A B S T R A C T The paper presents four equations for Fatigue Crack Growth Rate (FCGR) description taking into account J, CTOD, CMOD and K. CT specimens made of steel were tested for different values of stress ratio (R) by P = constant method. The influence of Rratio has been studied on crack propagation and crack initiation region. The experimental results show that J and CTOD, contrary to K and CMOD which are constant in R-ratio variations, vary with the variations of R-ratio in the range R = 0.3-0.6. Therefore, there is no need to enter R parameter directly in the well-known Paris equation if J or CTOD parameter is used instead of K in this equation. The constants of these equations are independent of loading unlike the constants of Paris equation. a = crack length A = constant coefficient in the equation A pl = plastic component of area under load-displacement curve b 0 = initial ligament (W − a 0 ) B = specimen thickness B * = characterize the material property (independent of stress ratio) C , C 0 , C 1 , C 2 , C 3 = material constant (constant coefficient in the equations) CMOD = crack mouth opening displacement CMOD max /CMOD min = crack mouth opening displacement value under maximum/minimum load level CTOD = crack tip opening displacement CTOD max /CTOD min = crack tip opening displacement value under maximum/minimum load level CTOD e /CTOD p = elastic/plastic component of crack tip opening displacement da dN = fatigue crack growth rate d s = arc length E = material elastic modulus G = energy release rate J = J-integral J el /J pl = elastic/plastic component of J-integral J IC = ductile fracture toughness J max /J min = J-integral value under maximum/minimum load level
In this paper, fatigue crack growth analysis and reliability evaluation of a reinforced cylindrical shell subjected to random loading have been studied. At first, random loading is extracted from an experimentally obtained power spectral density curve. Then, stress analysis of the shell is carried out using Abaqus® (ABAQUS Inc., Palo Alto, CA, USA) standard code with the aid of a shell‐to‐solid submodelling technique, and the critical positions susceptible of crack nucleation are determined. Then, the fatigue crack propagation is simulated three‐dimensionally in these regions using the Zencrack® software (Zentech International Ltd, London, UK), and the fatigue life and reliability are calculated using the central limit theory. For the evaluation of fatigue life of the full‐scale structure, a procedure of fatigue crack growth and linking up of the two adjacent cracks emanating from critical rivet holes is outlined under random cyclic loading. Using stochastic analysis, closed‐form relations are derived for the probability of failure and reliability.
Purpose
– The purpose of this paper is to use the fiber metal laminates (FML) composites as a patch for repairing a single notched specimen made of AL1035 aluminum alloy. The FML composite patch was bonded on one side of the cracked specimens by adhesive Araldite 2015. Then the fatigue crack growth tests were conducted on the specimens and the effects of both FML patch lay-up sequence and pre-crack angle on the fatigue life were investigated. Finally, the effect of repairing on the fracture parameters (SIF and crack propagation direction) at the crack front has also been calculated using three-dimensional finite element analysis.
Design/methodology/approach
– The fatigue crack growth tests were conducted on the specimens and the effects of both FML patch lay-up sequence and pre-crack angle on the fatigue life were investigated.
Findings
– The results show that the fatigue life of the patched specimens with inclined crack increased approximately 2-6.02 times compared to the un-patched specimens. In addition, the fatigue crack growth rate decreased significantly when the patch was used. Generally, the FML patch with Plate-Fiber-Fiber-AL lay-up has more efficiency than other lay-up sequences.
Originality/value
– Recently, composite patches are used in the structure repair processes to increase the service life of cracked components. The bonded patch method is one of the efficient methods among repairing methods. Today, the FMLs are used in the aircraft structures as a replacement of high-strength aluminum alloys due to their lightweight and high-strength properties. Many researches have been performed on single and double side repaired panels using composite patches. In this study, the FML composites have been used as a patch for repairing a single notched specimen made of AL1035 aluminum alloy.
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