Acoustic Emission during Fatigue Testing of Pressure Vessels

2006 ◽  
Vol 13-14 ◽  
pp. 147-152 ◽  
Author(s):  
Franz Rauscher
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Testing ◽  
Basic Mechanism ◽  
Pressure Vessels ◽  
Weld Defect ◽  
Gas Cylinders ◽  
Crack Growth Velocity

It is known that the basic mechanism of fatigue crack growth in ductile pressure vessel steels, which is repetitive blunting and re-sharpening of the crack tip, is a weak acoustic emission (AE) source. On the other hand, a large number of AE events occur during cyclic crack growth. Most AE events are caused by repetitive friction at the fracture surfaces, but these AE events show relatively weak correlation with the crack growth velocity. In the paper it is shown, based on examples – fatigue crack growth starting from an artificial weld defect, cycling of a natural crack defect, crack initiation and growth in gas cylinders - which information can be gained by relatively simple analyses of the AE data from cyclic pressure tests.

scholarly journals Some Questions Regarding the Interaction of Creep and Fatigue

1976 ◽  
Vol 98 (3) ◽  
pp. 235-243 ◽  
Author(s):  
L. A. James
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elevated Temperatures ◽  
Fatigue Testing ◽  
Creep Damage ◽  
Pressure Vessels ◽  
Crack Growth Behavior ◽  
Fatigue Process ◽  
Type 304

Data are presented from fatigue-crack growth tests conducted on Type 304 S.S. in inert environments at elevated temperatures which show that the thermal-activation noted in similar tests run in air environments is not present in the inert environment. Similar observations from the literature are reviewed, including the observation that the time-dependency noted in tests conducted in elevated temperature air environments is also greatly suppressed in inert environments. These findings suggest that an interaction between the fatigue process and the corrosive air environments is responsible for the thermally-activated time-dependent behavior often attributed to creep-fatigue interaction. Data are also presented which show that the fatigue-crack growth behavior of Type 304 S.S. subjected to significant creep damage prior to fatigue testing does not differ appreciably from the behavior of material not subjected to prior creep damage; again indicating minimal interaction between creep and fatigue. It is suggested that in the temperature range where pressure vessels and piping are generally designed to operate (i.e. below about one-half the absolute melting temperature of the alloy), the interaction between creep and fatigue is far less significant than once supposed, and that the major parameter interacting with the fatigue process is that of high temperature corrosion.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Study of fatigue crack growth in RAFM steel using acoustic emission technique

2016 ◽  
Vol 126 ◽  
pp. 107-116 ◽  
Author(s):  
M. Nani Babu ◽  
C.K. Mukhopadhyay ◽  
G. Sasikala ◽  
Shaju K. Albert ◽  
A.K. Bhaduri ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Acoustic Emission Technique ◽  
Rafm Steel

Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

2018 ◽  
Author(s):  
João Ferreira ◽  
José A. F. O. Correia ◽  
Grzegorz Lesiuk ◽  
Sergio Blasón González ◽  
Maria Cristina R. Gonzalez ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Mixed Mode ◽  
Pressure Vessels ◽  
Mode I ◽  
Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

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