The effect of location on closure measurements after overloads

In this paper a review of the literature on crack closure/opening load and crack tip shielding effects determination methods is presented. Commonly used ‘subjective’ (visual) and ‘non‐subjective’ approaches have been included. Procedures associated with the determination of an effective crack driving force for both Elber type and that of partial (or incremental) crack closure models have been covered. Comparison among different methods of analyses based on compliance and fatigue crack growth rate measurements is discussed together with their implications and difficulties in fatigue crack growth correlations.

Section: Introductionmentioning

confidence: 99%

“…A common assumption is that when the crack starts to close at the surface, the crack tip is fully shielded from further damage. The direct techniques include the following: optical and scanning electron microscopy observations, 11–23 , 52 photography, 24,25 optical and laser interferometry, 1 , 5 , 26–42 , 54 replica, 4 , 11 , 13 , 20–23 , 52 surface strain, 5 , 9 , 11 , 24 , 44–59 , 77–81 , 92 , 101 X‐ray tomography, 60–67 and caustics 68–73 …”

Section: Introductionmentioning

confidence: 99%

Methods for crack opening load and crack tip shielding determination: a review

and

Kujawski

2003

“…In the general case, and depending on the material work hardening properties, these two mechanisms could exist at the crack tip. It has been shown, however, see for example [15], that closure occurs below a load level, above which no crack closure would be observed (a different view has recently been discussed by Su and Sharpe [16]). In order to simplify the process of defining a dominant crack retardation mechanism, the applying load range can thus be selected so that the minimum load level is set above the possible closure load.…”

Section: The Driving Force Fakef During Crack Growth Retardationmentioning

confidence: 94%

PREDICTION OF FATIGUE CRACK GROWTH UNDER SINGLE OVERLOAD APPLICATION IN Ti‐6Al‐4V

Ghonem

Zeng

1991

This paper is concerned with the use of a Markovian stochastic crack growth model to predict crack growth behavior in zones affected by a single overload application. The model introduces an effective stress intensity factor in the definition of the transition intensity of the stochastic process. This in turn, generates a unified probability growth law that was used to predict scatter in single overload history. An experimental program was carried out on compact tension specimens of TidAI-4V material to generate sample crack growth curves, each of which contains three single overload zones. The sample curves were then manipulated into experimental constant probability growth curves. These curves were compared with those theoretically generated using the proposed model. A good agreement was established between these two data sets.

“…Since then, a number of different techniques have been used to achieve greater accuracy, faster measurements, and/or simpler experiments. Laser interferometry was also used to estimate the opening load at various positions behind the crack tip on a centre cracked specimen and a compact tension specimens both made of 2024‐T351 aluminium alloy . The technique was found to be advantageous for analysis where the displacement or the strain data experiences a steep gradient.…”

Section: Introductionmentioning

confidence: 99%

“…Laser interferometry was also used to estimate the opening load at various positions behind the crack tip on a centre cracked specimen and a compact tension specimens both made of 2024-T351 aluminium alloy. 13 The technique was found to be advantageous for analysis where the displacement or the strain data experiences a steep gradient. Optical and scanning electron microscopes were used to determine the opening load for a centre notched specimen and single-edge notched specimen made of 7091 aluminium alloy.…”

mentioning

confidence: 99%

Estimation of the opening load under variable amplitude loading

Moreno

López-Crespo

Cruces

et al. 2019

The crack opening/closure load concept is widely used to justify the fatigue crack growth behaviour with different load ratios and the load interaction effects. Many experimental techniques have been proposed to measure crack opening/closure load, and amongst them, compliance offset methods are widely used for their simplicity and consistency. In this paper, a modification of the ASTM method is proposed. The new method has a more general applicability as it can be applied to broadband variable amplitude loads. The method is described in detail and is applied on a 2024‐T351 aluminium alloy. The good correlation of the opening load estimated with the new method and the strip‐yield model implemented in Nasgro indicates that the new method could be used as an alternative for the cases where complex variable amplitude loads occur.