2022 Vol. 42, No. 7
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2022, 42(7): 072201.
doi: 10.11883/bzycj-2021-0421
Abstract:
In order to clarify the bubble pulsation process and pressure wave shock characteristics produced in the process of pulse discharge energy release in water, based on the principle of energy equivalence, the liquid-phase pulse energy was transformed into an explosion source with the same energy, and the fluid-structure coupling model of underwater explosion with needle-plate electrode structure was established in LS-DYNA software to simulate the bubble pulsation process on the upper surface of steel substrate. By comparing with the experimental physical images obtained by high-speed photography, it was found that the numerical simulation was highly consistent with the experimental results in terms of bubble morphology and time evolution scales. On this basis, the impact characteristics of the bubbles was further analyzed, and the results show that the maximum impact pressure of the shock wave on the steel base can reach 94.9 MPa when the discharge is carried out with a 4-mm gap at a voltage of 20 kV and a capacitance of 0.8 μF. Besides, the bubble radius, expansion, jet velocity, pulsation period and peak shock wave pressure enhance with the increase of the discharge energy and decrease with the rise of the hydrostatic pressure. Among them, the increase of water pressure has little effect on the bubble expansion rate. The peak value of secondary pressure wave rises from 2.89 MPa to 4.09 MPa with the increase of voltage (14−20 kV), which reaches 41.5%; and up from 5.15 MPa to 6.36 MPa with the rise of hydrostatic pressure (202.65−506.63 kPa), which reaches 23.5%. And the enhancement of discharge energy and water pressure improves the secondary pressure wave significantly. Meanwhile, with the improvement of transmission distance, the proportion of secondary pressure wave in the peak pressure of shock wave rises from 12.6% to 35.3%, and the secondary pressure wave at the far-field discharge location cannot be ignored.
In order to clarify the bubble pulsation process and pressure wave shock characteristics produced in the process of pulse discharge energy release in water, based on the principle of energy equivalence, the liquid-phase pulse energy was transformed into an explosion source with the same energy, and the fluid-structure coupling model of underwater explosion with needle-plate electrode structure was established in LS-DYNA software to simulate the bubble pulsation process on the upper surface of steel substrate. By comparing with the experimental physical images obtained by high-speed photography, it was found that the numerical simulation was highly consistent with the experimental results in terms of bubble morphology and time evolution scales. On this basis, the impact characteristics of the bubbles was further analyzed, and the results show that the maximum impact pressure of the shock wave on the steel base can reach 94.9 MPa when the discharge is carried out with a 4-mm gap at a voltage of 20 kV and a capacitance of 0.8 μF. Besides, the bubble radius, expansion, jet velocity, pulsation period and peak shock wave pressure enhance with the increase of the discharge energy and decrease with the rise of the hydrostatic pressure. Among them, the increase of water pressure has little effect on the bubble expansion rate. The peak value of secondary pressure wave rises from 2.89 MPa to 4.09 MPa with the increase of voltage (14−20 kV), which reaches 41.5%; and up from 5.15 MPa to 6.36 MPa with the rise of hydrostatic pressure (202.65−506.63 kPa), which reaches 23.5%. And the enhancement of discharge energy and water pressure improves the secondary pressure wave significantly. Meanwhile, with the improvement of transmission distance, the proportion of secondary pressure wave in the peak pressure of shock wave rises from 12.6% to 35.3%, and the secondary pressure wave at the far-field discharge location cannot be ignored.
2022, 42(7): 073101.
doi: 10.11883/bzycj-2022-0051
Abstract:
When studying the dynamic fracture behavior of cracked rock mass, dynamic fracture toughness is an important mechanical parameter to study the fracture characteristics of cracks, which can accurately reflect the energy required in the crack initiation and propagation stage. However, compared with the static fracture problem, it is difficult to obtain an analytical solution for dynamic fracture toughness. Therefore, many scholars measure the crack propagation speed by using crack propagation gauges, and then calculate the dynamic fracture toughness according to the universal function. In this way, the crack propagation speed plays a leading role in the calculation accuracy, but in the experiment, the crack propagation speed cannot be measured accurately due to the measuring instrument. In this paper, the fractal theory is used to correct this error. According to the fractal theory, the effects of deflected crack propagation trajectories on dynamic fracture properties of black sandstone under impact loads were studied. A traditional modified split Hopkinson pressure bar (SHPB) test device was used to conduct a dynamic impact test by using an improved single cleavage semi-circle (ISCSC) specimen, crack propagation speed and other fracture mechanics parameters were measured using crack propagation gauge (CPG). Subsequently, the fractal theory was applied to correct dynamic crack propagation speed and dynamic stress intensity factor, and the dynamic fracture toughness of black sandstone was also calculated using the experimental-numerical method. The research results indicate that the ISCSC specimen can be effectively applied to study the crack arrest behavior of rock materials. Crack propagation speed and dynamic fracture toughness after fractal correction are closer to the actual dynamic crack propagation characteristics. Comparisons between before and after the correction, the maximum error of the crack propagation speed of black sandstone material is 33.51%, and the maximum error of dynamic fracture toughness is 7.68%, indicating that it is more reasonable to use fractal theory to calculate dynamic fracture parameters such as crack propagation speed and dynamic fracture toughness.
