Paris' law

About: Paris' law is a research topic. Over the lifetime, 13815 publications have been published within this topic receiving 224818 citations. The topic is also known as: Paris-Erdogan law.

Dislocation modelling of fatigue cracks: an overview

Abstract: The intrinsic threshold behavior of fatigue cracks and the disappearance of any cyclic plastic deformation below a threshold value can be understood by taking into account the discreteness of plasticity with recourse to discrete dislocation models. The aim of this paper is to document the progress in the discrete dislocation modelling within the past twenty years and the resulting increase in the understanding of fatigue cracks. The problems addressed are (1) the nature of the intrinsic fatigue threshold, (2) the influence of microstructure and/or of the mean stress level on the crack tip deformation and (3) the physical reason for the minimum striation spacing at small stress intensity ranges. A particular purpose of this paper is to compare the different dislocation models proposed in the literature in order to differentiate aspects of fatigue crack growth that do and do not depend on modelling and on microstructural details.

A fatigue crack growth theory

Abstract: The fatigue crack growth model proposed by Frost and Dixon, based on the different crack tip geometries of a loaded and unloaded crack, is restated and extended using the stress intensity factor concept. The resulting crack growth predictions agree reasonably well both with experimental fatigue crack growth data, and data on the threshold stress necessary for fatigue crack growth.

Effect of test frequency on fatigue strength of low carbon steel

Abstract: Ultrasonic fatigue tests (test frequency: 20 kHz) and conventional tension-compression fatigue tests (10 Hz) have been conducted on annealed and 10% pre-strained specimens of 0.13 % carbon steel. Small holes were introduced on the specimen surface to investigate the effect of test frequency on small crack growth. The dynamic stress concentration factor and the stress intensity factor under ultrasonic fatigue tests were checked to be almost the same as those of conventional tension-compression fatigue tests. However, the fatigue properties were dependent on the test frequency. Ultrasonic fatigue tests showed longer fatigue life and lower fatigue crack growth rate for the annealed and 10% pre-strained specimens. Slip bands were scarce in the neighbourhood of cracks under ultrasonic fatigue tests, while many slip bands were observed in a wide area around the crack under conventional fatigue tests. In order to explain the effect of test frequency on fatigue strength, dynamic compression tests with Split Hopkinson bars were carried out. The stress level increases substantially with the strain rate. Thus, the increase in fatigue strength might be, to a large extent, due to a reduction in crack tip cyclic plasticity during ultrasonic fatigue tests.

Mode I fatigue cracking in a fiber reinforced metal matrix composite

Abstract: The mode I fatigue crack growth behavior of a fiber reinforced metal matrix composite with weak interfaces is examined. In the longitudinal orientation, matrix cracks initially grow with minimal fiber failure. The tractions exerted by the intact fibers shield the crack tip from the applied stress and reduce the rate of crack growth relative to that in the unreinforced matrix alloy. In some instances, further growth is accompanied by fiber failure and a concomitant loss in crack tip shielding. The measurements are compared with model predictions, incorporating the intrinsic fatigue properties of the matrix and the shielding contributions derived from the intact fibers. The magnitude of the interface sliding stress inferred from the comparisons between experiment and theory is found to be in broad agreement with values measured using alternate techniques. The results also indicate that the interface sliding stress degrades with cyclic sliding, an effect yet to be incorporated in the model. In contrast, the transverse fatigue properties are found to be inferior to those of the monolithic matrix alloy, a consequence of the poor fatigue resistance of the fiber/matrix interface.

A theoretical model for predicting fatigue crack growth rates in fibre‐reinforced metal laminates

Abstract: This paper is concerned with the development and application of an analytical model for predicting fatigue crack growth in fibre-reinforced metal laminates (FRMLs). An analytical model for the distribution of bridging traction is first introduced. Based upon observations of the delamination shapes in FRMLs under fatigue loading and a model for characterizing delamination growth in FRMLs, a model for predicting crack growth rates in CCT specimens of FRMLs is developed. The model is applied to two GLARE laminates (2/1, 3/2 lay-ups) under various cyclic stress levels and stress ratios. The predicted crack growth rates are compared with experimental data. The predicted crack growth rates agree well with the experimental results.