scholarly journals The Use of the Acoustic Emission Method to Identify Crack Growth in 40CrMo Steel

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2140 ◽  
Author(s):  
Aleksandra Krampikowska ◽  
Robert Pała ◽  
Ihor Dzioba ◽  
Grzegorz Świt
Keyword(s):  
Acoustic Emission ◽  
Brittle Fracture ◽  
Crack Growth ◽  
Crack Opening ◽  
Potential Drop ◽  
Growth Stages ◽  
Opening Displacement ◽  
Engineering Structures ◽  
Cracking Process ◽  
Ae Signals

The article presents the application of the acoustic emission (AE) technique for detecting crack initiation and examining the crack growth process in steel used in engineering structures. The tests were carried out on 40CrMo steel specimens with a single edge notch in bending (SENB). In the tests crack opening displacement, force parameter, and potential drop signal were measured. The fracture mechanism under loading was classified as brittle. Accurate AE investigations of the cracking process and SEM observations of the fracture surfaces helped to determine that the cracking process is a more complex phenomenon than the commonly understood brittle fracture. The AE signals showed that the frequency range in the initial stage of crack development and in the further crack growth stages vary. Based on the analysis of parameters and frequencies of AE signals, it was found that the process of apparently brittle fracture begins and ends according to the mechanisms characteristic of ductile crack growth. The work focuses on the comparison of selected parameters of AE signals recorded in the pre-initiation phase and during the growth of brittle fracture cracking.

The Fracture Toughness of Hardened Tool Steels

1987 ◽  
Vol 109 (4) ◽  
pp. 314-318 ◽  
Author(s):  
D. F. Watt ◽  
Pamela Nadin ◽  
S. B. Biner
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Crack Opening ◽  
Compact Tension ◽  
Testing Procedure ◽  
Tool Steels ◽  
Opening Displacement ◽  
Tempering Temperature ◽  
Toughness Testing

This report details the development of a three-stage fracture toughness testing procedure used to study the effect of tempering temperature on toughness in 01 tool steel. Modified compact tension specimens were used in which the fatigue precracking stage in the ASTM E-399 Procedure was replaced by stable precracking, followed by a slow crack growth. The specimen geometry has been designed to provide a region where slow crack growth can be achieved in brittle materials. Three parameters, load, crack opening displacement, and time have been monitored during the testing procedure and a combination of heat tinting and a compliance equation have been used to identify the position of the crack front. Significant KIC results have been obtained using a modified ASTM fracture toughness equation. An inverse relationship between KIC and hardness has been measured.

J-Integral and Crack Opening Displacement as Crack Initiation Criteria in Rubber

1986 ◽  
Vol 59 (5) ◽  
pp. 787-799 ◽  
Author(s):  
R. F. Lee ◽  
J. A. Donovan
Keyword(s):  
Crack Initiation ◽  
Carbon Black ◽  
Crack Growth ◽  
Crack Opening ◽  
Crack Tip ◽  
J Integral ◽  
Carbon Black Content ◽  
Opening Displacement ◽  
Critical Crack ◽  
Growth Initiation

Abstract 1. Evaluation of ∫σdδ where σ is the net section stress and δ is the deformed crack tip diameter requires only one specimen to characterize the initiation of crack growth in unfilled and carbon-black-filled NR. 2. ∫σdδ is equal to one half of the J-integral for crack growth initiation, which is identical to the Thomas tearing energy for a blunt notch. 3. The critical J-integral for crack initiation increases linearly with carbon black content. 4. The critical crack tip radius for crack initiation is independent of carbon black content, and the required crack tip region stress increases linearly with carbon black content.

scholarly journals Study of SENT specimens with a tilted notch to evaluate ductile tearing in spiral welded pipeline applications

2015 ◽  
Vol 6 (3) ◽  
pp. 8
Author(s):  
Maxime Deprez ◽  
Frédéric Keereman ◽  
Koen Van Minnebruggen ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Mechanical Response ◽  
Crack Opening ◽  
Angular Position ◽  
Structural Response ◽  
Potential Drop ◽  
Mixed Mode Loading ◽  
Single Edge ◽  
Opening Displacement ◽  
Ductile Tearing ◽  
Resistance Curves

