scholarly journals FRACTAL CHARACTERISTICS OF CRACK PROPAGATION IN COAL UNDER IMPACT LOADING

Fractals ◽  
2018 ◽  
Vol 26 (02) ◽  
pp. 1840014 ◽  
Author(s):  
YIXIN ZHAO ◽  
SHUANG GONG ◽  
CHENGGUO ZHANG ◽  
ZHENNAN ZHANG ◽  
YAODONG JIANG
Keyword(s):  
Fractal Dimension ◽  
Crack Propagation ◽  
Impact Loading ◽  
Crack Velocity ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Hopkinson Pressure Bar ◽  
Bedding Angle ◽  
Fractal Characteristics ◽  
Pressure Bar

This paper studied the fractal characteristics of crack propagation in coal containing beddings under impact loading condition. Split Hopkinson pressure bar (SHPB) system was applied to determine the prepared notched semi-circular bending specimens. The high-speed camera was used to record the propagation characteristics of cracks. The image processing method and fractal dimension calculation software are combined to further analyze the effects of bedding and loading rate on the fractal characteristics of crack propagation in coal. The experimental results presented that the presence of bedding has a remarkable impact on the crack propagation. The crack velocity of coal samples with [Formula: see text] bedding angle is of the maximum, however, the crack velocity of samples with [Formula: see text] bedding angle is of the minimum. Bedding angles also have obvious influence on the fractal dimension of cracking path, the bedding angle of [Formula: see text] being the largest, and those of [Formula: see text] and [Formula: see text] having the intermediate values, while those of [Formula: see text] and [Formula: see text] being the smallest. Several points of instantaneous fractal crack velocity are close to the Rayleigh wave velocity ([Formula: see text]). The crack velocities of coal specimens with bedding angles of [Formula: see text], [Formula: see text] and [Formula: see text] are prone to the high value.

scholarly journals Dynamic Crack Propagation and Fracture Behavior of Pre-cracked Specimens under Impact Loading by Split Hopkinson Pressure Bar

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Shijun Zhao ◽  
Qing Zhang
Keyword(s):  
Crack Propagation ◽  
Impact Loading ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Hopkinson Pressure Bar ◽  
Brazilian Disk ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Cracked Specimens

Deformation and fracture of brittle materials, especially crack propagation, have drawn wide attention in recent years. But dynamic crack propagation under impact loading was not well understood. In this paper, we experimentally tested Brazilian disk (BD) fine sandstone specimens containing pre-cracks under cyclic impact loading by the Φ 74 mm diameter split Hopkinson pressure bar (SHPB) test device. The pre-cracked specimens were named central straight through crack flattened Brazilian disk (CSCFBD). By using the low air-pressure loading conditions (0.1 MPa, equal to the impact velocity of 3.76 m/s), a series of dynamic impact tests were detected successfully, and the effects of pre-cracks on dynamic properties were analyzed. Experimental results show that the multiple cracks mostly initiate at/or near the pre-crack tips and then propagate in different paths and directions varying by inclination angles, leading to the ultimate failure. Compared to static or quasi-static loading, dynamic crack propagation and fracture behavior are obviously different. Furthermore, we characterized the crack propagation paths, directions, and fracture patterns and discussed the influences of the pre-cracks during the breakage process. We concluded that the results obtained are significant in investigating the failure mechanism and mechanical properties of brittle materials under impact loading.

scholarly journals Investigation of Mixed-Mode I/II Fracture under Impact Loading Using Split-Hopkinson Pressure Bar

2020 ◽  
Vol 10 (20) ◽  
pp. 7149
Author(s):  
Fei Wang ◽  
Zheming Zhu ◽  
Meng Wang ◽  
Hao Qiu ◽  
Lei Zhou ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Numerical Method ◽  
Impact Loading ◽  
Mixed Mode ◽  
Split Hopkinson Pressure Bar ◽  
Mode I ◽  
Mixed Mode Fracture ◽  
Hopkinson Pressure Bar ◽  
Mixed Mode Crack ◽  
Pressure Bar

