scholarly journals Fracture Parameters of Cement Mortar with Different Structural Dimensions Under the Direct Tension Test

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1850 ◽  
Author(s):  
Inkyu Rhee ◽  
Jun Seok Lee ◽  
Young-Sook Roh
Keyword(s):  
Fracture Mechanics ◽  
Fracture Energy ◽  
Size Effects ◽  
Cement Mortar ◽  
Aggregate Size ◽  
Tension Test ◽  
Crack Mouth Opening Displacement ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Structural Dimensions

In this paper, we measured the fracture properties of cement mortar—which is composed of sand and has a nearly constant diameter—using a direct tension test. Four double-notched mortar bar specimens with different structural dimensions were assessed. The failure load, load-crack mouth opening displacement, and elongation of the gauge length were measured under direct displacement control. The fractured surfaces were scanned and measured so that we could calculate the tensile strength accurately and determine the fracture energy and characteristic length. The average ratio of total fracture energy (GF) to specific fracture energy (Gf) was 1.94; this was lower than the typical value for concrete, of 2.5. The direct tension test showed that the double-notched mortar specimens had a smaller fracture processing zone after the initiation of tensile cracks, so the tail portion of the softening branch was small. This decreased the GF/Gf ratio. We verified this result based on a nonlinear fracture mechanics simulation and found that it agreed well with our experimental results. We also investigated the size effects of four different scaled specimens while holding the ratio of structural dimension, d, and notch length, a is constant, so that there was no shape effect. The traditional linear elastic fracture mechanics (LEFM) prediction and Bažant’s size effect law yield a gradient closer to 1/2 in the case of relatively large specimens. In the case of our cement mortar specimens, this prediction was not supported, where the value of the slope was 1/0.727. This was unexpected because LEFM predicts strong size effects. One possible explanation for this result is that the size effects of concrete are most often evaluated using a bending test; also, concrete has a larger maximum aggregate size than mortar. Due to the random heterogeneities in aggregate distribution, higher tail energies may be seen for concrete, leading to differences in the GF/Gf ratio. At the same time, the peak tensile stress could be affected by the relationship between structural dimensions and aggregate size.

A New Method to Test the Fracture Energy Based on Direct Tension

2011 ◽  
Vol 105-107 ◽  
pp. 1376-1379
Author(s):  
Zhong Hu Zhao
Keyword(s):  
Fracture Energy ◽  
Brittle Materials ◽  
Tension Test ◽  
Test Machine ◽  
Indirect Test ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Significant Parameter ◽  
Tensile Curve ◽  
Split Property

Fracture energy, which reflects the split property of brittle materials, is a significant parameter. For present tests of measuring it, the indirect test itself has insuperable disadvantage, while the direct tension test, in spite of an ideal way, is too limited to be widely applied in ordinary labs for its over high requirement for the test machine. The paper analyzed the disadvantage of the direct tension machine and improved it: a new elastic foundation of lower clamper replaced the original rigid one. Using the improved machine, the complete stress-strain tensile curve of the brittle materials was obtained easily. Further, the fracture energy could be calculated. Basing on studies, the paper recommended it may as well to get the fracture energy by improved direct tension machine.

scholarly journals An Innovative Test Method for Tensile Strength of Concrete by Applying the Strut-and-Tie Methodology

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2776 ◽  
Author(s):  
Wen-Cheng Liao ◽  
Po-Shao Chen ◽  
Chung-Wen Hung ◽  
Suyash Kishor Wagh
Keyword(s):  
Tensile Strength ◽  
Test Methods ◽  
Standard Test ◽  
Strength Test ◽  
Tension Test ◽  
Test Method ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Strut And Tie ◽  
Tensile Strength Test

Tensile strength is one of the important mechanical properties of concrete, but it is difficult to measure accurately due to the brittle nature of concrete in tension. The three widely used test methods for measuring the tensile strength of concrete each have their shortcomings: the direct tension test equipment is not easy to set up, particularly for alignment, and there are no standard test specifications; the tensile strengths obtained from the test method of splitting tensile strength (American Society for Testing and Materials, ASTM C496) and that of flexural strength of concrete (ASTM C78) are significantly different from the actual tensile strength owing to mechanisms of methodologies and test setup. The objective of this research is to develop a new concrete tensile strength test method that is easy to conduct and the result is close to the direct tension strength. By applying the strut-and-tie concept and modifying the experimental design of the ASTM C78, a new concrete tensile strength test method is proposed. The test results show that the concrete tensile strength obtained by this proposed method is close to the value obtained from the direct tension test for concrete with compressive strengths from 25 to 55 MPa. It shows that this innovative test method, which is precise and easy to conduct, can be an effective alternative for tensile strength of concrete.

