scholarly journals A Probabilistic Approach to Small Fatigue Crack Initiation and Sizing Using Acoustic Emission

2017 ◽  
Author(s):  
Azadeh Keshtgar ◽  
Mohammad Modarres
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Health Management ◽  
Fatigue Cracks ◽  
Probabilistic Approach ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Accurate Estimation ◽  
Small Fatigue Crack

One of the major concerns in structural health management (SHM) is the early detection of a growing crack. Using this, future damage due to crack propagation can be mitigated or eliminated by implementing proper repair and maintenance. Acoustic Emission (AE) is a non-destructive testing (NDT) method with potential applications for locating and monitoring fatigue cracks. The research presented in this paper focuses on SHM using AE. A novel AE signal analysis approach was proposed in order to detect crack initiation and assess small crack lengths. Experimental investigation indicated that initiation of a crack could be identified through the statistical analysis of the resulting features of the AE signals. A probabilistic AE-based model for small fatigue crack sizing was developed and the uncertainties of the model were estimated. In addition, a probabilistic model validation approach was implemented to confirm accurate estimation of the results. The outcome of this research can be used to evaluate the integrity of structures under fatigue loading. The proposed approach can also be applied as an approach to manage health and assess prognosis of structures.

scholarly journals Acoustic Emission Monitoring of Fatigue Crack Growth in Mooring Chains

2019 ◽  
Vol 9 (11) ◽  
pp. 2187 ◽  
Author(s):  
Ángela Angulo ◽  
Jialin Tang ◽  
Ali Khadimallah ◽  
Slim Soua ◽  
Cristinel Mares ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Large Scale ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Damage Initiation ◽  
High Level

Offshore installations are subject to perpetual fatigue loading and are usually very hard to inspect. Close visual inspection from the turret is usually too hazardous for divers and is not possible with remotely operated vehicles (ROVs) because of the limited access. Conventional nondestructive techniques (NDTs) have been used in the past to carry out inspections of mooring chains, floating production storage and offloading systems (FPSOs), and other platforms. Although these have been successful at detecting and assessing fatigue cracks, the hazardous nature of the operations calls for remote techniques that could be applied continuously to identify damage initiation and progress. The aim of the present work is to study the capabilities of acoustic emission (AE) as a monitoring tool to detect fatigue crack initiation and propagation in mooring chains. A 72-day large-scale experiment was designed for this purpose. A detailed analysis of the different AE signal time domain features was not conclusive, possibly due to the high level of noise. However, the frequency content of the AE signals offers a promising indication of fatigue crack growth.

Plastic Slip and Early Stage of Fatigue Damage in Polycrystals: Comparison between Experiments and Crystal Plasticity Finite Elements Simulations

2014 ◽  
Vol 891-892 ◽  
pp. 1711-1716 ◽  
Author(s):  
Loic Signor ◽  
Emmanuel Lacoste ◽  
Patrick Villechaise ◽  
Thomas Ghidossi ◽  
Stephan Courtin
Keyword(s):  
Fatigue Crack ◽  
Finite Elements ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Crystal Plasticity ◽  
Early Stage ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Plastic Slip

For conventional materials with solid solution, fatigue damage is often related to microplasticity and is largely sensitive to microstructure at different scales concerning dislocations, grains and textures. The present study focuses on slip bands activity and fatigue crack initiation with special attention on the influence of the size, the morphology and the crystal orientation of grains and their neighbours. The local configurations which favour - or prevent - crack initiation are not completely identified. In this work, the identification and the analysis of several crack initiation sites are performed using Scanning Electron Microscopy and Electron Back-Scattered Diffraction. Crystal plasticity finite elements simulation is employed to evaluate local microplasticity at the scale of the grains. One of the originality of this work is the creation of 3D meshes of polycrystalline aggregates corresponding to zones where fatigue cracks have been observed. 3D data obtained by serial-sectioning are used to reconstruct actual microstructure. The role of the plastic slip activity as a driving force for fatigue crack initiation is discussed according to the comparison between experimental observations and simulations. The approach is applied to 316L type austenitic stainless steels under low-cycle fatigue loading.

