AUTODYN Code Research Articles

Influence of Initiation Modes in the Bundle-Series Initiation of a Large Number of Shock Tubes by Detonators

The bundle-series initiation is currently used as the method for simultaneously transmitting blast signals from a detonator to a large number of shock tubes for blasting using shock tubes and its initiation modes affect the ability and probability of signal transmission. A numerical study of the influence of initiation modes on the pressure impulse generated by detonators and transmitted to a large number of shock tubes has been undertaken with ANSYS AUTODYN code and validated through experimental results of signal transmission probability of shock tubes. Numerical simulations and experiments used lateral and frontal bundle-series initiation modes for a large number of shock tubes. For a bundle of many shock tubes, peak pressures of pressure impulses affected within all shock tubes beside the first layer around a detonator, and signal transmission probabilities were higher for frontal bundle-series initiation mode than for lateral bundle-series initiation mode. The magnitude of a numerically obtained pressure impulse to a bundle of shock tubes shows a good correlation with the experimentally obtained signal transmission probability of shock tubes. Finally, the results are employed in the application of a frontal bundle-series initiation mode with the simultaneous bundle-series initiating a large number of shock tubes for blastings in mining and construction.

Influence of combination of coaxial cylindrical explosives on fragmentation and shock waves of a shelled composite charge

AbstractThis paper investigates fragmentation and shock waves generated by a novel coaxial cylindrical composite charge composed of an inner explosive, an intermediate inert material and an outer explosive widely used in tunable ammunition. Charges containing two types of explosive combinations were designed, and explosion experiments were conducted in two initiation modes: detonating only an inner explosive and detonating inner and outer explosives simultaneously. Results suggest the composite charge with higher inner‐detonation velocity and lower outer‐detonation velocity achieves more differentiated power output under different initiations. The differences in the average fragment mass and peak overpressure are as high as 34.5 % and 39.9 %, respectively, which are larger than 4.4 % and 8.4 % under the contrary explosive combination. On the basis of this observation, corresponding 2‐D and 3‐D models were simulated using AUTODYN code to investigate the evolution of the detonation waveform and detonation energy release. The numerically simulated initial shell expansion and later shock wave propagation of the composite charge agreed well with the experimental data. The errors in expansion radius and shock wave parameters (peak overpressure and specific impulse) are less than 6.6 % and 16.9 %, respectively, between the simulations and experiments. It was found that the particle velocity profile in the charge with lower outer‐detonation velocity lagged behind that of the charge with higher inner‐detonation velocity under inner initiation, while a wave front collision zone close to the outer charge appeared in the non‐detonation layer under simultaneous initiation.

Study of the coupling effect of elliptical cavities and cracks on tunnel stability under dynamic loads

This study to explore the coupling effect of elliptical cavities and cracks on the dynamic stability and failure modes of tunnels. A series of dynamic numerical simulations and model tests were conducted by using AUTODYN code and a modified drop hammer impact test device. A cracked tunnel model with an elliptical cavity was proposed in this study. The crack coalescence behaviour, crack initiation time and stress field around the elliptical cavity and the crack tips were calculated by using numerical simulation, and the dynamic initiation fracture toughness (DIFT) was also determined according to experimental and numerical results. According to these results, we conclude that the long and short axes of the elliptical cavity have a great influence on the crack coalescence behaviour and the stress field, and the long axis of the elliptical cavity has a greater influence than the short axis. When the inclination angle θ of the elliptical cavity is 90°, the stability of the crack is lowest, and when the inclination angle θ of the elliptical cavity is 45°, the effect of the elliptical cavity on the crack initiation behaviour is largest. DIFT was calculated and indicated that when the inclination angle of the elliptical cavity shows its smallest value, 90°, the cracked tunnel stability is lowest.

Investigation of dynamic fracture in VASCT samples under the effect of different loading modes

In order to clearly reveal the dynamic failure mechanism of cracked rock mass with mixed-mode I/II cracks under impact loads, a variable angle single cleavage triangle (VASCT) sample was proposed. A series of impact tests were implemented using a drop weight impact (DWI) apparatus, dynamic crack initiation time and crack speeds were measured using two strain gauges in the experimental process. AUTODYN code was applied to simulate crack propagation trajectories, and the simulation results of sample failure pattern and crack initiation time were in good agreement with experimental results. The maximum tangential stress around the crack tip was calculated and crack fracture mechanism was also discussed in numerical simulation. Dynamic initiation toughness of mixed-mode I/II crack was calculated using the experimental–numerical method. The results of this study revealed that dynamic crack initiation time becomes earlier with the increase of crack inclination angle α, but the crack speeds decrease with the crack inclination angle α; When crack inclination angle α changes from 0° to 10°, i.e., the failure modes of the pre-crack change from pure mode I fracture to mixed-mode I/II fracture, and the maximum tangential stress, crack initiation time and dynamic fracture toughness change sharply; With the increasing of crack inclination angle α, the variation of mode II dynamic fracture toughness is little, and the crack gradually transforms from opening to closing mode.