There is an increasing interest for the use of spiral welded pipelines in strain based design applications. Environmentally imposed loads are able to plastically deform the pipelines, meaning that their structural response is of the utmost importance. However, since the influence of the spiral weld is not fully grasped, further investigation is necessary. The mechanical response of the pipeline is not only influenced by its material properties, but also by the angular position of the welds. Subsequently, the effect of mixed mode loading is a crucial aspect when assessing the helical welds. To evaluate the ductile tearing of the pipeline material, multiple single edge notched tensile (SENT) tests - each with a tilted notch of 25° with respect to the transverse direction - were executed. The extension of the crack is assessed by means of potential drop measurements and finite element simulations. Resistance curves were realized by combining the crack opening displacement with the associated crack extension. This is an ongoing investigation and in this paper a first set of five tests are evaluated.

scholarly journals A theory of viscoelastic crack growth-Revisited (Revised)

2021 ◽  
Author(s):  
Richard A Schapery
Keyword(s):  
Crack Growth ◽  
Creep Compliance ◽  
Current Model ◽  
Crack Opening ◽  
Shift Factor ◽  
Analytical Relationship ◽  
Failure Zone ◽  
Opening Displacement ◽  
Linear Elastic Body ◽  
A Minor

Abstract A theory of viscoelastic crack growth developed nearly five decades ago is generalized to allow traction in the so-called failure zone that is a function of the crack opening displacement (COD). In earlier work, except for a minor exception, traction was specified. The current model leads to a nonlinear double integral that has to be solved for the COD before crack growth can be predicted. First, a closed-form, accurate approximation is found for a linear elastic body. We then show that this COD may be easily and accurately extended to linear viscoelasticity using a realistic, broad spectrum creep compliance. An analytical relationship between stress intensity factor and crack speed then follows. Consistent with earlier work, it is defined almost entirely by creep compliance. Five different failure zone tractions are employed; their differences are shown to have little effect on the crack growth other than through a speed shift factor. The Appendix discusses initiation of growth.

Mode Mixity in the Fracture Toughness Evaluation of Heat-Affected-Zone Material Using SEN(T) Experiment

2021 ◽  
Author(s):  
Sureshkumar Kalyanam ◽  
Yunior Hioe ◽  
Gery Wilkowski
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Heat Affected Zone ◽  
Crack Opening ◽  
Growth Direction ◽  
Mode I ◽  
Mode Ii ◽  
Mode Mixity ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

Abstract SEN(T) specimens provide good similitude for surface cracks (SC) in pipes, where a SC structure has lower constraint condition than typically used fracture toughness specimens such as SEN(B) , and C(T). Additionally, the SENT specimen eliminates concern of material anisotropy since the crack growth direction in the SENT is the same as in a surface-cracked pipe. While the existing recommended and industrial practices for SEN(T) have been developed based on assumption of homogenous or mono-material across the crack, their applicability for the evaluation of fracture toughness of heat-affected-zone (HAZ) were evaluated in this investigation. When conducting tests on SEN(T) specimens with prescribed notch/crack in the HAZ, the asymmetric deformation around the crack causes the occurrence of a combination of Mode-I (crack opening) and Mode-II (crack in-plane shearing) behavior. This mode mixity affects the measurement of the crack-tip-opening-displacement (CTOD) and evaluation of elastic-plastic fracture mechanics parameter, J. The CTOD-R curve depicts the change in toughness with crack growth, in a manner similar to the J-R curve methodology. The experimental observations of Mode-I and Mode-II behavior seen in tests of SEN(T) specimens with notch/crack in the HAZ and as the crack propagates through the weld/HAZ thickness were investigated. The issues related to and the changes needed to account for such behavior for the development of recommended practices or standards for SEN(T) testing of weld/HAZ are addressed.

