The Effects of Tensile Softening Curve Parameters on Fracture in Concrete Based on Initial Fracture Toughness Criterion

2014 ◽  
Vol 904 ◽  
pp. 232-235
Author(s):  
Long Bang Qing ◽  
Huan Huan Liu
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Peak Load ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Softening Curve ◽  
Initial Fracture ◽  
Tensile Softening

The effects of tensile softening curve parameters on the crack propagation P-CMOD and P-CTOD curves were analyzed using a calculation method which adopted the initial fracture toughness as the crack propagation criterion. The results showed that: the whole process of the P-CMOD and P-CTOD curves were affected by the tensile softening curve parameters, especially for the descending segment of the curves, but the peak load and critical crack mouth opening displacement were less affected.

Effect of Calcium Dissolution on the Fracture Properties of Concrete Exposed to Nitric Acid Environment

2011 ◽  
Vol 374-377 ◽  
pp. 1974-1978
Author(s):  
Hai Long Wang ◽  
Chun Ling Guo ◽  
Xiao Yan Sun
Keyword(s):  
Fracture Toughness ◽  
Nitric Acid ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Unstable Fracture ◽  
Crack Mouth ◽  
Acid Attack ◽  
Opening Displacement ◽  
Fracture Properties ◽  
Initial Fracture

The effect of calcium leaching by nitric acid on fracture properties of concrete was experimentally studied. The double-K fracture parameters were investigated using three-point bending beams, and the deterioration regularity of fracture properties of concrete chronically attacked by nitric acid was gotten on basis of these results. The load-crack mouth opening displacement curves under different nitric attack periods were obtained by pasting some strain gauges onto the pre-crack tip. On basis of the double-K criterion, the unstable fracture toughness as well as the initial fracture toughness was calculated according to the critical crack mouth opening displacement, the unstable fracture load and initial cracking load which can be obtained from the test. The experimental results indicated that the ratio of the initial fracture toughness to the unstable fracture toughness varied between 0.47 and 0.61 approximately. Both of the unstable fracture toughness and the initial fracture toughness decrease with attack period especially during the early 60 days, then drop to a stable trend gradually. In addition, the initial fracture toughness is less sensitive to acid attack compared with the unstable fracture toughness.

scholarly journals An Investigation of Softening Laws and Fracture Toughness of Slag-Based Geopolymer Concrete and Mortar

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5200
Author(s):  
Yao Ding ◽  
Yu-Lei Bai ◽  
Jian-Guo Dai ◽  
Cai-Jun Shi
Keyword(s):  
Fracture Toughness ◽  
Inverse Analysis ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Unstable Fracture ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Tension Softening ◽  
Initial Fracture ◽  
Crack Tip Opening

This paper aimed to determine the softening laws and fracture toughness of slag-based geopolymer (SG) concrete and mortar (SGC and SGM) as compared to those of Portland cement (PC) concrete and mortar (PCC and PCM). Using three-point bending (TPB) tests, the load vs. mid-span displacement, crack mouth opening displacement, and crack tip opening displacement curves (P-d, P-CMOD, and P-CTOD curves) were all recorded. Bilinear softening laws of the PC and SG series were determined by inverse analysis. Furthermore, the cohesive toughness was predicted using an analytical fracture model. The cohesive toughness obtained by experimental study was consistent with that predicted by analytical method, proving the correctness of the tension softening law obtained from inverse analysis. In addition, both initial and unstable fracture toughness values of SG mortar were lower than those of PC mortar given the same compressive strength. Moreover, the initial fracture toughness of SG concrete was generally lower than that of PC concrete, whereas the unstable fracture toughness exhibited an opposite trend.

scholarly journals Fracture Properties and Softening Curves of Steel Fiber-Reinforced Slag-Based Geopolymer Mortar and Concrete

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1445 ◽  
Author(s):  
Yao Ding ◽  
Yu-Lei Bai
Keyword(s):  
Fracture Toughness ◽  
Fracture Energy ◽  
Inverse Analysis ◽  
Steel Fiber ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Fiber Reinforced ◽  
Fiber Volume ◽  
Opening Displacement ◽  
Fracture Properties

