scholarly journals Influence of Graphite Powder on the Mechanical and Acoustic Emission Characteristics of Concrete

Buildings ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 18
Author(s):  
Wei He ◽  
Wenru Hao ◽  
Xia Meng ◽  
Pengchong Zhang ◽  
Xu Sun ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Compressive Strength ◽  
Acoustic Emission ◽  
Mouth Opening ◽  
Graphite Powder ◽  
Crack Mouth Opening Displacement ◽  
Cement Stone ◽  
Unstable Fracture ◽  
Sharp Rise ◽  
Ae Signals

In this paper, uniaxial compressive strength (UCS) test and three-point bending (TPB) test, together with an acoustic emission (AE) system, were performed to investigate the mechanical properties and AE characteristic changes of concrete with different graphite powder (GP) content. The results show that: (1) Poor adhesion and low interlocking of graphite with cement stone increase the initial defects of concrete, reducing its elastic modulus and the cyclo-hoop effect, and thus weakening the compressive strength. (2) For concrete with a low graphite content, the second sharp rise in ringing counts or energy released during the compressive process can be regarded as a failure alarm. However, as GP content increases, the second sharp rise fades away, while the first sharp rise becomes more visible. At high GP content, the first sharp rise is better for predicting failure. (3) The initial defects caused by GP significantly lower the initial fracture toughness, but its bridging effect greatly increases the critical crack mouth opening displacement and thus significantly enhances the unstable fracture toughness of concrete, by up to 9.9% at 9% GP content. (4) In contrast to compressive process, the sharp increase in AE signals preceding failure during the fracture process cannot be used to predict failure because it occurs too close to the ultimate load. However, as GP can significantly increase the AE signals and damage value in the stable period, such failure precursor information can provide a safety warning for damage development.

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.

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.

Experimental Study on Fracture Properties of Cementitious Materials

2007 ◽  
Vol 348-349 ◽  
pp. 157-160
Author(s):  
Yu Zhu ◽  
Shi Lang Xu
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Cement Paste ◽  
Mouth Opening ◽  
Material Design ◽  
Cementitious Materials ◽  
Crack Mouth Opening Displacement ◽  
Unstable Fracture ◽  
Opening Displacement ◽  
Fracture Properties

For micro-fiber reinforced strain-hardening cementitious materials, in addition to the basic characteristics and mechanical properties of fiber and interfacial properties between fiber and matrix, mechanical properties of matrix such as strength and crack resistance are essential parameters for material design, too. Therefore, the fracture properties of cement paste and mortar which are two most basal cementitious materials were studied, using three-point bending beams of which strength and depth are varied. Complete load versus crack mouth opening displacement (P-CMOD) curve directly obtained, and double-K fracture parameters ini Ic K and un Ic K were subsequently determined. The initial cracking load Pini was determined using resistant strain gauges. The results show that an apparent stable crack propagation before unstable failure was observed both in cement paste and in mortar. For cement paste, due to the influence of shrinkage crack, the divergence of the unstable fracture toughness un Ic K is more evident than initial fracture toughness ini Ic K .

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.

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.

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.

Research on Fracture-CMOD Toughness of Steel Fiber Reinforced Concrete

2010 ◽  
Vol 168-170 ◽  
pp. 1784-1787
Author(s):  
Xiao Wei Wang ◽  
Wen Ling Tian ◽  
Ling Ling Fan ◽  
Ming Jie Zhou ◽  
Xiao Yan Zhao
Keyword(s):  
Fracture Toughness ◽  
Reinforced Concrete ◽  
Steel Fiber ◽  
Estimation Error ◽  
Mouth Opening ◽  
Fiber Reinforced Concrete ◽  
Crack Mouth Opening Displacement ◽  
Fiber Reinforced ◽  
Steel Fiber Reinforced Concrete ◽  
Toughness Index

In order to study the fracture toughness of steel fiber reinforced concrete (SFRC) and the postcracking toughness evaluation method, the fracture toughness tests were done for the four types of steel fibers and three kinds of matrix strength. According to the experiment curves of the load and the crack mouth opening displacement (Load-CMOD), the fracture toughness of SFRC was studied; the formulas of the postcracking toughness coefficient and the Fracture-CMOD toughness index were established. The experiment results show that the Fracture-CMOD toughness index can reflect sensitively to the effect on concrete toughness of the type of the steel fiber, and then it is avoid that the estimation error of the initial cracking point led to the evaluation error of the toughness.Comparison with other fibers B fiber shows the best crack resistance and the toughening ability.

Optimal Design for the Maximum Load of Three-Point Bending Concrete Beam Based on the Analyzing of Critical Crack-Mouth Opening Displacement

2012 ◽  
Vol 193-194 ◽  
pp. 954-957
Author(s):  
Xue Qin Wang ◽  
Lin Wang
Keyword(s):  
Optimal Design ◽  
Concrete Beam ◽  
Mouth Opening ◽  
Maximum Load ◽  
Least Square ◽  
Crack Mouth Opening Displacement ◽  
Engineering Practice ◽  
Unstable Fracture ◽  
Resistance Curve ◽  
Three Point Bending

An optimal design method for the maximum load of three-point bending concrete beam is proposed in this study. The statistics model is built according to the theory of GR resistance curve. With the help of least square method and Matlab® computing platform, the optimal design results are very similar of the experimental results, and thus a new criterion for unstable fracture in crack extension resistance curve theories is constructed. It can able to monitor safety and stability of specimens in engineering practice at any time.

scholarly journals Validation of Acoustic Emission (AE) Crack Detection in Aerospace Grade Steel Using Digital Image Correlation

2010 ◽  
Vol 24-25 ◽  
pp. 221-226 ◽  
Author(s):  
Rhys Pullin ◽  
Mark J. Eaton ◽  
James J. Hensman ◽  
Karen M. Holford ◽  
Keith Worden ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Digital Image Correlation ◽  
Crack Growth ◽  
Digital Image ◽  
Crack Detection ◽  
Peak Load ◽  
Fatigue Loading ◽  
Image Correlation ◽  
Crack Mouth Opening Displacement ◽  
Ae Signals

Acoustic Emission (AE) is a passive form of non-destructive testing that relies on the detection and analysis of stress waves released during crack propagation. AE techniques are successfully employed number of industries there remains some scepticism in aerospace engineering. The reported investigation details a single four point bend test specimen undergoing fatigue loading. This test is part of a much larger programme designed to demonstrate a technology readiness level (TRL) of five of the use of AE to detect crack initiation and growth in landing gear structures. The completed test required that crack growth had to be monitored to allow a comparison with the detected and located AE signals. The method of crack monitoring had to be non-contact so as not to produce frictional sources of AE in the crack region, preventing the use of crack mouth opening displacement gauges. Furthermore adhesives on the specimen surface had to be avoided to eliminate the possibility that the detected AE was from adhesive cracking, thus the use of strain gauges or foil crack gauges was not possible. A method using Digital Image Correlation (DIC) to monitor crack growth was investigated. The test was stopped during fatigue loading at 1000 cycle intervals and a DIC image captured at peak load. The displacement due to crack growth was observed throughout the investigation and the results compared with the detected AE signals. Results showed a clear correlation between AE and crack growth and added further evidence of TRL5 for detecting fractures in landing gears using AE.

Sign in / Sign up

Export Citation Format

Share Document