scholarly journals Fracture toughness and crack growth of brackish ice using chevron-notched specimens

1994 ◽  
Vol 40 (135) ◽  
pp. 415-426 ◽  
Author(s):  
Lars Stehn
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Opening ◽  
Initial Crack ◽  
Effect Study ◽  
Small Scale ◽  
Opening Displacement ◽  
Critical Crack ◽  
Experimental Calibration ◽  
Brackish Ice

AbstractField-test equipment called FIFT (a Field Instrument for Fracture toughness Tests on ice) was used in both field and laboratory fracture-toughness tests on brackish sea ice from the Gulf of Bothnia. An experimental calibration was performed and a compliance expression was then derived for the Short Rod Chevron Notched (SRCN) specimen. Using the SRCN configuration, for which the initial crack growth is shown to be stable, and measured load-point displacements, preliminary crack-growth velocities are found. The obtained estimated crack velocity is, on average,ȧe= 20 ms−1, albeit with a large standard deviation. The results indicate that critical crack (crack-jumping) growth occurs. The apparent fracture toughness,KQ, was found to have a pronounced dependency on porosity in the form of brine volume. The results obtained are derived from a linearly elastic fracture mechanics (LEFM) theory. Consequently, the tests were designed to satisfy small-scale yielding requirements in terms of notch sensitivity and brittleness. The linearity of the load vs crack-opening displacement curves together with a size-effect study, showing that the specimen is notch-sensitive for grain-sizes ranging from 1.6 to nearly 100 mm, indicate that LEFM could be applicable.

scholarly journals Fracture toughness and crack growth of brackish ice using chevron-notched specimens

1994 ◽  
Vol 40 (135) ◽  
pp. 415-426
Author(s):  
Lars Stehn
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Crack Opening ◽  
Initial Crack ◽  
Effect Study ◽  
Small Scale ◽  
Opening Displacement ◽  
Critical Crack ◽  
Experimental Calibration ◽  
Brackish Ice

AbstractField-test equipment called FIFT (a Field Instrument for Fracture toughness Tests on ice) was used in both field and laboratory fracture-toughness tests on brackish sea ice from the Gulf of Bothnia. An experimental calibration was performed and a compliance expression was then derived for the Short Rod Chevron Notched (SRCN) specimen. Using the SRCN configuration, for which the initial crack growth is shown to be stable, and measured load-point displacements, preliminary crack-growth velocities are found. The obtained estimated crack velocity is, on average,ȧe= 20 ms−1, albeit with a large standard deviation. The results indicate that critical crack (crack-jumping) growth occurs. The apparent fracture toughness,KQ, was found to have a pronounced dependency on porosity in the form of brine volume. The results obtained are derived from a linearly elastic fracture mechanics (LEFM) theory. Consequently, the tests were designed to satisfy small-scale yielding requirements in terms of notch sensitivity and brittleness. The linearity of the load vs crack-opening displacement curves together with a size-effect study, showing that the specimen is notch-sensitive for grain-sizes ranging from 1.6 to nearly 100 mm, indicate that LEFM could be applicable.

A Finite Element Study of Stable Crack Growth Under Plane Stress Conditions: Part II—Influence of Hardening

1987 ◽  
Vol 54 (4) ◽  
pp. 846-853 ◽  
Author(s):  
R. Narasimhan ◽  
A. J. Rosakis ◽  
J. F. Hall
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Plane Stress ◽  
Crack Opening ◽  
Stable Crack Growth ◽  
Small Scale ◽  
Opening Displacement ◽  
Element Analysis ◽  
Critical Crack ◽  
Perfectly Plastic

A detailed finite element analysis is performed to model quasi-static crack growth under plane stress, small-scale yielding conditions in elastic-plastic materials characterized by isotropic power law hardening and the Huber-Von Mises yield surface. A nodal release procedure is used to simulate crack extension. Results pertaining to the influence of hardening on the extent of active yielding and the near-tip stress and deformation fields are presented. Clear evidence of an elastic unloading wake following the active plastic zone is found, but no secondary (plastic) reloading along the crack flank is numerically observed for any level of hardening. A ductile crack growth criterion based on the attainment of a critical crack opening displacement at a small microstructural distance behind the tip, is employed to investigate the nature of the J resistance curves under plane stress. In addition, the same criterion is employed to investigate the influence of hardening on the potential for stable crack growth under plane stress. It is found that predictions based on a perfectly plastic model may be unconservative in this respect, which is qualitatively similar to the conclusions reached in antiplane shear and Mode I plane strain.

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.

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.