When studying the dynamic fracture behavior of cracked rock mass, dynamic fracture toughness is an important mechanical parameter to study the fracture characteristics of cracks, which can accurately reflect the energy required in the crack initiation and propagation stage. However, compared with the static fracture problem, it is difficult to obtain an analytical solution for dynamic fracture toughness. Therefore, many scholars measure the crack propagation speed by using crack propagation gauges, and then calculate the dynamic fracture toughness according to the universal function. In this way, the crack propagation speed plays a leading role in the calculation accuracy, but in the experiment, the crack propagation speed cannot be measured accurately due to the measuring instrument. In this paper, the fractal theory is used to correct this error. According to the fractal theory, the effects of deflected crack propagation trajectories on dynamic fracture properties of black sandstone under impact loads were studied. A traditional modified split Hopkinson pressure bar (SHPB) test device was used to conduct a dynamic impact test by using an improved single cleavage semi-circle (ISCSC) specimen, crack propagation speed and other fracture mechanics parameters were measured using crack propagation gauge (CPG). Subsequently, the fractal theory was applied to correct dynamic crack propagation speed and dynamic stress intensity factor, and the dynamic fracture toughness of black sandstone was also calculated using the experimental-numerical method. The research results indicate that the ISCSC specimen can be effectively applied to study the crack arrest behavior of rock materials. Crack propagation speed and dynamic fracture toughness after fractal correction are closer to the actual dynamic crack propagation characteristics. Comparisons between before and after the correction, the maximum error of the crack propagation speed of black sandstone material is 33.51%, and the maximum error of dynamic fracture toughness is 7.68%, indicating that it is more reasonable to use fractal theory to calculate dynamic fracture parameters such as crack propagation speed and dynamic fracture toughness.
2022, 42(7): 073102.
doi: 10.11883/bzycj-2021-0525
Abstract:
Composite sandwich beams with a carbon fiber reinforced polymer (CFRP) square honeycomb core were designed and fabricated by using the interlocking method. The dynamic response and failure mechanism of fully-clamped and simply- supported sandwich beams subjected to low-velocity impact were investigated experimentally and the corresponding failure modes of the sandwich beams were obtained. Meanwhile, the damage evolvement process and the failure mechanism were analyzed in detail. Influences of the impact velocity, boundary conditions, the mass distributions of face sheets and the direction of the slots on the failure modes and load-carrying capacity of the sandwich beams were explored. The low-velocity impact experiments of composites specimens with two kinds of boundary conditions were carried out by using the drop-hammer impact test system. Three kinds of initial impact velocity were considered for the simply-supported and the fully- clamped sandwich beams sandwich beams, respectively. In the experiments, the time history curves of the impact load and the midspan deflection of the specimens were recorded by a load cell and a laser displacement sensor. Meanwhile, the deformation processes of the sandwich beams were captured by a high-speed camera. The experimental results show that the directions for the slots of the long ribs have significant influence on the failure modes of the sandwich beams. The sandwich core with the upward slots at the midspan has compression deformation whilst the cracking failure along the direction of the downward slots at the midspan is observed due to the tension, which results in the face-sheet debonding and rib fracture successively. It is found that for the same mass, the design of the thicker upper face sheet can enhance the impact resistance of the sandwich beams. The peak load and load-carrying capacity of the sandwich beams increase with increasing the impact velocity. The fully-clamped boundary conditions make the sandwich beams exhibit hardening post-failure behaviors obviously. After the initial failure at the midspan, the fully-clamped ends of the cores and the face-sheets of the sandwich beams experience the fracture failure.
Composite sandwich beams with a carbon fiber reinforced polymer (CFRP) square honeycomb core were designed and fabricated by using the interlocking method. The dynamic response and failure mechanism of fully-clamped and simply- supported sandwich beams subjected to low-velocity impact were investigated experimentally and the corresponding failure modes of the sandwich beams were obtained. Meanwhile, the damage evolvement process and the failure mechanism were analyzed in detail. Influences of the impact velocity, boundary conditions, the mass distributions of face sheets and the direction of the slots on the failure modes and load-carrying capacity of the sandwich beams were explored. The low-velocity impact experiments of composites specimens with two kinds of boundary conditions were carried out by using the drop-hammer impact test system. Three kinds of initial impact velocity were considered for the simply-supported and the fully- clamped sandwich beams sandwich beams, respectively. In the experiments, the time history curves of the impact load and the midspan deflection of the specimens were recorded by a load cell and a laser displacement sensor. Meanwhile, the deformation processes of the sandwich beams were captured by a high-speed camera. The experimental results show that the directions for the slots of the long ribs have significant influence on the failure modes of the sandwich beams. The sandwich core with the upward slots at the midspan has compression deformation whilst the cracking failure along the direction of the downward slots at the midspan is observed due to the tension, which results in the face-sheet debonding and rib fracture successively. It is found that for the same mass, the design of the thicker upper face sheet can enhance the impact resistance of the sandwich beams. The peak load and load-carrying capacity of the sandwich beams increase with increasing the impact velocity. The fully-clamped boundary conditions make the sandwich beams exhibit hardening post-failure behaviors obviously. After the initial failure at the midspan, the fully-clamped ends of the cores and the face-sheets of the sandwich beams experience the fracture failure.
