Fatigue limit

About: Fatigue limit is a research topic. Over the lifetime, 20489 publications have been published within this topic receiving 305744 citations. The topic is also known as: endurance limit & fatigue strength.

Properties and failure mechanisms of z-pinned laminates in monotonic and cyclic tension

Abstract: The effects of through-thickness reinforcement of carbon/epoxy laminates with thin pins on the in-plane tensile properties, tensile fatigue life and failure mechanisms are investigated. Tensile studies in the 0 fibre direction are performed on unidirectional and quasiisotropic laminates reinforced with different volume contents and sizes of fibrous composite z-pins. Microstructural analysis reveals that z-pinning causes several types of damage, including out-of-plane fibre crimping, in-plane fibre distortion, mild dilution of the in-plane fibre volume fraction due to laminate swelling, and clusters of broken fibres. In unidirectional composites, resin pockets form around pins and coalesce into continuous resin channels at higher z-pin contents. Young’s modulus falls only a few percent at most, due partly to in-plane fibre dilution and partly to fibre waviness. Monotonic tensile strength is degraded more significantly, falling linearly with both pin content and pin diameter. Comparison with prior data shows that the rate of degradation is evidently a strong function of the particular pin insertion method used. Failure mechanisms include fibre rupture, presumably affected by broken fibres, and, in unidirectional laminates, longitudinal splitting cracks emanating from resin pockets. Whereas non-pinned laminates show very modest fatigue effects, the pinned laminates exhibit strong fatigue effects, with strength falling by as much as 33% at 10 6 cycles. The slope of the fatigue life (S–N) curve tends to increase in magnitude with pin content and density. Limited evidence and prior literature suggest that the dominant fatigue mechanism may be progressive softening and fibre damage in misaligned segments of in-plane fibres. 2005 Elsevier Ltd. All rights reserved.

An empirical model for fatigue behavior prediction of glass fibre-reinforced plastic composites for various stress ratios and test frequencies

Abstract: Current models used to predict the fatigue life of glass fibre-reinforced plastic composites do not accurately consider the effects of load stress ratios and load frequencies. These models usually require significant amount of experimental data to establish a set of characteristic fatigue curves for a given composite. This paper proposes a fatigue model for glass fibre-reinforced plastic composites that includes the non-linear effect of stress ratio and load frequency on the fatigue life. The model can be used to predict the fatigue behavior of a composite material using a well-defined minimum number of tests. Fatigue data from the literature and selected research laboratories were used to test the model. Predictions were found to be in good agreement with all experimental data adequately accounting for the influence of test frequency and stress ratio on the fatigue life of composites.

Multiaxial Fatigue: A Survey of the State of the Art

Abstract: This paper surveys the current state of knowledge concerning multiaxial fatigue. Developments are presented in chronological order and are discussed so as to supplement existing reviews in this field. Emphasis is placed primarily on the criteria or methods of evaluation of fatigue strength under general multiaxial loading at room temperature. The survey indicates that the early development of the criteria was based on extensions of static yield theories to fatigue under combined stresses. These are stress-based criteria limited primarily to high-cycle fatigue. Most of the later criteria are strain-based. These criteria fall into two broad groups: the equivalent stress or strain type and the critical plane type. Most of these criteria commonly lack considerations of the cyclic stress-strain response. Their application to nonproportional loading suffers from difficulties in implementation or from inconsistencies with results of experiments. Recent approaches fall in the category of continuous damage evaluation methods. At present, these appear to be abstract or difficult to implement. All the above criteria are critically examined and compared. With this background, a new plastic work approach, proposed by the author, is discussed briefly.