Effect of crack length on mode I crack propagation under blasting loads

Dynamic response under blasting is significantly different from these under impacts, as an important factor of response law crack length has been paid less attention. In order to investigate the dynamic initiation and propagation law, propagation speed of mode I crack with different lengths in sandstone materials, a new configuration specimen named SICCD was applied in the blasting experiments. Crack initiation and propagation time were measured by crack propagation gauges (CPGs) to calculate the crack propagation speeds. Numerical models were established by using AUTODYN code to simulate the crack propagation and ABAQUS code to calculate the dynamic stress intensity factors (SIFs). The results show that the initiation time and delayed fracture time increases with the increase of pre-crack length and then the change tends to be flat when length exceeds 120 mm. The dynamic propagation speed of crack is variable and the propagation toughness is inversely proportional crack propagation speed. The shear stress τxy has little effect at initiation but increases obviously when overcoming the propagation resistance during the propagation process, and it does not play a major role which is consistent with the mode I fracture of the crack.

Study on the effects of joints orientation and strength on failure behavior in shale specimen under impact loads

As an anisotropic and jointed material, shale has been extensively investigated due to the rich unconventional gas reserved in the shale rock mass. In the process of hydraulic fracturing in jointed shale, joints may significantly affect hydraulic crack behavior under dynamic disturbance loads, such as crack propagation direction, speed and distance, which has a great effect on the efficiency of hydraulic fracturing and gas production. Therefore, it is of great significance to study crack dynamic propagation characteristics in shale with different orientation joints and dynamic strength. Impacting experiments were conducted on the single cleavage triangle (SCT) shale specimens with joint orientation 0°, 30°, 45°, 60° and 90°, respectively. A modified split Hopkinson pressure bar (SHPB) system was applied and AUTODYN code was used to simulate crack dynamic fracture behavior. For the case of a single joint and multiple parallel joints, crack propagation directions and trajectories were numerically analyzed. The experimental and numerical results indicate that joints have a great influence on crack dynamic propagation direction. In addition, the crack propagation speed of shale is positively related to the loading rate under dynamic loads. If joints are considered as thin layer material, dynamic tensile strength and elastic modulus of joints have a great effect on dynamic crack propagation behavior under impact loads.

Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

A new method for measuring the dynamic fracture toughness under blast loads using arc-edge rectangle with edge notches

Drilling and blasting method is a common method of rock fragmentation in engineering. Meanwhile, the dynamic behaviours of rocks under blasting loads are different from those under impact loads. In this paper, a large-size arc-edge rectangle with edge notches (LAREN) specimen was posed to investigate the dynamic fracture parameters of brittle rock materials under blasting load. Three types of radial pre-cracks with different lengths were used, combining with the crack propagation gauge velocity test system, and the crack initiation time and propagation time were obtained, so as to obtain the crack propagation speed which is to be modified by the fractal theory. Also, the specimen rationality was analyzed by AUTODYN code in depth. At last, the dynamic stress intensity factors were estimated by using nonlinear finite element software ABAQUS and experimental results. It is concluded that the LAREN specimens can effectively lower the influence of the reflected tensile stress wave (by 54.18%) on the dynamic crack initiation and propagation, and have good applicability in the measurement of dynamic fracture parameters under blasting. With the development of pre-crack length, the crack time becomes longer, the average propagation speed becomes smaller, and the fluctuation of speed becomes smaller and tends to be stable. The increase of the pre-crack length also leads to the gradual decrease in the test value of the crack initiation toughness, while the test value of the propagation toughness is not constant.