2022, 42(7): 073103.
doi: 10.11883/bzycj-2021-0244
Abstract:
By using a SHPB device combined with high-speed photography technology, low-velocity impact experiments of quartz glass beads with diameters of 7.90, 11.80 and 15.61 mm were carried out by means of respectively three kinds of transmission bars, i.e., steel bar, aluminum bar, and polymethyl methacrylate (PMMA) bar. According to the load-displacement curves in the breakage process of glass beads under different transmission bar conditions, combined with the load adjustment of glass beads under impact and the strain of glass beads during the experiment, the influence of stress adjustment on the breakage process of glass beads subjected to low-velocity impact is explored. The results show that under the same impact conditions, the adjustment of the material of the transmission bar will alter the load distribution in the glass bead during impact breakage, that is, the change of the wave impedance at the transmission end will change the reflected wave, which leads to the load adjustment in the process of multiple reflection loading. When the transmission bar is made of aluminum and PMMA, the load in the glass bead decreases obviously during the crushing process, and the stress adjustment duration of the glass bead becomes longer with more deformation of the cushion block during the loading process. When the transmission bar is made of steel, the strain in the glass bead is the largest at both ends, while the closer to the middle of the bead, the smaller the strain. For the glass beads loaded with aluminum and/or PMMA transmission bar, local unloading behavior is found at the transmission end of bead. By employing the PMMA transmission bar, the local stress and deformation both decrease, resulting in the glass bead being broken with larger deformation. It is further shown that glass bead breakage is controlled by local deformation and local deformation gradient.
By using a SHPB device combined with high-speed photography technology, low-velocity impact experiments of quartz glass beads with diameters of 7.90, 11.80 and 15.61 mm were carried out by means of respectively three kinds of transmission bars, i.e., steel bar, aluminum bar, and polymethyl methacrylate (PMMA) bar. According to the load-displacement curves in the breakage process of glass beads under different transmission bar conditions, combined with the load adjustment of glass beads under impact and the strain of glass beads during the experiment, the influence of stress adjustment on the breakage process of glass beads subjected to low-velocity impact is explored. The results show that under the same impact conditions, the adjustment of the material of the transmission bar will alter the load distribution in the glass bead during impact breakage, that is, the change of the wave impedance at the transmission end will change the reflected wave, which leads to the load adjustment in the process of multiple reflection loading. When the transmission bar is made of aluminum and PMMA, the load in the glass bead decreases obviously during the crushing process, and the stress adjustment duration of the glass bead becomes longer with more deformation of the cushion block during the loading process. When the transmission bar is made of steel, the strain in the glass bead is the largest at both ends, while the closer to the middle of the bead, the smaller the strain. For the glass beads loaded with aluminum and/or PMMA transmission bar, local unloading behavior is found at the transmission end of bead. By employing the PMMA transmission bar, the local stress and deformation both decrease, resulting in the glass bead being broken with larger deformation. It is further shown that glass bead breakage is controlled by local deformation and local deformation gradient.
2022, 42(7): 073104.
doi: 10.11883/bzycj-2021-0297
Abstract:
Four kinds of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites with different fiber content were obtained by mixing carbon fiber and polypropylene fiber into coral sand cement-based composites prepared by artificial seawater. Impact compression tests of this material under five strain rates were carried out with a 100-mm diameter split Hopkinson pressure bar. The parameters of Holmquist-Johnson-Cook model are determined by experimental data and parameter debugging. Based on Holmquist-Johnson-Cook model, LS-DYNA is used to simulate the impact compression of this material. By analyzing the failure mode, stress-strain curve and energy dissipation of the test blocks, the impact compression mechanical properties of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites are studied. The results are as follows. (1) The critical value of test strain rate is 200 s−1; when the test strain rate is greater than 200 s−1, the fiber network formed by hybrid carbon fiber and polypropylene fiber strengthens the toughening effect of the test block. (2) The peak stress of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites exhibits obvious strain rate effect, and the dynamic increase factor is highly sensitive to the strain rate. (3) The use of fine aggregate of coral sand results in more defects such as micro-cracks and micro-voids in the test block; after mixing carbon fiber and polypropylene fiber into the coral sand cement-based composites, the improvement of the impact compressive strength of the test block is limited, but the impact toughness of the coral sand cement-based composites is significantly enhanced. (4) LS-DYNA is used to numerically simulate the impact compression test process of hybrid carbon fiber (15.75 kg/m3) and polypropylene fiber (1.82 kg/m3), while the error between the simulation results of peak stress and the test results is within 5.97 %. The study is of great significance for the preparation of high performance coral sand cement-based composites and the emergency repair of offshore islands and reefs.
Four kinds of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites with different fiber content were obtained by mixing carbon fiber and polypropylene fiber into coral sand cement-based composites prepared by artificial seawater. Impact compression tests of this material under five strain rates were carried out with a 100-mm diameter split Hopkinson pressure bar. The parameters of Holmquist-Johnson-Cook model are determined by experimental data and parameter debugging. Based on Holmquist-Johnson-Cook model, LS-DYNA is used to simulate the impact compression of this material. By analyzing the failure mode, stress-strain curve and energy dissipation of the test blocks, the impact compression mechanical properties of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites are studied. The results are as follows. (1) The critical value of test strain rate is 200 s−1; when the test strain rate is greater than 200 s−1, the fiber network formed by hybrid carbon fiber and polypropylene fiber strengthens the toughening effect of the test block. (2) The peak stress of carbon-polypropylene hybrid fiber reinforced coral sand cement-based composites exhibits obvious strain rate effect, and the dynamic increase factor is highly sensitive to the strain rate. (3) The use of fine aggregate of coral sand results in more defects such as micro-cracks and micro-voids in the test block; after mixing carbon fiber and polypropylene fiber into the coral sand cement-based composites, the improvement of the impact compressive strength of the test block is limited, but the impact toughness of the coral sand cement-based composites is significantly enhanced. (4) LS-DYNA is used to numerically simulate the impact compression test process of hybrid carbon fiber (15.75 kg/m3) and polypropylene fiber (1.82 kg/m3), while the error between the simulation results of peak stress and the test results is within 5.97 %. The study is of great significance for the preparation of high performance coral sand cement-based composites and the emergency repair of offshore islands and reefs.
