design parameters are illustrated, taking advantage of experimental results from the extensive investigation carried out in the last years at the University of Padova. Needs of future research are eventually addressed.

Influence of load ratio on the biaxial fatigue behaviour and damage evolution in glass/epoxy tubes under tension–torsion loading

“…Proportional in phase axial and torsional loads were applied and the damage onset and evolution (nucleation and propagation of transverse cracks in the 90° layers) were monitored. To this end the lock-in thermographic technique was used, together with eye-observations carried out with the support of an internal lighting system (Figure 1 [12][13][14]). A flow of compressed air was used for tests at higher stress levels with λ 12 = 2 and R = -1 to avoid the specimen temperature to increase more than 5 °C.…”

“…With the aim to fill the lack of comprehensive experimental investigations and results of general validity, the authors recently developed a testing procedure suitable to characterise the matrixdominated fatigue response of unidirectional plies [12,13]. Glass/epoxy tubes with the fibres aligned at 90° with respect to the tube's axis and subjected to combined tension/torsion loadings were found to be the best solution to achieve a stress state characterised by the presence of σ 2 and σ 6…”

Multi-axial mechanical characterization of jute fiber/polyester composite materials

“…Multi-axial testing has attracted many researchers [26] by several reasons. For example, many component in service are actually under combind loadings which is represnted better by the multi-axial loading tests.…”

Structural Analysis of Large-Scale Vertical Axis Wind Turbines Part II: Fatigue and Ultimate Strength Analyses

“…This simplified method is used in the present fatigue design of wind turbine blades [14,30,31]. Although the influence of multi-axial loading has been considered by some other researchers, the results are still limited [32,33].…”