Study on small fatigue crack initiation and growth for friction stir welded joints

2019 ◽  
Vol 739 ◽  
pp. 71-85 ◽  
Author(s):  
Guoqin Sun ◽  
Chongwen Wang ◽  
Xinhai Wei ◽  
Deguang Shang ◽  
Shujun Chen
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Welded Joints ◽  
Fatigue Crack Initiation ◽  
Friction Stir ◽  
Small Fatigue Crack

scholarly journals Performance Evaluation of a Carbon Nanotube Sensor for Fatigue Crack Monitoring of Metal Structures

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4383
Author(s):  
Shafique Ahmed ◽  
Thomas Schumacher ◽  
Erik T. Thostenson ◽  
Jennifer McConnell
Keyword(s):  
Fatigue Crack ◽  
Carbon Nanotube ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Real Time ◽  
False Positive ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Resistance Change ◽  
Metal Structures

This article describes research that investigated the ability of a carbon nanotube (CNT) sensor to detect and monitor fatigue crack initiation and propagation in metal structures. The sensor consists of a nonwoven carrier fabric with a thin film of CNT that is bonded to the surface of a structure using an epoxy adhesive. The carrier fabric enables the sensor to be easily applied over large areas with complex geometries. Furthermore, the distributed nature of the sensor improves the probability of detecting crack initiation and enables monitoring of crack propagation over time. Piezoresistivity of the sensor enables strains to be monitored in real time and the sensor, which is designed to fragment as fatigue cracks propagate, directly measures crack growth through permanent changes in resistance. The following laboratory tests were conducted to evaluate the performance of the sensor: (1) continuous crack propagation monitoring, (2) potential false positive evaluation under near-threshold crack propagation conditions, and (3) crack re-initiation detection at a crack-stop hole, which is a commonly used technique to arrest fatigue cracks. Real-time sensor measurements and post-mortem fractography show that a distinguishable resistance change of the sensor occurs due to fatigue crack propagation that can be quantitatively related to crack length. The sensor does not show false positive responses when the crack does not propagate, which is a drawback of many other fatigue sensors. The sensor is also shown to be remarkably sensitive to detecting crack re-initiation.

scholarly journals Energy Dissipation Measurement in Improved Spatial Resolution Under Fatigue Loading

2019 ◽  
Vol 60 (2) ◽  
pp. 181-189
Author(s):  
A. Akai ◽  
D. Shiozawa ◽  
T. Yamada ◽  
T. Sakagami
Keyword(s):  
Fatigue Crack ◽  
Energy Dissipation ◽  
Crack Initiation ◽  
Fatigue Limit ◽  
Spatial Resolution ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Dissipated Energy ◽  
Damage Initiation ◽  
Slip Bands

Abstract Recently, a technique for rapidly determining a material’s fatigue limit by measuring energy dissipation using infrared thermography has received increasing interest. Measuring the energy dissipation of a material under fatigue loading allows the rapid determination of a stress level that empirically coincides with its fatigue limit. To clarify the physical implications of the rapid fatigue limit determination, the relationship between energy dissipation and fatigue damage initiation process was investigated. To discuss the fatigue damage initiation process at grain size scale, we performed high-spatial-resolution dissipated energy measurements on type 316L austenitic stainless steel, and observed the slip bands on the same side of the specimen. The preprocessing of dissipated energy measurement such as motion compensation and a smoothing filter was applied. It was found that the distribution of dissipated energy obtained by improved spatial resolution measurement pinpointed the location of fatigue crack initiation. Owing to the positive correlation between the magnitude of dissipated energy and number of slip bands, it was suggested that the dissipated energy was associated with the behavior of slip bands, with regions of high dissipated energy predicting the location of fatigue crack initiation.

Research on the Mechanism of Fatigue Crack Initiation of X60 Pipeline Steel after Per-Tension Deformation

2012 ◽  
Vol 197 ◽  
pp. 798-801
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fracture Characteristics ◽  
Metallic Inclusions ◽  
The Matrix

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the mechanism of fatigue crack initiation of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the mechanism of fatigue crack initiation is the typical cleavage fracture characteristics and the cracks mainly initiates from the non-metallic inclusions which was the local brittle fracture materials such as MnS inclusion. With the pre-tension deformation increase, the yield strength of the matrix was increased and the toughness decreased due to the work-hardening effect. With the effects of the non-metallic inclusions larger, the fatigue cracks initiated from the non-metallic inclusions easier.

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