2022, 42(7): 073105.
doi: 10.11883/bzycj-2021-0434
Abstract:
Sapphire (Al2O3) transparent ceramic glass has excellent light transmittance and retains the excellent mechanical properties comparing with traditional ceramics. In order to understand the relationship between strength and strain rate of sapphire transparent ceramic glass and its failure process, the electronic tensile machine and split Hopkinson bar equipment were used to load the specimen at different strain rates (10−4, 10−3, 10−2, 850, 1 100, 1 300, 1 450 s−1). The quasi-static and dynamic compression failure processes of specimen were recorded by high-speed camera. The experimental results show sapphire transparent ceramic glass is a typical brittle material with strain rate effect. With the increase of strain rate, the compressive strength of the sapphire transparent ceramic glass will also increase. The failure cycle of sapphire is long under quasi-static compression, and the crack will expand along the path with the weakest bearing capacity. In addition, the strength curve of sapphire will decline briefly and then continue to rise, which is caused by the increase and propagation of the number of cracks. In the process of dynamic compression, the sapphire reaches the cracking strength in many places, forming more crack sources, and then the crack forms and expands to split the sapphire. When the sapphire transparent ceramic glass is subjected to compression, cracks will appear in the region with the weakest bearing capacity in the process of loading; soon after the cracks take shape and expand along the loading direction, the cracks interlace to reach a saturation state; and finally reach the compressive strength failure. Under dynamic compression, however, due to the loading rate is much higher than the propagation of the crack, several crack sources appear in the sapphirine transparent ceramic glass within a very short period of time, which requires more energy to make the crack forming and extending, exhibiting as the strain rate effect on its macro-scale performance.
Sapphire (Al2O3) transparent ceramic glass has excellent light transmittance and retains the excellent mechanical properties comparing with traditional ceramics. In order to understand the relationship between strength and strain rate of sapphire transparent ceramic glass and its failure process, the electronic tensile machine and split Hopkinson bar equipment were used to load the specimen at different strain rates (10−4, 10−3, 10−2, 850, 1 100, 1 300, 1 450 s−1). The quasi-static and dynamic compression failure processes of specimen were recorded by high-speed camera. The experimental results show sapphire transparent ceramic glass is a typical brittle material with strain rate effect. With the increase of strain rate, the compressive strength of the sapphire transparent ceramic glass will also increase. The failure cycle of sapphire is long under quasi-static compression, and the crack will expand along the path with the weakest bearing capacity. In addition, the strength curve of sapphire will decline briefly and then continue to rise, which is caused by the increase and propagation of the number of cracks. In the process of dynamic compression, the sapphire reaches the cracking strength in many places, forming more crack sources, and then the crack forms and expands to split the sapphire. When the sapphire transparent ceramic glass is subjected to compression, cracks will appear in the region with the weakest bearing capacity in the process of loading; soon after the cracks take shape and expand along the loading direction, the cracks interlace to reach a saturation state; and finally reach the compressive strength failure. Under dynamic compression, however, due to the loading rate is much higher than the propagation of the crack, several crack sources appear in the sapphirine transparent ceramic glass within a very short period of time, which requires more energy to make the crack forming and extending, exhibiting as the strain rate effect on its macro-scale performance.
2022, 42(7): 073201.
doi: 10.11883/bzycj-2021-0359
Abstract:
In order to reduce the cost for the impact test of the full-size airframe structures, an incomplete similar model was established by the similarity theory. Based on dimensional analysis, the correction relation for the Johnson-Cook linear strain-rate function was formulated. Due to the limitation of manufacturing technology, the effect of the incomplete similar model with distorted thickness on similarity behaviors should be taken into account, so an exponential function was adopted to establish the correction formula for the distorted thickness model. The validity of the simulation model was then verified by comparisons relevant to the deformation on the fuselage, the strain-time curves of target plates and the final deformation profile. In addition, the influences of fragment angle, material property, distortion thickness and light weight on the deformation behavior of the fuselage structure were analyzed. The following main results were obtained. (1) Under the impact velocity of 150 m/s, the most severe impact conditions appear at the impact angle of 90° and the fragment attitude of 180º; by considering various factors, the 3.5-mm-thickness titanium alloy plate is regarded as the best choice for fuselage structures, and it is used as a full-size prototype to verify the similar method. Besides, it’s worth noting that an unconventional phenomenon takes place at the impact angle of 30º, while a reasonable explanation is given. (2) The effect of strain rate on the impact of tire fragments on the fuselage structure is not notable, so the incomplete similar model is in good agreement with the prototype results. (3) The incomplete scaled-down model corrected by this method can effectively predict the deformation behavior of prototype fuselage subjected to the impact of tyre fragments. Although there is a certain deviation between the model and the prototype on the time scale, on the spatial dimensions, the incomplete scaled-down model can effectively correct the prediction error for the maximum center deformation caused by the distortion thickness, and the corrected maximum error is less than 5.1%, indicating that the method can effectively guide the design for airframe structures.
