scholarly journals Crack Extension Resistance of Normal-Strength Concrete Subjected to Elevated Temperatures

2014 ◽  
Vol 2014 ◽  
pp. 1-12
Author(s):  
Jing Chen ◽  
Zhoudao Lu
Keyword(s):  
Crack Extension ◽  
Fracture Process ◽  
Elevated Temperatures ◽  
Process Zone ◽  
Splitting Method ◽  
Mouth Opening ◽  
Cohesive Force ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Normal Strength

Determination of the residual crack extension resistance curves (KR-curves) associated with cohesive force distribution on fictitious crack zone of complete fracture process is implemented in present research. The cohesive force distributes according to bilinear softening traction-separation law proposed by Petersson. Totally ten temperatures varying from 20°C to 600°C and the specimen size of230×200×200 mm with initial-notch depth ratios 0.4 are considered. The load-crack mouth opening displacement curves (P-CMOD) of postfire specimens are obtained by wedge-splitting method from which the stress intensity factor curves (K-curves) are calculated. In each temperature, with the distribution of cohesive force along the fracture process zone, the residual fracture toughnessKR(Δa) increases with increasing crack lengthΔa, whereas theKR-curves decrease with increasing temperaturesTmfor the thermal damage induced. The stability analysis on crack propagation demonstrates that when the residualKR-curve is higher thanK-curve, the crack propagates steadily; otherwise, the crack propagates unsteadily.

Experimental analysis of crack evolution in concrete by the acoustic emission technique

2015 ◽  
Author(s):  
J. Saliba ◽  
A. Loukili ◽  
J.P. Regoin ◽  
D. Grégoire ◽  
L. Verdon ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fracture Process ◽  
Process Zone ◽  
Mouth Opening ◽  
Acoustic Emissions ◽  
Plain Concrete ◽  
Crack Mouth Opening Displacement ◽  
Notch Depth ◽  
Opening Displacement ◽  
Magnitude Distribution

The fracture process zone (FPZ) was investigated on unnotched and notched beams with different notch depths. Three point bending tests were realized on plain concrete under crack mouth opening displacement (CMOD) control. Crack growth was monitored by applying the acoustic emission (AE) technique. In order to improve our understanding of the FPZ, the width and length of the FPZ were followed based on the AE source locations maps and several AE parameters were studied during the entire loading process. The bvalue analysis, defined as the log-linear slope of the frequency-magnitude distribution of acoustic emissions, was also carried out to describe quantitatively the influence of the relative notch depth on the fracture process. The results show that the number of AE hits increased with the decrease of the relative notch depth and an important AE energy dissipation was observed at the crack initiation in unnotched beams. In addition, the relative notch depth influenced the AE characteristics, the process of crack propagation, and the brittleness of concrete.

Experimental Determination of J-R Curves Using SENB Specimens and P-CMOD Data

2008 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Crack Extension ◽  
Mouth Opening ◽  
Cost Effective ◽  
Crack Mouth Opening Displacement ◽  
Simple Relationship ◽  
J Integral ◽  
Single Specimen ◽  
Opening Displacement ◽  
Load Line Displacement ◽  
Senb Specimen

Fracture toughness and J-R curves of ductile materials are often measured under the guidance of ASTM standard E1820 using the single specimen technique and the elastic unloading compliance method. For the standard single-edge notched bend [SENB] specimens, the load, load-line displacement (LLD), and crack-mouth opening displacement (CMOD) are required being measured simultaneously. The load-CMOD data are used to determine the crack extension, and the load-LLD data together with the crack extension are used to determine the J-integral values in a J-R curve test. Experiments have indicated that the CMOD measurement is very accurate, but the LLD measurement is difficult and less accurate in a fracture test on the SENB specimen. If the load-CMOD records is used to determine the crack extension and the J-integral values, experimental accuracies for the J-R curve testing would be increased, and the test costs can be reduced. To this end, this paper develops a simple relationship between LLD and CMOD that is used to convert the measured CMOD record to the corresponding LLD data, and then to calculate the J values for a growing crack in a J-R curve test on the SENB specimen using one single specimen technique. The proposed method is then verified by the experimental data of J-R curves for HY80 steel using the SENB specimens and the load-CMOD data only. The results show that the proposed method is more accurate and more cost-effective for the J-R curve testing.