Adding short steel fibers into slag-based geopolymer mortar and concrete is an effective method to enhance their mechanical properties. The fracture properties of steel fiber-reinforced slag-based geopolymer concrete/mortar (SGC/SGM) and unreinforced control samples were compared through three-point bending (TPB) tests. The influences of steel fiber volume contents (1.0%, 1.5% and 2.0%) on the fracture properties of SGC and SGM were studied. Load-midspan deflection (P-δ) curves and load-crack mouth opening displacement (P-CMOD) curves of the tested beams were recorded. The compressive and splitting tensile strengths were also tested. The fracture energy, flexural strength parameters, and fracture toughness of steel fiber-reinforced SGC and SGM were calculated and analyzed. The softening curves of steel fiber-reinforced SGC and SGM were determined using inverse analysis. The experimental results show that the splitting tensile strength, fracture energy, and fracture toughness are significantly enhanced with fiber incorporation. A strong correlation between the equivalent and residual flexural strengths is also observed. In addition, the trilinear strain-softening curves obtained by inverse analysis predict well of the load-displacement curves recorded from TPB tests.

TEST STUDY ON THE BEST PASTING LAYER OF FRP REINFORCED CONCRETE

2019 ◽  
Vol 27 (02) ◽  
pp. 1950105
Author(s):  
XIANGQIAN FAN ◽  
JUEDING LIU
Keyword(s):  
Fracture Toughness ◽  
Acoustic Emission ◽  
Reinforced Concrete ◽  
Crack Depth ◽  
Mouth Opening ◽  
Bending Test ◽  
Crack Mouth Opening Displacement ◽  
Displacement Curve ◽  
Crack Mouth ◽  
Opening Displacement

To optimize the strengthening method using the fiber reinforced polymer (FRP) for the reinforcement of the concrete structure with cracks, the three-point bending test was conducted on the concrete beams wrapped with different layers of FRP materials. The strain gauges were pasted on the surface of the specimens to measure the initial cracking load. The crack mouth opening displacement (CMOD) was utilized to test the load–crack mouth opening displacement curve. According to the improved calculation formula of the fracture toughness, the critical effect crack length [Formula: see text], initiation fracture toughness [Formula: see text] and instability fracture toughness [Formula: see text] of specimens were calculated. The test results showed that, under the same initial crack depth, the peak load of FRP reinforced concrete decreases with the increase of FRP pasting layer. When there was one layer wrapped over the specimen, the instability toughness of the specimen reached the maximum value and the crack resistance was the best. Based on acoustic emission testing method, the acoustic emission parameters of the above-mentioned concrete during fracture process were identified and collected. The optimal layer of the FRP reinforced concrete with cracks was analyzed from the acoustic emission method.

Test for Crack Opening Displacement of Steel Fiber Reinforced Concrete under Three-Point Bending

2010 ◽  
Vol 36 ◽  
pp. 157-161 ◽  
Author(s):  
Tin Gyi Zhang ◽  
Yuan Bao Leng ◽  
Dan Ying Gao
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Mouth Opening ◽  
Crack Tip ◽  
Crack Mouth Opening Displacement ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Critical Crack ◽  
Critical Crack Opening ◽  
Crack Tip Opening

Based on the principle of electrical measurement method, the clip gauge was made to measure the crack opening displacement (COD).Through the three-point bending test on the specimens of steel fiber reinforced high strength concrete (SFHSC), the effect of the fiber volume fraction (ρf) upon the critical crack opening displacement (the critical crack tip opening displacement and the critical crack mouth opening displacement) was studied. The result shows that the effect of ρf on mouth-tip ratio (the ratio of critical crack mouth opening displacement to critical crack tip opening displacement) can reflect its effect upon the critical crack opening displacement. According to the geometrical relationship between the initial crack length and the critical crack opening displacement，calculation method for the initial crack length was proposed. Based on the test result, the formula was established for calculating the critical crack tip opening displacement.