Mixed-mode fracture of construction building materials under impact loading is quite common in civil engineering. The investigation of mixed-mode crack propagation behavior is an essential work for fundamental research and engineering application. A variable angle single cleavage semi-circle (VASCSC) specimen was proposed with which the dynamic fracture test was conducted by using a Split-Hopkinson pressure bar (SHPB). Notably, the mixed-mode crack propagation velocity could be detected by the synchronized crack velocity measuring system. With experimental results, the dynamic initiation stress intensity factors KI and KII were calculated by the experimental-numerical method. Additionally, the crack path of mixed-mode I/II fracture can be predicated precisely by using numerical method. Thus, a comprehensive approach of investigation on mixed-mode I/II fracture under impact loading was illustrated in this paper. The study demonstrates that the mixed-mode I/II crack would transform from complicated mode I/II to pure mode I during crack propagation, and several velocity decelerations induced crack deflection. The dynamic initiation fracture toughness of mixed-mode crack was determined by the experimental-numerical method. The VASCSC specimen has a great potential in investigating mixed-mode fracture problems with the SHPB device.

scholarly journals Development of a True-Biaxial Split Hopkinson Pressure Bar Device and Its Application

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7298
Author(s):  
Shumeng Pang ◽  
Weijun Tao ◽  
Yingjing Liang ◽  
Shi Huan ◽  
Yijie Liu ◽  
...  
Keyword(s):  
Stress Wave ◽  
Impact Loading ◽  
Split Hopkinson Pressure Bar ◽  
Axial Stress ◽  
Dynamic Mechanical Properties ◽  
Stress Waves ◽  
Hopkinson Pressure Bar ◽  
Dynamic Mechanical ◽  
Split Hopkinson ◽  
Pressure Bar

Although highly desirable, the experimental technology of the dynamic mechanical properties of materials under multiaxial impact loading is rarely explored. In this study, a true-biaxial split Hopkinson pressure bar device is developed to achieve the biaxial synchronous impact loading of a specimen. A symmetrical wedge-shaped, dual-wave bar is designed to decompose a single stress wave into two independent and symmetric stress waves that eventually form an orthogonal system and load the specimen synchronously. Furthermore, a combination of ground gaskets and lubricant is employed to eliminate the shear stress wave and separate the coupling of the shear and axial stress waves propagating in bars. Some confirmatory and applied tests are carried out, and the results show not only the feasibility of this modified device but also the dynamic mechanical characteristics of specimens under biaxial impact loading. This novel technique is readily implementable and also has good application potential in material mechanics testing.

scholarly journals High strain rate behaviour of fiber reinforced concrete

2018 ◽  
Vol 183 ◽  
pp. 02012
Author(s):  
Miloslav Popovič ◽  
Jaroslav Buchar ◽  
Martina Drdlová
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Speed ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Compression ◽  
Fiber Reinforced Concrete ◽  
Hopkinson Pressure Bar ◽  
Static Test ◽  
Pressure Bar

The results of dynamic compression and tensile-splitting tests of concrete reinforced by randomly distributed short non – metallic fibres are presented. A Split Hopkinson Pressure Bar combined with a high-speed photographic system, was used to conduct dynamic Brazilian tests. Quasi static test show that the reinforcement of concrete by the non-metallic fibres leads to the improvement of mechanical properties at quasi static loading. This phenomenon was not observed at the high strain rate loading .Some explanation of this result is briefly outlined.