Crack dynamic propagation properties and arrest mechanism under impact loading

Crack dynamic propagation and arrest behaviors have received extensive attention over the years. However, there still remain many questions, e.g. under what conditions will a running crack come to arrest? In this paper, drop weight impact (DWI) tests were conducted to investigate crack arrest mechanism using single cleavage triangle (SCT) rock specimens. Green sandstone was selected to prepare the SCT specimens. Dynamic stress intensity factors (DSIFs) were calculated by ABAQUS code, and the critical DSIFs were determined by crack propagation speeds and fracture time measured by crack propagation gauges (CPGs). The test results show that the critical DSIF at propagation decreases with crack propagation speed. Numerical simulation for SCT specimens under different loading waves was performed using AUTODYN code. The reflected compressive wave from the incident and transmitted plates can induce crack arrests during propagation, and the number of arrest times increases with the wave length. In order to eliminate the effect of the incident and transmitted plates, models consisting of only one SCT specimen without incident and transmitted plates were established, and the same trapezoid-shaped loading wave was applied to the SCT specimen. The results show that for the SCT specimen with transmitted boundary (analogous to an infinite plate), the trapezoid-shaped loading wave cannot induce crack arrest anymore. The numerical results can well describe the occurrence of crack arrest in the experiments.

Effect of Pre-Existing Symmetrical Cracks on Propagation Behaviors of a Blast-Induced Crack

Defects such as voids, pores, and joints will transform into big scale cracks in the rock of tunnel surrounding under dynamic load like blasting and earthquake. In this paper, three kinds of symmetrical cracks were chosen as an example, and experiments and numerical simulations were conducted to study the effect of symmetric cracks on a blast-induced crack. The relationship of main crack propagation characteristic and distribution of symmetrical cracks was investigated. Some circular specimens using two kinds of material, PMMA and sandstone, including a center hole charged with a detonator and pre-existing cracks were used in the experiments. The test system consisted of an oscilloscope and an ultradynamic strain amplifier and crack propagation gauges (CPGs) were employed in monitoring propagation velocity. AUTODYN code was applied in numerical simulation to investigate the propagation behavior of main crack between symmetrical cracks. Linear equation of state and a modified major principal stress failure criterion was utilized to describe the status of rock material. Based on experimental and numerical results, it can be concluded that (1) the pre-existing symmetrical cracks have arrest effect on main crack propagation, (2) compressive stress in y-direction plays very important roles in crack arrest, and (3) the spacing of parallel cracks has a great influence on crack propagation length and velocity.

Study of crack arrest mechanism and dynamic behaviour using arc‐bottom specimen under impacts

AbstractIn this paper, a large size trapezoidal open crack with arc‐bottom (TOCAB) configuration specimen was proposed. Experiments were carried out using 0°, 60°, 90° and 120° TOCAB specimens under drop weight impacts with loading rate from 150 to 350 GPa/s. The crack length and crack speed were calculated by using fractal method. It shows that the crack speed corrected by fractal method is more than 12% the original speed calculated using the straight length. The AUTODYN code was employed to simulate crack propagation path and crack speed. The dynamic stress intensity factors (DSIFs) were calculated using ABAQUS code. The experimental and numerical results show that all the three TOCAB specimens have arresting function on running cracks; crack propagation velocity increases with loading rates; the critical DSIFs at initiation are higher than those at propagation. The study presents how to arrest a running crack and how to protect significant structures from being completely damaged.

Study on the arresting mechanism of two arrest-holes on moving crack in brittle material under impacts

To develop the technique of arresting running cracks is essential because it can be used to protect cracked structures being further damaged. In this paper, a specimen of large semicircular edge crack with two arrest-holes (LSECTH) was proposed. The specimens were made of cement, river sand, fly ash and water. Impact experiments were carried out in the LSECTH specimens with different two-hole spacing (35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm and 70 mm) under drop-weight impacts. Crack propagation gauges (CPGs) were used to monitor the fracturing time and crack speed. The interaction characteristic between the crack and two arrest-holes was investigated numerically by the AUTODYN code. In the numerical models, the failure criterion of maximum tensile stress and shear stress were employed for the brittle material. The crack propagation path, the circumferential stress of crack tip and the stress state between the two arrest-holes were analyzed. The calculation results indicate that compressive stresses between the two arrest-holes induced by the shape change from circle to ellipse play a key role in confining the vertical crack propagation. Both experimental and numerical results indicate that the two arrest-holes have suppressing action on moving crack; as the two arrest-hole spacing decreases, the suppressing action intensifies.

