Showing 4 results for Drop Weight Tear Test
Ali-Akbar Majidi, Sayyed Hashemi,
Volume 17, Issue 11 (1-2018)
Abstract
Fractography of drop weight tear test (DWTT) specimens has received great attention by researchers in recent years due to the complex fracture surface of this test specimen. In this research, macroscopic characteristics of fracture surface of spiral seam weld in API X65 pipeline steel are investigated for the first time using chevron-notched DWTT specimensTest specimens were machined from an actual steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm. Then chevron notch of 5.1, 10 and 15mm depth was placed in the center of each specimen and test samples were fractured under dynamic loading of 7m/s. Fractography of the fracture surface of test specimen with 5.1mm notch depth (as typical of test samples) showed that cleavage flat fracture initiated from the notch root (where stress intensity factor was high). Cleavage fracture changed immediately to ductile shear fracture, deviated to one side of specimen and grew extensively in heat affected zone, and finally terminated in base metal. Delaminations were observed in shear fracture area almost parallel to crack growth direction. After that, shear lips and inverse fracture appeared in hammer impacted area. By calculating the percent shear area from standard formulations, it was found that test specimen had above 95% shear area, and ductile fracture was the dominant fracture mode implying the fitness of tested steel for application in high-pressure gas transportation pipelines.
E. Fathi-Asgarabad, S.h. Hashemi,
Volume 20, Issue 5 (5-2020)
Abstract
One of the most important purposes of the drop weight tear test (DWTT) is to achieve the value of fracture energy for better evaluation of tested steel properties. In the present research, experimental and numerical measurement of fracture energy in drop weight tear test specimen with chevron notch on API X65 steel has been carried out. The purpose of the determination of this energy is to estimate the strength of material due to fracture. The test specimen was cut from an actual spiral seam welded steel pipe of API X65 grade with an outside diameter of 1219mm and wall thickness of 14.3mm and then it has been machined to standard size. Then chevron notch with a length of 5.1 was placed in the middle of the specimen and the specimen was fractured under dynamic loading with an initial impact velocity of 6.3m/s. The maximum force of 229kN and 225kN were achieved for experimental and numerical data, respectively by drawing force-displacement and energy-displacement curves. The fracture energy of the test sample for experimental and numerical data was obtained as 7085J and 6800J, respectively by evaluation of the area under the force-displacement curve. Based on the results of experimental curves, about %59 of fracture energy was used for crack propagation and the remaining was used for crack initiation and plastic deformation of test sample near anvils and striker regions. In the end, drawing a linear curve for fracture energy of specimen based on the hammer velocity showed that the slope of this curve could be a good criterion for estimating the energy loss and fracture behavior of the test specimen.
M. Tazimi, S.h. Hashemi, S. Rahnama,
Volume 20, Issue 10 (10-2020)
Abstract
In this study for the first time, changes in the thickness of the fracture cross-section of the inhomogeneous sample (with horizontal weld seam) of the API X65 steel, using drop weight tear test specimen have been investigated experimentally. The fracture surface of the test specimen consisted of three zones of base metal, heat affected zone and weld metal with different microstructure and mechanical properties. The most thickness reduction was in the cleavage fracture area of the notch root. In the base metal zone, thickness changes were constant which indicated the stable crack growth in this area. In both heat affected zones before and after the weld zone, the thickness changed with a constant slope. Due to the high hardness and low fracture energy of the weld zone, the lowest percentage of thickness changes was in this zone. Thickness in the weld zone increased with a constant slope due to the stretching of the weld zone to the end of the crack growth path by the force caused by the change of fracture mode from tensile to shear. Also in the reverse fracture zone, due to the increased in compressive strain caused by impact of the hammer on the sample, the thickness increases with a significant slope and reached the maximum value.
Soroush Gholami Moghaddam, Sayyed Hashemi,
Volume 23, Issue 2 (1-2023)
Abstract
The critical Crack Tip Opening Angle (CTOAc) is considered as a convenient parameter to characterize the crack arrest toughness of natural gas pipeline. Load-displacement curve is a comprehensive reflection of geometry, mechanical property and fracture behavior of a loaded specimen, so it would be highly advantageous to deduce (CTOAc) from load-displacement curve directly. From force-displacement curves, maximum force of 209kN and 207kN were obtained for experimental and numerical data, respectively. In this article, a combination of load-displacement and deformation of the drop weight tear test specimen was used to calculate the critical crack tip opening angle. For this purpose, the simplified single-specimen test method was used. The (CTOAc) is dependent on the slope of the steady-state crack growth region and the plastic rotation factor. Firstly, based on the fact that load decreases linearly with the increment of displacement during steady-state crack growth, the slope of the experimental load-displacement curve of API X65 steel in the steady-state crack growth region was obtained as 21.583. Secondly, by modeling the drop weight tear test in Abaqus software and using two methods of mises stress and neutral axis, the plastic rotation factor was obtained as 0.5688 and 0.5651, respectively. Finally, these
parameters were used and the critical crack tip opening angle was determined as 12.00 and 12.08 degrees.