Revised η-Factors for 3P SE(B) Fracture Specimens Incorporating 3-D Effects

2014 ◽  
Author(s):  
Rodolfo F. de Souza ◽  
Claudio Ruggieri
Keyword(s):  
Fracture Toughness ◽  
Mouth Opening ◽  
Estimation Procedure ◽  
Crack Mouth Opening Displacement ◽  
Evaluation Procedure ◽  
Specimen Thickness ◽  
Crack Mouth ◽  
Opening Displacement ◽  
Wide Range ◽  
Fracture Specimens

Standardized procedures to measure cleavage fracture toughness of ferritic steels in the DBT region most commonly employ three-point bend fracture specimens, conventionally termed SE(B) or SENB specimens. The evaluation protocol of fracture toughness for these crack configurations builds upon laboratory records of load and crack mouth opening displacement (CMOD) to relate plastic work with J (or, equivalently, CTOD). The experimental approach employs a plastic η-factor to relate the macroscale crack driving force to the area under the load versus crack mouth opening displacement for cracked configurations. This work provides revised η-factors derived from CMOD records applicable to estimate the J-integral and CTOD in SE(B) specimens with varying crack size and specimen configuration. Non-linear finite element analyses for plane-strain and 3-D models provide the evolution of load with increased CMOD which is required for the estimation procedure. The analysis matrix considers SE(B) specimens with W = 2B and W = B configurations with and without side grooves covering a wide range of specimen thickness, including precracked Charpy (PCVN) specimens. Overall, the present results provide further validation of the J and CTOD evaluation procedure currently adopted by ASTM 1820 while, at the same time, giving improved estimation equations for J incorporating 3-D effects which enter directly into more accurate testing protocols for experimental measurements of fracture toughness values using 3P SE(B) specimens.

scholarly journals Advanced Evaluation of the Freeze–Thaw Damage of Concrete Based on the Fracture Tests

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6378
Author(s):  
Barbara Kucharczyková ◽  
Hana Šimonová ◽  
Dalibor Kocáb ◽  
Libor Topolář
Keyword(s):  
Peak Load ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Experimental Program ◽  
Crack Model ◽  
Test Evaluation ◽  
Fracture Test ◽  
Opening Displacement ◽  
Freeze Thaw ◽  
Fracture Tests

This paper presents the results of an experimental program aimed at the assessment of the freeze–thaw (F–T) resistance of concrete based on the evaluation of fracture tests accompanied by acoustic emission measurements. Two concretes of similar mechanical characteristics were manufactured for the experiment. The main difference between the C1 and C2 concrete was in the total number of air voids and in the A300 parameter, where both parameters were higher for C1 by about 35% and 52%, respectively. The evaluation of the fracture characteristics was performed on the basis of experimentally recorded load–deflection and load–crack mouth opening displacement diagrams using two different approaches: linear fracture mechanics completed with the effective crack model and the double-K model. The results show that both approaches gave similar results, especially if the nonlinear behavior before the peak load was considered. According to the results, it can be stated that continuous AE measurement is beneficial for the assessment of the extent of concrete deterioration, and it suitably supplements the fracture test evaluation. A comparison of the results of fracture tests with the resonance method and splitting tensile strength test shows that all testing methods led to the same conclusion, i.e., the C1 concrete was more F–T-resistant than C2. However, the fracture test evaluation provided more detailed information about the internal structure deterioration due to the F–T exposure.

Use of Carbon Nanotubes to Improve Fracture Toughness of Polymer Concrete

2017 ◽  
Vol 2612 (1) ◽  
pp. 96-103 ◽  
Author(s):  
Ala Eddin Douba ◽  
Mehmet Emiroglu ◽  
Rafiqul A. Tarefder ◽  
Usama F. Kandil ◽  
Mahmoud Reda Taha
Keyword(s):  
Carbon Nanotubes ◽  
Fracture Toughness ◽  
Service Life ◽  
Microstructural Analysis ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Polymer Concrete ◽  
Direct Tension ◽  
Opening Displacement ◽  
Continuous Increase