Effect of Holes on Dynamic Crack Propagation under Impact Loading

In civil, geotechnical, and mining engineering, the investigation of the holes’ effect on dynamic crack propagation is essential because it can be used to predict possible fracture and protect cracked structures being further damaged. In this paper, a specimen made from polymethyl methacrylate (PMMA) with a pre-crack and two holes was proposed, and the Split-Hopkinson pressure bar was employed to investigate the effect of holes on dynamic crack propagation under impact loading. Notably, the locations of the holes were well designed with different two-hole spacing (12 mm, 16 mm, and 20 mm) and crack-hole distance (15 mm, 30 mm, and 45 mm). Crack propagation gauges were applied to monitor the fracturing time and crack extending velocity. The interaction characteristic between the crack and two holes was studied numerically using the AUTODYN code. In the numerical models, the failure criteria of maximum tensile stress and softening damage were employed for brittle material. The crack path, the propagating velocity, the particle velocity vector, and the stress state between the holes were analyzed. The calculation results indicate that compressive stresses between the two holes induced by the deformation of the holes play a crucial role in confining the vertical crack propagation. Both experimental and numerical results demonstrate that the holes have a suppressing action on the moving crack; as the two-hole spacing decreases, the suppressing action intensifies.

Numerical and experimental investigation on rock breaking performance with hydraulic splitter

In this work, a numerical model of rock breaking was established based on the AUTODYN code to reveal rock-breaking mechanisms and explain the principal of crack propagation. In addition, the orthogonal experimental design method was used, and the results were evaluated using a range and variance analysis to solve the problem of low efficiency associated with a hydraulic splitter. Finally, the numerical model was verified, and an optimal combination of the working parameters was obtained from the experiment. The results show that the factors influencing rock breaking are borehole margin, confining pressure, borehole depth, and borehole diameter. Moreover, the borehole margin was observed to have a considerable influence on the fracturing pressure. Additionally, the confining pressure has a certain influence, while the borehole depth and borehole diameter have a slight effect on the rock-breaking performance in this study. Furthermore, the optimal scheme was found to be A1B4C3D4, in which the borehole margin, borehole depth, borehole diameter, and confining pressure were 25 cm, 45 cm, 45 mm and 8 MPa, respectively.

Experimental and computational analysis of the uni-directional porous (UniPore) copper mechanical response at high-velocity impact

This study analysed the dynamic mechanical properties and unique phenomena of the cubic unidirectional porous (UniPore) copper sample at high-velocity impact. The cubic UniPore copper sample was mounted on a projectile and subjected to impact loading by using a powder gun. The deformation process of the specimens, which were oriented perpendicular to the direction of the pores, was successfully visualised using a high-speed video camera. The experimental observations were compared with the results of the computational simulations obtained through the ANSYS AUTODYN code. The computationally estimated deformed shape corresponds well to the experimental results. This major finding, that is, the unique phenomenon of the sample where it exhibited high pressure near the pore during the pore compression, was confirmed.

Suggested Methods for Determining Dynamic Fracture Toughness and Numerical Investigation of Cracking Processes under Impacting Loads

Initiation toughness, propagation toughness, and arrest toughness can be considered as threshold values to predict the dynamic behavior of cracks in initiation, propagation, and arrest. For rock materials, initiation toughness has been studied extensively, whereas propagation toughness and arrest toughness have received less attention. In this study, a single cleavage semicircle compression (SCSC) specimen was proposed, and Ya’meng black sandstone was selected to make the SCSC specimens. Impact tests were conducted using the SCSC specimens and a split Hopkinson pressure bar (SHPB) test system. Crack initiation time, propagation time, and propagation speed were measured using crack propagation gauges (CPGs). A high-speed photography (HSP) system was also used to observe the dynamic behavior of crack propagations and arrests. Dynamic stress intensity factors (SIFs) were calculated using ANSYS code, and the crack propagation path was simulated using AUTODYN code. The simulation results generally agree with the test results. Dynamic initiation toughness, propagation toughness, and arrest toughness were determined using an experimental–numerical method. The results show that crack propagation speeds vary during crack propagations, and cracks may arrest for one or more periods during propagation. Dynamic initiation toughness is proportional to the loading rate applied to the specimens, and arrest toughness is less than both initiation toughness and the propagation toughness for the Ya’meng sandstone.