In order to reduce the cost for the impact test of the full-size airframe structures, an incomplete similar model was established by the similarity theory. Based on dimensional analysis, the correction relation for the Johnson-Cook linear strain-rate function was formulated. Due to the limitation of manufacturing technology, the effect of the incomplete similar model with distorted thickness on similarity behaviors should be taken into account, so an exponential function was adopted to establish the correction formula for the distorted thickness model. The validity of the simulation model was then verified by comparisons relevant to the deformation on the fuselage, the strain-time curves of target plates and the final deformation profile. In addition, the influences of fragment angle, material property, distortion thickness and light weight on the deformation behavior of the fuselage structure were analyzed. The following main results were obtained. (1) Under the impact velocity of 150 m/s, the most severe impact conditions appear at the impact angle of 90° and the fragment attitude of 180º; by considering various factors, the 3.5-mm-thickness titanium alloy plate is regarded as the best choice for fuselage structures, and it is used as a full-size prototype to verify the similar method. Besides, it’s worth noting that an unconventional phenomenon takes place at the impact angle of 30º, while a reasonable explanation is given. (2) The effect of strain rate on the impact of tire fragments on the fuselage structure is not notable, so the incomplete similar model is in good agreement with the prototype results. (3) The incomplete scaled-down model corrected by this method can effectively predict the deformation behavior of prototype fuselage subjected to the impact of tyre fragments. Although there is a certain deviation between the model and the prototype on the time scale, on the spatial dimensions, the incomplete scaled-down model can effectively correct the prediction error for the maximum center deformation caused by the distortion thickness, and the corrected maximum error is less than 5.1%, indicating that the method can effectively guide the design for airframe structures.
2022, 42(7): 073301.
doi: 10.11883/bzycj-2021-0466
Abstract:
A shaped-charge jet compresses the target axially and radially simultaneously when the jet penetrates into a thick target, and then the axial penetration and radial crater growth occur. The research on axial penetration is abundant, but the research on radial crater growth is less and there is a certain error between theoretical prediction and experimental results. The radial crater growth equation of the shaped-charge jet was derived by considering the compressibility of the jet and target materials based on the compressible model of shaped-charge jet penetration and the Szendrei-Held equation. The main changes of equations are the stagnation pressure adopted value of the compressible model and the density changed with jet velocity. An approximate solution of the compressible model was given based on the Murnaghan equation of state in order to simplify the tedious calculation process of the complete compressible model, i.e., the calculation processes of stagnation pressure and density change were simplified. The prediction by this model is better than that by the Szendrei-Held equation compared with the experimental study of the shaped-charge jet crater growth in water. The main factors affecting the radial crater growth by the shaped-charge jet include jet radius, stagnation point pressure, target strength, target density at the stagnation point and shaped-charge jet velocity. This model can more accurately predict the crater growth of the shaped-charge jets penetrating into the compressible targets. It may be helpful to study the interference of shaped-charge jet penetration with liquid-confined structures.
A shaped-charge jet compresses the target axially and radially simultaneously when the jet penetrates into a thick target, and then the axial penetration and radial crater growth occur. The research on axial penetration is abundant, but the research on radial crater growth is less and there is a certain error between theoretical prediction and experimental results. The radial crater growth equation of the shaped-charge jet was derived by considering the compressibility of the jet and target materials based on the compressible model of shaped-charge jet penetration and the Szendrei-Held equation. The main changes of equations are the stagnation pressure adopted value of the compressible model and the density changed with jet velocity. An approximate solution of the compressible model was given based on the Murnaghan equation of state in order to simplify the tedious calculation process of the complete compressible model, i.e., the calculation processes of stagnation pressure and density change were simplified. The prediction by this model is better than that by the Szendrei-Held equation compared with the experimental study of the shaped-charge jet crater growth in water. The main factors affecting the radial crater growth by the shaped-charge jet include jet radius, stagnation point pressure, target strength, target density at the stagnation point and shaped-charge jet velocity. This model can more accurately predict the crater growth of the shaped-charge jets penetrating into the compressible targets. It may be helpful to study the interference of shaped-charge jet penetration with liquid-confined structures.
2022, 42(7): 074101.
doi: 10.11883/bzycj-2021-0453
Abstract:
Explosive-driven magnetic flux compression generator is a device that converts the chemical energy of explosives into electromagnetic energy. It has attracted great attention in the field of high energy density physics due to its wide application and important development prospect in magnetic field compression and material high pressure loading. CAEP has conducted a lot of research on CJ-100 device, which can stably generate an axial magnetic field of about 700 T. In order to investigate the loading capacity of CJ-100 device, the loading process and the effects of various device parameters are discussed by using the one-dimensional magnetohydrodynamics program SSS-MHD. The results show that the peak magnetic field that can be reached by the device is inversely proportional to the initial magnetic field, and the size of sample target has a great influence on the loading pressure. A sample target of iron/copper layered structure was designed for quasi-isentropic loading experiment of pure iron. The initial inner radius of the sample target was 3 mm, and the thickness of both iron and copper layer was 1 mm. The experiment was carried out on CJ-100 device with an initial magnetic field of 5.5 T, atmospheric pressure of several hundred Pa and ambient temperature. The free surface velocity of the sample target of about 6.43 km/s was measured with Photonic Doppler Velocimetry probes. SSS-MHD program with proper material models provided curve of velocity versus time that agree well with the experimental measurement. Simulation then shows that a quasi-isentropic loading pressure of 206 GPa is obtained in DT4 iron. The p-v curve of iron material is basically coincided with the theoretical isentropic line, indicating that the loading process of CJ-100 has a high isentropic degree.