Stable Crack Growth in Ceramics at Ambient and Elevated Temperatures

1993 ◽  
Vol 115 (3) ◽  
pp. 281-285 ◽  
Author(s):  
J. Y. Pastor ◽  
J. LLorca ◽  
J. Planas ◽  
M. Elices
Keyword(s):  
Fracture Behavior ◽  
Elevated Temperatures ◽  
Testing Machine ◽  
Mouth Opening ◽  
Stable Crack Growth ◽  
Hydraulic Testing ◽  
Crack Mouth Opening Displacement ◽  
Zirconia Ceramic ◽  
Opening Displacement ◽  
Stable Crack Propagation

Quasi-static, stable crack propagation tests in ceramics are presented. The tests are performed using a recently developed technique in which the crack mouth opening displacement (CMOD) is continuously monitored during the test by means of a laser extensometer, and this signal is employed to control a servo-hydraulic testing machine. The advantages of such tests to characterize the fracture behavior of ceramics at high temperature are described, and the technique is used to study the fracture behavior of an ytria-partially stabilized zirconia ceramic at ambient and elevated temperatures.

Fracture Parameters of Alkali-Activated Aluminosilicate Composites with Ceramic Precursor

2020 ◽  
Vol 309 ◽  
pp. 73-79
Author(s):  
Hana Šimonová ◽  
Ivana Kumpová ◽  
Iva Rozsypalová ◽  
Patrik Bayer ◽  
Petr Frantik ◽  
...  
Keyword(s):  
Fracture Process ◽  
Fracture Process Zone ◽  
Process Zone ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Crack Model ◽  
Mechanical Fracture ◽  
Ceramic Precursor ◽  
Fracture Parameters ◽  
Alkali Activated

This paper deals with selected alkali-activated aluminosilicate composites with a ceramic precursor in terms of their characterization using mechanical fracture parameters. Three composites were studied. They were manufactured using brick powder as a precursor and an alkaline activator with a dimensionless silicate modulus of Ms = 1.0, 1.2 and 1.4. The test specimens were nominally 40 × 40 × 160 mm in size and had a central edge notch with a depth of 1/3 of the specimen’s height. At least 6 specimens made of each composite were tested at the age of 28 days. The specimens were subjected to three-point bending tests, during which diagrams showing force vs. deflection at midspan (F–d diagrams) and force vs. crack mouth opening displacement (F–CMOD diagrams) were recorded. After the processing of these diagrams, values were determined for the static modulus of elasticity, effective fracture toughness (including its initiation component from the analysis of the first part of the F–CMOD diagrams), effective toughness and specific fracture energy using the effective crack model, Work-of-Fracture method, and Double-K fracture model. After the fracture experiments had been performed, compressive strength values were determined for informational purposes from one part of each specimen that remained after testing. In order to obtain visual information about the internal structure of the composites before and after the mechanical testing, the selected specimen was examined via X-ray microtomography. Tomographic measurements and image processing were performed for the qualitative and quantitative evaluation of internal structural changes with an emphasis on the calculation of porosimetry parameters as well as the visualization of the fracture process zone. The fractal dimension of the fracture surface and fracture process zone was determined. The porosity and microstructure images of selected samples taken from specimens were assessed.

scholarly journals Growth Ring Orientation Effects in Transverse Softwood Fracture

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5755
Author(s):  
Parinaz Belalpour Dastjerdi ◽  
Eric N. Landis
Keyword(s):  
Grain Orientation ◽  
Growth Ring ◽  
Process Zone ◽  
Mouth Opening ◽  
Strain Energy Release ◽  
Stable Crack Growth ◽  
Crack Mouth Opening Displacement ◽  
Type Specimens ◽  
Opening Displacement ◽  
Grain Angle

In this study, the fracture mechanics of eastern spruce were characterized in relation to end-grain orientation. Compact tension-type specimens with small pre-formed cracks were prepared such that grain angle varied relative to the load axis. Specimens were loaded under crack mouth opening displacement (CMOD) control as to maintain stable crack growth. Specimen fracture was characterized using both R-curve and bulk fracture energy approaches. The results showed that under a RT grain orientation, as well as grain deviations up to about 40∘, cracks will follow a path of least resistance in an earlywood region. As the grain angle exceeds 40∘, the crack will initially move macroscopically in the direction of maximum strain energy release rate, which extends in the direction of the pre-crack, but locally meanders through earlywood and latewood regions before settling once again in an earlywood region. At 45∘, however, the macroscopic crack takes a turn and follows a straight radial path. The results further show that RT fracture is macroscopically stable, while TR fracture is unstable. None of the end-grain fracture orientations showed rising R-curve behavior, suggesting that there is not a traditional fracture process zone in this orientation.