Interacting Fatigue Crack Growth Analysis with Boundary Cracklet Method

2012 ◽  
Vol 445 ◽  
pp. 1017-1022 ◽  
Author(s):  
A. Kadir Yavuz ◽  
A. Deniz Senalp ◽  
Halit S. Türkmen ◽  
S. Leigh Phoenix
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Power Series ◽  
Crack Growth ◽  
Crack Opening ◽  
Infinite Plate ◽  
Algebraic Equations ◽  
Engineering Structures ◽  
Linear Algebraic Equations ◽  
As Stress

In this study, interacting crack growth in an infinite plate is analyzed with new, fast and accurate Boundary Cracklet Method (BCM) developed by Phoenix and Yavuz. An interior crack is under consideration to watch its propagation because of cyclic loading which is very common for aerospace, naval and civil engineering structures. BCM is very useful to determine the overall stress field as well as stress intensity factors for crack tips and singular wedges at crack kinks. BCM uses integral equations expressed in terms of unknown edge dislocation distributions along crack lines. These distributions derive from an accurate representation of the crack opening displacements using power series basis terms obtained through wedge eigenvalue analysis, which leads to both polynomial and non-polynomial power series. The process is to choose terms of the series and their exponents such that the tractions on the crack faces are virtually zero compared to the far field loading. Applying the method leads to a set of linear algebraic equations to solve for the unknown weighting coefficients for the power series basis terms to make no use of numerical integrations unlike in other methods. Thats why, solution takes just a few seconds on a PC. A simple crack growth emanating from a triangular hole in an infinite plate is analyzed. The fatigue crack growth is assumed to follow Paris-Erdogan Law. The results are compared to those of other numerical methods. A parametric study is performed via graphs and tables to demonstrate the ability of BCM in analysis of fatigue crack growth.

A Fracture Mechanics Investigation on Crack Growth in Massive Forming

2005 ◽  
Vol 482 ◽  
pp. 339-342 ◽  
Author(s):  
Gernot Trattnig ◽  
Christof Sommitsch ◽  
Reinhard Pippan
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Hydrostatic Stress ◽  
Crack Opening ◽  
Crack Depth ◽  
High Stress ◽  
Symmetry Plane ◽  
Stress Triaxiality ◽  
Opening Displacement ◽  
Massive Forming

To understand the crack growth in massive forming and to consequentially avoid crack growth in workpieces, it is necessary to investigate its dependence on the crack depth and thus on the state of hydrostatic stress. Prior work shows that the crack opening displacement (COD) for shallow cracked tension specimens with low stress triaxiality is twice as high as for deep cracked specimens with high stress triaxiality. This work examines the crack growth in compression specimens with pre-cracked cylindrical upsetting samples. The compression samples were cut in the stress symmetry plane in order to observe crack initiation and crack growth by a single specimen technique. In this way it is possible to observe blunting, crack initiation and crack growth inside the upsetting specimens. The resulting COD does not differ significantly from the values achieved in tension samples with short surface cracks.

Deterministic Analysis Results Supporting xLPR Version 2 Code Development

2016 ◽  
Author(s):  
Do Jun Shim ◽  
David Rudland
Keyword(s):  
Crack Growth ◽  
Crack Opening ◽  
Opening Displacement ◽  
Deterministic Analysis ◽  
Depth Direction ◽  
Bending Loads ◽  
Inner Diameter ◽  
Low Probability ◽  
Areas Of Concern ◽  
Leak Before Break

The External Review Board (ERB) for xLPR (eXtremely Low Probability of Rupture) has raised questions regarding the possibility of non-LBB (Leak-Before-Break) conditions for several scenarios of crack growth. There are essentially two areas of concern that need to be addressed regarding this issue. The first is with regard to the effect of weld residual stresses (WRS) on through-wall crack growth where the axial WRS field has high values of compression near the mid thickness region. In this case, the crack growth in the depth direction will slow down when the crack reaches the compressive WRS field especially if the service bending loads are relatively small. However, the crack growth near the inner diameter (ID) surface may continue and possibly become very large and even possibly a 360-degree crack prior to leakage. This may lead to a non-LBB situation which the xLPR code needs to address. The second area of suggested study recommended by the ERB is related to the effect of WRS fields on through-wall crack (TWC) growth and its effect on crack opening displacement (COD) and therefore leak rate. This paper summarizes the efforts taken to address the ERB comments.

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