Explosive-driven magnetic flux compression generator is a device that converts the chemical energy of explosives into electromagnetic energy. It has attracted great attention in the field of high energy density physics due to its wide application and important development prospect in magnetic field compression and material high pressure loading. CAEP has conducted a lot of research on CJ-100 device, which can stably generate an axial magnetic field of about 700 T. In order to investigate the loading capacity of CJ-100 device, the loading process and the effects of various device parameters are discussed by using the one-dimensional magnetohydrodynamics program SSS-MHD. The results show that the peak magnetic field that can be reached by the device is inversely proportional to the initial magnetic field, and the size of sample target has a great influence on the loading pressure. A sample target of iron/copper layered structure was designed for quasi-isentropic loading experiment of pure iron. The initial inner radius of the sample target was 3 mm, and the thickness of both iron and copper layer was 1 mm. The experiment was carried out on CJ-100 device with an initial magnetic field of 5.5 T, atmospheric pressure of several hundred Pa and ambient temperature. The free surface velocity of the sample target of about 6.43 km/s was measured with Photonic Doppler Velocimetry probes. SSS-MHD program with proper material models provided curve of velocity versus time that agree well with the experimental measurement. Simulation then shows that a quasi-isentropic loading pressure of 206 GPa is obtained in DT4 iron. The p-v curve of iron material is basically coincided with the theoretical isentropic line, indicating that the loading process of CJ-100 has a high isentropic degree.
2022, 42(7): 075101.
doi: 10.11883/bzycj-2022-0044
Abstract:
To effectively protect the underground structures subjected to ground shock, a new protective component made of foam concrete was proposed. Different from the mechanism of the solid foam concrete layer protection, under the action of ground shock, the proposed components firstly exhibited brittlely fracture, and the fractured parts underwent recontact and compaction, in which the ground shock truncation, load transferred reduction and load form modification on the structures were achieved with the response of the designed components. A field experiment was conducted and the comparison of the dynamic response of the structure (with different protection scenarios, i.e. without protection, with a solid foam concrete layer protection and with the proposed component layer protection) suggested that the superior protective performance was achieved with the fracture, recontact, compaction of the new component. Due to the brittle fracture, the load transfer could be significantly reduced under a relatively low ground shock level, with which the negative protection effect using solid foam concrete layer could be avoided. Subjected to a relatively strong ground shock, the proposed component layer tended to compaction, and its protection effect gradually approached that with the solid foam concrete layer.
To effectively protect the underground structures subjected to ground shock, a new protective component made of foam concrete was proposed. Different from the mechanism of the solid foam concrete layer protection, under the action of ground shock, the proposed components firstly exhibited brittlely fracture, and the fractured parts underwent recontact and compaction, in which the ground shock truncation, load transferred reduction and load form modification on the structures were achieved with the response of the designed components. A field experiment was conducted and the comparison of the dynamic response of the structure (with different protection scenarios, i.e. without protection, with a solid foam concrete layer protection and with the proposed component layer protection) suggested that the superior protective performance was achieved with the fracture, recontact, compaction of the new component. Due to the brittle fracture, the load transfer could be significantly reduced under a relatively low ground shock level, with which the negative protection effect using solid foam concrete layer could be avoided. Subjected to a relatively strong ground shock, the proposed component layer tended to compaction, and its protection effect gradually approached that with the solid foam concrete layer.
2022, 42(7): 075102.
doi: 10.11883/bzycj-2021-0332
Abstract:
In order to study the blast-resistance characteristics of polyurea sprayed reinforced brick infill walls, a prototype explosion test of polyurea sprayed reinforced frame infill walls was carried out based on an improved large-scale explosion test device. This test device eliminates the influence of the sparse wave formed by the air shock wave at the edge of the wall and the diffraction behind the wall on the real blast resistance test dynamic response of the wall, and significantly improves the accuracy of the blast resistance test of brick infill walls strengthened with polyuria. The dynamic response characteristics, failure process and mode of reinforced brick walls under explosion load were analyzed, and the failure mechanism was revealed. The results show that under small deformation conditions, polyurea reinforcement can improve the blast-resistance of infilled wall members. Under large deformation conditions, polyurea reinforcement can increase the ductility of filled wall members. The system stiffness of reinforced brick wall changes continuously during forced vibration, and the maximum difference is 133%. With the decrease of the proportional distance, the failure mode of the reinforced brick wall gradually changes from bending failure to shear failure. The polyurea thickness of more than 6 mm can effectively limit the local shear failure phenomenon. The theoretical calculation model based on the resistance function of brick wall and polyurea coating can accurately predict the forward displacement response process of two-way brick wall reinforced by back blasting surface under explosion.
In order to study the blast-resistance characteristics of polyurea sprayed reinforced brick infill walls, a prototype explosion test of polyurea sprayed reinforced frame infill walls was carried out based on an improved large-scale explosion test device. This test device eliminates the influence of the sparse wave formed by the air shock wave at the edge of the wall and the diffraction behind the wall on the real blast resistance test dynamic response of the wall, and significantly improves the accuracy of the blast resistance test of brick infill walls strengthened with polyuria. The dynamic response characteristics, failure process and mode of reinforced brick walls under explosion load were analyzed, and the failure mechanism was revealed. The results show that under small deformation conditions, polyurea reinforcement can improve the blast-resistance of infilled wall members. Under large deformation conditions, polyurea reinforcement can increase the ductility of filled wall members. The system stiffness of reinforced brick wall changes continuously during forced vibration, and the maximum difference is 133%. With the decrease of the proportional distance, the failure mode of the reinforced brick wall gradually changes from bending failure to shear failure. The polyurea thickness of more than 6 mm can effectively limit the local shear failure phenomenon. The theoretical calculation model based on the resistance function of brick wall and polyurea coating can accurately predict the forward displacement response process of two-way brick wall reinforced by back blasting surface under explosion.