Assessment of Fracture Toughness and Fatigue Crack Growth Threshold of a Welded Joint Constituent of a Steam Turbine LP Rotor

2014 ◽  
Author(s):  
M.-H. Herman Shen ◽  
Sajedur Akanda ◽  
Xia Liu ◽  
Peng Wang
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Steam Turbine ◽  
Crack Growth ◽  
Welded Joint ◽  
Crack Opening ◽  
Crack Size ◽  
Turbine Rotor ◽  
Opening Displacement ◽  
Stable Crack Propagation

In order to ensure safety and reliability of steam turbine welded rotors, the present investigation focuses on evaluation of crack initiation, growth, and resistance parameters of base metal (BM), weld metal (WM) and heat affected zone (HAZ) of a steam turbine rotor welded joint constituent. The experimental part consists of three-point bending conducted on single edge notch bend specimens to induce stable crack propagation. The crack size was calculated by incorporating the crack opening displacement measured by a clip-gage, in a compliance method. The fatigue crack threshold was obtained from a crack growth rate curve according to ASTM E647 and the fracture toughness was determined from a J-based resistance curve according to ASTM E1820. From the experimental results the fatigue crack threshold is found to be a function of loading ratio rather than a single material parameter. From the fracture toughness results, the WM and the BM are found to have similar KIc values whereas HAZ is found to have slightly better KIc values although HAZ had little crack extension during the experiments.

Evaluation of Wedge Splitting Fracture Tests Using the Double-K Model: Analysis of the Effect of Hemp Fibre Dosage and Length in Concrete Specimens

2016 ◽  
Vol 249 ◽  
pp. 142-146
Author(s):  
Hana Šimonová ◽  
Ivana Havlíková ◽  
Jakub Sobek ◽  
Alaa Abdulrahman ◽  
Zbyněk Keršner ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Critical Crack ◽  
Hemp Fibre ◽  
Fracture Tests ◽  
Critical Crack Opening ◽  
Wedge Splitting

This paper deals with the results obtained from the employment of a selected fracture model to evaluate wedge splitting fracture tests carried out on hemp fibre concrete specimens. The research work was focused mainly on the effect of the dosage and length of hemp fibres on the initiation part of crack propagation in concrete specimens, and on critical crack opening displacement. Concrete mixtures with different volumetric dosages (0.5, 1.0 and 2.0 %) and fibre lengths (10, 20 and 40 mm) were prepared, and six identical specimens were cast from each mixture. Specimens were also cast from a reference mixture, which was without fibres. The specimens were provided with an initial notch and tested using the wedge splitting test method. Load versus crack mouth opening displacement diagrams were recorded during testing and (after data filtering and appropriate modifications) subsequently evaluated using the Double-K fracture model. This model allows the evaluation of two material parameters – the initiation fracture toughness, which defines the onset of stable crack propagation, and the unstable fracture toughness, which defines the onset of unstable cracking or failure. Finally, the critical crack opening displacement was determined with the assumption of the bilinear function of softening in tension.

A New Methodology for Estimating Fracture Criterion of Thin Sheets

2009 ◽  
Vol 417-418 ◽  
pp. 305-308
Author(s):  
Kalyan Kumar Ray ◽  
Ashmita Patra ◽  
Debashish Bhattacharjee
Keyword(s):  
Fracture Toughness ◽  
Crack Opening ◽  
Specimen Thickness ◽  
Interstitial Free ◽  
Thin Sheets ◽  
If Steel ◽  
Opening Displacement ◽  
Critical Crack ◽  
Suggested Technique ◽  
Critical Crack Opening

A simple and reliable method has been proposed for determining fracture toughness of thin sheets. The principle of the method considers that critical crack opening displacement (c) corresponds to a specific amount of load drop during fracture toughness tests. The suggested technique yields c value for an interstitial free (IF) steel as 2.04 mm in excellent correspondence with an indirect estimate of 1.97 mm from the popular energy extrapolation technique. The magnitude of c for IF steel sheets is found to decrease with decreasing thickness in agreement with the expected variation of this criterion with specimen thickness in gross yielding fracture mechanics (GYFM) regime.

scholarly journals Analysis influence of Dmax on fracture mechanics parameters of concrete made of limestone aggregate at three point bending.

2007 ◽  
Vol 1 (1) ◽  
pp. 005-016
Author(s):  
Grzegorz Golewski
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Fracture Mechanics ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Initial Crack ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Load Displacement

The analysis of concrete behaviour taking into account fracture mechanics method makes it possible to describe the origin and development of the damages occurring in it, which is impossible in case of using global strength characteristics of composite. In the work the experiment results were presented regarding the determination of the influence of grain-size distribution of coarse aggregate on the crack mechanics parameters of limestone concretes as defined according to the I mode of crack propagation at bending. Two types of optimal composition of grains were used with Dmax up to 8 and up to 16 mm. During the experiments the basic parameters of fracture mechanics were determined: critical value of stress intensity factors: : and KIc, fracture energy GF, critical crack tip opening displacement CTODc and unit work of failure JIc. During the fracture toughness tests the method of loading samples based on RILEM recommendations was used. For basic experiments six beams with one initial crack were used. In the course of the experiments carried out, two dependencies were recorded for each sample: load – displacement of crack outlet opening and load - displacement of the point of applied force. In the course of the tests carried out it was found out that the higher fracture toughness was characteristic of concretes with the grain - size distribution up to 16 mm. The results presented in the work can be used in designing concretes in order to obtain materials characterized by the minimum number of initial defects which, thanks to increased fracture toughness, can increase to the reliability of construction work.

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