Bridge deck overlays often require materials that are durable and easy to apply and that have a long fatigue life. In many applications, polymer concrete (PC) has been chosen not only because it meets such requirements but also because it offers additional features such as high friction. However, the service life of PC overlays is reduced, and cracking occurs because of the continuous increase in traffic loads. This paper investigates the use of multiwalled carbon nanotubes (MWCNTs) to improve the fracture toughness and fatigue service life of PC. Pristine MWCNTs (P-MWCNTs) and MWCNTs functionalized with carboxyl (COOH-MWCNTs) were used at 0.0- (neat), 0.5-, 1.0-, 1.5-, and 2.0-wt.% contents. Three-point bending tests of notched beams were carried out in which the loading rate was controlled by crack mouth opening displacement. Direct tension tests were also used to examine the effect of MWCNTs on the tensile properties of PC. The results showed that MWCNTs improved the fracture toughness of PC by up to 56% and 112% for P-MWCNTs and COOH-MWCNTs, respectively. Samples prepared with P-MWCNTs showed increased ductility; samples with COOH-MWCNTs provided increased tensile strength. Microstructural analysis with a scanning electron microscope and Fourier transform infrared spectroscopy revealed how different types of MWCNTs at different weight contents influenced the behavior of PC.

scholarly journals Stimulated autogenous-healing capacity of fiber-reinforced mortar incorporating healing agents for recovery against fracture and mechanical properties

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Abdul Salam Buller ◽  
Fahad-ul-Rehman Abro ◽  
Tariq Ali ◽  
Sadam Hussain Jakhrani ◽  
Abdul Hafeez Buller ◽  
...  
Keyword(s):  
Peak Load ◽  
Mouth Opening ◽  
Bending Test ◽  
Crack Mouth Opening Displacement ◽  
Partial Recovery ◽  
Self Healing ◽  
Fiber Reinforced ◽  
Opening Displacement ◽  
Digital Microscope ◽  
Set Up

Abstract This study aimed to investigate the effect of autogenous healing capacity with the addition of expansive and crystalline agents on mechanical and fracture behaviors of fiber-reinforced (FR) mortar specimens with crack mouth opening displacement (CMOD) controlled test set-up. The experimental results of a self-healing approach of FR mortar were analyzed in terms of first cracking peak load (FCPL) increase, index of fracture toughness recovery (IFTR), and index of fracture energy recovery (IFER). Initially, the specimens were pre-cracked at different crack widths ranging from 30 μm to 200 μm after 28-days of curing. After pre-cracking, the specimens were kept in water for 56- and 120-day healing. A controlled three-point bending test (PBT) was applied on prism specimen having a central notch of 40 mm depth for pre-cracking as well as the post-conditioning stage for determining the FCPL. However, the crack surfaces were monitored by a high-range digital microscope and scanning electron microscope (SEM) to examine the nature of healed products near the damaged area. Test results revealed that a significant recovery of small cracks (≤50 μm) could be achieved for self-healing specimens by using healing agents (HA), while for large cracks (≥100 μm) partial recovery could be achieved after the 120-day healing period.

Determination of Pipe Girth Weld Fracture Toughness Using Sent Specimens

2010 ◽  
Author(s):  
Henryk G. Pisarski
Keyword(s):  
Fracture Toughness ◽  
Axial Strain ◽  
Mouth Opening ◽  
Estimation Procedure ◽  
Crack Mouth Opening Displacement ◽  
Specimen Preparation ◽  
Opening Displacement ◽  
Crack Tip Constraint ◽  
J Estimation

This paper reviews the basis for the use of SENT or SE(T) specimens as described in DNV RP F108, their limitations and aspects about specimen preparation testing and analysis procedures that need to be addressed in order to standardise the test better. Examples are given comparing the effect of crack tip constraint in a SE(T) specimen with a circumferential crack in a pipe subjected to axial straining and axial strain plus internal pressure. The variations in crack front straightness, the effect of specimen geometry on the J resistance curve as well as the accuracy of the J estimation procedure are presented. The use and limitations of CTOD estimation procedure based on measurement of crack mouth opening displacement as a fracture toughness parameter is discussed.

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