2022, 42(7): 075103.
doi: 10.11883/bzycj-2021-0495
Abstract:
To identify the anti-explosion performance, dynamic response and typical failure mode of a reinforced concrete beam-slab composite structure, the explosion experiment was conducted by the shock tube, which was used to simulate the long-lasting long-distance explosion shock wave. The failure form of the reinforced concrete beam-slab composite structure, the shock wave variation curve and the displacement change at the center point of the backside surface were obtained through the experiment. The dynamic response process of the reinforced concrete beam-slab composite structure is numerically simulated by finite element software. Compared with the experimental results, it is found that the simulated failure phenomenon is similar to the experimentally observed one, and the peak displacement at the center point of the backside surface is also close to the experimental one. Both of these have verified the accuracy and applicability of the numerical model adopted. On this basis, the dynamic response and failure process of the beam-slab composite structure under the simplified triangular explosion shock wave load are analyzed. The simplified triangular explosion shock wave used in numerical simulation has the same impulse as that in experiment but different peak values and durations. According to the deflection-span ratio a and the failure form, the failure patterns are classified into four modes as light failure, moderate failure, severe failure and complete failure. The results show that the cracks are firstly distributed along the diagonal of the backside surface of the reinforced concrete beam-slab composite structure. Under the same impulse, with the increase of the peak value of the explosion load, the damage degree of the beam-slab composite members gradually deepens. Meanwhile, the failure mode changes from a bending failure to a combined bending-shear failure, and finally appears as a punching failure. The failure of the plate part of composite members occurs earlier than the cross-beam part, while the former’s damage degree is greater than the latter’s.
To identify the anti-explosion performance, dynamic response and typical failure mode of a reinforced concrete beam-slab composite structure, the explosion experiment was conducted by the shock tube, which was used to simulate the long-lasting long-distance explosion shock wave. The failure form of the reinforced concrete beam-slab composite structure, the shock wave variation curve and the displacement change at the center point of the backside surface were obtained through the experiment. The dynamic response process of the reinforced concrete beam-slab composite structure is numerically simulated by finite element software. Compared with the experimental results, it is found that the simulated failure phenomenon is similar to the experimentally observed one, and the peak displacement at the center point of the backside surface is also close to the experimental one. Both of these have verified the accuracy and applicability of the numerical model adopted. On this basis, the dynamic response and failure process of the beam-slab composite structure under the simplified triangular explosion shock wave load are analyzed. The simplified triangular explosion shock wave used in numerical simulation has the same impulse as that in experiment but different peak values and durations. According to the deflection-span ratio a and the failure form, the failure patterns are classified into four modes as light failure, moderate failure, severe failure and complete failure. The results show that the cracks are firstly distributed along the diagonal of the backside surface of the reinforced concrete beam-slab composite structure. Under the same impulse, with the increase of the peak value of the explosion load, the damage degree of the beam-slab composite members gradually deepens. Meanwhile, the failure mode changes from a bending failure to a combined bending-shear failure, and finally appears as a punching failure. The failure of the plate part of composite members occurs earlier than the cross-beam part, while the former’s damage degree is greater than the latter’s.
2022, 42(7): 075401.
doi: 10.11883/bzycj-2021-0417
Abstract:
To study the effects of magnetic fields on the gas explosion, considering equivalent acetylene premixed combustible gas as the research object, the effects of different magnetic field intensities on acetylene explosion characteristics were studied experimentally. The explosion pressure and flame propagation velocity were measured simultaneously by transient pressure sensors and a detonation velocity instrument, respectively. The results show that the magnetic fields reduce the explosion pressure and the pressure rise rate of acetylene. With increasing magnetic field intensity, the suppression effect is more significant. Along the direction of flame propagation, the magnetic fields first promote and then suppress the explosion flame propagation velocity of acetylene, and the inhibition effect is stronger than the promotion effect. In these experimental conditions, the average propagation velocity of the explosion flame decreased by 38.94% under lower magnetic fields intensity, and at higher magnetic fields intensity, it decreased by 49.62%. To further study the impact mechanism of magnetic fields on premixed combustible gas explosion, the acetylene explosion free radicals reaction process was simulated numerically by Chemkin-Pro software. The chain reactions, rate of products, and sensitivity are analyzed. And the key radical and reaction paths of acetylene explosion are obtained. Combined with the force analysis of magnetic fields on free radicals, it is deduced that magnetic fields change the reaction paths of acetylene to produce carbon dioxide and water, which is the main internal reason for the decrease in explosion parameters. The different free radicals have different molar masses and magnetization. Lorentz force and gradient magnetic field force have stronger effects on small molecular weight free radicals than on large molecular weight free radicals. The calculation shows that the magnetic fields change the trajectory of the free radicals, cause the aggregation of free radicals with the same small molecular weight, and produce a wall effect, which reduces collisions between key free radicals and the rate of elementary reactions, resulting in a decrease of explosion intensity.