Investigation on surface quality of high-speed cutting titanium alloy Ti6Al4V based on Split-Hopkinson pressure bar

2020 ◽  
Vol 234 (10) ◽  
pp. 1293-1301 ◽  
Author(s):  
Zhanfei Zhang ◽  
Zengqiang Wang ◽  
Wenhu Wang ◽  
Ruisong Jiang ◽  
Yifeng Xiong
Keyword(s):  
Surface Roughness ◽  
Surface Topography ◽  
Surface Quality ◽  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Cutting Speed ◽  
Depth Of Cut ◽  
Hopkinson Pressure Bar ◽  
High Speed Cutting ◽  
Pressure Bar

High-speed cutting technology has the characteristics of high material removal rate and excellent processing quality. To investigate the surface quality of high-speed cutting Ti6Al4V alloy, the orthogonal cutting experiment is the cutting device based on improved Split-Hopkinson pressure bar carried out with a cutting speed of about 7–16 m/s. Surface roughness, residual stress and three-dimensional surface topography are examined to characterize the surface quality. And the chip geometry parameters are measured to analyze the formation mechanism of surface topography. The result shows that cutting force and surface roughness increase rapidly with the increase in depth of cut. In the meantime, the periodic microwaves appeared on the machined surface, and their amplitudes increase with the increase in depth of cut. However, surface roughness, residual stress and microwave amplitude all decrease with the increase in cutting speed. Moreover, it is found that the evolution trend of chip thickness and surface roughness with cutting parameters is very similar. Therefore, it can be inferred that there is a strong relationship between surface topography and chip morphology.

An improved method for compressive stress-strain measurements at very high strain rates

1992 ◽  
Vol 438 (1902) ◽  
pp. 153-170 ◽  
Keyword(s):  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Pure Copper ◽  
High Strength ◽  
Tungsten Alloy ◽  
High Speed Photography ◽  
Hopkinson Pressure Bar ◽  
Stress Strain ◽  
Split Hopkinson ◽  
Pressure Bar

This paper describes a modification of the split Hopkinson pressure bar, to allow compression testing of high strength metals at a strain rate of up to about 10 5 s –1 . All dimensions are minimized to reduce effects of dispersion and inertia, with specimens of the order of 1 mm diameter. Strain is calculated from the stress record and calibrated with high-speed photography. Particular attention has been paid to the accuracy of the technique, and errors arising from nonlinearity in the instrumentation, dispersion, frictional restraint and inertia have all been quantitatively assessed. Stress–strain results are presented of Ti 6A14V alloy, a high strength tungsten alloy, and pure copper.

Thermo-Mechanical Aspects of Adiabatic Shear Failure of AM50 and Ti6Al4V Alloys

2008 ◽  
Author(s):  
D. Rittel ◽  
Z. G. Wang
Keyword(s):  
High Speed ◽  
Shear Failure ◽  
Split Hopkinson Pressure Bar ◽  
Adiabatic Shear ◽  
Maximum Temperature ◽  
Hopkinson Pressure Bar ◽  
Gauge Section ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
Deformation Patterns

The thermo-mechanical aspects of adiabatic shear band (ASB) formation are studied for two commercial alloys: Mg AM50 and Ti6Al4V. Tests are carried out on shear compression specimens (SCS). The evolution of the temperature in the deforming gauge section is monitored in real time, using an array of high speed infrared detectors synchronized with a Kolsky apparatus (split Hopkinson pressure bar). The evolution of the gage temperature is found to comprise 3 basic stages, in agreement with Marchand and Duffy’s simultaneous observations of mechanical data and gauge deformation patterns (1988). The onset and full formation stages of ASB are identified by combining the collected thermal and mechanical data. Full development of the ASB is identified as the point at which the measured and calculated temperature curves intersect and diverge thereon. At that stage, the homogeneous strain assumption used in calculating the maximum temperature rise is no longer valid.

A texture and microstructure analysis of high speed rolling of AZ31 using split Hopkinson pressure bar results

2013 ◽  
Vol 48 (19) ◽  
pp. 6656-6672 ◽  
Author(s):  
M. Sanjari ◽  
A. Farzadfar ◽  
T. Sakai ◽  
H. Utsunomiya ◽  
E. Essadiqi ◽  
...  
Keyword(s):  
High Speed ◽  
Split Hopkinson Pressure Bar ◽  
Microstructure Analysis ◽  
Hopkinson Pressure Bar ◽  
Split Hopkinson ◽  
Pressure Bar
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