Development of Weight Functions for Modelling Delayed Hydride Cracking Initiation at a Blunt Flaw

2004 ◽  
Author(s):  
Douglas A. Scarth ◽  
Joanna Wu ◽  
Ted Smith ◽  
Dennis M. Kawa
Keyword(s):  
Stress Distribution ◽  
Process Zone ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Weight Functions ◽  
Zone Model ◽  
Engineering Process ◽  
Opening Displacement ◽  
Wide Range ◽  
Cubic Polynomial

Delayed Hydride Cracking (DHC) in Zr-2.5 Nb alloy material is of interest to the CANDU (Canada Deuterium Uranium) industry in the context of the potential to initiate DHC at a blunt flaw in a CANDU reactor pressure tube. The material is susceptible to DHC when there is diffusion of hydrogen atoms to the flaw, precipitation of hydride platelets, and development of a hydrided region at the flaw tip. The hydrided region can then fracture to the extent that a crack forms, and is able to grow by the DHC crack growth mechanism. An engineering process-zone model for evaluation of DHC initiation at a blunt flaw that takes into account flaw geometry has been developed. The model is based on representing the stress relaxation due to hydride formation, and crack initiation, by an infinitesimally thin process zone. Application of the engineering process-zone model requires calculation of the stress intensity factor, and the crack-mouth opening displacement, for a fictitious crack at the tip of a blunt flaw. In the current model, calculation of these quantities is based on a cubic polynomial fit to represent the stress distribution ahead of the blunt flaw tip, where the stress distribution is generally calculated by finite element analysis. However, the cubic polynomial is not always an optimum fit to the stress distribution for very small root radius flaws, due to the large stress gradients near the flaw tip. Application of the weight function method will enable a more accurate representation of the flaw-tip stress distribution for the calculation of the stress intensity factor and the crack-mouth opening displacement. Weight functions for a crack at the tip of a blunt flaw in a thin wall cylinder have been developed for implementation into the engineering process-zone model. These weight functions are applicable to a wide range of blunt flaw depths and root radii, as well as a wide range of flaw-tip crack depths. The development and verification of the weight functions is described in this paper. The verification calculations are in reasonable agreement with alternate solutions, and have confirmed that the weight functions have reasonable accuracy for engineering applications of the process-zone methodology.

An Experimental Study of Failure in Circumferentially Notched Elastomer Cylinders

1993 ◽  
Vol 66 (4) ◽  
pp. 646-663 ◽  
Author(s):  
Claudia J. Quigley ◽  
Robert Dooley ◽  
David M. Parks
Keyword(s):  
Crack Extension ◽  
Large Deformations ◽  
Inner Core ◽  
Mouth Opening ◽  
Stretch Ratio ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Qualitative And Quantitative ◽  
Filled Elastomers ◽  
Tearing Energy

Abstract Cylindrical dumbbell specimens containing deep circumferential cracks were loaded in tension until failure to investigate the fracture process in thick carbon black filled elastomers. Failure occurred at large deformations and was characterized by material tearing and small amounts of slow stable crack extension until rupture. The tearing process itself consisted of two distinct phenomena, delamination and crack extension. Upon load application, parabolic and asymmetric blunting of the crack tip was observed followed by a visible separation of the fabricated crack surfaces into upper and lower crack surfaces connected by an inner core of elastomer material. Localized material failure, identified as delamination, occurred along the outer surface of this inner core between the fabricated crack surfaces. Crack extension in the load direction was found above and below the fabricated crack surfaces. Both qualitative and quantitative aspects of failure were studied. Load and crack mouth opening displacement (CMOD) histories were examined, and the stretch ratio and tearing energy at rupture were measured. Finally, a model describing the tearing process was discussed.

scholarly journals Influence of notch orientation on ductile tearing in SENT specimens