To study the effects of magnetic fields on the gas explosion, considering equivalent acetylene premixed combustible gas as the research object, the effects of different magnetic field intensities on acetylene explosion characteristics were studied experimentally. The explosion pressure and flame propagation velocity were measured simultaneously by transient pressure sensors and a detonation velocity instrument, respectively. The results show that the magnetic fields reduce the explosion pressure and the pressure rise rate of acetylene. With increasing magnetic field intensity, the suppression effect is more significant. Along the direction of flame propagation, the magnetic fields first promote and then suppress the explosion flame propagation velocity of acetylene, and the inhibition effect is stronger than the promotion effect. In these experimental conditions, the average propagation velocity of the explosion flame decreased by 38.94% under lower magnetic fields intensity, and at higher magnetic fields intensity, it decreased by 49.62%. To further study the impact mechanism of magnetic fields on premixed combustible gas explosion, the acetylene explosion free radicals reaction process was simulated numerically by Chemkin-Pro software. The chain reactions, rate of products, and sensitivity are analyzed. And the key radical and reaction paths of acetylene explosion are obtained. Combined with the force analysis of magnetic fields on free radicals, it is deduced that magnetic fields change the reaction paths of acetylene to produce carbon dioxide and water, which is the main internal reason for the decrease in explosion parameters. The different free radicals have different molar masses and magnetization. Lorentz force and gradient magnetic field force have stronger effects on small molecular weight free radicals than on large molecular weight free radicals. The calculation shows that the magnetic fields change the trajectory of the free radicals, cause the aggregation of free radicals with the same small molecular weight, and produce a wall effect, which reduces collisions between key free radicals and the rate of elementary reactions, resulting in a decrease of explosion intensity.
2022, 42(7): 075402.
doi: 10.11883/bzycj-2021-0470
Abstract:
The pyrolysis and oxidation characteristics and flame propagation characteristics in the semi-enclosed vertical pipe of lauric acid dust and stearic acid dust were studied by using the synchrotron thermal analyzer, improved Hartmann explosive test device and high-speed photography system, the pyrolysis kinetics was analyzed by Coats-Redfern method to obtain the kinetic parameters, and the influence of pyrolysis and oxidation characteristics on the law of flame propagation during the explosion and combustion of lauric acid and stearic acid dust was analyzed and discussed. The results show that, when the dust cloud concentration is 125 g/m3, the flame front structure of lauric acid dust cloud is smoother than stearic acid dust, but the flame propagation speed of stearic acid dust is significantly greater than that of lauric acid dust; with the increase of dust cloud concentration, the flame front structure of lauric acid dust and stearic acid dust gradually becomes discrete, and the flame propagation speed gradually increases, but the speed difference gradually decreases. The average flame propagation speed of lauric acid dust is higher than that of stearic acid dust at a dust cloud concentration of 750 g/m3, and the flame structure continuity is significantly reduced. The difference in flame propagation between lauric acid dust and stearic acid dust at low concentrations is mainly determined by the oxidation exothermic characteristics of the fast pyrolysis stage. The larger the pre-exponential factor, the more active sites involved in the pyrolysis and oxidation reactions, the larger the oxidation exothermic heat, the faster the exothermic rate, the faster the flame propagation speed, and the faster the flame frontal structure transition from smooth continuous to discrete complex. And with the increase of dust cloud concentration, the flame propagation difference is gradually controlled by the activation energy and the mass transport process of oxygen in the preheating zone of the flame front. The greater the activation energy, the greater the oxygen consumption, the faster the oxygen consumption rate, the easier it will lead to the decrease of flame propagation speed, the more complex the flame front, and the decrease of flame structure continuity.
The pyrolysis and oxidation characteristics and flame propagation characteristics in the semi-enclosed vertical pipe of lauric acid dust and stearic acid dust were studied by using the synchrotron thermal analyzer, improved Hartmann explosive test device and high-speed photography system, the pyrolysis kinetics was analyzed by Coats-Redfern method to obtain the kinetic parameters, and the influence of pyrolysis and oxidation characteristics on the law of flame propagation during the explosion and combustion of lauric acid and stearic acid dust was analyzed and discussed. The results show that, when the dust cloud concentration is 125 g/m3, the flame front structure of lauric acid dust cloud is smoother than stearic acid dust, but the flame propagation speed of stearic acid dust is significantly greater than that of lauric acid dust; with the increase of dust cloud concentration, the flame front structure of lauric acid dust and stearic acid dust gradually becomes discrete, and the flame propagation speed gradually increases, but the speed difference gradually decreases. The average flame propagation speed of lauric acid dust is higher than that of stearic acid dust at a dust cloud concentration of 750 g/m3, and the flame structure continuity is significantly reduced. The difference in flame propagation between lauric acid dust and stearic acid dust at low concentrations is mainly determined by the oxidation exothermic characteristics of the fast pyrolysis stage. The larger the pre-exponential factor, the more active sites involved in the pyrolysis and oxidation reactions, the larger the oxidation exothermic heat, the faster the exothermic rate, the faster the flame propagation speed, and the faster the flame frontal structure transition from smooth continuous to discrete complex. And with the increase of dust cloud concentration, the flame propagation difference is gradually controlled by the activation energy and the mass transport process of oxygen in the preheating zone of the flame front. The greater the activation energy, the greater the oxygen consumption, the faster the oxygen consumption rate, the easier it will lead to the decrease of flame propagation speed, the more complex the flame front, and the decrease of flame structure continuity.