Study on the Fracture Behavior of Cracks Emanating from Tunnel Spandrel under Blasting Loads by Using TMCSC Specimens

Radial cracks may exist around tunnel edge, and these cracks may propagate and weaken tunnel stability under nearby blasting operations. In order to study the blast‐induced fracture behavior of radial cracks emanating from a tunnel spandrel, a tunnel model containing a spandrel crack (TMCSC) with different inclination angles was proposed in this paper. Crack propagation gauges (CPGs) and strain gauges were used in the experiments to measure crack initiation moment and propagation time. Finite difference models were established by using AUTODYN code to simulate crack propagation behavior and propagation path. ABAQUS code was used to calculate dynamic stress intensity factors (SIFs). The results show that (1) crack inclination angles affect crack initiation angles and crack propagation lengths significantly; (2) critical SIFs of both mode I and mode II decrease gradually with the increase of the crack propagation speed; (3) the dynamic energy release rates vary during crack propagation; and (4) there are “crack arrest points” on the crack propagation paths in which the crack propagation speed is very small.

Study on dynamic fracture behavior of mode I crack under blasting loads

Dynamic fracture behavior under impacting loads has been well studied, but for that under blasting loads, less attention has been paid. In order to investigate mode I crack propagation behavior of brittle materials under blasting, a new configuration specimen, i.e. single internal crack circular disc (SICCD) specimen was proposed in this paper, and it was applied in the blasting experiments. Crack propagation gauges (CPGs) were stuck along crack propagation paths to measure crack initiation and propagation time and crack propagation speeds. Green sandstone and PMMA were selected to make the SICCD specimens. Finite difference models were established by using AUTODYN code according to the SICCD specimen dimension and the loading curve measured near the borehole. Generally, the simulation results of crack propagation paths agree with the test results. Finite element code ABAQUS was applied in the calculation of dynamic stress intensity factors (SIFs), and the curves of dynamic SIFs versus time were obtained. By using these curves and the breaking time of the CPG wires, the mode I critical dynamic SIFs in initiation and in propagation were obtained. The results show that the measuring method of the critical dynamic SIFs of brittle materials under blasting presented in this paper is feasible and applicable. During crack propagations, the crack speed is not a constant, and the critical dynamic SIFs in propagation decreases with the increase of crack propagation speeds.

Study of the effect of loading rates on crack propagation velocity and rock fracture toughness using cracked tunnel specimens

In the process of tunnel blasting excavation, radial cracks could be induced. To investigate the effect of loading rates on crack propagation velocity and rock initiation toughness, a new cracked tunnel specimen was proposed in this paper, and drop weight impact experiments were conducted. The crack propagation velocity and crack initiation time were measured by using crack propagation gauges (CPGs), and the measuring results were applied in the determination of initiation toughness. In order to validate the effectiveness of the cracked tunnel specimens and to predict the test results, finite difference numerical models were established by using AUTODYN code. The simulation results of crack propagation speeds and delayed fracture time generally agree with the experimental results, and crack arrest phenomena occur during crack propagation. The dynamic stress intensity factors (SIFs) were calculated by using ABAQUS code, and the initiation toughness under different loading rates was obtained by using experimental-numerical method. The studying results show that crack propagation speeds and initiation toughness increase with loading rates, but as the loading rate is larger than a certain value, the crack speeds tend toward a stable value; Delayed fracture time decreases with the increase of loading rates, and as the loading rate is larger than a certain value, it tends toward a stable value.

Study of mode I crack dynamic propagation behaviour and rock dynamic fracture toughness by using SCT specimens

AbstractTo study crack dynamic propagation behaviour and rock dynamic fracture toughness, a single cleavage triangle (SCT) specimen was proposed in this paper. By using these specimens and a drop‐weight test system, impact experiments were conducted, and the crack propagation velocity and the fracture time were measured by using crack propagation gauges. To examine the effectiveness of the SCT specimen and to predict the test results, finite difference numerical models were established by using AUTODYN code, and the simulation results showed that the crack propagation path agrees with the test results, and crack arrest phenomena could happen. Meanwhile, by using these numerical models, the crack dynamic propagation mechanism was investigated. Finite element code ABAQUS was applied in the calculation of crack dynamic stress intensity factors (SIFs) based on specimen dimension and the loading curves measured, and the curves of crack dynamic SIFs versus time were obtained. The fracture toughness (including initiation toughness and propagation toughness) was determined according to the fracture time and crack speeds measured by crack propagation gauges. The results show that the SCT specimen is applicable to the study of crack dynamic propagation behaviour and fracture toughness, and in the process of crack propagation, the propagation toughness decreases with crack propagation velocity, and the crack arrest phenomena could happen. The critical SIF of an arrest crack (or arrest toughness) was higher than the crack propagation toughness but was lower than the initiation toughness.