2014 ◽  
Vol 5 (1) ◽  
pp. 8
Author(s):  
Robin Turtelboom ◽  
Pieter Vandenbroucke ◽  
Koen Van Minnebruggen ◽  
Stijn Hertelé ◽  
Matthias Verstraete ◽  
...  
Keyword(s):  
Mixed Mode ◽  
Crack Extension ◽  
Mouth Opening ◽  
Potential Drop ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Mixed Mode Loading ◽  
Opening Displacement ◽  
Ductile Tearing ◽  
Plastic Behaviour

There is a growing interest for the use of spiral welded pipes in strain based design related applications. Since the influence of the spiral weld on the plastic behaviour of the pipe is not yet fully understood, further research on this topic is required. An important aspect of this plastic behaviour is the effect of mixed mode loading on weld defects located in the helical weld. This paper elaborates on the first experimental trials to evaluate ductile tearing by means of single edge notched tensile specimen (SENT) testing with slanted notches. Tests were performed on two SENT specimens, one with a slanted notch and another with a straight notch in order to investigate the influence of mixed mode loading. The crack mouth opening displacement and crack extension were determined experimentally by means of digital image correlation and potential drop measurements respectively. The crack extension and the potential drop measurements were related by means of finite element simulations.

Comparison study of crack propagation in rubberized and conventional prestressed concrete sleepers using digital image correlation

2021 ◽  
pp. 095440972110205
Author(s):  
Guoqing Jing ◽  
Du yunchang ◽  
Ruilin You ◽  
Mohammad Siahkouhi
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Prestressed Concrete ◽  
Mouth Opening ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Experimental Program ◽  
Pure Bending ◽  
Opening Displacement ◽  
Rubber Concrete

Rubber concrete (RC) has been confirmed to be suitable for concrete sleeper production. This paper studies the cracking behaviour of conventional and rubber-reinforced concrete sleepers based on the results of an experimental program. The cracking behaviour in the pure bending zone was analysed up to a load of 140 kN. The crack mouth opening displacement (CMOD) was accordingly measured using a digital image correlation (DIC) method. The DIC results show that the rubber prestressed concrete sleeper (RPCS) has a resistance against crack initiation that is 20% greater than that of the conventional prestressed concrete sleeper (CPCS) under the same loading condition; however, due to the higher crack growth rate of the RPCS, the first crack detected by the operator forms at 60 kN, which corresponds to a strength approximately 9% lower compared with the 65 kN load at which the first crack is detected in the CPCS. Before the first crack (60 kN), the RPCS has a deflection 35% lower than that of the CPCS, but after cracking, at loads of 80 kN, 100 kN and 140 kN, the RPCS has a deflection 15%, 4% and 24% higher than that of the CPCS, respectively.

Effects of Weld Strength Mismatch on Estimation Procedures for J and CTOD Fracture Parameters Using SE(B) Specimens

2007 ◽  
Author(s):  
Gustavo H. B. Donato ◽  
Claudio Ruggieri
Keyword(s):  
Mouth Opening ◽  
Estimation Procedure ◽  
Primary Objective ◽  
Weld Strength ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Fracture Parameters ◽  
Wide Range ◽  
Estimation Procedures ◽  
Fracture Specimens

This work presents an exploratory development of J and CTOD estimation procedures for welded fracture specimens under bending based upon plastic eta factors and plastic rotation factors. The techniques considered include: i) estimating J and CTOD from plastic work and ii) estimating CTOD from the plastic rotational factor. The primary objective is to gain additional understanding on the effect of weld strength mismatch on estimation techniques to determine J and CTOD fracture parameters for a wide range of a/W-ratios and mismatch levels. Very detailed non-linear finite element analyses for plane-strain models of SE(B) fracture specimens with center cracked, square groove welds provide the evolution of load with increased load-line displacement and crack mouth opening displacement which are required for the estimation procedure. The results show that levels of weld strength mismatch within the range ±20% mismatch do not affect significantly J and CTOD estimation expressions applicable to homogeneous materials, particularly for deeply cracked fracture specimens. The present analyses, when taken together with previous studies, provide a fairly extensive body of results which serve to determine parameters J and CTOD for different materials using bend specimens with varying geometries and mismatch levels.

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