Statistical Distribution of Failure Stress Values from Superpave® Direct Tension Test

2002 ◽  
Vol 1810 (1) ◽  
pp. 72-77
Author(s):  
Raj Dongré ◽  
Charles Antle
Keyword(s):  
Weibull Distribution ◽  
Standard Test ◽  
Tension Test ◽  
Failure Stress ◽  
Test Method ◽  
Direct Tension ◽  
Data Set ◽  
Direct Tension Test ◽  
Data Points ◽  
Made In

A statistically robust method was developed using the Weibull distribution to identify and eliminate outliers from the failure stress determinations. The method is applicable to any failure stress data set that follows the Weibull distribution; however, in this application, it was developed for the AASHTO standard test method for conducting the direct tension test (DTT). A large number of stress-at-failure measurements with the DTT were made in the course of instructing users of this device. These data, all for the same asphalt, provided the means for studying the nature of the distribution of the breaking strength of these asphalt specimens. The training database contains more than 900 data points. The current AASHTO practice of eliminating the lowest two stress values was found to be reasonable. However, it is an arbitrary method that may lead to problems in the future. On the basis of the results of this study, the procedure is recommended for use and implementation in the next AASHTO version of the DTT standard.

An Unconfined Direct Tension Test for Compacted Clays

1974 ◽  
Vol 2 (3) ◽  
pp. 163 ◽  
Author(s):  
SF Etris ◽  
YR Fiorini ◽  
KC Lieb ◽  
IC Moore ◽  
AL Batik ◽  
...  
Keyword(s):  
Tension Test ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Compacted Clays

Development of Superpave Direct Tension Test Device

1997 ◽  
Vol 1586 (1) ◽  
pp. 32-39 ◽  
Author(s):  
Raj Dongré ◽  
John D’Angelo ◽  
Steve McMahon
Keyword(s):  
Asphalt Binder ◽  
Tension Test ◽  
Asphalt Binders ◽  
Temperature Control System ◽  
Materials Testing ◽  
Direct Tension ◽  
Direct Tension Test ◽  
New Device ◽  
Failure Properties ◽  
User Friendly

The redesign and evaluation of the Superpave direct tension test (DTT) are described. The prototype of the DTT device was developed during the Strategic Highway Research Program (SHRP). The DTT device, an integral part of the new Superpave asphalt binder specification, was developed to test asphalt binders and determine their failure properties, such as the stress and strain at failure. The strain at failure is used in the Superpave asphalt binder specification to determine the lowest temperature at which the asphalt can be used to avoid low-temperature thermal cracking. When the SHRP program was completed, an affordable specification version of the prototype SHRP-DTT device was introduced for field implementation. Unfortunately, this version was plagued with mechanical problems, producing excessive variability and inconsistency in data. The device also was less user-friendly than other test devices that were being implemented for the asphalt binder specification. These problems led to implementation delays and difficulties. The problems were addressed by FHWA in cooperation with Instron Corporation of Canton, Massachusetts (a manufacturer of materials testing equipment). On the basis of recommendations made by FHWA, Instron developed a new, easy-to-use specification-type DTT device. This device is compact (approximately one-tenth the size of the original) and uses a fluid-based temperature control system similar to that used in the bending beam rheometer. The new device also employs feedback elongation (strain) rate control. However, unlike the previous device, the new DTT uses an extensometer between the loading pins instead of a laser to measure elongation (strain). The evaluation and resulting recommendations by FHWA, which led to the development of the new specification-type devices are discussed. The repeatability and testing protocols also are discussed.

scholarly journals A New Direct Tension Test Method for Soils and Soft Rocks

2020 ◽  
Vol 43 (6) ◽  
pp. 20190308
Author(s):  
Yanrong Li ◽  
Fanfan Guan ◽  
He Su ◽  
Adnan Aydin ◽  
Mary Antonette Beroya-Eitner ◽  
...  
Keyword(s):  
Tension Test ◽  
Test Method ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Soft Rocks
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